Radionuclide behaviour and transport in a coniferous woodland ecosystem: vegetation, invertebrates and wood mice, Apodemus sylvaticus

Abstract

Activity concentrations of radionuclides (134Cs, 137Cs, 238Pu, 239+240Pu and 241Am) were measured in vegetation, invertebrates and wood mice, Apodemus sylvaticus, collected in Lady Wood, a coniferous woodland in the vicinity of the British Nuclear Fuels reprocessing plant at Sellafield, Cumbria, UK. Vegetation was of low diversity and biomass with activity concentrations ranging from 1 to 5 Bq kg−1 (134Cs), 0.3–0.5 Bq kg−1 (238Pu), 0.8–8 Bq kg−1 (239+240Pu), and 0.6–16 Bq kg−1 (241Am), dry wt. Caesium-137 activity concentrations were high compared to the reference site in Cheshire, varying between 65 and 280 Bq kg−1. Marked inter-specific and temporal differences in radionuclide activity concentrations were recorded for invertebrate populations. Caesium-137, 238Pu, 239+240Pu and 241Am activity concentrations in detritivorous invertebrates were consistently higher than in all other invertebrate groups reflecting contamination of the leaf litter. The activity concentrations in detritivores increased during the autumn and winter, reflecting changes in diet as food sources varied throughout the year. Activity concentrations in invertebrates caught in Lady Wood were generally an order of magnitude higher than for the reference site. Activity concentrations in wood mice varied between 7 and 150 Bq kg−1 (137Cs), 0.1–0.3 Bq kg−1 (238Pu), 0.1–0.6 Bq kg−1 (239+240Pu) and 0.2–0.4 Bq kg−1 (241Am). There were clear differences in the activity concentration of 137Cs (P less than 0.01), 239+240Pu (P less than 0.05) and 241Am (P less than 0.05) in animals caught in Lady Wood compared to the reference site. However, the activity concentrations for 238Pu were similar at both sites, reflecting a low gastrointestinal transfer. Seasonal variation in activity concentrations was observed for 137Cs, 238Pu and 241Am. This variation is attributed to changes in the age structure of the population and diet throughout the year.