THE SEVESO STUDIES ON EARLY AND LONG-TERM EFFECTS OF DIOXIN EXPOSURE - A REVIEW

The industrial accident that occurred in the town of Seveso, Italy, in 1976 exposed a large population to substantial amounts of relatively pure 2,3,7,8-tetrachlorodibenzo-p-dioxin. Extensive monitoring of soil levels and measurements of a limited number of human blood samples al lowed classification of the exposed population into three categories, A (highest exposure), B (median exposure), and R (lowest exposure). Ea rly health investigations including liver function, immune function, n eurologic impairment, and reproductive effects yielded inconclusive re sults. Chloracne (nearly 200 cases with a definite exposure dependence ) was the only effect established with certainty. Long-term studies we re conducted using the large population living in the surrounding nonc ontaminated territory as reference. An excess mortality from cardiovas cular and respiratory diseases was uncovered, possibly related to the psychosocial consequences of the accident in addition to the chemical contamination. An excess of diabetes cases was also found. Results of cancer incidence and mortality follow-up showed an increased occurrenc e of cancer of the gastrointestinal sites and of the lymphatic and hem atopoietic tissue. Experimental and epidemiologic data as well as mech anistic knowledge support the hypothesis that the observed cancer exce sses are associated with dioxin exposure. Results cannot be viewed as conclusive. The study is continuing in an attempt to overcome the exis ting limitations (few individual exposure data, short latency period, and small population size for certain cancer types) and to explore new research paths (e.g., differences in individual susceptibility).