The rate of 2,2-dichloropropane transformation in mineral micropores: implications of sorptive preservation for fate and transport of organic contaminants in the subsurface.

Nanometer scale pores are ubiquitous in porous geologic media (soils and sediments). Sorption of organic contaminants in micropores (< or = 2 nm) can inhibittheir hydrolytic transformation due to the limited availability of reactive water within hydrophobic micropore spaces. As a test case, we studied the dehydrohalogenation of 2,2-dichloropropane (2,2-DCP) sorbed in the micropores of several model mineral solids. In the micropores of a hydrophobic dealuminated Y zeolite, CBV-780, 2,2-DCP dehydrohalogenation proceeded significantly slower than in bulk aqueous solution and eventually stopped. This was attributed to the depletion of reactive water molecules in the micropore spaces. The 2,2-DCP sorbed in the micropores of more hydrophilic solids (aquifer sediment, aquifer sand, and silica gel) also transformed slower than in aqueous solution, and the reaction no longer followed first-order kinetics. Results of transport modeling support that reactive contaminants sorbed in microporous minerals can be preserved over geological time scales under conditions that limit desorption. This study shows that hydrophobic micropores in geological media may act as an important sink for anthropogenic organic contaminants in the subsurface, and that sorption in micropores may significantly increase the persistence of the sorbed contaminants.