Presence of insecticidal veterinary medicines in dandelions (Taraxacum officinalis) in public parks in the Netherlands

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Ragas This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7398333/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 23 Dec, 2025 Read the published version in Environmental Sciences Europe → Version 1 posted 9 You are reading this latest preprint version Abstract The aim of this study was to investigate the presence of insecticidal veterinary medicines in public parks in the Netherlands and to determine whether those substances might pose a threat to the local entomofauna. Fifteen parks were selected throughout the country, and volunteers took composite samples of dandelion plants. Samples were collected in 2021 and 2022. In total, nine insecticidal veterinary medicines were detected, including two isomers of permethrin and two metabolites of fipronil. As four out of the six parent compounds detected are currently mainly on the market for use on pets, it is plausible that these substances originate from dogs and cats visiting the parks. The other two compounds, i.e., phoxim and etofenprox, are likely to have originated from airborne deposition, as earlier studies have reported the presence of these substances in polyurethane air filters and in untreated vegetation. Toxicological literature indicates that the concentrations found for permethrin, imidacloprid, fipronil and its metabolites are likely to trigger negative effects in butterflies feeding on the dandelions. veterinary medicines pets insecticides dandelion biodiversity public parks entomofauna Figures Figure 1 Figure 2 Figure 3 Figure 4 Summary The presence of insecticidal veterinary medicines in dandelion plants growing in 15 public parks in the Netherlands was investigated. Such substances were found in all samples, except in the control. Based on an analysis of the available literature, we conclude that part of these substances is likely to originate from treated dogs and that the detected concentrations are likely to have negative impacts on the local entomofauna. Highlights Seven insecticidal veterinary medicines were measured in dandelion samples taken from 15 parks All dandelion samples, except the control sample, contained insecticidal veterinary medicines In total, nine insecticidal veterinary medicines were detected (including isomers and metabolites) The concentrations detected were high enough to trigger acute and chronic effects in the entomofauna Part of the veterinary medicines are likely to originate from dogs and cats Introduction In Europe, the USA and many other countries, dogs and other pets are often treated against parasites like fleas, ticks and others, with parasite prevention products, also known as parasiticides (Wells and Collins, 2022 ; Lavan et al., 2017 ). These products contain active substances acting as insecticides, acaricides, larvicides, and insect growth regulators. Lavan et al. ( 2017 ) report that, on average, dogs in the USA receive 4-4.6 anti-parasitic treatments per year. Wells and Collins ( 2022 ) indicate that parasiticides accounted for £725 million (€890 M, $ 1,010 M) of sales in the UK in 2019, equalling 39% of the UK animal medicines market. After application, residues of parasiticides can spread into the environment. Teerlink et al. ( 2017 ) showed that after bathing dogs, a large fraction of the applied fipronil and its metabolites could be detected in the rinsate and concluded that this likely is a source of water pollution. Indeed, several authors published studies about the pollution of surface waters in the USA and Europe by substances that are used to treat pets (Perkins et al., 2024 ; Teerlink et al., 2017 ). For example, insecticidal veterinary medicines have been detected in numerous English rivers (Perkins et al., 2021 ). The Netherlands is a densely populated country with a large number of dogs and other pets. The Divebo society estimated the number of dogs in 2018 around 1.7 million (Divebo, 2019 ). The majority of them are treated with veterinary medicines, creating the possibility of water and soil pollution. Diepens et al. ( 2023 ) detected different veterinary medicines (among which imidacloprid and fipronil) in dog hairs, in dog urine and in Dutch surface waters after the swimming of dogs. Therefore, the situation in the Netherlands (Water Forum, 2023 ) appears to be similar to that in the UK and the USA. In addition to surface waters, anti-parasiticides are likely to pollute other environments, particularly urban parks, as these are frequently visited by pet owners and their dogs. Public parks do not only have a recreational function but also provide opportunities for the development of nature and biodiversity (Cornelis & Hermi, 2004 ; Santos et al., 2019 ; Kümmerling & Müller, 2012 ; Nilon, 2011 ). However, treated pets may leave residues of parasiticides, e.g., when they come into direct contact with the local park vegetation or through their excrements. These residues may accumulate in plants, posing a potential risk for organisms consuming these plants such as certain insect species, thereby threatening biodiversity. However, Wells and Collins ( 2022 ) identified a big data gap concerning the presence and impact of active ingredients of veterinary medicines in urban green spaces. Also for the Netherlands, no studies have yet been published about contamination of the terrestrial urban areas with insecticidal veterinary medicines. The aim of the present study was to investigate the presence of parasiticides in plants from public parks in the Netherlands. Dandelions were collected from 15 public parks and public gardens (Fig. 1 ) and analyzed for 661 substances, including several parasiticides. We compared the results for the parasiticides with ecotoxicity data for different species of insects to determine the potential ecological risks posed by these pollutants in urban parks. Materials and methods Public parks Fifteen public parks and public gardens in the Netherlands were selected for sampling; mainly in cities and some in rural areas (Fig. 2 ). These public parks were accessible to citizens and their pets. Public parks in the Netherlands are frequently mown by service providers (either public or private). The grass and herb vegetation in these parks is sometimes grazed by free living ducks, swans and geese. Large grazers such as ruminants are rare in Dutch public parks. The use of crop protection products, including insecticides, is forbidden in public parks since 1/7/2018 (Rijksoverheid, 2018 ). Sampling We chose to sample dandelions ( Taraxacum officinalis ) because these plants are widely present in Dutch parks and do not have a protected status. While dandelions have in some cases been used for environmental monitoring of heavy metals (Kabata-Pendias & Dudka, S., 1991 ), they have not yet been used to monitor veterinary medicines. Volunteers collected composite dandelion samples over a distance of at least 100 meters within the parks. One control site was chosen at an organic dairy farm (site 16 in Fig. 1 ), where animals were not treated with insecticidal veterinary medicines. At each site, the above-ground plants were harvested, consisting of leaves, flowers, flower stalks, and some flower heads bearing seeds. The composite samples (consisting of at least 100 plants) were collected by hand (without gloves) by volunteers having no pets at home (in order to avoid potential cross-contamination of veterinary medicines by body contact). The dandelion samples were taken randomly across the parks. In the case of forested parks, dandelions were only sampled along footpaths, due to their absence elsewhere. Sampling took place from 8/4/2022 till 29/5/2022, except for location Groene Hart Park (site 1 in Fig. 1 ), where sampling took place on 25/10/2021. In order to avoid contamination of the samples with soil, the plants were cut at a height of around 5 cm and put into a plasticized paper bag provided by the laboratory. The sample bags were first transported to a central freezer where they were stored at -18⁰C. After sampling was completed, the samples were collected by a courier and transported to the laboratory in a cooled van at 5°C The coordinates, names and characteristics of the 16 sampling sites are specified in Table S1 of the Supplementary Material (SM). It was checked visually at each sampling site whether ruminant grazing was applied as management measure, because ruminants treated with insecticidal veterinary medicines could spread those compounds in the vegetation. The presence of fences, excrements and of drinking water were used as criteria. Chemical analysis Sample preparation and chemical analysis were performed by Eurofins (Graauw, the Netherlands) between December 12th 2021 and June 7th, 2022. Sample processing and chemical analysis are described in Section S2 of the SM. Samples were analysed for 661 pesticides (Tabel S3 in the SM), including 300 insecticides and acaricides. Various of the 661 substances analysed are used as veterinary medicines (Table 1 ). Those allowed on the Dutch market were identified through the database of CBG (CBG, 2024 ). The dry matter content of all samples was determined by dividing the freeze-dried weight by the fresh weight. The Limit of Quantification (LOQ) was determined for each sample (Table S4 in the SM). For measurements above the LOQ, a 95% confidence interval is reported assuming a maximum measurement uncertainty of 50% (in accordance with SANTE 11312/2021). This means that the true value is assumed to lie between 0.5 and 1.5 times the measured value with a probability of 95%. For measurements exceeding the Limit of Detection (LOD) but below the LOQ, the confidence interval is not specified. All measured values above the LOD were included in the calculations. For negative results, the concentration was assumed to be zero. Toxicological assessment In order to determine the toxicity of the detected veterinary medicines for butterflies and bees, literature research in the Web of Science was conducted on December 5th, 2024. Search terms used were ‘name of the substance’, ‘butterfly’, ‘butterflies’ and ‘bee’. In case no relevant toxicological information for butterflies was found, LD 50 ’s for bees were used. The LD 50 for honeybees was extracted from the PPDB database (PPDB, 2024a ). In case no endpoints for bees and butterflies were found, toxicity values for other insects were taken as an indicator. Results Measurements The fresh weight of the samples varied between 371 and 1034 grams per composite sample. The average sample weight was 726 grams (± 174 grams). Table 1 lists the name, CAS number, the Limit of Quantification (LOQ), and the range of concentrations based on fresh and dry weight for all veterinary medicines detected in the 15 samples from parks, including isomers and metabolites. For permethrin, two isomers were detected. For fipronil, two metabolites were detected. In the sample of the organic pasture, no veterinary medicines were detected. Table 1 The veterinary medicines found in the 16 composite dandelion samples of this study, their LOQ*, their CAS-number, the range of concentrations in the samples based on fresh and dry weight. Name of veterinary medicine CAS number Limit of Quantification (microgram per kg fresh sample) Range of positive concentrations (microgram per kg fresh weight) Range of positive concentrations (microgram per kg dry matter) Fipronil 120068-37-3 0.3–1.93 0.30–0.95 1.9–7.9 Fipronil-sulphide 120067-83-6 0.31 0.08 0.7 Fipronil-sulfone 120068-36-2 0.3–0.31 0.18–0.31 1.6–2.6 Imidacloprid 138261-41-3 0.3–0.31 1.56–2.06 13.7–17.2 Permethrin-cis 61949-76-6 0.3–0.59 0.34–1.93 3-16.1 Permethrin-trans 61949-77-7 0.3–0.59 0.53–3.53 4.7–27.2 Dinotefuran 165252-70-0 0.37 3.99 27.7 Etofenprox 80844-07-1 0.31–0.37 0.44–2.13 3.1–15.7 Phoxim 14816-18-3 0.3 2.06 18.1 *The limit of quantification (LOQ) is a range, because most substances were found in more than one sample with different LOQ’s Table 1 shows that the concentration of veterinary medicines on the basis of fresh weight varied from 0.08–3.99 micrograms per kg, and on the basis of dry weight from 0.7–27.2 micrograms per kg. The highest concentrations were found for permethrin-trans (3.53 micrograms per kg fresh weight) and for dinotefuran (3.99 micrograms per kg fresh weight). From all 300 insecticides and acaricides included in the analysis package and that are not being used as veterinary medicines (Table S3 in SM), only three compounds were detected, i.e., cyenopyrafen, diphenylamine and pp‘DDE. These three insecticides were detected once in dandelions of site №2, site №1 and site №11, respectively. Figure 3 shows the detection frequency of insecticidal veterinary medicines. Fipronil, permethrin and etofenprox were most often detected. The other five veterinary medicines and metabolites were only detected in some of the 15 public parks. Figure 4 shows that nine out of 15 samples contained 2 or more veterinary medicines, while 6 samples contained only one veterinary medicine. At two sites (sites №1 and №12), six veterinary medicines were detected. Table S4 of the SM lists all measured concentrations of the veterinary medicines and other insecticides in the 16 samples (15 from parks and one control). It shows that permethrin-cis and permethrin-trans were detected in the same samples. No parks, except for site №6, were grazed by ruminants in the last 25 years. Most parks, except for site №2, were established before the beginning of this century. Compounds originating from previous agricultural use could therefore be excluded. In site №2 fipronil was found (Table S4 ). This substance is prohibited for field applications since 10 years (Ctgb, 2025 ). Toxicological data Table 2 lists relevant toxicological data extracted from public literature and databases for the compounds listed in Table 1 . For dinotefuran, etofenprox and phoxim only endpoints for bees and a fly were found. Table 2 Toxicity data from international studies of insecticidal veterinary medicines found in our study Name of veterinary medicine Author(s) Organism Endpoint Concentration in matrix (micrograms) Fipronil Gols et al., 2020 Pieris brassicae Reduced life expectancy & cumulative egg production 1 microgram per kg dry matter in leaves Fipronil-sulphide Bhatt et al., 2023 Soil microorganisms, vertebrates and invertebrates Oxidative stress Toxicity comparable to fipronil Fipronil-sulfone Bhatt et al., 2023 Oxidative stress Imidacloprid Whitehorn et al., 2018 Krishnan et al., 2021 Pieris brassicae Danaus plexippus Pupation period affected Larval mortality Water applied contained 1 microgram per liter 5 micrograms per kg fresh weight in leaves Permethrin-cis Hoang & Rand, 2015 ; Hoang et al., 2011 Peterson et al., 2019 Junonia coenia , Vanessa cardui, Heliconius charitonius , Eumaeus atala & Anartia jatrophae Vanessa cardui Reduced survival fifth larval instar Reduced survival of larvae 1 microgram of permethrin per square meter of foliage 1 microgram per kg fresh weight Permethrin-trans Dinotefuran Yasuda et al., 2017 Apis cerana LD 50 adults 0.0014 micrograms per bee Etofenprox PPDB, 2024e Apis Mellifera LD 50 adults > 0.038 micrograms per bee Phoxim Wang et al., 2013 Bactrocera dorsalis LD 50 adults 0.007 micrograms per fly Discussion Origin of insecticidal veterinary medicines The dandelion samples contained 1–6 insecticidal veterinary medicines that are not on the market for crop protection in the Netherlands, but in some cases as biocides (Ctgb, 2025 ). In case veterinary medicines found were not allowed as plant protection products, there could be direct link with the veterinary medicines that are used to treat pets. Another monitoring study on insecticides in untreated rural locations (Buijs et al., 2024 ) found fipronil, fipronil sulfone, fipronil sulfide, etofenprox and permethrin occasionally in grasses, oak leaves and polyurethan air filters, but with an incidence of less than 5%. A similar French study (ANSES, 2020 ) detected permethrin, etofenprox and fipronil were detected in ambient air, but with an incidence of less than 1%. In Germany, etofenprox was occasionally detected in tree bark with an incidence of 3.7% (Hoffman et al., 2019). Given these low detection frequencies, it is unlikely that the presence of these substances in the dandelions of Dutch public parks can be explained by transport from through ambient air after application in other areas. We hypothesize that the presence of most insecticidal veterinary medicines in the 15 public parks and public gardens in the Netherlands is due to dogs, and other pets that are treated with parasiticides, visiting the parks and leaving behind hairs, vomit, urine and faeces. Unfortunately, hairs, vomit, urine and faeces from pets in public parks were not sampled and analyzed in the present study, but it would be worthwhile to include these in future studies. Dogs are typically kept on a lead by their owners, which would be expected to result in relatively high pollution levels along the footpaths where dandelions typically grow. Most dogs are regularly (once a month, or once in two months) treated with doses of active ingredients that vary from 54 milligrams of dinotefuran, 67 milligrams of fipronil to 635 milligrams of permethrin (Wells and Collins, 2022 ). Cats could be an additional source of contamination as the same veterinary medicines are often used on them. For permethrin in site №6, we identified another potential source, i.e., sheep that sometimes graze on the dike in the park and that might be treated with permethrin. Phoxim was present in only one sample. In the Netherlands phoxim is only permitted for use in controlling parasitic mites on chickens. However, in an earlier study, phoxim was frequently detected in oak leaves from nature conservation areas in the Netherlands, suggesting that the substance can in principle originate from other sources than pets (Buijs et al., 2024 ). Phoxim is a very volatile substance, which facilitates air transport (PPDB, 2024f ). We therefore hypothesize that the presence of phoxim in the dandelions could be due to background pollution of this substance in the Netherlands. However it is unclear why the concentration detected in dandelions from the park site №1 (18.1 microgram per kg of dry matter) was substantially higher than those in the oak leaves analyzed by Buijs et al. ( 2024 ; less than 8 micrograms per kg of dry matter). Etofenprox is not allowed in the Netherlands for the treatment of animals, but was present in 5 out of 15 samples. In other EU member countries, it is allowed as a crop protection agent (EU, 2024 ). Except for treatments against parasites, another potential source of residues might be the food given to pets. In several EU member states, etofenprox is allowed as an insecticide on food crops. However, analysis of pet food was not included in our study. Potential ecological impacts In this section, we discuss the most relevant ecotoxicological data per compound individually. Fipronil Fipronil is a systemic and persistent insecticide, highly toxic to several terrestrial beneficial insects (PPDB, 2024b ). Gols et al. ( 2020 ) published a study about chronic effects of low concentrations of fipronil in cabbage plants on the development of the farmland butterfly Pieris brassicae. They observed that even 1 microgram of fipronil per kg dry matter in cabbage plants had a negative impact on life expectancy and cumulative egg production (Table 2 ). The established concentrations of fipronil and its metabolites in our study were much higher than 1 microgram per kg dry matter, namely 1.9–7.9 micrograms. If the toxicity for Pieris brassicae would be representative for all butterflies that feed on dandelions, this would mean that 8 out of 15 of the samples of this study would have a strong negative impact on butterfly species. Fipronil sulfone and fipronil sulfide According to Bhatt et al. ( 2023 ), these two fipronil metabolites have a toxicity that is comparable to the toxicity of the parent compound, depending on the specific test organism used (Table 2 ). However, in his review no data are presented about butterflies or honeybees. The metabolites were found in 2 dandelion samples in a concentration from 0.7–2.6 microgram per kg dry matter. These samples also contained the parent compound fipronil. We therefore think that the reported concentrations are likely to have substantial impact on the development of species like the farmland butterfly Pieris brassicae . Imidacloprid Imidacloprid is a systemic acting insecticide that is persistent and highly toxic to bees and other beneficial non-target invertebrates. Whitehorn et al. ( 2018 ) demonstrated that plants irrigated with water containing concentrations as low as 1 microgram imidacloprid per liter negatively impacted the pupation period and the size of Pieris brassicae butterflies that fed on these plants. Krishnan et al. ( 2021 ) measured the resulting concentrations in the plants and concluded that mortality of the monarch butterfly larvae ( Danaus Plexippus) increased of 5 micrograms/kg or more of imidacloprid in fresh milkweed ( Asclepias spp .) leaves (Table 2 ). The imidacloprid concentration in the dandelion samples was 13.7 micrograms at site №1 and 17.2 at site №12 on basis of dry matter (Table S4 in SM). Rondeau et al. ( 2014 ) highlighted the fact that neonicotinoid insecticides, based on natural toxin nicotine, are of particular concern for insects because they bind virtually irreversibly to the nicotinic-acetylcholine receptors in the insect nervous system, so the damage can accumulate and therefore the toxic effects can be reinforced with chronic exposure. According to their observations, safe doses for insects cannot be established. Therefore, we conclude that the measured concentrations of imidacloprid in dandelions of Dutch public parks are likely to be toxic for butterflies. Permethrin This broad-spectrum insecticide is in the Netherlands only approved for use as a biocide and as veterinary medicine. According to the PPDB ( 2024c ), permethrin is moderately persistent and has a high toxicity to aquatic and terrestrial invertebrates. In addition, permethrin is classified as a neurotoxicant, an endocrine disruptor and it affects development and reproduction. According to Hoang and Rand ( 2015 ) and Hoang et al. ( 2011 ), applications higher than 1 microgram of permethrin per square meter of foliage had an acute negative impact on 5 butterfly species native to Florida (USA), i.e., Junonia coenia , Vanessa cardui, Heliconius charitonius , Eumaeus atala and Anartia jatrophae (Table 2 ). Peterson et al. ( 2019 ) determined that 1 microgram of permethrin per kg fresh weight leave of milkweed ( Asclepias spp .) reduced survival of Vanessa cardui butterfly larvae, with only 30% developing into butterflies. We found 0.87–5.46 micrograms of permethrin per kg fresh weight in dandelion leaves (the total of cis- and trans permethrin). Cis- and trans permethrin were found in 8 of the 15 samples. This suggests that 8 out of 15 dandelion samples likely contained for specific butterflies’ dangerous concentrations of permethrin. Dinotefuran In one dandelion sample, 27.7 micrograms of dinotefuran per kg dry matter was measured. The concentration in the fresh leaves was 4.0 micrograms per kg. Dinotefuran is a broad-spectrum neonicotinoid insecticide used to control a wide range of sucking pests (PPDB, 2024d ). No literature was found on the effect of dinotefuran on butterflies. The contact acute LD₅₀ for the European honeybee ( Apis mellifera) amounts to more than 0.023 micrograms (PPDB, 2024d ). For Asian Honeybees ( Apis cerana ), an LD 50 of 0.0014 micrograms per bee has been determined (Yasuda et. al., 2017 ). This value is substantially lower than the LD 50 value for imidacloprid (0.0037 micrograms per bee). Additional research needs to be done to determine the toxicity of dinotefuran in plant tissue of dandelions to various insects, since the exposure in LD 50 tests is very different. Etofenprox Etofenprox is a broad-spectrum pyrethroid insecticide (PPDB, 2024e ). Although no relevant literature was found concerning the impact of etofenprox on butterflies or honeybees, the LD 50 toxicity values of etofenprox and permethrin for honeybees are comparable. The LD 50 of etofenprox amounts to more than 0.038 micrograms per bee (PPDB, 2024e ) and of permethrin 0.024 micrograms per bee PPDB ( 2024c ). Phoxim Phoxim is, except for the use against mites on chickens, also used as insecticide and acaricide to control stored-product pests such as ants and some soil insects (PPDB, 2024f ). As this substance is not regarded as a crop protection agent, but as a veterinary medicine, there has been no legal necessity to determine LD 50 value for honeybees. No other toxicity endpoints were found also for bees or butterflies. Studies about its toxicity to other insects indicates that its LD 50 toxicity for flies (7 nanograms per fly) is comparable with the toxicity of fipronil (Wang et al., 2013 ). If the LD 50 value of phoxim for flies would be indicative for its effects on butterflies and bees, a negative impact on both insect species seems plausible. Overall interpretation of found substances Comparison of measured concentrations of the individual insecticidal veterinary medicines in dandelions with toxic reference values makes it plausible that these concentrations can be toxic to butterflies and honeybees. In 9 of the 15 dandelion samples, more than one substance was found and there are more insecticidal veterinary substances on the market that we did not test for, like fluralaner, flumethrin, pyriprol and other substances (CBG, 2024 ). Therefore, it is likely that the harvested dandelion samples were toxic to butterflies, honeybees and other insects. According to Green et al. ( 2023 ), the toxicity threshold levels of insecticides such as imidacloprid, permethrin and fipronil are comparable in honeybees ( Apis mellifera) and painted lady butterfly ( Vanessa cardui) larvae. This observation implies that the discussed toxicity threshold levels might have a much wider meaning than just for those insects discussed. Wider impact on public parks ecology The majority of dandelions in public parks are located in close proximity to footpaths. However, in early spring, dandelions represent a significant proportion of the flowers in the parks. At this time of year, the nectar from contaminated flowers forms a substantial part of the food for honeybees and other insects in the parks and may threaten their health and reproduction. Conclusions The results of this study revealed that all the public parks under review were contaminated with insecticidal veterinary medicines. Given the fact that seven of the substances are not permitted in agriculture, it is probable that the substances found in dandelion plants originated from dogs and other pets. It is also worth noting that etofenprox and phoxim are not permitted to be applied on pets. This suggests that these substances may have originated from other sources, possibly from the air. This possibility is supported by the fact that both substances have also been found in air filters and oak leaves in rural areas of the Netherlands. As this study focused exclusively on dandelion plants, we are thus unable to comment on the contamination of other plant species. Additionally, as the majority of dandelion plants were growing alongside footpaths, we were unable to draw conclusions about contamination in other parts of the parks. In other parts of the parks, measurements could be done of other plants than dandelions. Based on existing literature on the toxicity of the identified substances for butterflies, honeybees, and other insects, it is probable that the concentrations found have a significant negative impact on local insect populations. More research is needed to determine the source of the insecticidal veterinary medicines and the impact of contaminants on park biodiversity. Follow-up studies should also include other popular insecticidal veterinary medicines, such as fluralaner and flumethrin. Declarations Acknowledgements Pesticide analysis in vegetation and in cattle excrements: Mr. Khalid Bensbaho, Mrs. Elisa Platjouw, Mrs. Eline Pilaet (of the Eurofins laboratory Graauw); photograph: Mrs. Natasha Nozdrina; Inspiration in order to conduct this study – Mrs. Marlonneke Willemsen; Taking dandelion samples; Marlonneke Willemsen, Dr. Frans Verkleij, Hella Leguijt, Natasha Nozdrina and board members of the Stichting ‘Tuin van Haarlem’ Notification The research has first been published in a research report in Dutch language (Buijs and Mantingh, 2023); CRediT authorship contribution statement Jelmer Buijs: Writing – original draft, Validation, Supervision, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Ad M.J. Ragas: Writing – review & editing, Validation, Supervision, Methodology, Formal analysis, Data curation, Conceptualization. Alfons Uitewaal: editing & language support. A. Margriet Mantingh: Writing – original report, Methodology, Investigation. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding This work was supported by Stichting Tuin van Haarlem, Duurzaamheidsplatform Zuidplas, the city of Schagen, Mr. Olsthoorn and Mrs. Mantingh. All sponsors were located in the Netherlands Data availability The data generated during and/or analyzed during the current study are provided in 4 Supplementary SM data files. Consent to Publish declaration not applicable Ethics and Consent to Participate declarations not applicable References ANSES, 2020. Campagne nationale exploratoire des pesticides dans l’air ambient. 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Journal of Economic Entomology, 110(2), 2017, 447–452. doi: 10.1093/jee/tox032 Additional Declarations No competing interests reported. Supplementary Files SMTableS1Samplelocations.docx SMSectionS2SampleprocessingC.docx SMTableS3ListofcompoundsA.docx SMTableS4Originalmeasuredvalues.docx Cite Share Download PDF Status: Published Journal Publication published 23 Dec, 2025 Read the published version in Environmental Sciences Europe → Version 1 posted Editorial decision: Revision requested 20 Oct, 2025 Reviews received at journal 03 Oct, 2025 Reviews received at journal 25 Sep, 2025 Reviewers agreed at journal 18 Sep, 2025 Reviewers agreed at journal 18 Sep, 2025 Reviewers invited by journal 18 Sep, 2025 Editor assigned by journal 26 Aug, 2025 Submission checks completed at journal 23 Aug, 2025 First submitted to journal 18 Aug, 2025 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. 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16:56:55","extension":"html","order_by":16,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":105422,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7398333/v1/8fcd0c98749380e50ae27971.html"},{"id":92435533,"identity":"0cbf6617-879f-4dbb-8b13-e2cd63915087","added_by":"auto","created_at":"2025-09-29 16:56:54","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1278714,"visible":true,"origin":"","legend":"\u003cp\u003eFlowering dandelions in April 2022 with honeybee (photograph by Mrs. Natasha Nozdrina).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7398333/v1/7962d4b97796bf4f6152307c.png"},{"id":92435529,"identity":"757535b3-18eb-4c58-ac76-e7201ad84f3b","added_by":"auto","created_at":"2025-09-29 16:56:54","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":400962,"visible":true,"origin":"","legend":"\u003cp\u003eSampling sites of dandelion leaves in public parks in the Netherlands in 2021 and 2022.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7398333/v1/cef12401054fa195977c7353.jpeg"},{"id":92436652,"identity":"9ac4f911-90b3-493d-b8f0-99eed876b322","added_by":"auto","created_at":"2025-09-29 17:12:54","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":14899,"visible":true,"origin":"","legend":"\u003cp\u003eDetection frequency of 9 insecticidal veterinary medicines in 15 dandelion samples from public parks in the Netherlands\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7398333/v1/94f100642bbb676ab5f4a117.png"},{"id":92436653,"identity":"f7685e4a-063b-42d9-8fad-c85aedc09619","added_by":"auto","created_at":"2025-09-29 17:12:54","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":151578,"visible":true,"origin":"","legend":"\u003cp\u003eThe number of veterinary medicines found per dandelion sample from each of the 15 parks and the control\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7398333/v1/11de0009b4699337d81061e3.jpeg"},{"id":99172423,"identity":"17ac3a44-e876-4dd6-962c-0c59d8335ff2","added_by":"auto","created_at":"2025-12-29 16:09:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3017308,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7398333/v1/16af2d56-1546-427e-822e-8d4f2626ee6f.pdf"},{"id":92435530,"identity":"72228f18-303d-4f16-8cde-c55249e28b3c","added_by":"auto","created_at":"2025-09-29 16:56:54","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":19637,"visible":true,"origin":"","legend":"","description":"","filename":"SMTableS1Samplelocations.docx","url":"https://assets-eu.researchsquare.com/files/rs-7398333/v1/055bdf29a8d306e700bdc7ff.docx"},{"id":92435870,"identity":"19cc94bf-5c8b-4a43-850f-61ca55c7981f","added_by":"auto","created_at":"2025-09-29 17:04:54","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":16727,"visible":true,"origin":"","legend":"","description":"","filename":"SMSectionS2SampleprocessingC.docx","url":"https://assets-eu.researchsquare.com/files/rs-7398333/v1/6a3b14a7e538abcd3ab3c4c6.docx"},{"id":92435538,"identity":"65a872c5-4d22-4ce2-bec7-e743d7d0dead","added_by":"auto","created_at":"2025-09-29 16:56:54","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":41669,"visible":true,"origin":"","legend":"","description":"","filename":"SMTableS3ListofcompoundsA.docx","url":"https://assets-eu.researchsquare.com/files/rs-7398333/v1/258f65c0abf1943fafe85089.docx"},{"id":92436803,"identity":"55ff815b-6b20-43cd-b161-27201af79be5","added_by":"auto","created_at":"2025-09-29 17:20:54","extension":"docx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":30012,"visible":true,"origin":"","legend":"","description":"","filename":"SMTableS4Originalmeasuredvalues.docx","url":"https://assets-eu.researchsquare.com/files/rs-7398333/v1/fbe1c54d911228fd07c65958.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Presence of insecticidal veterinary medicines in dandelions (Taraxacum officinalis) in public parks in the Netherlands","fulltext":[{"header":"Summary","content":"\u003cp\u003eThe presence of insecticidal veterinary medicines in dandelion plants growing in 15 public parks in the Netherlands was investigated. Such substances were found in all samples, except in the control. Based on an analysis of the available literature, we conclude that part of these substances is likely to originate from treated dogs and that the detected concentrations are likely to have negative impacts on the local entomofauna.\u003c/p\u003e"},{"header":"Highlights","content":"\u003cul\u003e\n \u003cli\u003eSeven insecticidal veterinary medicines were measured in dandelion samples taken from 15 parks\u003c/li\u003e\n \u003cli\u003eAll dandelion samples, except the control sample, contained insecticidal veterinary medicines\u003c/li\u003e\n \u003cli\u003eIn total, nine insecticidal veterinary medicines were detected (including isomers and metabolites)\u003c/li\u003e\n \u003cli\u003eThe concentrations detected were high enough to trigger acute and chronic effects in the entomofauna\u003c/li\u003e\n \u003cli\u003ePart of the veterinary medicines are likely to originate from dogs and cats\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"Introduction","content":"\u003cp\u003eIn Europe, the USA and many other countries, dogs and other pets are often treated against parasites like fleas, ticks and others, with parasite prevention products, also known as parasiticides (Wells and Collins, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Lavan et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). These products contain active substances acting as insecticides, acaricides, larvicides, and insect growth regulators. Lavan et al. (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) report that, on average, dogs in the USA receive 4-4.6 anti-parasitic treatments per year. Wells and Collins (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) indicate that parasiticides accounted for \u0026pound;725\u0026nbsp;million (\u0026euro;890 M, \u003cspan\u003e$\u003c/span\u003e1,010 M) of sales in the UK in 2019, equalling 39% of the UK animal medicines market.\u003c/p\u003e\u003cp\u003eAfter application, residues of parasiticides can spread into the environment. Teerlink et al. (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) showed that after bathing dogs, a large fraction of the applied fipronil and its metabolites could be detected in the rinsate and concluded that this likely is a source of water pollution. Indeed, several authors published studies about the pollution of surface waters in the USA and Europe by substances that are used to treat pets (Perkins et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Teerlink et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). For example, insecticidal veterinary medicines have been detected in numerous English rivers (Perkins et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe Netherlands is a densely populated country with a large number of dogs and other pets. The Divebo society estimated the number of dogs in 2018 around 1.7\u0026nbsp;million (Divebo, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The majority of them are treated with veterinary medicines, creating the possibility of water and soil pollution. Diepens et al. (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) detected different veterinary medicines (among which imidacloprid and fipronil) in dog hairs, in dog urine and in Dutch surface waters after the swimming of dogs. Therefore, the situation in the Netherlands (Water Forum, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) appears to be similar to that in the UK and the USA.\u003c/p\u003e\u003cp\u003eIn addition to surface waters, anti-parasiticides are likely to pollute other environments, particularly urban parks, as these are frequently visited by pet owners and their dogs. Public parks do not only have a recreational function but also provide opportunities for the development of nature and biodiversity (Cornelis \u0026amp; Hermi, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Santos et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; K\u0026uuml;mmerling \u0026amp; M\u0026uuml;ller, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Nilon, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). However, treated pets may leave residues of parasiticides, e.g., when they come into direct contact with the local park vegetation or through their excrements. These residues may accumulate in plants, posing a potential risk for organisms consuming these plants such as certain insect species, thereby threatening biodiversity. However, Wells and Collins (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) identified a big data gap concerning the presence and impact of active ingredients of veterinary medicines in urban green spaces. Also for the Netherlands, no studies have yet been published about contamination of the terrestrial urban areas with insecticidal veterinary medicines.\u003c/p\u003e\u003cp\u003eThe aim of the present study was to investigate the presence of parasiticides in plants from public parks in the Netherlands. Dandelions were collected from 15 public parks and public gardens (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and analyzed for 661 substances, including several parasiticides. We compared the results for the parasiticides with ecotoxicity data for different species of insects to determine the potential ecological risks posed by these pollutants in urban parks.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003ePublic parks\u003c/p\u003e\u003cp\u003eFifteen public parks and public gardens in the Netherlands were selected for sampling; mainly in cities and some in rural areas (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). These public parks were accessible to citizens and their pets. Public parks in the Netherlands are frequently mown by service providers (either public or private). The grass and herb vegetation in these parks is sometimes grazed by free living ducks, swans and geese. Large grazers such as ruminants are rare in Dutch public parks. The use of crop protection products, including insecticides, is forbidden in public parks since 1/7/2018 (Rijksoverheid, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eSampling\u003c/p\u003e\u003cp\u003eWe chose to sample dandelions (\u003cem\u003eTaraxacum officinalis\u003c/em\u003e) because these plants are widely present in Dutch parks and do not have a protected status. While dandelions have in some cases been used for environmental monitoring of heavy metals (Kabata-Pendias \u0026amp; Dudka, S., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1991\u003c/span\u003e), they have not yet been used to monitor veterinary medicines.\u003c/p\u003e\u003cp\u003eVolunteers collected composite dandelion samples over a distance of at least 100 meters within the parks. One control site was chosen at an organic dairy farm (site 16 in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), where animals were not treated with insecticidal veterinary medicines. At each site, the above-ground plants were harvested, consisting of leaves, flowers, flower stalks, and some flower heads bearing seeds. The composite samples (consisting of at least 100 plants) were collected by hand (without gloves) by volunteers having no pets at home (in order to avoid potential cross-contamination of veterinary medicines by body contact). The dandelion samples were taken randomly across the parks. In the case of forested parks, dandelions were only sampled along footpaths, due to their absence elsewhere. Sampling took place from 8/4/2022 till 29/5/2022, except for location Groene Hart Park (site 1 in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), where sampling took place on 25/10/2021. In order to avoid contamination of the samples with soil, the plants were cut at a height of around 5 cm and put into a plasticized paper bag provided by the laboratory. The sample bags were first transported to a central freezer where they were stored at -18⁰C. After sampling was completed, the samples were collected by a courier and transported to the laboratory in a cooled van at 5\u0026deg;C\u003c/p\u003e\u003cp\u003eThe coordinates, names and characteristics of the 16 sampling sites are specified in Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e of the Supplementary Material (SM). It was checked visually at each sampling site whether ruminant grazing was applied as management measure, because ruminants treated with insecticidal veterinary medicines could spread those compounds in the vegetation. The presence of fences, excrements and of drinking water were used as criteria.\u003c/p\u003e\u003cp\u003eChemical analysis\u003c/p\u003e\u003cp\u003eSample preparation and chemical analysis were performed by Eurofins (Graauw, the Netherlands) between December 12th 2021 and June 7th, 2022. Sample processing and chemical analysis are described in Section S2 of the SM. Samples were analysed for 661 pesticides (Tabel S3 in the SM), including 300 insecticides and acaricides. Various of the 661 substances analysed are used as veterinary medicines (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Those allowed on the Dutch market were identified through the database of CBG (CBG, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The dry matter content of all samples was determined by dividing the freeze-dried weight by the fresh weight. The Limit of Quantification (LOQ) was determined for each sample (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e in the SM). For measurements above the LOQ, a 95% confidence interval is reported assuming a maximum measurement uncertainty of 50% (in accordance with SANTE 11312/2021). This means that the true value is assumed to lie between 0.5 and 1.5 times the measured value with a probability of 95%. For measurements exceeding the Limit of Detection (LOD) but below the LOQ, the confidence interval is not specified. All measured values above the LOD were included in the calculations. For negative results, the concentration was assumed to be zero.\u003c/p\u003e\u003cp\u003eToxicological assessment\u003c/p\u003e\u003cp\u003eIn order to determine the toxicity of the detected veterinary medicines for butterflies and bees, literature research in the Web of Science was conducted on December 5th, 2024. Search terms used were \u0026lsquo;name of the substance\u0026rsquo;, \u0026lsquo;butterfly\u0026rsquo;, \u0026lsquo;butterflies\u0026rsquo; and \u0026lsquo;bee\u0026rsquo;. In case no relevant toxicological information for butterflies was found, LD\u003csub\u003e50\u003c/sub\u003e\u0026rsquo;s for bees were used. The LD\u003csub\u003e50\u003c/sub\u003e for honeybees was extracted from the PPDB database (PPDB, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2024a\u003c/span\u003e). In case no endpoints for bees and butterflies were found, toxicity values for other insects were taken as an indicator.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eMeasurements\u003c/p\u003e\u003cp\u003eThe fresh weight of the samples varied between 371 and 1034 grams per composite sample. The average sample weight was 726 grams (\u0026plusmn;\u0026thinsp;174 grams). Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e lists the name, CAS number, the Limit of Quantification (LOQ), and the range of concentrations based on fresh and dry weight for all veterinary medicines detected in the 15 samples from parks, including isomers and metabolites. For permethrin, two isomers were detected. For fipronil, two metabolites were detected. In the sample of the organic pasture, no veterinary medicines were detected.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThe veterinary medicines found in the 16 composite dandelion samples of this study, their LOQ*, their CAS-number, the range of concentrations in the samples based on fresh and dry weight.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026minus;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eName of veterinary medicine\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCAS number\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eLimit of Quantification (microgram per kg fresh sample)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eRange of positive concentrations (microgram per kg fresh weight)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eRange of positive concentrations (microgram per kg dry matter)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFipronil\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e120068-37-3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.3\u0026ndash;1.93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.30\u0026ndash;0.95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1.9\u0026ndash;7.9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFipronil-sulphide\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e120067-83-6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFipronil-sulfone\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e120068-36-2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.3\u0026ndash;0.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.18\u0026ndash;0.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1.6\u0026ndash;2.6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eImidacloprid\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e138261-41-3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.3\u0026ndash;0.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.56\u0026ndash;2.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e13.7\u0026ndash;17.2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePermethrin-cis\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e61949-76-6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.3\u0026ndash;0.59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.34\u0026ndash;1.93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e3-16.1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePermethrin-trans\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e61949-77-7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.3\u0026ndash;0.59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.53\u0026ndash;3.53\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e4.7\u0026ndash;27.2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDinotefuran\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e165252-70-0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.37\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e3.99\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e27.7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEtofenprox\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e80844-07-1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.31\u0026ndash;0.37\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.44\u0026ndash;2.13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e3.1\u0026ndash;15.7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePhoxim\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e14816-18-3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e18.1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"5\"\u003e*The limit of quantification (LOQ) is a range, because most substances were found in more than one sample with different LOQ\u0026rsquo;s\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows that the concentration of veterinary medicines on the basis of fresh weight varied from 0.08\u0026ndash;3.99 micrograms per kg, and on the basis of dry weight from 0.7\u0026ndash;27.2 micrograms per kg. The highest concentrations were found for permethrin-trans (3.53 micrograms per kg fresh weight) and for dinotefuran (3.99 micrograms per kg fresh weight). From all 300 insecticides and acaricides included in the analysis package and that are not being used as veterinary medicines (Table \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e in SM), only three compounds were detected, i.e., cyenopyrafen, diphenylamine and pp\u0026lsquo;DDE. These three insecticides were detected once in dandelions of site №2, site №1 and site №11, respectively.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the detection frequency of insecticidal veterinary medicines. Fipronil, permethrin and etofenprox were most often detected. The other five veterinary medicines and metabolites were only detected in some of the 15 public parks. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows that nine out of 15 samples contained 2 or more veterinary medicines, while 6 samples contained only one veterinary medicine. At two sites (sites №1 and №12), six veterinary medicines were detected. Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e of the SM lists all measured concentrations of the veterinary medicines and other insecticides in the 16 samples (15 from parks and one control). It shows that permethrin-cis and permethrin-trans were detected in the same samples.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eNo parks, except for site №6, were grazed by ruminants in the last 25 years. Most parks, except for site №2, were established before the beginning of this century. Compounds originating from previous agricultural use could therefore be excluded. In site №2 fipronil was found (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). This substance is prohibited for field applications since 10 years (Ctgb, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eToxicological data\u003c/p\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e lists relevant toxicological data extracted from public literature and databases for the compounds listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. For dinotefuran, etofenprox and phoxim only endpoints for bees and a fly were found.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eToxicity data from international studies of insecticidal veterinary medicines found in our study\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eName of veterinary medicine\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAuthor(s)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOrganism\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eEndpoint\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eConcentration in matrix (micrograms)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFipronil\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eGols et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2020\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003ePieris brassicae\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eReduced life expectancy \u0026amp; cumulative egg production\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1 microgram per kg dry matter in leaves\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFipronil-sulphide\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eBhatt et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2023\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSoil microorganisms, vertebrates and invertebrates\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eOxidative stress\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eToxicity comparable to fipronil\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFipronil-sulfone\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eBhatt et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2023\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eOxidative stress\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eImidacloprid\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eWhitehorn et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2018\u003c/span\u003e\u003c/p\u003e\u003cp\u003eKrishnan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003ePieris brassicae\u003c/em\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eDanaus plexippus\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePupation period affected\u003c/p\u003e\u003cp\u003eLarval mortality\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eWater applied contained 1 microgram per liter\u003c/p\u003e\u003cp\u003e5 micrograms per kg fresh weight in leaves\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePermethrin-cis\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eHoang \u0026amp; Rand, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Hoang et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2011\u003c/span\u003e\u003c/p\u003e\u003cp\u003ePeterson et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e\u003cem\u003eJunonia coenia\u003c/em\u003e, \u003cem\u003eVanessa cardui, Heliconius charitonius\u003c/em\u003e, \u003cem\u003eEumaeus atala \u0026amp; Anartia jatrophae\u003c/em\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eVanessa cardui\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eReduced survival fifth larval instar\u003c/p\u003e\u003cp\u003eReduced survival of larvae\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e1 microgram of permethrin per square meter of foliage\u003c/p\u003e\u003cp\u003e1 microgram per kg fresh weight\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePermethrin-trans\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDinotefuran\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eYasuda et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2017\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eApis cerana\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eLD\u003csub\u003e50\u003c/sub\u003e adults\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.0014 micrograms per bee\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEtofenprox\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePPDB, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eApis Mellifera\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eLD\u003csub\u003e50\u003c/sub\u003e adults\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026gt;\u0026thinsp;0.038 micrograms per bee\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePhoxim\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eWang et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2013\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eBactrocera dorsalis\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eLD\u003csub\u003e50\u003c/sub\u003e adults\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.007 micrograms per fly\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eOrigin of insecticidal veterinary medicines\u003c/p\u003e\u003cp\u003eThe dandelion samples contained 1\u0026ndash;6 insecticidal veterinary medicines that are not on the market for crop protection in the Netherlands, but in some cases as biocides (Ctgb, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). In case veterinary medicines found were not allowed as plant protection products, there could be direct link with the veterinary medicines that are used to treat pets.\u003c/p\u003e\u003cp\u003eAnother monitoring study on insecticides in untreated rural locations (Buijs et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) found fipronil, fipronil sulfone, fipronil sulfide, etofenprox and permethrin occasionally in grasses, oak leaves and polyurethan air filters, but with an incidence of less than 5%. A similar French study (ANSES, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) detected permethrin, etofenprox and fipronil were detected in ambient air, but with an incidence of less than 1%. In Germany, etofenprox was occasionally detected in tree bark with an incidence of 3.7% (Hoffman et al., 2019). Given these low detection frequencies, it is unlikely that the presence of these substances in the dandelions of Dutch public parks can be explained by transport from through ambient air after application in other areas.\u003c/p\u003e\u003cp\u003eWe hypothesize that the presence of most insecticidal veterinary medicines in the 15 public parks and public gardens in the Netherlands is due to dogs, and other pets that are treated with parasiticides, visiting the parks and leaving behind hairs, vomit, urine and faeces. Unfortunately, hairs, vomit, urine and faeces from pets in public parks were not sampled and analyzed in the present study, but it would be worthwhile to include these in future studies. Dogs are typically kept on a lead by their owners, which would be expected to result in relatively high pollution levels along the footpaths where dandelions typically grow. Most dogs are regularly (once a month, or once in two months) treated with doses of active ingredients that vary from 54 milligrams of dinotefuran, 67 milligrams of fipronil to 635 milligrams of permethrin (Wells and Collins, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Cats could be an additional source of contamination as the same veterinary medicines are often used on them. For permethrin in site №6, we identified another potential source, i.e., sheep that sometimes graze on the dike in the park and that might be treated with permethrin.\u003c/p\u003e\u003cp\u003ePhoxim was present in only one sample. In the Netherlands phoxim is only permitted for use in controlling parasitic mites on chickens. However, in an earlier study, phoxim was frequently detected in oak leaves from nature conservation areas in the Netherlands, suggesting that the substance can in principle originate from other sources than pets (Buijs et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Phoxim is a very volatile substance, which facilitates air transport (PPDB, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2024f\u003c/span\u003e). We therefore hypothesize that the presence of phoxim in the dandelions could be due to background pollution of this substance in the Netherlands. However it is unclear why the concentration detected in dandelions from the park site №1 (18.1 microgram per kg of dry matter) was substantially higher than those in the oak leaves analyzed by Buijs et al. (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; less than 8 micrograms per kg of dry matter).\u003c/p\u003e\u003cp\u003eEtofenprox is not allowed in the Netherlands for the treatment of animals, but was present in 5 out of 15 samples. In other EU member countries, it is allowed as a crop protection agent (EU, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Except for treatments against parasites, another potential source of residues might be the food given to pets. In several EU member states, etofenprox is allowed as an insecticide on food crops. However, analysis of pet food was not included in our study.\u003c/p\u003e\u003cp\u003ePotential ecological impacts\u003c/p\u003e\u003cp\u003eIn this section, we discuss the most relevant ecotoxicological data per compound individually.\u003c/p\u003e\n\u003ch3\u003eFipronil\u003c/h3\u003e\n\u003cp\u003eFipronil is a systemic and persistent insecticide, highly toxic to several terrestrial beneficial insects (PPDB, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2024b\u003c/span\u003e). Gols et al. (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) published a study about chronic effects of low concentrations of fipronil in cabbage plants on the development of the farmland butterfly \u003cem\u003ePieris brassicae.\u003c/em\u003e They observed that even 1 microgram of fipronil per kg dry matter in cabbage plants had a negative impact on life expectancy and cumulative egg production (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The established concentrations of fipronil and its metabolites in our study were much higher than 1 microgram per kg dry matter, namely 1.9\u0026ndash;7.9 micrograms. If the toxicity for \u003cem\u003ePieris brassicae\u003c/em\u003e would be representative for all butterflies that feed on dandelions, this would mean that 8 out of 15 of the samples of this study would have a strong negative impact on butterfly species.\u003c/p\u003e\n\u003ch3\u003eFipronil sulfone and fipronil sulfide\u003c/h3\u003e\n\u003cp\u003eAccording to Bhatt et al. (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), these two fipronil metabolites have a toxicity that is comparable to the toxicity of the parent compound, depending on the specific test organism used (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). However, in his review no data are presented about butterflies or honeybees. The metabolites were found in 2 dandelion samples in a concentration from 0.7\u0026ndash;2.6 microgram per kg dry matter. These samples also contained the parent compound fipronil. We therefore think that the reported concentrations are likely to have substantial impact on the development of species like the farmland butterfly \u003cem\u003ePieris brassicae\u003c/em\u003e.\u003c/p\u003e\n\u003ch3\u003eImidacloprid\u003c/h3\u003e\n\u003cp\u003eImidacloprid is a systemic acting insecticide that is persistent and highly toxic to bees and other beneficial non-target invertebrates. Whitehorn et al. (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) demonstrated that plants irrigated with water containing concentrations as low as 1 microgram imidacloprid per liter negatively impacted the pupation period and the size of \u003cem\u003ePieris brassicae\u003c/em\u003e butterflies that fed on these plants. Krishnan et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) measured the resulting concentrations in the plants and concluded that mortality of the monarch butterfly larvae (\u003cem\u003eDanaus Plexippus)\u003c/em\u003e increased of 5 micrograms/kg or more of imidacloprid in fresh milkweed (\u003cem\u003eAsclepias spp\u003c/em\u003e.) leaves (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The imidacloprid concentration in the dandelion samples was 13.7 micrograms at site №1 and 17.2 at site №12 on basis of dry matter (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e in SM). Rondeau et al. (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) highlighted the fact that neonicotinoid insecticides, based on natural toxin nicotine, are of particular concern for insects because they bind virtually irreversibly to the nicotinic-acetylcholine receptors in the insect nervous system, so the damage can accumulate and therefore the toxic effects can be reinforced with chronic exposure. According to their observations, safe doses for insects cannot be established. Therefore, we conclude that the measured concentrations of imidacloprid in dandelions of Dutch public parks are likely to be toxic for butterflies.\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003ePermethrin\u003c/h2\u003e\u003cp\u003eThis broad-spectrum insecticide is in the Netherlands only approved for use as a biocide and as veterinary medicine. According to the PPDB (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2024c\u003c/span\u003e), permethrin is moderately persistent and has a high toxicity to aquatic and terrestrial invertebrates. In addition, permethrin is classified as a neurotoxicant, an endocrine disruptor and it affects development and reproduction. According to Hoang and Rand (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) and Hoang et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), applications higher than 1 microgram of permethrin per square meter of foliage had an acute negative impact on 5 butterfly species native to Florida (USA), i.e., \u003cem\u003eJunonia coenia\u003c/em\u003e, \u003cem\u003eVanessa cardui, Heliconius charitonius\u003c/em\u003e, \u003cem\u003eEumaeus atala\u003c/em\u003e and \u003cem\u003eAnartia jatrophae\u003c/em\u003e (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Peterson et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) determined that 1 microgram of permethrin per kg fresh weight leave of milkweed (\u003cem\u003eAsclepias spp\u003c/em\u003e.) reduced survival of \u003cem\u003eVanessa cardui\u003c/em\u003e butterfly larvae, with only 30% developing into butterflies. We found 0.87\u0026ndash;5.46 micrograms of permethrin per kg fresh weight in dandelion leaves (the total of cis- and trans permethrin). Cis- and trans permethrin were found in 8 of the 15 samples. This suggests that 8 out of 15 dandelion samples likely contained for specific butterflies\u0026rsquo; dangerous concentrations of permethrin.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eDinotefuran\u003c/h3\u003e\n\u003cp\u003eIn one dandelion sample, 27.7 micrograms of dinotefuran per kg dry matter was measured. The concentration in the fresh leaves was 4.0 micrograms per kg. Dinotefuran is a broad-spectrum neonicotinoid insecticide used to control a wide range of sucking pests (PPDB, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2024d\u003c/span\u003e). No literature was found on the effect of dinotefuran on butterflies. The contact acute LD₅₀ for the European honeybee (\u003cem\u003eApis mellifera)\u003c/em\u003e amounts to more than 0.023 micrograms (PPDB, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2024d\u003c/span\u003e). For Asian Honeybees (\u003cem\u003eApis cerana\u003c/em\u003e), an LD\u003csub\u003e50\u003c/sub\u003e of 0.0014 micrograms per bee has been determined (Yasuda et. al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). This value is substantially lower than the LD\u003csub\u003e50\u003c/sub\u003e value for imidacloprid (0.0037 micrograms per bee). Additional research needs to be done to determine the toxicity of dinotefuran in plant tissue of dandelions to various insects, since the exposure in LD\u003csub\u003e50\u003c/sub\u003e tests is very different.\u003c/p\u003e\n\u003ch3\u003eEtofenprox\u003c/h3\u003e\n\u003cp\u003eEtofenprox is a broad-spectrum pyrethroid insecticide (PPDB, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024e\u003c/span\u003e). Although no relevant literature was found concerning the impact of etofenprox on butterflies or honeybees, the LD\u003csub\u003e50\u003c/sub\u003e toxicity values of etofenprox and permethrin for honeybees are comparable. The LD\u003csub\u003e50\u003c/sub\u003e of etofenprox amounts to more than 0.038 micrograms per bee (PPDB, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2024e\u003c/span\u003e) and of permethrin 0.024 micrograms per bee PPDB (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2024c\u003c/span\u003e).\u003c/p\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003ePhoxim\u003c/h2\u003e\u003cp\u003ePhoxim is, except for the use against mites on chickens, also used as insecticide and acaricide to control stored-product pests such as ants and some soil insects (PPDB, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2024f\u003c/span\u003e). As this substance is not regarded as a crop protection agent, but as a veterinary medicine, there has been no legal necessity to determine LD\u003csub\u003e50\u003c/sub\u003e value for honeybees. No other toxicity endpoints were found also for bees or butterflies. Studies about its toxicity to other insects indicates that its LD\u003csub\u003e50\u003c/sub\u003e toxicity for flies (7 nanograms per fly) is comparable with the toxicity of fipronil (Wang et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). If the LD\u003csub\u003e50\u003c/sub\u003e value of phoxim for flies would be indicative for its effects on butterflies and bees, a negative impact on both insect species seems plausible.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eOverall interpretation of found substances\u003c/h2\u003e\u003cp\u003eComparison of measured concentrations of the individual insecticidal veterinary medicines in dandelions with toxic reference values makes it plausible that these concentrations can be toxic to butterflies and honeybees. In 9 of the 15 dandelion samples, more than one substance was found and there are more insecticidal veterinary substances on the market that we did not test for, like fluralaner, flumethrin, pyriprol and other substances (CBG, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Therefore, it is likely that the harvested dandelion samples were toxic to butterflies, honeybees and other insects. According to Green et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), the toxicity threshold levels of insecticides such as imidacloprid, permethrin and fipronil are comparable in honeybees (\u003cem\u003eApis mellifera)\u003c/em\u003e and painted lady butterfly (\u003cem\u003eVanessa cardui)\u003c/em\u003e larvae. This observation implies that the discussed toxicity threshold levels might have a much wider meaning than just for those insects discussed.\u003c/p\u003e\u003cp\u003eWider impact on public parks ecology\u003c/p\u003e\u003cp\u003eThe majority of dandelions in public parks are located in close proximity to footpaths. However, in early spring, dandelions represent a significant proportion of the flowers in the parks. At this time of year, the nectar from contaminated flowers forms a substantial part of the food for honeybees and other insects in the parks and may threaten their health and reproduction.\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe results of this study revealed that all the public parks under review were contaminated with insecticidal veterinary medicines. Given the fact that seven of the substances are not permitted in agriculture, it is probable that the substances found in dandelion plants originated from dogs and other pets. It is also worth noting that etofenprox and phoxim are not permitted to be applied on pets. This suggests that these substances may have originated from other sources, possibly from the air. This possibility is supported by the fact that both substances have also been found in air filters and oak leaves in rural areas of the Netherlands.\u003c/p\u003e\u003cp\u003eAs this study focused exclusively on dandelion plants, we are thus unable to comment on the contamination of other plant species. Additionally, as the majority of dandelion plants were growing alongside footpaths, we were unable to draw conclusions about contamination in other parts of the parks. In other parts of the parks, measurements could be done of other plants than dandelions. Based on existing literature on the toxicity of the identified substances for butterflies, honeybees, and other insects, it is probable that the concentrations found have a significant negative impact on local insect populations. More research is needed to determine the source of the insecticidal veterinary medicines and the impact of contaminants on park biodiversity. Follow-up studies should also include other popular insecticidal veterinary medicines, such as fluralaner and flumethrin.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch4\u003eAcknowledgements\u003c/h4\u003e\n\u003cp\u003ePesticide analysis in vegetation and in cattle excrements: Mr. Khalid Bensbaho, Mrs. Elisa Platjouw, Mrs. Eline Pilaet (of the Eurofins laboratory Graauw); photograph: Mrs. Natasha Nozdrina; Inspiration in order to conduct this study \u0026ndash; Mrs. Marlonneke Willemsen; Taking dandelion samples; Marlonneke Willemsen, Dr. Frans Verkleij, Hella Leguijt, Natasha Nozdrina and board members of the Stichting \u0026lsquo;Tuin van Haarlem\u0026rsquo;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNotification \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe research has first been published in a research report in Dutch language (Buijs and Mantingh, 2023);\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJelmer Buijs: Writing \u0026ndash; original draft, Validation, Supervision, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Ad M.J. Ragas: Writing \u0026ndash; review \u0026amp; editing, Validation, Supervision, Methodology, Formal analysis, Data curation, Conceptualization. Alfons Uitewaal: editing \u0026amp; language support. A. Margriet Mantingh: Writing \u0026ndash; original report, Methodology, Investigation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of Competing Interest \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by Stichting Tuin van Haarlem, Duurzaamheidsplatform Zuidplas, the city of Schagen, Mr. Olsthoorn and Mrs. Mantingh. All sponsors were located in the Netherlands\u003c/p\u003e\n\u003ch2\u003eData availability\u003c/h2\u003e\n\u003cp\u003eThe data generated during and/or analyzed during the current study are provided in 4 Supplementary SM data files.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish declaration \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003enot applicable\u003c/p\u003e\n\u003ch2\u003eEthics and Consent to Participate declarations\u003c/h2\u003e\n\u003cp\u003enot applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003e\u003cstrong\u003eANSES, 2020. \u003c/strong\u003eCampagne nationale exploratoire des pesticides dans l’air ambient. 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DOI 10.7717/peerj.4772\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003eYasuda, M., Sakamoto, Y., Goka, K., Nagamitsu, K., Taki, H., 2017. \u003c/strong\u003eInsecticide Susceptibility in Asian Honeybees (Apis cerana (Hymenoptera: Apidae)) and Implications for Wild Honey Bees in Asia. \u003cem\u003eJournal of Economic Entomology, 110(2), 2017, 447–452. \u003c/em\u003edoi: 10.1093/jee/tox032\u003c/li\u003e\n\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":"environmental-sciences-europe","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"eseu","sideBox":"Learn more about [Environmental Sciences Europe](http://enveurope.springeropen.com)","snPcode":"12302","submissionUrl":"https://submission.nature.com/new-submission/12302/3","title":"Environmental Sciences Europe","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"veterinary medicines, pets, insecticides, dandelion, biodiversity, public parks, entomofauna","lastPublishedDoi":"10.21203/rs.3.rs-7398333/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7398333/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe aim of this study was to investigate the presence of insecticidal veterinary medicines in public parks in the Netherlands and to determine whether those substances might pose a threat to the local entomofauna. Fifteen parks were selected throughout the country, and volunteers took composite samples of dandelion plants. Samples were collected in 2021 and 2022. In total, nine insecticidal veterinary medicines were detected, including two isomers of permethrin and two metabolites of fipronil. As four out of the six parent compounds detected are currently mainly on the market for use on pets, it is plausible that these substances originate from dogs and cats visiting the parks. The other two compounds, i.e., phoxim and etofenprox, are likely to have originated from airborne deposition, as earlier studies have reported the presence of these substances in polyurethane air filters and in untreated vegetation. Toxicological literature indicates that the concentrations found for permethrin, imidacloprid, fipronil and its metabolites are likely to trigger negative effects in butterflies feeding on the dandelions.\u003c/p\u003e","manuscriptTitle":"Presence of insecticidal veterinary medicines in dandelions (Taraxacum officinalis) in public parks in the Netherlands","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-29 16:56:49","doi":"10.21203/rs.3.rs-7398333/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-20T14:25:33+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-03T15:37:00+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-26T00:06:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"108545474741932632752473451631679553604","date":"2025-09-18T16:24:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"213578361986430510524245426341404524883","date":"2025-09-18T16:09:23+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-09-18T13:52:01+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-26T11:04:30+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-23T14:31:36+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Sciences Europe","date":"2025-08-18T09:50:56+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-sciences-europe","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"eseu","sideBox":"Learn more about [Environmental Sciences Europe](http://enveurope.springeropen.com)","snPcode":"12302","submissionUrl":"https://submission.nature.com/new-submission/12302/3","title":"Environmental Sciences Europe","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"659d1d0e-cfeb-48cf-817c-3265417fcb2a","owner":[],"postedDate":"September 29th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-29T16:03:59+00:00","versionOfRecord":{"articleIdentity":"rs-7398333","link":"https://doi.org/10.1186/s12302-025-01293-5","journal":{"identity":"environmental-sciences-europe","isVorOnly":false,"title":"Environmental Sciences Europe"},"publishedOn":"2025-12-23 15:57:23","publishedOnDateReadable":"December 23rd, 2025"},"versionCreatedAt":"2025-09-29 16:56:49","video":"","vorDoi":"10.1186/s12302-025-01293-5","vorDoiUrl":"https://doi.org/10.1186/s12302-025-01293-5","workflowStages":[]},"version":"v1","identity":"rs-7398333","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7398333","identity":"rs-7398333","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}