Prediction of the toxic impact on the freshwater microalgae Scenedesmus intermedius produced by the interaction of copper sulfate and copper oxychloride in a binary mixture with glyphosate

Resumen

The high population growth worldwide causes a high demand for food with an increase in the use of different agrochemicals, with pesticides and herbicides being the primary pollutants of anthropogenic origin in the environment. One of the critical aims of ecotoxicology is the evaluation of toxic effects of mixtures of chemical substances that can have additive, synergistics or antagonistics effects in different ecosystems. For this reason, the aims of this research were to: 1) estimate the individual subchronic toxicity of agrochemicals copper oxychloride [Cu₂(OH)₃Cl], copper sulfate (CuSO₄), and glyphosate (Gly-BH) on the inhibition of population growth of the freshwater chlorophyte Scenedesmus intermedius, and 2) predict the antagonistic, synergistic, or additive behaviour of binary mixtures of Gly-BH with Cu₂(OH)₃Cl and CuSO₄ through the Combination Index Equation (CIE). The individual toxicity order at 7 days of exposure in S. intermedius was CuSO₄ (IC₅₀ 2.70 mg/l) > Gly-BH (IC₅₀ 4.03 mg/l) with no statistical differences between both agrochemicals and > Cu₂(OH)₃Cl (IC₅₀ 25.59 mg/l) with a major tolerance if it compared with the other chemicals. For the binary mixture of CuSO₄/Gly-BH, an antagonistic effect was observed (combination index CI > 1), but with lower toxicity (IC₅₀ 7.40 mg/l) when compared with the individual responses of these compounds. However, in the mixture, Cu₂(OH)₃Cl/Gly-BH was more toxic with a synergistic response (IC₅₀ 0.85 mg/l) even between 5 and 30 times higher. These results highlight the importance of studying interactions of chemical substances in ecosystems to establish a better evaluation and regulation of their environmental impact.