Ecological Risk of Radiocesium Contamination and Dose Rate Estimation in Anuran Tadpole in Aquatic Environments

Ecological Risk of Radiocesium Contamination and Dose Rate Estimation in Anuran Tadpole in Aquatic Environments | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Ecological Risk of Radiocesium Contamination and Dose Rate Estimation in Anuran Tadpole in Aquatic Environments Ashok Kumar Shrestha This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6331961/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Radioactive cesium contamination in inland water bodies following the Fukushima Nuclear Power Plant accident in Japan has persisted for over a decade, potentially causing chronic effects on aquatic biota. This study aimed to understand the transfer factors influenced by environmental parameters and the resulting dose rates of radiocesium in tadpole larvae between river and lake ecosystems. In total, 2830 tadpoles from river ecosystem and 3056 tadpoles from lake ecosystem were analyzed in 80 and 33 composite samples respectively from Fukushima region. The relative effects of environmental parameters in radiocesium concentration ratio in tadpole larvae were compared between river and lake ecosystems using the generalized linear model. The average radiocesium concentration ratio in tadpole did not significantly vary between river and lake ecosystems (i.e., 6063.69 L/kg and 6071.59 L/kg respectively). While water depth exhibited a negative correlation as a prominent parameter affecting radiocesium transfer in lake ecosystems, environmental factors like water depth, temperature, and suspended solids showed significant impact in radiocesium transfer in tadpoles within river ecosystems, as revealed by generalized linear model analysis. Though algae and detritus materials significantly contribute to tadpole larvae nutrition in aquatic habitats, the multivariate analysis did not identify significant variables. Sediment emerged as a common factor facilitating the high transfer rate of radiocesium in tadpoles within aquatic environments. Observations estimated dose rates of radiocesium below 1 µGyh -1 in both river and lake ecosystems. However, tadpoles in the river ecosystem experienced higher radiocesium dose rates than those in lake ecosystems (i.e., 0.15 and 0.09 µGyh -1 respectively). This highlights the vulnerability of tadpoles in aquatic environments to external sources of radiocesium present in these habitats. Aquatic organisms Anuran tadpoles Environmental factors Fukushima Radioactive cesium Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction In March 2011, the magnitude 9.0 East Japan Earthquake followed by a devastating tsunami caused accident of nuclear reactor at the Fukushima Dai-ichi Nuclear Power Plant resulted in the emission of the large quantities of radionuclide into the environment. Radionuclide including radiocesium (137Cs) becomes major radionuclide contamination in the environment after nuclear power plant accident (Ishii et al. 2020 ). It is because of the long half-life (i.e., 30.2 years), persistence in the environment, and can be readily bioaccumulated especially by the aquatic organisms from aquatic environment. The Ministry of the Environment, Japan has been conducted long-term monitoring since 2012, following the FDNPP accident. This monitoring involves tracking radiocesium levels in various locations within aquatic environments, including water, sediments, and surrounding biota such as plants and animals. The annual survey data indicates that even after a decade since the accident, concentrations of radiocesium in sediment and aquatic organisms still exceed 100 Bq/kg fresh weight in some location, surpassing the Japanese regulatory limit (MoE 2021 ). This indicates that the threat of radiocesium in the aquatic organisms are still remaining and may have chronic effect on the aquatic biota. Inland water bodies such as river system, lakes, ponds, and reservoirs can acts as a transporter of radiocesium in both dissolved and particulate forms, resulting source of radiocesium bioaccumulation to the bottom of the aquatic food chain, e.g., phytoplankton and macrophytes; (Harvey and Patrick 1967 ; Fisher 1985 ; Warnau et al. 1996 ; Heldal et al. 2001 ) and can then be transferred to higher trophic levels such as fish (Pentreath 1973 ; Zhao et al. 2001 ; Mathews and Fisher 2009 ). Many studies have investigated the effect of radiocesium after the nuclear power-plant accident on aquatic biota, revealing the presence and distribution of radiocesium contamination in the aquatic environment (Fujino et al. 2018 ; Ishii et al. 2020 ; Fujino et al. 2021 ; Wada et al. 2023 ). Because of the short to long growing period, depending on species in the aquatic environments, aquatic organisms can readily accumulate both dissolved and particulate radiocesium from their environments. However, the accumulation of radiocesium by aquatic organisms may depend on various other biotic and abiotic factors (Tagami et al. 2018 ). Water chemistry parameters play a significant role in aquatic ecosystems as they strongly influence the physiology of aquatic organisms (Metian et al. 2019 ). For instance, an increase in water temperature can elevate the concentration factors of dissolved radiocesium in various species, such as fish (Srivastava et al. 1994 ), and algae (Styron et al. 1976 ; Boisson et al. 1997 ), as reviewed by Metian et al. ( 2019 ). However, some studies have shown reverse effects on the accumulation of radiocesium (i.e., 134Cs) in fish species. In contrast, a decrease in concentration factors was observed in Carassius auratus concerning an increase in water temperature (Srivastava et al. 1994 ). Conversely, Ishii et al. ( 2020 ) noted a negative correlation, though not statistically significant, between water temperature and radiocesium concentration factors in fish species sampled from the Fukushima region. Additionally, dissolved potassium concentration significantly affects accumulation of radiocesium in fish, either by increasing elimination rates (Cocchio et al. 1995 ) or by decreasing uptake (Smith et al. 2002 ). Similar effects have been observed in the green-lipped mussel Perna viridis (Ke et al. 2000 ) and the microcrustacean Daphnia magna (Hagstrom 2002 ). Furthermore, previous studies demonstrated that pH has no influence on the bioaccumulation of radiocesium in the fishes in freshwater environment (Ishii et al., 2020 ). Although studies have extensively investigated the bioaccumulation of radiocesium in various aquatic organisms, there is limited mention of tadpole larvae and the potential effects of environmental factors influencing radiocesium transfer (Tagami et al. 2018 ). Within the amphibian group, tadpoles undergo complete development in aquatic environments until they reach maturity, transitioning into terrestrial environments as adults. Tadpoles exhibit diversity and abundance across various freshwater habitats, playing pivotal roles in aquatic food webs due to their ability to reach high densities and biomass (Montaña et al. 2019 ). They serve as vital prey for other consumers and facilitate the transfer of nutrients and energy between aquatic and terrestrial ecosystems(Whiles et al. 2006 ; Capps et al. 2015 ). Despite their significance, only a limited number of studies have highlighted the investigation of the radiological effects on amphibian groups, specifically tadpoles (Sakai et al. 2014 ; Tagami et al. 2018 ). However, a drawback of the previous studies is the low sample size used to analyzed concentration ratio and dose rate (Orizaola 2022 ), and randomly used the data generated from both lotic and lentic ecosystems of tadpoles and adult frogs (e.g. Ishii et al., 2020 ; Tagami et al., 2018 ). According to the International Atomic Energy Agency (International Atomic Energy Agency 2010 ), the concentration ratio refers to the ratio of radionuclide concentration in biota from all pathways (including water, sediment, and ingestion/dietary) based on per unit tissue fresh weight, compared to that in water. Typically, transfer factors of radionuclides, including radiocesium, are expressed as water-to-biota ratios, and the IAEA 2010 provides a summary of concentration ratios for various aquatic organisms, including tadpoles (e.g., 3.0 × 10 3 Lkg − 1 fresh weight; N = 3). However, previous studies in the Fukushima region revealed different concentration ratios of radiocesium from water to tadpoles, reporting 3.5 × 10 3 Lkg − 1 fresh weight; N = 59 (Tagami et al., 2018 ), 5.7 × 10 3 Lkg − 1 fresh weight; N = 49 for river ecosystems, and 7.2 × 10 3 Lkg − 1 fresh weight; N = 3 for lake ecosystems (Ishii et al., 2020 ). The variability in sample size and temporal fluctuations during tadpole sampling might significantly impact the levels of radiocesium activity and its concentration ratios (Orizaola, 2022 ; Ishii et al., 2020 ). The transfer of radiocesium through aquatic ecosystems is intricate, often simplified and described using terms such as the distribution coefficient (K d ) (the ratio of radionuclide activity concentration in the particulate phase to dissolved concentration, as per IAEA 2010) and concentration ratios. While concentration ratios and K d values, along with the activity concentration of radiocesium, are pivotal elements within models used for radiological risk assessments (Wood et al., 2013 ), these parameters frequently span multiple orders of magnitude for a single radionuclide. Consequently, they stand as the primary source of uncertainty in risk assessments, particularly when site-specific data is lacking(Johansen et al. 2012 ; Beresford and Willey 2019 ). Thus, the aim of this study was to investigate how environmental factors (e.g., biotic and abiotic) effects the transfer coefficient (concentration ratio) of 137Cs in Anura tadpoles in various (river and lake) ecosystems using the 10 years-long monitoring data. Additionally, the study aimed to estimate dose rates corresponding to these findings for the purpose of risk analysis. The single order Anura tadpole larvae including two specified species (e.g., Rana catesbeianus and Lithobates catesbeianus ) and one unknown species (mentioned by data surveyor MOE in the monitoring data sheet) is used for this study. Concentration ratio and dose rate estimation of radiocesium in tadpoles were separately analyzed in lake and river ecosystems and compared the mean values for further risk analysis. Materials and Methods Data extraction : The data used for this study was extracted from the Ministry of Environment, Government of Japan, had continuously monitored radiocesium concentration in water, sediment and biota including suspended solids and organic matter since 2012 to 2021, after Fukushima Dai-Ichi nuclear powerplant accident due to mega earthquake hits in Japan. Radiocesium monitoring at five rivers River Abukuma system, River Uda, River Mano, River Niida, River Ota and three lakes, Lake Hayama, Lake Akimoto and Lake Inawashiro, shown in supporting Fig. 1. From each site, live aquatic organisms including Anura tadpole frogs (hereafter called A. tadpole), water and sediment of adjacent sites were collected four times in a year representing spring, summer, autumn and winter season. During the survey, general item concerning water quality parameters such as depth of water, temperature, pH, dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), electrical conductivity (EC), salinity, total organic carbon (TOC), suspended solid (SS) and turbidity. Radiocesium activity concentration measurement in A. tadpole, water and sediment using the standard methods established by the Japanese ministry of education, culture, sport, science and technology (MEXT) (see MOE Open-source data). Due to the low mass of individual tadpoles, collected samples were bulked for a given specific site and measured the radiocesium activity concentration. A. tadpole including unknown species, Lithobates catesbeianus and Rana catesbeianus were collected from river (total no. of tadpole 2830; U. species, 2605; L. catesbeianus , 191; R. catesbeianus , 34) and lake (total no. of tadpole 3056; U. species, 3035; L. catesbeianus , 21). No R. catesbeianus were recorded in lake sampling sites in the specified location. See details in the supplementary file. Calculation of Cs concentration ratio The transfer of radionuclides into the whole body of organisms is primarily defined by the concentration ratio of the surrounding media. The concentration ratio, in this context, refers to the ratio of radionuclide concentration in the entire biota's body (Cb) resulting from all exposure pathways, including water, sediment, and ingestion/dietary pathways, per unit tissue fresh weight, relative to that in the water (Cw) (IAEA, 2010). To calculate the concentration ratio, the concentration of radiocesium accumulation in A. tadpoles per unit of radiocesium concentration in the water at the same sites and during the same season only were used. The concentration ratio for Cs137 and Cs134 was determined using the database specific to each site. However, Cs134 was not detected in many sites, making it difficult to express the concentration ratio (please refer to the supplementary file for details on CR for Cs134). Consequently, only Cs137 data was used to explain the transfer value of radionuclides to A. tadpoles in both river and lake ecosystems. Radiocesium concentration (Cs137) in biota that fell below the lower limit value was not considered when calculating the concentration ratio. Estimation of Dose rate : The radiocesium dose rate for A. tadpoles was estimated using the ERICA (Environmental Risk from Ionising Contaminants: Assessment and Management) assessment tool, version 2 (2.0.221) (Brown et al. 2008) with some modifications. The ERICA tool is commonly used for risk assessment in wildlife due to the dispersion of radionuclides in the environment. It includes three tiers: tier 1, tier 2, and tier 3. Among these, tier 2 was used to estimate the external, internal, and total dose rates of radiocesium, along with the risk quotient (RQ). Radiocesium concentration activity data were used to estimate the dose rate. However, the total dose rate for 137Cs was considered for the risk quotient, as there were many data below detection for Cs-134 in biota which the data insufficient to comparison with 137Cs. Default parameters, such as the ERICA dose rate screening value of 10 µGy/h and an uncertainty factor (UF) of three, indicate a test for a 5% probability of exceeding the dose screening value, assuming that the RQ distribution is exponential. The geometry for tadpoles is not listed in the new version of the ERICA assessment tool. Therefore, we created a new geometry for tadpoles using the dimensions provided by ICRP (2008), with tadpoles measuring 1.5 cm in length, 0.75 cm in width, and 0.75 cm in height. The average body mass of individual tadpoles was calculated as 0.442 g from the provided datasets. In addition, the average concentration ratio and coefficient of distribution (Kd) for rivers and lakes were 6063.69 and 20047.3, and 6071.59 and 1687.3, respectively. Tadpoles fully develop in aquatic habitats until they reach adulthood and were modeled at the sediment-water interface (Tagami et al. 2018 and Flecker et al. 1999). Therefore, the occupancy factor for A. tadpoles was assumed to be 50/50 in water and sediment surfaces. Furthermore, the radiation weighting factors were set at 10, 1, and 1 for alpha, beta, and gamma radiation, respectively. Statistical analysis : The relative water quality parameters and concentration ratio of radiocesium in A. tadpoles for each ecosystem type were analyzed using the generalized linear model (GLM). The number of bulk tadpole samples used for radiocesium measurements in rivers (N=80) and lakes (N=33) were determined separately. Environmental factors such as, water depth, temperature, pH, DO, EC, COD, TOC, salinity, and suspended solid were considered for the effect in concentrations ratio of radiocesium accumulate by A. tadpole. The concentration ratio values of radionuclide were log-transformed, however, other remains same without log-transformed. Furthermore, the possible exposure pathways were analyzed using multiple regression analysis. The exposure pathways including radiocesium concentrations in water, sediment and food materials were taken for the data analyzed. The important sources of food for tadpoles in aquatic habitat are plankton including green algae and coarse particulate organic matter depending on the habitat types (ICRP, 2008; Verburg et al. 2007). According to the study of Montana et al. (2019) reported that approximately 16 food categories were found in the guts of tadpoles with algae exhibiting the highest frequency of occurrences in green plants material. Therefore, we assumed that the small green plants either floated or attached are the major source of radiocesium transform to the tadpole while they feed from their habitat. In this study, we took radiocesium concentration data of green plants such as algae, Oedogonium, spirogyra, small pondweed, and sphagnum. The temporal and spatial data of radiocesium accumulation by A. tadpoles were analyzed using the one-way analysis of variance (ANOVA). The student-t test was used to compare the means of radiocesium concentration accumulation by A. tadpoles between two ecosystem types. Data normality was analyzed using the Shapiro test. The differences were considered to be statistically significant at p <0.05. All statistical tests were performed using the RStudio software (RStudio team, 2023, version 4.3.1). Results The radiocesium concentration ratios in river and lake ecosystems ranged from 268 to 22,619.05 L/kg and 137.5 to 30,400 L/kg, with average radiocesium concentrations of 6,063.69 L/kg and 6,071.59 L/kg, respectively (Fig. 1 ). Seasonal changes of 137Cs concentration ratio in A. tadpole were shown in Fig. 2 . In the lake ecosystem, fall and winter season had drastically decreased 137Cs concentration ratio, however, the average concentration ratio in fall was observed highest than spring and summer season in river ecosystem. Although, the concentration ratio was increased, it was statistically significantly decreased in winter season (One-way ANOVA, p < 0.01 ). Moreover, the average radiocesium activity concentration in A. tadpoles sampled from rivers and lakes was 279.931 Bq/kg, ranging from 5.2 to 1700 Bq/kg and 98.288 Bq/kg, ranging from 2.2 to 400 Bq/kg, respectively. The detailed information of radiocesium activity concentration in water, sediment, foods and A. tadpoles are presented in the supplementary file. The prominent factors affecting the transformation of 137Cs nuclide in A. tadpole concentration ratios were evaluated using a Generalized Linear Model (GLM), and the results are presented in Table 1. The estimated coefficients represent standardized effects, making them comparable within the model across parameters. In the river model, environmental factors such as water depth (0.54) and water temperature (0.05) had significantly positive effects in whole-body radiocesium concentration ratio (Table 1). However, suspended solids (-0.04) had a significant negative effect. Other factors, like COD and EC, also exhibited a negative relationship, whereas pH, DO, salinity, and TOC had a positive impact, although it was not statistically significant (Fig. 3 ). In contrast, the lake model revealed that only one parameter, water depth (-0.11), had a significantly negative effect on the transfer of RC nuclide in the lentic environment (Table 1). A. tadpoles were exposed to RC nuclides from water, sediment, and food in their natural habitat. However, we analyzed the most effective pathways using multiple linear regression methods (see Eq. 1) and developed equations for those that were found to be significant. $$\:Y={a}_{0}+{a}_{1}{\beta\:}_{1}+{a}_{2}{\beta\:}_{2}+{a}_{3}{\beta\:}_{3}+\dots\:\dots\:\dots\:\dots\:..{{a}_{n}\beta\:}_{n}\cdots\:\cdots\:\cdots\:\cdots\:\cdots\:1$$ Where, Y represents the predicted or expected value of the dependent variables, a 0 to a n represents the estimated regression coefficients, and β 1 to β n represent the independent variables. The river model revealed that two independent variables, water and sediment, were the most effective factors for radiocesium bioaccumulation in A. tadpoles (Fig. 4 a, p < 0.001 ). Conversely, in the lake model, sediment ( p < 0.05 ) was the sole factor that significantly affected radiocesium accumulation in A. tadpoles (Fig. 4 b). Despite the importance of food and nutrients for all living organisms, the model did not effectively incorporate food materials into the pathway model for radiocesium accumulation by A. tadpoles. In addition, the relationship between whole body Cs137 concentration in tadpole and possible exposure pathways, i.e., water, sediment and food are shown in Fig. 5 . Table 2 presents the estimation of dose rates, including internal, external, and total dose rates of radiocesium activity using the ERICA tools for non-human biota A. tadpoles based on ecosystem types. In the river ecosystem, the average wet weight per tadpole for unknown species was calculated to be 1.44 ± 0.24 g, with the lowest total dose rate estimation at 0.12 ± 0.03 (0.006–1.31) µGyh − 1 . Conversely, the highest dose rate was estimated for R. catesbenianus , with a total dose rate of 0.31 ± 0.15 (0.09–0.99) µGyh − 1 , and an average weight per tadpole of 6.07 ± 2.48 g. In the lake ecosystem, the total dose rate of radiocesium for unknown species of tadpole was lower, at 0.086 ± 0.015 (0.006-0.3) µGyh − 1 , with an average wet weight per tadpole of 1.0 ± 0.28 g compared to river tadpoles. Overall, the dose rate of radiocesium for A. tadpoles was observed to be higher in the river ecosystem than in the lake ecosystem (Fig. 6 ). Discussion The radiocesium accumulation in aquatic biota from their environments after a catastrophic disaster of nuclear power plant accident monitoring over a decade in the history showed that radiocesium are to be readily available to tadpole and other aquatic organisms either dissolved or particles deposited on the bottom of the surface. Tadpoles are diverse and abundant in various freshwater habitats, such as river and lake ecosystems. However, despite differences in the food web structure between river and lake ecosystems, the concentration ratio of 137Cs to tadpoles did not differ significantly (t-test, p > 0.05). A previous study by Ishii et al. ( 2020 ) revealed a large variation in 137Cs concentration ratios in tadpoles between lake and river ecosystems. However, the sample size for lake ecosystems was considerably low (N = 3) compared to river ecosystems (N = 49). Additionally, the IAEA reported lower values for concentration ratios of 137Cs to tadpoles than this study in aquatic environments with a low sample size (N = 3). This suggests that previous studies may have either underestimated or overestimated concentration ratio values in the tadpoles of lake sample. In contrast, our study utilized long-term monitoring data from similar regions and timescales, resulting in more stable data representing the same order of tadpoles based on aquatic ecosystems. The RC nuclide uptake in aquatic organisms including tadpoles is likely affected by several environmental factors in freshwater environments. We found that water depth is a common factor for both ecosystems, but it has a significant positive correlation in the river ecosystem and a significant negative correlation in the lake ecosystem ( p < 0.05 ). The variation of water depth at sampling sites in river ecosystems were lower (i.e., 0.26–0.97 m) than lake ecosystem (i.e., 0.2–13.5 m), which reflects the increment of water depth may negatively effect on transfer of 137Cs to the tadpoles. Similarly, dissolved oxygen has a positive effect on the transfer of RC nuclide in river, but a negative effect was observed in the lake model; however, it was not statistically significant. Moreover, temperatures were positively correlated, but suspended solids showed a significant negative correlation with the concentration ratio of 137Cs in the whole body of tadpoles in the river ecosystem. However, these correlations were not observed for lake tadpoles, possibly because the temperature and suspended solids had a wider range in rivers than in lakes. The findings of Tsuji et al. ( 2023 ) reported that temperatures had a strong positive correlation with the dissolved 137Cs in the Fukushima region, indicating that the dissolved 137Cs concentrations increases with rising water temperatures in the river ecosystem. These dissolved 137Cs compounds are bioavailable to aquatic organisms and can increase the transfer rate of radionuclides in tadpoles. Rivers from forested areas receive large amounts of organic particles and topsoil during the rainy season (Sakai et al., 2021 ), which may influence the concentration of dissolved 137Cs and adsorption into clay minerals and deposition of 137Cs nuclides in the bottom sediment. The amphibian tadpoles in aquatic environments are exposed to various sources of radiocesium present in their habitat. For example, Takahara et al. ( 2015 ) reported that radiocesium accumulation in amphibian tadpoles is mainly from food, including green algae and detritus materials. However, the results of this study contradict the previous studies as food is not a significant parameter for the transfer of radiocesium particles in tadpole in both ecosystems. In this study, phytoplankton and attached green algae were considered as the source of food in tadpoles but due to the inconsistency of data availability for all sampling periods may be influenced on the performance of this parameter on the model test. Despite the poor transfer of Cs from food, the use of a global bioaccumulation model indicated that the trophic pathways were the main uptake route of Cs in the aquatic organisms (Metian et al. 2019 ). The test of the multiple linear models shows that sediment, as a source of particulate radiocesium, was a common source of radiocesium accumulation in tadpoles in both river and lake ecosystems. Although the concentration of radiocesium in water was lower than in sediments and food materials, the river model shows that radiocesium accumulation from water is significant but not in the lake ecosystem. Dissolved radiocesium in aquatic environments usually occurs after the leaching of tree leaves in mountain streams (Sakai et al. 2021 ), which are interacts with dissolved radiocesium, leading to its deposition into bottom sediment (Gomi et al. 2018 ). Meanwhile, dissolved radiocesium binds with mineral particles and becomes particulate radiocesium, which can be re-emitted into the aquatic environment and transported downstream. While radiocesium-bearing particles are generally not bioavailable, Okumura et al. ( 2019 ) reported that the particles weather very slowly (0.014 µm/year in pure water) and may be sources of dissolved radiocesium. This is because sediment particles in aquatic environments are major source of radiocesium re-emission for a long-term exposure to aquatic organisms. A previous study by Fujii et al. ( 2018 ) reported high elevated radiocesium concentrations observed in fine sediment particles, along with organic matter primarily characterized by autochthonous origin. Meanwhile, radiocesium was found to accumulate in or be directly associated with organic compounds in the sediment, such as lignin-derived and nitrogen compounds (Mikutta et al. 2005 ; Fujii et al. 2018 ). Additionally, Fujino et al. ( 2018 ) observed a higher cesium concentration in the digestive tracts of aquatic insect larvae of Stenopsyche marmorata compared to other body parts such as muscles and extra-alimentary tissues. In addition, rapid cesium excretion from the digestive tract, with most of the remaining stable cesium found in extra-alimentary tissues. This suggests that radiocesium accumulation from external sources, such as sediment and food, is the primary source for aquatic organisms. The dose assessment of RC in A. tadpole in Fukushima region was estimated using the ERICA tool including external, internal, and total dose rate estimated for both river and lake ecosystems. The total dose rate in tadpole larvae were below the dose rate screening value of 10 µGyh − 1 predicted in the ERICA risk assessment for all samples of river and lake ecosystems. However, an average total dose rate in tadpole from river environment was estimated 1.5-fold higher than the lake ecosystem. This indicates that the tadpole from the river environment is quite vulnerable to the radiocesium. River environments receive radiocesium from different land use systems including the forest land in the head stream (Takahara et al. 2015 ) and agricultural land. In addition, the estimation of the external dose rate was literally higher than the internal dose rate of radiocesium. However, when calculating the risk quotient while estimating the external and internal dose rates of radiocesium, it was determined that the dose rate was below the risk threshold for A. tadpoles. In conclusion, this study examined the transfer factor of radiocesium 137Cs concentration in tadpoles living in aquatic environments using a decade-long monitoring dataset from the Ministry of Environment, Japan, following the Fukushima Daiichi Power Plant disaster. Radiocesium concentrations in sediment, green plants (including algae and other aquatic periphytons), and aquatic animals are still detectable, posing a potential risk of chronic toxicity and accumulation in higher trophic levels. The radiocesium concentration ratio observed in tadpoles was 6063.69 L/kg and 6071.59 L/kg wet weight in river and lake ecosystems, respectively. The transfer of radiocesium is significantly influenced by factors such as water temperature, suspended solids, and sediment, as confirmed by a generalized linear model. Although radiocesium has been detected in tadpoles, the estimated dose rate remains below 1 µGyh − 1 , indicating a low risk to aquatic organisms. However, tadpoles in river ecosystems experienced higher radiocesium dose rates (0.15 µGyh − 1 ) compared to those in lake ecosystems 0.09 µGyh − 1 ). These findings contribute to assessing the potential radioactive contamination, its transfer to aquatic organisms, and the possibility of its transformation at higher trophic levels. Declarations Acknowledgement : I thank the Ministry of Environment, Government of Japan, for providing open-source data for everyone. I acknowledge Saitama University for providing the space and internet access, allowing me to download and read research articles freely. Funding : The author declares that no funds, grants, or other support were received during the preparation of this manuscript. Authors’ Contributions: I confirm that I am the sole author of this manuscript and take full responsibility for the conception and design of the study, data acquisition, analysis and interpretation, and manuscript preparation. Ethical Approval : This article does not contain any studies conducted with human participants or animals that require ethical approval. Consent to Participate: This is not applicable. Consent to Publish : This is not applicable. Competing Interests : The author has no competing interests to declare. Data availability Statement: The dataset utilized/analyzed in this current study and related materials will be available from the corresponding author upon a reasonable request. References Beresford NA, Willey N (2019) Moving radiation protection on from the limitations of empirical concentration ratios. 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Sci Total Environ 427–428:238–246. https://doi.org/10.1016/j.scitotenv.2012.04.031 Ke C, Yu KN, Lam PKS, Wang WX (2000) Uptake and depuration of cesium in the green mussel Perna viridis. Mar Biol 137:567–575. https://doi.org/10.1007/s002270000373 Mathews T, Fisher NS (2009) Dominance of dietary intake of metals in marine elasmobranch and teleost fish. Sci Total Environ 407:5156–5161. https://doi.org/10.1016/j.scitotenv.2009.06.003 Metian M, Pouil S, Fowler SW (2019) Radiocesium accumulation in aquatic organisms: A global synthesis from an experimentalist’s perspective. J Environ Radioact 198:147–158. https://doi.org/10.1016/j.jenvrad.2018.11.013 Mikutta R, Kleber M, Kaiser K, Jahn R (2005) Review : Organic Matter Removal from Soils using Hydrogen Peroxide ,. Soil Sci Soc Am J 69:120–135 MoE (2021) Radioactive material monitoring surveys of the water environment Montaña CG, Silva SDGTM, Hagyari D, Wager J, Tiegs L, Sadeghian C, Schriever TA, Schalk CM (2019) Revisiting “what do tadpoles really eat?” A 10-year perspective. Freshw Biol 64:2269–2282. https://doi.org/10.1111/fwb.13397 Okumura T, Yamaguchi N, Dohi T, Iijima K, Kogure T (2019) Dissolution behaviour of radiocaesium-bearing microparticles released from the Fukushima nuclear plant. Sci Rep 9:1–9. https://doi.org/10.1038/s41598-019-40423-x Orizaola G (2022) Amphibians in Field Radioecology: A Review and Perspective. In: Wood MD, Mothersill CE, Taskanova G, Cresswell T, Woloschak GE (eds) Biomarkers of radiation in the Environment Robust tools for risk assessment. Springer Nature B.V., pp 185–203 Pentreath RJ (1973) The roles of food and water in the accumulation of radionuclides by marine teleost and elasmobranch fish. In: Radioactive contamination of the marine environment. pp 421–434 Sakai M, Gomi T, Nunokawa M, Wakahara T, Onda Y (2014) Soil removal as a decontamination practice and radiocesium accumulation in tadpoles in rice paddies at Fukushima. Environ Pollut 187:112–115. https://doi.org/10.1016/j.envpol.2014.01.002 Sakai M, Tsuji H, Ishii Y, Ozaki H, Takechi S, Jo J, Tamaoki M, Hayashi S, Gomi T (2021) Untangling radiocesium dynamics of forest-stream ecosystems: A review of Fukushima studies in the decade after the accident. Environ Pollut 288. https://doi.org/10.1016/j.envpol.2021.117744 Smith JT, Kudelsky A V., Ryabov IN, Daire SE, Boyer L, Blust RJ, Fernandez JA, Hadderingh RH, Voitsekhovitch O V. (2002) Uptake and elimination of radiocaesium in fish and the “size effect.” J Environ Radioact 62:145–164. https://doi.org/10.1016/S0265-931X(01)00157-6 Srivastava A, Reddy SJ, Kelber O, Urich K, Denschlag O (1994) Uptake and release kinetics of 134Cs by Goldfish (Carassius auratus) and 137Cs by Zebra fish (Brachydanio rerio) in controlled aquatic environment. J Radioanal Nucl Chem 182:63–69 Styron CE, Hagan TM, Campbell DR, Harvin J, Whittenburg NK, Baughman GA, Bransford ME, Saunders WH, Williams DC, Woodle C, Dixon NK, Mcneill CR (1976) Effects of temperature and salinity on growth and uptake of 65zn and 137cs for six marine algae. J Mar Biol Assoc United Kingdom 56:13–20. https://doi.org/10.1017/S0025315400020397 Tagami K, Uchida S, Wood MD, Beresford NA (2018) Radiocaesium transfer and radiation exposure of frogs in Fukushima Prefecture. Sci Rep 8:1–11. https://doi.org/10.1038/s41598-018-28866-0 Takahara T, Endo S, Takada M, Oba Y, Nursal WI, Igawa T, Doi H, Yamada T, Okuda T (2015) Radiocesium accumulation in the anuran frog, Rana tagoi tagoi, in forest ecosystems after the Fukushima Nuclear Power Plant accident. Environ Pollut 199:89–94. https://doi.org/10.1016/j.envpol.2015.01.018 Tsuji H, Nishikiori T, Ito S, Ozaki H, Watanabe M, Sakai M, Ishii Y, Hayashi S (2023) Influential factors of long-term and seasonal 137Cs change in agricultural and forested rivers: Temperature, water quality and an intense Typhoon Event. Environ Pollut 338. https://doi.org/10.1016/j.envpol.2023.122617 Wada T, Hinata A, Furuta Y, Sasaki K, Konoplev A, Nanba K (2023) Factors affecting 137Cs radioactivity and water-to-body concentration ratios of fish in river and pond environments near the Fukushima Dai-ichi Nuclear Power Plant. J Environ Radioact 258. https://doi.org/10.1016/j.jenvrad.2022.107103 Warnau M, Fowler SW, Teyssié JL (1996) Biokinetics of selected heavy metals and radionuclides in two marine macrophytes: The seagrass Posidonia oceanica and the alga Caulerpa taxifolia. Mar Environ Res 41:343–362. https://doi.org/10.1016/0141-1136(95)00025-9 Whiles MR, Lips KR, Pringle CM, Kilham SS, Bixby RJ, Brenes R, Connelly S, Colon-Gaud JC, Hunte-Brown M, Huryn AD, Montgomery C, Peterson S (2006) The effects of amphibian population declines on the structure and function of neotropical stream ecosystems. Front Ecol Environ 4:27–34. https://doi.org/10.1890/1540-9295(2006)004[0027:TEOAPD]2.0.CO;2 Wood MD, Beresford NA, Howard BJ, Copplestone D (2013) Evaluating summarised radionuclide concentration ratio datasets for wildlife. J Environ Radioact 126:314–325. https://doi.org/10.1016/j.jenvrad.2013.07.022 Zhao X, Wang WX, Yu KN, Lam PKS (2001) Biomagnification of radiocesium in a marine piscivorous fish. Mar Ecol Prog Ser 222:227–237. https://doi.org/10.3354/meps222227 Tables Table 1: Generalized liner model (GLM) for river and lake ecosystem. Effect of each independent variables for concentration ratio of radicesium accumulation by tadpole frog for river and lake ecosystem. The most prominent environmental factors are shown in bold color. The estimated parameters for each predictor variable after the model averaging are listed. The coefficient of determination R 2 was 0.38 for the best river model and 0.70 for the best lake model. Table 2: Comparison of radiocesium activity (Cs 137 ) and estimated absorbed dose rate in different species from the river and lake ecosystem. Supplementary Files 2025.03.31SupportingDocument.xlsx Cite Share Download PDF Status: Posted Version 1 posted 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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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6331961","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":488810539,"identity":"5e1412b9-ff25-42ff-aa15-33bef15dfe3b","order_by":0,"name":"Ashok Kumar Shrestha","email":"data:image/png;base64,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","orcid":"","institution":"Saitama University Graduate School of Science and Engineering: Saitama Daigaku Daigakuin Rikogaku Kenkyuka","correspondingAuthor":true,"prefix":"","firstName":"Ashok","middleName":"Kumar","lastName":"Shrestha","suffix":""}],"badges":[],"createdAt":"2025-03-29 05:18:04","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6331961/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6331961/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":87459145,"identity":"32b74eec-3f5e-4869-ab4b-6393f24224d8","added_by":"auto","created_at":"2025-07-24 05:33:22","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":84450,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of Cs137 CR (L kg\u003csup\u003e-1\u003c/sup\u003e) in tadpole frog in river (N = 80) and lake (N = 33) ecosystems. The student t-test did not show significance change between these two ecosystems (p \u0026gt; 0.05).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6331961/v1/686e1acb1a2c4516cd365ecc.png"},{"id":87459140,"identity":"15187c81-214a-4081-a874-09096bde1bc4","added_by":"auto","created_at":"2025-07-24 05:33:21","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":110461,"visible":true,"origin":"","legend":"\u003cp\u003eSeasonal change in 137Cs concentration ratio transfer to the tadpole frog in river ecosystem (a) and lake ecosystem (b).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6331961/v1/71e34e6a6bdd89f36bba422a.png"},{"id":87459143,"identity":"ce74fe3f-6f6c-4f22-bccd-c75ab35a82e5","added_by":"auto","created_at":"2025-07-24 05:33:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":302787,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation between environmental parameters and concentration ratio (CR) of radiocesium in tadpole frog in river (red open circle) and lake (filled black circle) ecosystem. The lines represent GLM model predictions for whole-body concentration ratio of Cs137 in tadpole when the effect of environmental parameters was significant (P \u0026lt; 0.05) for rivers (red line) and lakes (black line).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6331961/v1/2ce9aed06c5c44df7f8ba349.png"},{"id":87459154,"identity":"32492d99-e9bd-4979-af86-f8d5181f8ee1","added_by":"auto","created_at":"2025-07-24 05:33:22","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":152246,"visible":true,"origin":"","legend":"\u003cp\u003eRadiocesium accumulation exposure pathways in tadpole frog. The multiple linear regression analysis found that sediment (p\u0026lt;0.001) and water (p\u0026lt;0.05) could be biologically important determinant in river ecosystem; however, a single factor, sediment (p\u0026lt;0.05) could be important factor for bioaccumulation of radioceiusm in lake ecosystem.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6331961/v1/4be4d42f08f686051f4b561b.png"},{"id":87460471,"identity":"da886c6d-ba0b-46d5-a615-1aa4e0350b1b","added_by":"auto","created_at":"2025-07-24 05:49:22","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":172206,"visible":true,"origin":"","legend":"\u003cp\u003eRelationships between whole body Cs137 concentration in tadpole and possible exposure pathways, (a) water, (b) sediment, and (c) food. The colors indicate samples from rivers (red open circle) and lakes (black filled circle). The lines represent linear regression model predictions for whole-body Cs137 accumulation in tadpole when the effect of exposure pathways was significant (p\u0026lt; 0.05) for rivers (red line) and lakes (black line).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6331961/v1/9c7353768aad796b04061344.png"},{"id":87460265,"identity":"7c927718-c6e8-4a2f-89cf-d1ee54a54de9","added_by":"auto","created_at":"2025-07-24 05:41:22","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":51687,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of dose rate of Cs137 in river and lake system. EDR = External Dose Rate; IDR = Internal Dose Rate; TDR = Total Dose Rate; RQ = Risk Quotient. RQ is unitless. Error bar indicates standard error.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6331961/v1/c058c4a96bbbf8210889295e.png"},{"id":87461074,"identity":"5c677af2-bf1b-41e2-a3b4-13c692642fcf","added_by":"auto","created_at":"2025-07-24 05:57:23","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1440225,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6331961/v1/99613992-0a28-4d29-a711-587d33b867d3.pdf"},{"id":87459151,"identity":"9af3201c-af56-45f8-8e25-394cd53caa00","added_by":"auto","created_at":"2025-07-24 05:33:22","extension":"xlsx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":262125,"visible":true,"origin":"","legend":"","description":"","filename":"2025.03.31SupportingDocument.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-6331961/v1/7fba8854b356af96a7309278.xlsx"}],"financialInterests":"","formattedTitle":"Ecological Risk of Radiocesium Contamination and Dose Rate Estimation in Anuran Tadpole in Aquatic Environments","fulltext":[{"header":"Introduction","content":"\u003cp\u003eIn March 2011, the magnitude 9.0 East Japan Earthquake followed by a devastating tsunami caused accident of nuclear reactor at the Fukushima Dai-ichi Nuclear Power Plant resulted in the emission of the large quantities of radionuclide into the environment. Radionuclide including radiocesium (137Cs) becomes major radionuclide contamination in the environment after nuclear power plant accident (Ishii et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). It is because of the long half-life (i.e., 30.2 years), persistence in the environment, and can be readily bioaccumulated especially by the aquatic organisms from aquatic environment.\u003c/p\u003e \u003cp\u003eThe Ministry of the Environment, Japan has been conducted long-term monitoring since 2012, following the FDNPP accident. This monitoring involves tracking radiocesium levels in various locations within aquatic environments, including water, sediments, and surrounding biota such as plants and animals. The annual survey data indicates that even after a decade since the accident, concentrations of radiocesium in sediment and aquatic organisms still exceed 100 Bq/kg fresh weight in some location, surpassing the Japanese regulatory limit (MoE \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This indicates that the threat of radiocesium in the aquatic organisms are still remaining and may have chronic effect on the aquatic biota.\u003c/p\u003e \u003cp\u003eInland water bodies such as river system, lakes, ponds, and reservoirs can acts as a transporter of radiocesium in both dissolved and particulate forms, resulting source of radiocesium bioaccumulation to the bottom of the aquatic food chain, e.g., phytoplankton and macrophytes; (Harvey and Patrick \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1967\u003c/span\u003e; Fisher \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1985\u003c/span\u003e; Warnau et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1996\u003c/span\u003e; Heldal et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2001\u003c/span\u003e) and can then be transferred to higher trophic levels such as fish (Pentreath \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e1973\u003c/span\u003e; Zhao et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Mathews and Fisher \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Many studies have investigated the effect of radiocesium after the nuclear power-plant accident on aquatic biota, revealing the presence and distribution of radiocesium contamination in the aquatic environment (Fujino et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Ishii et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Fujino et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Wada et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Because of the short to long growing period, depending on species in the aquatic environments, aquatic organisms can readily accumulate both dissolved and particulate radiocesium from their environments. However, the accumulation of radiocesium by aquatic organisms may depend on various other biotic and abiotic factors (Tagami et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWater chemistry parameters play a significant role in aquatic ecosystems as they strongly influence the physiology of aquatic organisms (Metian et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). For instance, an increase in water temperature can elevate the concentration factors of dissolved radiocesium in various species, such as fish (Srivastava et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1994\u003c/span\u003e), and algae (Styron et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1976\u003c/span\u003e; Boisson et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1997\u003c/span\u003e), as reviewed by Metian et al. (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). However, some studies have shown reverse effects on the accumulation of radiocesium (i.e., 134Cs) in fish species. In contrast, a decrease in concentration factors was observed in \u003cem\u003eCarassius auratus\u003c/em\u003e concerning an increase in water temperature (Srivastava et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). Conversely, Ishii et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) noted a negative correlation, though not statistically significant, between water temperature and radiocesium concentration factors in fish species sampled from the Fukushima region. Additionally, dissolved potassium concentration significantly affects accumulation of radiocesium in fish, either by increasing elimination rates (Cocchio et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1995\u003c/span\u003e) or by decreasing uptake (Smith et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). Similar effects have been observed in the green-lipped mussel \u003cem\u003ePerna viridis\u003c/em\u003e (Ke et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2000\u003c/span\u003e) and the microcrustacean \u003cem\u003eDaphnia magna\u003c/em\u003e (Hagstrom \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). Furthermore, previous studies demonstrated that pH has no influence on the bioaccumulation of radiocesium in the fishes in freshwater environment (Ishii et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Although studies have extensively investigated the bioaccumulation of radiocesium in various aquatic organisms, there is limited mention of tadpole larvae and the potential effects of environmental factors influencing radiocesium transfer (Tagami et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWithin the amphibian group, tadpoles undergo complete development in aquatic environments until they reach maturity, transitioning into terrestrial environments as adults. Tadpoles exhibit diversity and abundance across various freshwater habitats, playing pivotal roles in aquatic food webs due to their ability to reach high densities and biomass (Monta\u0026ntilde;a et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). They serve as vital prey for other consumers and facilitate the transfer of nutrients and energy between aquatic and terrestrial ecosystems(Whiles et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Capps et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Despite their significance, only a limited number of studies have highlighted the investigation of the radiological effects on amphibian groups, specifically tadpoles (Sakai et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Tagami et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). However, a drawback of the previous studies is the low sample size used to analyzed concentration ratio and dose rate (Orizaola \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), and randomly used the data generated from both lotic and lentic ecosystems of tadpoles and adult frogs (e.g. Ishii et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Tagami et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAccording to the International Atomic Energy Agency (International Atomic Energy Agency \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), the concentration ratio refers to the ratio of radionuclide concentration in biota from all pathways (including water, sediment, and ingestion/dietary) based on per unit tissue fresh weight, compared to that in water. Typically, transfer factors of radionuclides, including radiocesium, are expressed as water-to-biota ratios, and the IAEA 2010 provides a summary of concentration ratios for various aquatic organisms, including tadpoles (e.g., 3.0 \u0026times; 10\u003csup\u003e3\u003c/sup\u003e Lkg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e fresh weight; N\u0026thinsp;=\u0026thinsp;3). However, previous studies in the Fukushima region revealed different concentration ratios of radiocesium from water to tadpoles, reporting 3.5 \u0026times; 10\u003csup\u003e3\u003c/sup\u003e Lkg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e fresh weight; N\u0026thinsp;=\u0026thinsp;59 (Tagami et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), 5.7 \u0026times; 10\u003csup\u003e3\u003c/sup\u003e Lkg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e fresh weight; N\u0026thinsp;=\u0026thinsp;49 for river ecosystems, and 7.2 \u0026times; 10\u003csup\u003e3\u003c/sup\u003e Lkg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e fresh weight; N\u0026thinsp;=\u0026thinsp;3 for lake ecosystems (Ishii et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The variability in sample size and temporal fluctuations during tadpole sampling might significantly impact the levels of radiocesium activity and its concentration ratios (Orizaola, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Ishii et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The transfer of radiocesium through aquatic ecosystems is intricate, often simplified and described using terms such as the distribution coefficient (K\u003csub\u003ed\u003c/sub\u003e) (the ratio of radionuclide activity concentration in the particulate phase to dissolved concentration, as per IAEA 2010) and concentration ratios. While concentration ratios and K\u003csub\u003ed\u003c/sub\u003e values, along with the activity concentration of radiocesium, are pivotal elements within models used for radiological risk assessments (Wood et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), these parameters frequently span multiple orders of magnitude for a single radionuclide. Consequently, they stand as the primary source of uncertainty in risk assessments, particularly when site-specific data is lacking(Johansen et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Beresford and Willey \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThus, the aim of this study was to investigate how environmental factors (e.g., biotic and abiotic) effects the transfer coefficient (concentration ratio) of 137Cs in Anura tadpoles in various (river and lake) ecosystems using the 10 years-long monitoring data. Additionally, the study aimed to estimate dose rates corresponding to these findings for the purpose of risk analysis. The single order Anura tadpole larvae including two specified species (e.g., \u003cem\u003eRana catesbeianus\u003c/em\u003e and \u003cem\u003eLithobates catesbeianus\u003c/em\u003e) and one unknown species (mentioned by data surveyor MOE in the monitoring data sheet) is used for this study. Concentration ratio and dose rate estimation of radiocesium in tadpoles were separately analyzed in lake and river ecosystems and compared the mean values for further risk analysis.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003e\u003cstrong\u003eData extraction\u003c/strong\u003e:\u003c/p\u003e\n\u003cp\u003eThe data used for this study was extracted from the Ministry of Environment, Government of Japan, had continuously monitored radiocesium concentration in water, sediment and biota including suspended solids and organic matter since 2012 to 2021, after Fukushima Dai-Ichi nuclear powerplant accident due to mega earthquake hits in Japan. Radiocesium monitoring at five rivers River Abukuma system, River Uda, River Mano, River Niida, River Ota and three lakes, Lake Hayama, Lake Akimoto and Lake Inawashiro, shown in supporting Fig. 1. From each site, live aquatic organisms including Anura tadpole frogs (hereafter called A. tadpole), water and sediment of adjacent sites were collected four times in a year representing spring, summer, autumn and winter season. During the survey, general item concerning water quality parameters such as depth of water, temperature, pH, dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand (COD), electrical conductivity (EC), salinity, total organic carbon (TOC), suspended solid (SS) and turbidity. Radiocesium activity concentration measurement in A. tadpole, water and sediment using the standard methods established by the Japanese ministry of education, culture, sport, science and technology (MEXT) (see MOE Open-source data). Due to the low mass of individual tadpoles, collected samples were bulked for a given specific site and measured the radiocesium activity concentration. A. tadpole including unknown species, \u003cem\u003eLithobates catesbeianus\u003c/em\u003e and \u003cem\u003eRana catesbeianus\u003c/em\u003e were collected from river (total no. of tadpole 2830; U. species, 2605; \u003cem\u003eL. catesbeianus\u003c/em\u003e, 191; \u003cem\u003eR. catesbeianus\u003c/em\u003e, 34) and lake (total no. of tadpole 3056; U. species, 3035; \u003cem\u003eL. catesbeianus\u003c/em\u003e, 21). No \u003cem\u003eR. catesbeianus\u003c/em\u003e were recorded in lake sampling sites in the specified location. See details in the supplementary file.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCalculation of Cs concentration ratio\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe transfer of radionuclides into the whole body of organisms is primarily defined by the concentration ratio of the surrounding media. The concentration ratio, in this context, refers to the ratio of radionuclide concentration in the entire biota\u0026apos;s body (Cb) resulting from all exposure pathways, including water, sediment, and ingestion/dietary pathways, per unit tissue fresh weight, relative to that in the water (Cw) (IAEA, 2010). To calculate the concentration ratio, the concentration of radiocesium accumulation in A. tadpoles per unit of radiocesium concentration in the water at the same sites and during the same season only were used. The concentration ratio for Cs137 and Cs134 was determined using the database specific to each site. However, Cs134 was not detected in many sites, making it difficult to express the concentration ratio (please refer to the supplementary file for details on CR for Cs134). Consequently, only Cs137 data was used to explain the transfer value of radionuclides to A. tadpoles in both river and lake ecosystems. Radiocesium concentration (Cs137) in biota that fell below the lower limit value was not considered when calculating the concentration ratio.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEstimation of Dose rate\u003c/strong\u003e:\u003c/p\u003e\n\u003cp\u003eThe radiocesium dose rate for A. tadpoles was estimated using the ERICA (Environmental Risk from Ionising Contaminants: Assessment and Management) assessment tool, version 2 (2.0.221) (Brown et al. 2008) with some modifications. The ERICA tool is commonly used for risk assessment in wildlife due to the dispersion of radionuclides in the environment. It includes three tiers: tier 1, tier 2, and tier 3. Among these, tier 2 was used to estimate the external, internal, and total dose rates of radiocesium, along with the risk quotient (RQ). Radiocesium concentration activity data were used to estimate the dose rate. However, the total dose rate for 137Cs was considered for the risk quotient, as there were many data below detection for Cs-134 in biota which the data insufficient to comparison with 137Cs. Default parameters, such as the ERICA dose rate screening value of 10 \u0026micro;Gy/h and an uncertainty factor (UF) of three, indicate a test for a 5% probability of exceeding the dose screening value, assuming that the RQ distribution is exponential.\u003c/p\u003e\n\u003cp\u003eThe geometry for tadpoles is not listed in the new version of the ERICA assessment tool. Therefore, we created a new geometry for tadpoles using the dimensions provided by ICRP (2008), with tadpoles measuring 1.5 cm in length, 0.75 cm in width, and 0.75 cm in height. The average body mass of individual tadpoles was calculated as 0.442 g from the provided datasets. In addition, the average concentration ratio and coefficient of distribution (Kd) for rivers and lakes were 6063.69 and 20047.3, and 6071.59 and 1687.3, respectively. Tadpoles fully develop in aquatic habitats until they reach adulthood and were modeled at the sediment-water interface (Tagami et al. 2018 and Flecker et al. 1999). Therefore, the occupancy factor for A. tadpoles was assumed to be 50/50 in water and sediment surfaces. Furthermore, the radiation weighting factors were set at 10, 1, and 1 for alpha, beta, and gamma radiation, respectively.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatistical analysis\u003c/strong\u003e:\u003c/p\u003e\n\u003cp\u003eThe relative water quality parameters and concentration ratio of radiocesium in A. tadpoles for each ecosystem type were analyzed using the generalized linear model (GLM). The number of bulk tadpole samples used for radiocesium measurements in rivers (N=80) and lakes (N=33) were determined separately. Environmental factors such as, water depth, temperature, pH, DO, EC, COD, TOC, salinity, and suspended solid were considered for the effect in concentrations ratio of radiocesium accumulate by A. tadpole. The concentration ratio values of radionuclide were log-transformed, however, other remains same without log-transformed.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFurthermore, the possible exposure pathways were analyzed using multiple regression analysis. The exposure pathways including radiocesium concentrations in water, sediment and food materials were taken for the data analyzed. The important sources of food for tadpoles in aquatic habitat are plankton including green algae and coarse particulate organic matter depending on the habitat types (ICRP, 2008; Verburg et al. 2007). According to the study of Montana et al. (2019) reported that approximately 16 food categories were found in the guts of tadpoles with algae exhibiting the highest frequency of occurrences in green plants material. Therefore, we assumed that the small green plants either floated or attached are the major source of radiocesium transform to the tadpole while they feed from their habitat. In this study, we took radiocesium concentration data of green plants such as algae, Oedogonium, spirogyra, small pondweed, and sphagnum.\u003c/p\u003e\n\u003cp\u003eThe temporal and spatial data of radiocesium accumulation by A. tadpoles were analyzed using the one-way analysis of variance (ANOVA). The student-t test was used to compare the means of radiocesium concentration accumulation by A. tadpoles between two ecosystem types. Data normality was analyzed using the Shapiro test. The differences were considered to be statistically significant at p \u0026lt;0.05. All statistical tests were performed using the RStudio software (RStudio team, 2023, version 4.3.1).\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe radiocesium concentration ratios in river and lake ecosystems ranged from 268 to 22,619.05 L/kg and 137.5 to 30,400 L/kg, with average radiocesium concentrations of 6,063.69 L/kg and 6,071.59 L/kg, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Seasonal changes of 137Cs concentration ratio in A. tadpole were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. In the lake ecosystem, fall and winter season had drastically decreased 137Cs concentration ratio, however, the average concentration ratio in fall was observed highest than spring and summer season in river ecosystem. Although, the concentration ratio was increased, it was statistically significantly decreased in winter season (One-way ANOVA, \u003cem\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.01\u003c/em\u003e). Moreover, the average radiocesium activity concentration in A. tadpoles sampled from rivers and lakes was 279.931 Bq/kg, ranging from 5.2 to 1700 Bq/kg and 98.288 Bq/kg, ranging from 2.2 to 400 Bq/kg, respectively. The detailed information of radiocesium activity concentration in water, sediment, foods and A. tadpoles are presented in the supplementary file.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe prominent factors affecting the transformation of 137Cs nuclide in A. tadpole concentration ratios were evaluated using a Generalized Linear Model (GLM), and the results are presented in Table\u0026nbsp;1. The estimated coefficients represent standardized effects, making them comparable within the model across parameters. In the river model, environmental factors such as water depth (0.54) and water temperature (0.05) had significantly positive effects in whole-body radiocesium concentration ratio (Table\u0026nbsp;1). However, suspended solids (-0.04) had a significant negative effect. Other factors, like COD and EC, also exhibited a negative relationship, whereas pH, DO, salinity, and TOC had a positive impact, although it was not statistically significant (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). In contrast, the lake model revealed that only one parameter, water depth (-0.11), had a significantly negative effect on the transfer of RC nuclide in the lentic environment (Table\u0026nbsp;1).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA. tadpoles were exposed to RC nuclides from water, sediment, and food in their natural habitat. However, we analyzed the most effective pathways using multiple linear regression methods (see Eq.\u0026nbsp;1) and developed equations for those that were found to be significant.\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:Y={a}_{0}+{a}_{1}{\\beta\\:}_{1}+{a}_{2}{\\beta\\:}_{2}+{a}_{3}{\\beta\\:}_{3}+\\dots\\:\\dots\\:\\dots\\:\\dots\\:..{{a}_{n}\\beta\\:}_{n}\\cdots\\:\\cdots\\:\\cdots\\:\\cdots\\:\\cdots\\:1$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere, Y represents the predicted or expected value of the dependent variables, a\u003csub\u003e0\u003c/sub\u003e to a\u003csub\u003en\u003c/sub\u003e represents the estimated regression coefficients, and β\u003csub\u003e1\u003c/sub\u003e to β\u003csub\u003en\u003c/sub\u003e represent the independent variables. The river model revealed that two independent variables, water and sediment, were the most effective factors for radiocesium bioaccumulation in A. tadpoles (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, p\u0026thinsp;\u003cem\u003e\u0026lt;\u0026thinsp;0.001\u003c/em\u003e). Conversely, in the lake model, sediment (\u003cem\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/em\u003e) was the sole factor that significantly affected radiocesium accumulation in A. tadpoles (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). Despite the importance of food and nutrients for all living organisms, the model did not effectively incorporate food materials into the pathway model for radiocesium accumulation by A. tadpoles. In addition, the relationship between whole body Cs137 concentration in tadpole and possible exposure pathways, i.e., water, sediment and food are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;2 presents the estimation of dose rates, including internal, external, and total dose rates of radiocesium activity using the ERICA tools for non-human biota A. tadpoles based on ecosystem types. In the river ecosystem, the average wet weight per tadpole for unknown species was calculated to be 1.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24 g, with the lowest total dose rate estimation at 0.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03 (0.006\u0026ndash;1.31) \u0026micro;Gyh\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Conversely, the highest dose rate was estimated for \u003cem\u003eR. catesbenianus\u003c/em\u003e, with a total dose rate of 0.31\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15 (0.09\u0026ndash;0.99) \u0026micro;Gyh\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and an average weight per tadpole of 6.07\u0026thinsp;\u0026plusmn;\u0026thinsp;2.48 g. In the lake ecosystem, the total dose rate of radiocesium for unknown species of tadpole was lower, at 0.086\u0026thinsp;\u0026plusmn;\u0026thinsp;0.015 (0.006-0.3) \u0026micro;Gyh\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, with an average wet weight per tadpole of 1.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28 g compared to river tadpoles. Overall, the dose rate of radiocesium for A. tadpoles was observed to be higher in the river ecosystem than in the lake ecosystem (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe radiocesium accumulation in aquatic biota from their environments after a catastrophic disaster of nuclear power plant accident monitoring over a decade in the history showed that radiocesium are to be readily available to tadpole and other aquatic organisms either dissolved or particles deposited on the bottom of the surface. Tadpoles are diverse and abundant in various freshwater habitats, such as river and lake ecosystems. However, despite differences in the food web structure between river and lake ecosystems, the concentration ratio of 137Cs to tadpoles did not differ significantly (t-test, p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). A previous study by Ishii et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) revealed a large variation in 137Cs concentration ratios in tadpoles between lake and river ecosystems. However, the sample size for lake ecosystems was considerably low (N\u0026thinsp;=\u0026thinsp;3) compared to river ecosystems (N\u0026thinsp;=\u0026thinsp;49). Additionally, the IAEA reported lower values for concentration ratios of 137Cs to tadpoles than this study in aquatic environments with a low sample size (N\u0026thinsp;=\u0026thinsp;3). This suggests that previous studies may have either underestimated or overestimated concentration ratio values in the tadpoles of lake sample. In contrast, our study utilized long-term monitoring data from similar regions and timescales, resulting in more stable data representing the same order of tadpoles based on aquatic ecosystems.\u003c/p\u003e \u003cp\u003eThe RC nuclide uptake in aquatic organisms including tadpoles is likely affected by several environmental factors in freshwater environments. We found that water depth is a common factor for both ecosystems, but it has a significant positive correlation in the river ecosystem and a significant negative correlation in the lake ecosystem (\u003cem\u003ep\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/em\u003e). The variation of water depth at sampling sites in river ecosystems were lower (i.e., 0.26\u0026ndash;0.97 m) than lake ecosystem (i.e., 0.2\u0026ndash;13.5 m), which reflects the increment of water depth may negatively effect on transfer of 137Cs to the tadpoles. Similarly, dissolved oxygen has a positive effect on the transfer of RC nuclide in river, but a negative effect was observed in the lake model; however, it was not statistically significant. Moreover, temperatures were positively correlated, but suspended solids showed a significant negative correlation with the concentration ratio of 137Cs in the whole body of tadpoles in the river ecosystem. However, these correlations were not observed for lake tadpoles, possibly because the temperature and suspended solids had a wider range in rivers than in lakes. The findings of Tsuji et al. (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) reported that temperatures had a strong positive correlation with the dissolved 137Cs in the Fukushima region, indicating that the dissolved 137Cs concentrations increases with rising water temperatures in the river ecosystem. These dissolved 137Cs compounds are bioavailable to aquatic organisms and can increase the transfer rate of radionuclides in tadpoles. Rivers from forested areas receive large amounts of organic particles and topsoil during the rainy season (Sakai et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), which may influence the concentration of dissolved 137Cs and adsorption into clay minerals and deposition of 137Cs nuclides in the bottom sediment.\u003c/p\u003e \u003cp\u003eThe amphibian tadpoles in aquatic environments are exposed to various sources of radiocesium present in their habitat. For example, Takahara et al. (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) reported that radiocesium accumulation in amphibian tadpoles is mainly from food, including green algae and detritus materials. However, the results of this study contradict the previous studies as food is not a significant parameter for the transfer of radiocesium particles in tadpole in both ecosystems. In this study, phytoplankton and attached green algae were considered as the source of food in tadpoles but due to the inconsistency of data availability for all sampling periods may be influenced on the performance of this parameter on the model test. Despite the poor transfer of Cs from food, the use of a global bioaccumulation model indicated that the trophic pathways were the main uptake route of Cs in the aquatic organisms (Metian et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe test of the multiple linear models shows that sediment, as a source of particulate radiocesium, was a common source of radiocesium accumulation in tadpoles in both river and lake ecosystems. Although the concentration of radiocesium in water was lower than in sediments and food materials, the river model shows that radiocesium accumulation from water is significant but not in the lake ecosystem. Dissolved radiocesium in aquatic environments usually occurs after the leaching of tree leaves in mountain streams (Sakai et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), which are interacts with dissolved radiocesium, leading to its deposition into bottom sediment (Gomi et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Meanwhile, dissolved radiocesium binds with mineral particles and becomes particulate radiocesium, which can be re-emitted into the aquatic environment and transported downstream. While radiocesium-bearing particles are generally not bioavailable, Okumura et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) reported that the particles weather very slowly (0.014 \u0026micro;m/year in pure water) and may be sources of dissolved radiocesium. This is because sediment particles in aquatic environments are major source of radiocesium re-emission for a long-term exposure to aquatic organisms.\u003c/p\u003e \u003cp\u003eA previous study by Fujii et al. (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) reported high elevated radiocesium concentrations observed in fine sediment particles, along with organic matter primarily characterized by autochthonous origin. Meanwhile, radiocesium was found to accumulate in or be directly associated with organic compounds in the sediment, such as lignin-derived and nitrogen compounds (Mikutta et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Fujii et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Additionally, Fujino et al. (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) observed a higher cesium concentration in the digestive tracts of aquatic insect larvae of \u003cem\u003eStenopsyche marmorata\u003c/em\u003e compared to other body parts such as muscles and extra-alimentary tissues. In addition, rapid cesium excretion from the digestive tract, with most of the remaining stable cesium found in extra-alimentary tissues. This suggests that radiocesium accumulation from external sources, such as sediment and food, is the primary source for aquatic organisms.\u003c/p\u003e \u003cp\u003eThe dose assessment of RC in A. tadpole in Fukushima region was estimated using the ERICA tool including external, internal, and total dose rate estimated for both river and lake ecosystems. The total dose rate in tadpole larvae were below the dose rate screening value of 10 \u0026micro;Gyh\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e predicted in the ERICA risk assessment for all samples of river and lake ecosystems. However, an average total dose rate in tadpole from river environment was estimated 1.5-fold higher than the lake ecosystem. This indicates that the tadpole from the river environment is quite vulnerable to the radiocesium. River environments receive radiocesium from different land use systems including the forest land in the head stream (Takahara et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) and agricultural land. In addition, the estimation of the external dose rate was literally higher than the internal dose rate of radiocesium. However, when calculating the risk quotient while estimating the external and internal dose rates of radiocesium, it was determined that the dose rate was below the risk threshold for A. tadpoles.\u003c/p\u003e \u003cp\u003eIn conclusion, this study examined the transfer factor of radiocesium 137Cs concentration in tadpoles living in aquatic environments using a decade-long monitoring dataset from the Ministry of Environment, Japan, following the Fukushima Daiichi Power Plant disaster. Radiocesium concentrations in sediment, green plants (including algae and other aquatic periphytons), and aquatic animals are still detectable, posing a potential risk of chronic toxicity and accumulation in higher trophic levels. The radiocesium concentration ratio observed in tadpoles was 6063.69 L/kg and 6071.59 L/kg wet weight in river and lake ecosystems, respectively. The transfer of radiocesium is significantly influenced by factors such as water temperature, suspended solids, and sediment, as confirmed by a generalized linear model. Although radiocesium has been detected in tadpoles, the estimated dose rate remains below 1 \u0026micro;Gyh\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, indicating a low risk to aquatic organisms. However, tadpoles in river ecosystems experienced higher radiocesium dose rates (0.15 \u0026micro;Gyh\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) compared to those in lake ecosystems 0.09 \u0026micro;Gyh\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). These findings contribute to assessing the potential radioactive contamination, its transfer to aquatic organisms, and the possibility of its transformation at higher trophic levels.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e: I thank the Ministry of Environment, Government of Japan, for providing open-source data for everyone. I acknowledge Saitama University for providing the space and internet access, allowing me to download and read research articles freely.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e: The author declares that no funds, grants, or other support were received during the preparation of this manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; Contributions:\u0026nbsp;\u003c/strong\u003eI confirm that I am the sole author of this manuscript and take full responsibility for the conception and design of the study, data acquisition, analysis and interpretation, and manuscript preparation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e: This article does not contain any studies conducted with human participants or animals that require ethical approval.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate:\u0026nbsp;\u003c/strong\u003eThis is not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish\u003c/strong\u003e\u003cstrong\u003e:\u0026nbsp;\u003c/strong\u003eThis is not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e:\u0026nbsp;The author has no competing interests to declare.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u0026nbsp;\u003c/strong\u003eStatement: The dataset utilized/analyzed in this current study and related materials will be available from the corresponding author upon a reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eBeresford NA, Willey N (2019) Moving radiation protection on from the limitations of empirical concentration ratios. J Environ Radioact 208\u0026ndash;209. https://doi.org/10.1016/j.jenvrad.2019.106020\u003c/li\u003e\n \u003cli\u003eBoisson F, Hutchins DA, Fowler SW, Fisher NS, Teyssie JL (1997) Influence of temperature on the accumulation and retention of 11 radionuclides by the marine alga Fucus vesiculosus (L.). Mar Pollut Bull 35:313\u0026ndash;321. https://doi.org/10.1016/S0025-326X(97)00092-1\u003c/li\u003e\n \u003cli\u003eCapps KA, Berven KA, Tiegs SD (2015) Modelling nutrient transport and transformation by pool-breeding amphibians in forested landscapes using a 21-year dataset. Freshw Biol 60:500\u0026ndash;511. https://doi.org/10.1111/fwb.12470\u003c/li\u003e\n \u003cli\u003eCocchio LA, Beamish FWH, Rodgers DW (1995) \u0026nbsp; Effects of water chemistry and temperature on radiocesium dynamics in rainbow trout, Oncorhynchus mykiss . 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Sci Total Environ 407:5156\u0026ndash;5161. https://doi.org/10.1016/j.scitotenv.2009.06.003\u003c/li\u003e\n \u003cli\u003eMetian M, Pouil S, Fowler SW (2019) Radiocesium accumulation in aquatic organisms: A global synthesis from an experimentalist\u0026rsquo;s perspective. J Environ Radioact 198:147\u0026ndash;158. https://doi.org/10.1016/j.jenvrad.2018.11.013\u003c/li\u003e\n \u003cli\u003eMikutta R, Kleber M, Kaiser K, Jahn R (2005) Review : Organic Matter Removal from Soils using Hydrogen Peroxide ,. Soil Sci Soc Am J 69:120\u0026ndash;135\u003c/li\u003e\n \u003cli\u003eMoE (2021) Radioactive material monitoring surveys of the water environment\u003c/li\u003e\n \u003cli\u003eMonta\u0026ntilde;a CG, Silva SDGTM, Hagyari D, Wager J, Tiegs L, Sadeghian C, Schriever TA, Schalk CM (2019) Revisiting \u0026ldquo;what do tadpoles really eat?\u0026rdquo; A 10-year perspective. Freshw Biol 64:2269\u0026ndash;2282. https://doi.org/10.1111/fwb.13397\u003c/li\u003e\n \u003cli\u003eOkumura T, Yamaguchi N, Dohi T, Iijima K, Kogure T (2019) Dissolution behaviour of radiocaesium-bearing microparticles released from the Fukushima nuclear plant. Sci Rep 9:1\u0026ndash;9. https://doi.org/10.1038/s41598-019-40423-x\u003c/li\u003e\n \u003cli\u003eOrizaola G (2022) Amphibians in Field Radioecology: A Review and Perspective. In: Wood MD, Mothersill CE, Taskanova G, Cresswell T, Woloschak GE (eds) Biomarkers of radiation in the Environment Robust tools for risk assessment. Springer Nature B.V., pp 185\u0026ndash;203\u003c/li\u003e\n \u003cli\u003ePentreath RJ (1973) The roles of food and water in the accumulation of radionuclides by marine teleost and elasmobranch fish. In: Radioactive contamination of the marine environment. pp 421\u0026ndash;434\u003c/li\u003e\n \u003cli\u003eSakai M, Gomi T, Nunokawa M, Wakahara T, Onda Y (2014) Soil removal as a decontamination practice and radiocesium accumulation in tadpoles in rice paddies at Fukushima. Environ Pollut 187:112\u0026ndash;115. https://doi.org/10.1016/j.envpol.2014.01.002\u003c/li\u003e\n \u003cli\u003eSakai M, Tsuji H, Ishii Y, Ozaki H, Takechi S, Jo J, Tamaoki M, Hayashi S, Gomi T (2021) Untangling radiocesium dynamics of forest-stream ecosystems: A review of Fukushima studies in the decade after the accident. Environ Pollut 288. https://doi.org/10.1016/j.envpol.2021.117744\u003c/li\u003e\n \u003cli\u003eSmith JT, Kudelsky A V., Ryabov IN, Daire SE, Boyer L, Blust RJ, Fernandez JA, Hadderingh RH, Voitsekhovitch O V. (2002) Uptake and elimination of radiocaesium in fish and the \u0026ldquo;size effect.\u0026rdquo; J Environ Radioact 62:145\u0026ndash;164. https://doi.org/10.1016/S0265-931X(01)00157-6\u003c/li\u003e\n \u003cli\u003eSrivastava A, Reddy SJ, Kelber O, Urich K, Denschlag O (1994) Uptake and release kinetics of 134Cs by Goldfish (Carassius auratus) and 137Cs by Zebra fish (Brachydanio rerio) in controlled aquatic environment. J Radioanal Nucl Chem 182:63\u0026ndash;69\u003c/li\u003e\n \u003cli\u003eStyron CE, Hagan TM, Campbell DR, Harvin J, Whittenburg NK, Baughman GA, Bransford ME, Saunders WH, Williams DC, Woodle C, Dixon NK, Mcneill CR (1976) Effects of temperature and salinity on growth and uptake of 65zn and 137cs for six marine algae. J Mar Biol Assoc United Kingdom 56:13\u0026ndash;20. https://doi.org/10.1017/S0025315400020397\u003c/li\u003e\n \u003cli\u003eTagami K, Uchida S, Wood MD, Beresford NA (2018) Radiocaesium transfer and radiation exposure of frogs in Fukushima Prefecture. Sci Rep 8:1\u0026ndash;11. https://doi.org/10.1038/s41598-018-28866-0\u003c/li\u003e\n \u003cli\u003eTakahara T, Endo S, Takada M, Oba Y, Nursal WI, Igawa T, Doi H, Yamada T, Okuda T (2015) Radiocesium accumulation in the anuran frog, Rana tagoi tagoi, in forest ecosystems after the Fukushima Nuclear Power Plant accident. Environ Pollut 199:89\u0026ndash;94. https://doi.org/10.1016/j.envpol.2015.01.018\u003c/li\u003e\n \u003cli\u003eTsuji H, Nishikiori T, Ito S, Ozaki H, Watanabe M, Sakai M, Ishii Y, Hayashi S (2023) Influential factors of long-term and seasonal 137Cs change in agricultural and forested rivers: Temperature, water quality and an intense Typhoon Event. Environ Pollut 338. https://doi.org/10.1016/j.envpol.2023.122617\u003c/li\u003e\n \u003cli\u003eWada T, Hinata A, Furuta Y, Sasaki K, Konoplev A, Nanba K (2023) Factors affecting 137Cs radioactivity and water-to-body concentration ratios of fish in river and pond environments near the Fukushima Dai-ichi Nuclear Power Plant. J Environ Radioact 258. https://doi.org/10.1016/j.jenvrad.2022.107103\u003c/li\u003e\n \u003cli\u003eWarnau M, Fowler SW, Teyssi\u0026eacute; JL (1996) Biokinetics of selected heavy metals and radionuclides in two marine macrophytes: The seagrass Posidonia oceanica and the alga Caulerpa taxifolia. Mar Environ Res 41:343\u0026ndash;362. https://doi.org/10.1016/0141-1136(95)00025-9\u003c/li\u003e\n \u003cli\u003eWhiles MR, Lips KR, Pringle CM, Kilham SS, Bixby RJ, Brenes R, Connelly S, Colon-Gaud JC, Hunte-Brown M, Huryn AD, Montgomery C, Peterson S (2006) The effects of amphibian population declines on the structure and function of neotropical stream ecosystems. Front Ecol Environ 4:27\u0026ndash;34. https://doi.org/10.1890/1540-9295(2006)004[0027:TEOAPD]2.0.CO;2\u003c/li\u003e\n \u003cli\u003eWood MD, Beresford NA, Howard BJ, Copplestone D (2013) Evaluating summarised radionuclide concentration ratio datasets for wildlife. J Environ Radioact 126:314\u0026ndash;325. https://doi.org/10.1016/j.jenvrad.2013.07.022\u003c/li\u003e\n \u003cli\u003eZhao X, Wang WX, Yu KN, Lam PKS (2001) Biomagnification of radiocesium in a marine piscivorous fish. Mar Ecol Prog Ser 222:227\u0026ndash;237. https://doi.org/10.3354/meps222227\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable 1: Generalized liner model (GLM) for river and lake ecosystem. Effect of each independent variables for concentration ratio of radicesium accumulation by tadpole frog for river and lake ecosystem. The most prominent environmental factors are shown in bold color. The estimated parameters for each predictor variable after the model averaging are listed. The coefficient of determination R\u003csup\u003e2\u003c/sup\u003e was 0.38 for the best river model and 0.70 for the best lake model.\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/58895_8739fc6c57c1c19a/58895_custom_files/img1753334470.png\" width=\"828\" height=\"464\" style=\"text-align: start; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); font-size: medium; font-family: \u0026quot;\u0026quot;;\"\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eTable 2: Comparison of radiocesium activity (Cs\u003csup\u003e137\u003c/sup\u003e) and estimated absorbed dose rate in different species from the river and lake ecosystem.\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/58895_8739fc6c57c1c19a/58895_custom_files/img1753334405.png\" width=\"1056\" height=\"460\"\u003e\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Aquatic organisms, Anuran tadpoles, Environmental factors, Fukushima, Radioactive cesium","lastPublishedDoi":"10.21203/rs.3.rs-6331961/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6331961/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRadioactive cesium contamination in inland water bodies following the Fukushima Nuclear Power Plant accident in Japan has persisted for over a decade, potentially causing chronic effects on aquatic biota. This study aimed to understand the transfer factors influenced by environmental parameters and the resulting dose rates of radiocesium in tadpole larvae between river and lake ecosystems. In total, 2830 tadpoles from river ecosystem and 3056 tadpoles from lake ecosystem were analyzed in 80 and 33 composite samples respectively from Fukushima region. The relative effects of environmental parameters in radiocesium concentration ratio in tadpole larvae were compared between river and lake ecosystems using the generalized linear model. The average radiocesium concentration ratio in tadpole did not significantly vary between river and lake ecosystems (i.e., 6063.69 L/kg and 6071.59 L/kg respectively). While water depth exhibited a negative correlation as a prominent parameter affecting radiocesium transfer in lake ecosystems, environmental factors like water depth, temperature, and suspended solids showed significant impact in radiocesium transfer in tadpoles within river ecosystems, as revealed by generalized linear model analysis. Though algae and detritus materials significantly contribute to tadpole larvae nutrition in aquatic habitats, the multivariate analysis did not identify significant variables. Sediment emerged as a common factor facilitating the high transfer rate of radiocesium in tadpoles within aquatic environments. Observations estimated dose rates of radiocesium below 1 µGyh\u003csup\u003e-1\u003c/sup\u003e in both river and lake ecosystems. However, tadpoles in the river ecosystem experienced higher radiocesium dose rates than those in lake ecosystems (i.e., 0.15 and 0.09 µGyh\u003csup\u003e-1\u003c/sup\u003e respectively). This highlights the vulnerability of tadpoles in aquatic environments to external sources of radiocesium present in these habitats.\u003c/p\u003e","manuscriptTitle":"Ecological Risk of Radiocesium Contamination and Dose Rate Estimation in Anuran Tadpole in Aquatic Environments","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-24 05:33:17","doi":"10.21203/rs.3.rs-6331961/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4adedfc4-5af6-45c5-a757-315971d32a9d","owner":[],"postedDate":"July 24th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-07-24T05:33:17+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-24 05:33:17","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6331961","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6331961","identity":"rs-6331961","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}