Long-term effects of chemical disasters. Lessons and results from Seveso.

Fourteen years after its occurrence (10 July 1976) the Seveso accident is still considered the prototype for chemical disasters. Thousands of persons were potentially exposed to dioxin after an uncontrolled development during the manufacture of trichlorophenol in a chemical plant. The most evident adverse health effect ascertained was chloracne (193 cases). Other reversible early effects noted were peripheral neuropathy and liver enzyme induction. The ascertainment of other, possibly severe sequelae of dioxin exposure (e.g., birth defects) was hampered by inadequate information; however, generally, no increased risks were evident. Mortality studies shed some light on the long-term effects. An unusual cardiovascular mortality pattern was reported in the exposed population. Cancer mortality findings after 10 years do not allow firm conclusions to be drawn, but are suggestive of a departure from expectations for certain types of cancer; the ongoing cancer incidence study will further explore these hypotheses. A variety of lessons were learned after this accident, and some have been incorporated into international regulations regarding industrial activities and environmental safety. This paper focuses on lessons relevant to the design and conduct of health studies in the aftermath of chemical disasters, with special emphasis given to identification of the study population, ascertainment of individual exposure, and attainment of information.