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

Abstract

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 spatial and temporal distribution of physicochemical parameters and pesticide concentrations. To evaluate water quality and the ecological risk associated with pesticide exposure, we utilized 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, indicating inadequate conditions for aquatic life. Statistical analyses revealed that dissolved oxygen (DO), total dissolved solids (TDS), and nitrate-nitrogen (NO₃-N) were key factors influencing the quality of river water. 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 exhibited values that were insufficient to support aquatic life. The RQmean and RQmax indicated a high ecotoxicological risk in all aquatic ecosystems, with malathion concentrations exhibiting a robust 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 development of management strategies and effective watershed management, particularly in natural reserve areas.

Keywords: Agriculture; Contamination; Ecotoxicology; Rivers; Threat.