Canadian Community Sees Significant Decline in Proportion of Male Births

Newswise — There has been a precipitous decline since 1994 in male births in the Chippewas of the Aamjiwnaang First Nation community near Sarnia, Ontario, Canada, according to a study accepted today for publication in the peer-reviewed journal Environmental Health Perspectives (EHP). The community studied lives on reserve land in the St. Clair River Area of Concern, immediately adjacent to several large petrochemical, polymer, and chemical industrial plants.

After the community expressed concerns about an apparent decrease in male births, researchers analyzed live birth records from 1984 to 2003. They discovered that from 1984 to 1993, the community's sex ratio was stable and within expected parameters. But starting in 1994, the percentage of male births began to decline sharply, and the significant drop-off continued through 2003.

Sex ratio—the proportions of male and female births within a population—is a key indicator of the reproductive health of a population. Worldwide, between 50.4% and 51.9% of births are males, and this percentage is typically very stable. For Canada it is generally reported that 51.2% of births are male. In the 10-year period from 1994 to 2003, the proportion of male births in the Aamjiwnaang community steadily declined, accounting for only 41.2% of births. In the five years from 1999 to 2003, the decline was even more pronounced, totaling only 34.8% of births.

"Although normal variation in sex ratio can be expected in any population, especially with a small sample size, the extent of the sex ratio deviation appears to be outside the range of normal," the study authors write.

Ongoing studies of the St. Clair River Area of Concern have found changes in the sex ratios and reproductive ability of fish, bird, and turtle populations, which are thought to be due to exposures to endocrine-disrupting chemicals (EDCs).

While the present study does not seek to determine the presence of chemicals such as EDCs and the extent to which those factors may have contributed to suddenly shifting sex ratios, a 1996 assessment of the soil and sediment conditions in the reserve land found "high concentrations of several contaminants."

The authors suggest further study to analyze potential causes for the decline in male births.

"Although there are several potential factors that could be contributing to the observed decrease in sex ratio of the Aamjiwnaang First Nation, the close proximity of this group to a large aggregation of industries and potential exposures to compounds that may influence sex ratios warrants further assessment into the types of chemical exposures for this population," the authors write.

The lead author of the study was Constanze A. Mackenzie of the University of Ottawa. Other authors included Ada Lockridge and Margaret Keith. Funding for the research was provided by the McConnell Foundation, Ecosystem Health Program, Faculty of Medicine, University of Western Ontario. Find the article free of charge at http://ehp.niehs.nih.gov/docs/2005/8479/abstract.html .

EHP is published by the National Institute of Environmental Health Sciences, part of the U.S. Department of Health and Human Services. EHP is an Open Access journal. More information is available online at http://www.ehponline.org/. Brogan & Partners Convergence Marketing handles marketing and public relations for EHP, and is responsible for the creation and distribution of this press release.