Research Watch: Benzene trends

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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-

VOL. 30, NO. 1, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 9 A