Chemical of current interest--benzene

Overview of benzene-induced aplastic anaemia

The scientific literature is replete with reports of cases of benzene-induced toxicity to the haematopoietic system. These mainly involve aplastic anaemia, the first cases of which were reported in 1897. At high level of benzene exposure (air concentration > 100 p.p.m.), the incidence of aplastic anaemia is approximately 1/100 individuals exposed, but this drops precipitously at lower levels of exposure (10-20 p.p.m.) to around 1/10,000. Factors that affect susceptibility may include high liver cytochrome P450 2E1 activity and low folic acid intake. The mechanism of benzene-induced aplastic anaemia remains unclear, but is likely to involve: (a) metabolism of benzene in the liver; (b) transport of metabolites to the marrow and their secondary activation to toxic quinones and free radicals by peroxidase enzymes; (c) induction of apoptosis, DNA damage and altered differentiation in early progenitor cells; and (d) depletion of the stem cell pool.

Benzene--a review of the literature from a health effects perspective

A literature review of the impact on human health of exposure to benzene was conducted. Special emphasis in this report is given to the health effects reported in excess of national norms by participants in the Benzene Subregistry of the National Exposure Registry--people having documented exposure to benzene through the use of benzene-contaminated water for domestic purposes. The health effects reported in excess (p < or = .01) by some or all of the sex and age groups studied were diabetes, kidney disease, respiratory allergies, skin rashes, and urinary tract disorders; anemia was also increased for females, but not significantly so.

Effects of benzene on splenic, thymic, and femoral lymphocytes in mice

Chronic exposure to high concentrations of benzene, primarily by inhalation, can affect the function of the human immune system. Limited data are available on the immunotoxic effects of low concentrations of benzene. This study evaluated the effects of 1, 5, 10, 100, and 200 ppm benzene on lymphocytes in mice exposed by inhalation for up to 8 weeks. Exposure to 100 or 200 ppm benzene induced rapid and persistent reductions in femoral B-, splenic T- and B-, and thymic T-lymphocytes. The percentage of femoral B-lymphocytes and thymic T-lymphocytes in apoptosis was increased 6- to 15-fold by 200 ppm benzene compared to controls. Replication of femoral B-lymphocytes was increased during the exposure period in the bone marrow as a compensation for the lymphocyte loss induced by 100 and 200 ppm benzene. Exposure of mice to 10 ppm benzene or less did not have a statistically significant effect on numbers or replication of the lymphocyte populations evaluated. A reduced number of splenic B-lymphocytes after 2 weeks of exposure to benzene appeared to be the most sensitive end point and time point for evaluating benzene cytotoxicity in this study.