Int J Occup Environ Health. 2008 Apr-Jun;14(2):138-43.
Sex ratio changes as sentinel health events of endocrine disruption.
Study Centre for Carcinogenesis and Primary Prevention of Cancer, Ghent University, Belgium. firstname.lastname@example.org
The production and widespread use of synthetic chemicals since the 1940s have resulted in ubiquitous contamination of fish, wildlife and human populations. Since the 1960s, observers have documented major damage to wildlife reproduction across the globe, and subsequently, damage to reproductive health in exposed humans as well. The sex ratio in human communities and populations can be readily measured to ascertain whether reproductive effects, such as subtle birth defects of the reproductive tract caused by exposures to chemicals, might be occurring. Male to female sex ratios appear to be declining in populations in several parts of the globe, possibly as a result of prenatal exposures to chemicals. Sex ratio data for communities with unusual occupational or environmental exposures can be compiled using traditional epidemiological techniques in pursuit of environmental justice. Local, regional and national population health researchers and occupational hygienists can use health statistics to examine sex ratios as sentinel health events that might portend patterns of subtle structural birth defects of the reproductive tract and functional deficits in neurodevelopment.
Endocrine disrupting chemicals and gender
EDCs and Sex Ratios
Sex ratio–the proportion of male to female live births–is very constant on a worldwide basis, typically ranging from 102 to 108 male births for every 100 female births. In recent years, however, a number of reports have suggested that environmental and occupational exposures to EDCs may be altering the sex ratio within given human populations.
In one such study, appearing in the July 2005 edition of Human Reproduction, a group of Swedish researchers analyzed blood and semen samples from 149 fishermen to investigate whether exposure to the persistent organochlorine pollutants CB-153 (a PCB) and p,p´-DDE affected the proportion of Y- and X-chromosome-bearing sperm. They discovered that elevated exposure levels of both chemicals were positively associated with a higher proportion of Y-chromosome sperm. The researchers conclude that their findings add to evidence that exposure to persistent organic pollutants may alter the offspring sex ratio, with the higher proportion of Y-chromosome sperm likely tending to lead to a higher proportion of male births.
A study appearing in the October 2005 issue of EHP takes an epidemiologic approach to the issue. Constanze Mackenzie, a member of the Faculty of Medicine at the University of Ottawa, and colleagues report a distinct skewing of the sex ratio within members of the Aamjiwnaang First Nation community near Sarnia, Ontario. They found a severe decline in the proportion of boys born among the Aamjiwnaang over the last five years, and a lesser though still significant decline over the past ten years. Although no causal factors were determined, the authors note that the community is located in immediate proximity to several large petrochemical, polymer, and chemical plants, and that previous studies–such as those following the 1976 industrial accident in Seveso, Italy–have shown that exposure to contaminants such as EDCs can impact sex ratios within small communities near such industrial facilities. The authors suggest that further assessment should be pursued to identify potential exposures among community members. [For more details on this study, see “Shift in Sex Ratio,” p. A686 this issue.]