- 64 of the low uptake of Sr9° and normal values for calcium. For conditions of equal fallout, the Sr990-calcium ratio is a good deal less for fish than for such calcium-rich terrestrial food products as milk (Schaefer 1958). The principal radioisotopes found in fish are nonfission products, of whieh zn? appears at this time to present the greatest potential hazard (Table V). In samples from the western Pacific and from the United States, gn©5 was identified in tuna muscle (Kawabata 1956b; Hiyama 1957) and has been found in trace quantities in foods analyzed by Murthy et al. (1959). The values re- ported by Murthy et al. were higher for oysters and clams than for land crops and, in terms of wuc/kg were as follows: Chesapeake Bay oysters, January 1959, 178; Chesapeake Bay oysters, March 1958, clams, May 1958, 40. 124s and East Coast hard-shelled ‘The MPC for zn©5, 106 wuc/kg, as caiculated from Handbook 69, is considerably greater than the present values for oysters and clams. The concentration of zn©5 was not unexpected as Chipman (1959) found that oysters, clams and scallops concentrate large amounts of zinc, thousands of times above its level in sea water. Because the local fallout in the vicinity of the