Screening and Risk Evaluation of Organic Contaminants in an Urban Wetland Fed with Wastewater Effluents

Wastewater release in an urban wetland in Mexico City entails discharging complex mixtures of hundreds of chemical substances into the aquatic system. Therefore, in order to identify the most important contaminants, a GC–MS screening method coupled with deconvolution software was used. LC 50 values from ECOSAR and Toxic Units were obtained to identify the organic pollutants-of-concern and to pinpoint the most ecotoxic sites. The results showed that, even though the area has intensive farming, agrochemicals are not of concern. Industrial and domestic groups make up from about 30%–66% of the pollutants for all sites. Of the 189 identified substances, 17 were detected 44% of the time and the Toxic Unit showed that terbutol, coprostanol, and hexadecane were capable of generating considerable adverse effects on the aquatic ecosystem. Total Toxic Units for each site exhibited a decreasing trend as they distanced from the urban and agricultural area.