Toluene and Xylene
Toluene (methylbenzene, methylbenzol, phenylmethane, toluol) and xylene (dimethylbenzene, methyltoluene, and xylol) are common aromatic solvents found in glues, inks, dyes, lacquers, varnishes, paints, paint removers, pesticides, cleaners, and degreasers. The largest source of exposure is in the production and use of gasoline. Toluene and xylene are clear, colorless liquids with a sweet, pungent odor that is detectable at low air concentrations. They are less dense than water and highly volatile, readily producing flammable and toxic concentrations at room temperature. The vapor is heavier than air and may accumulate in low-lying areas. Toluene frequently is intentionally abused by inhaling lacquer thinner and paints (particularly spray paints) to induce a “sniffer’s high.”
Mechanism of toxicity
Toluene and xylene cause generalized CNS depression. Like other aromatic hydrocarbons, they may sensitize the myocardium to the arrythmogenic effects of catecholamines. They are mild mucous membrane irritants that affect the eyes and the respiratory and GI tracts.
Pulmonary aspiration may cause a hydrocarbon pneumonitis (See Hydrocarbons).
Chronic abuse of toluene can cause diffuse CNS demyelination, renal tubular damage, and myopathy.
Kinetics. Symptoms of CNS toxicity are apparent immediately after inhalation of high concentrations and 30–60 minutes after ingestion. Pulmonary effects may not appear for up to 6 hours after exposure. Toluene is metabolized by alcohol dehydrogenase and by several cytochrome P-450 isoenzymes to benzyl alcohol (CYP2E1), p-cresol (CYP2E1, CYP2B6, CYP1A2), and o-cresol (CYP1A2). The presence of ethanol can inhibit toluene metabolism and prolong systemic toxicity.
Toxic dose
Ingestion. As little as 15–20 mL of toluene is reported to cause serious toxicity. A 60-mL dose was fatal in a male adult, with death occurring within 30 minutes. The Environmental Protection Agency (EPA) oral reference dose (RfD), or maximum acceptable oral dose, is 0.08 mg/kg/d.
Inhalation.
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