Induction of aryl hydrocarbon hydroxylase (AHH) activity in rat hepatoma cell line serves as a simple and rapid method to detect minute (pg) amounts of certain classes of compounds, e.g., dibenzo-p-dioxins, dibenzofurans, and biphenyls. This method may provide a quick screen for such substances in extracts from foods prior to chemical identification. AHH activity is measured by conversion of benzo[a]pyrene (BP) to 3-hydroxy BP in homogenized cell extracts from control and treated cultures and is reported as pmol product formed/mg protein/min. Substances screened by this method include polyhalogenated analogs of dibenzo-p-dioxin (24 compounds), dibenzofuran (11 compounds), biphenyl (7 compounds), and extracts from several food sources. Response of the most reactive compound, 2,3,7,8-tetrachlorodibenzop- dioxin (TCDD) was used to prepare a standard curve, and the AHH activity induced by mole doses of test substance is reported as an ED50 response (the estimated dose needed to produce 50% maximum enzyme induction). The AHH activity induced by food extracts is equated to the standard curve and reported as TCDD equivalents. A potent ED50 response in cell culture appears to correlate well with known toxic responses in other mammalian and avian systems for certain test substances. This correlalation suggests that the cell culture enzyme induction method is a useful model for screening food extracts that are suspected to be contaminated with polychlorinated planar substances. A collaborative study would demonstrate the reproducibility of the method.

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A sensitive biological test to detect the presence of certain contaminants, such as highly toxic halogenated dioxins, dibenzofurans, and biphenyls in foods, was applied to extracts of fresh water fish that had been prepared by a food extraction-cleanup procedure developed by the Food and Drug Administration for pesticides and industrial chemicals. Aryl hydrocarbon hydroxylase (AHH) activity in a rat hepatoma cell line was used as the biological detection system for residues that induce enzyme activity. The induction of AHH activity by the extracts was compared with a standard AHH-induction curve for the most active compound known, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and results were computed as TCDD equivalents. Several dilutions of fish extracts were used to produce AHH-induction curves from which an optimal dose-response range was determined and used to estimate TCDD equivalents. Cleaned-up extracts of fish obtained from different water bodies in the United States were examined for AHH activity. The samples which had low levels of polyhalogenated contaminants produced low biological activity, while a higher activity was obtained from fish that contained higher levels of polyhalogenated contaminants. The results suggest that the fish extracts can be screened for AHH inducers before chemical analysis.