THE IMPORTANCE OF SURFACE-AREA IN METAL SORPTION BY OXIDES AND ORGANIC-MATTER IN A HETEROGENEOUS NATURAL SEDIMENT

This study provides empirical validation of current trace metal sorpti on theory in a small urban river. We demonstrate that trace metal comp lexation reactions occur predominantly at the suspended particulate su rface involving surface layers of Fe oxides and organic matter. Associ ated surface areas of these geochemical fractions were calculated wher e possible, using the total surface area (TSA) of the suspended partic ulate matter pool (SPM) in conjunction with estimates of suspended par ticulate Fe and Mn oxides (SPOX) and organic matter (SPOM) concentrati ons. Iron and Mn oxides concentrations were estimated using an extract ion scheme. For two samples where no SPOM or Mn oxides were present, e stimates of Fe oxides associated surface area were determined which co mpared favourably to literature estimates, providing further evidence for acceptable selectivity of extraction schemes. The utility of liter ature estimates of surface areas for single component sediments in het erogeneous sediments was also assessed. In mixed sediment samples, exp osed surface areas of discrete phases are probably reduced due to mixe d layering effects of the coatings, and the use of constants to estima te the surface areas of individual fractions does not work, since the relationship between the concentration of a given sedimentary fraction and its exposed surface area is no longer predictable.