Chapter 32 - Reducing Leachability and Bioaccessibility of Toxic Metals in Soils, Sediments, and Solid/Hazardous Wastes Using Stabilized Nanoparticles

Abstract

Toxic metals such as chromium and lead have been widely detected at thousands of priority sites in the United States. To mitigate the toxic effects on human and environmental health, it is essential to reduce the leachability and bioaccessibility of these metals. Although the concept of in situ immobilization has elicited great interest for decades, cost-effective in situ treatment technologies for reducing leachability and bioaccessibility of metals remain lacking. This chapter aims to illustrate the concept and promise of in situ metal immobilization using some newly developed stabilized nanoparticles that can be delivered and dispersed into various porous media and can bind these metals strongly. Two toxic metals including Cr(VI) and Pb(II) were selected as prototype contaminants, and accordingly, uses of two types of nanoparticles (zero valent iron (ZVI) and iron phosphate) are illustrated. Stabilized ZVI nanoparticles were prepared using a carboxymethyl cellulose (CMC) as a stabilizer, and in situ reductive immobilization of Cr(VI) in water and in a sandy loam soil was illustrated. Stabilized iron phosphate (vivianite) nanoparticles were synthesized with CMC as a stabilizer for in situ immobilization of Pb(II) in soils. The CMC-stabilized nanoparticles were shown to effectively reduce the toxicity characteristic leaching procedure (TCLP) leachability and physiologically based extraction test (PBET) bioaccessibility of Pb(II) in three representative soils (calcareous, neutral, and acidic). The stabilization of the ZVI nanoparticles is attributed to the adsorption of CMC molecules to the surface of the nanoparticles. This latest knowledge sheds light on developing alternative in situ immobilization strategies for remediation of contaminated sites with toxic metals using stabilized mineral nanoparticles.