A speciation methodology to study the contributions of humic-like and fulvic-like acids to the mobilization of metals from compost using size exclusion chromatography-ultraviolet absorption-inductively coupled plasma mass spectrometry and deconvolution analysis

High performance size-exclusion chromatography (HP-SEC) with UV absorption for organic matter detection and inductively coupled plasma mass spectrometry (ICP-MS) for elemental detection have been used to study the mobilization of metals from compost as a function of pH and the molecular mass of their complexes with dissolved organic matter (DOM). Due to its heterogeneous nature, organic matter mobilized from compost shows a continuous distribution of molecular masses in the range studied (up to 80 kDa). In order to differentiate between the contribution of humic and fulvic acids (FA) to the organic matter mobilized in the pH range 5-10, their UV absorption chromatographic profiles have been deconvoluted with respect to the adjusted gaussian profiles of the humic and fulvic acids isolated from compost. Results show a preponderant contribution of fulvic acids at low pH values and an increasing percentage of humic acids (HA) mobilized at basic pH (up to 49% of total DOM at pH 10). A similar deconvolution procedure has been applied to the ICP-MS chromatograms of selected metals (Co, Cu, Pb and Bi). In general, both fulvic and humic acids contribute to the mobilization of divalent transition metals, such as copper or cobalt, whereas bismuth or lead are preferably associated to humic acids. Non-humic substances (HS) also contribute to the mobilization of cations, especially at acidic pHs. These conclusions have been extended to different elements based on deconvolution analysis results at pH 7.