Medical Health Encyclopedia

Most evidence on the hormone of chemical estrogens has occurred in animals and birds. Tests of single chemicals containing estrogen have reported little danger for people. Some studies suggest, however, that exposure to more than one of these chemicals may be very harmful. At this time, there is no strong evidence supporting a serious harmful effect in people who have normal exposure to these chemicals. Major efforts are underway to determine the extent of any possible harm from these chemicals.

Hydrocarbons and Other Industrial Chemicals. In one 2000 study, workers in a rubber factory who were chronically exposed to hydrocarbons (ethylbenzene, benzene, toluene, and xylene) had lower than average sperm counts and sperm qualities. (In one 2001 study, men who smoked and worked in petrochemical plants had particularly poor sperm quality.) Still, not all major studies have confirmed the effects of these chemicals and evidence showing any significant effect on fertility is weak.

Exposure to Heavy Metals. Chronic exposure to heavy metals such as lead, cadmium, or arsenic may affect sperm quality. Trace amounts of these metals in semen seem to inhibit the function of enzymes contained in the acrosome, the membrane that covers the head of the sperm.

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Radiation Treatments. X-rays and other forms of radiation affect any rapidly dividing cell, so cells that produce sperm are quite sensitive to radiation damage. Cells exposed to significant levels of radiation may take up to two years to resume normal sperm production and, in severe circumstances, may never recover.

Low Semen Levels

Men with fertility problems because of low semen levels when they ejaculate may have a structural abnormality in the tubes transporting the sperm. (A normal amount of semen is 2.5 to 5 mL, or about 1/2 to 1 teaspoon.)

Varicocele