Transfer of cadmium and mercury to sheep tissues

Toxic heavy metals such as cadmium and mercury can enter the diet of farm a nimals by a variety of environmental exposure routes and, hence, contaminat e food products derived from those animals. Therefore, there is a need to b e able to predict the likely levels of contamination in animal tissues if e xposed to a contaminated diet and also to estimate how rapidly an animal wi ll decontaminate once the source of contamination is removed from the diet. Data on the transfer and excretion rates of Cd and Hg from tissues have pr eviously been inadequate to allow the development of dynamic models to pred ict changes in the degree of contamination of different tissues of ruminant s. A study is described during which a group of sheep were given a single o ral administration of Cd-109 and Hg-203. Measurements of the concentrations of the radioisotopes in tissue samples were subsequently made over a perio d of 1 year. The resultant data we re used to develop compartment models to describe the behavior of the two metals in sheep tissues. To our knowledge the models developed are the first to allow the time-dependent prediction of the potential Cd and Hg contamination of animal-derived food products. P reviously only advised transfer coefficients were available; we demonstrate that these are of little value for cadmium and mercury due to their slow r ates of accumulation and excretion.