Distribution of cobalt 60 in a mollusc, a crustacean and a freshwater teleost: Variations as a function of the source of pollution and during elimination

Abstract

Radioisotopes of cobalt (^57,58,60Co) are present in nuclear test debris as well as in effluents of the non-military nuclear industry. The stable isotope, which is a constituent of vitamin B₁₂, has very important biological functions.

For each species, three experiments were carried out: (1) starved animals were immersed in ⁶⁰Co-contaminated water; (2) animals were immersed in contaminated water and received radioactive food and (3) animals were placed in fresh water without any pollutant but received contaminated food. Radiation doses were calculated for contamination via both food and water.

When ⁶⁰Co is taken up directly from water, the most contaminated organs are external ones, especially the shell of the snail Lymnaea palustris and the exoskeleton and feeding appendages of the crayfish Astacus leptodactylus. Contamination via food is responsible for a relatively greater accumulation of radiocobalt in internal organs. The cobalt content of muscles—that is to say the edible parts of crayfish and common carp Cyprinus carpio—is very low. The highest concentrations recorded are in the visceral mass of the snail, the digestive gland of the crayfish and the kidneys of the carp.

Internal doses for these organs are considerably higher than those for entire animals. Therefore, as a result of ⁶⁰Co distribution, they are critical organs for the freshwater species. Except for the carp, external radiation is very weak compared with internal radiation.

A strong retention of ⁶⁰Co is observed for the shell of L. palustris while the desorption of radiocobalt from the exoskeleton of A. leptodactylus is easier. In carp, the ⁶⁰Co taken up by the gut from food, as well as from water, is rapidly eliminated.