Speciation of chromium in river sediments by graphite furnace-atomic absorption spectrometry after microwave-assisted extraction

Rivers could be polluted by receiving wastes from municipal and industrial sources as well as runoff from agricultural land. This could leave river sediments contaminated with potentially toxic elements (PTEs) including chromium (Cr). The aim of this study was to assess and quantify total Cr and hexavalent Cr (Cr(VI)) in sediment samples, obtained from Mokolo and Blood Rivers in the Limpopo Province, South Africa. Sediment samples were collected from ten sampling points from each river. Microwave-assisted acid digestion and microwave-assisted extraction methods were employed to obtain a simple, rapid and safe method for the determination of total Cr and Cr(VI) in sediments, respectively. The accuracy of the method was confirmed by employing a sediment standard reference material (SRM 8704). Total Cr and Cr(VI) in sediment samples were quantified using flame-atomic absorption spectrometry (F-AAS) and graphite furnace-atomic absorption spectrometry (GF-AAS), respectively. The total Cr concentrations in sediments of Blood and Mokolo Rivers ranged from 129 to 253 μg/g and 25.7 to 193 μg/g, respectively. The Cr(VI) in sediments was extracted by employing 0.1 M Na₂CO₃ as a leaching reagent. The extraction procedure was followed by atomic spectrometric measurements and provided satisfactory results with percentage recoveries of 94.9% to 105%. The leached Cr(VI) was quantified by GF-AAS after filtration of the sample solutions through a hydrophilic Millipore PVDF 0.45 µm filter. The levels of Cr(VI) in sediment samples of Blood and Mokolo Rivers were in the range of 0.410 to 1.32 μg/g and 0.180 to 1.04 μg/g, respectively. Low limit of detection (LOD) and limit of quantification (LOQ) values were achieved using the leaching method described in this study.