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.