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Establishment of MAK Values

Tasks of the Working Group

The task of this working group, the largest in the Commission, is the derivation of MAK values for chemical substances on the basis of experience gained in the handling of these substances, with respect to their toxicological, occupational health or occupational hygiene effects. The MAK value is the maximum permissible concentration of a substance as a gas, vapour or aerosol in the air at the workplace which, according to current knowledge, does not normally affect worker health or cause unreasonable nuisance even with repeated and long-term exposure, usually 8 hours a day, but assuming an average weekly working time of 40 hours.

The MAK values reflect scientifically based criteria for health protection, not the technical or economic feasibility of implementation. Since 2001, the usual procedure and general principles for the derivation of MAK values have been described in Section I of the List of MAK and BAT Values.

MAK values are conceived and applied as 8-hour averages. However, the actual concentrations of chemical substances in the workplace air often exhibit considerable fluctuations. Levels exceeding the average require limitation to prevent local irritation, unreasonable nuisance and adverse systemic effects. Therefore, substance-specific excursion factors (ratio between the permissible short-term concentration peak and the MAK value) are established for individual substances. More information is available in Section VI of the List of MAK and BAT Values.

Substances are also evaluated and classified in terms of their carcinogenic effects (see Section III), risks during pregnancy (see Section VIII), germ cell mutagenic effects (see Section IX), sensitising effects (see Section IV), and contribution to systemic toxicity after percutaneous absorption (see Section VII).

Descriptions of the procedures followed by the Commission in evaluating these factors are given in the corresponding sections of the List of MAK and BAT Values.

The derivation of a MAK value and the evaluation of the various factors, such as physicochemical properties, toxicity after one or more exposures, irritation of the skin or mucous membranes, sensitisation, percutaneous absorption, reproductive toxicity, and carcinogenic and germ cell mutagenic effects are clearly explained in detail in scientific documentation that takes account of all scientific data relating to humans and animals. This information is published in the series Gesundheitsschädliche Arbeitsstoffe, toxikologisch-arbeitsmedizinische Begründungen von MAK-Werten by Wiley-VCH. Looking at individual cases and taking account of all available toxicological information on a substance allows a more differentiated and diverse evaluation than one based on strictly defined rules.

Since 1972, over 1000 substances have been evaluated and 55 supplementary publications have been added to the collection of scientific documents.

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