BEHAVIOR OF TRACE-METALS IN SOILS OF HIDALGO, MEXICO

A study was conducted to determine the behavior of heavy metals in soils from district of irrigation 03, Hidalgo, Mexico. Samples of water, soils and plants were collected from plots irrigated with wastewater over different management periods. Additionally, another plot irrigated with groundwater was used as the control (S1). In water samples from some sites the concentrations of Cd, Fe and Mn were above the permissible limit fixed by Mexican laws. In soil samples from sites S4, S5 and S6 with 23, 59 and 72 years of irrigation management respectively, the concentrations of Cu was three times greater than that determined in S1, whereas the levels of Zn in S5 and S8 were ten times higher, compared to the same S1. However, the concentrations of Fe, Ni, Cr, Cd and Pb in S5 were only between three and five times greater than those found in the control plot. In all these sites, except in the control, amounts of Fe, Mn, Zn and Cu extracted with DTPA increased when irrigation time increased. DTPA extractable Cd and Pb were 50 and 21 times higher than their levels in S1, respectively. The concentration of Pb and Cd in plant tissues from sites with 23 years of irrigation averaged 8.5 and 0.55 mg kg(-1) respectively, suggesting a potential for heavy metal phytotoxicity.