| Abstract
| - Associations with functional groups of natural organicmatter (NOM) are of great importance for bioavailability,toxicity, and mobility of trace metals in soils and waters. Inthis study, the coordination chemistry of copper, Cu(II),in organic soils and dissolved organic matter (DOM) fromsoils and streams was investigated by extended X-rayabsorption fine structure (EXAFS) spectroscopy. In bothsoil organic matter (SOM) and DOM (990−11 000 μg Cu g-1dry weight, pH 2.8−6.3), Cu(II) was coordinated by 4 oxygen/nitrogen (O/N) atoms at a distance of 1.92−1.95 Å inthe first coordination shell. These four atoms are positionedin the equatorial plane of a Jahn−Teller distortedoctahedron. In samples with a pH of 4.8−6.3, a secondcoordination shell with 2.0−3.8 C atoms was located at adistance of 2.76−2.86 Å. A significant improvement (19−39%) of the fit was obtained by including a third coordinationshell with 2.0−3.8 O/C atoms involved in single scatteringat an average distance of 3.69 Å and multiple scatteringat an average distance of 4.19 Å. Our results provide evidencefor inner-sphere complexation of Cu(II) in NOM andsuggest that Cu(II) is complexed by either one or two five-membered chelate rings involving possible combinationsof amino, carboxyl, or carbonyl functional groups. Ion activitymeasurements showed that less than 0.2% of total Cuwas in the form of free Cu2+ in our samples at pH 4.8−6.3.
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