AEGL-2 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.

AEGL-3 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience life-threatening health effects or death.

Airborne concentrations below the AEGL-1 represent exposure concentrations that could produce mild and progressively increasing but transient and nondisabling odor, taste, and sensory irritation or certain asymptomatic, nonsensory effects. With increasing airborne concentrations above each AEGL, there is a progressive increase in the likelihood of occurrence and the severity of effects described for each corresponding AEGL. Although the AEGL values represent threshold concentrations for the general public, including susceptible subpopulations, such as infants, children, the elderly, persons with asthma, and those with other illnesses, it is recognized that individuals, subject to idiosyncratic responses, could experience the effects described at concentrations below the corresponding AEGL.

SUMMARY

Hexafluoroacetone (HFA) is a colorless gas with a musty odor used in the synthesis of various polymers, medicines, agriculture chemicals, and as an intermediate in various organic syntheses. HFA is highly reactive, reacting vigorously with water and resulting in a series of hydrates (sesquihydrate, monohydrate, and dihydrate) and ultimately producing a stable trihydrate.

There are no inhalation exposure-response data on humans exposed to HFA and no information regarding an odor threshold.

Information on lethality was available from studies in rats and dogs, and evidence of testicular degeneration was found in rats after acute inhalation exposure to HFA. A 30-min LC50 (lethal concentration, 50% lethality) of 900 ppm and a 3-h LC50 of 275 ppm were reported for rats. Other studies reported no lethality after a single 30-min exposure to HFA at 3,600 ppm or after a single 4-h exposure at 200 ppm (300 ppm for HFA nonahydrate). Effects, including lethality, appeared to be mediated systemically and often occurred during postexposure periods. The most prevalent nonlethal responses were lacrimation and salivation during exposure and developmental effects in the offspring of dams exposed to HFA for several days during gestation. Exposure of male rats to HFA resulted in testicular degeneration after repeated exposures at 12 ppm or a single 4-h exposure at 200 ppm.

The mode of action for HFA-induced toxicity is uncertain. The effects of HFA appeared to be systemically mediated with pulmonary damage in rats occurring only at concentrations exceeding minimal lethality levels. Results of



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