BIOLOGICAL TRANSPORT OF RADIOCESIUM IN A SEMINATURAL GRASSLAND ECOSYSTEM .1. SOILS, VEGETATION AND INVERTEBRATES

An unused area of the British Nuclear Fuels plc low level waste dispos al site at Drigg in Cumbria, together with a control site in Cheshire, have been used to investigate the behaviour of Cs-137 in semi-natural grasslands over the period 1985-1988. Both sites showed significant i nputs of Cs-137 and Cs-134 from the Chernobyl incident in 1986, estima ted at up to 7330 Bq/m2 at Drigg and less than 230 Bq/m2 in Cheshire. The total deposit at Drigg was within the range of other observations in the area and could be explained without assuming any input from was te disposal operations on the site Surface soil horizons showed the hi ghest levels of Cs-137 and Cs-134. During the study period, the domina nt contribution to radiocaesium in soil and vegetation was from Cherno byl. Significant inter-specific variation in caesium concentrations of grasses was observed with an exponential decrease from June 1986 thro ugh to the summer of 1987, followed by a secondary peak in autumn 1987 . Samples collected in the spring of 1988 showed Cs-137 concentrations approaching pre-Chernobyl levels. Marked inter-specific and temporal differences in concentrations of radiocaesium were recorded for invert ebrate populations. Radioactivity levels in herbivorous invertebrates were approximately proportional to levels in their diet with concentra tions decreasing from the 1986 summer peak recorded after the input of Chernobyl radioactivity to the low levels observed during the summer of 1987. Herbivorous and predatory invertebrates showed similar concen trations of Cs-137 but both groups were lower in radiocaesium than det ritivorous species.