Assessment of arsenate bioavailability in iron-rich environments: development of a high-pressure liquid chromatography method of quanitification for arsenate sorbed by Fe3+-substituted chelating resins in arsenic-bearing ferrihydrite suspensions

摘要

Given that the mobility, bioavailability, and toxicity of arsenate in natural systems is oftencontrolled by the strong binding capacity of iron oxyhydroxides, the objective of this study was todocument the interactions of Dowex M4195 Fe3+-substituted chelating resins (a potential fieldbasedtool for the quantification of potential arsenate bioavailability) and arsenic-bearingferrihydrite (AFH) as a function of suspension pH, suspension concentration, and backgroundelectrolyte concentration. In 0.5 g AFH/L (0.001 M NaNO3) suspensions, arsenate sorption tothe resins was proportional to the degree of acidification of the AFH suspensions by the resins.H+-enhanced dissolution of ferrihydrite artificially increased the arsenate in solution, causing aconsistent overestimation of potential arsenate bioavailability. Resin-induced acidification wasdecreased with increasing suspension concentration. Arsenate sorption to the resins in 0.5 g/Lsuspensions at pH 8 decreased with increasing NaNO3 concentrations, reflecting the decreasingactivity of arsenate under these conditions. The results of this study indicate that the high buffercapacity of natural soils would prevent acidification as a result of resin introduction. Thus,Dowex M4195 Fe3+-substituted chelating resins should provide a reasonable assessment ofpotential arsenate bioavailability from poorly-crystalline iron oxide minerals. Possibly moreimportantly, Dowex M4195 Fe3+-substituted chelating resins appear to be a new choice ofpassive equilibrium sampling device that should work well for the determination of bioavailablearsenate concentrations in the field.