ANALYSIS OF RIVERINE METAL-ORGANIC COMPLEXES BY GAS CHROMATOGRAPHY-INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY

Organic matter in rivers waters represents a continuous size spectrum from small molecules to organisms. It has been long held that organic matter plays heavily in the complexation of metals in aquatic environments. Although studies show that the proportion of organic-complexed metals varies with metals such as Hg and Cu strongly complexed by organic ligands there is a paucity in understanding of the extent to which these complexes occur in the dissolved phase (operationally defined as less than 0.45 um). We studied the organic-metal complexes in the dissolved load of a series of agricultural receiving streams in Arkansas. We selected these streams based on the delivery rates of fresh organic matter to the streams and the relative abundances of dissolved metals to ensure that the dissolved load would contain appreciable amounts of organic-metal complexes. The dissolved organic matter components were identified by GC-MS. We quantified the total dissolved metal concentrations by DRC-ICP-MS. We assessed the relative abundance of organic-metal complexes by GC-ICP-MS. As expected organic-metallic complexes were most abundance for metals such as Mo, Cu, and Hg. Interesting up to 20% of the rare earth elements occurred in organic complexes. These data have important consequences for the study of river chemistry, in particular, these data point to the importance of measurement of naturally occurring metal-organic complexes and the advantages of GC-ICP-MS.