One of the long-term goals of research in environmental chemistry has been the quantitative description and prediction of metal interactions with DOM.  George Aiken contributed significantly to this effort because a large proportion of the metal binding data has come from laboratory measurements using materials isolated using techniques that George and his colleagues pioneered, starting nearly four decades ago.  To assess how far we have come, we compiled a data set of c. 2000 published metal speciation measurements made on samples of freshwaters, estuarine and coastal waters, and open ocean waters, and applied the WHAM7 model to calculate metal speciation.  Comparison of the measured and predicted speciation variables for the whole data set showed that agreements are best for freshwaters, followed by estuarine and coastal waters, then open ocean waters.  Comparison of model predictions with measurements by different analytical techniques suggests that competitive ligand / stripping voltammetry methods overestimate metal complexation by DOM, and therefore underestimate free metal ion concentrations.  When measurements by other methods are compared with predictions, for all metals, reasonable agreement with little bias is obtained for conditions where the ratio of bound metal to DOM exceeds 10<sup>-6</sup> mol g<sup>-1</sup>, but at lower ratios the model predictions of [M] are mostly higher than the measured values, and the predictions of metal binding mostly lower.  Research is needed to establish whether this reflects analytical error or the failure of the model to represent natural

Can we predict metal binding by DOM?

253rd National Meeting (2017)

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