Trace elemental distribution in soil and compost-derived humic acid molecular fractions and colloidal organic matter in municipal wastewater by flow field-flow fractionation-inductively coupled plasma mass spectrometry (flowFFF-ICP-MS)

Humic acids (HA) are heterogeneous, dark-colored, organic macromolecules fo und in soil and aquatic systems that play a crucial role in complexation, t ransportation and cycling of trace elements in ecosystems. Flow field-flow fractionation-inductively coupled plasma mass spectrometry (flow FFF-ICP-MS ) is applied to study trace metals complexed to soil-, peat- and compost-de rived HA and colloidal organic matter (COM) in municipal wastewater. Monomo dal elemental fractograms with different polydispersities demonstrate that Cu, Fe. Mn, Pb and Zn are bound to a broad range of HA molecular size fract ions. Molecular weights (M-p) and diffusion coefficients (D-p) at peak maxi mum for HA or various origins were determined by flow FFF. The average M-p of nine replicate measurements of investigated HA ranged from 3950 to 3790 Da while their diffusion coefficients varied from 1.72 x 10(-6) cm(2) s(-1) for peat-derived HA to 1.66 x 10(-6) cm(2) s(-1) for compost-derived HA, i ndicating very small variations among the HA under investigation. Elemental fractograms were also obtained for aqueous COM in municipal wastewater aft er on-line preconcentration. Fractograms clearly showed the gradual reducti on of COM content for primary through secondary treatment. Elemental COM fr actograms also demonstrated that the bulk of Al, Cu, Fe, Pb, Mn and Zn was complexed to organic macromolecules while a fraction of Al, Zn, Mn and halo gens (Cl, Br and I) was present as dissolved ionic species. Copper, Fe and Zn signals decreased during wastewater treatment. This investigation demons trate,,, precipitation and Subsequent removal of metal ions that are associ ated with COM as Sludge.