COMBINATION TOXICOLOGY OF COPPER, ZINC, AND CADMIUM IN BINARY MIXTURES CONCENTRATION-DEPENDENT ANTAGONISTIC, NONADDITIVE, AND SYNERGISTIC EFFECTS ON ROOT GROWTH IN SILENE VULGARIS

摘要

Using Silene vulgarus(Moench) Garcke as a test plant, the combination toxicology of Cu, Cd, and Zn was studied. Plants were exposed to single metals and binary metal mixtures in a factorial design. Root elongation after 3 d of exposure was used as a toxicity endpoint. The responses to mixtures were classihed using nonaddition, response addition, and, where possible, concentration addition as reference models. In all the metal combinations tested, the nature of the joint effect appeared to be strongly concentration-dependent. The responses were approximately nonadditive (Cu/Zn, Cu/Cd) or antagonistic (Zn/Cd) with respect to root growth inhibition as long as the concentrations of both components of the mixture were kept within the slightly toxic range. As soon as one of the mixture components exceeded a critical level of toxicity, synergism was the predominant joint effect, even when the concentration of the other component was nontoxic under single-metal exposure.further increases of the metal concen- trations eventually decreased the degree of synergism, possibly as a result of increasing antagonisms at the level of metal uptake. The strongly synergistic effects of root-internal metals in the more concentrated mixtures seemed to be due to sensitizing secondary effects other than saturation of common cellular detoxification mechanisms.