Impact of soil-chemical interactions on the bioavailability of naphthaleneand 1-naphthol

The bioavailability of sorbed naphthalene and 1-naphthol was determined for two sandy soils differing primarily in organic matter content. Different s orption conditions were maintained over a 2 d equilibration period to estim ate the extent that oxidative coupling contributed to the strong binding of these compounds to the soils. Weakly sorbed test compounds were removed th rough 50 successive water extractions and the bioavailability of the remain ing sorbed fraction was determined by the addition of aerobic, test compoun d-degrading bacteria to soil slurry reactors. Soils were then incubated und er aerobic conditions for 90 d. Biodegradation rates were determined by mon itoring (CO2)-C-14 evolution and the soil-associated non-mineralized residu e 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 naphthale ne from the low NOM soil. Of the remaining material, 5.7-16.9% of 1-naphtho l 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 limi ted the bioavailability of 1-naphthol in both soils. Naphthalene bioavailab ility was not greatly limited because it can not directly participate in st rong binding reactions. (C) 1999 Elsevier Science Ltd. All rights reserved.