Nine production workers with a history of chloracne from exposure to polychlorinated dibenzo-p-dioxins (PCDDs) in 1971-1973 had a median level of 340 pg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) per gram blood lipid (range 98-659 pg/g) in 1990. This was significantly higher than blood levels in 4 reference subjects without chloracne and no known exposure from the same plant (median 18, range 8-28 pg/g) and in 17 external referents (median 16, range less than 5-23 pg/g). We therefore consider chloracne to be a reliable indicator of heavy dioxin exposure in a cohort of herbicide production workers and will use its former presence in 159 cases as a substitute for exposure when investigating cancer morbidity and mortality in a multicenter cohort study.

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