Chapter 12
Biologically Mediated Dissipation of Polyaromatic Hydrocarbons in the Root Zone 1
A. P. Schwab and M. K. Banks Downloaded by UNIV OF ARIZONA on April 20, 2013 | http://pubs.acs.org Publication Date: August 12, 1994 | doi: 10.1021/bk-1994-0563.ch012
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Departments of Agronomy and Civil Engineering, Kansas State University, Manhattan, KS 66506
Soil contaminated with petroleum sludge is often bioremediated by tillage and addition of nitrogen and phosphorus to stimulate microbial degradation of the hazardous compounds. This "landfarming" technique is effective in reducing concentrations of a variety of chemicals during the early stages of treatment, but degradation rates severely decline thereafter, especially for recalcitrant compounds such as polyaromatic hydrocarbons (PAHs). However, the presence of vegetation can enhance the degradation of these compounds. In a greenhouse experiment, the degradation of PAHs was greater in the presence of plants than in their absence. Target PAHs were detectable in the plant tissue, but the total quantity of uptake was insignificant. Enhanced microbial activity was apparently responsible for increased dissipation of target PAHs. Establishment of vegetation holds promise as an inexpensive yet effective means of passive remediation of sites contaminated with petroleum hydrocarbons.
A common environmental problem associated with pumping and refining crude oil is the disposal of petroleum sludge. The sludge is usually very viscous or solid and can be treated by incorporation into soil. If the soil is frequently tilled and fertilized, soil microorganisms will be stimulated and organic contaminants biodegraded. Unfortunately, biodegradation of the more recalcitrant and potentially toxic contaminants, such as the polyaromatic hydrocarbons (PAHs), is rapid at first but quickly declines. The establishment of vegetation in soils contaminated with hazardous organics can help stimulate bioremediation (1). Generally, plants will grow well only in moderately contaminated soil, and the use of plants to enhance biodegradation of organics is limited to the upper 2 m of the soil profile (2).
0097-6156/94/0563-0132$08.00/0 © 1994 American Chemical Society In Bioremediation through Rhizosphere Technology; Anderson, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.
Downloaded by UNIV OF ARIZONA on April 20, 2013 | http://pubs.acs.org Publication Date: August 12, 1994 | doi: 10.1021/bk-1994-0563.ch012
12.
SCHWAB & BANKS
Polyaromatic Hydrocarbons in the Root Zone
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Despite these restrictions, establishment of vegetation can be an economic, effective, low maintenance approach to waste remediation and stabilization. Plants can interact directly with hazardous organic compounds through accumulation or degradation (3). Uptake of the contaminant by plant roots can be an active process involving specific enzymes and the expenditure of energy or a passive process in which neutral, hydrophilic compounds move unimpeded into the roots along with water (4). In either case, uptake of the pollutant is usually a direct function of concentration in the soil solution. Within the plant, the contaminant can be irreversibly adsorbed (2), accumulated in cells, or transported in the plant's vascular system (4). Plants often are able to metabolize toxic organics, and plant species tolerant to specific compounds can possess metabolic protection and significantly degrade an accumulated chemical (5). The content of PAHs in plants has been assessed in many urban, agricultural, and pristine environments. Concentrations in leaves generally range from
