By Andrew McGlashen
Environmental Health News
Straddling the brawny sweep of the St. Lawrence River, where New York, Quebec and Ontario meet, the territory called Akwesasne has long provided fish that feed the 12,000 members of the Mohawk Nation there.
But the junction of their ancestral legacy with their region’s industrial legacy has exposed the Mohawk to high levels of polychlorinated biphenyls, or PCBs.
Now research suggests that the human health risk and gender-bending potential of these widespread and long-lasting pollutants are greater than previously recognized, and the Mohawk aren’t the only ones who should worry.
Mounting evidence has shown that PCBs mimic estrogen, a female sex hormone, and can cause male bodies to develop feminine characteristics.
But the chemicals can induce a previously undiscovered double-whammy by also hindering the production of testosterone, the chief male sex hormone, according to the study, published online in May in the journal Environmental Health Perspectives.
Low testosterone can alter development of the reproductive system of young males and reduce sperm counts, perhaps impairing fertility.
“The punchline is pretty clear: The higher the exposure to PCBs, the lower the testosterone in men,” said senior author David O. Carpenter, director of the Institute for Health and the Environment at the University of Albany.
The latest finding is part of a two-decade project in which Carpenter and other researchers at universities in New York have examined an array of possible health effects among the Mohawk from exposure to the PCBs that pollute the Akwesasne territory and nearby areas.
The blood of 703 Mohawk adults, including 257 men, was sampled to investigate the effects of pesticides and PCBs, industrial compounds that were commonly used until banned in the late 1970s. PCBs have been shown to impair brain development and thyroid function, and increase the risk of cancer, diabetes and heart disease, among other effects, Carpenter said.
None of the three pesticides tested – hexachlorobenzene, DDE and mirex – had any obvious effect on the men’s testosterone. But the researchers found a clear link between concentrations of PCBs and the men’s hormone levels- the first study to do so in humans, according to Carpenter. Previous research with lab animals and wild animals, including polar bears, has linked high levels of PCBs with reduced testosterone. Scientists in recent years, however, have examined chemicals that mimic estrogen, with less focus on their ability to also block male hormones.
Although the new study showed a clear correlation between PCBs and testosterone, it couldn’t show that the contamination definitely caused the hormonal change, since it was undertaken in a real-world community full of variables, and not in a laboratory.
Still, the results offer the strongest evidence yet that PCBs lower testosterone, which scientists widely suspect, said Heather Hamlin, a postdoctoral fellow at University of Florida who studies the endocrine effects of environmental contaminants.
“We know for a fact that sperm concentrations have gone down in human populations over the last fifty years,” she said. “And sperm concentrations are indicators of testosterone levels, so you can go from A to B to C pretty easily.”
The researchers do not know if the men in the study have any symptoms of lowered testosterone. They did not check because the findings were unexpected. The men may still fall within the range of testosterone levels considered normal.
“The mean testosterone levels between the highest and the lowest PCB tertiles differ by about 25%, but testosterone levels in the general population do vary widely and it is not certain what effects would result from reductions in testosterone levels of this magnitude,” the authors wrote.
Previously, Carpenter’s research team found that Mohawk youth in the Akwesasne territory also have impaired thyroid function linked to the PCBs that they were exposed to in the womb and during breastfeeding. Normal thyroid activity is essential to brain development and other bodily functions.
Akwesasne is “a really beautiful spot,” said Craig Arquette, a member of the tribe who serves on the Akwesasne Task Force on the Environment, a group that assisted the researchers. “It’s a really great place to be, growing up.”
But it’s also an ideal place to study the effects of persistent contaminants such as PCBs, which were used by three aluminum foundries immediately upstream.
The chemicals have contaminated local fish and remain in sediment around the St. Lawrence and its tributaries, resulting in the area’s designation as a Great Lakes Area of Concern – one of 43 toxic hotspots identified in a water-quality pact between the United States and Canada. Some areas were designated Superfund sites, which ranked them among the nation’s most hazardous spots.
The contamination prompted government advisories in the 1980s warning against eating the area’s polluted fish, so the Mohawk had to turn away part of their heritage.
“Overall, we don’t eat as much fish as we used to,” Arquette said. “There were families that made their living on providing fish for the community. But to be providing fish that was harmful – they couldn’t do it, so they had to stop that profession.”
And while a diet with less fish means less exposure to toxic pollution, it comes with other health problems.
“People are switching from the healthier fish diet to, you know, a box of macaroni and cheese,” he said. “So that’s made it a diabetic community.”
Progress has been made in cleaning up the pollution, Arquette said, but there’s a long way to go.
Although their cultural and geographic circumstances put the Mohawk at higher risk, the levels of PCBs in their bodies are “not that much greater than the background population,” Carpenter said. “You would not be surprised to find people with similar concentrations among the general population.”
The study’s results are therefore relevant to everyone, he said, since PCBs were widely used in electrical equipment and other industrial applications. They remain in the environment for an extremely long time and can be carried thousands of miles by wind and currents.
“It is a big problem on a global scale,” Carpenter said. “The public is really not aware of how dangerous PCBs are. But the reality is that we’re doing a very poor job of cleaning up these things. Our knowledge about how dangerous they are is growing faster than their levels are decreasing.”
Long-lived as PCBs are, though, they already have been banned worldwide. That’s not the case with similar chemicals.
“I think one important point is that there are a number of chemicals that are structurally very similar and that may have similar effects,” said Jonathan Chevrier, an epidemiologist who studies PCBs and other chemicals at the University of California at Berkeley School of Public Health.
Common flame retardants known as PBDEs, for example, are widely used in computers, cell phones, furniture and other household items.
Lab animals exposed to PBDEs have some of the same effects as those exposed to the old PCBs. But scientists know less about PBDEs than they do about PCBs, Chevrier said, so it’s unclear if their human health effects are as serious.
“The levels of these chemicals have been increasing exponentially in the US and in other countries,” he added. “Since they’re structurally similar, that’s a question we need to ask.”
Andrew McGlashen is a 2009 graduate of Michigan State University’s Knight Center for Environmental Journalism.