Sex and the sewage

A new study links sewage sludge, used as pasture fertilizer, to stunted testes in fetal lambs. The finding signals a developmental problem that could have consequences in adult male sheep.

Researchers in Scotland treated lamb pastures for 5 years with either conventional inorganic fertilizers or sewage sludge, the nutrient-rich by-product from sewage-treatment plants. The scientists applied the fertilizers so that they would provide equal amounts of the plant nutrient nitrogen.

In the fifth year, ewes that had grazed on each field for the study’s duration were slaughtered three-quarters of the way through their pregnancies. Although all these sheep weighed about the same, the female fetuses from sludge-treated pastures were 12 percent smaller, and their brothers 15 to 36 percent smaller, than fetal lambs from conventionally fertilized sites.

Testes of the fetal males from sludge-fertilized pastures were no more than two-thirds the size of those in males from sludgefree fields, according to the team’s report in the November Environmental Health Perspectives. Sludge-exposed fetal males also had far lower blood concentrations of testosterone—the primary male-sex hormone—and another hormone that is produced by testes cells that produce sperm.

Study coauthor Richard M. Sharpe of Queen’s Medical Research Institute in Edinburgh hypothesizes that unidentified chemicals in sludge caused the diminished testis size and the hormone effects. He says that his group now intends to determine whether the effects persist into adulthood and any effect they might have on the animals’ reproductive capacity. If this hypothesis holds, then these chemicals may pose a reproductive risk to people as well, Sharpe’s team argues.

Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

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