sites (2). Toxic metal species extensively found at these Nitrilotriacetic acid (NTA) is extensively used in different inwaste sites can be complexed by organic chelates. This comdustries because of its excellent chelating properties. Introduction plex formation can result in increased subsurface movement of NTA into the natural environment is a concern because of of heavy metal and radionuclide species, initially to the adjamobilization of heavy metal species that may be otherwise bound cent and later to distant soil and ground waters.
to natural particulate matter. The present study investigates the Additionally, NTA (along with zeolite A and polycarboxadsorption behavior of Pb(II) and NTA, both as individual species ylates) has been used as a substitute detergent for tripolyand as complex species onto titanium dioxide. This adsorption phosphate because of eutrophication concerns in rivers and information is important in considering the TiO 2 -assisted photocatalytic treatment of these metal-organic complexes. Pb(II) lakes (3). Other sources of metal-NTA contaminants inshows a typical cationic type of adsorption behavior, whereas NTA clude water hardness control systems (4). Use of NTA on demonstrates an anionic type of adsorption trend. Results from a large scale is expected to result in mobilization and consestoichiometric ternary systems show a gradual increase in Pb(II) quently increased human uptake of toxic metal species that adsorption and a decrease in NTA removal with an increase in may normally be attached to the natural biota and particulate pH. However, for the cases of Pb(II) ú NTA, increased NTA material in the environment. Furthermore, attachment of adsorption as compared to pure NTA systems was noted even at NTA to the biological sludge during wastewater treatment higher pH. Model predictions employing MINTEQA2 software has also been reported ( 5). Land application of such a followed the experimental trends. Experimental and model results sludge, which may result in groundwater contamination and from ternary systems suggest adsorption of free Pb(II) and NTA, heavy metal mobilization, is an environmental concern. Nevas well as ternary Ti-NTA-Pb(II) and Ti-O-Pb(II) -NTA 20 species. The cationic-type complexation, i.e., Ti-O-Pb(II) -ertheless, biodegradation of NTA in subsurface sandy soils NTA 20 , was essential for the successful NTA adsorption model-and in biological treatment plants, which may result in reing, especially at higher pH and for Pb ú NTA systems, where duced NTA concentrations, has also been described (6, 7). significant NTA adsorption was noted even at very high pH values.
Lead has been extensively found both in soils and in Most of the previous metal-ligand adsorption studies did not congroundwater at several DOE waste sites (2). Also, Pb(II) sider such a surface complexation. However, the present results is a common pollutant and is found in wastes from numerous indicate that any groundwater transport modeling of such pollutdifferent sources, including the plating and battery manufacants will require the inclusion of cationic-type surface complexturing industries. Pb(II) that is present in the form of ation, in addition to other surface species.