Biological tolerance values: change in a paradigm concept from assessment of a single value to use of an average.

Since 1981 biological tolerance values for occupational exposure (BAT values) have been published in the List of MAK and BAT Values of the Deutsche Forschungsgemeinschaft (DFG). In 2007 the list includes threshold limit values for more than 90 substances. The BAT value was defined as the maximum permissible quantity of a chemical substance or its metabolites or the maximum permissible deviation from the norm of biological parameters induced by these substances. The biological limit values derived by other commissions (ACGIH, SCOEL) are to be understood as averages, which may well be exceeded individually, in contrast to the BAT values that were defined as ceiling values and thus did not allow an excess of values in the individual employee. The DFG Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has now revised the concept of biological limit values. The BAT value describes the concentration of a chemical substance, of its metabolites or of an effect indicator in appropriate biological material derived by occupational medical and toxicological criteria, at which the health of an employee is usually not affected, even after repeated or long-term exposure. In this case, derivation of the BAT value is based on the average internal exposures. With this redefinition of the German BAT value, it will be possible to better harmonize the values with those provided by other commissions, which are also based on an average concept.