Ecological risk assessment of pesticides in the Mijares River (eastern Spain) impacted by citrus production using wide-scope screening and target quantitative analysis

The widespread use of pesticides, especially in agricultural areas, makes necessary to control their presence surrounding surface waters. current study was designed investigate the occurrence and ecological risks pesticides transformation products a Mediterranean river basin impacted by citrus production. Nineteen sites were monitored three campaigns distributed over different seasons. After qualitative screening, 24 compounds selected for subsequent quantitative analysis. As expected, lower section most contaminated, with total concentration >5 µg/L two near discharge area wastewater treatment plants. highest concentrations found September, after applications when flow is reduced. Ecological calculated using mixture toxicity approaches (Toxic Unit multi-substance Potentially Affected Fraction), which revealed high acute chronic imidacloprid invertebrates, moderate-to-high diuron, simazine 2,4-D primary producers, thiabendazole invertebrates fish. This shows that intensive production effluents containing pesticide residues from post-harvest processing plants are threatening freshwater biodiversity. Further actions recommended reduce emissions.