The acute effect of toxaphene and the dechlorinated products that are formed in reducing sediments were determined for two estuarine fish, spot (Leiostomus xanthurus) and white mullet (Mugil curema). The reductively dechlorinated mixture was prepared by incubating toxaphene with anoxic salt marsh sediment for 3 wk and isolating the products, which were analyzed by packed and glass capillary gas chromatography. The 96-h LC50 (flow through) for toxaphene was 0.92 and 2.88 μg/L for spot and mullet, respectively, agreeing well with reported toxicities for the two species. Sediment-degraded toxaphene was almost as toxic to spot (LC50 = 1.10 μg/L) as the parent pesticide, while mullet were about three times more susceptible to the degraded form (LC50 = 1.02 μg/L). Bioaccumulation was similar for both forms of toxaphene, with factors of 2000–6000 over the 96-h exposure period.

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