Bioavailability of naphthalene associated with natural and synthetic sorbents

Bacteria differ in their abilities to degrade hydrophobic xenobiotic compounds which are associated with solid sorbents and nonaqueous phase liquids (NAPLs) in the environment. Here, we assess the bioavailability of naphthalene sorbed to forest soils, river sediment, and a variety of synthetic sorbents to two bacterial species studied previously using agricultural soils as sorbents. Using a mineralization kinetics approach, we determined that, for an Alcaligenes sp. (strain NP-Alk), sorbed naphthalene was unavailable for degradation and slow desorption limited the extent of mineralization in all sorbent systems. Pseudomonas putida strain 17484 had direct and immediate access to a portion of the sorbed naphthalene associated with all natural sorbents and facilitated the desorption of additional naphthalene for degradation. Naphthalene associated with forest soils was less available than naphthalene sorbed to agricultural soils or river sediments. Aging soil-naphthalene slurries (up to 3 yr equilibration) progressively diminished both the rate and extent of naphthalene degradation by strain 17484. Exposure of soil interior sorption sites by sonication of 3 yr old slurries increased naphthalene availability to this organism. Differential access to surface-sorbed naphthalene in soil studies, due to the attachment propensities of the two organisms, accounted for the observed bioavailability results. Sorption to granular activated carbon (GAC) virtually precluded naphthalene degradation by either organism, whereas naphthalene sorbed to XAD-2 resin, hexadecyltrimethylammonium (HDTMA)-modified smectite and Tenax was more rapidly desorbed and degraded in studies with strain 17484. The porosities and naphthalene binding characteristics of the sorbents appeared to control bioavailability.