RESEARCH WATCH
BIODEGRADATION Hexavalent chromium Hexavalent chromium is mutagenic, carcinogenic, and teratogenic and often is found with aromatic wastes in many industrial waste effluents. Reduction of hexavalent chromium to innocuous trivalent chromium using microorganisms in aromatic substrates has not been demonstrated. H. Shen and Y-T. Wang studied hexavalent chromium reduction by bacterial culture using phenolic substrates. A co-culture of Escherichia coli and Pseudomonas pulida in liquid cultures containing hexavalent chromium was inoculated with selected aromatic compounds. Phenol, 2-chlorophenol, p-cresol, 2,6dimethylphenol, 3,4-dimethylphenol, 3,5-dimethylphenol, benzene, and toluene were evaluated as electron donors. The rate of reduction and substrate utilization was influenced by the bacterial composition of the co-culture. Results indicated that all compounds evaluated could be used as electron donors by the co-culture, enabling simultaneous reductive detoxification of chromium and aromatic contaminants. (Appl. Environ. Microbiol 1995, 67(7), 2754-58)
Distinguishing between recent and past oil spills One approach to evaluating the impact of a crude oil spill along a coast where other spills have occurred is to use naturally occurring stable isotopes of carbon to distinguish tar sources. K. A. Kvenvolden and associates used this technique in Alaska's Prince William Sound, site of the 1989 Exxon Valdez oi\ spill. They sampled 61 flattened tar balls, analyzing for carbon-isotopic (513C) and hydrocarbon-biomarker signatures to evaluate the sources. The 5,3C range of tar balls was tightly grouped (-23.7 ± 0.2 parts per thousand) and was distinct from 28 Exxon Valdez crude oil residues (-29.4 ± 0.1 parts per thousand). Similar distinctions were observed for selected biomarker ratios. Results indicated that the tar-ball characteristics related to oil products from Monterey Formation (California) crude oils used in Alaska prior to 1970. The authors attribute much of the release of stored fuel oils and asphalts to storage tank failures during the 1964 Alaska earthquake. (Environ. Sci. Technol., this issue, 2684-94)
rather than dicots, were grown. (J. Environ. Quoi. 1995, 24, 782-85)
Rhizosphere effects Laboratory studies have shown that plants may degrade organic compounds through interaction of the plant with the rhizosphere (the soil adjacent to the roots). Here, the microbial population of the soil differs either in quantity or quality from the soil located further from the roots. J. J. Boyle and J. R. Shann evaluated the effect of rhizosphere versus nonrhizosphere soil on the mineralization of several organic compounds. No differences were found in the mineralization of phenol or 2,4-DCP. But rhizosphere soils had significantly higher rate constants for 2,4-D and 2,4,5-T. The rate of mineralization also was greater in rhizosphere soils in which monocots,
Dechlorinating TCDD Anaerobic sediments are an environmental sink for polychlorinated dibenzo-p-dioxins (PCDD). J.E.M. Beurskens and colleagues reported that an aerobic microbial consortium obtained from sediment contaminated with hexachlorobenzene (HCB) and polychlorinated biphenyl (PCB) could dechlorinate 1,2,3,4tetrachlorodibenzo-p-dioxin (TCDD). The microbial consortium was removed from the sediment and the dechlorinating organisms were enriched by two successive additions of an HCB and lactate inoculum. After the second amount of HCB was depleted, a third inoculum was added containing TCDD at a con-
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centration 300 times its aqueous solubility. Samples from the active incubation showed no changes in TCDD concentration. But increases in the concentrations of di- and trichlorinated PCDD arose from TCDD dechlorination for 12 days, after which the activity ceased. The authors attributed the lack of decrease in TCDD concentration to the initial spiked concentration being in excess of solubility; TCDD continued to enter solution, keeping the concentration constant. (Environ. Toxicol. Chem. 1995, 14(6), 939-43)
BIOREMEDIATION White rot fungi and PCBs The white rot fungus, Phanerochaete chrysosporium, has been demonstrated in degrading a host of recalcitrant compounds using a nonspecific extracellular oxidation system. J. S. Yadav and colleagues investigated the ability of P. chrysosporium to degrade PCB mixtures using congener-specific gas chromatographic analysis. Aroclors 1242, 1254, and 1260 were inoculated into liquid cultures of P. chrysosporium under both high- and low-nitrogen-defined media culture conditions and then incubated for 15 or 30 days. Maximum degradation was 60.9%, 30.5%, and 17.6% for Aroclors 1242, 1254, and 1260, respectively. More extensive degradation was demonstrated with malt extract medium. Although there have been no studies that conclusively demonstrate aerobic microbial degradation of Aroclor 1260, this was the first to show net degradation of the compound by P. chrysosporium. (Appl. Environ. Microbiol. 1995, 61(7), 2560-65)
MEASUREMENTS Microwave extraction Improved analytical methods that reduce solvent usage, increase sample throughput, and improve analyte
