Chloroform was extensively used to induce
The oxidative and reducing pathways of chloroform metabolism have been described, although in vivo data are limited. Carbon dioxide is the main metabolite of chloroform produced by metabolic oxidative pathways in the body. The oxidation pathway also produces active metabolites, including phosgene (Pohl and Krishna 1978; Pohl et al. 1977), which was determined in vitro by phenobarbital induction (Testai and Vittozzi 1986; Tomasi et al. 1985; Wolf et al. 1977), while the reduction pathway generates dichloromethyl carbene radicals (measured in vitro and in vivo, with and without phenobarbital induction). Both oxidative and reductive metabolism proceed through a cytochrome P450 (CYP) -dependent enzymatic activation step. The balance between oxidative and reductive pathways depends on species, tissue, dose, and oxygen tension (Ammann et al. 1998; Testay and Vitozzi 1986). In intact mammals, oxidative tension may prevent any significant metabolism through the reductive pathway (Mansuy et al. 1977; Pohl, etc. 1977). Phosgene is produced by chloroform oxidation, dechlorination to trichloroethanol, and spontaneous dehydrogenation of trichloroethanol. One molecule of hydrochloric acid is generated by dechlorination of trichloromethane ethanol, and another two molecules of hydrochloric acid are generated by hydrolysis of phosgene, so three molecules of hydrochloric acid are generated during the conversion of chloroform to carbon dioxide (Pohl et al. 1980).
Chloroform was mainly used in the production of refrigerant HCFC-22 (chlorodifluoromethane or hydrochlorofluorocarbon 22) for use in air conditioners or large supermarket freezers. These have been banned in new equipment since 2004, and are being phased out from existing machinery.
Chloroform is used in pesticide formulations, as a solvent and chemical intermediate in laboratories and industry, as a cleansing agent, in the production of dyes, in fire extinguishers and in the pharmaceutical and rubber industries. It is also used in the manufacture of fluorocarbon plastics, resins and propellants.
In the past, chloroform was extensively used to induce and maintain medical anaesthesia. Its use as an anaesthetic was discontinued due to the severe adverse health effects associated with its use.
Chloroform can exist naturally in the environment. It is also released into the environment from workplaces where it is manufactured.
Chloroform is indirectly produced when chlorine reacts with organic compounds. Therefore, a number of water disinfection processes including chlorination of drinking water, waste water and swimming pools contribute to the formation and release of chloroform into the environment. Disinfection processes at pulp and paper plants are also potential sources of chloroform.
Exposed to chloroform
People may be exposed to chloroform by breathing contaminated air or by eating food containing chloroform. Drinking water may also be a source of exposure to very small amounts of chloroform.
Workers involved in the production and use of chloroform and those working at sites where chloroform is indirectly produced (for example water treatment plants), may be exposed to higher levels of chloroform than the general population. However, safe limits are enforced to protect the employees; such levels are below those that are thought to cause harmful effects.
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