Toxic heavy metals such as cadmium and mercury can
enter the diet of farm animals by a variety of environmental
exposure routes and, hence, contaminate food products
derived from those animals. Therefore, there is a need to
be able to predict the likely levels of contamination in
animal tissues if exposed to a contaminated diet and also
to estimate how rapidly an animal will 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 previously been inadequate to allow the
development of dynamic models to predict changes in
the degree of contamination of different tissues of ruminants.
A study is described during which a group of sheep
were given a single oral administration of 109Cd and 203Hg.
Measurements of the concentrations of the radioisotopes
in tissue samples were subsequently made over a period of
1 year. The resultant data were 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. Previously only advised transfer coefficients
were available; we demonstrate that these are of little
value for cadmium and mercury due to their slow rates of
accumulation and excretion.