Distribution and risk assessment of potentially toxic elements in urban wastewaters of Mexico City

The present study assessed the contamination of potentially toxic elements (Cd, Co, Cu, Fe, Mn, Ni, Pb, and Zn) in urban wastewaters from Mexico City, Mexico, using atomic absorption spectroscopy for risk assessment. A total of thirty-two water samples were systematically collected from the River de los Remedios (n = 17), River Tlalnepantla (n = 4), and River San Javier (n = 11) in the northern part of the metropolitan area. Results showed that average elemental concentrations, in mg L^-1, followed the order: Mn (0.39) < Pb (0.17) < Fe (0.12) < Cu, Ni, Zn (0.06) < Co, Cd (0.02), reflecting the impact of raw industrial and domestic discharges from the highly urbanized region. Concentrations of Pb and Cd surpassed the legal limits of 0.03 and 0.004 mg L^-1, respectively, for wastewater discharge. Statistical analysis of physicochemical parameters and element levels indicated that industrial activities are the main sources of PTEs. The level of pollution was assessed using the heavy metal evaluation index (HEI), contamination factor (CF), and Nemerow pollution index (NPI); results indicated moderate contamination by Pb and overall slight pollution. Human risk assessment calculated for the inhalation and dermal exposure pathways in adults and children indicated that Cd and Pb were the most critical elements that could pose adverse health effects to the local population. Dermal contact was identified as the potential exposure pathway that could pose potential risks to human health. The findings of this study indicate a deteriorating status of the aquatic system in Mexico City, primarily due to the persistent discharge of untreated wastewater, which poses a significant risk to environmental integrity and human health within the urban area.