Potomac Conservancy blames chemical runoff for intersex fish

By David A. Fahrenthold
Washington Post Staff Writer
Thursday, November 12, 2009

Pollutants that mimic natural hormones have created a "toxic stew" in the Potomac River, altering the sexual development and the immune systems of fish, a local nonprofit group warned in a report Wednesday.

In its third annual "State of the Nation's River" report, the Potomac Conservancy focused on concerns first raised in 2003, when fish began dying in large numbers in such Potomac tributaries as the Shenandoah River.

As scientists investigated those fish kills, they found that male bass around the Potomac watershed were growing eggs.

The report says it appears that chemicals -- it's still not certain which ones -- in the water are interfering with the hormones that guide development in the fish. It said that potential causes include animal hormones from manure washing off farm fields in the rain and human hormones and pharmaceuticals that are flushed out with treated sewage.

It seems likely, the report said, that the cause is not a single chemical but a mixture whose components might be different around the river. Pesticides might dominate in rural areas, for instance, and human hormones downstream of a sewage plant.

Hedrick Belin, the conservancy's president, said that the best solution to the problem was to try to keep these chemicals out of the water in the first place. That, he said, could entail increased testing to figure out which chemicals have hormone-mimicking properties or installing measures to keep animal waste from washing downstream.

The report said it's also unclear what these chemicals mean for the health of people in the Washington area, where the Potomac is the original source of much of the region's tap water.

Hormone-mimicking chemicals "don't set our river on fire. They don't wash up onshore. We're not seeing them; we're not able to smell them," Belin said. "But the intersex fish . . . is a clear signal that something is wrong."

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