Resumo

ARCEGA-CABRERA, Flor; CASTILLO-BLUM, Silvia E.  e  ARMIENTA, Ma. Aurora. Tetraethyl lead release from sediments in a mine-impacted tropical river. Rev. Int. Contam. Ambient [online]. 2010, vol.26, n.2, pp.119-127. ISSN 0188-4999.

Desorption kinetics of tetraethyl lead, under changing pH and controlled temperature, Eh and dissolved oxygen, in a mining-impacted Mexican tropical river, was examined using samples placed in a closed system. The objective of this study was to determine the potential environmental risk for local residents from the tetraethyl lead present in the water column. Statistical and geochemical methods elucidated the potential environmental threat of free tetraethyl lead (TEL). Specifically, analysis of water samples from three stations in the Taxco River basin indicated that altering pH caused significant changes in the concentration of TEL in the water column. Since this study was performed on a closed controlled system that contained sediments and water from the river, desorption from sediments caused by changing pH is the mechanism by which TEL increases in the river water. Since the samples used for this study are natural samples collected in the river, it is assumed that this behavior could be expected in the river if a suddenly decrease in pH occurs. It is probable that the processes of TEL desorption depend on several variables, since fitted curves, for changes in TEL release with time, go from linear (direct relationship) to polynomial (co-linearity) suggesting a complexity of interacting factors. Therefore, factor analysis was used to tease out how the geochemical characteristics of sediments and pH interact to control TEL concentration's changes. Factor analysis showed that the most probable sources of TEL present in the Taxco River basin, are wet deposition, run-off, and leaching of the hydrological basin. TEL in situ microbial formation is probably not a source in this particular area. In the sample taken from a station near a tailing and an active mine, TEL concentrations at pH 6.0 exceeded the recommended safe limit established by the US EPA (4.6 x 10^-7 mol m^-3) and as a result could represent a potential environmental risk for local residents.

Palavras-chave : México; Taxco; tetraethyl lead; kinetics; mining pollution; factor analysis.