title: pH-dependent release of cadmium, copper, and lead from natural and sludge-amended soils.
abstract: The pH-dependent release of cadmium, copper, and lead from soil materials was studied by use of a stirred flow cell to quantify their release and release rates, and to evaluate the method as a test for the bonding strength and potential mobility of heavy metals in soils. Soil materials from sludge-amended and nonamended A horizons from a Thai coarse-textured Kandiustult and a Danish loamy Hapludalf were characterized and tested. For each soil sample, release experiments with steady state pH values in the range 2.9 to 7.1 and duration of 7 d were performed. The effluent was continuously collected and analyzed. Release rates and total releases were higher for the Hapludalf than the Kandiustult and higher for the sludge-amended soils than the nonamended soils. With two exceptions the relative release rates (release rate/total content of metal in soil) plotted vs. steady state pH followed the same curves for each metal, indicating similar bonding strengths. These curves could be described by a rate expression of the form: relative release rate = k[H+]a, with specific a (empirical constant) and k (rate constant) parameters for each metal demonstrating that metal release in these systems can be explained by proton-induced desorption and dissolution reactions. With decreasing pH, pronounced increases in release rates were observed in the sequence cadmium > lead > copper, which express the order of metal lability in the soils. The flow cell system is useful for comparison of metal releases as a function of soil properties, and can be used as a test to rank soils with respect to heavy metal leaching.
authors.affiliation: Dep. of Soil Science, Kasetsart University, Phaholyathin, Chatujak, Bangkok, 10900, Thailand.
authors.forename: Orathai
authors.initials: O
authors.lastname: Sukreeyapongse
authors.forename: Peter E
authors.initials: PE
authors.lastname: Holm
authors.forename: Bjarne W
authors.initials: BW
authors.lastname: Strobel
authors.forename: Supamard
authors.initials: S
authors.lastname: Panichsakpatana
authors.forename: Jakob
authors.initials: J
authors.lastname: Magid
authors.forename: Hans Christian Bruun
authors.initials: HC
authors.lastname: Hansen
mesh_terms: D000327:Adsorption; D002104:Cadmium / Q000032:analysis* / Q000737:chemistry; D003300:Copper / Q000032:analysis* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007854:Lead / Q000032:analysis* / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis*; D014872:Water Movements; D014873:Water Pollutants / Q000032:analysis*
chemical_list: D012989:Soil Pollutants; D014873:Water Pollutants; D002104:Cadmium; D007854:Lead; D003300:Copper