Selenium and its redox speciation in rainwater from sites of Valparaiso region in Chile, impacted by mining activities of copper ores

The determination of the total concentration of selenium does not provide s ufficient information about its toxicity and its bioavailability. The deter mination of its chemical forms is the basis for understanding the biogeoche mical cycle in terrestrial and aquatic ecosystems and for detecting the spe cies which might be toxic to biota. In this work we describe an analytical procedure to carry out the redox speciation of selenium present at Ultratra ce levels in rainwater from sites of Valparaiso region in Chile, impacted b y mining activities of copper ores. A simple preconcentration step of the r ainwater sample on a rotavapor system, in vacuum at low temperature permits the concentration of the different redox selenium species until levels qua ntifiable by sensitive techniques such as differential pulse cathodic strip ping voltammetry or by spectrometric techniques, based on the hydride gener ation and detection by atomic absorption or atomic fluorescence spectrometr y. These techniques coupled to redox chemical reactions allow the redox spe ciation of selenium. The results show that the open evaporation system can be used to concentrate water samples when the aim of the analysis is the de termination of the total selenium concentration. On the contrary, to carry out its redox speciation only the preconcentration. performed on rotavapor system, in vacuum can be used. When synthetic solutions containing differen t redox species of selenium, at ultratrace levels, were slowly evaporated o n open system, Se(II) and Se(IV) were oxidized. The optimized procedure was then applied to the selenium determination and its redox speciation in rai nwater samples collected in sites impacted by mining activities of copper o res. It was found that the amounts of total selenium in rainwater, as coppe r, from Puchuncavi valley decrease exponentially with the distance from the source, indicating that these elements in this region arise from the indus trial complex Las Ventanas. In the redox speciation of selenium, Se(IV) and Se(VI) were the species found in all rainwater samples analyzed, providing selenium in species which are most favorable for their uptake by the veget ation grown in these soils. (C) 2001 Elsevier Science Ltd. All rights reser ved.