Biodegradation of non-desorbable naphthalene in soils

The degradation of naphthalene was studied in soil-slurry systems, and a quantitative model was developed to evaluate the bioavailability of sorbed-phase contaminant. Four soils with different organic matter contents were used as sorbents. Two naphthalene-degrading organisms, Pseudomonas putida G7 and NCIB 9816-4, were also selected. Sorption isotherms and single and series dilution desorption studies were conducted to evaluate distribution coefficients, desorption parameters, and the amount of non-desorbable naphthalene. Biodegradation kinetics were measured in soil extract solutions and rate parameters estimated. Bioavailability assays involved establishing sorption equilibrium, inoculating the systems with organisms, and measuring naphthalene concentrations in both sorbed and dissolved phases over time. For all four soils, the sorption isotherms were linear, and desorption could be described by a model involving three types of sites: equilibrium, nonequilibrium, and non-desorption. Enhanced bioavailability, as evidenced by faster than expected degradation rates based on liquid-phase concentrations, were observed in soils with the higher sorption distribution coefficients. These observations could be described using model formulations that included solid-phase degradation. In all soils studied, degradation of non-desorbable naphthalene was observed.