Are chemicals the culprit?
UPdate Summer 2007
The case of the missing boys is drawing international attention. Over the past three decades, the birth rate of boys has dropped. The most dramatic case was found near Sarnia, Ontario, in a native community surrounded by petrochemical plants. In the community of Aamjiwnaang, the number of boys born since the mid 1990’s has decreased at a rate never before seen anywhere in the world. Twice as many girls as boys are now being born in Aamjiwnaang. In the US and Japan, over a quarter of a million boys are missing, compared to the 1970 sex ratio of boys to girls.
Dr. Devra Davis, lead researcher of a US-Japanese study into the skewed birth rates, believes that the imbalance may be a result of widespread exposure to hormone-mimicking pollutants. She believes that exposure to these industrial pollutants by pregnant women, and by men before they help conceive, may contribute to the imbalance.
“We hypothesize that the decline in sex ratio in industrial countries may be due, in part, to prenatal exposure to metalloestrogens and other endocrine disrupting chemicals,” the study states. This chemical category includes some pesticides, dioxin, and methylmercury. Methylmercury is a pollutant generated by coal-fired power plants and other industrial sources. It is commonly found in seafood.
In an interview with Martin Mittlestaedt of the Globe and Mail, Dr. Davis, stated that while the cause of the decline in male births isn't known, it could be linked to a number of other male reproductive problems which are also increasing. These include falling sperm counts and rising rates of testicular cancer. Davis said that during fetal development males may be more sensitive to pollutants that mimic hormones, leading to increased fetal deaths and reproductive problems later for the surviving males, the Globe and Mail reported.
Dr. Davis is director of the Center for Environmental Oncology at the University of Pittsburg, which focuses on possible environmental causes of cancer. The study, conducted by researchers in the US and Japan, was published in April 2007 in Environmental Health Perspectives.
Male vulnerability to hormone mimicking pollutants is not a problem unique to humans. A Swedish study found that frogs which began life as male tadpoles were changed into females by exposure to pollutants which mimic estrogen. The pollutants were similar to those presently detected in bodies of water in Europe, the US and Canada.
Researchers exposed tadpoles to the pollutants in varying doses. Tadpoles exposed to the weakest concentration were twice as likely to become female than the average. Of those exposed to the heavier dose, 95-100% became female.
An earlier US study found sex-reversal of male frogs which were exposed to a single pesticide that produced estrogen-like compounds.
"The results are quite alarming," said co-author Cecilia Berg. "We see these dramatic changes by exposing the frogs to a single substance. In nature there could be lots of other compounds acting together."
"Pesticides and other industrial chemicals have the ability to act like estrogen in the body," Berg said. "That is what inspired us to do the experiment.
The frog study is published in the May issue of Environmental Toxicology and Chemistry.
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