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OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

CAS: 77-78-1; Chemical Formula: (CH3)2SO4

OSHA's former limit for dimethyl sulfate was 1 ppm TWA, with a skin notation. The ACGIH considers this substance a suspected human carcinogen and has given it a classification of A2 (ACGIH 1986/Ex. 1-3, p. 212). The ACGIH's TLV-TWA for this substance is 0.1 ppm with a skin notation. OSHA proposed, and the final rule establishes, a 0.1 ppm TWA PEL, with a skin notation, for dimethyl sulfate, which is an oily, colorless liquid with a faint, onion-like odor. NIOSH (Ex./8-47, Table N6A) concurs with the selection of this limit and considers dimethyl sulfate to be a potential human carcinogen.

Dimethyl sulfate is commonly used in the manufacture of many organic chemicals. It has been shown to be carcinogenic in rats by inhalation exposure, subcutaneous injection, and prenatal exposure. The rat is the only animal species in which the carcinogenesis of dimethyl sulfate has been tested (IARC 1982c, as cited in ACGIH 1986/Ex. 1-3, Appendix A).

The carcinogenic activity of dimethyl sulfate was investigated in male rats chronically exposed to subcutaneous injections of 8 or 16 mg/kg body weight per week (Druckrey, Preussman, Nashed, and Ivanovic 1966/Ex. 1-245). Local sarcomas with metastases to the lung and regional lymph nodes were observed at both dose levels. A single subcutaneous injection of dimethyl sulfate (50 mg/kg) also produced local sarcomas with metastases to the lung (Druckrey, Kruse, Preussman et al. 1970/Ex. 1-246). However, tumors did not develop following chronic weekly intravenous injections of dimethyl sulfate (2 or 4 mg/kg) (Druckrey, Kruse, Preussman et al. 1970/Ex. 1-246). Control data were not reported for either of these studies.

The carcinogenic potential of dimethyl sulfate exposure by inhalation was also evaluated in male rats (Druckrey, Kruse, Preussman et al. 1970/Ex. 1-246). Animals were exposed to approximately 3 or 10 ppm dimethyl sulfate for one hour per day, five times weekly, for 130 days. Malignant tumors developed in 15 percent (3/20) of the rats exposed at 3 ppm and in 18 percent (5/27) of the rats exposed at 10 ppm.

Pregnant rats were exposed to a single intravenous injection of dimethyl sulfate (20 mg/kg body weight) on day 15 of gestation and the incidence of malignant tumors in the offspring was investigated for one year. Tumors were reported in 7/59 of the offspring. However, the incidence of tumors in the control group was not indicated. The results of this study are complicated because several rats died (number of deaths not specified) from the acute toxic effects of dimethyl sulfate, and the incidence of tumors in the control group was not reported.

There is little information available regarding the carcinogenicity of dimethyl sulfate in humans. A case study of workers exposed to dimethyl sulfate reported that three workers developed bronchial cancer (Druckrey, Preussman, Nashed, and Ivanovic 1966/Ex. 1-245). However, an epidemiological study by the E.I. du Pont de Nemours Company (1975, as cited in ACGIH 1986/Ex. 1-3, p. 213) demonstrated no increase in the incidence of respiratory cancer among workers exposed to dimethyl sulfate.

OSHA considered the possibility of performing a quantitative risk assessment for dimethyl sulfate and concluded that the studies described above did not have sufficient dose-response data to provide an adequate basis for such a risk assessment (see Ex. 85). Dimethyl sulfate induces malignant tumors in animals both by inhalation and ingestion, and there is thus sufficient evidence in animals to predict that workers exposed to dimethyl sulfate are at significant risk of developing cancer, which OSHA considers to be a material impairment of health; exposures at levels only three times the former PEL (1 ppm) resulted in a significant number of tumors. No comments, other than those from NIOSH were received on dimethyl sulfate. OSHA concludes that reducing the former limit to 0.1 ppm as an 8-hour TWA with a skin notation will substantially reduce the significant risk of cancer mortality associated with exposure to dimethyl sulfate.

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