Mothers and children of a First Nations tribe living in one of Canada’s most industrialized regions are highly exposed to estrogen-blocking chemicals, according to a new study.

The research is the first to confirm the Aamjiwnaang community’s fears of elevated exposure to pollutants, and it may help shed some light on why the tribe has an unusually low percentage of baby boys.

The findings do not prove that chemicals are causing fewer baby boys in the community, but they provide some limited evidence suggesting a possible link.

“While we’re far from a conclusive statement, the kinds of health problems they experience – neurodevelopment, skewed sex ratios – are the health effects we would expect from such chemicals and metals, ”said Niladri Basu, lead author of the study and associate professor at McGill University in Montreal.

The reservation is within 15 miles of “Chemical Valley,” a region along the U.S.-Canada border near Lake Huron with more than 50 industrial facilities, including oil refineries and chemical manufacturers.

Forty-two pairs of Aamjiwnaang mothers and children were tested for the study. For four types of polychlorinated biphenyls (PCBs), the average levels found in the children ranged from 2 to 7 times higher than the average Canadian child. The mothers’ average levels were about double the Canadian average for three of the compounds.

PCBs were widely used industrial compounds until they were banned in the 1970s in the United States and Canada because they were building up in the environment.

Eating fish is the most common exposure route for PCBs. But a survey revealed the community eats very little fish, so the high levels of PCBs remain “a puzzle,” Basu said. He suspects the chemicals are still in the soil and air from decades ago.

The Aamjiwnaang First Nation community has about 2,000 tribe members, with about 850 living on the reservation near Sarnia, Ontario, just east of Michigan’s thumb across the St. Clair River. The name Aamjiwnaang means “at the spawning stream,” a nod to the tribe’s rich historical relationship with the nearby river and its fish. Fish advisories warning of contamination have been ubiquitous there since the 1970s.

The tribe received international attention in 2005 when scientists reported that baby boys accounted for only 35 percent of births there compared with 51.2 percent nationwide. The University of Ottawa researchers concluded that the decline may “partly reflect effects of chemical exposures.”

The new study reported that the types of PCBs that are elevated in the Aamjiwnaang community are the same types linked to reduced male births in a small study of women in New York.

“I'm struck by the elevated PCB levels,” said Nancy Langston, a professor of environmental history at Michigan Technological University who was not involved in the study. “And the fact that all are anti-estrogenic.”

Some PCBs are anti-estrogenic, which means they block the hormone, while others are estrogenic, which means they mimic it.

Hormones are necessary for proper fetal development but it’s not understood how, or if, hormone-disrupting chemicals in the environment may alter human sex ratios.

The new study was small and didn’t investigate any health problems, so it’s important to not jump to any conclusions, said Shanna Swan, a professor and vice-chair for research and mentoring at the Icahn School of Medicine at Mount Sinai.

“Chemicals have been linked to altered sex ratios. But things like stress can alter ratios, too,” Swan said.

No one has studied the tribe’s sex ratio since the original research, which was based on births from 1999 through 2003. Swan surveyed the community to see if there was interest in a follow-up study. The answer was no.

“There was sensitivity to outsiders coming in and studying them. There’s no question there’s exposure, it’s clearly a polluted place. But this is their ancestral home … what do they get out of you telling them how badly off they are?” said Swan, who specializes in reproductive effects of environmental chemicals.

In addition to PCBs, the mothers and children had elevated levels of cadmium, some perfluorinated chemicals and the pesticides hexachlorocyclohexane and DDT compared with the Canadian average.

Sharilyn Johnston, environmental coordinator of the tribe’s health and environment committee, said the findings were somewhat expected, stoking a fear that already has changed Aamjiwnaang.

“There’s a constant odor issue, many people just do not want to be outside,” she said. “We used to be able to go into areas to hunt and fish that are now blocked off with fence lines that say ‘No Trespassing.’ Centuries of industrial development have impacted traditions and land use.”

In addition to the skewed sex ratio, 23 percent of Aamjiwnaang children have learning or behavioral difficulties– a rate about six times higher than children in a neighboring county, according to a 2005 community study.

The asthma rate for children on the reservation is about 2.5 times higher than the rest of the county, according to a 2007 study by Ecojustice, a Canadian environmental organization.

Birth complications also are commonplace. Of 132 women surveyed in the community in 2005, 39 percent had at least one stillbirth or miscarriage. The average for U.S. women is 15 percent, according to the National Institutes of Health.

As oil sands production ramps up in Canada, there’s fear that Aamjiwnaang’s problems will worsen, Basu said.

Enbridge, an energy transport company, wants to boost and reverse the flow of a pipeline that currently runs from east to west across Canada, in part to send oil sands petroleum to refineries in in Ontario and Quebec, according to a company press release.

Suncor Energy’s Sarnia refinery already expanded its capacity to bring in crude from Alberta oil sands in 2007 as part of a $1 billion upgrade. Oil and gas investment in the oil sands – mostly located in northern Alberta – has increased from $4.2 billion in 2000 to about $26.9 billion in 2012, according to the Alberta Energy Department.

Langston said the oil sands activity would “without a doubt” compound the problems for Aamjiwnaang and other indigenous communities in both Canada and the United States.

Areas experiencing a boom in petrochemical refining are already experiencing health problems. Men in Fort Saskatchewan – downwind of refineries and chemical manufacturers and oilsands processors – suffer from leukemia and non-Hodgkin lymphoma at higher rates than neighboring communities, according to a new study. Two known carcinogens – butadiene and benzene – were found at higher levels in rural Fort Saskatchewan than in many of the world’s most polluted cities, the authors wrote.

Isobel Simpson, lead author of the study and a chemist at the University of California, Irvine, said it is not clear if the oil sands boom has spread its reach to Sarnia yet. But she and the co-authors have been advocating for a more cautious approach as refining communities increase production.

“Things are really starting to ramp up. Fort Saskatchewan and other communities are frustrated with pollutants and have been trying for years to be heard,” Simpson said. “We are pushing for a more prudent approach, one that seeks to reduce known carcinogens and other harmful contaminants.”

Johnston said the tribe’s focus remains on the more immediate problems.

“We continue to go to the regulators – they’re the ones who are allowing these pollutants to be released,” she said. “They’re the ones who can refine and set standards that reduce pollution among our people.”

Basu wants to conduct more research – including a larger sample and examining more health data. But it will take time, money and continued trust from a tribe that has long felt slighted by outsiders. The Ministry of the Environment directed media requests to the Aboriginal Affairs and Northern Development Canada, which did not return requests for comment.

“The community has been complaining about health problems and pollution for decades,” he said. “We’d like to get to a point where we can look at a certain chemical and say ‘that’s causing these health problems.’”

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.