Polonium-210 content of marine shrimp: Variation with biological and environmental factors

Abstract

The concentrations of ²¹⁰Po and ²¹⁰Pb were determined in more than 30 species of marine shrimp. Samples were collected in the years 1977 to 1980; most were from the Mediterrancean Sea near Monaco, the remainder from Kuwait, South Africa, USA and Great Britain. The median ²¹⁰Po concentration was 8.0 pCi g^-1 dry wt in the whole shrimp and 85 pCi g^-1 dry in the hepatopancreas; the corresponding ²¹⁰Po:²¹⁰Pb activity ratios were 77 and 138, respectively. The range of concentrations covered more than two orders of magnitude for both nuclides. The variations in the levels of ²¹⁰Po, in particular, could be related to biological and environmental factors; thus, penaeid shrimp had ²¹⁰Po at median concentrations some three to four times higher than carid shrimp, and there was a steady increase in the median ²¹⁰Po concentration as one moved from estuarine to coastal to pelagic to deep-pelagic species. ²¹⁰Po levels were highest in 3 species of deep-pelagic penaeids, where a median ²¹⁰Po concentration in the whole shrimp of 43 pCi g^-1 dry wt was found. The natural radiation dose received by the hepatopancreas of such individuals will be of the order of 100 rem per yr. Elevated ²¹⁰Po was also found in 4 species collected near Kuwait. The ²¹⁰Po data are interpreted as indicating changes in the food regime of different shrimp; specifically it is suggested that ²¹⁰Po-rich items such as hepatopancreas, faecal pellets and organic particulates are likely to be important in the diet of shrimp which feed at depth in the ocean. It is suggested further that the ultimate availability of ²¹⁰Po to the foodchain depends on its form in sea water, and the need for information concerning the degree of organic binding of ²¹⁰Po in natural waters in stressed.