- 63 chemically similar elements. The abundance in sea water of strontium and calcium, which is chemically similar to strontium, is part of the reason that Sr90 is not abundant in marine organisms (Table IV). Another factor is the low specific activity for sr9° in sea water due to mixing and dilutien by ocean waters. The low level of csl47 in marine organisms cannot be accounted for entirely for the same reasons, because the stable isotopes of cesium are scarce in the sea. However, potassium, an element chemically similar to cesium, is abundant (Table IV) and also, the specific activity for Csl57 in sea water is low. The Sr?° in canned tuna fish and salmon has been determined by the Health and Safety Laboratory of the U.S. Atomic Energy Commission. In 48 analyses of samples re- ceived between April 20, 1956 and August 8, 1957, the highest value was ,.004 wuc/g, wet weight (U. S. Atomic Energy Commission report HASL 42 1958). Because the values were very low and there seemed to be no trend in time or location, arily. the sampling was discontinued tempor- The health hazard from Sr9° which is determined from the ratio of Sr9° to calcium is low for fish because