NEW ORLEANS On any given day, some 750,000 U.S feedlots are beefing up between 11 million and 14 million head of cattle. The vast majority of these animals will receive muscle-building steroids – hormones they will eventually excrete into the environment. But traditional notions about where those biologically active pollutants end up may need substantial revising, several new studies find.

They were reported at the annual meeting of the Society of Environmental Toxicology and Chemistry, which ended Monday.

A typical feedlot cow will shed 50 pounds of urine and feces per day. These wastes may be collected in lagoons or composted for later use in fertilizing fields.

Throughout the past decade, scientists have become concerned about environmental risks that these wastes might pose if they wash, untreated, into waterways. Evidence has certainly linked waters receiving runoff from feedlots with sex alterations in fish – females that exhibit some masculinization and males that look somewhat feminized.

But indicting specific livestock hormones to such changes is proving tricky. And one reason, argues Alan Kolok of the University of Nebraska, in Omaha, is that scientists have made a number of what now appear to be questionable assumptions. Such as that the excreted hormones affecting fish will always be in the water, that downstream concentrations of these steroids will be greater than upstream values and that hormone levels in tiny streams will be more concentrated than in substantially bigger waterways.