Biological reference values - An approach for the assessment of biomonitoring data

Introduction
In general, health based biological exposure limits are established for biological monitoring in the prevention of occupational diseases. However, this approach is not feasible for chemicals with the ability to produce adverse effects without threshold concentrations, e.g. genotoxic carcinogens. For this reason the Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area of the Deutsche Forschungsgemeinschaft (MAK commission) evaluates biological reference values for chemical compounds at the workplace, called “Biologische Arbeitsstoff-Referenzwerte” (BAR).

Methods
BARs correspond to the 95th percentile of background levels of substances present in biological materials in a reference population of persons of working age who are not occupationally exposed to the substances without regarding effects on health. Evaluating the reference values, factors as age, sex, social status, residential environment and life style must be taken into account.

Results
Since 2008, the MAK commission established BARs for 17 chemical compounds or groups of chemicals and published BAR documentations in German and English. Due to a distinct influence of smoking habits on biomarker levels several BARs were based only on data from non-smoking populations.

Discussion
The BAR approach of the MAK commission allows the identification of additional occupational exposure to hazardous substances by comparison biomonitoring results with general background levels. An exceeding of a BAR does not indicate an inacceptable health risk; however the BAR may be used as goal-setting in the improvement of occupational hygiene.