[Behavior of environmental contaminants in farm livestock]

Knowledge about pharmacokinetic factors is essential to evaluate the consequences of the exposure of farm animals to high levels of environmental contaminants. The bioavailability, which depends on for instance the exposure route and the matrix in which the contaminant is embedded, is of primary importance. The exposure of an animal expressed as internal dose rate is determined by the efficiency of the various elimination processes. If the combined rate of these processes is low, high body concentrations relative to exposure rate will occur. Metabolic elimination may lead to the formation of toxic metabolites and in that case it is necessary to study these metabolites as well. Residue problems may occur as a consequence of substance properties and/or the presence of specific binding proteins in organs and tissues. Finally, pharmacokinetic studies should be conducted at various levels of exposure as some kinetic processes may be non-linear in nature.