Determination of no effect levels of heavy metals for rainbow trout using hepatic metallothionein

Rainbow trout ( Salmo gairdneri) were exposed to various sublethal concentrations of a mixture of zinc, copper and cadmium for periods of time ranging from 4 to 16 weeks and the concentration of metallothionein (MT) in the livers was determined. The data were described by linear regressions of hepatic MT (with 95% confidence limits) against concentration of metal. From these data could be determined a “no observable effect” concentration for each metal at which the concentration of hepatic MT in exposed fish was not distinguishable from that in unexposed fish. The value thus determined was in close agreement with estimates of the “no observable effect” concentrations of zinc, copper and cadmium calculated for soft water by other authors. The elevation of hepatic MT in rainbow trout therefore appears to provide a useful biological response for the estimation of “no observable effects” of zinc, copper and cadmium in mixture in the natural environment.