Determination of mercury evasion in a contaminated headwater stream

Evasion from first- and second-order streams in a watershed may be a significant factor in the atmospheric recycling of volatile pollutants such as mercury; however, methods developed for the determination of Hg evasion rates from larger water bodies are not expected to provide satisfactory results in highly turbulent and morphologically complex first- and second-order streams. A new method for determining the Hg evasion rates from these streams, involving laboratory gas-indexing experiments and field tracer tests, was developed in this study to estimate the evasion rate of Hg from Gossan Creek, a first-order stream in the Upsalquitch River watershed in northern New Brunswick, Canada. Gossan Creek receives Hg-contaminated groundwater discharge from a gold mine tailings pile. Laboratory gas-indexing experiments provided the ratio of gas-exchange coefficients for zero-valent Hg to propane (tracer gas) of 0.81+/-0.16, suggesting that the evasion mechanism in highly turbulent systems can be described by the surface renewal model with an additional component of enhanced gas evasion probably related to the formation of bubbles. Deliberate field tracer tests with propane and chloride tracers were found to be a reliable and practical method for the determination of gas-exchange coefficients for small streams. Estimation of Hg evasion from the first 1 km of Gossan Creek indicates that about 6.4 kg of Hg per year is entering the atmosphere, which is a significant fraction of the regional sources of Hg to the atmosphere.     

Effect of a nonionic surfactant on biodegradation of slowly desorbing PAHs in contaminated soils

The influence of the nonionic surfactant Brij 35 on biodegradation of slowly desorbing polycyclic aromatic hydrocarbons (PAHs) was determined in contaminated soils. We employed a soil originated from a creosote-polluted site, and a manufactured gas plant soil that had been treated by bioremediation. The two soils differed in their total content in five indicator 3-, 4-, and 5-ring PAHs (2923 mg kg(-1) and 183 mg kg(-1) in the creosote-polluted and bioremediated soils, respectively) but had a similar content (140 mg kg(-1) vs 156 mg kg(-1)) of slowly desorbing PAHs. The PAHs present in the bioremediated soil were highly recalcitrant. The surfactant at a concentration above its critical micelle concentration enhanced the biodegradation of slowly desorbing PAHs in suspensions of both soils, but it was especially efficient with bioremediated soil, causing a 62% loss of the total PAH content. An inhibition of biodegradation was observed with the high-molecular-weight PAHs pyrene and benzo[a]pyrene in the untreated soil, possibly due to competition effects with other solubilized PAHs present at relatively high concentrations. We suggest that nonionic surfactants may improve bioremediation performance with soils that have previously undergone extensive bioremediation to enrich for a slowly desorbing profile.     

Hydrogen isotopic enrichment: an indicator of biodegradation at a petroleum hydrocarbon contaminated field site

Compound-specific carbon and hydrogen isotope analysis was used to investigate biodegradation of benzene and ethylbenzene in contaminated groundwater at Dow Benelux BV industrial site. delta13C values for dissolved benzene and ethylbenzene in downgradient samples were enriched by up to 2+/-0.5 per thousand, in 13C, compared to the delta13C value of the source area samples. delta2H values for dissolved benzene and ethylbenzene in downgradient samples exhibited larger isotopic enrichments of up to 27+/-5 per thousand for benzene and up to 50+/-5 per thousand for ethylbenzene relative to the source area. The observed carbon and hydrogen isotopic fractionation in downgradient samples provides evidence of biodegradation of both benzene and ethylbenzene within the study area at Dow Benelux BV. The estimated extents of biodegradation of benzene derived from carbon and hydrogen isotopic compositions for each sample are in agreement, supporting the conclusion that biodegradation is the primary control on the observed differences in carbon and hydrogen isotope values. Combined carbon and hydrogen isotope analyses provides the ability to compare biodegradation in the field based on two different parameters, and hence provides a stronger basis for assessment of biodegradation of petroleum hydrocarbon contaminants.     

Petroleum hydrocarbon biodegradation under seasonal freeze-thaw soil temperature regimes in contaminated soils from a sub-Arctic site

Several studies have shown that biostimulation in ex situ systems such as landfarms and biopiles can facilitate remediation of petroleum hydrocarbon contaminated soils at sub-Arctic sites during summers when temperatures are above freezing. In this study, we examine the biodegradation of semivolatile (F2: C10-C16) and nonvolatile (F3: C16-C34) petroleum hydrocarbons and microbial respiration and population dynamics at post- and presummer temperatures ranging from -5 to 14 °C. The studies were conducted in pilot-scale tanks with soils obtained from a historically contaminated sub-Arctic site in Resolution Island (RI), Canada. In aerobic, nutrient-amended, unsaturated soils, the F2 hydrocarbons decreased by 32% during the seasonal freeze-thaw phase where soils were cooled from 2 to -5 °C at a freezing rate of -0.12 °C d(-1) and then thawed from -5 to 4 °C at a thawing rate of +0.16 °C d(-1). In the unamended (control) tank, the F2 fraction only decreased by 14% during the same period. Biodegradation of individual hydrocarbon compounds in the nutrient-amended soils was also confirmed by comparing their abundance over time to that of the conserved diesel biomarker, bicyclic sesquiterpanes (BS). During this period, microbial respiration was observed, even at subzero temperatures when unfrozen liquid water was detected during the freeze-thaw period. An increase in culturable heterotrophs and 16S rDNA copy numbers was noted during the freezing phase, and the (14)C-hexadecane mineralization in soil samples obtained from the nutrient-amended tank steadily increased. Hydrocarbon degrading bacterial populations identified as Corynebacterineae- and Alkanindiges-related strains emerged during the freezing and thawing phases, respectively, indicating there were temperature-based microbial community shifts.     

Cyclodextrin enhanced biodegradation of polycyclic aromatic hydrocarbons and phenols in contaminated soil slurries

This work aimed to evaluate the relative contribution of soil catabolic activity, contaminant bioaccessibility, and nutrient levels on the biodegradation of field-aged polycyclic aromatic hydrocarbons and phenolic compounds in three municipal gas plant site soils. Extents of biodegradation achieved, in 6 week-long soil slurry assays, under the following conditions were compared: (i) with inoculation of catabolically active PAH and phenol-degrading microorganisms, (ii) with and without hydroxypropyl-beta-cyclodextrin supplementation (HPCD; 100 g L(-1)), and finally (iii) with the provision of additional inorganic nutrients in combination with HPCD. Results indicated no significant (p < 0.05) differences between biodegradation endpoints attained in treatments inoculated with catabolically active microorganisms as compared with the uninoculated control. Amendments with HPCD significantly (p < 0.05) lowered biodegradation endpoints for most PAHs and phenolic compounds. Only in one soil did the combination of HPCD and nutrients consistently achieve better bioremediation endpoints with respect to the HPCD-only treatments. Thus, for most compounds, biodegradation was not limited by the catabolic activity of the indigenous microorganisms but rather by processes resulting in limited availability of contaminants to degraders. It is therefore suggested that the bioremediation of PAH and phenol impacted soils could be enhanced through HPCD amendments. In addition, the biodegradability of in situ and spiked (deuterated analogues) PAHs following 120 days aging of the soils suggested that this contact time was not sufficient to obtain similar partitions to that observed for field-aged contaminants; with the spiked compounds being significantly (p < 0.05) more available for biodegradation.     

Enzyme studies during the production of agadagidi Part 1. Amylase activities

Amylase activities in fermenting agadagidi is reported. Highest amounts of reducing sugars produced by amylase activities in fermenting plantain chips, agadagidi samples and associated microorganisms were obtained at 30 and 35 °C. The best pH range for enzyme activity was 5.1–7.2.     

Electron-beam treatment of aromatic hydrocarbons that can be air-stripped from contaminated groundwater. 1. Model studies in aqueous solution

As a model for the electron-beam degradation of volatile aromatics (benzene, toluene, ethylbenzene, xylenes, BTEX) in groundwater strip gas, to be reported in Part 2, the gamma-radiolysis of benzene has been studied in aqueous solutions. Addition of *OH to the aromatic ring gives rise to hydroxycyclohexadienyl radicals which either dimerize or disproportionate. The various dimers undergo acid-catalyzed water elimination yielding biphenyl. Phenol is formed upon disproportionation directly, but also via dihydroxycyclohexadiene which subsequently undergoes acid-catalyzed water elimination. Co-radiolysis of benzene with nitrite generates *NO2 in addition to the hydroxycyclohexadienyl radical. These not only interact with one another (product: nitrobenzene via nitro-hydroxycyclohexadienes) but the *NO2 radical is also capable of abstracting cyclohexadienylic hydrogens. This reaction leads to the formation of 2- and 4-nitrophenol and to further nitrated products that were not identified. These are suggested to be formed in an analogous reaction of *NO2 with the hydroxycylohexadienyl dimers. The effect of O2 on these reactions and the relevance for the gas-phase radiolysis of BTEX is discussed.     

Collagen and its rational content in meat products: Part 1. Analytical studies

Computer-assisted simulation has been used to study the effect of collagen content on the biological value of meat proteins. It has been shown that an increase in the collagen content from 2·5% to 15-20% of the total amount of proteins contained in minced meat tangibly enhances protein utilization for tissue synthesis. Hence, the above collagen content in meat products heightens their nutritional and biological value and renders them more suited for human metabolism.     

A multitracer test proving the reliability of Rayleigh equation-based approach for assessing biodegradation in a BTEX contaminated aquifer

Compound-specific stable isotope analysis (CSIA) is one of the most important methods for assessing biodegradation activities in contaminated aquifers. Although the concept is straightforward, the proof that the method cannot be only used for a qualitative analysis but also to quantify biodegradation in the subsurface was missing. We therefore performed a multitracer test in the field with ring-deuterated (d5) and completely (d8) deuterium-labeled toluene isotopologues (400 g) as reactive tracers as well as bromide as a conservative tracer. The compounds were injected into the anoxic zone of a BTEX plume located down-gradient of the contaminant source. Over a period of 4.5 months the tracer concentrations were analyzed at two control planes located 24 and 35 m downgradient of the injection well. Deuterium-labeled benzylsuccinate was found in the aquifer, indicating the anaerobic biodegradation of deuterated toluene via the benzylsuccinate synthase pathway. Three independent methods were applied to quantify biodegradation of deuterated toluene. First, fractionation of toluene-d8 and toluene-d5 using the Rayleigh equation and an appropriate laboratory-derived isotope fractionation factor was used for the calculation of the microbial decomposition of deuterated toluene isotopologues (CSIA-method). Second, the biodegradation was quantified by the changes of the concentrations of deuterated toluene relative to bromide. Both methods gave similar results, implying that the CSIA-method is a reliable tool to quantify biodegradation in contaminated aquifers. The results of both methods yielded a biodegradation of deuterated toluene isotopologues of approximately 23-29% for the first and 44-51% for the second control plane. Third, the mineralization of deuterated toluene isotopologues was verified by determination of the enrichment of deuterium in the groundwater. This method indicated that parts of deuterium were assimilated into the biomass of toluene degrading microorganisms.     

Pilot-scale in situ bioremediation of uranium in a highly contaminated aquifer. 1. Conditioning of a treatment zone

To evaluate the potential for in situ bioremediation of U(VI) to sparingly soluble U(IV), we constructed a pilot test facility at Area 3 of the U.S. Department of Energy Natural and Accelerated Bioremediation Research (NABIR) Field Research Center (FRC) in Oak Ridge, TN. The facility is adjacent to the former S-3 Ponds which received trillions of liters of acidic plating wastes. High levels of uranium are present, with up to 800 mg kg(-1) in the soil and 84-210 microM in the groundwater. Ambient groundwater has a highly buffered pH of approximately 3.4 and high levels of aluminum (12-13 mM), calcium (22-25 mM), and nitrate (80-160 mM). Adjusting the pH of groundwater to approximately 5 within the aquifer would deposit extensive aluminum hydroxide precipitate. Calcium is present in the groundwater at levels that inhibit U(VI) reduction, but its removal by injection of a high pH solution would generate clogging precipitate. Nitrate also inhibits U(VI) reduction and is present at such high concentrations that its removal by in situ denitrification would generate large amounts of N2 gas and biomass. To establish and maintain hydraulic control, we installed a four well recirculation system parallel to geologic strike, with an inner loop nested within an outer loop. For monitoring, we drilled three boreholes perpendicular to strike across the inner loop and installed multilevel sampling tubes within them. A tracer pulse with clean water established travel times and connectivity between wells and enabled the assessment of contaminant release from the soil matrix. Subsequently, a highly conductive region of the subsurface was prepared for biostimulation by removing clogging agents and inhibitors and increasing pH. For 2 months, groundwater was pumped from the hydraulically conductive zone; treated to remove aluminum, calcium, and nitrate, and supplemented with tap water; adjusted to pH 4.3-4.5; then returned to the hydraulically conductive zone. This protocol removed most of the aqueous aluminum and calcium. The pH of the injected treated water was then increased to 6.0-6.3. With additional flushing, the pH of the extracted water gradually increased to 5.5-6.0, and nitrate concentrations fell to 0.5-1.0 mM. These conditions were judged suitable for biostimulation. In a companion paper (Wu et al., Environ. Sci. Technol. 2006, 40, 3978-3987), we describe the effects of ethanol addition on in situ denitrification and U(VI) reduction and immobilization.     

Enhanced biodegradation of beta- and delta-hexachlorocyclohexane in the presence of alpha- and gamma-isomers in contaminated soils

The chlorinated insecticide hexachlorocyclohexane (HCH) has been used extensively in the past, and contaminated sites are present throughout the world. Toward their bioremediation, we isolated a bacterium Pseudomonas aeruginosa ITRC-5 that mediates the degradation of all the four major isomers of HCH under aerobic conditions, both in liquid-culture and contaminated soils. In liquid-culture, the degradation of alpha- and gamma-HCH is rapid and is accompanied with the release of 5.6 micromole chloride ions and 4.1 micromole CO2 micromole(-1) HCH-isomer. The degradation of beta- and delta-isomers is slow, accompanied with the release of 0.9 micromole chloride ions micromole(-1) HCH-isomer, and results in a transient metabolite 2,3,4,5,6-pentachlorocyclohexan-1-ol. The strain ITRC-5 also mediates the degradation of alpha-, beta-, gamma-, and delta-isomers in contaminated soils, where degradation of otherwise persistent beta- and delta-HCH is enhanced severalfold in the presence of alpha- or gamma-HCH. The degradation of soil-applied beta- and delta-HCH under aerobic conditions has not been reported earlier. The isolate ITRC-5 therefore demonstrates potential for the bioremediation of HCH-wastes and contaminated soils.     

Characteristics of Rhodococcus pyridinovorans PYJ-1 for the biodegradation of benzene, toluene, m-xylene (BTX), and their mixtures

The degradation rates of benzene, toluene, and m-xylene (BTX) by Rhodococcus pyridinovorans PYJ-1, were highest at 30, 50, and 25 mg/l, respectively. The degradation rate was highest for toluene (0.106 mg/mg-protein x h) followed by benzene and m-xylene at the optimum pH and temperature of 7 and 32 degrees C, respectively. For BTX mixtures, toluene was the preferred substrate, but degradation of each BTX was competitively inhibited by other BTX compounds. The degradation rate of each component of in the BTX mixture decreased by 57-89% depending on the concentration (1-5 mg/l) of the component compared with that of the component as a single substrate.     

In situ assessment of biodegradation potential using biotraps amended with 13C-labeled benzene or toluene

Stable isotope fractionation analysis of an aquifer heavily contaminated with benzene (up to 850 mg L(-1)) and toluene (up to 50 mg L(-1)) at a former hydrogenation plant in Zeitz (Saxonia, Germany) has suggested that significant biodegradation of toluene was occurring. However, clear evidence of benzene biodegradation has been lacking at this site. Determining the fate of benzene is often a determining factor in regulatory approval of a risk-based management strategy. The objective of the work described here was the demonstration of a new tool that can be used to provide proof of biodegradation of benzene or other organics by indigenous microorganisms under actual aquifer conditions. Unique in situ biotraps containing Bio-Sep beads, amended with 13C-labeled or 12C nonlabeled benzene and toluene, were deployed at the Zeitz site for 32 days in an existing groundwater monitoring well and used to collect and enrich microbial biofilms. Lipid biomarkers or remaining substrate was extracted from the beads and analyzed by mass spectrometry and molecular methods. Isotopic analysis of the remaining amounts of 13C-labeled contaminants (about 15-18% of the initial loading) showed no alteration of the 12C/13C ratio during incubation. Therefore, no measurable exchange of labeled compounds in the beads by the nonlabeled compounds in the aquifer materials occurred. Isotopic ratio analysis of microbial lipid fatty acids (as methyl ester derivatives) from labeled benzene- and toluene-amended biotraps showed 13C enrichment in several fatty acids of up to delta (13C) 13400%o, clearly verifying benzene and toluene biodegradation and the transformation of the labeled carbon into biomass by indigenous organisms under aquifer conditions. Fatty acid profiles of total lipid fatty acids and the phospholipid fatty acid fraction and their isotopic composition showed significant differences between benzene- and toluene-amended biotraps, suggesting that different microbial communities were involved in the biodegradation of the two compounds.     

Effects of trace element concentration on enzyme controlled stable isotope fractionation during aerobic biodegradation of toluene

The effects of iron concentration on carbon and hydrogen isotopic fractionation during aerobic biodegradation of toluene by Pseudomonas putida mt-2 were investigated using a low iron medium and two different high iron media. Mean carbon enrichment factors (epsilonc) determined using a Rayleigh isotopic model were smaller in culture grown under high iron conditions (epsilonc = -1.7+/-0.1%) compared to low iron conditions (epsilonc = -2.5+/-0.3%). Mean hydrogen enrichment factors (epsilonH) were also significantly smaller for culture grown under high iron conditions (epsilonH = -77 +/-4%) versus low iron conditions (EpsilonH = -159+/-11%). A mechanistic model for enzyme kinetics was used to relate differences in the magnitude of isotopic fractionation for low iron versus high iron cultures to the efficiency of the enzymatic transformation. The increase of carbon and hydrogen enrichment factors at low iron concentrations suggests a slower enzyme-catalyzed substrate conversion step (k2) relative to the enzyme-substrate binding step (k-l) at low iron concentration. While the observed differences were subtle and, hence, do not significantly impact the ability to use stable isotope analysis in the field, these results demonstrated that resolvable differences in carbon and hydrogen isotopic fractionation were related to low and high iron conditions. This novel result highlights the need to further investigate the effects of other trace elements known to be key components of biodegradative enzymes.     

Monitoring biodegradation of ethene and bioremediation of chlorinated ethenes at a contaminated site using compound-specific isotope analysis (CSIA)

Chlorinated ethenes are commonly found in contaminated groundwater. Remediation strategies focus on transformation processes that will ultimately lead to nontoxic products. A major concern with these strategies is the possibility of incomplete dechlorination and accumulation of toxic daughter products (cis-1,2-dichloroethene (cDCE), vinyl chloride (VC)). Ethene mass balance can be used as a direct indicator to assess the effectiveness of dechlorination. However, the microbial processes that affect ethene are not well characterized and poor mass balance may reflect biotransformation of ethene rather than incomplete dechlorination. Microbial degradation of ethene is commonly observed in aerobic systems but fewer cases have been reported in anaerobic systems. Limited information is available on the isotope enrichment factors associated with these processes. Using compound-specific isotope analysis (CSIA) we determined the enrichment factors associated with microbial degradation of ethene in anaerobic microcosms (ε = -6.7‰ ± 0.4‰, and -4.0‰ ± 0.8‰) from cultures collected from the Twin Lakes wetland area at the Savannah River site in Georgia (United States), and in aerobic microcosms (ε = -3.0‰ ± 0.3‰) from Mycobacterium sp. strain JS60. Under anaerobic and aerobic conditions, CSIA can be used to determine whether biotransformation of ethene is occurring in addition to biodegradation of the chlorinated ethenes. Using δ(13)C values determined for ethene and for chlorinated ethenes at a contaminated field site undergoing bioremediation, this study demonstrates how CSIA of ethene can be used to reduce uncertainty and risk at a site by distinguishing between actual mass balance deficits during reductive dechlorination and apparent lack of mass balance that is related to biotransformation of ethene.     

Biochemical studies on some non conventional sources of protein Part 1. Tomato seeds and peels

Tomato seeds and skin wastes contain considerable amounts of protein (16.6, 5.7%) respectively. After protein hydrolysis from both seeds and peels the presence of 17 amino acids was stated. The amino acid scores (chemical scores) of tomato pomace were calculated using the FAO/WHO provisional amino acid scoring pattern and reasonable biological value was confirmed. The essential amino acid content and biological value of seed proteins are higher than that of skin proteins. Fe, Zn, Cu and Mn in seeds and peels were predominant among the micro-minerals. K and P were found to be present in greater quantities than Na in seeds and peels.     

Catalysis of PAH biodegradation by humic acid shown in synchrotron infrared studies

The role of humic acid (HA) in the biodegradation of toxic polycyclic aromatic hydrocarbons (PAHs) has been the subject of controversy, particularly in unsaturated environments. By utilizing an infrared spectromicroscope and a very bright, nondestructive synchrotron photon source, we monitored in situ and, over time, the influence of HA on the progression of degradation of pyrene (a model PAH) by a bacterial colony on a magnetite surface. Our results indicate that HA dramatically shortens the onset time for PAH biodegradation from 168 to 2 h. In the absence of HA, it takes the bacteria about 168 h to produce sufficient glycolipids to solubilize pyrene and make it bioavailable for biodegradation. These results will have large implications for the bioremediation of contaminated soils.     

Electron-beam treatment of aromatic hydrocarbons that can be air-stripped from contaminated groundwater. 2. Gas-phase studies

The electron-beam (EB) degradation of volatile aromatics (benzene, toluene, ethylbenzene, xylenes: BTEX) in groundwater strip gas, which in the present work has been modeled by the introduction of the desired aromatic(s) to a stream of air or another gas, such as oxygen, is initiated essentially by the addition of *OH radicals to the aromatic ring, giving rise to hydroxycyclohexadienyl radicals, which form the corresponding peroxyl radicals upon addition of oxygen. As studied in some detail with benzene as a BTEX representative, various reactions of these lead to numerous oxidation products in a cascade of reactions, including the decomposition of products under the prevailing conditions of high turnover of the initial aromatic. Importantly, hydroxycyclohexadienylperoxyl radical formation is partly reversible, and the reactions of the hydroxycyclohexadienyl radicals, which thus have a significant presence in these systems, must therefore also be taken into consideration. In the gas phase, in contrast to the aqueous phase (see Part 1), the reactions of the hydroxycyclohexadienyl radicals lead to oligomeric products that appear to contribute, in addition to ionic clusters, to nucleation for the aerosols observed. Various nitrated products, among them nitrophenols, are observed when air is used for the stripping. However, these studies did not clear the pilot plant stage, since BTEX degradation using a bioreactor carried out in parallel was so successful that the EB technology was judged to be noncompetitive. As for the latter, expensive equipment consisting of a stripper, the EB machine, and an aerosol precipitator would be required. The condensed aerosols are biorefractory and would require further treatment for detoxification.