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This paper addresses the modelling of cesium sorption in non-equilibrium and nonlinear conditions with a two-site model. Compared to the classical K d approach, the proposed model better reproduced the breakthrough curves observed during continuous-flow stirred tank reactor experiments conducted on two contrasted soils. Fitted parameters suggested contrasted conditions of cesium sorption between 1) equilibrium sites, with low affinity and high sorption capacity comparable to CEC and 2) non-equilibrium sites, with a fast sorption rate (half-time of 0.2-0.3 h), a slow desorption rate (half-time of 3-9 days) and a very low sorption capacity (0.02-0.04% of CEC). Comparison of EK sites densities with sorption capacities derived from the literature suggests that the EK equilibrium and kinetic sites might correspond to ion exchange and surface complexation of soil clay minerals respectively. This work stresses the limits of the K d model to predict 137 Cs sorption in reactive transport conditions and supports an alternative non-equilibrium nonlinear approach., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Laurent Garcia-Sanchez reports financial support was provided by Electricité de France., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Radionuclides 129 I (t 1/2  = 15.7 × 10 6 years) and 131 I (t 1/2  = 8.02 days) are both introduced into the environment as a result of nuclear human activities. Environmental transfer pathways and fluxes between and within ecosystems are essential information for risk assessment. In forest ecosystems, humus degradation over time could result in re-mobilization and then downward migration and/or volatilization of intercepted 129 I. In order to estimate the scale of these processes, humus (mull and moder forms) sampled under deciduous and coniferous forests were spiked with 125 I - (t 1/2  = 59.4 days), as a surrogate for 129 I, in order to study the evolution of its water-soluble and organic fractions as well as the volatilization rate during humus degradation at laboratory scale. To our knowledge, this is the first time that interactions between iodine and contrasting forms of forest humus have been investigated. The evolution of native stable iodine ( 127 I) pools in unspiked humus was also studied. The nature of the humus' organic matter appears to be a factor that impacts on the proportions of water-soluble and organic fractions of iodine and on their evolution. Iodine-125 was mainly organically bound (fraction for mulls and moders: ∼54-59 and 41-49%, respectively) and no clear evolution was observed within the 4-month incubation period. A large decrease in 125 I water-solubility occurred, being more marked for mull (from ∼14-32 to 3-7%) than for moder (from ∼21-37 to 7-19%) humus. By contrast, a significant fraction was not extractible (∼38-43%) and varied in inverse proportion to the water-soluble fraction, suggesting a stabilization of iodine in humus after wet deposit. The nature of the humus organic matter also impacted on 125 I volatilization. Although of the same order of magnitude, the total volatilization of 125 I was higher for moders (∼0.039-0.323%) than for mulls (∼0.015-0.023%) within the 4-month incubation period. Volatilization rates for mulls were correlated with the water-soluble fraction, implying that volatilization of 125 I could occur from the humus solution. Our results showed that humus is thus a zone of iodine accumulation by association with organic matter and that potential losses by lixiviation are significantly more important compared to volatilization., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The long-term consequences of the nuclear disaster at the Fukushima Daiichi Nuclear Power Plant (FDNPP) that occurred on March 2011, have been scarcely studied on wildlife. We sampled Japanese tree frogs (Dryophytes japonicus), in a 50 -km area around the FDNPP to test for an increase of DNA damages and variation of DNA methylation level. The ambient dose rate ranged between 0.4 and 2.8 μGy h -1 and the total estimated dose rate absorbed by frogs ranged between 0.3 and 7.7 μGy h -1 . Frogs from contaminated sites exhibited a dose-dependent increase of global genomic DNA methylation level (5-mdC and 5-hmdC) and of mitochondrial DNA damages. Such DNA damages may indicate a genomic instability, which may induce physiological adaptations governed by DNA methylation changes. This study stresses the need for biological data combining targeted molecular methods and classic ecotoxicology, in order to better understand the impacts on wildlife of long term exposure to low ionizing radiation levels., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Tritium, a radioactive isotope of hydrogen of natural and anthropogenic origin, is ubiquitously present in the environment. Effluents of nuclear centers of production are significant anthropogenic sources. With the upcoming project of thermonuclear fusion, tritium releases in the environment may increase. It is therefore important to characterize the ecological risk linked to tritium. The effects of tritiated water (HTO) were therefore studied in zebrafish larvae exposed for 10 d to different dose rates, 1.1 × 10 2 , 4.1 × 10 2 , and 3.8 × 10 3  µGy/h for larvae corresponding, respectively, to a water contamination of 10 4 , 10 5 , and 10 6  Bq/mL of HTO. Those dose rates were higher than 10 μGy/h, which is the threshold recommended to start monitoring ecosystems where radiological contaminants are present. Mortality, embryo-larval development, immune toxicity, genotoxicity, neurotoxicity, and alterations of tissues were investigated. The results showed that HTO exposure induced DNA damage and reactive oxygen species production and modulated the expression of genes involved in detoxification processes. Moreover, modifications of the muscular tissues (degradation of myofibrils at 4 d post fertilization and disorganization of mitochondria at later stages) were observed. The results differed with HTO dose rates and with developmental stages. These results will drive future research for the development of new HTO-sensitive biomarkers and will allow us to progress in the characterization of the modes of action of tritium in fish. Environ Toxicol Chem 2020;39:648-658. © 2019 SETAC., (© 2019 SETAC.)

Tritium ( 3 H) is mainly released into the environment in the form of tritiated water (HTO) by nuclear power plants and nuclear fuel reprocessing plants. To better understand how organisms may be affected by contamination to 3 H it is essential to link observed effects to a correct estimation of absorbed dose rates. Due to quick isotopic exchanges between 3 H and hydrogen, 3 H measurement is difficult in small organisms such as zebrafish embryo, a model in ecotoxicological assay. This work aimed to optimise tritium measurement protocol to better characterise internalisation by early life stages of zebrafish. Zebrafish eggs were exposed at one HTO activity concentration of 1.22 × 10 5 Bq/mL. This activity was calculated to correspond to theoretical dose rates of 0.4 mGy/h, where some deleterious effects are expected on young fish. A protocol for the preparation of biological samples was adapted from the method classically used to segregate the different forms of tritium in organisms. To deal with very quick isotopic exchanges of 3 H with hydrogen, the impacts of washing by non-tritiated water as well as the bias induced by absorbed tritium around organisms on the measured activity concentration were studied. We managed to develop protocols to perform total tritium and total organically bound tritium (OBT) activity concentrations measurements in zebrafish eggs and larvae. The measurement of these both forms allowed the calculation of tissue-free-water-tritium (TFWT). To better understand total tritium internalisation, a study of total tritium kinetics from 4 hpf (hour post-fertilization) to 168 hpf was performed. OBT and TFWT were also assessed to complete the total tritium internalisation kinetics. The internalisation is a rapid phenomenon reaching a steady-state within 24 h after the beginning of contamination for total tritium and TFWT, with concentration factors and TFWT/HTO close to unity. OBT formation seemed to be slower. It appeared that OBT content in organisms was low with an OBT/TFWT ratio of about 8% for both stages (24 hpf and 96 hpf). To verify absorbed dose rates at key developmental stages (24 hpf eggs and 96 hpf larvae), they were calculated from total tritium activity concentrations after exposure at 1.22 × 10 5 and 1.22 × 10 6 Bq/mL, as these two activity concentrations were used to assess effects of tritium in another part of the study. Dose rates calculated from total tritium activity concentrations measured in 24 hpf eggs and 96 hpf larvae were consistent with the nominal ones, which validates the robustness of the protocol developed in the present study., (Copyright © 2019. Published by Elsevier Ltd.)

Tritium ( 3 H) is a radioactive isotope of hydrogen. In the environment, the most common form of tritium is tritiated water (HTO). The present study aimed to identify early biomarkers of HTO contamination through the use of an aquatic model, the zebrafish (Danio rerio). We used the zebrafish embryo-larvae model to investigate the modes of action of HTO exposure at dose rates of 0.4 and 4 mGy/h, dose rates expected to induce deleterious effects on fish. Zebrafish were exposed to HTO from 3 hpf (hours post fertilization) to 96 hpf. The transcriptomic effects were investigated 24 h and 96 h after the beginning of the contamination, using mRNAseq. Results suggested an impact of HTO contamination, regardless of the dose rate, on genes involved in muscle contraction (tnnt2d, tnni2a.4, slc6a1a or atp2a1l) and eye opacity (crygm2d9, crygmxl1, mipb or lim2.3) after 24 h of contamination. Interestingly, an opposite differential expression was highlighted in genes playing a role in muscle contraction and eye opacity in 24 hpf embryos when comparing dose rates, suggesting an onset of DNA protective mechanisms. The expression of h2afx and ddb2 involved in DNA repair was enhanced in response to HTO exposure. The entrainment of circadian clock and the response to H 2 O 2 signalling pathways were enriched at 96 hpf at 0.4 mGy/h and in both stages after 4 mGy/h. Genes involved in ROS scavenging were differentially expressed only after 24 h of exposure for the lowest dose rate, suggesting the onset of early protective mechanisms against oxidative stress. Effects highlighted on muscle at the molecular scale were confirmed at a higher biological scale, as electron microscopy observations revealed sarcomere impairments in 96 hpf larvae for both dose rates. Together with other studies, the present work provides useful data to better understand modes of action of tritium on zebrafish embryos-larvae., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The effects of 137 Cs deposit forms on its ageing in soil have not yet been reported. Soluble and Solid 137 Cs input forms were mixed with the mineral soils collected under Fukushima's coniferous and broadleaf forests, incubated under controlled laboratory, and examined the evolution of 137 Cs availability over time. Results show that the extracted 137 Cs fraction with water was less than 1% for the soluble input form and below detection limit for the solid input forms. Likewise, with an acetate reagent, the extracted 137 Cs fraction ranged from 46 to 56% for the soluble input and from 2 to 15% for the solid input, implying that the nature of the 137 Cs contamination strongly influences its extractability and mobility in soil. Although the degradation of organic materials was apparent, its impact on the 137 Cs extractability was found to be weak. Nevertheless, more Ac-available 137 Cs was obtained from broadleaf organic material mixes than the coniferous counterparts, suggesting that the lignified nature of latter tend to retain more 137 Cs. When extrapolated to a field context, more available 137 Cs fraction may be expected from wet-derived contaminated forest soils than contaminated via solid-derived inputs. Such information could be helpful for radioecological management schemes in contaminated forest environments., (Copyright © 2018 Elsevier B.V. All rights reserved.)

To characterize environmental risks linked to former uranium mines in the Limousin region of France, a study was conducted on fish health effects from uranium releases. Two private ponds were compared in this study, one with uranium contamination and one background site, upstream of the mining zone. Roach, Rutilus rutilus, were caged for 28 days in both ponds. Physico-chemical parameters of water and sediments and bioaccumulation of metals in several organs were determined. After 14 and 28 days of caging, immune, oxidative stress, biotransformation, neurotoxicity and physiological parameters were measured. Iron and aluminium were quantified in the water of both sites; however, barium and manganese were only present in the water of the uranium contaminated site. Uranium was present in both sites but at very different concentrations. The sediments from the uranium contaminated site contained high levels of radioactive elements coming from the disintegration chain of uranium. Results of biological parameters indicated stimulation of immune parameters and of oxidative stress and a decrease of AChE in fish caged in the uranium contaminated pond compared to the uranium-free pond. Overall, the results determined roach health status in the context of pollution from poly-metallic mining. The data strengthen our knowledge of the environmental risk assessment associated with radioactive substances in the environment.

The main objectives of this study were to evaluate uranium (U) toxicity in the crayfish Procambarus clarkii at a low dose of exposure and to discriminate between the chemotoxicity and radiotoxicity of U. We conducted two sets of experiments using either 30 μg L(-1) of depleted uranium (DU) or (233)U, which differ from each other only in their specific activity (DU=1.7×10(4)Bqg(-1), (233)U=3.57×10(8)Bqg(-1)). The endpoints were oxidative stress responses and mitochondrial functioning in the gills and hepatopancreas, which were measured in terms of enzyme activities and gene expression levels. U accumulation levels were measured in different organs (gills, hepatopancreas, stomach, intestine, green gland, muscles, and carapace), and internal dose rates in the hepatopancreas were compared after DU and (233)U exposures. Significant U accumulation occurred in the organs of P. clarkii, and mitochondrial damage and antioxidant responses were detected. Despite the huge difference (21,000×) in the specific activities of DU and (233)U, few significant differences in biological responses were detected in P. clarkii exposed to these two pollutants. This finding indicates that the radiotoxicity was low compared to the chemotoxicity under our exposure conditions. Finally, genes expression levels were more sensitive markers of U toxicity than enzyme activities., (Copyright © 2012 Elsevier Inc. All rights reserved.)