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.

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