Risk in the quality of aquatic ecosystems exposed to pesticides in a natural protected area of influence in western Mexico

Environmental assessment of water quality, using physical, chemical, and microbiological parameters, is crucial for understanding the conditions of water resources and ensuring the health of aquatic life and its ecological functions. Our objective was to evaluate the quality of aquatic ecosystems exposed to pesticides within a natural protected area of influence in the Sierra de Manantlan Biosphere Reserve in western Mexico. We assessed the spatio-temporal distribution of physicochemical parameters and pesticide concentrations. To evaluate water quality and the ecological risk from pesticide exposure, we used the Canadian Council of Ministers of the Environment Water Quality Index (CCME-WQI) and the Ecotoxicological Risk Quotient (RQ), respectively. Water quality indices showed low values ranging from 15.49 to 44.9 at sites classified as semi-disturbed, disturbed, and drains, which indicating inadequate conditions for aquatic life. Statistical analyses determined that dissolved oxygen (DO), total dissolved solids (TDS), and NO₃-N were key factors influencing river water quality. The pesticides cyhalothrin, malathion, and methomyl were present in at least 80% of the study sites. When their concentrations were included in the CCME-WQI, all sites showed values insufficient to support aquatic life. The RQmean and RQmax showed high ecotoxicological risk in all aquatic ecosystems, with concentrations of malathion, which indicated a particularly strong negative relationship with the CCME-WQI. The findings of this study provide a risk analysis of water resource quality due to pesticide contamination, which can inform the establishment of management strategies and appropriate watershed management, particularly for natural reserve areas