RESEARCH WATCH
BIODEGRADATION Groundwater radionuclides Chelating agents used to decontaminate nuclear facilities can also increase the mobility of low-level radioactive liquid wastes disposed in shallow land trenches. S. C. Brooks and colleagues studied effects of aquifer solid-phase surfaces on the bioavailability of cobalt-citrate complexes in a simulated groundwater environment. Large amounts of 60Co are disposed in shallow trenches, and citric acid is used in reactor cleaning. Sand with iron coatings adsorbed more organic ligand than sand without the coatings. Bacteria capable of biodegrading the citrate were more active on this material. The authors suggest that this effect was because of nutrient sorption, such as phosphorus, to the iron coatings rather than a direct effect of the coatings on bacterial activity. {Environ. Toxicol. Chem. 1997,16, 862-70)
TNT degrader found Nitroaromatic compounds such as the explosive 2,4,6-trinitrotoluene (TNT) have many industrial uses, including dyes, pesticides, pharmaceuticals, and solvents. Their degradation products in soil, wastewater, and air are often toxic. S. Montpas and colleagues reported the first degradation of TNT by a strain of Serratia marcescens isolated from soil in a site contaminated with TNT. The organism used TNT as its sole source of carbon and energy. At an initial concentration of 50 mg/L"1, TNT was totally degraded within two days. Several reduction intermediates, including 4-amino-2,6-dinitrotoluene and 2-amino-4,6-dinitrotoluene, were detected during the biodegradation. The authors also found that rapid degradation of TNT was dependent on the presence of a surfactant that promotes release of degrading enzymes from the microorganism. (Biotechnol. Lett. 1997, 19, 291-94)
Understanding contaminant bioavailability in sediments The toxicity of contaminants in sediments to bottom-dwelling organisms cannot be reliably predicted without knowing the bioavailability of the pollutants. L Standley studied how the bioavailability of dieldrin to an oligochaete (a worm) relates to sediment composition. The partitioning of dieldrin to four different sediments was best explained by the amount of solvent-extractable sedimentary organic matter. Bioaccumulation of dieldrin by the oligochaete was affected by sediment carbon content and organism lipid content. However, significant variability between samples remains, implying that bioavailability is also dependent on specific sediment composition. The author suggests current chemical measures of partitioning do not accurately reflect biological extractability. [Environ. ScL Techno/., this issue, pp. 2577-83)
BIOREMEDIATION Petroleum biomarkers Chemical biomarkers in crude oils and petroleum products can be traced unambiguously to biological precursor compounds such as pristane, phytane, hopanes, and steranes. M. Whittaker and S. J. T. Pollard did an empirical study of various biomarkers used to determine source and weathering characteristics of petroleum releases to the environment. Five biomarker indices distinguished between crude oils from different geological backgrounds. The tricyclic terpanes:hopanes ratio was unlikely to change with weathering of crude oil and therefore was the best index for determining the source. Low ratios of n-alkanes:hopane and phytane:hopane indicated a reduced bioremediation potential of contaminated soil mixtures. They can be used to determine the bioremediation potential of petroleum hydrocarbons in the environment. {Environ. Toxicol. Chem. 1997, 16, 1149-58)
Surfactants and PAHs Surfactants can aid the bioremediation of PAHs and other low-solubility contaminants in soil and water. K. Jahan and co-workers evaluated the effect on nonionic surfactants in facilitating PAH biodegradation in soil and water. Four commercially
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available nonionic surfactants were tested using batch and continuousflow reactors inoculated with a mixed microbial culture that had been acclimated to PAH. Studies indicated that low surfactant concentrations could promote mineralization of PAH without causing inhibitory or toxic effects to the culture. This work identified factors used to select an appropriate surfactant and provided important information for the design of an in situ PAH bioremediation system. These include hydrocarbon solubilizing power, sorptive properties, environmental fate, and toxicity. {Water Environ. Res. 1997, 69, 317-25)
CONTROL Biofilter clogging Filter clogging limits the potential of biofiltration, an otherwise attractive technique for purifying emissions of VOCs. A. R. Pedersen and colleagues reported the kinetics of biofilm growth, which is responsible for clogging, in a laboratory-scale biological trickling filter for treating toluene. A rapid colonization of the biofilter occurred within three days. Various toluene-degrading organisms were isolated from the biofilm. Pseudomonas putida {P. putida) was chosen as a representative toluenedegrading organism. It detached
VOL. 31, NO. 9, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 3 9 5 A
