The environmental impact of metals in biosolids to plants, animals and the human food chain has been studied for decades. From the related literature, it can be concluded that, by addition of biosolids to soil, the overall chemical reactivity in the soil system is altered beyond that of the simple addition of trace elements due to the addition of chemically active surfaces (i.e., OC, Fe and Mn oxides) from biosolids processing. The purpose of this presentation is to discuss how X-ray fluorescence (XRF) and x-ray absorption near-edge structure (XANES) spectroscopy techniques can be employed to observe distribution and association of metals with Fe and Mn phases; to identify phases of Fe and Mn, and metal binding mechanisms in biosolids.

Elemental correlations derived from elemental mapping showed strong correlations between Fe with Cd, Cr, Mn, Pb, or Zn before and after removal of OC. Except for Fe and Cr, the spatial correlations of metals with Mn were poor before removal of OC. The consistency of correlations between Fe and trace metals before and after the oxidation of majority of organic matter in these samples provide indirect evidence for trace metals being associated with the Fe oxides, and correlates with our previous Cd adsorption and desorption studies. Further the XANES analysis indicated a sorption and incorporation of those metals with the Fe-oxide phases as the possible mechanisms of metal retention by Fe phases.

This study suggests that even if the metals were associated with organic matter, decomposition of organic matter will not result in substantial release of the trace metals as free ions because they will become associated with nearby Fe and Mn compounds. Further synchrotron based micro scale techniques may be able to provide information about reaction products in biosolids amended soil systems.