and injection port hardware of commercial bags. The authors report that use of Teflon valves in the homemade bags cut losses of VOCs by more than 50%. (Environ. Sci. Technol., 1996, 30, 3115-17)
MODELING Warming and pollution Could higher global temperatures associated with global climate change increase the public health risks from pollution? T E. McKone and co-workers examined the effects of regional temperature change on risks associated with releases of hexachlorobenzene (HCB), a ubiquitous air, soil, and water pollutant. They applied a fugacity model to predict changes in partitioning between environmental compartments. It assumed a regional environment typical of the western United States, and a global average temperature increase of 5 °C. The increase had little impact on the magnitude of human health risks from HCB released into air or water. Other impacts of climate change, such as precipitation changes and sea level rise, may influence risk assessments for toxic chemicals as well, but these were not addressed. (Risk Analysis 1996, 16(3), 377-93)
Forest management Because many goals in forest management are dependent on landscape features, planners are using spatial analysis as a way to predict the effect of management activities on resources. P. Bettinger and colleagues report a case study in which they tested the ability of a spatial model, SNAP II+, to evaluate selected land management goals in a small Oregon forest watershed. Five scenarios were evaluated for their simultaneous impacts on logging revenue, terrestrial and aquatic habitat protection, and other ecosystem values. Model predictions were consistent with expectations over the short term: Eliminating harvesting in riparian zones maintained aquatic habitats but reduced revenues. The researchers state that the model shows promise for evaluating management tradeoffs in watershed analysis. (Environ. Manage. 1996, 20(4), 565-77)
Mussels as bioindicators of water contamination Marine bivalve molluscs have been used as indicators to assess concentrations of bioavailable contaminants in coastal waters. N. S. Fisher and co-workers used mussels to assess levels of six metals (Ag, Am, Cd, Co, Pb, and Zn). Mussels maintained in the laboratory in running seawater and caged in the field for four months showed similar metal absorption and efflux patterns. Metals accumulated from water generally were bound to the shell, whereas those ingested from food were associated with soft body parts. But different uptake routes were observed: Cd was accumulated from water; Am, Se, and Co from ingested food; and Zn and Ag accumulated significantly via both routes. The authors propose that fecal pellets deposited under mussel beds play an important role in biogeochemical cycling of metals in coastal ecosystems. (Environ. Sci. Technol., this issue, 3232-42)
PESTICIDES Mirex dechlorination Sorption of organic pollutants to humic substances affects the pollutant's chemical reactivity. S. B. Burns and colleagues developed a kinetic model that describes the effects of sorption to humic substances on photodechlorination of the pesticide mirex. The rate constant for the mirex reaction increased with the concentration of dissolved organic carbon and reached a limiting value at about 3 mg/L. The model indicated that photodechlorination of mirex in humic acid solution was limited to the humic-sorbed phase. Reactivity observed on addition of scavengers confirmed the hypothesis that the dissolved and bound mirex experience different photochemical environments. (Environ. Sci. Technol, 1996, 30, 2934-41)
organism could degrade TCE under growth-limited conditions, but high concentrations of TCE led to an increase in the concentrations of toluene needed to maintain cometabolic conditions. (Appl. Environ. Microbiol. 1996, 62, 886-91)
BTEX biodegradation
TCE bioreactor
Groundwater contamination from leaking fuel storage tanks is a worldwide problem. Microorganisms that degrade fuel hydrocarbons offer a promising remediation approach. C-I. Chen and R. T. Taylor studied the degradative activities of two thermophilic bacteria in the Thermus species on nonoxygenated monoaromatic hydrocarbons, known as BTEX (benzene, toluene, ethylbenzene, xylenes). All BTEX compounds were degraded significantly, by 10-40%. The time-dependent extent of biodegradation varied with the initial concentration of BTEX Biodegradation increased when the bacteria were pregrown on catechol and o-cresol. Chen and Taylor used labeled substrates to show that a fraction of the benzene and toluene was metabolized to C0 2 and water-soluble products. (Biotechnol. Bioeng. 1995, 48, 614-24)
The bacterium Burkholderia (Pseudomonas) cepacia G4 is an important degrader of trichloroethylene (TCE). Degradation of TCE by B. cepacia G4 is a cometabolic event that requires the presence of toluene or other aromatic compounds as a primary substrate. From an engineering standpoint, it is desirable to limit the degree of bacterial growth while maintaining high degradation rates to enhance bioreactor performance. A. E. Mars and colleagues investigated the performance of B. cepacia G4 in the degradation of TCE by using a growth-limited, fed-batch culture and toluene as the growth substrate. Results indicate that this
The ability of methanotrophic bacteria to rapidly degrade chlorinated solvents has received much recent study. Methanotrophic growth using methane or methane-air mixtures has typically been required for the degradation of trichloroethylene (TCE). M. W. Fitch and colleagues evaluated the ability of a methanotroph, Methylosinus trichosporium OB3b, strain PP358, to degrade TCE using methanol as the primary growth substrate. The authors investigated the kinetics of TCE degradation under carbon- and oxygen-
REMEDIATION
4 7 0 A • VOL. 30, NO. 11, 1996/ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
Methanol cultures
