Impact of soil-chemical interactions on the bioavailability of naphthalene and 1-naphthol

The bioavailability of sorbed naphthalene and 1-naphthol was determined for two sandy soils differing primarily in organic matter content. Different sorption conditions were maintained over a 2 d equilibration period to estimate the extent that oxidative coupling contributed to the strong binding of these compounds to the soils. Weakly sorbed test compounds were removed through 50 successive water extractions and the bioavailability of the remaining sorbed fraction was determined by the addition of aerobic, test compound-degrading bacteria to soil slurry reactors. Soils were then incubated under aerobic conditions for 90 d. Biodegradation rates were determined by monitoring ¹⁴CO₂ evolution and the soil-associated non-mineralized residue was measured by combustion of the soil after the 90 d period. Successive water extractions removed 38.7–64.3% of 1-naphthol and 62.4% of naphthalene from the high NOM soil and 67.2–82.9% of 1-naphthol and 72.3% of naphthalene from the low NOM soil. Of the remaining material, 5.7–16.9% of 1-naphthol and 73.3% of naphthalene in the high NOM soil and 3.7–6.0% of 1-naphthol and 34.2% of naphthalene in the low NOM soil was mineralized after 90 d. In contrast, >85% of both test compounds were mineralized in the absence of soil. Experimental evidence suggests that oxidative coupling reactions limited the bioavailability of 1-naphthol in both soils. Naphthalene bioavailability was not greatly limited because it can not directly participate in strong binding reactions.