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Benzene, a clear, volatile liquid with an acrid, aromatic odor, is one of the most widely used industrial chemicals. It is a constituent by-product in gasoline, and it is used as an industrial solvent and as a chemical intermediate in the synthesis of a variety of materials. Benzene can be found in dyes, plastics, insecticides, and many other materials and products. It is generally not present in household products.

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  1. Mechanism of toxicity. Like other hydrocarbons, benzene can cause a chemical pneumonia if it is aspirated. See Hydrocarbons for a general discussion of hydrocarbon toxicity.

    1. Once absorbed, benzene causes CNS depression and may sensitize the myocardium to the arrhythmogenic effects of catecholamines.

    2. Benzene is also known for its chronic effects on the hematopoietic system, which are thought to be mediated by a reactive toxic intermediate metabolite.

    3. Benzene is a known human carcinogen (ACGIH Category Al, IARC Group 1).

  2. Toxic dose. Benzene is absorbed rapidly by inhalation and ingestion and, to a limited extent, percutaneously.

    1. Acute ingestion of 2 mL may produce neurotoxicity, and as little as 15 mL has caused death.

    2. The recommended workplace limit (ACGIH TLV-TWA) for benzene vapor is 0.5 ppm (1.6 mg/m3) as an 8-hour time-weighted average. The short-term exposure limit (STEL) is 2.5 ppm. The level considered immediately dangerous to life or health (IDLH) is 500 ppm. A single exposure to 7500–20,000 ppm can be fatal. Chronic exposure to air concentrations well below the threshold for smell (2 ppm) is associated with hematopoietic toxicity.

    3. The US Environmental Protection Agency maximum contaminant level (MCL) in water is 5 ppb.

  3. Clinical presentation

    1. Acute exposure may cause immediate CNS effects, including headache, nausea, dizziness, tremor, convulsions, and coma. Symptoms of CNS toxicity should be apparent immediately after inhalation or within 30–60 minutes after ingestion. Severe inhalation may result in noncardiogenic pulmonary edema. Ventricular arrhythmias may result from increased sensitivity of the myocardium to catecholamines. Benzene can cause chemical burns to the skin with prolonged or massive exposure.

    2. After chronic exposure, hematologic disorders such as pancytopenia, aplastic anemia, and acute myelogenous leukemia and its variants may occur. Causality is suspected for chronic myelogenous leukemia, chronic lymphocytic leukemia, multiple myeloma, Hodgkin disease, and paroxysmal nocturnal hemoglobinuria. There is an unproven association between benzene exposure and acute lymphoblastic leukemia, myelofibrosis, and lymphomas. Chromosomal abnormalities have been reported, although no effects on fertility have been described in women after occupational exposure.

  4. Diagnosis of benzene poisoning is based on a history of exposure and typical clinical findings. With chronic hematologic toxicity, erythrocyte, leukocyte, and thrombocyte counts may first increase and then decrease before the onset of aplastic anemia.

    1. Specific levels. Note: Smoke from one cigarette contains 60–80 mcg of benzene; a typical smoker inhales 1–2 mg of benzene daily. This may confound measurements of low-level benzene exposures.

      1. Urine phenol levels may be useful for monitoring workplace benzene exposure (if diet is carefully controlled for phenol products). A spot urine phenol measurement higher than 50 mg/L suggests excessive ...

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