Fluorinated aliphatics such as the freons and closely related compounds have also been used in the workplace, in consumer goods, and in stationary and mobile air conditioning systems. Because of the severe damage they cause to the ozone layer in the troposphere, their use has been limited or eliminated by international treaty agreements. The common halogenated aliphatic solvents also create serious problems as persistent water pollutants. They are widely found in both groundwater and drinking water as a result of poor disposal practices.
Table 56–1 includes recommended OSHA PELs for several of these compounds (see also http://www.osha.gov, Table Z-1).
1. Mechanism of action and clinical effects—In laboratory animals, the halogenated hydrocarbons cause central nervous system (CNS) depression, liver injury, kidney injury, and some degree of cardiotoxicity. Several are also carcinogenic in animals and are considered probable human carcinogens. Trichloroethylene and tetrachloroethylene are listed as “reasonably anticipated to be a human carcinogen” by the US National Toxicology Program, and as class 2A probable human carcinogens by IARC. These substances are depressants of the CNS in humans. Chronic workplace exposure to halogenated hydrocarbon solvents can cause significant neurotoxicity with impaired memory and peripheral neuropathy. All halohydrocarbon solvents can cause cardiac arrhythmias in humans, particularly in situations involving sympathetic excitation and norepinephrine release.
Hepatotoxicity is also a common toxic effect that can occur in humans after acute or chronic halohydrocarbon exposures. Nephrotoxicity can occur in humans exposed to carbon tetrachloride, chloroform, and trichloroethylene. Chloroform, carbon tetrachloride, trichloroethylene, and tetrachloroethylene carcinogenicity have been observed in lifetime exposure studies performed in rats and mice and in some human epidemiologic studies. Dichloromethane (methylene chloride) is a potent neurotoxin, a generator of CO in humans, and a probable human carcinogen. It has been widely used as a paint stripper, plastic glue, and for other purposes. Epidemiologic studies of workers who have been exposed to aliphatic hydrocarbon solvents that include dichloromethane, trichloroethylene, and tetrachloroethylene have found significant associations between the agents and renal, prostate, and testicular cancer. Trichloroethylene is now considered a class 1, known human carcinogen by IARC; renal cancers and non-Hodgkin’s lymphoma have been reported. Other cancers are increased but their incidence has not reached statistical significance.
2. Treatment—There is no specific treatment for acute intoxication resulting from exposure to halogenated hydrocarbons. Management depends on the organ system involved.
Benzene is used for its solvent properties and as an intermediate in the synthesis of other chemicals. It remains an important component of gasoline. Benzene may be found in premium gasolines at concentrations of about 1.5%. In cold climates such as Alaska, benzene concentrations in gasoline may reach 5% in order to provide an octane boost. It is one of the most widely used industrial chemicals in the world. The current PEL is 1.0 ppm in the air (see Table 56–1 and http://www.osha.gov, Table Z-1), and a 5 ppm limit is recommended for skin exposure. The National Institute for Occupational Safety and Health (NIOSH) and others have recommended that the exposure limits for benzene be further reduced to 0.1 ppm because excess blood cancers occur at the current PEL.