The radiation exposure of fish in the period of the Techa river peak contamination

Waterborne radioactive releases into the Techa River from the Mayak Production Association in Russia during 1949–1956 resulted in downstream contamination of the river ecosystem. The discharged liquid waste contained both short-lived isotopes (95Zr, 95Nb, 103,106Ru, 141,144Ce, 91Y, 89Sr and 140Ba with half-life from 3 days to 1.02 years) and the long-lived 90Sr and 137Cs (half-life - 28.79 y and 30.07 y, respectively). Even now, when two half-lives of 90Sr and 137Cs have passed, the contamination in the upper river region (about 70 km from the source of releases) is still relatively high. Current anthropogenic dose rates calculated for the fish of the Techa River depend on the distance along the stream and decrease from 150 to 3 μGy day−1. Radiation exposure of fish is expected to have been much higher at the time of the releases. The aim of the study was to evaluate the dose rates for the most common fish species of the river, viz., roach (Rutilus rutilus), perch (Perca fluviatilis) and pike (Esox lucius), in the period of peak contamination of the upper reaches of the Techa River from 1950 to 1951. To achieve this objective, calculation of both internal and external dose rates was performed. For dose rate calculation, the contamination of the river compartments was modeled, body-size dependent dose coefficients were evaluated, morphometric data were analyzed. Maximum dose rates were obtained for roach; minimum – for pike, it depends on fish lifestyle (time spent at the bottom). In the period before September 1950, fish of the upper reaches are assessed to have been exposed to dose rates exceeding the screening level equal to 240 μGy day−1. From September 1950 up to the end of 1952 the fish dose rates along the Techa River were found to be close to the UNSCEAR threshold equal to 9.6 × 103 μGy day−1 or even much more higher (up to 1.9 × 105 μGy day−1). Extremely high historical dose rates did not lead to the difference in fish size and fish growth rate currently observed in the Techa River and in the comparison waterbody (the Miass River). Discussion includes the description of radiation effects observed currently in the river fish. Today the effects observed in hematopoietic system may be the consequence of radiation exposure of fish over several generations. For example, long term dwelling of fish in the radioactively contaminated environment leads to their adaptation to chronic radiation exposure. At the same time, an increase their sensitivity and decrease their adaptive capacity to respond to other stress factors can be observed

Evaluation of distribution coefficients and concentration ratios of 90Sr and 137Cs in the Techa River and the Miass River

Empirical data on the behavior of radionuclides in aquatic ecosystems are needed for radioecological modeling, which is commonly used for predicting transfer of radionuclides, estimating doses, and assessing possible adverse effects on species and communities. Preliminary studies of radioecological parameters including distribution coefficients and concentration ratios, for 90Sr and 137Cs were not in full agreement with the default values used in the ERICA Tool and the RESRAD BIOTA codes. The unique radiation situation in the Techa River, which was contaminated by long-lived radionuclides (90Sr and 137Cs) in the middle of the last century allows improved knowledge about these parameters for river systems. Therefore, the study was focused on the evaluation of radioecological parameters (distribution coefficients and concentration ratios for 90Sr and 137Cs) for the Techa River and the Miass River, which is assumed as a comparison waterbody. To achieve the aim the current contamination of biotic and abiotic components of the river ecosystems was studied; distribution coefficients for 90Sr and 137Cs were calculated; concentration ratios of 90Sr and 137Cs for three fish species (roach, perch and pike), gastropods and filamentous algae were evaluated. Study results were then compared with default values available for use in the well-known computer codes ERICA Tool and RESRAD BIOTA (when site-specific data are not available). We show that the concentration ratios of 137Cs in whole fish bodies depend on the predominant type of nutrition (carnivores and phytophagous). The results presented here are useful in the context of improving of tools for assessing concentrations of radionuclides in biota, which could rely on a wider range of ecosystem information compared with the process limited the current versions of ERICA and RESRAD codes. Further, the concentration ratios of 90Sr are species-specific and strongly dependent on Ca2+ concentration in water. The universal characteristic allows us to combine the data of fish caught in the water with different mineralization by multiplying the concentration of Ca2+. The concentration ratios for fishes were well-fitted by Generalized Logistic Distribution function (GLD). In conclusion, the GLD can be used for probabilistic modeling of the concentration ratios in freshwater fishes to improve the confidence in the modeling results. This is important in the context of risk assessment and regulatory