Benzene is a flammable liquid that evaporates quickly. Benzene occurs in nature but most benzene is made from crude oil. Benzene is a very important industrial chemical used to make a vast array of other chemicals and products.
Environmental Fate and Transport
Benzene evaporates readily from surface water and surficial soil. Benzene in the air generally decomposes in a few days. Benzene in the soil can persist for a long time, especially if there is little oxygen in the soil. Benzene in soil can move down to groundwater and then move with groundwater as groundwater flows. Benzene can persist in groundwater for years. However, benzene can also evaporate from deeper soils and groundwater and move through the soil in vapor form, though benzene that does so usually breaks down when it encounters sufficient oxygen in the soil. Benzene does not generally accumulate in plants or animals.
Although volcanoes and forest fires emit benzene, human activity is the principal source of the benzene to which we are likely to be exposed. Burning coal and oil, evaporation from facilities that use or store benzene or products containing benzene (like gas stations), and tobacco smoke are all important sources of benzene exposure. Leaks, discharges, and disposal of benzene-containing products also contribute. For example, leaking underground storage tanks at gas stations can contaminate soil and groundwater with benzene and other chemicals. Because benzene evaporates so readily and is present in tobacco smoke, most human exposure is via breathing. Something like half of benzene exposure in the United States is from tobacco smoke. Exposure can also occur by drinking water that contains benzene or breathing benzene that evaporates from contaminated water when cooking, showering, or bathing. Other sources of benzene exposure include working with benzene at a job, or living near an industrial facility that produces or uses benzene, or a place where wastes containing benzene were disposed of.
Benzene can get into our bodies via breathing, eating, drinking, or through the skin. Benzene that gets into our bodies moves into the bloodstream and is carried around the body. Some benzene can be stored for a while in body fat and bone marrow. The liver and bone marrow convert benzene into other chemicals, some of which are harmful. Those other chemicals, called metabolites, are discharged in urine within a few days.
Health effects from benzene exposure depend in part on the quantity and duration of exposure. Effects can include feeling sleepy, increased heart rate, dizziness, confusion, headaches, tremors, unconsciousness, and at very high exposures, coma or death. Other effects can include but are not limited to eye irritation, problems with blood cell formation, anemia, or bleeding. Benzene is known to cause certain kinds of leukemia.
The preceding paragraphs are summarized from the Public Health Statement for Benzene published by the Agency for Toxic Substances and Disease Registry.
Additional Cancer Assessments
U.S. EPA's Integrated Risk Information System states that benzene is a known human carcinogen.
The National Institutes of Health has determined that benzene is known to be a human carcinogen.
The International Agency for Research on Cancer has determined that "There is sufficient evidence in humans for the carcinogenicity of benzene. Benzene causes acute myeloid leukaemia in adults. Positive associations have been observed for non-Hodgkin lymphoma, chronic lymphoid leukaemia, multiple myeloma, chronic myeloid leukaemia, acute myeloid leukaemia in children, and cancer of the lung." (IARC, page 297).