The relationship between concentrations of plutonium and americium in soil interstitial waters and their uptake by plants

Large soil cores (23.5 cm diameter), containing elevated concentrations of plutonium and americium derived from fuel reprocessing effluents (typically 2000–3000 but up to 10000 Bq kg−1 239,240Pu and 3000–5000 but up to 15 000 Bq kg−1 241Am), 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 plutonium and americium taken up determined. These data, combined with data from earlier, in-situ sampling of soil pore waters and from analysis of soil cores, allow estimation of soil-plant transfers. If these are expressed 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 ratio of concentrations in plant tissues to those in the soil solution is much higher; 40–110 l kg−1 for 239,240Pu and 210–640 l kg−1 for 241Am. There appears to be a consistent relationship between soil-plant transfer and the in-situ solid-solution distribution coefficient (Rd).