Chlorpyrifos-induced toxicity in scenedesmus sp. t24 and synechococcus sp. d24

The widespread use of chlorpyrifos, an organophosphate insecticide, raises concerns regarding its impact on non-target aquatic organisms. This study evaluated the toxicological responses of Synechococcus sp. D24 and Scenedesmus sp. T24 exposed to chlorpyrifos at 0.01-10 mg/L. Growth inhibition, chlorophyll a content, photosynthetic efficiency (Fv/Fm), and superoxide dismutase (SOD) activity were assessed to determine physiological stress. Scenedesmus sp. T24 showed high sensitivity, exhibiting strong reductions in growth, chlorophyll a, and Fv/Fm even at low concentrations, accompanied by a continual decline in SOD activity. In contrast, Synechococcus sp. D24 demonstrated greater tolerance, with moderate physiological alterations and a biphasic SOD response indicating possible adaptation at low exposure levels. The EC₅₀ values (0.95 µg/L and 9.5 µg/L, respectively) confirmed clear species-specific differences. These results highlight the ecological risks of chlorpyrifos contamination and support the use of microalgae as sensitive bioindicators in aquatic toxicology and environmental monitoring.