Toxicokinetic interactions and survival of Hyalella azteca exposed to binary mixtures of chlorpyrifos, dieldrin, and methyl mercury.

Chemical mixture interactions of chlorpyrifos, dieldrin, and methyl mercury were evaluated in Hyalella azteca. Survival of adult and juvenile organisms was evaluated following exposure to individual chemicals and in binary combinations. Binary interactions of the model chemicals on survival of adult and juvenile H. azteca were evaluated by concentration-response curve analysis as additive, synergistic, antagonistic, or independent. Chlorpyrifos and methyl mercury interacted additively, while dieldrin interacted independently with both chlorpyrifos and methyl mercury. Toxicodynamic interactions were evaluated by measuring accumulation and elimination of each model toxicant in the presence of a second toxicant. Chlorpyrifos significantly increased the amount of methyl mercury accumulated in the first 12 h of exposure. Dieldrin did not interact with chlorpyrifos or methyl mercury in the accumulation or elimination experiments. Accumulation of chlorpyrifos was not observed. Results of the current investigation demonstrate that chlorpyrifos and methyl mercury interact additively, which would otherwise be predicted to act independently.