-2l y be py the leaves of plants and thus circumvent fixation on the soll. r to Residual contamination from fallout a year or more old would have an insignificant effect on rate of decline during the first 150 i¢le, days if the total contamination from each detonation were of the he game order of magnitude or the first less than the second. This was the case following the Nectar test at Belle Island, which had residual contamination from the Mike test (1.5 years previous to Nectar). After approximately 150 days following fallout, the rate of decline becomesless than the rate of decay of mixed fission products, reflecting the relative concentration by the lsiand organisms of the long-lived isotopes cs?37 ana sr?°. Other iso- topes, both fission products and neutron induced products, are by involved, but cs137 ana sr?° with their daughters account for 80 per cent or more of the total activity in land organisms two years following the Nectar test. This is true even though these isotopes together contribute only 18 per cent of the total activity from mixed fission products at that time. On a basis of fission ylelds, Cst37 and gr 70 would contribute no more than 35 per cent of the (p total activity even if all of the activity at Belle Island were from the Mike test. Cett4 activity is low (1% in crabs) in the island organisms because of its low rate of uptake by land plants from soil.“* On the other hand, in marine organisms radiocerium does enter into the food chain in significant amounts (26%--71% of the total B-activity) 2°76 It therefore appears that in so far as the long-lived radioactive fission products strontium, cesium and cerium are concerned ridy' Sa AEE