Summary in French and Spanish.

Evaluates the risks to human health and the environment posed by two partially halogenated chlorofluorocarbons: dichlorofluoromethane (HCFC 21) and chlorodifluoromethane (HCFC 22). These two methane derivatives were selected for evaluation because of their potential use as substitutes for those fully halogenated chlorofluorocarbons that are being phased out as a result of the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. The evaluation is intended to assist industry in its urgent search for acceptable substitute chemicals, most notably for use as refrigerants, as propellants in aerosols, and as blowing agents for the production of polystyrene. While data on human toxicity are thoroughly reviewed, the greatest challenge is to find the most accurate models for predicting levels of release to the environment and estimating the potential of these chemicals to deplete the ozone layer. Because HCFC 21 is no longer produced for any commercial purposes, most data assessed come from studies of HCFC 22. Current environmental levels of both chemicals are judged to be extremely low and highly unlikely to cause direct effects on human health. A review of models for estimating atmospheric residence times and routes of transport to the stratosphere concludes that the ozone-depleting potential of both chemicals is considerably lower than that of the fully halogenated chlorofluorocarbons. While HCFC 21 has the advantage of a much shorter tropospheric lifetime, studies have linked exposure to liver damage. Concerning the toxicity of HCFC 22, evidence from the vast majority of studies is reassuring. The report concludes that HCFC 22 is an acceptable transient substitute for the chlorofluorocarbons included in the Montreal Protocol. HCFC 21 could not be recommended as a substitute in view of its potential toxic effects on the liver.

eng rus.

WHODOC

WHO monograph

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