The far-reaching Endocrine Disruptor Screening Program dates to 1996, when Congress ordered the EPA to begin testing chemicals for their potential to interfere with the human endocrine system. By some accounts the legislation was prompted by the publication earlier that year of a book titled Our Stolen Future. Called “an environmental thriller” by The Washington Post, the book, by two zoologists and an environmental journalist, called attention to a longtime concern of environmentalists: failing wildlife populations and strange deformities in the offspring of those that survived. For instance, there was a massive die-off of alligators after a 1980 pesticide spill in Florida’s Lake Apopka. Studies later found deformed sex organs in the offspring of the remaining gator population, even after tests showed the water in the lake to be apparently clean. Mink ranchers in the Great Lakes region who fed their animals local fish began noticing that the females weren’t producing pups, a problem later linked to PCB contamination. In California researchers found what came to be known in the press as “gay gulls”: same-sex seagull couples shacking up together in the nest, protecting eggs with abnormally thin shells that often harbored dead chicks. DDT was the suspected culprit.
Because of genetic selection, chemicals that might be harmful to humans might be judged nonharmful to the rat.
Confronted with these findings, scientists began to wonder whether small quantities of synthetic chemical compounds found in our food and water—and in everyday products like makeup, plastics, and bug spray—could be sabotaging human fertility, undermining our immune systems, or affecting prenatal development. When the public got wind of the possible threat and started demanding answers, the EPA’s Endocrine Disruptor Screening Program was born.
Twelve years and $76 million later, not a single chemical has been screened by the EPA for its potential to scramble male, female, and thyroid hormones. Before screening could begin in earnest, the agency had to make sure that the protocols used in the screens would be reliable and reproducible. In this validation phase, studies were conducted at several labs using the same protocol, with the results then compared to ensure that the screens are replicable across labs. In this preliminary phase, several rat strains were used, including ones known as Long-Evans Hooded and Wistar, but Sprague Dawley was always the top pick.
During the validation studies, Sprague Dawley and other strains were housed in polycarbonate cages with wire lids. In some tests their life spans were brief—around six to eight weeks. Juvenile males were dosed with chemicals, then decapitated and examined. Pubescent males and females were injected with atrazine and myriad other chemicals, then had ovaries removed and studied, tiny testicles weighed, and kidney and thyroid glands checked for toxic effects.
A 2003 white paper commissioned by the EPA notes that because companies have for decades conducted these kinds of tests on Sprague Dawley, there is a large database of information on them that is lacking for other strains. But a “reviewer’s appendix” to the white paper—in which an independent scientist is asked to critique the report—argues that Sprague Dawley may be a poor choice for endocrine disruptor screening because the animal was bred to be resistant to known environmental toxicants. Written by research geneticist Jimmy Spearow, then at U.C. Davis, the appendix presented evidence that other rat strains, including Fischer 344, were more sensitive to more chemicals than was Sprague Dawley. “Compared with several other strains that have been studied, the strain that is least sensitive to the most endocrine-disrupting chemicals has been identified, and the EPA is planning to use it in the screening assays,” says Spearow, now a staff toxicologist for the California EPA; he emphasizes that this is his personal opinion, based on previous work conducted at Davis. In 2007 the EPA finally acknowledged there was reason to believe that Sprague Dawley might be less sensitive to certain endocrine tests, which made critics like Spearow wonder what other toxic effects the rat had failed to catch all those years.
Which rat to use in the EPA study isn’t the only thing being fought over. There has been a pitched battle between the chemical industry and its many critics regarding the Endocrine Disruptor Screening Program itself, with some industry representatives questioning the very premise that endocrine disruption is a human health risk. At a recent industry-sponsored workshop on the endocrine disruptor program that included representatives from Procter & Gamble, Monsanto, the American Chemistry Council, and Dow, one speaker repeatedly prefaced the phrase “endocrine disruptor” with “quote unquote.”
“There will always be different interpretations of science,” says Angelina Duggan, an original member of the EPA advisory panel and today a managing scientist at Exponent, a chemical industry consulting firm. “Whether this issue is more emotion or science remains to be seen.”
