Avoid Benzene Exposure

A recent study that was published in Environmental Health Perspectives reveals a link between exposure to benzene and anomalies in the number of chromosomes present in men. The researchers in this study have concluded that men exposed to levels of benzene that are quite close to the permissible upper U.S. limits for this chemical will have an abnormal count of chromosomes in their sperm. The chromosome count may be either too few or too numerous. This abnormal sperm chromosome count is known as aneuploidy and can pose an obstacle to male fertility or to fetal development. Aneuploidy is the most common cause of miscarriage.

The study involved 66 factory workers in Tianjin, China. Half of the participants were from factories that make use of adhesives that contain benzene for the manufacture of shoes, sandpaper, and paper bags. The scientists therefore concluded that these men had been exposed to benzene. The researchers confirmed that this was the case by using air monitors to measure benzene levels in the workers' workplaces and also by measuring benzene and benzene metabolites in the urine of these workers through urine tests.

Common Chemical

Benzene is a common chemical used in various industries and is present in paints, marking pens, solvents, gasoline, and rubber products. Benzene is also found in exhaust from vehicles and in cigarette smoke.

As a control group, the scientists enrolled 33 participants who worked in either an ice cream factory or at a meat-packing plant—two workplaces where benzene would not be used.

Upper Limits

The men were divided into three groups for sperm aneuploidy comparison. The division of the groups was based on the level of benzene metabolites found in the urine of the participants: 33 unexposed, 17 men with low exposure, and 16 men with high exposure. Low exposure was deemed as exposure to levels close to the upper limits of U.S. government safety standards for occupational exposure to benzene.

The scientists then examined the sperm microscopically to count the number of chromosomes. 10,000 sperm were analyzed per man to get an idea of the ratio of sperm cells with aneuploidy. Based on their findings, it seems that men with a greater exposure to benzene in the workplace have 2-3 times the risk of having an abnormal sperm chromosome count than those men not exposed to benzene. Men with low exposure to benzene were found to have twice the risk for having at least some sperm with two X chromosomes in comparison with men who had no exposure to benzene.

The results of this study are discomfiting when you consider that those men in the low-exposure group had been exposed to levels of benzene on a par with the highest level deemed safe in the workplace within the U.S. Should one of the abnormal sperm manage to fertilize an egg, the result might be a miscarriage or a child that is born with a chromosomal disorder, for instance Klinefelter Syndrome (X-X-Y). The unasked question raised by the study is whether the U.S. should reconsider the permissible level for occupational benzene exposure.

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