WASHINGTON — Three weeks after an environmental group reported that herbicides are common in Midwestern drinking water, the EPA has called for a thorough examination of the chemicals to determine if they are too risky to use.
By calling for a review of the herbicides and linking them to breast cancer, the Environmental Protection Agency lands itself in the middle of an old but unresolved debate: How much risk is too much when it comes to cancer?
The evidence is there, scientists agree. Three widely applied herbicides-atrazine, cyanazine and simazine-increase the rate of breast cancer in some rats during laboratory testing. And most researchers agree that a carcinogen for rats is probably a carcinogen for humans.
But when it comes to calculating and judging relative risk, consensus falls apart.
“A carcinogen is a carcinogen,” said Marvin Legator, director of the University of Texas at Galveston’s Division of Environmental Toxicology. “Where we really have a problem is trying to put a number on it.”
The numbers reported by the Environmental Working Group in October are big. The activist group, which focuses on chemical contaminants in food and water, reported that 10.2 million people in the Midwest drink water containing two to four herbicides, and by drinking the water 3.5 million people in 120 communities are running a risk of getting cancer 10 to 100 times greater than some federal benchmarks allow.
Legator said such numbers are at best complex guesses and often “totally inaccurate.”
To arrive at cancer risk factors, researchers test varying doses of a chemical on animals, often rats.
Looking at the likelihood of cancer cases at doses ranging from massive to imperceptible, analysts adjust the numbers to represent the incidence of tumor growth for the doses a human would encounter.
“If we are forced to extrapolate from animals to people, we come up with . . . underestimates or overestimates,” Legator said. “God created risk assessors to make astrologers look good.”
Legator said it is very difficult to trace human cancers to one cause. In laboratories, chemicals are tested in animals one at a time.
“If you are exposed to a carcinogen, regardless of how small, it’s an incremental effect,” he said, and each factor-from pesticides to genes to diet-contributes to each individual’s chances of getting cancer.
“(Triazines might be) a contributing factor, but it’s only one. . . . In humans it’s (also) our genetic makeup, it’s also our lifestyle that determines whether we get cancer,” Legator said.
But Richard Wiles, vice president of the Environmental Working Group, said risk assessments are useful to determine just how toxic carcinogens are.
He said that regardless of the methods used, the federal government has set certain standards for food-standards that he said are more stringent than those for drinking water.
“Apply the standards that you have,” Wiles said.
David Baker, director of the Water Quality Laboratory at Ohio’s Heidelberg College, has another problem with the risks: They add up to what he called a “negligible” increase in cancer.
Even accepting the environmental organization’s methods, which Baker said he doesn’t, the herbicides would lead to between two and four more cases of cancer a year over 70 years, depending whether you account for just those 120 communities or for the entire region.
“If you had four additional cancers in Chicago in a year, it would not be noticed,” Baker said. “I think the risks are negligible.”
Wiles countered, however, that by translating the number of additional annual cases into the more common “lifetime” figure over 70 years, these herbicides alone would give about 200 people cancer.
“We don’t believe in negligible risks,” Wiles said.
“We think three people getting cancer a year is three too many, and that’s not necessary. There’s no need to put people’s health at risk for a surplus food supply.”