Other Halogenated Solvents
Dibromomethane CAS No. 74-95-3
1,1-Dichloroethane CAS No. 75-34-3
1,2-Dichloroethane (Ethylene dichloride) CAS No. 107-06-2
1,1-Dichloroethene (Vinylidene chloride) CAS No. 75-34-3
cis-1,2-Dichloroethene CAS No. 156-59-2
trans-1,2-Dichloroethene CAS No. 156-60-5
1,2-Dichloropropane CAS No. 78-87-5
1,1,1-Trichloroethane (Methyl chloroform) CAS No. 71-55-6
1,1,2-Trichloroethane CAS No. 79-00-5
1,1,2,2-Tetrachloroethane CAS No. 79-34-5
Tetrachloromethane (Carbon tetrachloride) CAS No. 56-23-5
The halogenated solvents are volatile organic chemicals consisting of a hydrocarbon chain or one hydrocarbon substituted with one or more chlorine or bromine atoms. Most of these chemicals are used as degreasers and solvents in various products such as paints. In the past, 1,1,1-trichloroethane was used as a dry cleaning agent, insect fumigant, and solvent in consumer products; more recently, its U.S. production has been restricted because of its principal use in manufacturing hydrofluorocarbons (Armstrong, et al., 2004; ATSDR, 2006). Production of 1,1,2,2-tetrachloroethane in the U.S. has ceased, and currently, it is only used as a chemical intermediate in the production of several other halogenated solvents (ATSDR, 2008). 1,1,2-trichloroethane, 1,2-dichloroethane and 1,1-dichloroethene are used in the synthesis of other chemicals, such as polyvinylidene. Tetrachloromethane use as a solvent and fumigant has been discontinued due to toxicity concerns, and its other major use, production of chlorofluorocarbon refrigerants, has been restricted as a result of regulations of ozone-depleting chemicals (ATSDR, 2005).
These volatile halogenated solvents may be released into the air from facilities that produce or use them, from contaminated waste water, or from hazardous waste sites. In surveys of U.S. drinking water, 1,1,1-trichloroethane was one of the most frequently detected chlorinated solvents; detected in less than 10 percent of domestic wells (Moran et al., 2007; Rowe et al., 2007). When 1,1,1-trichlorethane was available in consumer products, indoor air concentrations could exceed outdoor air concentrations (Wallace, et al., 1991). Because of their volatility, these halogenated solvents generally do not persist in soil or water. Workers involved in the production or use of these solvents may be exposed by inhalation or by dermal contact with the liquid solvents.
s Inhalation is the most common exposure route for the general population, including indoor sources from such as paints, adhesives, cleaning solutions, and aerosolized insecticide sprays; from industries producing these solvents; and from contaminated waste disposal sites (Armstrong et al., 2004; ATSDR, 2008 and 2001). Drinking water may contribute to exposure due to contaminated underground drinking water supplies. In general, these solvents are well absorbed by inhalation, dermal, or oral exposure. After absorption, small amounts may be exhaled in expired air, and the remaining amount rapidly distributed to tissues. 1,1,1-Trichloroethane is exceptional in that most of a dose is exhaled unchanged in expired air and less than 10 percent of a dose is metabolized (Monster, et al., 1979). Fatty tissues can transiently accumulate these solvents, which are slowly released back into the blood stream. Many of these halogenated solvents are metabolized to more water soluble metabolites that can be excreted in the urine. Hepatic transformation of tetrachloromethane may lead to the generation of reactive intermediate metabolites which may be responsible for liver toxicity (Weber et al., 2003). Other halogenated solvents may undergo similar metabolism to reactive intermediates that contribute to toxicity (Casciola and Ivanetich, 1984; IPCS, 2003; Raucy et al., 1993).
Human health effects from these solvents at low environmental doses or at biomonitored levels from low environmental exposures are unknown. Acute exposure to massive doses by either inhalation or ingestion can cause central nervous system depression and unconsciousness, cardiac dysrhythmias, and hepatic and renal injury. Eye and respiratory tract irritation may occur with exposure to high vapor concentrations of most of these solvents, and allergic contact dermatitis has been reported following 1, 2-dichloroethane dermal exposure (Baruffini et al., 1989). Exposures to vapor concentrations exceeding occupational standards have been associated with fatigue, headache, delayed reactions, and neuropsychological impairment (ATSDR, 2001; Bowler et al., 2003). Epidemiologic studies of workers exposed to various halogenated solvents have found occasional associations between exposure and reduced fertility and spontaneous abortion in women (Figa-Talamanca, 2006). In animal studies, reproductive toxicity has not been consistently demonstrated in the absence of maternal toxicity (IPCS, 1990, 1992, and 1993).
Experimental animals exposed chronically to high doses of each of these solvents developed tumors of the liver, lung, and kidney. In addition, lymphoid and hematopoietic tumors were observed with 1,2-dichloroethane and 1,1,1-trichloroethane; mammary gland tumors were observed with tetrachloromethane, 1,2-dichloroethane, and 1,1-dichloroethene. IARC has determined that the dichloroethanes and tetrachloromethane are possible human carcinogens; the other halogenated solvents in this section are not classifiable regarding human carcinogenicity. NTP has determined that tetrachloromethane and 1,2-dichloroethane are reasonably anticipated to be human carcinogens. With the exception of dibromomethane, the U.S. EPA has established drinking water standards and other environmental criteria. The FDA regulates several of these solvents in bottled water and as indirect food additives. Occupational standards and guidelines are available for most of these chemicals from OSHA and ACGIH, respectively. Further information on the halogenated solvents is available from ATSDR at: http://www.atsdr.cdc.gov/toxprofiles/index.asp.
Levels of halogenated solvents in blood reflect recent exposure. With the exception of tetrachloromethane in the NHANES 2001-2002 subsample, the other ten halogenated solvents were detectable few or none of the participants in the NHANES 2003-2004 and 2005-2006 subsamples. In a non-representative sample of adults in NHANES III (1988-1994), blood levels were also non-detectable or detected in <10% of samples, except for 1,1,1-trichloroethane which was detected in a majority of samples with a median of 0.13 µg/L (Ashley et al., 1994; Churchill et al., 2001). 1,1,1-Trichloroethane was not detected in children who underwent periodic blood testing as part of an environmental exposure study (Sexton et al, 2005 and 2006). In a study of German residents, 1,1,1-trichloroethane levels were of similar magnitude to the NHANES III study (Hajimiragha et al., 1986).
Finding a measurable amount of any of these halogenated solvents in blood does not imply that the level of the solvent causes an adverse health effect. Biomonitoring studies of blood halogenated solvents can provide physicians and public health officials with reference values so that they can determine whether or not people have been exposed to higher levels of halogenated solvents than levels found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.
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