Joan F. Braddock

The Fate of the Oil Spilled from the Exxon Valdez

Just after midnight on March 24, 1989, the 987-foot tank vessel Exxon Valdez grounded on Bligh Reef in Prince William Sound (PWS), Alaska, releasing approximately 10.8 million gallons of North Slope crude oil into the Sound. The energetic environmental conditions in PWS and the extensive cleanup activities led to wide dispersion of the Exxon Valdez oil, which simultaneously underwent biodegradation and photooxidation. Although some more refractory residuals of the petroleum (e.g., high molecular weight PAH, resins, and asphaltenes) persist, many of these constituents are not readily distinguishable from other petroleum sources and naturally occurring hydrocarbon residues. We estimate that approximately 20% of the spilled oil evaporated and underwent photolysis in the atmosphere; approximately 50% biodegraded either in-situ on beaches or in the water column; approximately 14% was recovered or disposed; < 1% remained in the water column (except as biodegradation products); approximately 2% remained on intertidal shorelines; and approximately 13% remained in subtidal sediments, mostly in the GOA and again mostly as highly weathered residuals. 60 refs., 3 figs., 2 tabs.

The Roles of Photooxidation and Biodegradation in Long-term Weathering of Crude and Heavy Fuel Oils

Abstract Although spilled oil is subject to a range of natural processes, only combustion, photooxidation and biodegradation destroy hydrocarbons and remove them from the biosphere. We present laboratory data that demonstrate the molecular preferences of these processes, and then examine some oil residues collected from previously documented releases to confirm the important roles that these processes play in removing spilled oil from both marine and terrestrial environments.

Biodegradation of petroleum hydrocarbons at low temperature in the presence of the dispersant Corexit 9500

Our study examined the effects of Corexit 9500 and sediment on microbial mineralization of specific aliphatic and aromatic hydrocarbons found in crude oil. We also measured gross mineralization of crude oil, dispersed crude oil and dispersant by a marine microbial consortium in the absence of sediment. When provided as carbon sources, our consortium mineralized Corexit 9500 the most rapidly, followed by fresh oil, and finally weathered oil or dispersed oil. However, mineralization in short term assays favored particular components of crude oil (2-methyl-naphthalene > dodecane > phenanthrene > hexadecane > pyrene) and was not affected by addition of nutrients or sediment (high sand, low organic carbon). Adding dispersant inhibited hexadecane and phenanthrene mineralization but did not affect dodecane and 2-methyl-naphthalene mineralization. Thus, the effect of dispersant on biodegradation of a specific hydrocarbon was not predictable by class. The results were consistent for both high and low oiling experiments and for both fresh and weathered oil. Overall, our results indicate that environmental use of Corexit 9500 could result in either increases or decreases in the toxicity of residual oil through selective microbial mineralization of hydrocarbons.

Microbial community analysis: a kinetic approach to constructing potential C source utilization patterns

Abstract The analysis of multiple substrate metabolism by assemblages of bacterial strains may be used to differentiate inocula from environmental samples. Biolog plates, 96-well microtiter plates containing nutrients, a single carbon test substrate in each well and a tetrazolium redox dye to monitor substrate oxidation, have been used for this purpose. One of the difficulties faced by users of this technique is determining which substrates have been metabolized. Reliance on single-time-point absorbance data for each well is problematic due to variably non-linear rates of color development for each well. Previous efforts to use color-normalized single plate readings have been successful in discriminating between environmental sample types, but substrate-use contributions to sample classifications vary depending on the duration of the plate incubation. We present a model based on the logistic equation for density-dependent population growth providing a good (low χ 2 ) fit to the sigmoidal kinetics of color development data. The kinetic parameters generated by the model can be used as surrogates for single-time-point data in constructing carbon source utilization patterns, and contribution of substrate use to sample classification does not depend on incubation time. This technique obviates the need to choose the time following inoculation to read the plate absorbance data and also provides two kinetic parameters that are invariant with respect to inoculum density. We provide a comparison of community potential substrate use analyses using single-time-point microplate data and parameters from our kinetic model.

Enhancement and inhibition of soil petroleum biodegradation through the use of fertilizer nitrogen: An approach to determining optimum levels

Laboratory studies were conducted to evaluate the relationship between soil water content and microbial response to soil nitrogen (N) in petroleum‐contaminated soils. Various levels of N were added to a sand, a sandy loam, and a silt loam. Measurements of the extent of biodegradation in each soil (petroleum loss or CO2 production) indicated that biodegradation was related to soil N expressed as a function of soil water (mg N/kg soil H2O or mg N/I) better than N expressed as a function of soil dry matter (mg N/kg soil). A loamy sand was treated with four levels of N (0, 250, 500, 750 mg N/kg soil) and incubated at three water contents (5.0, 7.5, and 10.0% on a dry soil weight basis). Soil water potential and O2 consumption were best related to N expressed on the basis of soil water. It is concluded that expressing N in units of mg N/kg soil H2O (easily obtained by dividing [mg N/kg dry soil] by [soil moisture content]) can be used to determine fertilization rates for bioremediation processes. On this basis...

Long-term effects on microbial communities after a subarctic oil spill

Abstract A combination of microbial assays was used to examine soil population structure and community-level metabolism at the site of a 1976 experimental crude oil spill conducted in Alaska. Estimates of total bacterial numbers and soil C mineralization potentials were not significantly different between pristine and hydrocarbon-affected soils. In contrast, net N mineralization potential was lower, metabolically active (FDA stain) bacteria were less abundant and hydrocarbon degrading microbes were more abundant in the oiled soils. Additionally, the effects of dilution on the kinetics of community-level substrate use were examined in multiple substrate microplates. Microplate kinetic patterns varied less with dilution and by season in oiled soils. In oiled soils, absence of seasonal variation in soil C mineralization potentials, coupled with the microplate data, indicated that population diversity (evenness, richness or both) was diminished compared to the pristine soils. Further analysis of microplate data suggested that the communities surviving in the oiled soils may be considered metabolic generalists. By using several independent microbial assays, differences in soil microbial community structure attributable to oiling could be seen decades after the spill event.

Two polyisoprenylated benzophenones from the trunk latex of Clusia grandiflora (Clusiaceae)

The polyisoprenylated benzophenones, chamones I and II, were isolated from the trunk latex of Clusia grandiflora (Clusiaceae) growing in southeastern Venezuela. A third benzophenone, nemorosone II, was isolated from the pollinator reward resin of the female flowers of the same plant. Chamone I and nemorosone II are structurally similar, differing only in the degree of prenylation. Bioassays of chamone I and nemorosone II using the honeybee pathogens, Paenibacillus larvae and Paenibacillus alvei, demonstrate that both have potent antibacterial activity, and that their structural differences affect both their bactericidal efficacies and their aqueous mobilities.

Distribution of hydrocarbon-degrading microorganisms in sediments from Prince William Sound, Alaska, following the Exxon Valdez oil spill

Abstract Biodegradation by naturally occurring populations of microorganisms is a major mechanism for the removal of petroleum from the environment. Therefore, measurements of microbial populations are an important component of contaminated site assessment studies. Over a 3 year period following the T V Exxon Valdez oil spill in Prince William Sound, Alaska, we counted numbers of hydrocarbon-degrading microorganisms in intertidal and subtidal sediments affected by the spill. We found significantly higher numbers of hydrocarbon-degrading microorganisms at sites within the path of the oil slick than at reference sites, indicating rapid acclimation of the resident microbial populations. In offshore surface sediments, we saw a temporal increase in numbers of hydrocarbon-degrading microorganisms. Our data suggest that microbial measurements are good indicators of exposure of sediments in Prince William Sound to hydrocarbons and of mobilization of oil to surface sediments offshore over time.

Integral biopile components for successful bioremediation in the Arctic

Timely bioremediation of petroleum-contaminated soils in the Arctic is possible with innovative engineering and environmental manipulation to enhance microbial activity beyond the natural effective season. Key parameters in extending the period of beneficial microbial activity in Arctic biopiles are temperature and substrate availability. A multidisciplinary team of engineers, microbiologists and electricians has designed and installed a thermally enhanced biopile at a diesel-contaminated gravel pad in Prudhoe Bay, AK. The combination of bioventing with active warming, fertilization and power cycling is working toward timely remediation at this site. Primary components for success are the (1) thermal insulation system (TIS) design, (2) microbiological monitoring plan, and (3) power optimization. (Alternate power sources are considered for use at this and future remote bioremediation sites.) This paper discusses the TIS design and extension of the effective treatment season, fertilization and the results of a treatability study that compared simple fertilization with application of commercially available bioproducts under simulated site conditions, and adjusting power utilization to prevent permafrost thaw. Through an integrated approach to bioremediation, we are treating diesel-contaminated soils at an Arctic site.

Nutrient and temperature interactions in bioremediation of cryic soils

Low temperatures and lack of available nutrients often limit the rate of microbial petroleum hydrocarbon degradation in contaminated cryic soils. Proper management of both these parameters may increase microbial respiration in such soils. Interactions between nutrient level and temperature could impact management decisions for both factors, but these interactions have not previously been adequately described. Petroleum-contaminated soils from two Alaskan sites were studied in separate laboratory experiments. Nutrients and incubation temperatures were independently varied so interactions between the two could be studied. Soil from a gravel pad near Barrow, AK responded positively to temperatures increasing from 5°C to 20°C, and to addition of 50 or 100 mg/kg of supplemental nitrogen. Soil from Ft. Wainwright, AK responded positively as temperatures were increased from 1°C to 21°C, but microbial respiration decreased when temperatures were raised to 41°C. Microbial activity increased when 100 or 200 mg/kg of supplemental nitrogen was applied. In both soils, there were positive interactions between soil temperature response and addition of nitrogen fertilizer. Microbial response to soil warming was accentuated by proper nitrogen management, and response to fertilizer application was greatest when soil was warmed.