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1000
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Abstract/Summary
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The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has re‐evaluated the maximum concentration at the workplace (MAK value) and the Pregnancy Risk Group of methyl vinyl ether [107‐25‐5]. There are no new data. Methyl vinyl ether was assessed in two 28 day inhalation studies, the first with 5 male and 5 female rats each and concentrations of 0, 500, 3500, 25 000 ml/m3 and a second with 10 male rats each and concentrations of 0, 150, 500, 1500 ml/m3. In the first study 3500 ml/m3 was the systemic NOAEC for females and local NOAEC for males and females. In male rats, changes in haematological and clinico‐chemical parameters were observed in all exposure groups independent of the concentration. These effects could not be reproduced in the second study. At 3500 ml/m3 the body weight gains of male rats were reduced. This reduction was not seen in the second study with a higher number of animals. Therefore the commission now evaluates the effects at 3500 ml/m3 as incidental, maybe due to the lower number of animals, and defined 3500 ml/m3 as NOAEC. As the margin of the MAK value of 200 ml/m3 to slight effects at 25 000 ml/m3 is large enough it also accounts for the increased respiratory volume at the workplace (the blood:air partition coefficient of methyl vinyl ether is > 5; see List of MAK‐ and BAT Values, Sections I b and I c). Therefore the MAK value of 200 ml/m3 is confirmed. Since a systemic effect is critical, Peak Limitation Category II is retained. No data concerning half‐life are available; therefore the default excursion factor of 2 is confirmed. For rats, the NOAEC for developmental toxicity after inhalation is 5000 ml methyl vinyl ether/m3, at 10 000 ml/m3 variations and retarded ossification were observed. Even considering the increased respiratory volume at the workplace the difference of the NOAEC for developmental toxicity to the MAK value is sufficient so that methyl vinyl ether remains assigned to Pregnancy Risk Group C.
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