Summary
Municipal solid waste landfill leachates from nine Norwegian landfill sites were separated by size-charge fractionation to determine the concentrations of metals present as (1) particulate matter (> 0.45 µm), (2) anionic/non-labile species (< 0.45 µm) and (3) free metals/labile compounds. The fractionation was done in the field on freshly sampled leachate in order to avoid changes in metal distribution due to oxidation and subsequent precipitation and agglomeration. The fractionation method consisted of filtration through a 0.45 µm syringe filter (to obtain total dissolved metals), both with and without a subsequent cation exchange column (to obtain anionic/non-labile metal species). The fractionated leachate samples were analysed by high resolution ICP-MS. The investigations showed that Cu and Pb were present predominantly (88-96 %) as particulate matter, with less than 1 % in the form of free metals/labile compounds. Of the Cd and Zn, somewhat less (65-79 %) was in the particulate form, with 8-18 % of these metals present as free metals/labile compounds. However, Cr and Ni showed a very different metal distribution to the other heavy metals, being mainly (69-79 %) in the non-labile dissolved form. Only 21-31 % of Cr and Ni was in the particulate matter, and 1.5 ? 4.6 % in the free/labile form. The particulate matter itself was almost entirely inorganic, indicating that the metals in this fraction were bound mainly in inorganic forms. Species fractionation can give important information on the mobility and potential bioavailability of metals, in contrast to the total concentrations usually reported. Since the metals discharged in landfill leachate are mainly bound to particulate or colloidal matter, their release into the environment presents a lower immediate aquatic toxicity risk than that of similar metal concentrations in more labile forms. However, potential changes in the physico-chemical form of the metals after their discharge to the environment must also be considered when evaluating the overall environmental risk. One way to reduce the discharge of metals in landfill leachate is the use of aeration/sedimentation tanks. To investigate possible changes in metal speciation in sedimentation tanks, freshly sampled leachate was stored for 48 hours before fractionation. Parts of the free metal/labile compounds were immobilized (converted to particulate matter) during aeration of the leachate. This effect was strongest for Cd and Zn, the metals which had the largest percentage of free/labile metals in the fresh leachate.