[Biological monitoring of chemical exposure]

In this paper we described the biological monitoring as a capable exposure assessment tool that has provided important information used in public health decisions. Biological monitoring is based on determination of biological markers of exposure which are presented as the quantity of a chemical substance or its metabolites or as the deviation of biological parameters (enzyme activity etc.) induced by this substance in exposed humans. The greatest advantage of biological monitoring is the fact that the biological marker of exposure is more directly related to the adverse effects than any environment measurement. Another advantage of biological monitoring is based on the reality that the nonoccupational background exposure (leisure activity, residency, dietary habits, smoking, etc.) may also be expressed in the biological level. Biological parameters can be unfortunately affected by various factors that influence the fate of xenobiotic in vivo. The "BEL" (BTV-biological tolerance value for occupational exposures) is defined as the maximum permissible quantity of a chemical substance or its metabolites or the maximum permissible deviation from the norm of biological parameters during or after exposure. It should be subject to regular revision in the light of new scientific data.