technique that can measure as little as 0.9 parts per trillion by volume (pptv) of VOCs in a continuous 10-min cycle. The reproducibility is 2% or better. The procedure involves drawing air samples through a Tenax cartridge followed by a helium flush. The cartridge then is thermally des-orbed into a cooled collection loop for 4 min at 200 "C in 6.5 s to flush the VOCs into a jet separator inter­face for an ion trap mass spectro­meter. MS operates at a rate of one SC3.H p e r second in the full-scan mode. Ivlethod detection limits range from 0 9 pptv for toluene to 60 pptv for 1 1 1-trichloroethane U.Am. Soc Mass Spectrom 1996 7(11) 1172-76)

POLICY

Environmental justice Recent studies by church groups,

suggest that environmental hazards are distributed disproportionately in disadvantaged communities. S. L. LjUtter and co-workers suggest that such conclusions depend strongly on the geographic scale chosen for analysis. Using South Carolina as an example, they correlated socioeco­nomic factors with location of toxic and hazardous waste facilities. Spa­tial analysis at the county level yielded the strongest correlations between low income and toxic sites. Smaller census tract and census block analysis demonstrated only weak correlations. On a statewide basis, there was a disproportionate burden on more affluent, white communities in urban areas, rather than low-income minority commu­nities. The authors suggest that small-scale spatial analyses may be required to resolve claims of envi­

ronmental injustice. {Risk Anal. 1996, 16(4), 517-26)

RISK Data extrapolation Propionaldehyde is a component of gasoline and diesel engine exhaust and cigarette smoke. It is used to make medicines and agricultural chemicals. Few data are available on its human health effects. D. J. Guth tests the hypothesis that the human risk of long-term exposure from pro­pionaldehyde can be determined by comparisons with better studied chemicals of similar structure. Guth compares the kinetics, metabolism, and acute exposure data of propion­aldehyde to acetalydehyde and formaldehyde. Based on similarities such 3.S comparable enzyme activity, acute inhalation studies and chemi­cal structures Vie

concludes that the noncancer toxicities of these two chemicals can be expected to be similar Guth believes that such ex­trapolations might avoid the need for costly subchronic and chronic tests {Hum Fcnl RUk Awpw 1199 2R) 580-901

Wildlife exposure Modeling wildlife exposures to toxic chemicals often is used for ecologi­cal risk assessments at hazardous waste sites. R. A. Pastorok and co­workers present a comprehensive survey of trends and recent advances in wildlife exposure assessment. This survey includes discussions of the components of basic wildlife expo­sure modeling, including food web and abiotic exposure pathway analy-ses Limitations of basic wildlife ex­posure models, such as the overly conservative and unrealistic nature

of most basic exposure models, are illustrated. Numerous new develop­ments in modeling exposure are pro­vided, including the use of toxicoki-netic modeling and Monte Carlo analysis of foraging patterns. {Hum. Ecol. Risk Assess. 1196, 2(3), 445-80)

Wildlife foraging Risk to wildlife that forage in areas with contaminated soil depends partly on spatial factors such as the size of foraging areas and contaminant distri­bution. J. S. Freshman and C. A. Men-zie present two models that incorpo­rate these considerations. One, the Curve Model, is a graphical model that illustrates potential wildlife ex­posures and effects on individuals, including chronic lethal, reproduc­tive, and acute lethal effects. The second, the Population Effects For­aging Model calculates the average percentage of adversely affected in­dividuals within a. local population A hypothetical hazardous waste site contaminated with a particular chemical is used to illustrate the utility of both models (Hum Ecol Risk Assess 1996 2(3) 481-98)

SOIL

Sorption studies Sorption of pollutants in soils can determine their transport, fate, bio­availability, and response to remedia­tion efforts. Although it is known that pollutants become more strongly sorbed with time, the mechanism of this effect is the subject of debate. B. Xing and J. J. Pignatello studied changes in the shape of the adsorp­tion isotherm for the chlorinated aromatic compounds, 1,3-dichloro-benzene, 2,4-dichlorophenol, and metolachlor sorbed to soils after periods of 1, 30, and 180 days. With time, the sorption intensity increased and the concentration dependence decreased Results cire consistent with a dual-mode sorption mecha­nism including partitioning and site-specific adsorption (Environ Toxicol Chem 1996 ,1 1282-88)

VOC loss in sludge The application of sewage sludge to agricultural land is an increasingly common disposal method. Yet con­cerns remain about release of vola­tile organic compounds (VOCs) and

New measurements of mercury kinetics Knowledge about the kinetics of Hg(ll) adsorption and desorption on soil is impor­tant to predict the transport and fate of contaminants, yet little information has appeared in the literature. Y. Yin and colleagues investigated adsorption and des­orption kinetics of Hgjll) on four soil types with a stirred-flow method. A biphasic pattern, involving an initial fast step followed by a slow step, was observed for both adsorption and desorption. Soil organic carbon content was the most impor­tant factor in determining Hg(ll) adsorption rates. For soils with higher organic carbon content, the time required to reach equilibrium was increased, as was the fraction of Hg(ll) persistent in the soil. The results may be useful in assessing the risk to groundwater from mercury-contaminated soils. {Environ. Sci. Technol., ,his issue, pp. 496-503)

VOL. 31, NO. 2, 1997/ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS " 6 9 A