Review of Inhalants - ARCHIVES - National Institute on Drug Abuse

ecent years, due to its recognized myelotosic potential. Benzene
is nevertheless <strong>of</strong>ten present in varying quantities in hydrocarbon
solvent mixtures, including gasoline (Parkinson, 1971; Runion,
1975) and assorted thinners and solvents (Carpenter et al.,
1975-1976).
Absorption and Distribution
Inhaled benzene is rapidly absorbed into the blood and distributed
throughout the body (Schrenk et al., 1941). In studies
involving exposure to relatively low vapor levels (25-100 ppm),
humans quickly approach a steady-state or equilibrium between
inhaled and exhaled vapor concentrations (Srbova et al., 1950;
Hunter, 1966). This equilibrium is largely governed by the
solubility <strong>of</strong> benzene in the blood, as data discussed by Patty
(1958) show rapid saturation <strong>of</strong> the blood in such circumstances.
Approximately 50 percent. <strong>of</strong> inhaled benzene is retained in subjects
in these studies, although individual variability is pronounced
Because <strong>of</strong> its lipophilicity, benzene is distributed to
tissues according to their fat content.. The highly perfused
lipoidal tissues, including the brain. are anticipated to most
rapidly accumulate benzene. This phenomenon would account. for
the rapid onset <strong>of</strong> narcosis upon exposure to concentrated organic
solvent vapors. The bone marrow possesses a quite high tissue/
blood partition coefficient for benzene, due to a high neutral fat
content (Sato et al., 1974). This is undoubtedly an important
factor in consideration <strong>of</strong> benzene’s myelotoxicity
Upon cessation <strong>of</strong> solvent exposure, benzene is eliminated from
the body at a rate dictated by a number <strong>of</strong> interdependent factars,
including alveolar ventilation, blood/tissue partition coefficients,
blood/air partition coefficient, and metabolism. Benzene
levels in the blood and exhaled air fall quickly during desaturation
(Hunter, 1966; Sato et al. , 1974). The human studies <strong>of</strong>
Srbova et al. (1950) and Sato et al. (1974) indicate that roughly
30-50 percent <strong>of</strong> systemically absorbed benzene is exhaled, which
agrees with findings <strong>of</strong> Parke and Williams (1953) in orally dosed
rabbits. Those tissues with greater blood perfusion and lower
lipid content will lose benzene most rapidly, while the poorly
perfused adipose tissue will most slowly release benzene. This
concept is supported by findings <strong>of</strong> Hunter and Blair (1972) that
more obese persons excrete larger proportions <strong>of</strong> inhaled benzene
as urinary metabolites than do their “slimmer” counterparts.
Adipose tissue apparently acts as a depot from which benzene is
gradually released and subject to metabolism.
Metabolism
The majority <strong>of</strong> benzene which is not exhaled is metabolized in the
liver to phenolic derivatives. These are excreted principally as
urinary sulfates and glucuronides. In an early study with
rabbits, Parke and Williams (1953) recovered approximately 35
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