From the Chickens to the Crabs - The Ripple Effect: The Fate of Freshwater in the Twenty-First Century - page 61

In the spring and summer of 2003 and 2004, her team discovered more intersex bass
on the Upper Potomac, near Sharpsburg, Maryland, and along the Shenandoah River.
“There was a gradation,” said Blazer. “The South Branch, which is fairly sparsely pop-
ulated, did not have as heavy a prevalence of intersex and fish kills as the Shenandoah
did, which is more heavily populated and has more agriculture.”
In 2005, Blazer found that over 80 percent of the male smallmouth she had trapped
in the Potomac, the Shenandoah, the Monocacy, and in Conococheague Creek were af-
fected by intersex, including every single male bass at four of her six test sites. Since
then, intermittent fish kills have occurred around the watershed, but “feminized” bass
have continued to appear year after year, most often in the spring pre-spawn period.
Intersex occurs in fish species around the world: white perch in the Great Lakes,
white suckers in Colorado, spottail shiners in the St. Lawrence River, shovelnose stur-
geon in the Mississippi, sharp-tooth catfish in South Africa, three-spine stickleback in
Germany, barbel in Italy, and roach fish in Britain. There have also been reports of pan-
thers with atrophied testicles; intersex alligators, mice, and frogs; seals with suppressed
immune systems; and female polar bears that have developed penislike stumps. (In a
condition known as imposex, which is an abbreviation for “the imposition of male sex
characteristics on female organisms,” female snails and other invertebrates have, on rare
occasions, developed male organs.)
In September 2009, the USGS released the most comprehensive study of intersex
yet, which revealed that it affects species across the country—in the Columbia, Color-
ado, Mississippi, Rio Grande, Apalachicola, Savannah, Chattahoochee, and Gila Rivers,
among others. The only basin in which researchers did not find at least one intersex fish
was the remote Yukon, in Alaska, where there are few people. Of the sixteen fish species
biologists examined at 111 sites, intersex was most common in bass: a third of all male
smallmouth bass and a fifth of all male largemouth bass were found to be intersex.
What could cause male bass to develop eggs? In the scientific literature, effluents
from wastewater treatment plants in England, and runoff from paper mills in Canada,
have been the primary focus of research. But when Blazer tested fish and water chem-
istry upstream and downstream of treatment plants on the Monocacy River and Cono-
cocheague Creek—both tributaries of the Potomac—“there was no significant differen-
ce between the two,” she said, indicating that something else was to blame. She noticed
“these were all heavy agricultural areas. More and more I began to think agricultural
runoff was driving this.”
A broad spectrum of man-made compounds is suspected of contributing to intersex,
but a prime suspect is high levels of estrogen in the water. Natural estrogens are sex hor-
mones, which help to modulate animals' immune response. Synthetic estrogens come
from pharmaceuticals such as birth-control pills, or agricultural runoff loaded with