Toxicity of binary-metal mixtures (As, Cd, Cu, Fe, Hg, Pb and Zn) in the euryhaline rotifer Proales similis: Antagonistic and synergistic effects

Abstract

Data regarding the effects of binary metal mixtures in marine zooplankton are scarce, particularly for rotifers. We examined the toxicity of 21 binary equitoxic mixtures of As, Cd, Cu, Fe, Hg, Pb, and Zn on the euryhaline rotifer Proales similis. The toxic units (TU₅₀) revealed that 20 of these binary mixtures exhibited synergistic effects (TU₅₀ < 1.00). The AsHg mixture showed a strong antagonistic effect (TU₅₀ = 2.39), whereas the HgCu interaction exhibited a significant synergistic effect (TU₅₀ = 0.29) on P. similis. TU₅₀ values were <0.60 in all cases that showed synergism (80 %). Regarding the MIXTOX analysis, 13 binary mixtures presented some level of synergism, while two mixtures presented only additivity. Results emphasize the need for environmental agencies to revise and readjust protection guidelines for marine biota in response to the evident synergistic effects occurring at metal mixtures concentrations below the current permissible limits.

Keywords: Additivity; Antagonism; Gulf of California; Potential toxic elements; Synergism.