| Abstract
| - The current work examines the effects of model allochtonous(humic substances) and autochtonous (microbial polysaccharides) natural organic matter (NOM) on Pb speciationand bioaccumulation. The results demonstrated thatpolysaccharides, in particular alginic acid, had complexingproperties and effects on Pb bioaccumulation by thegreen alga Chlorella kesslerii that were similar to equivalentcomplexing capacity of humic substances. Pb uptakedecreased in the presence of humic, alginic, andpolygalacturonic acids with respect to noncomplexed Pb,but accumulated Pb was higher than predicted frommeasured Pb2+ concentrations or from previous resultsobtained in the presence of simple synthetic ligands. Animproved fit between experimental observations andPb speciation was obtained by taking into account theformation of a ternary complex at the algal surface. Thecontribution of the ternary complexes to Pb bioaccumulationwas dependent on the relative binding constants of thePb to the NOM and to the binding sites on the biologicalsurface. In the presence of the humic acid, a decreasedsurface charge and increased membrane permeabilitywere considered to be of secondary importance to explainthe observation of increased Pb uptake with respect tothat predicted on the basis of [Pb2+]. The environmentalimplications of the results are discussed with respect to thedevelopment of site-specific water quality criteria.
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