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Methylene chloride (dichloromethane). Methylene chloride is widely used in industry
for paint stripping, as a blowing agent for foam, as solvent for
degreasing, in the manufacture of photographic film, as the carrier in rapiddry
paints, and in aerosol propellants. It is also used in the diphasic treatment
of metal surfaces, in the textile and plastics industry, and for extracting heatsensitive
edible fats and essential oils. It is estimated that almost 100,000 individuals
are exposed to methylene chloride in the workplace alone.
As with other solvents, methylene chloride has CNS depressant properties at
high levels of exposure and may lead rapidly to unconsciousness and death
(Moskowitz and Shapiro 1952; Winek et al. 1981; Tariot 1983; Sturmann et al.
1985; Horowitz 1986). This has been reported both in industrial settings
(Moskowitz and Shapiro 1952; Tariot 1983) and as a result of solvent inhalation
abuse (Sturmann et al. 1985; Horowitz 1986).
Methylene chloride has generally been considered safer than other chlorinated
hydrocarbons and has not attracted the attention it deserves as a possible
cause of chronic CNS dysfunction. Methylene chloride is metabolized to
carbon monoxide (Stewart and Fisher 1972; Kubic et al. 1974; Ratney et al.
1974; Astrand et al. 1975) and therefore both its hypoxia effect as well as its
narcotic actions must be considered regarding methylene chloride’s CNS-depressant
effects. Carbon monoxide, at high levels, and other forms of cerebral
hypoxia are known to cause permanent neurological sequelae.
The acute effects of exposure to methylene chloride have been studied in controlled
experiments in humans (Stewart et al. 1972; Gamberale et al. 1975;
Winneke 1981). In one study, 11 healthy nonsmokers were exposed to levels
of methylene chloride up to 1,000 ppm for 1 to 2 hours (Stewart et al. 1972).
Inhalation of methylene chloride at 500-1,000 ppm for this length of time was
followed promptly by a sustained (at 24 hours post-exposure) elevation of
carboxyhemoglobin. These levels, however, never reached above 10 percent
saturation. Visual evoked responses in the three subjects tested showed an
increase in peak to peak amplitudes after 2 hours of exposure and returned to
baseline 1 hour after termination of exposure. No untoward subjective symptoms
occurred at levels of exposure below 1,000 ppm. At exposure to concentrations
of 1,000 ppm, two of three subjects reported mild light headedness,
which promptly resolved after cessation of exposure.
The effects of methylene chloride exposure on three tests of cognitive function
(reaction time, short-term memory, calculation ability) were tested in 14
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