ENHANCED MOBILITY OF PB IN THE PRESENCE OF DISSOLVED NATURAL ORGANIC-MATTER

The speciation of Pb in batch experiments and its mobility under flowi ng conditions in column transport experiments were investigated to stu dy Pb behavior in a soil-water system in the presence of dissolved nat ural organic matter (DOM), peat humic acid (PHA) and peat fulvic acid (PFA). A sandy soil having a significant intraparticle porosity was us ed as the sorbing media. Batch equilibrium sorption isotherms for sing le components (Pb, PHA, and PFA) and for Pb in the presence of PHA and PFA were generated. Batch equilibrium experiments were also performed for both PHA and PFA to investigate Pb-DOM binding in the absence of soil. Single component (Pb, PHA, and PFA) and multicomponent (Pb-PHA a nd Pb-PFA) laboratory-scale column transport experiments were conducte d to assess transport behavior of Pb in the presence of DOM. Sorption isotherms indicated that the soil had a higher affinity for PHA than f or PFA. However, single component column transport experiments showed that PHA was less retarded than PFA. This anomaly was attributed to th e size exclusion of the larger PHA molecules from the intraparticle po rosity of the media under the geochemical conditions in the column. Pb retardation predicted by equilibrium equations based upon nonlinear i sotherm parameterization agreed well with observed retardation. Howeve r, equilibrium retardation equations overpredicted retardation of DOM, indicating sorption kinetic Limitations (chemical and/or physical non equilibrium), molecular size exclusion during column transport, or che mical heterogeneity of the DOM. In multicomponent column transport exp eriments, Pb retardation decreased by factors of 4-8 in the presence o f DOM. Multicomponent batch equilibrium experiments suggested that Pb mobility was governed by speciation of Pb with soluble DOM during tran sport, Thus, Pb eluted earlier In the presence of PHA than in the pres ence of PHA than in the presence of PFA because PHA had a higher affin ity for Pb binding than PFA. (C) 1997 Elsevier Science B.V.