RESUMENEn este estudio se recolectaron muestras de agua en el efluente de una planta de tratamiento de agua residual durante los meses de enero a julio de 2012. El objetivo fue determinar la concentración de metales pesados, así como evaluar la calidad agrícola del agua residual tratada. Los resultados del análisis de los elementos: cadmio (Cd), cobre (Cu), cromo (Cr), níquel (Ni), plomo (Pb) y zinc (Zn), muestran que la concentración de estos metales fue baja, por lo que, de acuerdo con la NOM-001-SEMARNAT-1996 el agua residual tratada cumple con la concentración permitida para su descarga en cuerpos receptores. Mediante las variables Ca 2+ , Mg 2+ , Na + , K + , CO 3 2-, HCO 3 -, Cl -, SO 4 2-, pH, conductividad eléctrica (CE) y relación de adsorción de sodio (RAS) se determinó su calidad agrícola. Los indicadores de salinidad muestran que el agua no es adecuada para la irrigación. Los valores de RAS fueron menores de 5,5 meq L -1 , y los valores conjuntos CE-RAS sugieren la clasificación del agua como C4-S1, lo que indica que el agua tiene restricciones de uso por el riesgo de salinidad al aplicarla al riego agrícola.Palabras clave: salinidad, sodicidad, irrigación. ABSTRACT In this study, water samples were collected from the effluent of a treatment plant wastewater during the months of January to July 2012. The objective was to determine the concentration of heavy metals, as well as evaluating the agricultural quality of the treated wastewater. The results of analysis of elements: cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), lead (Pb) and zinc (Zn),show that the concentration of these metals was low, so which, according to NOM-001-SEMARNAT-1996

Introduction: Mexico City generates an approximate volume of wastewater of 57 m3 s-1, the wastewater is conduct by the drainage network: main channel-west interceptor-central emitter, and conducted to Hidalgo State, during it course, an important volume is poured into irrigation channels and is used for crop irrigation in the Mezquital Valley.Method: in this study, nitrate (NO3-), phosphate (PO4-3) boron (B3+) and chloride (Cl-) content in 188 wastewater samples was determined. The objective was to assessment the risk of toxicity by specific ions (B3+ and Cl-) and the nutrients content (N, P, K, Ca y Mg) in wastewater used for crop irrigation.Results: the nitrate (NO3-) concentration was very heterogeneous (CV=59.83 %) and this was attributed to the lixiviation of nitrogen fertilizers. The maximum phosphate (PO4-3) value was 65.7 mg L-1, and its concentration was attributed to the discharge of household wastewater. The boron concentration (B3+) was less than 1.88 mg L-1. The risk of toxicity due to the use of wastewater in irrigation may cause a decrease the yield of sensitive crops, such as beans.Conclusion: untreated wastewater used in irrigation in Mezquital Valley, may cause toxicity problems in some crops; the nitrate and phosphate concentrations in wastewater of the Mexico City-Mezquital Valley drainage network were high, and these were attributed to the discharges of domestic and industrial wastewaters and to agricultural drainage, high concentrations of nitrate and phosphate represent a risk for aquatic organisms due to pollution and the possible eutrophication of water bodies. The risk of toxicity by B3+ and Cl-can have a negative effect on the germination and yield of bean crops.