| Abstract
| - Metal speciation in aquatic sediments is often characterizedusing wet chemical sequential extraction techniques.However, these methods are operationally defined andsubject to artifacts, particularly when dealing with anoxicsediments, in which metal sulfide precipitates are likelyto occur. Using X-ray absorption spectroscopy (XAS) and acid-volatile sulfide (AVS) analysis, we evaluated the effectivenessof one of the most widely used sequential extractionprotocols, the Tessier method, at determining Zn and Pbspeciation in anoxic wetland sediments. Sequential extractionresults significantly underestimated the amount of Znassociated with sulfide phases as compared to the othertwo approaches. XAS analysis of ZnS amended sedimentsindicates that the most likely source of this conflict is anearly dissolution of amorphous metal sulfide phases duringthe sequential extraction step corresponding to theextraction of iron and manganese oxides. The reagentmixture used in this step, hydroxylamine hydrochloride-HCl, is widely used in other sequential extraction protocols,including the BCR method, limiting their application toanoxic sediments. For this reason, current sequentialextraction techniques should only be used on anoxicsediments with caution, and/or in conjunction withcomplementary approaches to assess metal speciation.
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