Grantee Research Project Results
Final Report: Understanding Seasonal Variation of Bioavailability of Residual NAPL in the Vadose Zone
EPA Grant Number: R827133Title: Understanding Seasonal Variation of Bioavailability of Residual NAPL in the Vadose Zone
Investigators: Holden, Patricia , Keller, Arturo A.
Institution: University of California - Santa Barbara
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1998 through September 30, 2001
Project Amount: $425,000
RFA: EPA/DOE/NSF/ONR Joint Program on Bioremediation (1998) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management
Objective:
The current regulatory trend towards accepting intrinsic bioremediation as a long-term management scheme for residual organic pollutants in the subsurface for fuel spills is based on statistical evaluations of plume behavior for a limited array of pollutants. The effectiveness of intrinsic bioremediation towards protecting water supplies and human health is not known for many pollutants. In addition, the patterns of biodegradation that occur over seasonal time scales, the seasonality of intrinsic bioremediation, and its intermediate effectiveness, are unknown. Residual nonaqueous phase liquids (NAPLs) in the vadose zone, if left in place, have the potential to mobilize with seasonal moisture fluctuations. These seasonal variations in mass transfer along with the intrinsic microbial biodegradative response to moisture variations will determine bioavailability, which is a measure of the potential effectiveness of intrinsic bioremediation. Our research focuses on the determination of the effect of seasonal fluctuations in moisture content and soil temperature on abiotic and biotic fate and transport of hydrocarbons in the subsurface.
Summary/Accomplishments (Outputs/Outcomes):
Biotic Mechanisms in Bioavailability. In our work related to understanding the role of extracellular polymeric substances (EPS) in biodegradation, we continued studies to determine the nutritional conditions promoting EPS production. We found that there were significant differences in EPS production by Pseudomonas aeruginosa growing at a ratio of carbon to nitrogen (C/N) of 200 (see Figure 1, with glucose as the C source) as an unsaturated biofilm across a range of C/N conditions of 12 to 200. Biofilms grown with hexadecane, as compared to glucose-grown biofilms, produced less EPS (see Figure 2) and resulted in a lower total yield of biomass. Although a high C/N will promote EPS production, this is not achievable unless the carbon source is bioavailable. Thus, the low solubility of hexadecane is a possible explanation for the low production of EPS, even when hexadecane was in abundance. With higher solubility C sources, such as toluene, we expect that EPS would increase with increasing C/N because carbon substrate would be more bioavailable overall. In conjunction with our simulation of mass transfer and biodegradation, an implication of higher rainfall would be that the increased aqueous phase mass of toluene could lead to greater production of EPS. This remains to be tested. We continue to investigate the tradeoff between high gas phase mass transfer during dry conditions despite possible desiccation-dependent production of EPS, versus high solution phase mass transfer under wet conditions with the possible increased production of EPS. Because EPS is likely to be an important mass-transfer mediator, these mechanisms and the balance of their importance need to be established.
Figure 1. Production of Total Carbohydrate (TC) and Uronic Acid (Ur) EPS Relative to Cellular DNA and Total Protein by P. aeruginosa, Using Glucose as a Sole C Source. The effect of increasing C/N up to 200 is to significantly increase EPS production.
Figure 2. Glucose as a C Source Significantly Increases EPS Production by P. aeruginosa as Compared to Hexadecane as a C Source
Our interest in understanding nutritional controls on bacterial EPS production is to improve general, mechanistic models of biodegradation at the pore scale. To complement this work, we intend to improve the understanding of the occurrence of biofilms in vadose zone materials, and we are using a quantitative analytical chemical approach (e.g., see Figures 1 and 2) as well as a visual approach. The visual approach involves use of environmental scanning electron microscopy (ESEM), which enables the high-resolution imaging of specimens that are wet or dry and that do not have a conductive coating. The latter allows for visualizing samples in their native, unmasked state. Thus far, we have documented that we can use the water holding characteristics of EPS to reveal its presence on bacterially colonized unsaturated porous media (sand). We use two approaches. One approach is to electronically etch the specimen, and, where beam damage is highly sustained, this represents that soft matter in a heterogeneous (soft and hard matter) system. The second approach is to use the ESEM's unique capability in wetting/drying specimens while imaging. Regions of the porous media surfaces that retain water upon drying are those that are colonized by bacterial biofilms. In summation, we have advanced the understanding of bioavailability in unsaturated porous media by conducting experiments at the pore scale, in model experimental systems, and in simulations of mass transfer and biodegradation at the macroscale.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
| Other project views: | All 20 publications | 6 publications in selected types | All 6 journal articles |
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Holden PA, LaMontagne MG, Bruce AK, Miller WG, Lindow SE. Assessing the role of Pseudomonas aeruginosa surface-active gene expression to hexadecane biodegradation in sand. Applied and Environmental Microbiology 2002;68(5):2509-2518. |
R827133 (Final) |
not available |
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Saleta JL, Holden P. Imaging soil bacteria in an environmental scanning electron microscope. Microscopy and Microanalysis 2002;8(2):990-991. |
R827133 (Final) |
not available |
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Steinberger RE, Allen AR, Hansma HG, Holden PA. Elongation correlates with nutrient deprivation in Pseudomonas aeruginosa unsaturated biofilms. Microbial Ecology 2002;43(4):416-423. |
R827133 (Final) |
not available |
Supplemental Keywords:
sediments, chemical transport, chemicals, toxics, polycyclic aromatic hydrocarbon, PAH, bacteria, terrestrial, cleanup, environmental chemistry, biology, ecology, modeling, bioavailability, ecosystem protection, environmental exposure, risk, waste, water, bioremediation, contaminated sediments, ecological indicators, groundwater remediation, hydrology, chemical mixtures, nonaqueous phase liquid, NAPL, biodegradation, biological attenuation, chemical transport, ecological effects, ecological exposure, exopolymeric substances, fate and transport, mass transfer, natural bioattenuation, seasonal variation, vadose zone., RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Waste, Water, Ecological Indicators, Ecosystem Protection, chemical mixtures, Environmental Chemistry, Ecosystem/Assessment/Indicators, Contaminated Sediments, exploratory research environmental biology, Groundwater remediation, Ecological Effects - Environmental Exposure & Risk, Bioavailability, Ecological Effects - Human Health, Hydrology, Bioremediation, Chemical Mixtures - Environmental Exposure & Risk, ecological effects, ecology, bioremediation of soils, sediments, contaminated sediment, biological attenuation, NAPL, exoplymeric substances, seasonal variation, biodegradation, fate and transport, groundwater, water cycles, ecological exposure, natural bioattenuation, vadose zone, chemical transport, sedimentProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.