A new method for analysis of the toxicity of organophosphorus pesticide, dimethoate on rotifer based on response surface methodology.

This study analyzed the toxicity of organophosphorus pesticide, dimethoate on freshwater rotifer Brachionus calyciflorus, using swimming angular and linear speed alteration as the sub-lethal endpoints. Response surface methodology (RSM) was applied in experimental design and data analysis to consider two related factors: toxic concentration, exposure time and their interaction. In general, inhibition effect of the pesticide on rotifer swimming was observed clearly at any given toxicant concentration. The highest inhibition rates in angular and linear speed were obtained in the shortest exposure time (11.36 min) and the highest dimethoate concentration (1.85 mg L(-1)). The RSM used for the analysis of treatment combinations showed that a cubic polynomial regression model was in good agreement with experimental results, with R(2)=0.992 and 0.9997, for swimming angular speed inhibition rate and linear speed inhibition rate (p<0.01, F-test, respectively). 3D reference surface plots and contour plots showed that the toxic effect was influenced not only by dimethoate concentration, but also by the exposure time. A time-step effect was observed clearly. Thus, the pesticide dimethoate had toxic stress on the swimming behavior of rotifers.