Reversible sorption and irreversible binding of naphthalene and a-naphthol to soil: Elucidation of processes

The sorption and irreversible binding of naphthalene and a-naphthol to two sandy soils were evaluated. To determine the extent that biologically-mediated oxidative coupling contributed to the irreversible binding of a-naphthol, the presence/absence of O₂ 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 a-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 contacttimes 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.