Scientists have found more intersex fish in Maryland, this time on the Eastern Shore, and their research suggests one possible source of the gender-bending condition could be the poultry manure that is widely used there to fertilize croplands.
Six lakes and ponds on the Delmarva Peninsula sampled over the past two years have yielded male largemouth bass carrying eggs, according to University of Maryland scientists. Those are the first intersex fish reported there, though researchers found the condition several years ago in smallmouth bass in the Potomac and its tributaries, and recently found it in smallmouth bass in the Susquehanna.
Intersex fish are a concern, scientists say, because they could be indicators of contaminants in the water, affecting their growth and reproduction.
The intersex condition in the Shore fish is not as severe as it is among fish from the Potomac or Susquehanna, the researchers said, but it appears to be widespread, at least in largemouth bass in the peninsula's lakes and ponds.
"We find it in every lake that we look," said Daniel J. Fisher, senior research scientist at UM's Wye Research and Education Center in Queenstown. "We found fish with intersex in all of the lakes, and the percentage [with the condition] ranged from 33 percent of fish we sampled to 100 percent."
The Maryland lakes checked were Tuckahoe in Queen Anne's County and Smithville and Williston in Caroline County. In Delaware, Hearns Pond in Sussex County and Moores Lake and McColley Pond in Kent County were sampled. The sampling was performed under a grant from the U.S. Environmental Protection Agency.
In separate laboratory tests, the UM researchers said, they found the sex and development of certain juvenile fish were affected when exposed to water contaminated with poultry waste.
Working with other scientists, the UM researchers kept three species of laboratory fish — fathead minnows, sheepshead minnows and mummichogs — for three weeks in water dosed with the sex steroids produced by female chickens. While two of the species showed little or no effect, fathead minnows displayed changes in their gonads, or sex organs, and larval minnows experienced "pronounced feminization." Assistant research scientist Lance T. Yonkos, Fisher and other colleagues reported their findings in October's Environmental Toxicology and Chemistry journal.
Fisher stressed that the steroids or hormones used in the lab tests were produced by the chickens naturally and were not substances fed to the animals.
"We've actually measured those hormones in waste material," Fisher said. The substances have been detected in Delmarva streams after spring rains, he said.
Roughly 600 million chickens are raised annually on the Delmarva Peninsula. Estimates of the waste generated by them vary, from 600,000 tons to 1 million tons or more. Much of that poultry "litter," chicken manure mixed with wood shavings, is spread on croplands as fertilizer. The EPA has identified runoff of chemical fertilizer and manure from farm fields as a major source of the pollutants fouling the Chesapeake Bay.
Concerns have been raised about the possibility that arsenic added to chicken feed by some growers could trigger such intersex conditions in fish. Arsenic, used to control parasites in chickens, is just one of a variety of chemicals found at low levels in some waters that scientists say can act as an endocrine disruptor, potentially interfering with growth, reproduction and disease resistance. Environmental activists this week declared they would renew efforts to get Maryland lawmakers to ban the use of arsenic in chicken feed in the state.
But Fisher and Yonkos said they haven't detected arsenic in runoff from manure-fertilized farm fields they sampled, and they've only picked up the toxic chemical in one batch of poultry litter they sampled directly. Yonkos noted that the poultry manure they've used in their research has come mainly from growers raising chickens for Perdue Farms. The Salisbury-based poultry company has said it stopped adding arsenic-containing roxarsone to its birds' feed several years ago.
William Satterfield, executive director of Delmarva Poultry Industry Inc., representing many of the more than 1,600 growers on the peninsula, said the laboratory setup under which fish were exposed to poultry-waste hormones "seems extreme and not representative of real-world conditions. The levels being used by the researchers seem unrealistically high."
Fisher said the levels of hormones to which fish were exposed were similar to what researchers have measured in runoff from fields. But he acknowledged that the lab tests may not mirror water-quality conditions fish experience in the wild, where pollution may come in pulses and not remain constant for three weeks at a time.
That's why, he added in an email, "We now are going to streams and lakes in the 'real' world outside the lab to see if we see anything happening there."