Geochemical speciation of chromium related to sediments properties in the riverbed contaminated by tannery effluents

Abstract

Guadalentin River (SE Spain) has been affected by tannery industries, where their effluents, containing Cr, were spilled until 2003. The untreated tannery effluent is characterized by the presence of inorganic and organic substances including a basic chromium (III) sulfate salt. Chromium contents in sediments represent permanent environmental and human health risks. The main objectives of this research were to evaluate the contamination, the spatial distribution, and the speciation of chromium in the sediments. In order to determine the degree of Cr pollution and to evaluate the influence of sediment properties in the behavior of total Cr, Cr(VI), and Cr(III) concentrations, a sediment sampling was carried out in a stretch of 1500 m of the dry riverbed, from 0 to 100 cm deep. Total, soluble, and exchangeable Cr(III+IV) and Cr(III) were measured using graphite furnace atomic absorption spectrometry (GFAAS), and Cr(VI) was selectively extracted by EPA 3060A method. A physicochemical characterization of the riverbed sediments was done with the aim of evaluating the influence of some sediment properties related to the contents of total Cr and its speciation. Chromium total concentration was high in the riverbed (11–11099 mg kg−1) up to 100 cm deep, exceeding in almost all the study stretch, the background level, and the generic reference values of Cr for Murcia Province. The highest degrees of sediment pollution (over 10,000 mg Cr kg−1) are located 20–50 cm deep, at the first 600 m east of the city center, and in the last 300 m of the studied area, which reveals that the Cr contents in sediments are relatively higher near the discharge point of the tannery facilities. Chromium(III) is the predominant oxidation state with 95.87 % (mean value) of total Cr in the sediments. The results (maximum values 11099 Cr mg kg−1 and 79 Cr(VI) mg kg−1) indicated Cr leaching from the surface until 100 cm deep. Chromium(VI) represents 4.13 % of total Cr, so Cr(III) was the predominant oxidation state. The riverbed sediment pollution by Cr (total) and Cr(VI) was caused by an anthropogenic activity (tannery industry).