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 (CuSO 4 ) and zinc sulphate (ZnSO 4 ) 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 h, with LC 50 values derived via probit regression. CuSO 4 exhibited high toxicity, with LC 50 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. ZnSO 4 showed delayed toxicity, with LC 50 values ranging from 2102.31 µg/L (24 h) to 544.48 µg/L (72 h). CuSO 4 exposure resulted in significant toxicity even at low concentrations, with 100% mortality occurring at 250–300 µg/L within 48–72 h. In contrast, ZnSO 4 exhibited delayed toxicity, with complete mortality observed only at concentrations ≥ 1000 µg/L beyond 48 h. Heart rate monitoring served as a sensitive biomarker for physiological stress, with significant bradycardia and complete cardiac cessation at ≥ 5000 µg/L ZnSO 4 after 48 h. Recovery of molting and reproduction was evident at lower concentrations for both metals, suggesting resilience at sublethal levels. LC 50 values declined with exposure duration, indicating cumulative toxicity, with CuSO 4 showing markedly higher potency than ZnSO 4 . These findings reinforce the ecological relevance of M. macrocopa for freshwater risk assessment and highlight the importance of integrating sublethal biomarkers in regulatory ecotoxicology.