Hydrocarbon Mineralization Research Articles

Influence of inocula with prior hydrocarbon exposure on biodegradation rates of diesel, synthetic diesel, and fish-biodiesel in soil

To achieve effective bioremediation within short warm seasons of cold climates, microbial adaptation periods to the contaminant should be brief. The current study investigated growth phases for soil spiked with diesel, Syntroleum, or fish biodiesel, using microbial inocula adapted to the specific substrates. For modeling hydrocarbon degradation, multi-phase first order kinetics was assumed, comparing linear regression with nonlinear parameter optimization of rate constants and phase durations. Lag phase periods of 5 to >28d were followed by short and intense exponential growth phases with high rate constants (e.g. from kFish=0.0013±0.0002 to kSyntr=0.015±0.001d−1). Hydrocarbon mineralization was highest for Syntroleum contamination, where up to three times higher cumulative CO2 production was achieved than for diesel fuel, with fish biodiesel showing initially the slowest degradation. The amount of hydrocarbons recovered from the soil by GC–MS decreased in the order fish biodiesel>diesel>Syntroleum. During initial weeks, biodegradation was higher for microbial inocula adapted to a specific fuel type, whereby the main effect of the inoculum was to shorten the lag phase duration; however, the inoculum’s importance diminished after daily respiration peaked. In conclusion, addition of an inoculum to increase biodegradation rates was not necessary.

Soils Bioremediation of Hydrocarbons and Green Waste Elimination through Composting Process

The aim of this work was to study the mineralization of hydrocarbons during composting. For this purpose, soil/green waste mixtures were prepared at three different ratios (S/GW= 60/40, 70/30, 80/20) composted for 90 days. An unamended polluted soil (100% soil) was used as the control. The results indicate that the composting process greatly increased the overall rate of hydrocarbon mineralization. The greatest loss of hydrocarbons was obtained in the first compost with the most green waste (96%), followed by the second where losses were still high (78%). In the compost with the least green waste, the hydrocarbon concentration decreased by only 64%. The hydrocarbon level in the control system remained practically unchanged. In addition, mineralization time increased with increasing green waste ratios, the composting process played a considerable role in the biodegradation of petroleum hydrocarbons and minimized the green waste produced by restaurants and cafeterias. The data obtained will be useful for solid waste management policy making.

Fault Prediction Based on Dissolved Gas Concentration from Insulating Oil in Power Transformer Using Neural Network

Reliable and continued performance of power transformer is the key to profitable generation and transmission of electric power. Failure of a large power transformer not only results in the loss of expensive equipment, but it can cause significant guarantied damage as well. Replacement of that transformer can take up to a year if the failure is not disastrous and can result in tremendous revenue losses and fines. A power transformer in operation is subjected to various stresses like thermal stress and electrical stress, resulting in liberation of gases from the hydrocarbon mineral oil. Dissolved gas analysis is a technique used to assess incipient faults of the transformer by analyzing specific dissolved gas concentrations arising from the deterioration of the transformer. DGA is used not only as a diagnostic tool but also to track apparatus failure. In this research work the dissolved gas values measured for a 230kV / 110kV power transformer which are obtained from electricity board are used as references to the developed neural network. The neural network is trained and the transformer faults are predicted. The trained neural network shows the good performance for the prediction of fault in a 230kV/110kV power transformer.

Retention and Excretion of 3H in Rats Following the Intratracheal Intubation of Tritiated Pump Oil

Saturated hydrocarbon mineral oils in vacuum pumps used in ³H handling facilities often contain significant amounts of ³H (as much as several hundred GBq L⁻¹), and during maintenance the air around an open pump may contain MBq L of volatile and aerosol species. It follows that H-contaminated pump oils pose a workplace hazard-especially if inhaled deposits are retained in the lung. A long-term study (1-y duration) was undertaken to establish the retention time of ³H-pump oil in the lungs of rats. Excretion data was collected to establish the mechanism of oil clearance from the lung. Finally, liver data was collected both to indicate the levels of H in the rat body and to indicate either the presence or absence of the transfer of unmetabolized pump oil within cells from the lungs to liver. Within 1 d following intubation into the trachea, ∼16.5% of the emulsified pump oil had been rapidly mechanically cleared to feces, and 1.1%, present as HTO, or exchangeable H, was excreted in urine. 69.4% of the instilled dose remained in the lungs as the initial alveolar burden. Subsequently, H cleared from the lungs with a retention half-time of of 223 d. The lung burden was mostly cleared to feces-indicating that the pump oil droplets remaining in the lungs were behaving like insoluble particles, but the kinetics of clearance of particles and oil droplets may be different. Overall, it is concluded that inhaled H-pump oil should most likely be regarded as an insoluble particulate (ICRP Inhalation Type S) for the purposes of radiological protection dosimetry, but the possibility of Type M behavior cannot be excluded.

Development of hot-melt pressure–sensitive adhesives for transdermal drug delivery

Styrene–isoprene–styrene (SIS) copolymer was epoxidized by in situ epoxidation to prepare a series of epoxidized SIS resins (ESIS). Their epoxidation degrees, phase structures, and compatibility with hydrocarbon resin were characterized with 1H nuclear magnetic resonance spectroscopy, atomic force microscopy, and differential scanning calorimetry, respectively. These ESIS resins were melt-mixed with synthetic hydrocarbon resin, mineral oil, and antioxidants to fabricate a series of ESIS-based hot-melt pressure–sensitive adhesives (HMPSAs), which were used as carriers of transdermal drug delivery system. Their adhesive performances were measured, including holding power and 180o peel strength. Geniposide and oleanic acid were representatively chosen as hydrophilic and lipophilic drug, respectively. Their in vitro release behaviors in ESIS-based HMPSAs were investigated using a modified Franz-type horizontal diffusion cells. Although the introduction of epoxide groups could alter the compatibility and phase structures between SIS resins and additives, the adhesive performances were slightly affected, as SIS resins had lower epoxidation degree (<15%). It is even more important that the cumulative release rate of both hydrophilic and lipophilic drugs is markedly enhanced with the increase of epoxidation degree in these ESIS-based HMPSAs. Therefore, this kind of HMPSAs has a promising future as a carrier of transdermal drug delivery system as their SIS resins are appropriately epoxidized.

Intrinsic rates of petroleum hydrocarbon biodegradation in Gulf of Mexico intertidal sandy sediments and its enhancement by organic substrates

The rates of crude oil degradation by the extant microorganisms in intertidal sediments from a northern Gulf of Mexico beach were determined. The enhancement in crude oil degradation by amending the microbial communities with marine organic matter was also examined. Replicate mesocosm treatments consisted of: (i) controls (intertidal sand), (ii) sand contaminated with crude oil, (iii) sand plus organic matter, and (iv) sand plus crude oil and organic matter. Carbon dioxide (CO2) production was measured daily for 42 days and the carbon isotopic ratio of CO2 (δ13CO2) was used to determine the fraction of CO2 derived from microbial respiration of crude oil. Bacterial 16S rRNA clone library analyses indicated members of Actinobacteria, Bacteroidetes, and Chloroflexi occurred exclusively in control sediments whereas Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Firmicutes occurred in both control and oil contaminated sediments. Members of the hydrocarbon-degrading genera Hydrocarboniphaga, Pseudomonas, and Pseudoxanthomonas were found primarily in oil contaminated treatments. Hydrocarbon mineralization was 76% higher in the crude oil amended with organic matter treatment compared to the rate in the crude oil only treatment indicating that biodegradation of crude oil in the intertidal zone by an extant microbial community is enhanced by input of organic matter.

Responses of microbial community from northern Gulf of Mexico sandy sediments following exposure to deepwater horizon crude oil

In the present study, microbial community responses to exposure to unweathered Macondo Well crude oil and conventional diesel in a sandy beach environment were determined. Biodegradation was assessed in mesocosm experiments with differing fuel amounts (2,000 and 4,000 mg/kg) and with or without inorganic nutrient amendment. Carbon dioxide production was measured daily for 42 d. Aerobic alkane, total hydrocarbon, and polycyclic aromatic hydrocarbon (PAH) degraders were enumerated in treated and control mesocosms and changes in their abundances were measured weekly. Hydrocarbon mineralization occurred in all treatments. In the inorganic nutrient-amended treatments, the degradation rates were 2.31 and 2.00 times greater in the 2,000 mg/kg diesel and crude oil treatments, respectively, and 3.52 (diesel) and 4.14 (crude) times higher for the fuel types at the 4,000 mg/kg fuel concentrations compared to unamended treatments. Microbial lag phases were short (<3 d) and alkane and total hydrocarbon degrader numbers increased by five orders of magnitude compared to the uncontaminated treatments within 7 d in most treatments. Hydrocarbon degrader numbers in diesel and in crude oil treatments were similar; however, the PAH degraders were more abundant in the crude oil relative to diesel treatment. These findings indicate that hydrocarbon degradation by extant microbial populations in the northern Gulf of Mexico sandy beach environments can be stimulated and enhanced by inorganic nutrient addition.

Comparative toxicokinetics of low-viscosity mineral oil in Fischer 344 rats, Sprague–Dawley rats, and humans – Implications for an Acceptable Daily Intake (ADI)

Oral repeated-dose studies with low-viscosity mineral oils showed distinct species and strain differences, which are hypothesized to be due to differences in bioavailability, with Fischer 344 rats being more susceptible than Sprague–Dawley rats or dogs.Sensitive analytical methodology was developed for accurate measurement of low levels of mineral hydrocarbons and applied in single-dose toxicokinetics studies in rats and humans. Fischer 344 rats showed a 4-fold higher AUC0–∞ and consistently higher blood and liver concentrations were found than Sprague–Dawley rats. Hepatic mineral hydrocarbon concentration tracked the blood concentration in both strains, indicating that blood concentrations can serve as functional surrogate measure for hepatic concentrations. In human volunteers receiving 1mg/kg body weight of low-viscosity white oil, all blood concentrations of mineral hydrocarbons were below the detection limit. Comparison with threshold blood concentrations associated with NOAELs in both rat strains, indicate that the margin-of-exposure is at least 37-fold. Using an internal dose metric rather than applied dose reduces the uncertainty around the temporary ADI considerably since it intrinsically accounts for intra- and inter-species differences. The current data support replacement of the temporary ADI of 0.01mg/kg/day by a (permanent) ADI of at least 1.0mg/kg/day for low- and medium-viscosity mineral oils.

Microbial interactions during residual oil and n‐fatty acid metabolism by a methanogenic consortium

Carbon flow in a model methanogenic consortium capable of hydrocarbon degradation was investigated using a combination of stable isotope fractionation, protein-based stable isotope probing, and metaproteomics. Overall δ(13) C enrichment for methane and CO2 in the presence and absence of oil suggests that complex microbial interactions occur during methanogenic hydrocarbon mineralization. Specifically, the Δδ(13) C of CO2 was statistically identical in all incubations irrespective of oil presence, but the Δδ(13) C for methane was greater in the presence of oil compared with fatty acids alone. In addition, carbon from uniformly ((13) C) labelled n-fatty acids was distributed evenly among consortium members in the presence of oil, but used by relatively few community members when provided alone. In all incubations, aceticlastic and hydrogenotrophic methanogens were labelled to an equal extent, suggesting that no pathway is overwhelmingly dominant during methane production by the model consortium. Protein-based stable isotope probing identified key enzymes responsible for methanogenesis from CO2 and acetate labelled with 78.0 ± 4.4% and 73.3 ± 1.0% (13) C respectively. Results suggest that acetate was used directly by methanogens in the presence of n-fatty acids alone, and that methanogenesis from CO2 was a secondary process. Proteins capable of catalysing hydrocarbon activation by addition to fumarate were not found. Collectively, this study demonstrates that significant microbial cooperation is required to recover hydrocarbons as methane.

Comparative response of two organic biofilters treating ethylbenzene and toluene after prolonged exposure

The response of two biofilters filled with an organic waste material for treating ethylbenzene and toluene was studied for 415 and 472 operating days, respectively. The peak elimination capacities (ECMAX) recorded were 170gm−3h−1 for ethylbenzene (ECMAX) and 138gm−3h−1 for toluene. Regarding the degradation profile through the biofilters, an increase in the inlet concentration displaced the degradation profile into the downstream section. A sudden decrease in the performance of both biofilters occurred when the moisture content (MC) of the packing material exceeded 37% for ethylbenzene and 30% for toluene. Thus, a recommended MC value was established in the 15–30% range. Given the bioreactor was operated at a low MC level, fungi prevailed over bacteria. Nevertheless, synergism was detected between both microorganism types for the mineralization of the aromatic hydrocarbons.

Plant root exudates impact the hydrocarbon degradation potential of a weathered-hydrocarbon contaminated soil

Phytoremediation is a promising low cost technology for the cleanup of contaminated sites. However, specific plants may promote degradation under one set of conditions but not under another, and knowledge limitations surrounding the mechanisms of phytoremediation hamper attempts at optimization. We addressed this issue by examining how exudates released by Elymus angustus (wildrye) and Medicago sativa (alfalfa), grown under hydrocarbon-stressed or non-stressed conditions, impacted the degradation potential of microbial communities in a weathered hydrocarbon-contaminated soil. Degradation potential was assessed using mineralization assays with 14C-labeled hydrocarbons (hexadecane, naphthalene, phenanthrene) followed by DGGE of microbial communities and quantitative-PCR of genes associated with hydrocarbon degradation. All root exudates repressed hydrocarbon mineralization in soil microcosms, with exudates from hydrocarbon-stressed wildrye having the least repressive impact. Changes in degradation potential were not associated with changes in the dominant microbial community structure or with significant shifts in general microbial abundance. Degradation was, however, associated with functional changes in microbial communities. Mineralization of polyaromatic hydrocarbons (PAH) was highly correlated with copy numbers of catechol 2,3 dioxygenase and naphthalene dioxygenase, two genes involved in PAH degradation. Both gene copy numbers and mineralization parameters were significantly impacted by exudate composition, with specific compounds associated with either increased (acetate, alanine) or decreased (malonate) degradative capacity. The success of a given phytoremediation treatment is likely influenced by the relative amount of these and similar compounds within root exudates.

A comparative study of two techniques for determining photocatalytic activity of nitrogen doped TiO 2 nanotubes under visible light irradiation: Photocatalytic reduction of dye and photocatalytic oxidation of organic molecules

Nitrogen-doping (N-doping) is a popular strategy for promoting the absorption of visible light in TiO 2 and other photocatalysts. We have grown TiO 2 nanotubes onto non-conducting Pyrex in a one step process via single layer titanium films. In an attempt to improve the self-cleaning ability of vertically aligned TiO 2 nanotube arrays under visible light irradiation we have doped them with nitrogen and tested the resulting nanotube films by two representative test methods. The first method is an established dye-test which is typically used as a “quick-and-dirty” screening for activity. The second method is the gas-phase oxidation reaction of CO-oxidation and methane. The encouraging results of the dye tests are in conflict with the discouraging results of the gas-phase tests. The fact that the dye test gives a “false positive” underscores the dangers of extrapolating photocatalytic performance results from dye decoloration tests to more difficult redox reactions such as hydrocarbon mineralization.

CO2-Efflux Measurements for Evaluating Source Zone Natural Attenuation Rates in a Petroleum Hydrocarbon Contaminated Aquifer

In order to gain regulatory approval for source zone natural attenuation (SZNA) at hydrocarbon-contaminated sites, knowledge regarding the extent of the contamination, its tendency to spread, and its longevity is required. However, reliable quantification of biodegradation rates, an important component of SZNA, remains a challenge. If the rate of CO(2) gas generation associated with contaminant degradation can be determined, it may be used as a proxy for the overall rate of subsurface biodegradation. Here, the CO(2)-efflux at the ground surface is measured using a dynamic closed chamber (DCC) method to evaluate whether this technique can be used to assess the areal extent of the contaminant source zone and the depth-integrated rate of contaminant mineralization. To this end, a field test was conducted at the Bemidji, MN, crude oil spill site. Results indicate that at the Bemidji site the CO(2)-efflux method is able to both delineate the source zone and distinguish between the rates of natural soil respiration and contaminant mineralization. The average CO(2)-efflux associated with contaminant degradation in the source zone is estimated at 2.6 μmol m(-2) s(-1), corresponding to a total petroleum hydrocarbon mineralization rate (expressed as C(10)H(22)) of 3.3 g m(-2) day(-1).

CRYSTAL CHEMISTRY AND GENESIS OF ORGANIC MINERALS: A REVIEW OF OXALATE AND POLYCYCLIC AROMATIC HYDROCARBON MINERALS

Organic minerals are natural organic compounds with both a well-defined chemical composition and crystallographic properties; their occurrences reveal traces of the high concentration of certain organic compounds in natural environments. Thus the origin and process of formation of organic minerals will lead us to understand the fate and behavior of the organic molecules in the lithosphere. With the aim of their contribution to new developments in mineralogy, we subdivide organic minerals into two groups: (1) ionic organic minerals, in which organic anions and various cations are held together by ionic bonds, and (2) molecular organic minerals, in which electroneutral organic molecules are bonded by weak intermolecular interactions. This review is composed of four sections. The first section is concerned with the definition of both organic minerals and the above two groups. The second deals with crystal chemistry and geochemistry of oxalate minerals, which are the most typical ionic organic minerals. In this section, the role of (H 2 O) 0 is first discussed, as most oxalate minerals incorporate (H 2 O) 0 into their crystal structures. Then the phase relationships among hydrous and anhydrous calcium oxalate minerals, namely their structural hierarchy, are described, owing to the fact that they are the most abundant ionic organic minerals. In addition, the weak Jahn– Teller effect of the Fe 2+ ion is exemplified in humboldtine [Fe 2+ (C 2 O 4 )·2H 2 O]. The Fe 2+ ion causes distortions of octahedra in this organic mineral, though the effect has hardly been observed in inorganic minerals. In the third section, we describe the crystal chemistry and process of formation of polycyclic aromatic hydrocarbon (PAH) minerals, which are the most typical molecular organic minerals. Those of karpatite (C 24 H 12 ) and idrialite (C 22 H 14 ) are particularly considered in detail. In the fourth section, we summarize the characteristics of organic minerals and discuss their contribution to Earth and planetary sciences.

Mineralisation of target hydrocarbons in three contaminated soils from former refinery facilities

This study investigated the microbial degradation of 14C-labelled hexadecane, octacosane, phenanthrene and pyrene and considered how degradation might be optimised in three genuinely hydrocarbon-contaminated soils from former petroleum refinery sites. Hydrocarbon mineralisation by the indigenous microbial community was monitored over 23 d. Hydrocarbon mineralisation enhancement by nutrient amendment (biostimulation), hydrocarbon degrader addition (bioaugmentation) and combined nutrient and degrader amendment, was also explored. The ability of indigenous soil microflora to mineralise 14C-target hydrocarbons was appreciable; ≥16% mineralised in all soils. Generally, addition of nutrients or degraders increased the rates and extents of mineralisation of 14C-hydrocarbons. However, the addition of nutrients and degraders in combination had a negative effect upon 14C-octacosane mineralisation and resulted in lower extents of mineralisation in the three soils. In general, the rates and extents of mineralisation will be dependent upon treatment type, nature of the contamination and adaptation of the ingenious microbial community.

Field performance of alder- Frankia symbionts for the reclamation of oil sands sites

The Canadian province of Alberta is the world's largest producer of petroleum products from oil sands exploitation. Oil sands process-affected materials (OSPM), such as tailings sand, produced as a result of bitumen extraction, has low fertility, low organic matter content, it is alkaline, compactable, and contains residual hydrocarbons, making it a very inhospitable growth environment. The petroleum industry is currently involved in efforts to revegetate and remediate the tailings sand. One approach used is revegetation of the reclamation sites with Frankia-inoculated alders. Alders are primary succession trees that have the ability to grow in nutrient poor and waterlogged environments, in part because they form a symbiotic relationship with the nitrogen-fixing Actinobacteria, Frankia. In 2005, field trials were established at Syncrude Canada Ltd. The effect of Frankia-inoculated alders on soil quality was evaluated by monitoring the chemical and microbiological characteristics of the soil. The impact on the indigenous microbial community was also studied using hydrocarbon mineralization assays, and molecular approaches, such as denaturing gradient gel electrophoresis (DGGE). Plant parameters (biomass, nitrogen content) were measured to evaluate the impact of Frankia on alder health and growth. After two growth seasons, Frankia-inoculated and non-inoculated alders yielded comparable amounts of plant biomass and there was an increase in hydrocarbon (hexadecane, naphthalene and phenanthrene) mineralization where the reclamation site had been planted with alder- Frankia. The alder rhizosphere samples all had comparable hydrocarbon mineralization rates. DGGE profiles confirmed a change in the microbial communities of the bulk soil between unplanted and alder- Frankia treatments. Soil tests showed that alder- Frankia decreased soil pH (from 7.5 to 6.6, in 2006, and from 8.2 to 7.2 in 2007) and plant-available sodium content (70% reduction), and had a positive impact on soil organic matter content (increase in up to 6 times in alder- Frankia plots). The field results have confirmed that the alder- Frankia combination results in improved remediation capabilities and enhances soil quality. These improvements in soil quality of the reclamation site provide evidence of the potential of alder- Frankia symbionts to be part of a reclamation strategy for the reforestation of the site, and the re-establishment of a balanced ecosystem.

Highly Efficient and Mild Electrochemical Incineration: Mechanism and Kinetic Process of Refractory Aromatic Hydrocarbon Pollutants on Superhydrophobic PbO2 Anode

Aqueous aromatic hydrocarbons are chemically stable, high toxic refractory pollutants that can only be oxidized to phenols and quinone on either Pt or traditional PbO(2) electrodes. In this study, a novel method for the electrochemical incineration of benzene homologues on superhydrophobic PbO(2) electrode (hydrophobic-PbO(2)) was proposed under mild conditions. Hydrophobic-PbO(2) can achieve the complete mineralization of aromatic hydrocarbons and exhibit high removal effect, rapid oxidation rate, and low energy consumption. The kinetics of the electrochemical incineration was also investigated, and the results revealed that the cleavage of the benzene ring is a key factor affecting the incineration efficiency. Moreover, on hydrophobic-PbO(2), the decay of intermediates was rapid, and low concentrations of aromatics were accumulated during the reaction. The removal of the initial pollutants and the effects of oxidative cleavage were related to the number of methyl groups on the benzene ring. Specifically, the results of physical experiments and quantum calculations revealed that the charge density of carbon atoms increases with an increase in the number of methyl groups, which promotes the electrophilic attack of ·OH.

Fungal PAH-Metabolites Resist Mineralization by Soil Microorganisms

This study investigated the mineralization of water-soluble polycyclic aromatic hydrocarbon (PAH) metabolites produced by the soil fungus Cunninghamella elegans. Eleven soil fungi were screened for their ability to metabolize (14)C-phenanthrene, (14)C-fluoranthene, and (14)C-pyrene into water-soluble compounds. Eight fungi produced water-soluble metabolites from all or some of the PAHs. The composition of the water-soluble PAH-metabolites from the most effective solubilizer C. elegans was analyzed by an ultraperformance liquid chromatograph interfaced to a quadrupole time-of-flight mass spectrometer. Thirty-eight metabolites were detected. All of 34 identified metabolites were sulfate-conjugated. The mineralization of (14)C-metabolites, produced by C. elegans, was compared to mineralization of the parent (14)C-PAHs in soil slurries. It was hypothesized that the increased bioavailability and metabolic activation of the metabolites would increase mineralization in soil slurries compared to mineralization of the parent PAHs. Unexpectedly, the mineralization of the (14)C-metabolites was in all cases extremely slow compared to the mineralization of the parent (14)C-PAHs. Slow (14)C-metabolite mineralization was not caused by metabolite toxicity, neither was cometabolic mineralization of (14)C-metabolites stimulated by the presence of active PAH-degraders. High water solubility, low lipophilicity, and extremely slow mineralization of the metabolites indicate a potential problem of leaching of fungal PAH-metabolites to the groundwater.

Conceptions about Establishment of the Environmentally Harmless Oil Shale Mining and Chemical Complex

Estonian oil shale deposits have the age-old experience of mining and thermal processing of this hydrocarbon mineral, which is unique in its natural and chemical properties. Oil shale mining perspectives and experience of its burning and thermal processing accumulated by mining, power, and chemical industries of Estonia are very important factors of the economic development of the country on a whole. Authors have studied new methods of oil shale mining and its industrial use in the U.S., Australia, Russia, and Sweden. Production achievements of oil shale industries of Estonia have been analyzed as well. “Estonia” mine, with perspective reserves of this mineral as well as experience of exploitation of natural resources in mining operation areas, was taken as the basis for approval of the idea of complex use of oil shale and underground gotten mines. Technical and organizational development for establishment of environmentally safe and economically sound multi-product mining and chemical complexes at the Estonian oil shale deposits are given in the article.

PAH mineralization and bacterial organotolerance in surface sediments of the Charleston Harbor estuary

Semi-volatile organic compounds (SVOCs) in estuarine waters can adversely affect biota but watershed sources can be difficult to identify because these compounds are transient. Natural bacterial assemblages may respond to chronic, episodic exposure to SVOCs through selection of more organotolerant bacterial communities. We measured bacterial production, organotolerance and polycyclic aromatic hydrocarbon (PAH) mineralization in Charleston Harbor and compared surface sediment from stations near a known, permitted SVOC outfall (pulp mill effluent) to that from more pristine stations. Naphthalene additions inhibited an average of 77% of bacterial metabolism in sediments from the more pristine site (Wando River). Production in sediments nearest the outfall was only inhibited an average of 9% and in some cases, was actually stimulated. In general, the stations with the highest rates of bacterial production also were among those with the highest rates of PAH mineralization. This suggests that the capacity to mineralize PAH carbon is a common feature amongst the bacterial assemblage in these estuarine sediments and could account for an average of 5.6% of bacterial carbon demand (in terms of production) in the summer, 3.3% in the spring (April) and only 1.2% in winter (December).