Birth defects in the Seveso area after TCDD contamination.

A study on the frequency of birth defects was conducted in the area around Seveso, Italy, which was contaminated by 2,3,7,8-tetrachlorodibenzo-p-dioxin in July 1976; this has been the largest population ever exposed to dioxin. From Jan 1, 1977, to Dec 31, 1982, a total of 15,291 births (still and live) were examined, and malformations were reported to an ad hoc birth defects registry. In the most highly contaminated area, 26 births were observed. None of these infants had any major structural defect. Two infants had mild defects. The frequencies of major defects detected in the areas of low or very low contamination were 29.9/1000 and 22.1/1000, respectively. A frequency of 27.7/1000 was registered in the control area. Relative risks were calculated for specific categories of birth defects and for grouped malformations. Although the data collected failed to demonstrate any increased risk of birth defects associated with 2,3,7,8-tetrachlorodibenzo-p-dioxin, the number of exposed pregnancies was not big enough to show a low and specific teratogenic risk increase.