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Mining in Mexico has produced important economic benefits since pre-Hispanic times. On the other hand, tailings and rock wastes constitute potential pollution sources in many zones of the country. Taxco, about 150 km south-west of Mexico City, is one of the historical mining zones of Mexico. The environmental behaviour of metals from tailings in a branch of the Taxco river was investigated. Several communities use the Taxco river water along its flow. Samples were taken from tailings, river-waters and sediments. Field determinations included conductivity, pH, Eh, temperature and alkalinity of the water. Mineralogical and chemical analyses were performed in tailings and sediments. Water analyses included main ions, and metals in acidified filtered and unfiltered samples. Quartz, jarosite, pyrite, chalcopyrite, Fe oxihydroxides, gypsum, clay and silica minerals were identified in the tailings. All samples had an acid pH (2•50-4•16) and high concentrations of Pb (up to 2750 mg/kg), Zn (up to 690 mg/kg) and As (up to 3530 mg/kg). Mineralogical and chemical characteristics of tailings indicated occurrence of sulphide oxidation. Higher metal concentrations were found in unfiltered, acidified water samples than in filtered water samples in the year 2000: Fe (up to 21•2 mg/l), Zn (up to 13•4 mg/l) Pb (up to 0•115 mg/l) and As (up to 0•035 mg/l). Zn, Fe and Pb reached much higher concentrations in the dry season than in the rainy season. The Taxco river water does not comply with Mexican drinking water standards. High concentrations of Pb (up to 5280 mg/kg) and Zn (up to 33,500 mg/kg) were measured in sediments. Pb and Zn in sediments accumulated downflow in the dry season. A more uniform distribution was found in the rainy season. Results showed that metals are released from tailings as a result of sulphide oxidation and rain-water erosion. Metals are then transported by the river-water mainly in particulate form and, after settling, increase the concentration of metals in the sediments.

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In this work the determination of radon gas (222Rn) and the characterization of chemical elements in drinking water of the city Taxco was carried out. Ingesting or inhaling a small number of radionuclides, as well as water of poor chemical quality, can become a potential public health problem. We are collecting 8 samples of water from a spring, physicochemical parameters were measured in field on different days of the dry season. Measurements of 222Rn were performed in the laboratory with an AlphaGUARD equipment. The chemical quality was analyzed in laboratory too by means of mayor and minor ions, by volumetry and colorimetry. The sodium was determined by Flama Atomic Absorption Spectroscopy (FAAS). Trace elements were analyzed by were determined by Atomic Emission Spectroscopy with Plasma Coupled by Induction (ICP-AES). The concentrations of 222Rn present an average of 22.06 ± 2.52 BqL-1. The results obtained from the main ions and field parameters show a type of diluted sodium-calcium-bicarbonate water. The trace elements present are very small and not exceed the limit of quantification. Radon gas is produced by the igneous rock that is the top of the stratigraphic column, of the hydric recharge. Rainwater when descending through the fractures is impregnated with 222Rn gas and accumulated in the underlying rock that has sufficient porosity to accumulate water and gas in the Chacualco´s spring.