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

Activity concentrations of radionuclides Cs-134, Cs-137, Pu-238, Pu239+240 and Am-241) were measured in vegetation, invertebrates and wood mice, Apode mus sylvaticus, collected in Lady Wood, a coniferous woodland in the vicini ty of the British Nuclear Fuels reprocessing plant at Sellafield, Cumbria, UK. Vegetation was of low diversity and biomass with activity concentration s ranging from 1 to 5 Bq kg(-1) (Cs-134), 0.3-0.5 Bq kg(-1) (Pu-238), 0.8-8 Bq kg(-1) (Pu239+240), and 0.6-16 Bq kg(-1) (Am-241), dry wt. Caesium-137 activity concentrations were high compared to the reference site in Cheshir e, varying between 65 and 280 Bq kg(-1). Marked inter-specific and temporal differences in radionuclide activity concentrations were recorded for inve rtebrate populations. Caesium-137, Pu-238, Pu239+240 and Am-241 activity co ncentrations in detritivorous invertebrates were consistently higher than i n all other invertebrate groups reflecting contamination of the leaf litter . The activity concentrations in detritivores increased during the autumn a nd winter, reflecting changes in diet as food sources varied throughout the year. Activity concentrations in invertebrates caught in Lady Wood were ge nerally an order of magnitude higher than for the reference site. Activity concentrations in wood mice varied between 7 and 150 Bq kg(-1) (Cs-137), 0. 1-0.3 Bq kg(-1) (Pu-238), 0.1-0.6 Bq kg(-1) (Pu239+240) and 0.2-0.4 Bq kg(- 1) (Am-241). There were clear differences in the activity concentration of Cs-137 (P < 0.01), Pu239+240 (P < 0.05) and Am-241 (P < 0.05) in animals ca ught in Lady Wood compared to the reference site. However, the activity con centrations for Pu-238 were similar at both sites, reflecting a low gastroi ntestinal transfer. Seasonal variation in activity concentrations was obser ved for Cs-137, Pu-238 and Am-241. This variation is attributed to changes in the age structure of the population and diet throughout the year. (C) 19 99 Elsevier Science B.V. All rights reserved.