Determination of trace metals in cow's milk from waste water irrigated areas in Central Mexico by chemical treatment coupled to PIXE

The Mezquital valley is an area near Mexico City that has been irrigated since 1890 with wastewater. The use of such waters in agriculture increases soil fertility but at the same time provokes the accumulation of heavy and toxic metals in soils and plants. Cows grazing in these conditions could accumulate heavy and toxic metals in their milk. In this work, a coprecipitation method with APDC is coupled to PIXE for the analysis of Fe, Ni, Cu, Zn, Se and Pb in bovine milk from the Mixquiahuala area in the Mezquital valley. Milk samples were analyzed from cows with supervised and unsupervised feedings finding significant differences between the milks in the Cu, Pb and Zn content. However, no correlation between the type of milk and the metal content could be established. Lead does not represent a health risk for humans in its current concentration and other metals do not seem to be toxic. The transfer ratio from soil and plants to the milk is apparently low.