Environmental Degradation and Fragmentation of Microplastics: Dependence on Polymer Type, Humidity, UV Dose and Temperature

Environmental Degradation and Fragmentation of Microplastics: Dependence on Polymer Type, Humidity, UV Dose and Temperature | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Environmental Degradation and Fragmentation of Microplastics: Dependence on Polymer Type, Humidity, UV Dose and Temperature Patrizia Pfohl, Katherine Santizo, Joana Sipe, Mark Wiesner, Sam Harrison, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5244293/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Mar, 2025 Read the published version in Microplastics and Nanoplastics → Version 1 posted 9 You are reading this latest preprint version Abstract Depending on the environmental compartment, plastics are subjected to various stressors, including UV light, water, microbial exudates (enzymes), and temperature. Among these, stress on plastics from photo-chemical processes was identified as a leading exposure pathway of plastics, e.g., in the atmosphere or on the water surface. While the focus of earlier studies mainly was on deterioration of the chemical and mechanical properties, more recent studies demonstrate how photo-oxidation leads to fragmentation and release of secondary micro- and nanoplastic fragments, as well as low-molecular weight species. These studies tend to focus on a single exposure condition and a limited number of polymer types. Therefore, this study focuses on systematically evaluating the influence of temperature and relative humidity during simulated UV exposure on the fragmentation and degradation of five types of pristine microplastic powders: polypropylene, low density polyethylene, polyamide 6, high impact polystyrene and thermoplastic polyurethane. We quantified the dose-dependent release of water-soluble organics, as well as secondary micro- and nanoplastics (including their particle size distributions) and found that the polymer identity dictated the type and quantity of species released rather than the aging protocol. With this systematic assessment the generated data can be used in mechanistic microplastic fragmentation models to determine fragmentation rates and fragment size distributions. Microplastics fragmentation degradation photolysis environmental stresses Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 INTRODUCTION The presence of microplastics in the environment has been clearly proven by the large number of field studies conducted in recent years. 1 – 4 Still, the fate and behavior of microplastics, once released into the environment, remains unclear. 5 – 7 Researchers are currently trying to fill knowledge gaps regarding their persistency 8 , 9 and further degradation and fragmentation to potentially harmful nanoplastics or other species. 10 – 13 However, long-term field experiments come with several challenges, e.g. appropriate sampling, 14 , 15 , cross-contamination, 16 , 17 understanding the complexity of environmental impacts, 18 , 19 and micro- and nanoplastic extraction from complex environmental media. 20 , 21 The assumption that microplastics can persist for several decades requires additional accelerated lab-experiments to simulate and understand environmental fragmentation and degradation mechanisms of microplastics, thereby providing data for the parameterization of environmental fate and exposure models. 22 , 23 Environmental degradation of microplastics is based on several complex mechanisms that de-pend on the combination of stresses dominant in a particular environmental compartment. The polymer composition of microplastic particles is of high importance for several environmental processes like hydrolysis, 24 , 25 photolysis, 26 , 27 and enzyme-mediated reactions, 28 , 29 which can induce chemical degradation such as oxidation, crosslinking and chain cleavage. 30 , 31 This chemical degradation directly impacts the susceptibility to fragmentation under mechanical stress. 32 – 34 Literature indicates the importance of environmental stressors for secondary micro- and nanoplastic release and also highlights dissolved organic carbon (DOC) as an additional release pathway (Fig. 1 ). 7 , 35 – 39 Stress on plastics from UV exposure is commonly evaluated due to its potential to degrade plastics at faster rates than other environmental stresses. 40 Earlier studies looked at the mechanism of chain scissions in polymers due to photo-oxidation and photolysis, providing insight into molecular changes that promote the deterioration of useful properties of macroscopic plastic parts. 41 , 42 In turn, more recent studies demonstrate how photo-oxidation leads to fragmentation and degradation of microplastics. 43 – 45 These studies tend to focus on one exposure condition (a single stress) and a limited number of polymers, but in reality combinations of the aforementioned stressors contribute to degradation and fragmentation of microplastics in the environment. Overall, there is a lack of harmonized methods to obtain microplastic fragmentation and degradation rates under various environmental conditions, since up to now few studies addressed this issue. 8 , 32 , 46 , 47 Environmentally realistic fragmentation modelling requires release rates of fragmented particles for single and combined stresses, as well as extensive characterization and size distribution analysis for a large range of polymers. Therefore, this study focuses on systematically evaluating the influence of temperature and relative humidity during ultraviolet (UV) exposure on five pristine microplastic powders and characterizing the powders and their release products at specific time intervals. We recently reported how to measure fragmentation rates to secondary micro- and nanoplastic fragments and their dissociation into dissolved organics, 36 by specifically adapting the NanoRelease protocol 48 , 49 to determine release rates from polyamides (PA) and thermoplastic polyurethanes (TPU), but we only applied one dry UV aging protocol. Here, we additionally varied humidity and temperature conditions, and investigated microplastics from a single grade of each of the following materials: low-density polyethylene (LDPE), polypropylene (PP), and high impact polystyrene (HIPS) artificially aged with three different protocols. The goal was to cover a broad range of different types of polymers. Polyolefins are the most largely used plastic types (approx. 50% of the European plastics consumption). 50 HIPS and TPU have a more complex chemical composition (including phase separation) and therefore a higher potential for fragmentation. 51 One TPU and one PA that were already investigated in our previous study were included as benchmark materials. 36 We determined the chemical degradation, as well as release rates for secondary micro- and nanoplastic fragments, and for low-molecular-weight water-soluble organics. The generated data can be used for the parameterization of environmental fate models, such as the new open-source plastic fragmentation model FRAGMENT-MNP. 52 MATERIALS An injection-molding grade polyamide-6 (PA-6) acquired from BASF SE with intended use in carpets or in compounding, an aromatic thermoplastic polyurethane containing ether bonds in the polyol phase (TPU: TPU_ether_arom in our previous study 36 ) with intended use in cable sheathing, hoses, and films acquired from BASF Polyurethanes, polypropylene (PP; reactor elastomer modified) for application as an automotive coating acquired from Borealis, low density polyethylene (LDPE) acquired from LyondellBasell (relatively low molar mass) with intended use in toys, caps and closures, engineering parts, and sports and leisure equipment, and high impact polystyrene (HIPS) acquired from Formosa Chemicals & Fibre Corporation with intended use in 3D filament printing were used. PA-6, TPU and LDPE are specified as containing no additives. With the UV stabilizing additives contained, this PP grade is quite stress resistant and therefore serves as a negative control for UV stress. As described in our previous publication, 36 the PA-6 powder (< 80 µm) was produced for Selective Laser Sintering by BASF SE. Cryo-milling and sieving of granules from TPU (< 315 µm), 36 PP (< 500 µm), and LDPE (< 500 µm) as well as HIPS filament (< 500 µm) generated polydisperse polymer powders. Selected particle properties and images are provided in the Supporting Information (SI Fig. 1 , SI Table 1 and in our previous study 36 ). METHODS. Artificial UV aging following ISO 4892 (relative humidity = 50% or 75%) and Kalahari protocol . Three aging conditions, with varied UV intensity, temperature, and humidity, were applied for the investigations in this study. Artificial aging was performed using an Atlas SUNTEST XXL conforming to ISO 4892 standardized conditions (Sunlight spectrum, UV intensity of 60 W/m 2 (max. deviation ± 7.0%) in the wavelength range of 300–400 nm, Black Standard Temperature (BST) of 65°C). 36 , 53 Complementary to our previous study the relative humidity (RH) was varied (50% vs. 75%) and monitored. The third UV aging protocol was applied in an Atlas SUNTEST XLS + and is known as the “Kalahari protocol”, which is more aggressive (BST of 90°C, RH = 28%, measured) and is the preferred testing method for automotive coatings. 54 The same sample preparation in each of the aging protocols was applied as described before. 36 In short, thin powder layers (0.7 mm height, duplicates of each polymer) were artificially aged in a petri dish for 1000, 1500 and 2000 hours (216, 324, 432 MJ/m 2 for ISO4892 and for Kalahari) and partially covered with quartz glasses. The aged microplastics were analyzed regarding their surface chemistry via attenuated total reflectance Fourier-transform infrared spectroscopy (ATR FT-IR), their surface texture via scanning electron microscopy (SEM), and their molar mass distribution via gel permeation chromatography (GPC). Additionally, their thermal properties were analyzed via differential scanning calorimetry (DSC) and their particle size distributions via Fraunhofer light scattering. Sampling via ISO22293:2020 NanoRelease protocol. As described before, the NanoRelease protocol can be used for sampling and size-selective quantification of micro- and nanoplastic fragments released from polymers after weathering. 36 , 48 Similar to our previous study, 0.45 g of pristine or UV aged polymer powder were dispersed in 2 mL of ultrapure water with surfactant (sodium dodecyl sulfate, SDS, 1 g/L) and treated with 1 hour of ultrasonication (Sonorex Digital 10P, Bandelin, 100%, 20°C). For primary particle removal, the dispersion was then transferred to a centrifuge vial (Polypropylene 11x60 mm, Beckman Coulter) and left for 5 min for 1-g-sedimentation. The supernatant containing secondary fragments was analyzed by analytical ultracentrifugation with a refractive index detector (AUC-RI, secondary nanoplastics from 0.01 µm to 1 µm) and a single particle counter (secondary microplastics from 1 µm to 139 µm). 36 For the release rate assessment of low molecular weight organics, the same procedure was applied without adding surfactant and with an additional 0.02 µm filter step (Anotop ® , Whatman ® ) to measure the concentration of dissolved organic carbon (DOC). Details of the experimental conditions for ATR FT-IR, GPC, DSC, SEM, Fraunhofer light scattering, AUC-RI, single particle counter and DOC are described in the Supporting Information (SI). RESULTS AND DISCUSSION The intensity of chemical degradation depends on the UV aging conditions and on the polymer type. Chemical degradation of polymers leads to polymer chain cleavage and consequently to a molar mass reduction or crosslinking and consequently a molar mass increase depending on which mechanism is predominant. 30 , 55 Very specifically for UV aging of polymers, the carbonyl index increases by autoxidation and Norrish reactions. 56 , 57 According to literature, amorphous phases in polymers are more affected by UV degradation than crystalline phases, leading to the assumption that environmental aging of microplastics results in an enrichment of highly crystalline regions in microplastics. 35 , 38 , 58 In this study we considered the carbonyl index, the molar mass, and the crystallinity of microplastics to be the most relevant polymer properties to monitor chemical degradation induced by different UV aging protocols. UV aging led to an increase of the carbonyl index for four of the five polymers investigated in this study, in all three aging protocols (Fig. 2 a). The negative control PP was the only exemption, showing no significant differences in the carbonyl index, neither by variations of the UV aging protocol nor by the exposure duration. This is to be expected due to the UV stabilizing additives used in this polymer. 59 The heat map plot (Fig. 2 a) highlights the differences in the UV aging protocols and exposure duration for PA-6, HIPS, LDPE and TPU. In general, independent from the polymer type and the UV aging protocol, an increase of the carbonyl index was detected with increasing exposure duration. However, the resulting carbonyl index strongly depended on the polymer type. The aromatic polymers HIPS and TPU showed the highest values, followed by PA-6 and LDPE with significantly lower values, but still higher than the negative control PP. HIPS and TPU were also the materials with the most intense yellow discoloration, which can be explained by the generation of quinoid chromophore structures during UV irradiation. 60 The systematic increase of the carbonyl index of LDPE with increasing UV aging time depended on humidity during UV aging. Under 75% RH the carbonyl index was lower compared to the other UV aging protocols (Fig. 2 a), indicating that the presence of water molecules slowed down the formation of new carbonyl groups. Low molecular radicals (such as hydroxyl radical formed in the presence of water) can induce termination reactions and hence stop the propagation). 61 Temperature changes, tested in this study with the Kalahari protocol, seemed to have no influence on the formation of carbonyl groups on the surface of LDPE microplastics, but the Kalahari protocol was also the one with the lowest relative humidity of 28%. The carbonyl index of PA-6 was constant over almost all aging protocols and exposure duration (Fig. 2 a). A slightly higher carbonyl index was only observed after 1500 and 2000 h of UV aging with 75% RH, demonstrating that in the case of PA-6 the presence of water molecules supports the formation of new carbonyl groups. PA-6 is known for its high water uptake. 36 Temporal dependency was also observed for HIPS and TPU (Fig. 2 a). However, for the aromatic microplastics the highest values for the carbonyl index were obtained with the ISO 4892 50% RH protocol, indicating that higher temperatures and water content together do not favor the formation of carbonyl groups. In summary, we observed that a higher temperature was not decisive for the increase in the carbonyl index, but the presence of water had a more severe impact on the formation of carbonyl groups, especially when the microplastic type is susceptible. UV aging also led to a reduction of the microplastic molar masses for all polymers except LDPE and TPU, but the differences between the applied UV aging protocols were less pronounced than for the carbonyl index (Fig. 2 b, SI Table 2, SI Table 3). For PA-6, PP, and HIPS, no UV-induced crosslinking was observed, while for LDPE and TPU crosslinking was predominant and led to the formation of gel fractions. The presence of a gel fraction indicates that the polymer is crosslinked beyond the gel point. The weight-average molar mass of a sample crosslinked beyond the gel point is infinite while its number-average molar mass remains finite. With knowledge of the weight fraction of gel, the weight fraction of sol, the molar mass distribution of sol, one can provide a conservative estimate of the molar mass averages of the whole sample by assuming the gel fraction molar mass must exceed the molar mass exclusion limit of the GPC column used (in reality, the weight-average molar mass of the gel is infinite). These estimates for LDPE and TPU are provided in SI Table 3 and Fig. 2 b. PP showed the lowest molar mass reduction of maximum 20%. For PA-6, the molar masses were reduced by over 80% (number M n and mass-based M w ). For HIPS, M n was reduced to a much higher extent (60–80%) than M w (< 20%) and the polydispersity was increased (SI Table 2), implying preferred formation of shorter chains (chain cleavage closer to their terminal chain ends) instead of statistic chain cleavage at any position in the polymer chain. Considering that HIPS is a rubber (butadiene) modified PS this could also mean that one of the two polymer types contained was more affected than the other. Analogous to the observations for the carbonyl index, the molar mass reduction for PA-6 was more pronounced in the presence of water. For LDPE and TPU the molar masses and the weight-fractions of only the soluble polymer could be measured by GPC (SI Table 2), but as described above, molar mass averages of the whole samples were estimated conservatively (SI Table 3). The underlying crosslinking reaction mechanisms for the investigated TPU were described in our previous publication and are based on the recombination of radicals or peroxide bridges in the polyether-polyol soft segments. 36 Similar crosslinking mechanisms are expected for LDPE, since crosslinks are usually formed by the recombination of radicals within the polymer chain (P-P or P-O-O-P crosslinks). 62 For the comparison of the thermal properties, the melting points (T m ) of LDPE, PP and PA-6 were compared after treatment with the three UV exposure protocols (Fig. 2 c, SI Fig. 2 and SI Table 4). For HIPS, the glass transition temperature (T g ) was in the focus (SI Fig. 2 , SI Table 4). The DSC curves of TPU showed no pronounced T g or T m and will therefore not be discussed. The 1st heating curve shows the polymer state directly after the thermal pre-treatment (UV aging at specific temperatures), while the 2nd heating curve (commonly used for DSC data evaluation and comparison) shows the polymer properties after deletion of the thermal prehistory and rearrangement of chains and crystallites but still provides information on changes in the polymer properties due to aging. The UV treatment and especially the presence of water during UV aging had an influence on the T m of PA-6. With increasing aging duration and humidity, the melting temperature was reduced by up to 23°C. In addition, the increasing water content also led to a reduced melting enthalpy ∆H m (SI Fig. 3 ). We interpret that shorter polymer chains (confirmed by GPC measurements) and the presence of water molecules inside of PA-6 particles lead to higher chain mobility and therefore to a reduction of the T m and the crystallinity. 63 , 64 The T m of LDPE was slightly increased by around 3°C (Fig. 2 c, 2nd heating curve) and by around 7°C (1st heating curve) after 2000h of UV aging, which might indicate the degradation of the amorphous phases leading to a slight increase in crystallinity. 65 This was also confirmed by the analysis of ∆H m in the 1st heating curve before and after UV treatments (Fig. 2 c), showing an enthalpy increase. However, a decrease of ∆H m is observed in the 2nd heating curve (SI Table 4). Additionally, since UV aging was done at high temperature, chain rearrangement by tempering could also have led to the observed melting point increase. 66 Even though the molar mass reduction for PP was low, the T m and ∆H m of PP were reduced with increasing UV aging time, indicating polymer chain cleavage and consequently improved chain mobility (Fig. 2 c, SI Fig. 2 & 3 , SI Table 4). The investigation of the T g in HIPS showed the same trend: higher chain mobility due to polymer chain cleavage results in a T g reduction with increasing UV aging duration (SI Fig. 2 , SI Table 4). In general, it is known, that degradation of the amorphous phases happens before the degradation of the crystalline phases, because of their lower compactness and therefore reduced stability. 35 The polymer degradation leads to DOC release and volume loss. But in the case of a fully amorphous or fully crystalline polymer, this theory would not lead to an enrichment of crystalline phases. The PA-6 investigated here might be an example for a very crystalline polymer, while HIPS is completely amorphous. In both cases no crystallinity increase was observed. Changes of the ratio amorphous:crystalline therefore depend on the polymer type (and their chain properties, such as crystallinity, but also glass transition) and on the environmental conditions (improved chain mobility at higher temperature). Qualitative SEM images of the investigated microplastics and their surfaces before and after aging were taken to gain insights into possible fragmentation mechanisms (surface ablation vs. bulk fragmentation). 35 , 38 SI Figs. 4 and 5 display all particles throughout the three aging protocols at 2000 h compared to the pristine particles. In general, the images show that the features in each of the microplastic types were similar across the three protocols. Changes in the surface texture were observed for all polymer types with PP exhibiting only minimal micro-cracks after 2000h Kalahari aging (SI Fig. 5 ). Representative images (after 2000h Kalahari) of HIPS, LDPE, PA-6 and TPU are shown in Fig. 3 . Both HIPS and PA-6 had rough surfaces with nano-sized divots or cracks after aging, while the LDPE particles showed µm-sized cracks in aged particles and SEM images of the TPU indicated fragment release via surface ablation. The aged LDPE particles in Fig. 3 and SI Figs. 4 and 5 show distinct cracks over the full particle dimension indicating substantial degradation and the potential for fragmentation. The cracks in LDPE are shown to be approximately 10 µm in width, which is consistent across all 2000 h aged LDPE samples imaged. Additionally, UV aging of HIPS, LDPE, and PA-6 by the three different aging protocols led to a reduction of the particle sizes compared to the pristine powders, while for TPU an increase of the particle sizes was detected (SI Fig. 6 ). As described above, TPU does not have a distinct melting peak, but a broad melting area and additionally crosslinking was observed. Our results imply that the pristine TPU particles might have softened and crosslinked during the treatment, leading to chemically bonded TPU agglomerates. 67 , 68 Release kinetics for secondary micro- and nanoplastics and dissolved organics Since the impact of the different UV aging protocols on the various types of microplastics investigated influenced the release rates of the degradation species (secondary micro- and nanoplastics, dissolved organic carbon, DOC), a screening method was needed to decide which samples should be analyzed by the advanced techniques. In this study, we used the single particle counter to assess the release of secondary microplastics after all aging stresses were applied. The heat map in Fig. 4 shows the impact of the aging protocols on the fragmentation of the microplastic types investigated, comparing the total counts detected. For HIPS, LDPE, and TPU the total particle counts from the 1 to 139 µm range increased after UV aging, clearly showing the fragmentation of these materials and secondary microplastic release. HIPS showed the highest release of 7.3 ± 3.1∙10 8 counts per gram polymer after 2000 h aging via ISO4892, RH 75%, but this also had the broadest scatter in the duplicate measurements. The effect of the high temperature in the Kalahari protocol to HIPS also led to a high release of 5.4 ± 0.2∙10 8 counts per gram polymer and even the lowest recorded release of 2.8 ± 0.4∙10 8 counts per gram polymer (after 1000 h aging with ISO4892, RH 75% protocol) was still higher than any release from the other microplastic types in any protocol tested. In the case of LDPE, fragmentation was more pronounced at higher UV aging temperature (Kalahari 2000 h: 1.8 ± 0.3∙10 8 counts per gram polymer) and with increasing duration of the UV treatment. This trend was not observed for HIPS treated by Kalahari and ISO4892, RH 50%. Here, the fragmentation was higher after 1000 h, then lower after 1500 h and higher again after 2000 h UV treatment. This might be supported by the published surface ablation mechanism introduced by A. Andrady 35 : After 1000 h UV treatment, the HIPS surface fragments and secondary microplastics are released. Before the next surface layer can be affected, the previously formed fragments need to be removed from the particle surface or further degraded into nanoplastics and other species. This assumption is supported by measurements of the carbonyl index before and after NanoRelease (HIPS, 2000 h ISO4892, RH 50%) showing a reduction of the carbonyl index value by 3.5% after removal of the outermost aged layer. This observation was even more pronounced for LDPE (2000 h ISO4892, RH 50%), where the carbonyl index was reduced by 23.8% after the NanoRelease treatment. Specifically for HIPS, the blend structure can also influence its fragmentation. While the matrix consists of polystyrene, the dispersed phase is based on butadiene rubber. The two polymer types are affected differently by UV aging stresses, which highlights the high potential for defect formation or release of the dispersed phase as secondary micro- or nanoplastics, as observed with Carbon Black or silica fillers. 69 – 71 The aromatic TPU showed low, albeit consistent and measurable, secondary fragment release that increased as UV duration increased. In this case, the release was higher in presence of water (both ISO4892 protocols). In the absence of water, the molecular weight reduction was more pronounced for the investigated TPU, while the carbonyl index was higher in the presence of water. This might indicate that higher temperatures and low humidity lead to the formation of low-molecular polymer chains that would not be released as solid particles, 72 while conversely in this polymer the presence of water molecules favors fragmentation. For PP and PA-6 no increase or decrease in the total particle counts between 1 and 139 µm were detected after all UV aging stresses applied. Since the molecular mass reduction was low for PP and no increase of the carbonyl index detected (Fig. 2 a + b), we assume that the aging duration (and thus accumulated UV dose) was not sufficient to overcome the UV stabilizing additives and induce severe aging of this material. In case of the PA-6, however, the molar mass was drastically reduced and changes in the carbonyl index were detected (Fig. 2 a + b). Furthermore, the size distribution of PA-6 was changed after treatment with both ISO4892 protocols (Fig. 5 a). Numerous 1 µm sized particles were detected after UV aging with ISO4892, RH 50%, exceeding the total 1 µm particle counts of the pristine powder, while the total counts of larger particles were drastically reduced. After treatment with ISO4892, RH 75% exclusively the total particle counts of fragments with sizes from 4 to 30 µm were reduced. In contrast to that the total particle counts of all sizes were increased after any UV treatment of HIPS (Fig. 5 b). Assuming spherical particles, we converted the total particle counts into a mass (separately for each size fraction) and compared the different protocols and timepoints to the initial mass of 1-139 µm fragments detected (Fig. 5 c). With this assumption, the difference in the fragmentation and degradation mechanism of PA-6 and HIPS becomes clear: Since PA-6 takes up water during UV aging, bulk degradation can take place, which leads to shrinkage by bulk volume loss and therefore to a reduction of particle sizes and total particle counts. In contrast, fragmentation is the dominating mechanism during UV treatment of HIPS, attributed to surface ablation and release of daughter fragments, since total particle counts, and mass of fragments increased compared to the pristine material. Notably, the total particle counts of released fragments from HIPS are higher than from PA-6, but the total mass is lower due to the smaller sizes of fragments released. These results support the hypothesis of particle shrinkage for PA-6, as previously reported. 36 This is shown with the increase in 1 µm counts and nanoplastic release from PA-6 after UV aging without humidity control as well as the disappearance of released fragments after 3000 h of UV aging. Several authors concluded that the UV aging of microplastics not only leads to the release of solid secondary micro- and nanoplastics, but also leads to the release of DOC. 36 , 37 , 73 – 76 It is important to note that DOC is only detectable in the closed lab environment, not in environmental monitoring studies, due to filter sampling. The new data reported in this study shows how each polymer has distinct patterns of degradation into secondary microplastics, secondary nanoplastics, and DOC (Fig. 6 , SI Table 5), and that pattern was additionally modulated by humidity and temperature (Fig. 6 a,b,c and SI Table 5), but remained overall remarkably characteristic of each respective polymer. For PP, low releases of all species after all UV aging were detected, which also fits to the low changes in chemical degradation observed for this material. As mentioned before, the dominating transformation mechanism of HIPS is fragmentation in all UV aging protocols, due to the high release of microplastic fragments and low release of DOC and is also the case for LDPE. For both materials the ISO4892 protocol with RH 50% led to higher DOC and reduced secondary microplastic released compared to the other protocols. For PA-6 and TPU, the dominating transformation mechanism is dissolution, due to the high release of DOC and low release of micro- and nanoplastic fragments. In the case of TPU, we observed that the presence of water favors fragmentation, while the DOC release remains stable. With PA-6, we detected the disappearance of larger microplastic fragments (Fig. 5 a), but also the formation of nanoplastics and high DOC releases which implicates particle shrinkage without fragmentation. SI Fig. 6 in our previous publication 36 shows how nanoplastics were formed on the surface of the larger PA-6 particles (probably due to inhomogeneity in aging and non-uniformity of particles) after UV aging, but the half-life of formed nanoplastics remains unclear. In the case of PA-6 the presence of water during UV aging (ISO4892 vs. Kalahari) led to higher release of DOC. CONCLUSION In this study, several environmental stressors (UV, humidity, temperature) were applied with varying time periods to assess the release products from different types of polymers due to environmental aging. While the variation of the aging protocols slightly influenced the release of DOC, micro- and nanoplastics, the polymer composition dictated the species and amount of release products. Comparing both ISO4892 protocols, the presence of water contributed to radical termination mechanisms 61 which led for HIPS, LDPE and TPU to lower carbonyl indices and DOC release, but higher releases of micro- and nanoplastics. The aging and fragmentation mechanism of PA-6 differed from those of the other polymers, probably due to its capability to take up water: 36 instead of fragmentation, we observed a particle shrinkage mechanism, which is accelerated with increasing humidity, leading to higher DOC release. The Kalahari protocol operates at higher temperature, which should accelerate the aging, 61 but at lower humidity than the ISO4892 protocols. In consequence, for LDPE and HIPS the amount of released fragments was in between the release of both ISO4892 protocols. The DOC release from PA-6 was lower after Kalahari, since its main degradation mechanism is dictated by the presence of water. SI Fig. 7 shows the lack of a simple correlation between plastic degradation (here: carbonyl index) and fragmentation (here: microplastic counts), and instead highlights polymer-specific trends. These insights support Safe and Sustainable by Design strategies for new product developments by selecting material-additive combinations with low micro- and nanoplastic release or even low release of any species due to high polymer stability enhanced by stabilizing additives. In the context of environmental risk, it is important that the potential release of additives is also considered alongside release of the polymeric material. 77 This study did not consider additives, but it is worth noting that our negative control, PP, had low releases of all species due to the addition of UV stabilizing additives. While PP might seem preferential to other materials due to low polymer particle release, we did not assess additives contained or released from the microplastic particles, nor did we assess the impact of UV stabilizing additives on the other polymer compositions studied here. Work is currently ongoing to build predictive tools for additive release, which when combined with degradation and fragmentation modeling enabled by this study, will provide a powerful tool for assessing environmental risk. Currently, plastic fate and exposure models treat fragmentation simplistically (for example, using a constant fragmentation rate across degradation state and polymer size), or not at all. 22 , 78 – 81 Even models that include fragmentation often do so as a loss process, which ignores size-differential risk posed by smaller plastic particles, and ignores the loss of particle character for dissolved organics. This study, among others, clearly demonstrates the importance of a more refined approach to fragmentation modeling that considers degradation stresses encountered by plastics in the environment and tracks the full size-distribution of secondary plastic particles and low-molecular-weight species. The data presented herein provide an excellent basis on which to build such a modeling approach, enabling the generation of fragmentation rates and fragment size distributions that are a function of polymer type, additives package, shape (particle, pellet, film, molded article…), the pristine polymer molar mass distribution, particle size and degradation state. By linking the degradation state to stresses encountered in the environment, modelers can scale fragmentation rates according to which environmental compartment plastics are present in, enabling predictive calculations of fragmentation in the environment. For example, in the context of UV aging, plastic particles present in the atmosphere or at the surface of waterbodies are likely to undergo UV aging, whilst particles buried deep in soils will see little UV light (where other stresses, such as biodegradation, are more important). Integrating these refined fragmentation predictions into exposure models is crucial in enabling the environmental risk assessment of polymers that considers the full heterogeneity of plastics in the environment. Abbreviations ATR FT-IR Attenuated total reflectance Fourier-transform infrared spectroscopy AUC-RI Analytical ultracentrifugation with refractive index detector ∆H m Melt enthalpy DOC Dissolved organic carbon DSC Differential scanning calorimetry GPC Gel permeation chromatography HIPS High impact polystyrene LDPE Low density polyethylene M n Number average molecular weight M w Mass average molecular weight PP Polypropylene PA Polyamide SDS Sodium dodecyl sulfate SEM Scanning electron microscopy T g Glass transition temperature T m Melting point TPU Thermoplastic polyurethane UV ultraviolet Declarations ASSOCIATED CONTENT The following file is available free of charge: Additional information on technical properties of the polymers, micrographs of pristine and aged polymers, descriptions of analytical methods and controls, characterization of the investigated polymers before and after UV aging (DSC, GPC, Fraunhofer diffraction), determined releases from AUC, particle counter and DOC, correlation-plot: ∆counts of microplastics vs. carbonyl index increase (PDF). Ethics approval and consent to participate Not applicable. Consent for publication All authors have given approval to the final version of the manuscript. Competing Interests Some of the authors are employees of BASF SE, a company producing and marketing polymers, including plastics. Funding Sources This work was supported by Cefic Long Range Research Initiative under project LRI ECO59 (FRAGMENT-MNP). Author Contribution The manuscript was written and revised through contributions of all authors. All authors have given approval to the final version of the manuscript. PP and KS contributed equally to this work. KS and JS carried out the experiments for this study. SH and MW performed the data curation for modelling purposes. PP wrote the original draft with contributions from KS, JS, MW, SH, CS and WW. All authors approved the final version of the manuscript. WW, CS and MW supervised the project. Acknowledgement The authors sincerely thank Klaus Vilsmeier, Tanja Kiessig, Elke Schumacher, and Alexandre Tetrault for extensive data generation. We are also grateful to Maik Nowak (DSC), Rolf Tompers (DOC) and Bastiaan Staal (GPC on HIPS, TPU, PA) for their scientific advice on polymer analytics and to our project partners Antonia Prätorius (University of Amsterdam), Richard Cross and Gbotemi Adediran (UKCEH) for in depth discussions. We are especially thankful to Dow (David Meunier, Jing Hu, Jingwei Fan, Sarah Pei, Paul Balding, Jianbo Hou, Intan Hamdan) and LyondellBasell (Erik Rushton, Isabella Camurati, Mara Destro, Gabriele Tani) for their outstanding effort in the GPC analysis of partially UV degraded, fragmented, and crosslinked polyolefins. Data Availability The authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information files. 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Supplementary Files SIFragmentationcomparativeMicroplasticsNanoplastics.docx Cite Share Download PDF Status: Published Journal Publication published 06 Mar, 2025 Read the published version in Microplastics and Nanoplastics → Version 1 posted Editorial decision: Revision requested 27 Jan, 2025 Reviews received at journal 20 Jan, 2025 Reviewers agreed at journal 06 Jan, 2025 Reviews received at journal 04 Nov, 2024 Reviewers agreed at journal 23 Oct, 2024 Reviewers invited by journal 23 Oct, 2024 Editor assigned by journal 18 Oct, 2024 Submission checks completed at journal 18 Oct, 2024 First submitted to journal 11 Oct, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5244293","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":367611213,"identity":"d8845da2-5df3-4aef-bb54-482775e61fb8","order_by":0,"name":"Patrizia Pfohl","email":"","orcid":"","institution":"BASF SE","correspondingAuthor":false,"prefix":"","firstName":"Patrizia","middleName":"","lastName":"Pfohl","suffix":""},{"id":367611214,"identity":"db666cdf-5acf-4ea9-b907-ffc9aa5f632c","order_by":1,"name":"Katherine Santizo","email":"","orcid":"","institution":"BASF SE","correspondingAuthor":false,"prefix":"","firstName":"Katherine","middleName":"","lastName":"Santizo","suffix":""},{"id":367611215,"identity":"1f217f7e-4194-4c6e-9ea3-9d4d58ce01ec","order_by":2,"name":"Joana Sipe","email":"","orcid":"","institution":"Duke University","correspondingAuthor":false,"prefix":"","firstName":"Joana","middleName":"","lastName":"Sipe","suffix":""},{"id":367611216,"identity":"4e27bf4c-af0a-4933-a632-4edcbcc3fa7d","order_by":3,"name":"Mark Wiesner","email":"","orcid":"","institution":"Duke University","correspondingAuthor":false,"prefix":"","firstName":"Mark","middleName":"","lastName":"Wiesner","suffix":""},{"id":367611217,"identity":"fa05b4dc-cc56-4d22-9f73-9de33acc2486","order_by":4,"name":"Sam Harrison","email":"","orcid":"","institution":"UK Centre for Ecology \u0026 Hydrology","correspondingAuthor":false,"prefix":"","firstName":"Sam","middleName":"","lastName":"Harrison","suffix":""},{"id":367611218,"identity":"6dc7feb4-4c13-4ecb-8e43-4af8c2f3bc87","order_by":5,"name":"Claus Svendsen","email":"","orcid":"","institution":"UK Centre for Ecology \u0026 Hydrology","correspondingAuthor":false,"prefix":"","firstName":"Claus","middleName":"","lastName":"Svendsen","suffix":""},{"id":367611219,"identity":"6339b92a-8879-483e-98d2-57d25a5def65","order_by":6,"name":"Wendel Wohlleben","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABB0lEQVRIiWNgGAWjYJACCYYCEMnceICxgYGBXwLIqSCoxQBEMjaAtUjOAHLOkKTF4AYBLQbHew/e+GDAkNgv3dhw4OMOmzzj282PPxxgsJPTbcCh5cy5ZMsZQC0z5xxsODjzTFqx2Z1jZhIHGJKNzQ5g12J2I8dMmseAIXfDjcSGw7xthxO33UgwY/7AcCBxGy4t99+YSf+Bafnb9j9x84z0z0CH4dFyg8dMmgGmhbHtQOIGiRwDCXxa7M/kGFv2GEjUz5yR2HCw90xy4ow7Z8okDhjg9otk+xnDGz8qbIz5JZIPPvi5wy6xf3b75g8HKuzkcGmBAgl0AQO8ykfBKBgFo2AUEAAAJBBsmIUbw80AAAAASUVORK5CYII=","orcid":"","institution":"BASF SE","correspondingAuthor":true,"prefix":"","firstName":"Wendel","middleName":"","lastName":"Wohlleben","suffix":""}],"badges":[],"createdAt":"2024-10-11 07:53:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5244293/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5244293/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s43591-025-00118-9","type":"published","date":"2025-03-06T15:57:39+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":67119508,"identity":"42271888-c043-488b-ad5a-57dedcec4c02","added_by":"auto","created_at":"2024-10-21 11:02:17","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":388342,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic representation of fragmentation and degradation steps during the aging of microplastics in the environment. Due to chemical degradation, microplastic particles are more prone to mechanical stress, leading to surface abrasion or bulk fragmentation and secondary micro- and nanoplastic release, which might tend to form agglomerates. In parallel, dissolved organic carbon constitutes an additional release pathway forming its own degradation network.\u003csup\u003e35-38\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"floatimage153.png","url":"https://assets-eu.researchsquare.com/files/rs-5244293/v1/93dadd970d482b16c85d8edd.png"},{"id":67118851,"identity":"29d434b0-9c44-49b3-8cd9-58755b863750","added_by":"auto","created_at":"2024-10-21 10:54:17","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":431663,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in chemical properties observed after UV-humidity-temperature aging of different types of microplastics; a) carbonyl index for all polymers, all UV aging protocols and all timepoints; b) molar mass relative to pristine for all polymers after 2000h UV aging for all aging protocols: left part are number based molar masses M\u003csub\u003en\u003c/sub\u003e, right part are mass based molar masses M\u003csub\u003ew\u003c/sub\u003e; c) melt point T\u003csub\u003em\u003c/sub\u003e decrease for PA-6, melt point T\u003csub\u003em\u003c/sub\u003e increase for LDPE with increasing UV irradiation time (2\u003csup\u003end\u003c/sup\u003e heating curve), and changes in melting enthalpy ∆H\u003csub\u003em\u003c/sub\u003e for PP and LDPE after 2000h UV aging in all aging protocols (1\u003csup\u003est\u003c/sup\u003e heating curve).\u003c/p\u003e","description":"","filename":"floatimage220.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5244293/v1/7ac1073b236eed2eac013638.jpeg"},{"id":67118853,"identity":"96946926-d67c-4c6e-b895-01eb45794000","added_by":"auto","created_at":"2024-10-21 10:54:17","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":659971,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in the surface texture observed for HIPS, LDPE, PA-6 and TPU after 2000h aging via Kalahari protocol\u003c/p\u003e","description":"","filename":"floatimage334.png","url":"https://assets-eu.researchsquare.com/files/rs-5244293/v1/42b574f82d084d2282894db1.png"},{"id":67118849,"identity":"9c3d3652-a064-4f0d-86f4-0900a52cfa4f","added_by":"auto","created_at":"2024-10-21 10:54:17","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":92804,"visible":true,"origin":"","legend":"\u003cp\u003eTotal particle counts from 1 to 139 µm detected before and after UV aging of 5 different microplastic types by 3 different UV aging protocols and 3 timepoints. The UV aging protocols (Kalahari, ISO4892 50% and 75%) varied in temperature and relative humidity.\u003c/p\u003e","description":"","filename":"floatimage428.png","url":"https://assets-eu.researchsquare.com/files/rs-5244293/v1/11f83da05a79e61ffb751889.png"},{"id":67119510,"identity":"b89b7173-7343-4bb4-9880-0ba76d5bb6a7","added_by":"auto","created_at":"2024-10-21 11:02:17","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":266469,"visible":true,"origin":"","legend":"\u003cp\u003eTotal particle counts 1-139 µm detected for a) PA-6 and b) HIPS before and after 2000h UV aging by three different UV aging protocols (Kalahari, ISO4892 RH = 50% and RH = 75%). c) Conversion of the total particle counts (each size bin separately) into a total mass.\u003c/p\u003e","description":"","filename":"floatimage519.png","url":"https://assets-eu.researchsquare.com/files/rs-5244293/v1/b4a1c6b7374fae86ee676f46.png"},{"id":67119509,"identity":"3e22a47f-f6c5-4953-be17-9962ac64311f","added_by":"auto","created_at":"2024-10-21 11:02:17","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":134697,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of releases in mg per gram polymer of different release species (secondary microplastics, secondary nanoplastics, dissolved organic carbon) after 2000 h aging with different UV aging protocols, values of pristine material subtracted; a) Kalahari, b) ISO4892, RH=50%, c) ISO4892, RH=75%. For PA-6 the “microplastic release” was set to zero because only overall particle shrinkage (i.e., less mass) was detected after UV aging compared to the pristine material (compare to Figure 5).\u003c/p\u003e","description":"","filename":"floatimage610.png","url":"https://assets-eu.researchsquare.com/files/rs-5244293/v1/f28ea483599cc986016dbe26.png"},{"id":78183941,"identity":"e69ac53e-e894-413a-8ff2-cc3f69342c02","added_by":"auto","created_at":"2025-03-10 18:19:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2751708,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5244293/v1/b214cfe5-4c25-4bc9-abb0-ce523be798d5.pdf"},{"id":67118855,"identity":"1ca79622-2394-4ed9-a5e4-7378ae2ca47e","added_by":"auto","created_at":"2024-10-21 10:54:18","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":3293783,"visible":true,"origin":"","legend":"","description":"","filename":"SIFragmentationcomparativeMicroplasticsNanoplastics.docx","url":"https://assets-eu.researchsquare.com/files/rs-5244293/v1/a1f50c84181c8066a595c659.docx"}],"financialInterests":"Competing interest reported. Some of the authors are employees of BASF SE, a company producing and marketing polymers, including plastics.","formattedTitle":"Environmental Degradation and Fragmentation of Microplastics: Dependence on Polymer Type, Humidity, UV Dose and Temperature","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eThe presence of microplastics in the environment has been clearly proven by the large number of field studies conducted in recent years.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e–\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e Still, the fate and behavior of microplastics, once released into the environment, remains unclear.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e–\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e Researchers are currently trying to fill knowledge gaps regarding their persistency\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e and further degradation and fragmentation to potentially harmful nanoplastics or other species.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e–\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e However, long-term field experiments come with several challenges, e.g. appropriate sampling,\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e, cross-contamination,\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e understanding the complexity of environmental impacts,\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e and micro- and nanoplastic extraction from complex environmental media.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e The assumption that microplastics can persist for several decades requires additional accelerated lab-experiments to simulate and understand environmental fragmentation and degradation mechanisms of microplastics, thereby providing data for the parameterization of environmental fate and exposure models.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eEnvironmental degradation of microplastics is based on several complex mechanisms that de-pend on the combination of stresses dominant in a particular environmental compartment. The polymer composition of microplastic particles is of high importance for several environmental processes like hydrolysis,\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e photolysis,\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e and enzyme-mediated reactions,\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e which can induce chemical degradation such as oxidation, crosslinking and chain cleavage.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e This chemical degradation directly impacts the susceptibility to fragmentation under mechanical stress.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e–\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e Literature indicates the importance of environmental stressors for secondary micro- and nanoplastic release and also highlights dissolved organic carbon (DOC) as an additional release pathway (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e–\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e Stress on plastics from UV exposure is commonly evaluated due to its potential to degrade plastics at faster rates than other environmental stresses.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e Earlier studies looked at the mechanism of chain scissions in polymers due to photo-oxidation and photolysis, providing insight into molecular changes that promote the deterioration of useful properties of macroscopic plastic parts.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e In turn, more recent studies demonstrate how photo-oxidation leads to fragmentation and degradation of microplastics.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e43\u003c/span\u003e–\u003cspan class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e These studies tend to focus on one exposure condition (a single stress) and a limited number of polymers, but in reality combinations of the aforementioned stressors contribute to degradation and fragmentation of microplastics in the environment. Overall, there is a lack of harmonized methods to obtain microplastic fragmentation and degradation rates under various environmental conditions, since up to now few studies addressed this issue.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e46\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e Environmentally realistic fragmentation modelling requires release rates of fragmented particles for single and combined stresses, as well as extensive characterization and size distribution analysis for a large range of polymers.\u003c/p\u003e\n\u003cp\u003eTherefore, this study focuses on systematically evaluating the influence of temperature and relative humidity during ultraviolet (UV) exposure on five pristine microplastic powders and characterizing the powders and their release products at specific time intervals. We recently reported how to measure fragmentation rates to secondary micro- and nanoplastic fragments and their dissociation into dissolved organics,\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e by specifically adapting the NanoRelease protocol\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e to determine release rates from polyamides (PA) and thermoplastic polyurethanes (TPU), but we only applied one dry UV aging protocol. Here, we additionally varied humidity and temperature conditions, and investigated microplastics from a single grade of each of the following materials: low-density polyethylene (LDPE), polypropylene (PP), and high impact polystyrene (HIPS) artificially aged with three different protocols. The goal was to cover a broad range of different types of polymers. Polyolefins are the most largely used plastic types (approx. 50% of the European plastics consumption).\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e HIPS and TPU have a more complex chemical composition (including phase separation) and therefore a higher potential for fragmentation.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e One TPU and one PA that were already investigated in our previous study were included as benchmark materials.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e We determined the chemical degradation, as well as release rates for secondary micro- and nanoplastic fragments, and for low-molecular-weight water-soluble organics. The generated data can be used for the parameterization of environmental fate models, such as the new open-source plastic fragmentation model FRAGMENT-MNP.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"},{"header":"MATERIALS","content":"\u003cp\u003eAn injection-molding grade polyamide-6 (PA-6) acquired from BASF SE with intended use in carpets or in compounding, an aromatic thermoplastic polyurethane containing ether bonds in the polyol phase (TPU: TPU_ether_arom in our previous study\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e) with intended use in cable sheathing, hoses, and films acquired from BASF Polyurethanes, polypropylene (PP; reactor elastomer modified) for application as an automotive coating acquired from Borealis, low density polyethylene (LDPE) acquired from LyondellBasell (relatively low molar mass) with intended use in toys, caps and closures, engineering parts, and sports and leisure equipment, and high impact polystyrene (HIPS) acquired from Formosa Chemicals \u0026amp; Fibre Corporation with intended use in 3D filament printing were used. PA-6, TPU and LDPE are specified as containing no additives. With the UV stabilizing additives contained, this PP grade is quite stress resistant and therefore serves as a negative control for UV stress. As described in our previous publication,\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e the PA-6 powder (\u0026lt; 80 µm) was produced for Selective Laser Sintering by BASF SE. Cryo-milling and sieving of granules from TPU (\u0026lt; 315 µm),\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e PP (\u0026lt; 500 µm), and LDPE (\u0026lt; 500 µm) as well as HIPS filament (\u0026lt; 500 µm) generated polydisperse polymer powders. Selected particle properties and images are provided in the Supporting Information (SI Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, SI Table\u0026nbsp;1 and in our previous study\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e).\u003c/p\u003e\u003cp\u003eMETHODS. \u003cem\u003eArtificial UV aging following ISO 4892 (relative humidity = 50% or 75%) and Kalahari protocol\u003c/em\u003e. Three aging conditions, with varied UV intensity, temperature, and humidity, were applied for the investigations in this study. Artificial aging was performed using an Atlas SUNTEST XXL conforming to ISO 4892 standardized conditions (Sunlight spectrum, UV intensity of 60 W/m\u003csup\u003e2\u003c/sup\u003e (max. deviation ± 7.0%) in the wavelength range of 300–400 nm, Black Standard Temperature (BST) of 65°C).\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e Complementary to our previous study the relative humidity (RH) was varied (50% vs. 75%) and monitored. The third UV aging protocol was applied in an Atlas SUNTEST XLS + and is known as the “Kalahari protocol”, which is more aggressive (BST of 90°C, RH = 28%, measured) and is the preferred testing method for automotive coatings.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e The same sample preparation in each of the aging protocols was applied as described before.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e In short, thin powder layers (0.7 mm height, duplicates of each polymer) were artificially aged in a petri dish for 1000, 1500 and 2000 hours (216, 324, 432 MJ/m\u003csup\u003e2\u003c/sup\u003e for ISO4892 and for Kalahari) and partially covered with quartz glasses. The aged microplastics were analyzed regarding their surface chemistry via attenuated total reflectance Fourier-transform infrared spectroscopy (ATR FT-IR), their surface texture via scanning electron microscopy (SEM), and their molar mass distribution via gel permeation chromatography (GPC). Additionally, their thermal properties were analyzed via differential scanning calorimetry (DSC) and their particle size distributions via Fraunhofer light scattering.\u003c/p\u003e\u003cp\u003e\u003cem\u003eSampling via ISO22293:2020 NanoRelease protocol.\u003c/em\u003e As described before, the NanoRelease protocol can be used for sampling and size-selective quantification of micro- and nanoplastic fragments released from polymers after weathering.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e Similar to our previous study, 0.45 g of pristine or UV aged polymer powder were dispersed in 2 mL of ultrapure water with surfactant (sodium dodecyl sulfate, SDS, 1 g/L) and treated with 1 hour of ultrasonication (Sonorex Digital 10P, Bandelin, 100%, 20°C). For primary particle removal, the dispersion was then transferred to a centrifuge vial (Polypropylene 11x60 mm, Beckman Coulter) and left for 5 min for 1-g-sedimentation. The supernatant containing secondary fragments was analyzed by analytical ultracentrifugation with a refractive index detector (AUC-RI, secondary nanoplastics from 0.01 µm to 1 µm) and a single particle counter (secondary microplastics from 1 µm to 139 µm).\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e For the release rate assessment of low molecular weight organics, the same procedure was applied without adding surfactant and with an additional 0.02 µm filter step (Anotop\u003csup\u003e®\u003c/sup\u003e, Whatman\u003csup\u003e®\u003c/sup\u003e) to measure the concentration of dissolved organic carbon (DOC).\u003c/p\u003e\u003cp\u003eDetails of the experimental conditions for ATR FT-IR, GPC, DSC, SEM, Fraunhofer light scattering, AUC-RI, single particle counter and DOC are described in the Supporting Information (SI).\u003c/p\u003e"},{"header":"RESULTS AND DISCUSSION","content":"\u003cp\u003e\u003cem\u003eThe intensity of chemical degradation depends on the UV aging conditions and on the polymer type.\u003c/em\u003e Chemical degradation of polymers leads to polymer chain cleavage and consequently to a molar mass reduction or crosslinking and consequently a molar mass increase depending on which mechanism is predominant.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e Very specifically for UV aging of polymers, the carbonyl index increases by autoxidation and Norrish reactions.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e56\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e According to literature, amorphous phases in polymers are more affected by UV degradation than crystalline phases, leading to the assumption that environmental aging of microplastics results in an enrichment of highly crystalline regions in microplastics.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e In this study we considered the carbonyl index, the molar mass, and the crystallinity of microplastics to be the most relevant polymer properties to monitor chemical degradation induced by different UV aging protocols.\u003c/p\u003e\u003cp\u003eUV aging led to an increase of the carbonyl index for four of the five polymers investigated in this study, in all three aging protocols (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea). The negative control PP was the only exemption, showing no significant differences in the carbonyl index, neither by variations of the UV aging protocol nor by the exposure duration. This is to be expected due to the UV stabilizing additives used in this polymer.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e The heat map plot (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea) highlights the differences in the UV aging protocols and exposure duration for PA-6, HIPS, LDPE and TPU. In general, independent from the polymer type and the UV aging protocol, an increase of the carbonyl index was detected with increasing exposure duration. However, the resulting carbonyl index strongly depended on the polymer type. The aromatic polymers HIPS and TPU showed the highest values, followed by PA-6 and LDPE with significantly lower values, but still higher than the negative control PP. HIPS and TPU were also the materials with the most intense yellow discoloration, which can be explained by the generation of quinoid chromophore structures during UV irradiation.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e The systematic increase of the carbonyl index of LDPE with increasing UV aging time depended on humidity during UV aging. Under 75% RH the carbonyl index was lower compared to the other UV aging protocols (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea), indicating that the presence of water molecules slowed down the formation of new carbonyl groups. Low molecular radicals (such as hydroxyl radical formed in the presence of water) can induce termination reactions and hence stop the propagation).\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e Temperature changes, tested in this study with the Kalahari protocol, seemed to have no influence on the formation of carbonyl groups on the surface of LDPE microplastics, but the Kalahari protocol was also the one with the lowest relative humidity of 28%. The carbonyl index of PA-6 was constant over almost all aging protocols and exposure duration (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea). A slightly higher carbonyl index was only observed after 1500 and 2000 h of UV aging with 75% RH, demonstrating that in the case of PA-6 the presence of water molecules supports the formation of new carbonyl groups. PA-6 is known for its high water uptake.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e Temporal dependency was also observed for HIPS and TPU (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea). However, for the aromatic microplastics the highest values for the carbonyl index were obtained with the ISO 4892 50% RH protocol, indicating that higher temperatures and water content together do not favor the formation of carbonyl groups. In summary, we observed that a higher temperature was not decisive for the increase in the carbonyl index, but the presence of water had a more severe impact on the formation of carbonyl groups, especially when the microplastic type is susceptible.\u003c/p\u003e\u003cp\u003eUV aging also led to a reduction of the microplastic molar masses for all polymers except LDPE and TPU, but the differences between the applied UV aging protocols were less pronounced than for the carbonyl index (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb, SI Table\u0026nbsp;2, SI Table\u0026nbsp;3). For PA-6, PP, and HIPS, no UV-induced crosslinking was observed, while for LDPE and TPU crosslinking was predominant and led to the formation of gel fractions. The presence of a gel fraction indicates that the polymer is crosslinked beyond the gel point. The weight-average molar mass of a sample crosslinked beyond the gel point is infinite while its number-average molar mass remains finite. With knowledge of the weight fraction of gel, the weight fraction of sol, the molar mass distribution of sol, one can provide a conservative estimate of the molar mass averages of the whole sample by assuming the gel fraction molar mass must exceed the molar mass exclusion limit of the GPC column used (in reality, the weight-average molar mass of the gel is infinite). These estimates for LDPE and TPU are provided in SI Table\u0026nbsp;3 and Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb. PP showed the lowest molar mass reduction of maximum 20%. For PA-6, the molar masses were reduced by over 80% (number M\u003csub\u003en\u003c/sub\u003e and mass-based M\u003csub\u003ew\u003c/sub\u003e). For HIPS, M\u003csub\u003en\u003c/sub\u003e was reduced to a much higher extent (60–80%) than M\u003csub\u003ew\u003c/sub\u003e (\u0026lt; 20%) and the polydispersity was increased (SI Table\u0026nbsp;2), implying preferred formation of shorter chains (chain cleavage closer to their terminal chain ends) instead of statistic chain cleavage at any position in the polymer chain. Considering that HIPS is a rubber (butadiene) modified PS this could also mean that one of the two polymer types contained was more affected than the other. Analogous to the observations for the carbonyl index, the molar mass reduction for PA-6 was more pronounced in the presence of water. For LDPE and TPU the molar masses and the weight-fractions of only the soluble polymer could be measured by GPC (SI Table\u0026nbsp;2), but as described above, molar mass averages of the whole samples were estimated conservatively (SI Table\u0026nbsp;3). The underlying crosslinking reaction mechanisms for the investigated TPU were described in our previous publication and are based on the recombination of radicals or peroxide bridges in the polyether-polyol soft segments.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e Similar crosslinking mechanisms are expected for LDPE, since crosslinks are usually formed by the recombination of radicals within the polymer chain (P-P or P-O-O-P crosslinks).\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eFor the comparison of the thermal properties, the melting points (T\u003csub\u003em\u003c/sub\u003e) of LDPE, PP and PA-6 were compared after treatment with the three UV exposure protocols (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec, SI Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and SI Table 4). For HIPS, the glass transition temperature (T\u003csub\u003eg\u003c/sub\u003e) was in the focus (SI Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, SI Table\u0026nbsp;4). The DSC curves of TPU showed no pronounced T\u003csub\u003eg\u003c/sub\u003e or T\u003csub\u003em\u003c/sub\u003e and will therefore not be discussed. The 1st heating curve shows the polymer state directly after the thermal pre-treatment (UV aging at specific temperatures), while the 2nd heating curve (commonly used for DSC data evaluation and comparison) shows the polymer properties after deletion of the thermal prehistory and rearrangement of chains and crystallites but still provides information on changes in the polymer properties due to aging.\u003c/p\u003e\u003cp\u003eThe UV treatment and especially the presence of water during UV aging had an influence on the T\u003csub\u003em\u003c/sub\u003e of PA-6. With increasing aging duration and humidity, the melting temperature was reduced by up to 23°C. In addition, the increasing water content also led to a reduced melting enthalpy ∆H\u003csub\u003em\u003c/sub\u003e (SI Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). We interpret that shorter polymer chains (confirmed by GPC measurements) and the presence of water molecules inside of PA-6 particles lead to higher chain mobility and therefore to a reduction of the T\u003csub\u003em\u003c/sub\u003e and the crystallinity.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e63\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e64\u003c/span\u003e\u003c/sup\u003e The T\u003csub\u003em\u003c/sub\u003e of LDPE was slightly increased by around 3°C (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec, 2nd heating curve) and by around 7°C (1st heating curve) after 2000h of UV aging, which might indicate the degradation of the amorphous phases leading to a slight increase in crystallinity.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e65\u003c/span\u003e\u003c/sup\u003e This was also confirmed by the analysis of ∆H\u003csub\u003em\u003c/sub\u003e in the 1st heating curve before and after UV treatments (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec), showing an enthalpy increase. However, a decrease of ∆H\u003csub\u003em\u003c/sub\u003e is observed in the 2nd heating curve (SI Table 4). Additionally, since UV aging was done at high temperature, chain rearrangement by tempering could also have led to the observed melting point increase.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e66\u003c/span\u003e\u003c/sup\u003e Even though the molar mass reduction for PP was low, the T\u003csub\u003em\u003c/sub\u003e and ∆H\u003csub\u003em\u003c/sub\u003e of PP were reduced with increasing UV aging time, indicating polymer chain cleavage and consequently improved chain mobility (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec, SI Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e\u0026amp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, SI Table\u0026nbsp;4). The investigation of the T\u003csub\u003eg\u003c/sub\u003e in HIPS showed the same trend: higher chain mobility due to polymer chain cleavage results in a T\u003csub\u003eg\u003c/sub\u003e reduction with increasing UV aging duration (SI Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, SI Table\u0026nbsp;4). In general, it is known, that degradation of the amorphous phases happens before the degradation of the crystalline phases, because of their lower compactness and therefore reduced stability.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e The polymer degradation leads to DOC release and volume loss. But in the case of a fully amorphous or fully crystalline polymer, this theory would not lead to an enrichment of crystalline phases. The PA-6 investigated here might be an example for a very crystalline polymer, while HIPS is completely amorphous. In both cases no crystallinity increase was observed. Changes of the ratio amorphous:crystalline therefore depend on the polymer type (and their chain properties, such as crystallinity, but also glass transition) and on the environmental conditions (improved chain mobility at higher temperature).\u003c/p\u003e\u003cp\u003eQualitative SEM images of the investigated microplastics and their surfaces before and after aging were taken to gain insights into possible fragmentation mechanisms (surface ablation vs. bulk fragmentation).\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e SI Figs. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e display all particles throughout the three aging protocols at 2000 h compared to the pristine particles. In general, the images show that the features in each of the microplastic types were similar across the three protocols. Changes in the surface texture were observed for all polymer types with PP exhibiting only minimal micro-cracks after 2000h Kalahari aging (SI Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). Representative images (after 2000h Kalahari) of HIPS, LDPE, PA-6 and TPU are shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. Both HIPS and PA-6 had rough surfaces with nano-sized divots or cracks after aging, while the LDPE particles showed µm-sized cracks in aged particles and SEM images of the TPU indicated fragment release via surface ablation. The aged LDPE particles in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e and SI Figs. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e show distinct cracks over the full particle dimension indicating substantial degradation and the potential for fragmentation. The cracks in LDPE are shown to be approximately 10 µm in width, which is consistent across all 2000 h aged LDPE samples imaged.\u003c/p\u003e\u003cp\u003eAdditionally, UV aging of HIPS, LDPE, and PA-6 by the three different aging protocols led to a reduction of the particle sizes compared to the pristine powders, while for TPU an increase of the particle sizes was detected (SI Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). As described above, TPU does not have a distinct melting peak, but a broad melting area and additionally crosslinking was observed. Our results imply that the pristine TPU particles might have softened and crosslinked during the treatment, leading to chemically bonded TPU agglomerates.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e67\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e68\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003ch3\u003eRelease kinetics for secondary micro- and nanoplastics and dissolved organics\u003c/h3\u003e\u003cp\u003eSince the impact of the different UV aging protocols on the various types of microplastics investigated influenced the release rates of the degradation species (secondary micro- and nanoplastics, dissolved organic carbon, DOC), a screening method was needed to decide which samples should be analyzed by the advanced techniques. In this study, we used the single particle counter to assess the release of secondary microplastics after all aging stresses were applied. The heat map in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e shows the impact of the aging protocols on the fragmentation of the microplastic types investigated, comparing the total counts detected.\u003c/p\u003e\u003cp\u003eFor HIPS, LDPE, and TPU the total particle counts from the 1 to 139 µm range increased after UV aging, clearly showing the fragmentation of these materials and secondary microplastic release. HIPS showed the highest release of 7.3 ± 3.1∙10\u003csup\u003e8\u003c/sup\u003e counts per gram polymer after 2000 h aging via ISO4892, RH 75%, but this also had the broadest scatter in the duplicate measurements. The effect of the high temperature in the Kalahari protocol to HIPS also led to a high release of 5.4 ± 0.2∙10\u003csup\u003e8\u003c/sup\u003e counts per gram polymer and even the lowest recorded release of 2.8 ± 0.4∙10\u003csup\u003e8\u003c/sup\u003e counts per gram polymer (after 1000 h aging with ISO4892, RH 75% protocol) was still higher than any release from the other microplastic types in any protocol tested. In the case of LDPE, fragmentation was more pronounced at higher UV aging temperature (Kalahari 2000 h: 1.8 ± 0.3∙10\u003csup\u003e8\u003c/sup\u003e counts per gram polymer) and with increasing duration of the UV treatment. This trend was not observed for HIPS treated by Kalahari and ISO4892, RH 50%. Here, the fragmentation was higher after 1000 h, then lower after 1500 h and higher again after 2000 h UV treatment. This might be supported by the published surface ablation mechanism introduced by A. Andrady\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e: After 1000 h UV treatment, the HIPS surface fragments and secondary microplastics are released. Before the next surface layer can be affected, the previously formed fragments need to be removed from the particle surface or further degraded into nanoplastics and other species. This assumption is supported by measurements of the carbonyl index before and after NanoRelease (HIPS, 2000 h ISO4892, RH 50%) showing a reduction of the carbonyl index value by 3.5% after removal of the outermost aged layer. This observation was even more pronounced for LDPE (2000 h ISO4892, RH 50%), where the carbonyl index was reduced by 23.8% after the NanoRelease treatment. Specifically for HIPS, the blend structure can also influence its fragmentation. While the matrix consists of polystyrene, the dispersed phase is based on butadiene rubber. The two polymer types are affected differently by UV aging stresses, which highlights the high potential for defect formation or release of the dispersed phase as secondary micro- or nanoplastics, as observed with Carbon Black or silica fillers.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e69\u003c/span\u003e–\u003cspan class=\"CitationRef\"\u003e71\u003c/span\u003e\u003c/sup\u003e The aromatic TPU showed low, albeit consistent and measurable, secondary fragment release that increased as UV duration increased. In this case, the release was higher in presence of water (both ISO4892 protocols). In the absence of water, the molecular weight reduction was more pronounced for the investigated TPU, while the carbonyl index was higher in the presence of water. This might indicate that higher temperatures and low humidity lead to the formation of low-molecular polymer chains that would not be released as solid particles,\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e72\u003c/span\u003e\u003c/sup\u003e while conversely in this polymer the presence of water molecules favors fragmentation. For PP and PA-6 no increase or decrease in the total particle counts between 1 and 139 µm were detected after all UV aging stresses applied. Since the molecular mass reduction was low for PP and no increase of the carbonyl index detected (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea + b), we assume that the aging duration (and thus accumulated UV dose) was not sufficient to overcome the UV stabilizing additives and induce severe aging of this material. In case of the PA-6, however, the molar mass was drastically reduced and changes in the carbonyl index were detected (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea + b). Furthermore, the size distribution of PA-6 was changed after treatment with both ISO4892 protocols (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea). Numerous 1 µm sized particles were detected after UV aging with ISO4892, RH 50%, exceeding the total 1 µm particle counts of the pristine powder, while the total counts of larger particles were drastically reduced. After treatment with ISO4892, RH 75% exclusively the total particle counts of fragments with sizes from 4 to 30 µm were reduced. In contrast to that the total particle counts of all sizes were increased after any UV treatment of HIPS (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb). Assuming spherical particles, we converted the total particle counts into a mass (separately for each size fraction) and compared the different protocols and timepoints to the initial mass of 1-139 µm fragments detected (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ec). With this assumption, the difference in the fragmentation and degradation mechanism of PA-6 and HIPS becomes clear: Since PA-6 takes up water during UV aging, bulk degradation can take place, which leads to shrinkage by bulk volume loss and therefore to a reduction of particle sizes and total particle counts. In contrast, fragmentation is the dominating mechanism during UV treatment of HIPS, attributed to surface ablation and release of daughter fragments, since total particle counts, and mass of fragments increased compared to the pristine material. Notably, the total particle counts of released fragments from HIPS are higher than from PA-6, but the total mass is lower due to the smaller sizes of fragments released. These results support the hypothesis of particle shrinkage for PA-6, as previously reported.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e This is shown with the increase in 1 µm counts and nanoplastic release from PA-6 after UV aging without humidity control as well as the disappearance of released fragments after 3000 h of UV aging.\u003c/p\u003e\u003cp\u003eSeveral authors concluded that the UV aging of microplastics not only leads to the release of solid secondary micro- and nanoplastics, but also leads to the release of DOC.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e73\u003c/span\u003e–\u003cspan class=\"CitationRef\"\u003e76\u003c/span\u003e\u003c/sup\u003e It is important to note that DOC is only detectable in the closed lab environment, not in environmental monitoring studies, due to filter sampling. The new data reported in this study shows how each polymer has distinct patterns of degradation into secondary microplastics, secondary nanoplastics, and DOC (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, SI Table 5), and that pattern was additionally modulated by humidity and temperature (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea,b,c and SI Table 5), but remained overall remarkably characteristic of each respective polymer. For PP, low releases of all species after all UV aging were detected, which also fits to the low changes in chemical degradation observed for this material. As mentioned before, the dominating transformation mechanism of HIPS is fragmentation in all UV aging protocols, due to the high release of microplastic fragments and low release of DOC and is also the case for LDPE. For both materials the ISO4892 protocol with RH 50% led to higher DOC and reduced secondary microplastic released compared to the other protocols. For PA-6 and TPU, the dominating transformation mechanism is dissolution, due to the high release of DOC and low release of micro- and nanoplastic fragments. In the case of TPU, we observed that the presence of water favors fragmentation, while the DOC release remains stable. With PA-6, we detected the disappearance of larger microplastic fragments (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea), but also the formation of nanoplastics and high DOC releases which implicates particle shrinkage without fragmentation. SI Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e in our previous publication\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e shows how nanoplastics were formed on the surface of the larger PA-6 particles (probably due to inhomogeneity in aging and non-uniformity of particles) after UV aging, but the half-life of formed nanoplastics remains unclear. In the case of PA-6 the presence of water during UV aging (ISO4892 vs. Kalahari) led to higher release of DOC.\u003c/p\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003eIn this study, several environmental stressors (UV, humidity, temperature) were applied with varying time periods to assess the release products from different types of polymers due to environmental aging. While the variation of the aging protocols slightly influenced the release of DOC, micro- and nanoplastics, the polymer composition dictated the species and amount of release products. Comparing both ISO4892 protocols, the presence of water contributed to radical termination mechanisms\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e which led for HIPS, LDPE and TPU to lower carbonyl indices and DOC release, but higher releases of micro- and nanoplastics. The aging and fragmentation mechanism of PA-6 differed from those of the other polymers, probably due to its capability to take up water:\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e instead of fragmentation, we observed a particle shrinkage mechanism, which is accelerated with increasing humidity, leading to higher DOC release. The Kalahari protocol operates at higher temperature, which should accelerate the aging,\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e but at lower humidity than the ISO4892 protocols. In consequence, for LDPE and HIPS the amount of released fragments was in between the release of both ISO4892 protocols. The DOC release from PA-6 was lower after Kalahari, since its main degradation mechanism is dictated by the presence of water. SI Fig. 7 shows the lack of a simple correlation between plastic degradation (here: carbonyl index) and fragmentation (here: microplastic counts), and instead highlights polymer-specific trends. These insights support Safe and Sustainable by Design strategies for new product developments by selecting material-additive combinations with low micro- and nanoplastic release or even low release of any species due to high polymer stability enhanced by stabilizing additives.\u003c/p\u003e\u003cp\u003eIn the context of environmental risk, it is important that the potential release of additives is also considered alongside release of the polymeric material.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e77\u003c/span\u003e\u003c/sup\u003e This study did not consider additives, but it is worth noting that our negative control, PP, had low releases of all species due to the addition of UV stabilizing additives. While PP might seem preferential to other materials due to low polymer particle release, we did not assess additives contained or released from the microplastic particles, nor did we assess the impact of UV stabilizing additives on the other polymer compositions studied here. Work is currently ongoing to build predictive tools for additive release, which when combined with degradation and fragmentation modeling enabled by this study, will provide a powerful tool for assessing environmental risk.\u003c/p\u003e\u003cp\u003eCurrently, plastic fate and exposure models treat fragmentation simplistically (for example, using a constant fragmentation rate across degradation state and polymer size), or not at all.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e78\u003c/span\u003e–\u003cspan class=\"CitationRef\"\u003e81\u003c/span\u003e\u003c/sup\u003e Even models that include fragmentation often do so as a loss process, which ignores size-differential risk posed by smaller plastic particles, and ignores the loss of particle character for dissolved organics. This study, among others, clearly demonstrates the importance of a more refined approach to fragmentation modeling that considers degradation stresses encountered by plastics in the environment and tracks the full size-distribution of secondary plastic particles and low-molecular-weight species. The data presented herein provide an excellent basis on which to build such a modeling approach, enabling the generation of fragmentation rates and fragment size distributions that are a function of polymer type, additives package, shape (particle, pellet, film, molded article…), the pristine polymer molar mass distribution, particle size and degradation state. By linking the degradation state to stresses encountered in the environment, modelers can scale fragmentation rates according to which environmental compartment plastics are present in, enabling predictive calculations of fragmentation in the environment. For example, in the context of UV aging, plastic particles present in the atmosphere or at the surface of waterbodies are likely to undergo UV aging, whilst particles buried deep in soils will see little UV light (where other stresses, such as biodegradation, are more important). Integrating these refined fragmentation predictions into exposure models is crucial in enabling the environmental risk assessment of polymers that considers the full heterogeneity of plastics in the environment.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eATR FT-IR\u0026nbsp; \u0026nbsp; \u0026nbsp;Attenuated total reflectance Fourier-transform infrared spectroscopy\u003c/p\u003e\n\u003cp\u003eAUC-RI\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Analytical ultracentrifugation with refractive index detector\u003c/p\u003e\n\u003cp\u003e∆H\u003csub\u003em\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Melt enthalpy\u003c/p\u003e\n\u003cp\u003eDOC\u0026nbsp; \u0026nbsp;\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Dissolved organic carbon\u003c/p\u003e\n\u003cp\u003eDSC\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Differential scanning calorimetry\u003c/p\u003e\n\u003cp\u003eGPC\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Gel permeation chromatography\u003c/p\u003e\n\u003cp\u003eHIPS\u0026nbsp; \u0026nbsp;\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;High impact polystyrene\u003c/p\u003e\n\u003cp\u003eLDPE\u0026nbsp;\u0026nbsp;\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Low density polyethylene\u003c/p\u003e\n\u003cp\u003eM\u003csub\u003en\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Number average molecular weight\u003c/p\u003e\n\u003cp\u003eM\u003csub\u003ew\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Mass average molecular weight\u003c/p\u003e\n\u003cp\u003ePP\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Polypropylene\u003c/p\u003e\n\u003cp\u003ePA\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Polyamide\u003c/p\u003e\n\u003cp\u003eSDS\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Sodium dodecyl sulfate\u003c/p\u003e\n\u003cp\u003eSEM\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Scanning electron microscopy\u003c/p\u003e\n\u003cp\u003eT\u003csub\u003eg\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Glass transition temperature\u003c/p\u003e\n\u003cp\u003eT\u003csub\u003em\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Melting point\u003c/p\u003e\n\u003cp\u003eTPU\u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Thermoplastic polyurethane\u003c/p\u003e\n\u003cp\u003eUV \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;ultraviolet\u003c/p\u003e"},{"header":"Declarations","content":" \u003cp\u003eASSOCIATED CONTENT\u003c/p\u003e\n\u003cp\u003eThe following file is available free of charge: Additional information on technical properties of the polymers, micrographs of pristine and aged polymers, descriptions of analytical methods and controls, characterization of the investigated polymers before and after UV aging (DSC, GPC, Fraunhofer diffraction), determined releases from AUC, particle counter and DOC, correlation-plot: \u0026nbsp;∆counts of microplastics vs. carbonyl index increase (PDF).\u0026nbsp;\u003c/p\u003e\u003cp\u003e \u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent for publication\u003c/strong\u003e \u003cp\u003eAll authors have given approval to the final version of the manuscript.\u003c/p\u003e \u003cp\u003e\u003ch2\u003eCompeting Interests\u003c/h2\u003e\u003cp\u003eSome of the authors are employees of BASF SE, a company producing and marketing polymers, including plastics.\u003c/p\u003e\u003ch2\u003eFunding Sources\u003c/h2\u003e \u003cp\u003eThis work was supported by Cefic Long Range Research Initiative under project LRI ECO59 (FRAGMENT-MNP).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eThe manuscript was written and revised through contributions of all authors. All authors have given approval to the final version of the manuscript. PP and KS contributed equally to this work. KS and JS carried out the experiments for this study. SH and MW performed the data curation for modelling purposes. PP wrote the original draft with contributions from KS, JS, MW, SH, CS and WW. All authors approved the final version of the manuscript. WW, CS and MW supervised the project.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors sincerely thank Klaus Vilsmeier, Tanja Kiessig, Elke Schumacher, and Alexandre Tetrault for extensive data generation. We are also grateful to Maik Nowak (DSC), Rolf Tompers (DOC) and Bastiaan Staal (GPC on HIPS, TPU, PA) for their scientific advice on polymer analytics and to our project partners Antonia Pr\u0026auml;torius (University of Amsterdam), Richard Cross and Gbotemi Adediran (UKCEH) for in depth discussions. We are especially thankful to Dow (David Meunier, Jing Hu, Jingwei Fan, Sarah Pei, Paul Balding, Jianbo Hou, Intan Hamdan) and LyondellBasell (Erik Rushton, Isabella Camurati, Mara Destro, Gabriele Tani) for their outstanding effort in the GPC analysis of partially UV degraded, fragmented, and crosslinked polyolefins.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information files. Should any raw data files be needed in another format they are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eThompson RC, Olsen Y, Mitchell RP, Davis A, Rowland SJ, John AWG, McGonigle D, Russell AE. Lost at Sea: Where Is All the Plastic? 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Sci Total Environ. 2023;882:163437. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.scitotenv.2023.163437\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2023.163437\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"microplastics-and-nanoplastics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"mina","sideBox":"Learn more about [Microplastics and Nanoplastics](http://microplastics.springeropen.com)","snPcode":"43591","submissionUrl":"https://submission.nature.com/new-submission/43591/3","title":"Microplastics and Nanoplastics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Microplastics, fragmentation, degradation, photolysis, environmental stresses","lastPublishedDoi":"10.21203/rs.3.rs-5244293/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5244293/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDepending on the environmental compartment, plastics are subjected to various stressors, including UV light, water, microbial exudates (enzymes), and temperature. Among these, stress on plastics from photo-chemical processes was identified as a leading exposure pathway of plastics, e.g., in the atmosphere or on the water surface. While the focus of earlier studies mainly was on deterioration of the chemical and mechanical properties, more recent studies demonstrate how photo-oxidation leads to fragmentation and release of secondary micro- and nanoplastic fragments, as well as low-molecular weight species. These studies tend to focus on a single exposure condition and a limited number of polymer types. Therefore, this study focuses on systematically evaluating the influence of temperature and relative humidity during simulated UV exposure on the fragmentation and degradation of five types of pristine microplastic powders: polypropylene, low density polyethylene, polyamide 6, high impact polystyrene and thermoplastic polyurethane. We quantified the dose-dependent release of water-soluble organics, as well as secondary micro- and nanoplastics (including their particle size distributions) and found that the polymer identity dictated the type and quantity of species released rather than the aging protocol. With this systematic assessment the generated data can be used in mechanistic microplastic fragmentation models to determine fragmentation rates and fragment size distributions.\u003c/p\u003e","manuscriptTitle":"Environmental Degradation and Fragmentation of Microplastics: Dependence on Polymer Type, Humidity, UV Dose and Temperature","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-10-21 10:54:13","doi":"10.21203/rs.3.rs-5244293/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-01-27T09:07:33+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-01-20T13:41:48+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"278190570593777669530506408560345743254","date":"2025-01-06T10:10:41+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-04T17:15:31+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"296143479987689699359418324784869131503","date":"2024-10-23T11:27:08+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-10-23T10:49:27+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-10-18T09:44:04+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-10-18T09:43:35+00:00","index":"","fulltext":""},{"type":"submitted","content":"Microplastics and Nanoplastics","date":"2024-10-11T07:38:52+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"microplastics-and-nanoplastics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"mina","sideBox":"Learn more about [Microplastics and Nanoplastics](http://microplastics.springeropen.com)","snPcode":"43591","submissionUrl":"https://submission.nature.com/new-submission/43591/3","title":"Microplastics and Nanoplastics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"3a1dd780-3a6c-4ec4-9873-2b6931854ab7","owner":[],"postedDate":"October 21st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-03-10T17:47:27+00:00","versionOfRecord":{"articleIdentity":"rs-5244293","link":"https://doi.org/10.1186/s43591-025-00118-9","journal":{"identity":"microplastics-and-nanoplastics","isVorOnly":false,"title":"Microplastics and Nanoplastics"},"publishedOn":"2025-03-06 15:57:39","publishedOnDateReadable":"March 6th, 2025"},"versionCreatedAt":"2024-10-21 10:54:13","video":"","vorDoi":"10.1186/s43591-025-00118-9","vorDoiUrl":"https://doi.org/10.1186/s43591-025-00118-9","workflowStages":[]},"version":"v1","identity":"rs-5244293","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5244293","identity":"rs-5244293","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}