Deriving water-quality criteria for three emerging pesticides (chlorothalonil, trifluralin, dicofol) using the species sensitivity distribution method and the assessment factor method.

Rapid growth in domestic agriculture has made pesticides indispensable for safeguarding food security and boosting yields, yet their excessive use is now a major driver of environmental contamination and ecological degradation. This study focuses on three representative pesticides with distinct modes of action, documents their aqueous occurrence at μg/L levels, and quantifies their ecological toxicity to organisms spanning multiple trophic levels. In addition, this study combined two risk assessment methods to derive the acute and chronic water quality criteria for the three pesticides in seawater and freshwater. For chlorothalonil, the acute criteria were 0.002 μg/L in freshwater and 7 μg/L in seawater, and the chronic criteria were 0.02 μg/L and 0.056 μg/L, respectively. For trifluralin, the acute criteria were 8.5 μg/L in freshwater and 0.005 μg/L in seawater, and the chronic criteria were 0.507 μg/L and 0.01 μg/L, respectively. For dicofol, the acute criteria were 0.053 μg/L in freshwater and 0.06 μg/L in seawater, and the chronic criteria were 0.0904 μg/L and 1.9 μg/L, respectively. It can be seen that the criteria obtained by the RAF method were all lower than those obtained by the SSD method. Furthermore, the water quality criteria for chlorothalonil and trifluralin were lower in seawater than in freshwater, indicating that marine species may be more sensitive to the toxicity of chlorothalonil and trifluralin. This study used PNEC values and probabilistic risk assessment (PRA) to jointly evaluate ecological risks. The results showed the three pesticides at current environmental concentrations posed no actual harm to the ecosystem.