Investigators from the National Cheng Kung University Medical College, Taiwan, and the London School of Hygiene and Tropical Medicine, UK, studied the sex of over 2000 children born to individuals involved in the Yucheng oil accident, Taiwan, in 1979. These individuals were exposed to high concentrations of polychlorinated biphenyls (PCBs) by the ingestion of cooking oil. PCBs are more widely present at much lower concentrations.
Men exposed to PCBs before age 20 years had a 35% lower chance of having a baby boy than individuals matched for age and location who were not exposed to the pollutants. The male to female ratio for men exposed after 20 years of age was only 10% lower than in the control population; there was no significant difference in the male to female birth ratio among exposed women compared with women in the control population.
Yueliang Leon Guo comments: "The factors that determine sex are still under investigation, and the mechanisms of action that explain sex-ratio alterations are not yet understood. Sexual differentiation in human beings is controlled by genetic and hormonal factors. We propose that dioxin-like compounds might have a negative effect on the viability of the Y-chromosome carrying sperm or on the development of XY-fertilised eggs."