Lead and its inorganic compounds (inhalable fraction) except lead arsenate and lead chromate
MAK Value Documentation, supplement – Translation of the German version from 2022
Andrea Hartwig1 (Chair of the Permanent Senate Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area, Deutsche Forschungsgemeinschaft)MAK Commission2
1 Institute of Applied Biosciences, Department of Food Chemistry and Toxicology, Karlsruhe Institute of Technology (KIT), Adenauerring 20a, Building 50.41, 76131 Karlsruhe, Germany
2 Permanent Senate Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area, Deutsche Forschungsgemeinschaft, Kennedyallee 40, 53175 Bonn, Germany
Abstract
The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has re-evaluated lead [7439-92-1] and its inorganic compounds (except lead arsenate and lead chromate) considering all toxicological end points. After repeated exposure of workers, lead and its inorganic compounds show specific target organ toxicity in the nervous system, kidneys, cardiovascular and haematological system. The most sensitive toxic effects of lead and its inorganic compounds are nervous system disorders. Lead-induced neurological effects are also observed in infants and children and may result in a lifelong reduction of neurological function at low blood lead levels. As lead has a long half-life in humans, the most reliable and specific parameter for determining the internal lead burden is the blood lead concentration. Thus, the BAT value (biological tolerance value) of 150 μg/l blood must not be exceeded and its use is to be preferred over an air limit value. Nevertheless, a maximum concentration at the workplace (MAK value) of 0.004 mg/m3 for the inhalable fraction was derived by applying an updated and calibrated physiologically based pharmacokinetic (PBPK) model. As the critical effect is systemic, lead has been assigned to Peak Limitation Category II with an excursion factor of 8 due to its long half-life. As it has been demonstrated unequivocally that lead induces damage to the human embryo or foetus and that these effects are to be expected even if the MAK and BAT values are not exceeded, lead has been assigned to Pregnancy Risk Group A. The carcinogenic effects of lead and its inorganic compounds have been demonstrated in animal studies, but the data in humans are inconclusive. The primary mechanism of action is non-genotoxic and genotoxic effects play no or at most a minor part provided that the MAK and BAT values are observed. Lead and its inorganic compounds have thus been classified in Carcinogen Category 4. Skin contact is not expected to contribute significantly to systemic toxicity, but oral absorption via hand-mouth contact continues to be a critical factor. A skin sensitization potential is not expected from the data available. There are no data for sensitization of the respiratory tract.
