Toxicity Response and Swimming Speed Regularity in Daphnia magna After Short-Term Exposure to Diuron

The agricultural production process contributes to the global issue of pesticide pollution. Based on the static toxicity test of diuron (DCMU) on <i>Daphnia magna</i> (<i>D. magna</i>) for EC₅₀-48 h, a concentration range of 0.2 to 1 mg/L was set as sublethal concentrations, while lethal concentrations were set at 2 mg/L and 4 mg/L. This study analyzes the toxic response patterns of the swimming behavior indicators of <i>D. magna</i> exposed to different concentrations of DCMU. The results showed that the average speed (V) of <i>D. magna</i> decreased step by step with exposure time, regardless of exposure to sublethal concentration or lethal concentration. However, during the same short-term exposure period, the V of <i>D. magna</i> at lethal concentration was higher than that at sublethal concentration, which indicates that the swimming behavior of <i>D. magna</i> exposed to DCMU may be stimulated and accelerated. Compared to the control group, there is a statistically significant difference in the V of <i>D. magna</i> after short-term exposure, especially showing an extremely significant difference after 5 min of exposure. Evidently, compared to the traditional 48 h static toxicity testing method, the swimming behavior indicators of <i>D. magna</i> show a more sensitive response to DCMU after 5 min of exposure, making it more suitable for rapid toxicity detection. By expanding the range of exposure concentrations, it was found that the V indicator of <i>D. magna</i> responded significantly to a DCMU concentration of 0.05 mg/L after only 5 min of exposure, and a high degree of correlation was observed between the indicator and the exposure concentration. Through nonlinear fitting, the relationship between V and the dose-effect of DCMU toxicity presents an S-shaped curve, with R² > 0.9. Consequently, it becomes possible to study the dose-effect relationship between the changes in the swimming behavior indicators of <i>D. magna</i> and the stress concentration based on this theory. This further establishes a foundation for the development of comprehensive aquatic toxicity rapid detection technology based on the toxic response of swimming behavior indicators.