The researchers concluded that most of this arsenic came from natural sources, including an aquifer with the toxic element that stretches underground from Southern Maryland to St. Michaels and beyond.
But beyond this aquifer, the scientists also found elevated arsenic levels in surface water and shallow ground water in the Pocomoke River area of the Eastern Shore. This arsenic probably came from manure produced by the large number of poultry farms in this area, said Judith M. Denver, a supervisory hydrologist for the U.S. Geological Survey.
Denver said it's unlikely that people in the area are drinking the arsenic, because their wells are usually fairly deep and protected by layers of clay. "It's not likely that there's a lot of arsenic from poultry in drinking water because we don't drink surface water," Denver said.
Another study, by the Maryland Geological Survey, found arsenic levels violating federal health standards in 11 percent of 250 drinking wells sampled on the Eastern Shore and elsewhere in the state. But most of the arsenic was not in shallow wells where fertilizer was likely to seep in, said David W. Bolton, chief of the hydrology program at the state agency. This suggests that the arsenic was probably not from chicken manure but from the fossilized waste of ancient marine animals, he said. "It's definitely naturally occurring," Bolton said.
But toxicologist Ellen K. Silbergeld of the Johns Hopkins Bloomberg School of Public Health said a study that she and colleagues performed on hundreds of drinking wells in Maryland found higher arsenic levels near fields that had been spread with poultry manure. "We found that the practice of land-use chicken waste disposal is associated with elevated arsenic levels," Silbergeld said. The amounts found in the study were often in excess of federal health standards, she said.
Carole Morison, whose husband's family has been raising chickens near Pocomoke City for generations, sees the use of arsenic products as an example of the unhealthy industrialization of farming.
She said she earns about $4,000 a year from the chickens she raises in two 500-foot-long yellow metal buildings, but she doesn't own the birds.
Morison and her husband own the buildings and raise the chickens under contract with Perdue. The company dictates the diet and growing conditions, including the black-out curtains over the windows, she said. This induces the birds to sleep more and avoid wasting any energy they could use to get fatter.
Outside the chicken houses are two shiny cone-shaped bins, which she said the company fills every few days. She shows a "feed order shipment form" from Perdue for 51,900 pounds of feed that lists Roxarsone as an ingredient.
"They've bred the perfect chickens," Morison said, tiptoeing through mobs of eight-day old chicks on peanut-shell bedding. "They're bred to have larger breasts, because that's the desirable meat."
Behind the chicken houses is a shed, about 110 feet long and filled with hills of manure and the corpses of diseased birds. About twice a year, the waste is hauled away by a company that sells it for fertilizer.
"The question is, where does all the arsenic go, after it passes through the chickens?" she asked. "Is it washing off the fields into the water? Is it in the dust we breathe? We don't know."