[Is it possible to use sex ratio at birth as indicator of the presence of endocrine disrupters in environmental pollution?].

The sex ratio at birth (male births/total births) seems to be influenced by both biological and environmental factors. Endocrine Disrupters such as dioxin, DBCP and other pesticides have been studied as possible determinants of the decline in the sex ratio observed in some western countries. High serum concentration of dioxin in about two hundred fathers exposed during the well-known Seveso accident (1976), have been found associated with a significant decline in male births. The present study examines the possible variation of the sex ratio at birth in the offspring of the entire populations residing in the municipalities around the site of the Seveso accident. We observed a reduction of male births in the eight years following the accident (1977-1984) in the two municipalities with the highest level of contamination (Meda and Seveso). This effect was no longer detectable in the subsequent decades. No reduction in the sex ratio was observed when all considered municipalities are grouped in three exposure categories, according to their distance from the centre of the contaminated area. It is concluded that variations of the sex ratio may be detected only in populations with high exposure to dioxin, but this effect is concealed when the analysis of the sex ratio is based on large populations, with lower levels of exposure.