Combination ecotoxicity and testing of common chemical discharges to sewer using the Vibrio fischeri luminescence bioassay.

In order to investigate possible synergistic or antagonistic (more or less than additive) toxicity effects, mixtures of chemicals were tested in water using a microbial bioassay. Ten toxicants (3,4-dichloroaniline, 3,5-dichlorophenol, cadmium, chromium, copper, Lindane, linear alkylbenzene sulphonate, pentachlorophenol, toluene, zinc) were chosen on the basis of their common occurrence in industrial effluents within local waste water treatment plants. These toxicants also cover a wide range of modes of toxic action, namely, polar and non-polar narcosis, membrane disruption, respiratory disruption, uncouplers of oxidative phosphorylation, biochemical disruption and enzyme inhibition. Efficient screening for possible combination toxicity between toxicants involved testing the chemicals both singly and in triplet combinations. The triplets were based on four replicates of a balanced incomplete block design (BIB). A standardised Vibrio fischeri rapid toxicity bioluminescence assay was used. The combinations tested showed that only one mixture was found to be significantly more toxic than expected from the pure single-toxicant results. Two triplets were significantly less toxic. Further tests on the more toxic triplet showed that the effect was due to only one of the 45 pairs originally screened. It is concluded that synergistic effects in combinations of toxicants are rather rare in bioluminescence systems utilising common effluents discharged to sewer.