- 56 - form, The probable reason that the elements of fission products are not found in greater abundance in fish is that they are not physiologically important and, if present at all, are present in quantities that are difficult to detect by chemical methods. As the method of radioactivation analysis becomes more common, additional information on trace elements may be expected. Further inspection of Table IV shows that the elements of the fallout radioisotopes are scarce in sea water -- 5 parts per hundred million or less, with the exception of strontium; also, that the quantitative uptake by fish of these elements is not great as compared to the uptake of the other mineral elements of nutrition. However, the fact that the amount of these elements in sea water is even less than in fish results in large concentration factors which are not indicative of the amount of a radio- isotope i.that will be taken up (or of the hazard in terms of maximum permissible concentration) but only of the fact that there is an apparent physiological need for the element. It would be expected that radioisotopes of elements with the largest concentration factors would be taken up most readily from the sea.