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. LC50 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.

Comprehensive health evaluation of an urban wetland using quality indices and decision trees.

In a world where pristine water is becoming scarcer, the need to reuse water becomes imperative. In this context explaining the water quality, purpose fitness and the parameters or conditions of the water body to adjust so as to improve its quality, are of great relevance. The goal of the present study was the use of water, riverine, and biodiversity quality indices to assess the condition of the studied urban wetland, since no single index can provide a complete health assessment of a water body. Decision trees were also used to elucidate the best water parameters to mend in order to recover the overall health of the urban wetland. The decision trees identified relevant physicochemical parameters as well as their approximate concentration at which a healthy water environment can be sustained for zooplankton and proved to be a powerful and simple alternative to customary approaches. Suspended particles and phosphates proved to be important parameters with concentrations approximately lower than 88 mg L-1 and 11 mg L-1, respectively, for a good biodiversity index of zooplankton. Ammonia, total coliforms, BOD, nitrates, and sodium were the main parameters that affected the water quality index. The vegetation coverage and its structure were the driving factors in the riverine quality index of the wetland.