Cadmium chemical fractions in sediments: effect of grain size, pH, organic acids, and inorganic ions

In sediments, cadmium (Cd) contamination is an increasingly severe global problem facing environmental protection and human health. The mobility and biological toxicity of Cd are related to its chemical fractions. In this work, the European Community Bureau of Reference (BCR) sequential extraction procedure and inductively coupled plasma optical emission spectrometry (ICP-OES) technology were integrated to identify the effect of grain size, pH, organic acids, inorganic anions, and cations on the chemical fractions of Cd in sediments. The result indicated that the sediments with the fine grain (< 63 mu m) presented a good ability to combine Cd, while the coarse grains (> 250 mu m) exhibited a more exchangeable/acid-soluble fraction (78.14 wt%). Besides, the amount of Cd released from the sediment decreased dramatically with pH from 2 to 6 and leveled off in the pH range of 8-10. The more mobile fractions (exchangeable/acid-soluble fraction (F1) and reducible fraction (F2)) were significantly affected by pH, implying that pH was an important factor influencing the release of Cd into the upper water environment. For organic acids, which mainly affect the release of Cd in the exchangeable and carbonate-bound fraction, the influence of organic acid on the mobility of Cd in sediments followed the order: ethylenediaminetetraacetate acid (EDTA) > citric acid (CA) > tartaric acid (TA) > oxalic acid (OA). The impact of SO42-, Cl-, CO3,2- NO3-, Ca(II) and Mg(II) was not evident in the release of Cd from the sediment, while Al(III) and Fe(III) had a greater effect on the chemical fraction of Cd. The study outcomes provide fundamental knowledge for understanding the potential mobility of Cd in sediment.