RESEARCH WATCH
AIR Benzene trends Benzene, a known human carcinogen, is emitted to the atmosphere from both mobile and stationary sources. T. F. Dann and D. K. Wang monitored benzene in ambient air from more than 30 urban, suburban and rural locations in Canada between 1989 and 1993. They used this extensive database to determine trends in overall ambient concentrations such as seasonal and day-ofweek concentration variations, and source influence on concentration variations. The average benzene concentration was 3 ug/m 3 . At sites characterized predominantly by mobile sources, concentrations decreased 20%; concentrations at industrial source sites decreased 33%. Seasonal variation trends were similar for all sites; the highest concentrations occurred in winter months. Concentrations also were higher on weekdays, particularly at primarily mobile source sites. \J. Air Waste Manage. Assoc. 1995, 45(9), 695-702]
Pesticide metabolites contaminate groundwater Emerging evidence shows that pesticide metabolites are a major groundwater contaminant. D. W. Kolpin and colleagues studied pesticides and their metabolites in 303 wells in 12 Midwestern states. They analyzed 837 samples for alachlor, atrazine, cyanazine, dacthal, DDT, simazine, and selected metabolites. Of the six most frequently detected compounds, five were pesticide metabolites. About 25% of the wells sampled contained one or more of the pesticides above the reporting limit of 0.05 pg/L; metabolites were detected in 39.6% of the wells. Though regulatory levels have been set for most pesticides, levels for most metabolites have not been considered. The authors call for more study to determine degradation products and pathways for pesticides. [Environ. Sci. Technol., this issue, 335-40)
DRINKING WATER BIODEGRADATION Microbe transport The successful use of microbial inoculants in soils requires the microorganisms to contact the chemicals. Physical adsorption to soil particles or filtration by small pores may inhibit microbe transport. In a study conducted by M. Devare and M. Alexander, about 1% of bacterial cells were transported through soil columns (1.5 cm) receiving up to 3.5 pore volumes of water. Phenanthrene added to the top of the column was rapidly mineralized, but that placed at the bottom of the column was not. Results suggest that extrapolation of laboratory data to field biodegradation studies requires the consideration of factors related to transport of the inoculum to the substrate. (Soil Sci. Soc. Am. J. 1995, 59, 1316-20)
MEASUREMENTS Analyzing aerosols Analysis of organic compounds in atmospheric aerosols can be performed with solvent extraction methods, which have long collection periods, or with thermal desorption methods, which have shorter collection periods. Long collection periods are problematic because of air mass composition changes during sampling; thermal desorption methods can experience problems from thermal degradation or poor desorption of some compounds. K. J. Hansen and colleagues developed a method using an integrated sampling and supercritical fluid extraction (SFE) cell. They compared the procedure to thermal desorption, which has similar collection characteristics. The techniques proved to be complementary, with similar results on most compounds by both techniques. The SFE procedure improved detection of compounds with low volatility. The thermal desorption technique was more effective for some alkylbenzenes. [Anal. Chem. 1995, 67(19), 3541-49]
Microbial filtration The chlorine levels usually used in drinking water treatment are not very effective in removing Giardia cysts and Cryptosporidium oocysts. Conventional treatment processes and direct filtration are used to remove enough of the cysts and oocysts to make chlorination effective. E. C. Nieminski and J. E. Ongerth evaluated the effectiveness of water treatment plants that use conventional treatment and direct filtration for removing Giardia and Cryptosporidium. Results indicated that removal was highly correlated to raw water quality and system turbidity removal. The removal of cyst-size particulates was an indicator of cyst and oocyst removal effectiveness in either system. Removal of heterotrophic bacteria did not correlate with oocyst removal. (J. Am. Water Works Assn. 1995, 87, 96-106)
MODELING Bioconcentration potential In assessing toxicological risk from a xenobiotic chemical, its potential to bioconcentrate must be determined. A first-order, single-compartment model has been used to explain bioconcentration as a diffusive mass-transfer (DMT) process. The octanol-water partition coefficient acts as a predictive parameter for bioconcentration potential in this model. But it does not suitably characterize ionic surfactants. J. Tolls and D. Sijm used the model to examine the relationship between bioconcentration and hydrophobicity for surfactants. They found that the critical micelle concentration could be used to indicate the degree of hydropho-
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bicity. [Environ. Toxicol. Chem. 1995, 14(10), 1675-85]
MONITORING Cysts and oocysts Accurate, selective detection of Giardia cysts and Cryptosporidium oocysts in water supplies is essential for the proper monitoring and operation of drinking water treatment systems. M. R. Rodgers and colleagues have advanced a method to eliminate the interference from species of algae on current detection methods. They modified the American Society for Testing and Materials immunofluorescence method for detection of these organisms and tested for cross reaction with 54 algal species. Twenty-four exhibited some cross reaction. The investigators found that adding goat serum to the test matrix eliminated most of the algal cross reactivity and reduced background fluorescence. The method can be applied for more selective and accurate detection of these organisms in raw and drinking water samples. [Appl. Environ. Microbiol. 1995, 61(10), 3759-63]
POLICY Uniform risks assessment Environmental risks cannot be uniformly assessed and prioritized under current EPA programs and policies because of limited agency authority and lack of uniformity among environmental statutes. F. H. Habicht II addressed reforms that could enable EPA to uniformly assess risk while accommodating economic, social, and political factors. Reforms include legislating greater EPA discretion over its programs and budget allocations, increasing the use of comparative risk assessment, and refining risk assessment default values and methodologies. [Risk Policy Report 1995, 2(9), 21-22]
SOIL Bromide tracer uptake Because of bromide's low natural concentrations and low reactivity in the soil, it is often used as a hydrologic tracer or is mixed with nitrate
Seeking zero-valent iron's reaction mechanism Zero-valent iron has been shown to chemically reduce chlorinated hydrocarbons quickly and cheaply in laboratory and field demonstrations, but the mechanism this process uses is still uncertain. L I. Hardy and R. W. Gillham attempted to determine the reaction mechanism and products of iron in aqueous solutions. Hydrocarbons ranging from methane to pentanes were produced from aqueous C02 and subjected to the metal. The product distribution was similar to that found with Fischer-Tropsch hydrocarbon formation from CO and H2 over a metal catalyst. Results suggest that the reduction rate of chlorinated organics in groundwater cleanup may be limited by adsorption of hydrocarbon products onto the iron. (Environ. Sci. Technol., this issue, 57-65)
to measure denitrification rates. However, bromide uptake by growing crops may influence its use for these functions. R. R. Schnabel and colleagues added a bromide tracer to soils in which rye grass was grown. A wide range between 8 and 86% of the bromide was taken up by the crop. Results indicated that use of bromide in soil systems in which plants are actively growing can result in an error in determining transport properties or denitrification. (J. Environ. Qual. 1995, 24, 888-92)
TOXICOLOGY Predicting chronic toxicity An accurate method to predict chronic toxicity from acute toxicity data would reduce costs and increase the number of chronic estimates available. K. Sun and co-workers applied accelerated life testing to make such predictions. Accelerated life testing has been used to predict the service life of manufactured products. The researchers recorded the time of death for individuals exposed to various concentrations of toxicant. These data are fit to a model, which extrapolates from high to low dose and from short to long exposure times. Predictions compare favorably with measured chronic toxicity in most of the 26 cases stud-
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ied. [Environ. Toxicol. Chem. 1995, 14(10), 1745-52]
WASTEWATER Total chlorine-free effluent Concerned about chlorinated organic compounds, managers of kraft pulp mills are using elemental chlorine-free (ECF) and totally chlorinefree (TCF) bleaching processes. But there have been few studies of TCF wastewater. R. Saunamaki analyzed wastewater from a mill that converted to ECF with chlorine dioxide bleaching and TCF with peroxide bleaching. Chlorine compounds and COD in the mill effluent were reduced, and color was lightened, especially in TCF bleaching. However, effluent toxicity increased from excess peroxide in the TCF effluent, nitrogen emissions increased, and heavy metals removal efficiency decreased. [TappiJ. 1995, 78(8), 18592]
Pretreating wastes Hazardous waste can have toxic effects on activated sludge organisms, volatilize into the atmosphere, limit land disposal of sludges, and pass through water treatment systems without being removed. M. J. Kupferle and colleagues investigated anaerobic pretreatment of industrial wastes as a means to eliminate these problems. They studied bench-scale, fluidized, expanded-bed, granular activated carbon (GAC) systems with anaerobic biomass. The GAC beds were fed primary effluent spiked with 5% landfill leachate and 14 hazardous waste compounds. Compounds were adsorbed by the GAC, which was subsequently taken off line to allow biodegradation to occur. Results indicated effective removal of organics and regeneration of GAC. [Water Environ. Res. 1995, 67(6), 910-20] Contributors to Research Watch are Brian Eitzer, Connecticut Agricultural Experiment Station, New Haven, CT; Stephen Geiger, Remediation Technologies, Inc., King of Prussia, PA; Vincent Hand, Miami University, Institute of Environmental Sciences, Oxford, OH; Richard Hurst, CHEMPET Research Corp., Moorpark, CA; Louis Kovach, Ecolife Associates, Wilmington, DE; and Margaret Whittaker, NSF International, Ann Arbor, MI.
