Details

Autor(en) / Beteiligte

• Ahmed, Imad A.M.
• Hamilton–Taylor, John
• Bieroza, Magdalena
• Zhang, Hao
• Davison, William

Titel

Improving and testing geochemical speciation predictions of metal ions in natural waters

Ist Teil von

• Water research (Oxford), 2014-12, Vol.67, p.276-291

Ort / Verlag

Kidlington: Elsevier Ltd

Erscheinungsjahr

2014

Quelle

MEDLINE

Beschreibungen/Notizen

• The ability of WHAM VII and NICA-Donnan models to predict free-ion activities of Cu in natural waters was examined from two perspectives, (i) the presence of EDTA and NTA contaminants, (ii) the need to improve estimates of HA and FA concentrations. Potentiometric responses of a Cu(II) ion-selective electrode were investigated in five assays containing dissolved organic matter (DOM) isolated from a series of polluted (urban) and relatively unpolluted (upland) streams in northern England. The [Cu]/[DOC] ratio in these assays spanned an environmentally realistic range of ∼1–500 μmol/g. Reasonably good agreement between measured and predicted Cu2+ activities was obtained with both WHAM VII and NICA-Donnan models, assuming 65% of DOM as fulvic acid and including the measured EDTA and NTA concentrations, but generally the models overestimated the activities by a factor of ∼2. In contrast, the models over-predicted the Cu2+ activities by up to 2 orders of magnitude at low [Cu]/[DOC] ratios in urban waters if anthropogenic ligands were not included in the model simulations. Three-dimensional fluorescence excitation–emission matrix (EEM) spectroscopy was used to measure the functional properties of the isolated DOM and to estimate the fractions of FA and HA present. Using these fractions in the models gave improvements in predictions compared to the 65% FA assumption, as shown by higher correlations, reduced error and reduced bias. These results highlight various issues with the use of the available speciation models for predicting free ion concentrations in natural waters, such as the use of the Biotic Ligand Model (BLM) for the derivation of environmental standards. It is clearly necessary to measure EDTA and NTA in waters with urban influences, while fluorescence measurements offer the possibility of appreciably improving the accuracy of predictions. [Display omitted] •We report a new approach for representing reactive DOM in speciation calculations.•Fluorescence EEM provides a proxy for DOM components in different aqueous conditions.•Fluorescence-derived DOM as model input enabled Cu-speciation with improved accuracy.•Our new approach represents a way to overcome the problem of DOM natural variability.•Anthropogenic ligands coexisting with DOM are sources of errors in chemical speciation.