Serum dioxin levels in Seveso, Italy, population in 1976.

On July 10, 1976, an explosion at a chemical plant near Seveso, Italy, released a mixture of chemicals, including 2,3,7,8-tetrachlorodibenzo-p-dioxin and 2,4,5-trichlorophenol. As a result, several thousand people in the Seveso area may have been exposed to those chemicals. At that time, human exposure assessment was based primarily on soil levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin. Medical examinations of this potentially exposed population and control subjects were begun in 1976 and in some cases continued until 1985. In 1988, we began assessing human exposure in this population by measuring 2,3,7,8-tetrachlorodibenzo-p-dioxin in small volumes of serum specimens remaining from the medical examinations. As expected, we found that the median serum dioxin levels were highest among people who lived closest to the explosion and were progressively lower among groups living farther away. These measurements have allowed us to assess exposure more accurately among individuals in this population and to relate exposure to various health effects. We found that some individuals in the exposed population had among the highest serum dioxin levels ever reported, yet chloracne was the only unequivocal effect found; cancer risks are still being investigated. We also found that other individuals with as high or higher serum dioxin levels did not develop chloracne. We also found that the serum half-life of dioxin in this population was 7-8 years, which agrees with other findings although we do report some differences in the serum half-life of TCDD for women and children. We also observed an increase in the percentage of female newborns to parents who resided in Zone A at the time of the explosion, and we also report on the 1976 serum dioxin levels in people who later developed cancer.

Serum concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin and test results from selected residents of Seveso, Italy.

2,3,7,8-Tetrachlorodibenzo-p-dioxin levels (TCDD) were measured in serum specimens from Seveso, Italy, residents, who were potentially highly exposed to the 1976 explosion, and in controls. The residents were chosen so as to represent those who did and did not develop chloracne. Levels of TCDD as high as 56,000 parts per trillion (ppt) were found in these serum specimens that were collected in 1976. These TCDD levels are the highest ever reported, and yet almost all clinical laboratory tests on these individuals were normal; any abnormal test result was only transitory in nature. These findings are unique in linking clinical histories to TCDD levels following an acute exposure.

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.