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Dep. of Chemistry, Washington State Univ., 100 Sprout Road, Richland, WA 99352
Dep. of Natural Resources Science
Dep. of Food Science and Nutrition, Univ. of Rhode Island, Kingston, RI 02881
* Corresponding author ( apg{at}beta.tricity.wsu.edu).
ABSTRACT
Naphthalene sorption and biodegradation were quantified in three soils of varying organic C content using miscible displacement and batch incubation techniques. As anticipated, sorption increased with organic C content; the sorption rate coefficient and equilibrium sorption constant (Kd) were inversely related. Organic matter in solution (NOM) from the high-organic-matter soil decreased apparent sorption, which was also quantified using methanol as a cosolvent. A cosolvency power of 3.8 or 4.1 was determined. The initial biodegradation rate decreased with increasing sorption and was a function of naphthalene concentration in solution. The extent of biodegradation was greatest in the high-organic-matter soil and decreased when NOM was removed from the system. The observed dependence of biodegradation kinetics on sorption (this study and in the literature) prompted us to develop a simple approach for approximating a biodegradation rate constant for soil-water systems. This approach combines independently determined sorption parameters with the biodegradation rate constant determined for aqueous (soil-free) solution. The approach was applied to our data and to published data where sorption was shown to control naphthalene biodegradation. The approximated biodegradation rate constant was within 10% of the measured values for three cases, 20% for a fourth case, and was underestimated by five-to sevenfold for the high-organic-matter soil. The approach will be useful when applying management models for predicting contaminant fate and transport that require a degradation rate constant, or for estimating biodegradation rates in situations where cultured organisms are introduced for biodegradation.
Received for publication May 20, 1996.
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