effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.
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 levels 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 AEGLs represent threshold levels 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.
Xylene is found in a number of consumer products, including solvents, paints and coatings, and as a blend in gasoline. Mixed xylenes are composed of three isomers: m-xylene, o-xylene, and p-xylene, with the m-isomer predominating. Ethylbenzene is also present in the technical product formulation. Absorbed xylene is rapidly metabolized and is excreted almost exclusively in the urine as methylhippuric acid isomers in humans and as methylhippuric acid isomers and toluic acid glucuronides in animals. Xylene causes mucus irritation and affects the central nervous system (CNS) in humans and animals after acute inhalation exposure. Hepatic effects have been noted in humans after acute inhalation exposure to high concentrations and in rats after subchronic oral or inhalation exposure. No consistent developmental or reproductive effects were observed in the studies found in the available literature. Commercial xylene and all three isomers have generally tested negative for genotoxicity. Xylenes are currently not classifiable as to carcinogenicity by the International Agency for Research on Cancer (IARC) or the Environmental Protection Agency (EPA).
The AEGL-1 is based on the no-effect level for notable discomfort in human subjects. Only mild eye irritation was noted during a 30-min exposure to mixed xylenes at 400 ppm (Hastings et al. 1984). An interspecies uncertainty factor was not applied because the key study used human data. An intraspecies uncertainty factor of 3 was applied because slight eye irritation is caused by a