PHYSICOCHEMICAL EVALUATION OF SOILS AND ...

  PHYSICOCHEMICAL EVALUATION OF SOILS AND SEDIMENTS NEAR MINING OPERATIONS IN ASIENTOS, AGUASCALIENTES K. Mitchell, M. Ramos-Gómez, A. Guerrero-Barrera, L. Yamamoto-Flores; F. ThalassoSiret, F. Avelar-González UNIVERSIDAD AUTÓNOMA DE AGUASCALIENTES, Aguascalientes, México; CINVESTAV- IPN, México DF, México; ABSTRACT

Soils and sediments near mining activities are frequently direct receptors of mining waste and as such present a potential environmental risk. The study of this potential risk should include not only total metal quantification, but also the study of physicochemical characteristics that play an important role in their solubility, mobility and toxicity in affected sites. Thus, the aim of this study was to evaluate total metal concentrations and the physicochemical characteristics that may affect metal mobility in nearby soils and sediments of the Piedras Negras River in Asientos, Aguascalientes; an area recently affected by a substantial increase in mining activity. Soil and sediment sampling were carried out once during the dry season and once during the rainy season. Soil moisture and organic matter were initially determined. After pretreatment which consisted in drying and sieving through a 2mm mesh, cation exchange capacity and total metal content were determined. pH, redox potential, soluble salts were determined in a 1:10 dilution soil:water. Sediments from all sites were classified as very polluted according to guidelines established by the United States Environmental Protection Agency, and above the maximum permitted limits for commercial, residential and farm use according to the NOM-147-SEMARNAT/SSA1-2004 in at least 2 metals, in select cases, more than 200 times guideline values. 70% of soils from the 10 sample sites were classified in the same way. Though neutral conditions were predominant, 20% of samples from both substrates were moderately acidic in nature (