CADMIO, NÍQUEL Y PLOMO EN AGUA RESIDUAL, SUELO Y CULTIVOS EN EL VALLE DEL MEZQUITAL, HIDALGO, MÉXICO CADMIUM, NICKEL AND LEAD CONCENTRATIONS IN WASTEWATER, SOIL AND CROPS IN THE

As a result of the direct use of sewage water for more than 100 years to irrigate crops, heavy metals have accumulated in soils in the Mezquital Valley, Hidalgo State, Mexico. From January to November 1996 the present study was conducted to make a diagnosis of the accumulation and variability of the concentration of cadmium, nickel, and lead in water, soil as well as in maize ( Zea mays L.), wheat (Triticum aestivum), and lucerne (Medicago sativa). These crops are of major economical importance in this valley. Data obtained were used to show the need to regulate the accumulation of heavy metals in soils. Samples of water, soil, foliar tissue, and grains of maize and wheat were taken from seven sites with a variation in the time of use of the waste water. Total lead concentration in water of the Gran Canal del Desague was 0.13 mg L -1 , while in water of the dam was 0.054 mg L-1. The coefficient obtained from the division of the concentration of cadmium in the foliar tissue and in grain of wheat, decreased in four of the seven sites. In site Tlahualilpan1 the variation was 1.5 (March) to 0.9 (April); this shows that Cd was transferred to the grain and from there to the food chain. In five of the seven sites, lead stayed in the wheat leaves; the calculated coefficient increased from 0.8 (March) to 2.4 (April) in the Tlahualilpan1 site. Nickel coefficient in wheat, decreased in the seven sites, and this shows that nickel was transferred to the grain.