Acute toxicity bioassay using <b> <i>Paramecium caudatum</i> </b> , a key member to study the effects of monocrotophos on swimming behaviour, morphology and reproduction

Abstract

The toxic effects of an organophosphorous insecticide, monochrotophos (MCP) were investigated on Paramecium caudatum in static acute toxicity tests (10 min and 2 h). The lethal concentrations (50%) were determined by probit method, for technical monocrotophos as 60 and 40.6 mg L−1, respectively. We have combined conventional light microscopy and a computerized video tracking system to determine behavioural and morphological changes in paramecium on exposure to MCP. Paramecia exposed to highest concentrations (90–100 mg L−1) used for 10 min exposure, exhibited initial increase with subsequent decrease in mobility with enormous blebbing, leading to lysis of cells. In the second set of experiments, the cells exposed to lethal concentration (40.6 mg L−1) for 2 h were under stress, and reduced their locomotor behaviour, i.e. distance travelled per unit time (mm in 6 min) and swimming speed (mm s−1) with increased time of exposure. In the third set of experiments, the number of generations and generation time in 24 h was evaluated with respect to the different sub lethal concentrations (5, 10, 15 and 20 mg L−1) of toxicant. The number of generations decreased and generation time extended significantly in a concentration dependent manner. The results indicate that the Paramecium toxicity assay could be used as a complimentary system to rapidly elucidate the cytotoxic potential of insecticides.