Dimethyl sulphate; a hidden problem in occupational medicine

Abstract

Background: In a chemical plant, alkylating agents (mainly ethylene oxide and propylene oxide, but also dimethyl sulphate) are utilised for the production of special surfactants.

Aims: To determine possible uptakes of dimethyl sulphate by workers using N-methylvaline.

Methods: Sixty two workers in a chemical plant (38 smokers, 24 non-smokers) with potential exposure to dimethyl sulphate were monitored with respect to their blood levels of N-methylvaline. Ten laboratory workers without exposure to methylating agents were controls. Blood samples of eight workers from a specific working area were analysed for N-methylvaline in a follow up investigation four months later.

Results: The 95th centile for N-methylvaline was 80.7 µg/l blood in the exposed workers compared to 12.4 µg/l blood in controls. In a hot spot area, 10 workers exceeded the German exposure equivalent value for dimethyl sulphate (40 µg/l blood) up to fourfold. In contrast, dimethyl sulphate has not been detectable in workplace air in this area. In a follow up investigation of eight of these 10 workers, N-methylvaline levels were significantly lower, but still increased.

Conclusions: The present study is to our knowledge the first to report increased N-methylvaline levels after occupational exposure to dimethyl sulphate. As ambient monitoring values in the plant could not explain this exposure, skin contact was considered to be the main route of uptake for this substance. Dimethyl sulphate may therefore represent an occupational problem that has been generally underestimated in the past.