A new study, published in the journal Environmental Health Perspectives has found a link between benzene exposure and an abnormal number of chromosomes in men. According to the study, men exposed to benzene at levels close to the U.S. permissible limit are more likely to have an abnormal number of chromosomes in their sperm — either too few or too many. The condition, known as aneuploidy, can hinder fertility and fetal development, and is the largest known cause of miscarriages.
For the study, researchers enrolled 66 men working in factories in Tianjin, China. Half of the men were recruited from factories that used benzene-containing adhesives to produce shoes, paper bags and sandpaper. Benzene is a common industrial chemical that can be found in gasoline, paints, marking pens, rubber products and solvents. It is also released in cigarette smoke and vehicle exhaust. The men from these plants were considered to have been exposed to benzene. This exposure was confirmed via personal air monitors that measured benzene levels in the air at their workplace, as well as urine tests to indicate the levels of benzene and benzene metabolites in the men’s urine.
The researchers also enrolled 33 men who worked in a meat-packing plant and an ice cream factory and were not exposed to benzene. Based on their levels of urinary metabolites of benzene, the men were divided into three groups for comparison of sperm aneuploidy: 33 unexposed, 17 low-exposed and 16 high-exposed. In this study, “low exposure” meant levels of benzene that are similar to the maximum level that the U.S. government deems safe for occupational exposure.
Researchers then examined the men's sperm under a microscope and visually identified the number chromosomes. For each man, 10,000 sperm were analyzed to determine the number of sperm cells with aneuploidy. According to their results, men exposed to benzene at work are two to three times more likely to have an abnormal numbers of chromosomes in their sperm than men who have not been exposed to the chemical. Men with low exposure to benzene were twice as likely to have some sperm with two X chromosomes than men with no exposure.
This is unsettling when you remember that the men in the "low-exposure” group were exposed to levels of benzene that are similar to the maximum level deemed safe for workplace exposure in the U.S. If one of these abnormal sperm fertilize an egg, the result could be miscarriage or a child that suffers from chromosomal disorders, such as Klinefelter Sydrome (X-X-Y).
The obvious question this study raises is whether or not the U.S. permissible limit for occupational benzene exposure is sufficient to protect men from reproductive harm. What do you think?