Population responses of Daphnia laevis to endocrine disruptors: a molecular docking by binding active site to arginine kinase

Endocrine disruptors can alter biological functions in aquatic organisms at low levels. Triclosan, a commonly used active ingredient in personal care products around the world, is frequently detected in the environment. Likewise, 4-nonylphenol is used in products such as plastics, personal care products, and cleaning agents. Zooplankton species such as cladocerans are used in acute and chronic ecotoxicological assays. Daphnia laevis is a commonly found cladoceran in Mexican water bodies and has been used in previous ecotoxicological experiments. In this work, median effective concentration of triclosan and 4-nonylphenol (EC₅₀, 24 h) for immobilization for the cladoceran were derived. Based on the acute toxicity data (368.6 and 200 µg L⁻¹, respectively), three sublethal concentrations of both compounds (30, 60, 120 and 10, 20, 40 µg L⁻¹, respectively) were used to evaluate population responses. Population growth curves of D. laevis were affected significantly, indicating decreases in peak abundances in all treatments (0.5 for triclosan and 1 ind mL⁻¹ for 4-nonylphenol) compared to controls (2 ind mL⁻¹). The effect of the exposition of both endocrine disruptors was significant in the majority of the treatments; however, 4-nonylphenol was more toxic to D. laevis, than triclosan. This can be explained through the great number of interactions of binding sites on the amino acid, arginine kinase, contributing to the inhibition of the regulation of cellular energy used in survival and reproductive pathways of the cladoceran.