Screening model The assessment of risks from pollutants flowing into groundwater at Superfund or other hazardous waste sites can require extensive field data and groundwater modeling calculations. A screening model that takes only seconds to run on a 386-based PC has been developed by Arthur S. Rood at the Idaho National Engineering Laboratory. The GWSCREEN model calculates contaminant release from source volume, contaminant transport in the unsaturated zone, and contaminant transport in the saturated zone. Results compare favorably with other models. (Environ. Professional 1994,16, 196-210)
GROUNDWATER Groundwater tracer Anions such as bromine or chlorine are commonly used as groundwater tracers. In situations in which inorganic anions cannot be used (e.g., multiple injection points requiring multiple tracers, or a requirement of more than one tracer in a single area), other tracer compounds will be necessary. Carl Benson and Robert Bowman of the New Mexico Institute of Mining and Technology investigated fluorinated derivatives of benzoic acid (FBAs) as tracers. Tri- and tetrafluorobenzoates with low dissociation constants (piTa 2.71-3.54) were compared to bromine in a series of laboratory transport studies. In general, the FBAs behaved similarly to bromine in sandy-textured materials with neutral to alkaline pH values and low organic carbon fractions. Some sorption of the FBAs occurred in acidic media with high organic carbon fractions. Although the study did not simulate anaerobic conditions, the results indicate that FBAs exhibit good qualities as groundwater tracers and could be used as alternatives to bromine. However, the cost of the FBA and sorption of some of the FBAs to high organic carbon media make bromine the tracer of first choice. [Soil Sci. Soc. Am. J. 1994,58, 1123-29)
LAW Environment symposium A current issue of Ecology Law Quarterly [1994, 21(2)] is devoted to the Environment and Law Symposium, a
Real biomagnification? Elevated levels of environmental toxins in aquatic organisms as a function of position in the food chain (trophic level) have been shown to occur in a number of cases. Are these increases due to bioaccumulation or are they species-dependent? Gerald LeBlanc attempts to distinguish between the two by demonstrating that order-of-magnitude differences in concentrations of chemicals can occur among aquatic organisms at different trophic levels even though laboratory studies do not support a major biomagnification effect at steady-state equilibrium. LeBlanc explains this dichotomy by pointing out that species differences in bioconcentration can be mistaken for biomagnification. He concludes that bioconcentration differences from trophic level to trophic level result from increased lipid content and decreased chemical elimination efficiency as trophic level increases. A mathematical equation is produced that allows bioconcentration to be estimated and assessed in evaluating biomagnification. (Environ. Sci. Technol., this issue, p. 154)
national gathering of 30 speakers from the judiciary, academia, government, and private practice. Five extensive discussions are reprinted that focus on issues such as the relationship among science, environment, and the law; liberty and environmental ethics; public versus private environmental regulation; and the future of U.S. environmental policy. Land, air, water, and property rights are debated in an environmental context, as are free market approaches to environmental protection (e.g., sulfur dioxide pollution permits). Historical accounts of the environmental movement are told from opposing political ideologies. The explosive growth in environmental regulations is explained, and major judicial decisions affecting the environment are reviewed. Featured panelists include senior members of the Sierra Club's Legal Defense Fund, the White House Office of Environmental Policy, and environmental law and science experts from academe.
MEASUREMENTS Supercritical fluid extraction Techniques for extracting organic compounds from solid matrices that can reduce the use of organic solvents and decrease the time required for extraction are highly desirable. One such method, supercritical fluid extraction (SFE), was investigated by Steven Hawthorne, Yu Yang, and David Miller of the University of North Dakota. They used supercritical and subcritical water in a conventional SFE apparatus for the ex-
traction of low-polarity organic compounds. They found that raising the extraction temperature of water at elevated pressures dramatically lowered the dielectric constant of water, which in turn greatly enhanced the solubility of low-polarity organics in the water. The studies covered various temperatures and pressures. For example, the researchers report complete extraction of PAH from a soil matrix in 15 min at the subcritical conditions of 250 °C and 50 bars, conditions sufficiently mild that the SFE extraction vessel's integrity is not compromised. (Anal. Chem. 1994, 66, 2912-20)
Negative ion MS The quadrupole ion trap mass spectrometer (QITMS) is becoming a popular analytical instrument because it is sensitive and versatile yet relatively small and inexpensive. One aspect of that versatility that has not yet been fully examined is the use of negative chemical ionization in QITMS. David Berberich and Richard Yost of the University of Florida have characterized and optimized reaction times and applied voltages in a QITMS system for the detection of negative ions. Their results show that QITMS systems have a limited ability to form thermal electrons. Thus negative ions are more likely to form through dissociative electron capture (using more energetic electrons) than through the electron capture mode. Negative chemical ionization (NCI) requires longer ionization and sample formation reaction times than does positive chemical ionization (PCI). The authors also report on the utility of a mass selected NCI mode of operation using the [OH]"
VOL. 29, NO. 1, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY • 1 1 A
ion. (J. Am. Soc. Mass Spectrom. 1994, 5, 757-64)
Two-dimensional GC Decreasing the time required for a gas chromatographic analysis increases sample throughput and allows meth ods development. Zaiyou Liu and col leagues at the Centers for Disease Control and Southern Illinois Univer sity have developed a comprehensive two-dimensional gas chromatographic system that achieves fast and selective analysis of semivolatile pesticides. Their system uses a two-stage ther mally modulated interface to link two analytical columns of differing polarity within a single GC oven. The system was tested with a 15-component pes ticide mixture. Results showed com plete resolution of the pesticides in
