RESEARCH WATCH
AIR
Extensive snowmobile pollution
Particulate mercury. A review, with 52 references, is provided on published methods and techniques for sampling, determination, and speciation of particulate mercury in ambient air. (Lu, J. Y; Schroeder, W. H. "Sampling and Determination of Particulate Mercury in Ambient Air: A Review," Water, Air, Soil Pollut. 1999, 112 (3-4), 279-295)
Snowmobiles are a popular way for visitors to explore Yellowstone National Park during winter, with more than 60,000 visits during the 1997-1998 season, but little is known about their pollution impacts. G. Bishop and coworkers used nondispersive infrared remote sensing equipment to measure in-use snowmobile emissions of carbon monoxide and hydrocarbons. Results indicate that conventional two-stroke engine designs used in snowmobiles are a major source of these pollutant emissions and are attributable to extensive blowby of the unburned fuel, oil, and air mixture, which is poorly regulated by simple carburetors. (Environ. Sci. Techno/., this issue, pp. 3924-3926)
CHEMISTRY Natural organic matter. The structure and amount of natural organic matter influence the oxidation rates of ozone (0 3 ) and hydroxyl (OH) radicals with hydrophobic organic acids. (Westerhoff, R; Aiken, G.; Amy, G.; Debroux, J. "Relationships Between the Structure of Natural Organic Matter and Its Reactivity Towards Molecular Ozone and Hydroxyl Radicals," Water Res. 1999, 33 (10), 2265-2276)
CLIMATE CHANGE CO2 concentration. In contrast to conventional ice core estimates of 270 to 280 parts per million by volume (ppmv), the stomatal frequency signal in tree leaves suggests that early Holcene carbon dioxide concentrations were well above 300 ppmv. (Wagner, E, Bohncke, S. J. P.; Dilcher, D. L.; Kurschner, W. M.; Van Geel, B.; Visscher, H. "Century-Scale Shifts in Early Holocene Atmospheric CO? Concentration,"Scz'ence 1999 284 (5422), 1971-1973)
CONTAMINANTS PCBs. The reproductive ecology and behavior of tree swallows breeding
at several sites along the PCB-contaminated Hudson River are studied. (McCarty, J. P.; Secord, A. L. "Reproductive Ecology of Tree Swallows {Tachycineta bicolor) With High Levels of Polychlorinated Biphenyl Contamination," Environ. Toxicol. Chem. 1999,18 (7), 1433-1439) Transport properties. The transport properties of the aqueous solutions of benzene, dichloromethane, and trichloroethylene through extended polyvinyl chloride and high-density polyethylene geomembranes are investigated. (Xiao, S., Moresol, C ; Burzyk, A.; Pintauro, P.; De Kee, D. "Transport of Organic Contaminants in Geomembranes Under Stress," /. Environ. Eng,. 1999 125 (7), 647-652)
ECOTOXICOLOGY Population dynamics. Population growth rates seem to be a better measure of responses to toxicants than individual-level effects because the former integrate potentially complex interactions among life history traits and provide a more relevant measure of ecological impact. (Forbes, V E.; Calow, P. "Is the Per Capita Rate of Increase a Good Measure of Population-Level Effects in Ecotoxicology?" Environ. Toxicol. Chem. 1999 18 (7), 1544-1556)
4 7 0 A • NOVEMBER 1, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
LANDFILLS Organic fate/metal releases. The degradation of humic matter and hence the release of toxic metals can be substantially decreased if potential buildup of hydraulic gradients are avoided and if the landfill is located below the water surface. (Bozkurt, S.; Moreno, L.; Neretnieks, I. "Long-Term Fate of Organics in Waste Deposits and Its Effect on Metal Release," Sci. Total Environ. 1999,228 (2-3), 135-152)
METALS Low-cost sorbents. A review with 80 references concerning potentially lowcost sorbents for heavy metals is given. (Bailey, S. E.; Olin, T. J.; Bricka, R. M.; Adrian, D. D. "A Review of Potentially Low-Cost Sorbents for Heavy Metals," Water Res. 1999,33 (11), 2469-2479)
METHODS Risk assessment. The probabilistic approach of accounting for parameter value uncertainty is examined, and a comparison with the Monte Carlo probabilistic approach is provided. (Guyonnet, D.; Come, B.; Perrochet, P.; Parriaux, A. "Comparing Two Methods for Addressing Uncer-
