Chapter 11
Volatilization and Mineralization of Naphthalene in Soil—Grass Microcosms
Downloaded by UNIV OF MISSOURI COLUMBIA on April 20, 2013 | http://pubs.acs.org Publication Date: August 12, 1994 | doi: 10.1021/bk-1994-0563.ch011
J. W. Watkins, D. L. Sorensen, and R. C. Sims Civil and Environmental Engineering Department, Utah State University, Logan, UT 84322-4110
The potential for vegetation-enhanced biodegradation of naphthalene in artificially contaminated soil was studied in laboratory microcosms. Microcosms containing soil without plants and soil supporting two-month old Bell Rhodesgrass were treated with naphthalene and spiked with [7- C]naphthalene. Compressed air was continuously passed through each microcosm, through a trap to collect volatile organics, and through a trap for C O . The microcosms were incubated under artificial lighting with a 16 h photoperiod for 25 days. After incubation, soil was solvent extracted and combusted to recover bound radiolabel. Volatilization losses during operation and analysis prevented reaching a mass balance of the radiolabel. Naphthalene volatilization was enhanced by vegetation but mineralization was decreased in vegetated microcosms in comparison to those without vegetation. 14
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Polycyclic aromatic hydrocarbon (PAH) compounds may be toxic and carcinogenic. Soils can become contaminated with PAH compounds from many industrial sources including wood preservatives, coal gasification wastes, and petrochemical wastes. Many PAH compounds, especially those with two and three ring structures, are biodegradable and can serve as growth substrate for microorganisms. Higher molecular weight PAH compounds may be cometabolized by soil microorganisms, with soil half-lives of several hundred days (7). Plant-enhanced biodegradation of PAH compounds is a recent area of research and is based on the hypothesis- that increased microbial activity associated with plant roots will accelerate biodegradation. Aprill and Sims (2) showed a statistically significant increase in disappearance of benz(a)anthracene, benzo(a)pyrene, chrysene and dibenz(a, h)anthracene from soils vegetated with eight different prairie grasses compared to unvegetated soils. Wheat straw (3), trichloroethylene (4), surfactants (5), parathion (6, 7), and diazinon (7) have all been shown to degrade faster in soil/plant systems when compared with soil degradation alone. Naphthalene is the smallest PAH and has the physiochemical properties listed in Table I. The partition coefficients in Table I were calculated from structure-
0097-6156/94A)563-0123$08.00A) © 1994 American Chemical Society In Bioremediation through Rhizosphere Technology; Anderson, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
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activity relationships (8). Naphthalene was biodegraded in soil relatively rapidly under aerobic conditions (9) and may be distributed among the gas, liquid, and solid phases in unsaturated soil (10,11,12,13,14). Environmental fate models that use partition coefficients sometimes exclude die affects of biota on the fate of chemicals (15). The predominant mechanism(s) (i.e., sorptive immobilization, translocation by leaching or volatilization, or biodegradation) effecting the fate of naphthalene in contaminated soil
Downloaded by UNIV OF MISSOURI COLUMBIA on April 20, 2013 | http://pubs.acs.org Publication Date: August 12, 1994 | doi: 10.1021/bk-1994-0563.ch011
Table I.
Physical properties and degradation half-life of naphthalene Property Reference Value Molecular Weight 128 Aqueous solubility 30mg/L (1) Vapor Pressure (20° C) 0.049 torr (») logKd 0.67 (*) logKoe 3.11 («) logKow 3.37 (8) logK -1.97 (8) tl/2 2.1 days (8) Kd = concentration in soil/concentration in water. Koc = K
