Radiation exposure and risk assessment to earthworms in areas contaminated with naturally occurring radionuclides.

The assessment of radiation exposure on biota is one of the main parts of environment protection system. Earthworms have been recognized as an important organism group in the terrestrial ecosystems. According to many researchers the potential risks of naturally occurring radionuclides for soil invertebrates were not significant because the exposure doses to the invertebrate populations were low. Our study aimed to assess the radiation exposure and the radiological risks from naturally occurring radionuclides for earthworm populations at four sites. This research was based on three dosimetric approaches simultaneously: ERICA and RESRAD-BIOTA-the commonly used ones, and also on the original method proposed by Thomas and Liber (Environment International, 27, 341-353, 2001) for aquatic organisms. To calculate radiation dose rates to soil invertebrates inhabiting background and contaminated areas, the specific activities of radionuclides in soil, and, depending on the model, the default, or determined in this study, input mass-geometric parameters had been applied. The weighted absorbed dose rates calculated by different models and site-specific data were 0.3-1.4 μGy/h for the background and from 3.4 to 170 μGy/h for the contaminated sites. Analysis of radiation risks for earthworms indicated that 226 Ra was the key contributor to the external dose rate; 226 Ra and 210 Po played a dominant role in formation of internal dose rate for radioecological situations in our study. More conservative radiation risk assessments were derived from RESRAD-BIOTA tool. Dose assessments obtained using various models had shown that there are real environmental situations in which the radiological risks to reference organisms are significantly higher than the lowest benchmark protection level proposed for ecosystems.