Research Watch: Selecting models - Environmental Science

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Soil amendment caution The presence of PCDD/F and PCB contaminants in sewage sludge raises concerns about their use as a soil amendment. E. Eljarrat and colleagues studied the fate of these compounds in mixtures of sewage sludge and soil. Contaminant concentration levels in the mixtures generally tracked sewage sludge application rates. PCDD levels in sludge-treated soils were 1.2-11.6 times greater than corresponding levels in untreated soils. Contaminant isomer profiles in treated soils closely resemble those found in sewage sludge, whereas contaminant concentration levels sometimes exceeded proposed levels in Germany for agricultural and horticultural land use applications. {Environ. Sci. Techno!., this issue, pp. 2765-71)

ing polymerization of (S)-2-ethoxy4-isopropyl-5(4/f)-oxazolone. The molecular weight of the polypeptide was independent of the monomer feed ratio and increased with decreasing preparation temperature, thereby showing high solubility in organic solvents. (Macromolecules 1997, 30, 1863-68)

GROUNDWATER Selecting models Groundwater models facilitate groundwater protection programs, but few communities are able to choose an appropriate model from among the hundreds of models available for studying contamination problems; subjective judgment is frequently the norm. To avoid model and data misuse, X. Wang proposes a graphic information system-supported model, divided into four classes based on complexity of the aquifer and contaminant reactivity. Rule-based expert knowledge is then used to evaluate groundwater models and available data as well as to indicate data limitations and the suitability of models for specific applications. {Environ. Manage. 1997, 21, 607-15)

and co-workers compared the performance of ASE and SFE with three traditional techniques (ultrasonication and Soxhlet and methanolic saponification extractions) for extracting aliphatic hydrocarbons and PAHs from marine sediment and particulate matter. They found equal accuracy and precision among all five techniques. (Anal. Chem. 1997, 69, 2171-80)

Toxicity test bias The Microtox assay measures concentrations of contaminants in aqueous or solid environmental media, but care must be taken to correct for biases. A. H. Ringwood and colleagues studied Microtox toxicity test results for contaminants in high silt-clay estuarine sediments. They found that adsorption of bacteria to the silt-clay particle fraction can bias interpretation of results from field studies and may lead to overestimation of contaminant effects in muddy areas. The authors present several methods for normalizing Microtox test results and correcting for sediment composition effects, and they recommend using the test in conjunction with other toxicity indicators. {Environ. Toxicol. Chem. 1997, 16, 1135-40)

RISK

MEASUREMENTS Method comparison The reliable determination of toxic compounds such as PAHs in environmental samples is a major concern. Traditional analysis methods are time-consuming and often require the use of toxic solvents. Two new techniques, accelerated solvent extraction (ASE) and supercritical fluid extraction (SFE), reduce solvent usage and extraction times. O. P. Heemken

Benchmarking models The reliability of multimedia risk assessment models can be examined through benchmarking analyses. W. B. Mills and colleagues compared results obtained from using three models—RESRAD, MMSOILS, and MEPAS—to predict exposure point concentrations and carcinogenic risks resulting from uranium-238 and methylene chloride leakage from a hypothetical landfill. All three models evaluate contaminant fate

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and transport in unsaturated and saturated subsurface zones, surface water, and the atmosphere. Each model identified groundwater as the pathway that produces the highest risks. However, predictions of factors such as peak volatile flux, saturated zone concentrations, and transport speeds differed by several orders of magnitude because of different mathematical formulations and model assumptions. {Risk Analysis 1997, 17, 187-201)

Credibility problems Cultural, institutional, and political problems related to risk analyses and their use are serious obstacles to environmental decision making. The National Center for Environmental Decision-making Research, a National Science Foundation center, surveyed environmental decision making in the United States. The investigation was based on in-depth interviews with industry, congressional, environmental, and governmental officials or staff involved in decision making. B. E. Tonn and J. H. Peretz report that almost all decision makers face a credibility problem because of a lack of foresight in planning future environmental policies and the increasing political influence over technical issues. {Risk Policy Report 1997, 4, 33-36)

Quake hazmat dangers Little attention is given to documenting earthquake-initiated hazardous materials release (EIHR) events, despite the dangers they can pose to affected communities. EIHR events occur more frequently than hurricanes or floods. M. K. Lindell and R. W. Perry used data from the Northridge, Calif., earthquake to evaluate EIHR events. That earthquake caused more documented EIHR events than any previous earthquake in the United States. The authors provide proportional estimates of EIHR probabilities and explore their relevance to earthquake hazard management issues and development of risk assessments; but because of the site specificity of EIHR events, these estimates cannot be generalized. Consequently, the authors propose comprehensive loss estimation studies to characterize potential EIHR risks in other earthquake zones and an approach for carrying out such studies. {Risk Analysis 1997, 17, 147-56)