Assessing pesticide pollution in surface water of two basins in western Mexico: spatiotemporal variability, potential ecological risk assessment, and pesticides prioritization.

This study analyzed the presence of pesticides in surface waters of two basins in western Mexico, through an analysis of spatiotemporal variability, a potential ecological risk assessment and a prioritization analysis. Eighty water samples were collected at 10 sites distributed in the Marabasco basin and the Armería sub-basin during the years 2023 and 2024, covering the dry and wet seasons. Forty-nine pesticides were analyzed by gas chromatography coupled to mass spectrometry and high-performance liquid chromatography tandem mass spectrometry, of which 20 were detected. The herbicides ametryn, atrazine and 2,4-D and the insecticides DEET and diazinon showed the highest detection frequencies. Picloram (8.22 ng/mL), pyraclostrobin (4.25 ng/mL), fipronil (2.41 ng/mL), and diazinon (1.64 ng/mL) reached the highest recorded concentrations. Statistical analysis showed that the wet season increased both the frequency of detection and the concentrations of several pesticides; however, the presence of these compounds was detected at all sampling sites throughout the study period. The potential ecological risk assessment using the risk quotient calculation showed that insecticides such as fipronil, diazinon, and chlorpyrifos and the fungicide carbendazim pose significant risks to algae, aquatic invertebrates and fish in both average and worst-case scenarios. The prioritization identified eight priority pesticides based on frequency and magnitude of risk. The results showed a significant impact on aquatic ecosystems, mainly associated with the intensive use of insecticides in agricultural and domestic activities. It is recommended that integrated pesticide management measures and environmental regulations be strengthened to reduce the risks identified and to preserve the quality of the region's water resources. HIGHLIGHTS: • Eight pesticides were detected in all samples of surface water. • Eight pesticides were evaluated for temporal statistical analysis of surface waters. • Irrigated and rainfed agricultural areas exhibited the highest pesticide diversity. • Six different pesticides were detected in potential risk concentrations. • Ametryn and diazinon were identified as requiring priority attention.