The dynamics of vegetation contamination by radionuclides on a tide washed pasture in the Mersey Estuary

Measurements of ¹³⁷Cs, ^239/240Pu and ²⁴¹Am contamination in substrate and vegetation on a tide washed pasture in the Mersey Estuary have enabled the dynamic response of vegetation contamination resulting from individual inundation events to be observed. Vegetation contamination is almost entirely due to external contamination by sediment, although there is some evidence for a small contribution from root uptake for ¹³⁷Cs, with a transfer factor from substrate to internal plant of about 0.003. Marked temporal variation is consistent with contamination by deposition of suspended sediments during tidal inundations, subsequently decreasing with a halflife of 20–30 days. Overall accumulation factors (total plant:substrate) are lower than those observed for the few pastures and saltmarshes studies further north in Cumbria, and consistent with the lower inundation frequency of the Mersey Estuary site.