Abstract
Little knowledge is available about the influence of cation competition and metal speciation on trivalent chromium (Cr(III)) toxicity. In the present study, the effects of pH and selected cations on the toxicity of trivalent chromium (Cr(III)) to barley (Hordeum vulgare) root elongation were investigated to develop an appropriate biotic ligand model (BLM). Results showed that the toxicity of Cr(III) decreased with increasing activity of Ca2+ and Mg2+ but not with K+ and Na+. The effect of pH on Cr(III) toxicity to barley root elongation could be explained by H+ competition with Cr3+ bound to a biotic ligand (BL) as well as by the concomitant toxicity of CrOH2+ in solution culture. Stability constants were obtained for the binding of Cr3+, CrOH2+, Ca2+, Mg2+ and H+ with binding ligand: log KCrBL 7.34, log KCrOHBL 5.35, log KCaBL 2.64, log KMgBL 2.98, and log KHBL 4.74. On the basis of those estimated parameters, a BLM was successfully developed to predict Cr(III) toxicity to barley root elongation as a function of solution characteristics.
Highlights
Chromium is one of the most widely used metals in modern industry [1], and it could be transferred into the environment through the waste products during various industrial processes [2], [3]
Distribution of chromium species in different pHs Resin-extractable Cr by Dowex M4195 was not detected in the test medium, which implied that there was no Cr(III) oxidized to Cr(VI) during the experiment period
The results indicate that biotic ligand model (BLM) can predict barley root elongation much better than free ion activity model (FIAM) when Cr3+ plus CrOH2+ as toxic species and the competition of H+, Mg2+ and Ca2+ with the binding sites of barley root are incorporated in the Cr(III)-BLM
Summary
Chromium is one of the most widely used metals in modern industry [1], and it could be transferred into the environment through the waste products during various industrial processes [2], [3]. It has, become a common contaminant in waters and soils. Little focus on research into the influence of competition and speciation on Cr toxicity. Studies in aquatic toxicology have shown that the competition of other cations and the speciation of metals pose great influence on their toxicity [9], [10]. A risk assessment considering the effects of cation competition and metal speciation is needed to properly assess the risk of Cr(III)
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