THE RELATIONSHIP BETWEEN CONCENTRATIONS OF PLUTONIUM AND AMERICIUM INSOIL INTERSTITIAL WATERS AND THEIR UPTAKE BY PLANTS

Large soil cores (23.5 cm diameter), containing elevated concentration s of plutonium and americium derived from fuel reprocessing effluents (typically 2000-3000 but up to 10000 Bq kg-1 Pu-239, Pu-240 and 3000-5 000 but up to 15 000 Bq kg-1 Am-241), were collected from three zones of a salt marsh in west Cumbria. The standing vegetation was removed, the cores placed in a greenhouse and the vegetation allowed to regrow. After 2 months, the regrowth was harvested and the amount of plutoniu m and americium taken up determined. These data, combined with data fr om earlier, in-situ sampling of soil pore waters and from analysis of soil cores, allow estimation of soil-plant transfers. If these are exp ressed simply as the ratio of the activity concentrations in the plant tissues to those in the soil, the values lie in the range 10(-5)-10(- 6), comparable to those found by many other workers. However, the rati o of concentrations in plant tissues to those in the soil solution is much higher; 40-110 1 kg-1 for Pu-239, Pu-240 and 210-640 1 kg-1 for A m-241. There appears to be a consistent relationship between soil-plan t transfer and the in-situ solid-solution distribution coefficient (Rd ).