Short-term ecotoxicity of a mixture of five metals to the zebra mussel Dreissena polymorpha.

Abstract

Konemann (1981) observed that a mixture of a large number of organic toxicants with the same mode of action, had an additive effect on survival of fish. However, it has been suggested that the potential for addition may be reduced when sublethal instead of lethal parameters are studied (Hermens et al. 1984; Deneer et al. 1988). Furthermore, it is likely that inorganic toxicants, like metals, have different modes or sites of action. Consequently, metals may affect a specific biological endpoint differently. Therefore, it is likely to expect deviations from concentration addition when sublethal effects of a mixture of metals are determined. Indeed, studies on the effects of binary sublethal metal mixtures found such deviations from additivity, either less or more than concentration addition (Mohan et al. 1986; Van Gestel and Hensbergen 1997; Weltje, 1998). Kraak et al. (1994a), studying the effects of binary metal mixtures on the filtration rate of the zebra mussel (Dreissena polymorpha), also observed more as well as less than additive effects. However, a mixture of three metals (Cu, Zn and Cd) was concentration additive. Although this could be purely incidental, it could also be argued that the deviations from concentration addition were “averaged out” in a mixture consisting of more than two metals. Based on the latter assumption, it could be suggested that a mixture of several metals is not likely to deviate from additivity. However, when the number of compounds in a mixture increases, the concentration of the individual compounds decreases. This may imply that in such a mixture essential metals (Cu, Zn, Ni) do not, or to a lesser extent, contribute to the toxicity of the mixture, because low concentrations of essential metals are under metabolic control (Amiard