The DFG's Senate commission for the investigation of health hazards of chemical compounds in the work area has presented the 1999 list of MAK and BAT values and submitted it to the Federal Ministry for Labour and Social Affairs as an aid to improve industrial safety. The list contains proposed MAK values, i.e. the maximum admissible concentration of a chemical substance present as gas, vapour or aerosol in the workplace air which, according to current knowledge, does not have any adverse effects on the health of the workers concerned even if they are exposed for eight hours daily for a longer period of time. In addition, the substances are classified according to their carcinogenic, genotoxic and sensitising effects as well as their potential to pose a risk to reproduction and to be absorbed percutaneously. Compared with the previous year there were 64 changes and new entries.
16 carcinogenic substances were reviewed and/or classified. It should be noted that this year crystalline silicon dioxide, i.e. quartz, cristobalite and tridymite, were classified as category 1 carcinogenic substances (substances that have been shown to produce cancer in humans).
Epidemiological studies as well as animal experiments have shown that there is a causal relationship between quartz exposure and an increased incidence of lung cancer. Although silicosis points to a high quartz exposure, it is not possible at present to define a scientifically validated limit in order to prevent a health hazard.
Michler's ketone was assigned to category 2, i.e. substances to be considered
carcinogenic in humans (as indicated by animal experiments). Tetrahydrofuran and
cresol, solvents that are potential tumour-inducing substances, were placed in
category 3 (substances suspected of having a carcinogenic potential), and so
were metallic mercury and its inorganic compounds after its organic compounds
had already been placed in this category earlier. Neutralised cross-linked
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