In Situ Speciation Measurements of Trace Metals in Headwater Streams

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• 作者：Kent W. Warnken ; Alan J. Lawlor ; Stephen Lofts ; Edward Tipping ; William Davison ; Hao Zhang
• 刊名：Environmental Science & Technology
• 出版年：2009
• 出版时间：October 1, 2009
• 年：2009
• 卷：43
• 期：19
• 页码：7230-7236
• 全文大小：255K
• 年卷期：v.43,no.19(October 1, 2009)
• ISSN：1520-5851

文摘

Concentrations of Al, Fe, Mn, Ni, Cu, Cd, Pb, and Zn were measured using DGT (diffusive gradients in thin-films) devices deployed in situ in 34 headwater streams in Northern England. Mean values of filtered samples analyzed by ICP-MS (inductively coupled plasma mass spectrometry) were used, along with DOC (dissolved organic carbon), pH and major ions, to calculate the distribution of metal species using the speciation code WHAM. DGT-measured concentrations, [Me]_DGT, of Zn and Cd were generally similar to concentrations in filtered samples, [Me]_filt. For the other metals, [Me]_DGT was similar to or lower than [Me]_filt. Calculation of the maximum dynamic metal from the speciation predicted using WHAM showed that most of the lower values of [Cu]_DGT could be attributed to the dominance of Cu−fulvic acid complexes, which diffuse more slowly than simple inorganic species. Similar calculations for Al, Pb, and Mn were consistent with appreciable proportions of these metals being present as colloids that are not simple complexes with humic substances. Differences between WHAM predictions and the measured [Ni]_DGT indicated that WHAM used with the default binding parameters underestimates Ni binding to natural organic matter. Plots of [Me]_DGT versus the ratio of bound metal to DOC provided slight evidence of heterogeneous binding of Pb and Cu, while results for Mn, Cd, and Zn were consistent with weak binding and complete lability.