RESEARCH WATCH
ASSESSmEnT Bounding analyses Bounding analyses can be useful as simplified, conservative, quantitative analyses of environmental impacts, but when should they be used? R. E. Saylor and L. N. McCold considered whether such analyses impede or advance the purposes of the Na tional Environmental Policy Act (ΝΕΡΑ). They reviewed four uses of bounding analyses: (1) insignificant impacts, (2) generic environmental documents, (3) programmatic ΝΕΡΑ documents, and (4) accidents. Be cause bounding analyses require less detail, the researchers found that such analyses can be used earlier in planning, consistent with ΝΕΡΑ re quirements. Bounding analyses should be used more widely and are preferable to vague, qualitative fore casts that do not advance the pur poses of ΝΕΡΑ, they conclude. (Envi ron. Prof. 1994, 16, 285-91)
SFE used to determine PCBs in fish tissue Supercritical fluid extraction (SFE) is replacing soxhlet extraction because it reduces solvent use, generates less waste, and increases throughput. R. Hale and M. Gaylor developed a method to apply SFE to the determination of polychlorinated biphenyls (PCBs) in fish tissue. Lyophilized fish tissue is packed in the extraction vessel and a plug of neutral alumina is added. The PCBs are extracted from the matrix with unmodified C02 at 150 °C and 350 atmosphere, and the solid phase is trapped. The alumina in the extraction vessel retains the lipids so the solvent rinse of the trap can be directly analyzed by gas chromatography with electron capture detection. The results show no significant differences compared to analyses using soxhlet extraction and gel permeation cleanup techniques. (Environ. Sci. Technol., this issue, 1042-47)
Improving solubility BIODEGRADATIOn Biofilm on plastics Biodégradation techniques that treat groundwater contaminated with low concentrations of benzene, toluene, ethylbenzene, and xylene (BTEX) are important for effective bioremediation of gasoline and fuel spill sites. R. D. Neufeld and colleagues developed a biofilm on plastic surfaces, using activated sludge inoculum and high nutrient conditions to address this need. Bioreactors consisted of cylindrical polymethylacrylate tubes with polypropylene packing. During a four-month period, the researchers biodegraded target organics—toluene introduced in 10-20 mg/L concentrations—in a continuous flow system. The study demonstrated the system's capability to degrade low levels of toluene and indicated that this capability can be extended to other BTEX compounds. [Water Environ. Res. 1994, 66(7), 899-904)
Biodégradation of hydrophobic hydrocarbons in soils and sediments often is limited by compound solubility and lack of transport to the active metabolism site. Previous studies indicate that surfactants can help increase degradation by increasing aqueous-phase concentrations through either solubilization or desorption from soil or sediment surfaces. S. A. Churchill and colleagues studied the addition of an oleophilic fertilizer (Inipol ΕΑΡ 22) or a rhamnolipid biosurfactant to buffered solutions of pure bacterial cultures and sparingly soluble hy drocarbons. The oleophilic fertilizer also introduces nitrogen and phos phorus. Both surfactants increased dispersion, emulsification, and min eralization of hexadecane and octadecane. In all cases, the oleophilic fertilizer was more effective than the rhamnolipid. Less mineralization occurred with aromatic hydrocar bons (toluene and 2-methylnaphtha-
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lene); again the oleophilic fertilizer was more effective. (/. Environ. Qual. 1995, 24, 19-28)
mEASUREmEnTS Trace organics Methods for on-site monitoring of trace levels of volatile organic com pounds (VOCs) in water and wastewa ter are needed to comply with envi ronmental regulations. S. Bauer and D. Solyom report on a membrane in troduction mass spectrometry (MIMS) system that should prove useful for such monitoring. Their system cou ples a direct insertion capillary mem brane to an ion trap mass spectrome ter. For the VOCs listed in EPA method 524.2 (purge and trap GC/MS), detec tion limits with 1 inL of sample were
