Radium uptake by earthworms E. fetida after exposure to contaminated soil

Radium-226 is one of the most important radionuclides for assessing the radiation exposure in terrestrial ecosystems in terms of its significant contribution to the internal and total dose rates. A laboratory culture of Eisenia fetida was exposed to soil contaminated with ²²⁶Ra and ²³⁸U during two months. These nuclides entered the soil as a result of industrial radium production (Vodny, Komi Republic, Russia). The concentrations of ²²⁶Ra and ²³⁸U were 89000 ± 9000 and 2130 ± 270 Bq kg^-1 of soil. Bioaccumulation of ²²⁶Ra was investigated in E. fetida exposed to the radioactive soil or to a mixture containing the same radioactive soil diluted with peat and sand. The activity concentrations of ²²⁶Ra in E. fetida were higher after exposure to the contaminated soil compared to the mixture. The literature data on the radium accumulation in earthworms were considered also. Our experiments showed that the concentration ratio (CR) of ²²⁶Ra in E. fetida varied from 5.5 × 10^-4 to 4.5 × 10^-3 Bq kg^-1 f.w./Bq kg^-1 d.w. The average CRs were (6.7 ± 1.7) × 10^-4 for the earthworms E. fetida from the soil mixture and (3.2 ± 1.2) × 10^-3 for those from the radioactive soil. These CRs for ²²⁶Ra were up to two orders of magnitude lower than the values calculated by us from the results obtained by other researchers for natural earthworm populations in areas with lower levels radioactivity.