Composting cuts manure’s toxic legacy

From Minneapolis, at the Second International Conference on Pharmaceuticals and Endocrine Disrupting Chemicals in Water.

Livestock naturally excrete large amounts of estrogen and testosterone, hormones that can harm crops and wildlife when farmers use manure as fertilizer (SN: 7/15/95, p. 44). A study now shows that farmers can rid chicken manure of much of this unwanted hormonal baggage by composting the wastes.

Heldur Hakk of the Agriculture Department’s Biosciences Research Laboratory in Fargo, N.D., and his colleagues collected manure from egg-laying chickens and mixed it with hay, straw, decomposing leaves, and some starter compost. Then, they added water and heaped the mix atop impermeable pads in long compost piles. Periodically, they turned the compost to maximize the bacteria-driven degradation, which generates heat.

Although the manure’s starting concentrations of testosterone and estrogen averaged 187 parts per billion (ppb) and 95 ppb, respectively, amounts of both hormones fell gradually over 19 weeks–to a mere 13 ppb for testosterone and 16 ppb for estrogen. Initially, Hakk notes, the breakdown of testosterone proceeded at three times the rate of that of estrogen.

The heaped compost cooled before either hormone fully disappeared, which means that some could have leached out and flowed downstream if the compost were spread as fertilizer. Hakk’s team didn’t assay the finished compost for any breakdown products of estrogen or testosterone, some of which are hormonally active. Hakk said his group plans to investigate such hormone-breakdown residues in new compost heaps containing manure from cattle and swine.

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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