Biological reference values for chemical compounds in the work area (BARs): an approach for evaluating biomonitoring data.

Biological monitoring is a routine method that has been applied in occupational medical practice for many years. A requirement for its application is the availability of criteria suitable for evaluating biomonitoring data. Health-based threshold values are particularly useful as a criterion, yet only for substances for which effect thresholds can reliably be determined. For substances for which the concept of health-based threshold values is not applicable, the Working Group Setting of Threshold Limit Values in Biological Materials of the DFG Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has recently established "Biologische Arbeitsstoff-Referenzwerte" (BARs, Biological Reference Values for Chemical Compounds in the Work Area) as an approach for evaluating biomonitoring data. The BAR represents the upper reference concentration of a biomarker in the general adult population without occupational exposure to the agent. It is derived from biomonitoring data of a sample of a defined population group. In general, a BAR corresponds to the 95th percentile of the sample distribution. Ideally, national environmental surveys including human biomonitoring results are used as basis for deriving BARs. The influence of age, sex, social status, residential area and life style factors on background exposure is considered in the evaluation of these values. Because tobacco smoking is the most frequent influencing factor, several BARs have been determined for non-smokers only. To date, BARs for 17 substances or substance groups are listed in the List of MAK and BAT Values 2011. BARs for another five substances have been discussed, but have not been established because of the insufficient scientific database. Establishing the BARs aims to facilitate the evaluation of human exposure to chemical compounds for which no health-based threshold values can be derived but an adequate assessment of exposure is required due to their toxicity. The application of BARs does not permit a toxicological evaluation, but does allow the occurrence and the extent of occupational exposure to hazardous substances to be proved.