Critical Assessment on the Current Situation of the Atoyac and Salado Rivers from Oaxaca State, Mexico

Rivers worldwide are increasingly affected by pollution from untreated wastewater, industrial effluents, agricultural runoff, and solid waste. In Mexico, the Atoyac and Salado rivers in Oaxaca present critical cases of environmental degradation. This study provides a comprehensive assessment of their current condition by integrating a review of scientific studies reported in the literature with updated field measurements conducted at representative sampling points. The results reveal severe deterioration in water quality, with key physicochemical parameters—such as total dissolved solids, chemical oxygen demand, total nitrogen, and fats and oils—consistently exceeding the permissible limits established in the standard NOM-001-SEMARNAT-2021. For instance, chemical oxygen demand reached values as high as 2112 mg/L, approximately 10 times higher than the regulatory limit (210 mg/L), highlighting the severity of organic pollution in these rivers. These findings indicate a high load of organic and inorganic pollutants associated with anthropogenic activities, including urbanization, industrial discharges, and inadequate wastewater management. In contrast, pH and temperature values remain within acceptable ranges. Most heavy metals and cyanides were found below regulatory limits, suggesting no immediate risk from these contaminants. However, continuous monitoring of these heavy metals and cyanides is necessary, as they could represent a public health problem in the future. Overall, this study underscores the urgent need for integrated and multidisciplinary strategies to restore and sustainably manage these river systems, considering both environmental and socio-environmental dimensions.