SANTHOSHA PENTAGARI AND NAGESWARARA RAO AMANCHI
Abstract
The freshwater ciliate protozoan Paramecium caudatum was utilized to investigate the potential toxic and functional impacts of the insecticide Dimethoate, an organophosphate and acaricide. During acute toxicity tests, lower concentrations slightly reduced cell motility, whereas higher doses caused abnormal rocking movements, eventually leading to complete immobility. The median lethal concentration (LC50) after 3 hours of exposure was calculated as 0.1 ppm. Exposure to Dimethoate resulted in notable cellular deformities, including cell swelling, an oval-shaped appearance, and at higher concentrations, a reduction in body length accompanied by cytoplasmic darkening. Leakage of cellular contents further indicated damage to the cell membrane. Altered activity of the contractile vacuole was observed after 20 minute exposure to concentrations of 0.001, 0.005, 0.01, and 0.03 ppm, suggesting disruption of osmoregulatory functions. Observed disturbances in phagocytosis and vacuolar activity imply that Dimethoate may exert significant physiological effects on P. caudatum. Due to their ease of culture, short life cycles, rapid responses, and reproducibility in experiments, ciliates like Paramecium prove to be valuable model for assessing toxicity, physiological effects, and environmental risk.