RESEARCH WATCH
BIODEGRADATION
Petroleum hydrocarbons J. E. Landmeyer and co-workers investigated the use of carbon isotopic ratios to indicate the zonation of petroleum hydrocarbon biodegradation. Their study focused on the biodegradation of jet-fuel in a shallow aquifer. Jet-fuel sampled from a groundwater monitoring well exhibited a light carbon isotopic signature (-27 per mille). Dissolved inorganic carbon (DIC) in groundwater had 813C values ranging from -28 to +11.9 per mille over the four-year period. Carbon isotopic variations were influenced by the infiltration of rainwater carrying dissolved oxygen and sulfate Biodegradation followed rainfall under aerobic and sulfatereducing conditions; DIC exhibited lighter carbon isotopic signatures The absenrp of significant rainfall led *_ methanogenic hpavier DIC carbon thnrs cnncluHp that 813C values of DTP mav hp HSPH tn pvaluatp the ?n
natinn nf hvHrnrarhnn hinnWraria tion rontrollpH hv phanoino hvHrnlogic conditions. {Environ- Sci. T
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BIOREMEDIATION Gaseous nutrients In situ bioremediation has been demonstrated as an effective alternative to treatment for organic contaminants in the vadose zone. However, providing nutrients in aqueous solution to indigenous microbes often is a challenging engineering problem. Indigenous methanotrophic communities are easier to stimulate because they can use the gas methane for energy and molecular nitrogen as a nutrient source. K-H. Chu and L. Alvarez-Cohen evaluated the degradation of trichloroethylene (TCE) by methane-oxidizing cultures using different nitrogen sources: nitrate ammonia and molecular ni-
Measuring atmospheric reactions of smog-forming organics The use of environmental models often is limited by the data available to verify the models' accuracy. In developing a comprehensive airshed model, M. P. Fraser and co-workers developed a coordinated sampling program in the Los Angeles air basin. During a recent severe smog episode, samples were collected simultaneously at five locations and analyzed for gas- and particle-phase concentrations of 141 organic compounds. Pollutant transformation resulting from atmospheric reactions was clearly evident. As pollutants moved downwind reactive hydrocarbons were depleted organics were enriched in the particle phase and chloride was depleted from particles {Environ Sci Technol ,his issue 17*31-43)
trogen. Results indicated that the cultures using molecular nitrogen were as effective at oxidizing TCE as those using the other two sources and exhibited the highest TCE transformation capacity. This demonstrated that gases such as oxygen, methane, and nitrogen, which are relatively soluble and easily deliverable to microbial communities, can significantly affect the capability of those microbes to remediate chlorinated organic contaminants. [Water Environ. Res. 1996, 68(1), 76-82)
MEASUREMENTS Metals in bacteria A simple technique has been developed that shows how heavy metals are removed from wastewater by bacterial cells in anaerobic digesters. M. O. Ginter and A. M. Grobicki found that metal ions accumulating outside bacterial cells could be extracted from the sludge by hydro-
0013-936X/96/0930-185A$12.00/0 © 1996 American Chemical Society
chloric acid while metals inside the biomass remained insoluble. The metal content of each fraction was quantified by flame atomic absorption spectrometry. The method is reported to overcome problems associated with existing techniques, such as requiring large sample volumes, separating only by particle size, and involving labor-intensive and time-consuming processes. The method requires only 10 mL of sample and is rapid accurate and reproducible. {Water Res.1995 29(12) 2780-84)
SVOC extraction New procedures are needed for liquid-liquid extraction of nonvolatile and semivolatile organic compounds (SVOCs) from water with reduced extraction times. E. S. Farrell and G. E. Pacey developed a new thermospray liquid-liquid extractor that recovers 80-100% of the SVOCs present in a water sample in less than an hour. The system consists of several thermospray probes within a multiport 300-mL extraction vessel, a dual-stage condenser, and solventsample delivery systems. The au_ thors report that extraction efficiency increased with probe temperature In a series of five 100-mL samDles spiked with SVOCs at 2 2 ug/mL the method showed an RSD of less than 1 City for 1 1 of 1 4. comnounds samnlpd 1996 fifif1) 93-991
Phenolic compounds A new method has been developed for determining the octanol-water partition coefficient {Kow ), which is often used to predict the environmental fate of a compound, based on SPME. However, this method has performed poorly for predicting the fate of phenolic compounds. J. R. Dean and colleagues modified the SPME procedures to enable log K determinations for phenolic compounds at log K values less than 3 5 They used an 85-um polyacrylate-coated fiber to extract the phenolic compounds from a pH 2 buffer
VOL. 30, NO. 5, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 1 8 5 A
solution. They then analyzed the fiber by gas chromatography with flame ionization detection. After extraction times were optimized to ensure equilibrium, the method showed an RSD of less than 5% with good correlation to literature K[)w values. {Anal. Chem. 1996, 68(1), 130-33)
MODELING PAH in soils Given the toxicity and carcinogenic effects of polynuclear aromatic hydrocarbons (PAHs), knowing their environmental fate is important. S. Karimi-Lotfabad and colleagues investigated the PAH retention by montmorillonite clay and three other soils under varying times and moisture contents. Anthracene and, in some cases pyrene or phenanthrene was added to soils and extracted (EPA Method 3540) to evaluate the recoverable fraction of PAHs. As much as 100% of the anthracene and could not be extracted Phenanthrene was retained to a smaller deeree; UD to 25% was not extractable More detailed experiindicated that PAHs may oliffnmpn7P to higher weight aromatics Water inhibited the reaction but t^ rpactinn occurred anthrarnulH not he biodppraded hv an active harterial culture The re lt aa tpd that air or o pn J
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be subject to significant errors because of the polymerization of PAHs on soil surfaces, (Environ) Sci. Tech-
Improving solubility prediction The water solubility of a chemical must be taken into account when predicting its fate and effect in the environment. However, this parameter often is unavailable and must be estimated from the octanol-water partition coefficient (Kovl). W. M. Meylan and co-workers reported significant improvements to the current method for predicting solubility. Building on the 276 compounds originally used to develop regression equations they determined solubility by calculating its regression against K using an additional 1450 compounds They also included melting point and molecular weight
Solid state speciation of lead A device that measures X-ray absorption or fluorescence, called EXAFS spectroscopy, has been applied to the speciation analysis of lead in solid fractions of contaminated soils. This technique probes the structural environment around atoms up to a distance of 3-4 A and is sensitive to changes in neighboring atoms. A. Manceau and co-workers demonstrated that a range of model lead precipitates exhibited different EXAFS spectra. Four groups of compounds were distinguished based on the average distances of lead to its nedfBst neighbor represented by Pb-salicylate -sulfate ids and -tetramethyl EXAFS was then iisefi a
