Abstract
Estimating internal exposure or dose of dioxins and related chemicals such as dibenzofurans and dioxinlike polychlorinated biphenyls is relatively straightforward in laboratory animals because a known dose is given and the amount absorbed can be measured. In wildlife, direct tissue measurement and measurement of environmental samples have both recently been used to estimate exposure. Until recently, human studies used only indirect indicators such as skin lesions to qualitatively estimate exposure to these chlorinated organic compounds. Environmental measurements have also sometimes been used to estimate human exposure. Dioxins in human tissue were not measured until the 1970s, when 2,3,7,8-tetrachlorodibenzo-p-dioxin was measured in mothers' milk; congener-specific measurement of dioxins and dibenzofurans in tissues (blood, milk, and adipose tissue) of the general population and exposed workers was first performed in the United States in the 1980s. Measurement in a sensitive and specific fashion of the 17 toxic dioxin and dibenzofuran congeners currently found in human tissue from industrial countries began in the 1980s. The use of known chemical standards, capillary columns, high resolution gas chromatography and mass spectrometry (GC-MS) has now become relatively common. GC-MS analysis of blood is currently accepted as the gold standard for estimating human exposure to dioxins. However, analyses are still costly and time consuming, and worldwide there are few qualified laboratories. There is currently a lack of knowledge concerning kinetics at higher and lower exposure levels for most of the toxic dioxin congeners and of levels in target tissues of concern.