Heavy Metal Dispersion in a Hydrological Sub-Basin as Consequence of Mining Activity in Taxco, Guerrero (Southern Mexico)

Abstract

The mining industry generates high concentrations of heavy metals (HMs) susceptible to being released into surface and ground water. The objective of this work was to determine the concentration and dispersion of HMs in surface water and ground water in a hydrological sub-basin located in southwest Mexico. The samples were collected as following: 24 samples from streams, rivers, and one lake, and 15 samples from springs, located along the Taxco-Cocula sub-basin. A total of 78 samples were collected in the dry and rainy seasons. Physicochemical parameters, major ions, and HMs were analyzed. The pH, Eh, electrical conductivity, and total dissolved solids were analyzed in situ, while the concentrations of anions, cations, and HMs were measured in the laboratory. The results were treated with multivariate analysis and PHREEQC simulation. The highest recorded values (in mg/L) were in surface water, where the HMs in the dry season were Al (28.63), As (0.60), Cd (1.78), Cu (1.10), Fe (68.27), Mn (21.47), Pb (0.02), and Zn (208.80). These high concentrations exceed the limits established by national and international regulations for drinking water. The ground water did not indicate pollutants associated to the mining industry. On the other hand, in the rainy season, the surface water showed a decrease in the concentrations of the measured heavy metals. The hypsometric gradient and the hydrogeological and meteorological characteristics of the Taxco-Cocula sub-basin are the factors that contribute to the dilution and dispersion of the HMs along the 60 km of its length.