Establishment of a simple cleanup procedure and bioassay for determining 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity equivalents of environmental samples

The study was aimed at establishing a bioassay for the determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity equivalents (TEQs) in environmental samples. Specifically, development of a rapid cleanup procedure adapted to the needs of the bioassay and simplification of the measurement of its endpoint, the induction of 7-ethoxyresorufin O-deethylase (EROD) in rat H4IIEC3/T hepatoma cells, were desired. The results indicate that a single 'sandwich' column suffices to remove substances that may interfere with the bioassay from extracts of various environmental matrices such as sewage sludge, compost, soil, sediment, fly ash, tissue filter dust, and fire residue. The cumbersome conventional in vitro assay for EROD activity on cells exposed to the test material in culture plates could readily be replaced by a simple assay on intact cells grown and treated in 96-well microtiter plates. TEQ values obtained from the bioassays were consistently higher than those derived from chemical analysis of dibenzo-p-dioxins/furans and biphenyls by a factor of 1.5-3.0 depending on the matrix used. The results indicate that this bioassay, which combines a simple cleanup and a rapid procedure for measuring biological effects, offers a cost- and time- effective alternative to chemical analysis when screening large numbers of samples from complex environmental matrices.