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Last Edited: 3/23/2009

Sex Ratio and the Environment

How might the population sex ratio be related to the environment?

Concern regarding the influence of environmental factors upon sex ratios stems from the fact that so many persistent chemical pollutants have the potential to alter human sex hormones and their regulation.  Investigators looking at 250 years of data in Finland1 suggested that sex ratio in that country rose between 1750 and the first part of the 20th-century but has declined since.  They noted that that the decline appears to have begun prior to widespread exposure to the industrial pollutants that are of most concern today.  Other investigators have noted that the ratio varies substantially by country, possibly having to do with distances of various countries from the equator.2, 3

Other researchers have noted that the sex ratio of newborns may change near the sites of environmental disasters such as the Chernobyl accident4 and a widespread release of hexachlorobenzene in the 1950s in Turkey.5  Communities living in proximity to potential environmental hazards have reported changes in sex ratios.6  All told, scientists know little about what may cause these patterns.

1.    Vartiainen T, Kartovaara L, Tuomisto J. Environmental chemicals and changes in sex ratio:  analysis over 250 years in Finland. Environmental Health Perspectives. 1999;107:813-815.
2.    Grech V, Vassallo-Agius P, Savona-Ventura C. Declining male births with increasing geographical latitude in Europe. Journal of Epidemiology and Community Health. 2000;54:244-246.
3.    Grech V, Vassallo-Agius P, Savona-Ventura C. Secular trends in sex ratios at birth in North America and Europe over the second half of the 20th century. Journal of Epidemiology and Community Health. 2003;57:612-615.
4.    Scherb H, Voigt K. Trends in the human sex odds at birth in Europe and the Chernobyl nuclear power plant accident. Reproductive Toxicology. 2007;23:593-599.
5.    Jarrell F, Gocmen A, Akyol D, Brant R. Hexachlorobenzene exposure and the proportion of male births in Turkey, 1935-1990. Reproductive Toxicology. 2002;16:65-71.
6.    Mackenzie C, Lockridge A, Keith M. Declining sex ratio in a First Nation community. Environmental Health Perspectives. 2005;113:1295-1298.