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Count Down: Chemicals linked to inferior sperm

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11:19am, May 28, 2003
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Men's exposure to some compounds common in cosmetics and plastics is associated with sperm abnormalities, a new study suggests. The data don't establish a causative link between so-called phthalates and aberrant semen, but they bolster the case that phthalate concentrations typically seen in healthy people may have a negative effect on male reproduction.

Scientists have been working for years to understand the causes in developed countries of an apparent half-century-long decline in sperm quality–lower counts, reduced motility, and higher fractions appearing malformed. One hypothesis attributes this trend to the increasing prevalence of certain hormonally active chemicals, including phthalates, in the environment and in people's bodies.

Phthalates are used in cosmetics, deodorants, and many plastics that make up food packaging, children's toys, and medical devices. Studies indicate that the chemicals can interfere with sex hormones and impair reproductive health in animals (SN: 4/3/99, p. 213: http://www.sciencenews.org/sn_arc99/4_3_99/fob3.htm).

To look for links between phthalate exposures and sperm characteristics, Susan M. Duty and Russ Hauser of the Harvard School of Public Health in Boston and their colleagues analyzed semen and urine samples from 168 men. These volunteers were attending a clinic for couples experiencing difficulty conceiving a child.

The researchers analyzed volunteers' semen for sperm counts, sperm motility, and sperm shape and tested their urine for concentrations of eight phthalates that the body produces from more complex forms. Five of these compounds showed up in urine samples from at least 75 percent of the volunteers.

In the May Epidemiology, the researchers report an association between sperm count and urine concentrations of two compounds, monobutyl phthalate and monobenzyl phthalate. Among the volunteers, those with the highest concentrations of those compounds had the lowest sperm counts. Volunteers' monobutyl phthalate concentrations were also inversely correlated with sperm motility.

Those findings extend to men a pattern previously observed in rodents. However, in the animal experiments, the rodents received unusually large amounts of phthalates, whereas the men in the recent study had urine phthalate concentrations similar to those in the U.S. population at large (SN: 2/22/03, p. 120: Available to subscribers at Proof of Burden).

The new study is one of the first to link phthalate exposure to reproductive health in people, says Shanna H. Swan of the University of Missouri in Columbia. While not conclusive, the findings could "explain a substantial fraction of the reported decline in semen quality" in men in industrialized countries, she says.

Environmental epidemiologist Jane A. Hoppin of the National Institute of Environmental Health Sciences (NIEHS) in Research Triangle Park, N.C., says the new study adds heft to the notion that phthalates affect male fertility at concentrations common in U.S. men. Comments by both Hoppin and Swan appear in the issue of Epidemiology reporting the new Harvard results.

Interestingly, the two phthalates that the study links to semen abnormalities have not been considered the most toxic ones on the basis of animal studies, says Paul M. Foster, a reproductive toxicologist at NIEHS in Research Triangle Park.

The new study didn't find a correlation between the men's reproductive characteristics and urine concentrations of another phthalate that is so toxic to young animals that the European Union recently prohibited its use in cosmetics.

If further studies establish that phthalates are human-reproductive toxins, researchers will also need to determine how people can best reduce their exposures to the chemicals, Duty says.

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