Concentrations of iron-55 in commercial fish species from the North Atlantic

Abstract

Concentrations of the weapon-test, fallout radionuclide iron-55 have been reported for migratory species, such as the Pacific salmon, which suggest a marked decrease in concentration with decrease in latitude of the point of capture. This situation has been examined for North Atlantic cod stocks in order to provide data for a species representative of a large geographical area, but divided into more or less distinct stocks each with a restricted territory, in order to provide further data on the importance of latitude in determining iron-55 concentrations. The data obtained show that there is a marked dependence upon latitude, Arctic cod averaging 90 pCi ⁵⁵Fe/mg Fe compared with 15 pCi ⁵⁵Fe/mg Fe for cod from middle latitudes. The mechanisms that could lead to such distribution are examined, and it is concluded that deposition of this radionuclide was exceptionally high over the sea in northern latitudes compared with its deposition on land, and that this pattern of deposition, taken together with the very high biological availability of the material at the time of deposition, has led to the very high specific activities found in northern latitudes and recorded for Arctic cod stocks in particular.