Lethal and Sublethal Effects of Copper sulphate and Zinc sulphate on Moina Macrocopa: Implications for Freshwater Risk Assessment

Freshwater ecosystems are increasingly threatened by trace metal contamination arising from agricultural, industrial, and domestic effluents. Among these, copper sulphate (CuSO₄) and zinc sulphate (ZnSO₄) are widely used compounds that, despite their benefits, pose ecological risks to non-target aquatic organisms. The present study was motivated by the urgent need to evaluate their impact on Moina macrocopa , a sensitive cladoceran bioindicator species frequently employed in ecotoxicological assessments. The study systematically evaluates the lethal and sublethal toxic effects of copper sulphate and zinc sulphate on Moina macrocopa . Lethal toxicity was assessed through mortality observations over 8–72 hours, with LC₅₀ values derived via probit regression. CuSO₄ exhibited high toxicity, with LC₅₀ values declining from 264.46 µg/L (8 h) to 45.3 µg/L (72 h), indicating a sharp increase in lethality with exposure time. ZnSO₄ showed delayed toxicity, with LC₅₀ values ranging from 2102.31 µg/L (24 h) to 544.48 µg/L (72 h). Sublethal endpoints including molting, brood chamber development, heart rate alterations, behavioral changes, and structural deformities were concurrently monitored. CuSO₄ exposure resulted in significant toxicity even at low concentrations, with 100% mortality occurring at 250–300 µg/L within 48–72 hours. In contrast, ZnSO₄ exhibited delayed toxicity, with complete mortality observed only at concentrations ≥ 1000 µg/L beyond 48 hours. Heart rate monitoring served as a sensitive biomarker for physiological stress, with significant bradycardia and complete cardiac cessation at ≥ 5000 µg/L ZnSO₄ after 48 hours. Recovery of molting and reproduction was evident at lower concentrations for both metals, suggesting resilience at sublethal levels. LC₅₀ values declined with exposure duration, indicating cumulative toxicity, with CuSO₄ showing markedly higher potency than ZnSO₄. These findings reinforce the ecological relevance of M. macrocopa for freshwater risk assessment and highlight the importance of integrating sublethal biomarkers in regulatory ecotoxicology.