Soluble organic fraction selective, oxidation

Total concentrations in the sediment do not necessarily reflect either the biologically or chemically reactive fraction of metals or substrates. Thus, -we have used partial extraction techniques to characterize different phases of both metal and substrate. Under different estuarine conditions, hydrous oxides may vary in crystallinity and in their associations -with other substrates (e.g., organics). The nature of the organic materials may also vary greatly. Different extractants remove different quantities of these substrates, in response to differences in substrate form ( ). We may not assume that extractants selectively remove trace metals from any single sorption substrate (2 +), but differences in trace metal solubility among extractants may be useful to empirically separate metal forms susceptible to different treatments. Statistical association... 

Figure 12.9 shows the effect of oxidizing and reducing conditions (redox potential) on the distribution of copper among several selected forms in river sediment. Under oxidized conditions, the copper was primarily tied up with iron because the extractant nsed to remove the reducible fraction primarily extracts the iron fonnd in the insoluble ferric form that is microbially reduced to a more soluble ferrous form, which would release bound copper. The insoluble organic copper decreases as the amount of copper coprecipitated with the increase in iron oxidation. The diethylene triamine pentaacetic acid (DTPA) extractable Cu showed little change with redox condition. 

---