Reversible Sorption and Irreversible Binding of Naphthalene and α-Naphthol to Soil: Elucidation of Processes

The sorption and irreversible binding of naphthalene and α-naphthol to two sandy soils were evaluated. To determine the extent that biologically-mediated oxidative coupling contributed to the irreversible binding of α-naphthol, the presence/absence of O 2 and the presence/absence of biological activity were varied during the sorption period to operationally define biological coupling conditions. After a 2-d sorption period, sorbed material was removed by successive water and solvent extractions, alkali extractions, and combustion. Nonextracted material was defined as the amount of test compound remaining after solvent extraction ( Q NONEX ). Naphthalene that was not extracted after the 2-d sorption period was caused by mass transfer-limited entrapment within micropores and was used to estimate the fraction of entrapped α-naphthol. The principle of superposition was applied to the α-naphthol results to determine the contribution of individual irreversible binding processes. Biologically-mediated oxidative coupling accounted for 49.4 ± 15.0% of Q NONEX of α-naphthol. Oxidative coupling catalyzed by mineral surfaces accounted for 40.5 ± 15.8% of Q NONEX of α-naphthol. Over contact times up to 200 d, nonextracted naphthalene increased from 1.6% to 11.7% of the initially sorbed material, coincident with the biological production of a more polar metabolite.