Benzene, a highly flammable, 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. Industries with the highest benzene usage include leather production, electronics manufacturing, machinery manufacturing and spray painting. Benzene is generally not present in household products.

Like other hydrocarbons, benzene can cause a chemical pneumonia if it is aspirated. (See 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 (IARC Group 1).

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 7,500-20,000 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.

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/acute nonlymphocytic leukemia and its variants may occur. Causality is suspected for chronic myelogenous leukemia, chronic lymphocytic leukemia, multiple myeloma, non-Hodgkin lymphoma, 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.

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 occupational exposure. Urinary trans-muconic acid and S-phenylmercapturic acid (SPMA) are more sensitive and specific indicators of low-level benzene exposure but are usually not readily available. SPMA in urine is normally less than 15 mcg/g of creatinine.
   2. Benzene can also be measured in expired air for up to 2 days after exposure.
   3. Blood levels of benzene or metabolites are not clinically useful except after an acute exposure. Normal levels are less than 0.5 mcg/L.
2. Other useful laboratory studies include CBC, electrolytes, BUN, creatinine, liver function tests, cardiac troponin, ECG monitoring, and chest radiography (if aspiration is suspected).

1. Emergency and supportive measures
   1. Maintain an open airway and assist ventilation if necessary.
   2. Treat coma, seizures, arrhythmias, and other complications if they occur.
   3. Be cautious with the use of any beta-adrenergic agents (eg, epinephrine, albuterol) because of the possibility of dysrhythmias due to myocardial sensitization.
   4. Monitor vital signs and ECG for 12-24 hours after significant exposure.
2. Specific drugs and antidotes. There is no specific antidote.
3. Decontamination
   1. Inhalation. Immediately move the victim to fresh air and administer oxygen if available.
   2. Skin and eyes. Remove clothing and wash the skin; irrigate exposed eyes with copious amounts of water or saline.
   3. Ingestion. Administer activated charcoal orally if conditions are appropriate (see Table I-37). Consider gastric aspiration with a small flexible tube if the ingestion was large (eg, >150-200 mL) and occurred within the previous 30-60 minutes.
4. Enhanced elimination. Dialysis and hemoperfusion are not effective.