Maximum workplace concentration values and carcinogenicity classification for mixtures

In Germany, the Commission for the Investigation of Health Hazards of Chemi cal Compounds in the Work Area (MAK Commission) generally sets maximum work place concentration values (i.e., a proposed occupational exposure level [O EL]) for single substances, not for mixtures. For mixtures containing subst ances with a genotoxic and carcinogenic potential, the commission considere d it scientifically inappropriate to establish a sale threshold. This appro ach is currently under discussion. Carcinogenic mixtures are Categorized ac cording to either the carcinogenicity of the mixture or the classification of the carcinogenic substances included, in regulating exposure to mixtures , an approach similar to that used by the American Conference oi Government al Hygienists is proposed: For components with the same target organ and mo de of action or interfering metabolism, synergistic effects must be expecte d and the respective OELs must be lowered. However, ii there is proof that the components act independently, the OELs of the individual compounds are not considered to be modified. In the view of the commission, calculating O ELs for solvent mixtures according to their liquid phase composition is not justified, and the setting of scientifically based OELs for complex mixtur es is not possible.