nated pesticides from environmental matrices. They also showed a greater recovery of high molecular weight PAHs from diesel materials than that obtained using Soxhlet extraction. {Anal. Chem. .997, 69(20)) 4210-4219)
RISK Perception of probability The way risks are communicated to the public influences how they are perceived. M. Siegrist compared how risks expressed as a probability of occurrence and those expressed as a frequency of occurrence affect riskavoidant behavior. Results indicate that people are willing to spend more money to avoid a risk when it is expressed as a frequency. This suggests that risks expressed as frequencies the preferred format to emphasize risk reduction to a OOPUlation that tends to underestimate risks. Perceived differences between high and low risks diminished when risks expressed as probabilities of occurrence {Risk Anal 1997 17{4) 507-510)
Waste site cleanups Cleanup activities at Superfund sites reduce health risks to area residents, but they create occupational risks to on-site workers. J. T. Cohen and coworkers performed a hypothetical case study comparing remediation worker fatalities with cancer deaths among a resident population surrounding a hazardous waste site. A metric was used showing that occupational fatalities affect a relatively young population, although cancer deaths usually occur much later in life. Calculated results suggest that risks to cleanup workers can exceed the public health benefits of remediating a hazardous waste site and confirm the importance of considering fatalitv risks to remedial workers {Risk Anal 1997 27(4) 419-425)
WASTE WATER Produced water treatment Produced water from gas and oilwell operations is possibly the largest single source of waste generated in the United States. The water con-
tains grease, oil, and other contaminants and must be cleaned up before being disposed of or used. S. M. Santos and M. R. Wiesner performed bench-scale membrane filtration pilot tests of produced water obtained from operating oil and gas wells. Results indicate that the technique can reduce water contaminants to levels below current and anticipated regulatory limits. The economic feasibility of the method for full-scale operations should not be generalized; the utility of membrane filtration is specific to the site being cleaned up. {Water Environ. Res. .197, 69(6), 1120-1127)
WATER Zebra mussels and metals Biological organisms can play an important role in affecting the environmental distribution of metals in water. R L. Klerks and co-workers evaluated high densities of zebra mussels, Dreissena polymorpha, on the cycling of copper, zinc, and nickel in Lake Erie. The metals are incorporated from the lake water into animal tissue and are subsequendy deposited on the lake bottom mrough normal elimination processes (feces production). They found that the animals can erTi" ciently remove metals from the water more than doubling the rate at which metals are added to the lake bottom by other mechanisms The metal removal rate from the water column by zebra mussels is estimated to be 10-17% per dav of the amounts present {Can J Fish Aquat Sci 1997 54 1630-1638)
Contributors: Michael Brauer, University of British Columbia, Vancouver; Brian Eiizer, Connecticut Agricultural Experiment Station, New Haven, Conn.; Stephen Geiger, Remediation Technologies, Inc., King of Prussia, Pa.; Vincent Hand, Miami University, ,nstitute of Environmental Sciences, Oxford, Ohio; Louis Kovach, Ecolife Associates, Wilmington, Del; Geoffrey Nobes, McGill University, Montreal, Canada; Raewyn Town, Queen's University yf Belfast, Northern Ireland; and Margaret Whittaker, NSF International, Ann Arbor Mich.
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