small native community living in the shadows of Sarnia's chemical
valley has had an unusual distinction: Researchers believe it has one
of the most skewed sex ratios in the world.
For reasons that are not known, the percentage of male births in the
community, known as the Aamjiwnaang First Nation, began to fall
precipitously in the mid-1990s. By 2003, newborn girls outnumbered boys
by about 2 to 1. It was a dramatic reversal of what is considered
normal in human populations - a modest excess of male births - the
trend that had previously prevailed on the reserve.
New figures on the reserve's birth rates presented yesterday at a
conference in Sarnia indicate that the extent of the male birth dearth
may be diminishing, although only slightly. In 2004, equal numbers of
boys and girls were born, the first time since the mid-1990s that the
reserve has had a birth ratio approaching normal. The next year,
however, the number of baby girls once again exceeded boys. Figures for
2006 are not yet available.
Margaret Keith, one of the researchers who compiled the data,
cautioned in an interview that annual figures comparing the number of
male to female births in a small population can be volatile, but the
longer-term trend to fewer male births seems to be persisting.
"Because we only have a year ... where it doesn't look too far off,
I just think it's too early to draw any conclusions" that the area is
returning to a normal birth ratio, said Ms. Keith, a researcher at the
Sarnia office of the Occupational Health Clinics for Ontario Workers.
She said that over the past five years, only 42 per cent of births
have been male, well under the national figure of 51.2 per cent. While
she said she hopes the birth data will revert to normal "to me, it
looks like the trend is still there."
The unusual birth ratio in the community, which has major
petrochemical plants on two sides and is downwind of high-polluting
U.S. power plants, has attracted worldwide attention. There is an
international trend observed in many industrialized countries,
including Canada, the United States, the Netherlands and Japan, to
lower-than-expected percentages of male births, although the drop in
large populations is very slight.
Nonetheless, the observation that the birth ratio is changing has
fuelled speculation that long-term exposure to pollutants from
industries might be a factor. Many researchers have been looking to the
reserve for clues about the trend because it is a small community that
is easy to study where residents are likely to have above-average
exposure to many synthetic chemicals.
At the conference yesterday, organized by Aamjiwnaang and funded in
part by Health Canada, experts said that the global trend to lower than
expected numbers of male births is not fully understood, but is thought
to be firmly established because it is being observed simultaneously in
so many different places.
"This is a global issue. It's not something that's located either
just in North America or for that matter in the Sarnia area," said
Warren Foster, director of the Centre for Reproductive Care at McMaster
University. "There is a weight of evidence that says that there is
something going on."
He said the factors behind the trend "are very poorly understood,"
but that evidence has emerged linking air pollutants and hormone
exposures to these changes, among other factors.
Details on the sex ratio at Aamjiwnaang emerged in 2004, when
residents of the community began remarking that they had no trouble
fielding girls' sports teams while boys often complained of not having
friends of their sex nearby.
A peer-reviewed scientific study on the birth ratio, published the
next year in Environmental Health Perspectives and authored in part by
Ms. Keith, estimated that there was only a 1-per-cent probability that
the long period of low numbers of male births compared with females was
a statistical fluke.
The sex ratio at a nearby reserve was found to be normal, suggesting the Sarnia trend wasn't due to cultural or genetic factors.
Scientists have observed that over time, about 106 males are born
for every 100 females, a way that nature has compensated for higher
rates of mortality among boys.
Separate data presented at the conference from Lambton County's
community health services department found that from the early 1980s to
2001, there were no unusual changes in the sex ratio at birth in the
non-native community in Sarnia and surrounding areas.