The effects on mitochondrial respiratory parameters of heavy metals, such as Cu, Ni, Pb, Cd, Zn, Ag, Hg, were recorded by using thein vitro response of submitochondrial particles (SMP) from beef heart mitochondria.
The toxicity of these elements was estimated by determining their effects on the energy-coupled reverse electron transfer (RET), which is induced by ATP and succinate at first site level of the respiratory chain in SMP.
The RET rate was easily monitored by recording spectrophotometrically at 340 nm the production of NADH, arising from the reduction of exogenous NAD+ by RET.
The toxicity values were expressed as the toxicant molar concentration which decreases the rate of reduction of NAD+ to an extent of 50 percent (EC50). The toxicity increased in the following order: Ni2+<Pb2+<Zn2+< Cd2+<Hg2+<Cu2+<Ag+.
The SMP data were compared with the toxicity values obtained from a variety of biological systems currently used for toxicity testing. The results obtained demonstrate that the SMP test generally provides a good estimate of metal toxicity for several fish and invertebrate species. This is demonstrated by the statistical parameters obtained in the regression analysis. The broadened 95% confidence intervals and, in particular, the poor correlations obtained for some aquatic organisms can be ascribed to the more complex metabolic interactions and competing toxic pathways in aquatic organisms, when compared to SMP.