National Toxicology Program

Production and Producers:

Methylal can be prepared by the catalytic vapor phase oxidation of methanol in the presence of small amounts of hydrochloric acid; from methanol and paraformaldehyde in the presence of calcium chloride and hydrochloric acid; and from formaldehyde and methanol according to patents assigned to Dow Chemical Co. in the mid-1950s (Budavari, 1989). Methylal can be synthesized from methanol by an electrooxidation process described in a patent assigned to the E.I. duPont Co. (Fedkiw et al., 1993). Methylal is one of a group of linear and cyclic acetals for which Hoechst A-G has recently been assigned a patent for a continuous industrial manufacturing process using a natural circulation reactor (Arnold et al., 1996).

Methylal is listed in the EPA's TSCA Inventory (STN International, 1994, 1995). United States production of methylal in 1989 was reported to be in the range of 1.2 - 6.4 million pounds based on non-confidential data received by the EPA (Walker, 1995a). No other quantitative information on annual production was found in the available literature. Methylal is listed as a chemical in commerce in the U.S. International Trade Commission (USITC) publication, Synthetic Organic Chemicals, US Production and Sales, 1993 (USITC, 1994). The reporting company was listed as Hoechst Celanese Corp., Chemical Group, Inc.; but no production or sales quantities were included. According to the USITC, separate statistics were not published to avoid disclosure of individual company operations; however, the USITC reporting guidelines specify that each company's report of a chemical represents production > 4,500 kg [10,000 lbs] or sales > $10,000. Based on a search of recent literature sources, including chemical industry catalogs, directories, and databases, the companies presented in Table 1 have been identified as producers/suppliers of methylal, recent patent assignees for its preparation and/or use, or companies providing toxicity study results to the EPA in response to a § TSCA 8(d) rule (Fisher Scientific, undated; Lewis, 1993; Chemical Information Services, Inc., 1994; Hunter, 1994; Kuney 1995; TCI America, 1994; Van, 1994; Chemical Information Services, Inc., 1995; CIS, 1995; STN International, 1994, 1995, 1996).

Table 1. Companies producing or supplying methylal

Use Pattern:

Methylal has several use areas. They include: chemical intermediate; solvent; fuel, fuel additive; and polymer modifier (Budavari, 1989; ACGIH, 1992; Lewis, 1993; STN International, 1995, 1996). Some examples of these uses and some specialty uses are presented in Table 2. Methylal was formerly used as a surgical anaesthetic; it was found to be slower acting with a more transitory effect than diethyl ether (Proctor et al., 1988).

Table2. Uses of methylal

Human Exposure:

There is potential for exposures to methylal in occupational, consumer and environmental settings by inhalation, ingestion, and skin and eye contact. Methylal's low boiling point and vapor characteristics, combined with its wide use as a solvent, constitute a vapor hazard, according to Plog (1988). Occupational exposures to methylal as an air contaminant may occur during its production and use. Its documented presence as an indoor air pollutant indicates a potential for general population exposures (Sexton et al., 1985).

The National Occupational Exposure Survey (NOES), which was conducted by the National Institute for Occupational Safety and Health (NIOSH) between 1981 and 1983,estimated that 156,795 workers, including 21,092 female employees, were potentially exposed to methylal in the workplace. The NOES database does not contain information on the frequency, level, or duration of exposure to workers of any chemical listed therein (NIOSH, 1990)

Environmental Occurrence:

Methylal is not known to occur naturally. However, methylal has been identified as an air pollutant and water pollutant from waste water treatment (Verschueren, 1983).

Sexton et al. (1985) reported methylal as a common domestic indoor air pollutant. Wadden and coworkers (1994) also identified methylal as a volatile organic compound (VOC) emitted into the atmosphere.

Pollution of natural waters in Russia by methylal was attributed to its chemical use in the pharmaceutical industry (Korolev et al., 1993). Gholson et al. (1991) measured emissions of VOCs, including methylal, from quiescent liquid surfaces in hazardous waste treatment facilities.

Regulatory Status:

The ACGIH-recommended threshold limit value-time weighted average (TLV-TWA) for methylal is 1000 ppm (3110 mg/m³) based on acute and subchronic animal data and clinical experience with methylal. No short term exposure limit (STEL) has been recommended to date (ACGIH, 1992, 1995). The Occupational Safety and Health Administration (OSHA) has established a permissible exposure limit-time weighted average (PEL-TWA) of 1000 ppm for methylal; and the National Institute for Occupational Safety and Health (NIOSH) has established a recommended exposure limit (REL) of 1,000 ppm (NIOSH, 1992).

The Environmental Protection Agency (EPA), in response to a request from the U.S. Consumer Product Safety Commission (CPSC), issued an 8(d) final rule in the Federal Register 52 #84:16022 (01 May 1987) requiring submission of unpublished health and safety studies by past, current, and prospective manufacturers, importers, and processors (STN International, 1994).

The following action has been taken by the TSCA Interagency Testing Committee (ITC) on methylal: scored for biological effects in 1977 with a notation of slight to mod erate mutagenic and carcinogenic potential (Walker, 1995b).