A recent study found that residents of Canadian communities who were exposed to emissions from polluting industries such as oil refineries, metal smelters, and pulp mills gave birth to more females than males, a reversal of the normal sex ratio. This is likely due to high levels of common air pollutants called dioxins and is not a surprising finding, according to James Argo, a medical geographer with the IntrAmericas Centre for Environment and Health, who conducted the study. “There is a very strong association [in the scientific literature] between chronic exposure to dioxins and an inverted sex ratio,” he said.
The study is the second phase of a three-part project to examine the links between early exposure to industrial pollution and the development of cancer. In the early 1990s, Argo documented the lifetime residences of 20,000 people who had cancer and 5,000 “control” subjects who did not have the illness. The database was developed to inform research about people’s exposure to industrial pollutants throughout their lifetimes, including prenatal exposure, Argo said.
The inverted sex ratios became apparent when Argo looked at the genders of children born to parents who lived within 25 kilometers of a polluting industry. The percentage of girls was higher in all of the nearly 90 communities surveyed, and in some communities, residents gave birth to as few as 46 males for every 54 females, compared to a normal sex ratio of 51 males for every 49 females. Chronic exposure to dioxins “interferes with the process of conception,” so people who have been exposed for over 20 years or so “will have a higher probability of giving birth to females,” Argo said.
The third phase of the project will use Argo’s latest findings on inverted sex ratios to examine the documented rise in female reproductive cancers. With more females than males in a population, there is likely to be a greater incidence of breast, uterine, ovarian, and cervical cancers in that group, he explained. But male reproductive health problems are also on the rise, he noted.
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