Benzene, an aromatic hydrocarbon that is a natural component of crude oil and natural gas, is toxic to the blood
and blood-forming organs. Epidemiological studies have established an association between benzene exposure and acute
myeloid leukemia, and increasing evidence also indicates a possible association between benzene and multiple myeloma.
A specific benzene-associated myelodysplastic syndrome has also been suggested. Chronic hematotoxic effects of benzene
exposure, including reduced lymphocyte, neutrophil and platelet counts in peripheral blood, have been detected at
occupational exposure below a level that had previously been considered not to cause any health effects. Whether these
abnormalities represent bone marrow damage and/or initial events in the development of a true neoplastic disease is not
known. Together with a reported nonlinear relationship between benzene exposure and the level of various metabolites,
favoring production of biologically reactive quinones at exposure below 1 part per million, these observations suggest that
benzene even at low exposure levels may contribute to the risk of acute myeloid leukemia or myelodysplastic syndrome,
especially among genetically susceptible individuals.