The proportion of male babies being born in the United States and Japan has been steadily declining since 1970, according to a report published in June.
In the United States there has been an overall drop of 17 males per 10,000 births; in Japan there has been a decline of 37 males per 10,000 births. In addition, the proportion of fetal deaths that are male rose from just over half to nearly two-thirds between 1972 and 1999. Epidemiologist Devra Davis of the University of Pittsburgh Cancer Institute and her colleagues analyzed the figures, drawn from statistics compiled by the U.S. National Center for Health Statistics and the Japanese Vital Statistics Bureau.
Davis can’t say why the shift is occurring, but she suspects the cause is exposure to estrogen-mimicking chemicals in the environment: so-called metalloestrogens like arsenic and mercury, as well as pesticides, solvents, plastics, including phthalates (see story #42, page 46), and PCBs. That suspicion is borne out by a 2004 study of four areas in the Russian Arctic in which the ratio of female to male births was an astonishing 2.5:1 in women who had more than four micrograms of PCB per liter of blood.
A further study in October of last year found an average ratio of female to male births of 54:46 in about 90 Canadian communities, a shift that James Argo of the IntrAmericas Centre for Environment and Health in Ontario attributes to dioxin pollution from nearby oil refineries, metal smelters, coke ovens, and pulp mills.
“Something is affecting the ability of parents to make boy babies,” Davis says. “It’s part of a growing mosaic that is identifying serious problems in reproductive health that really do require further examination and explanation.