Speciation of heavy metals in landfill-leachate polluted groundwater

Anaerobic leachate polluted groundwater samples were collected downgradient of a Danish landfill. The groundwater samples were spiked with heavy metal s at concentrations within the range of metal concentrations found in landf ill leachates (100 mu g Cd l(-1) 500 mu g Ni l(-1), 1000 mu g Zn l(-1), 100 0 mu g Cu l(-1) and 1000 mu g Pb l(-1)) and divided under anaerobic conditi ons: into colloidal (screen-filtration and cross-flow ultrafiltration), org anic (anion-exchange) and dissolved inorganic species of the heavy metals. The distribution of the heavy metals between the different size-fl actions showed that a substantial, but highly varying part of the heavy metals was associated with the colloidal fractions (Cd: 38-45%, Ni: 27-56%, Zn: 24-45% , Cu: 86-95%, Pb: 96-99%). These colloidal bound metals were furthermore as sociated primarily with the organic fraction, except for Zn, which was asso ciated mainly with the inorganic fractions Dissolved Cd, Cu and Pb were mai nly associated with dissolved organic carbon, while Ni was also present as carbonate complexes and Zn as carbonate complexes and free divalent Zn. Mos t of the metals present in the colloidal fractions would have been sampled as dissolved if the commonly used filter size of 0.45 mu m had been used, s ince very little metal was found in colloids larger than 0.40 mu m (Pb < 15 %, Cd < 10%, Zn < 5%, Ni and Cu < 1%). The results indicate that heavy meta ls in leachate-polluted groundwater are strongly associated with Small-size colloidal matter and organic molecules. The behavior of heavy metals in th e environment is thus expected to differ from that of truly dissolved heavy metals. (C) 1999 Elsevier Science Ltd, All rights reserved.