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Areas around Sarnia, Ont., that are heavily exposed to air pollution from chemical plants are having an unusual baby boom: unexpectedly high numbers of girls.

The surfeit of girls is occurring south and east of this gritty Southern Ontario industrial city, a region known as Canada's Chemical Valley, where prevailing northwest winds generally blow whatever is coming out of Sarnia's smokestacks.

Places most affected by these emissions have about 100 fewer boys under 5 than expected, according to federal census data. In one native community, the Aamjiwnaang First Nation, twice as many girls are being born as boys.

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The trend is causing a dispute among public health officials. Some fear residents are being exposed to gender-bending pollutants, while others caution that the results could reflect the normal variability of the sex of children born in small populations each year.

The association representing Sarnia's major industries wants birth data in the region of about 125,000 analyzed because it fears emissions are being blamed, without proof, for skewing the sex ratio.

"We're encouraging the appropriate authorities to do a full scientific study, not only of Aamjiwnaang, but of the community," said Scott Munro, general manager of the Sarnia-Lambton Environmental Association, a group financed by Shell Canada, Imperial Oil and 13 other large Chemical Valley firms.

Throughout much of the industrialized world, researchers have been tracking a recent decline in the percentage of boys, prompting worries that pollutants are altering birth numbers.

"Our assumption is that there is something causing . . . premature mortality" among males during reproduction, said Jim Brophy, head of Sarnia's Occupational Health Clinics for Ontario Workers.

"Males may be more susceptible to these exposures."

Sarnia is in the spotlight over the sex of children mainly because Aamjiwnaang is having one of the world's most extreme female baby booms. The reserve is also nearly surrounded by chemical plants.

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It is normal to have about 105 boys born for every 100 girls, reflecting the way nature keeps the population in balance by compensating for higher male mortality rates. But in Aamjiwnaang, twice as many girls are being born.

A study on the dearth of boys was published last month in Environmental Health Perspectives, a science journal, and it concluded the sex ratio "appears to be outside the range of normal" and is "statistically significant."

The study estimated there was only a 1-per-cent probability that the results were due to chance.

Although the study didn't look at Lambton County -- the region in which Sarnia is the largest city -- federal census data show variations from the national average depending on exposure to the plume from the plants.

Downwind areas tend to have above average proportions of girls, although no place has a surfeit as extreme as Aamjiwnaang's. Upwind areas, by contrast, have more boys, while the rate in Sarnia is slightly below average.

On the reserve, the sex ratio findings have been greeted "with fear," says Ron Plain, the spokesman for the reserve's environmental group.

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Sarnia has one of the most extensive petrochemical complexes in the world, accounting for about 40 per cent of Canada's output of such products as synthetic rubber, polyvinyl chloride and plastics. The area also is the site of one of Canada's largest hazardous-waste dumps.

About 20 of the plants have such large pollution emissions that records of the releases must be submitted to Environment Canada.

Unusual sexual attributes have also been observed in wildlife exposed to effluent from the chemical plants. In the St. Clair River, which flows through Chemical Valley, Environment Canada scientists have caught feminized male snapping turtles with diminished penis sizes.

Besides Aamjiwnaang, the lowest sex ratio was in Moore Township, a community right next to the reserve.

The census data indicate that about 100 more boys among children aged 4 and under living near the chemical plants are needed to bring the area's sex ratio to the national average. The boy shortfall is about 40 in the small reserve and 60 in the much larger non-native community south and east of the plants, out of a population of 1,640 children.

Chris Greensmith, the county's acting medical officer of health, cautions that the census data may be due to chance. A slight natural variability in the numbers of boys and girls born in a given place each year is considered normal.

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However, the trend on the reserve was so far from normal that it deserves more study. "We have to say that it raises a flag," Dr. Greensmith said. "It obviously raises questions."

The reserve's sex ratio was stable near the national average in the 10 years before 1993, but the proportion of boys has declined precipitously since. The study reviewed the birth ratio for a second nearby native community further from the plants, and it was near normal, suggesting genetics or lifestyle do not explain what is happening.

Scientists do not have a thorough understanding of what causes variability in the sex of newborns.

Gender is associated with some pollutants, such as dioxin, which causes men who are heavily exposed to father more girls. Fertility drugs cause more females to be born, as does smoking. Mercury exposure also leads to more female births.

"There is still a dispute over what is driving the sex-ratio change, whether industrial pollutants are doing it," said John Jarrell, a professor of gynecology at the University of Calgary and author of a study that found a decline in Canada's sex ratio since the 1970s.

Dr. Jarrell said those living near Sarnia's smokestacks have chronic long-term exposure to small amounts of many pollutants, rather than the high doses of a single compound that would make a link between a specific chemical and the sex ratio easier to spot. He said low-level pollution is under investigation to see if it is capable of changing hormone levels.

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If pollutants are tipping the sex ratio, scientists suspect contaminants are either altering parents' hormonal makeup or causing more prenatal male mortality. About 120 males are conceived for every 100 females, indicating that male vulnerability is high anyway during reproduction.

"Males are more representative in reproductive disasters, so they are a weaker sex," Dr. Jarrell said.

Tracking the effects

This compilation of case studies indicates how a parent's exposure to environmental hazards can affect the gender of his or her child.

Exposure type If the mother is exposed ... If the father is exposed ...
Dioxin Not documented Fewer boys born
PCBs Fewer boys born Inconclusive
Pesticides Fewer boys born Fewer boys born
Methylmercury Fewer boys born Not documented
Petroleum Fewer girls born Fewer girls born
Air pollution Inconclusive Inconclusive
Radiation Fewer boys born Inconclusive
Infertility treatment Fewer boys Not documented
Smoking Fewer boys born Fewer boys born

SOURCE: ENVIRONMENTAL HEALTH PERSPECTIVES

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