A STUDY OF PLUTONIUM AND AMERICIUM CONCENTRATIONS IN SEA-SPRAY ON THESOUTHERN SCOTTISH COAST

Seapray and seawater have been collected from the southern Scottish co ast and, for comparison, from Cumbria in north west England during 198 9 and 1991. The occurrence of sea-to-land transfer of the actinides pl utonium and americium in seaspray was observed on these coasts using m uslin screens (a semi-quantitative technique most efficient for collec ting large spray droplets) and high-volume conventional air samplers. The actinides and fine particulate in the spray were present in relati vely higher concentrations than measured in the adjacent seawater, i.e . the spray was enriched in particulate actinides. The net efficiency of the muslin screens in collecting airborne plutonium isotopes and Am -241 generally appeared to be about 20%. A review of earlier published concentrations of Pu-239+240 and Am-241, measured in aerosol and depo sition for over a year several tens of metres inland, was carried out. This suggested that airborne activities are up to five times higher i n Cumbria than in southern Scotland. However, neither the new data col lected in 1989 and 1991 nor this older data suggests any enhancement o f seaspray actinide enrichment in southern Scotland compared with Cumb ria. This finding contrasts with earlier, more limited comparisons tha t suggested such a difference. There is clear evidence of considerable localised spatial and temporal variability in aerosol actinide enrich ment over the beaches in both areas. Enrichment varies between 20 and 500 relative to the adjacent surf-zone waters. However, the average en richment in spray based on the continuous measurements made further in land is likely to be at the lower end of this range.