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.