Interaction of cadmium and benzo[a]pyrene in mummichog ( Fundulus heteroclitus): Effects on acute mortality

Mummichog ( Fundulus heteroclitus), a common estuarine fish species, were exposed to cadmium (Cd) and benzo[a]pyrene (BP) to study the effects of single and combined exposure on acute mortality. Experiments were performed to establish acute, 14 day LD 50 values for Cd and BP after intraperitoneal injection. Combinations of 5.6–56 mgkg −1 BP and 0.1–10mgkg −1 Cd were injected concomitantly to investigate interactive effects on mortality. The calculated LD 50 value for BP was 35.7 mgkg −1 (95% confidence interval (c.i.): 29.3–43.6), the LD 50 value for Cd was 6.5 mgkg −1 (95% c.i.: 4.4–9.5). Based on the LD 50 values, toxic units were calculated for the combined dosages of Cd and BP. The results showed that when Cd was dosed at sublethal levels together with lethal BP doses, mortality was lower than expected. When BP was dosed at sublethal levels with sublethal Cd doses, mortality was higher than expected. These results indicate that, depending on the concentrations of the compounds, both synergistic and antagonistic effects can occur when mummichog are exposed to a combination of Cd and BP. Possible mechanisms for these interactive effects may include the inhibition of P450 by Cd and the inactivation of metallothioneins by reactive BP metabolites.