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 Na­tional 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. Be­cause bounding analyses require less detail, the researchers found that such analyses can be used earlier in planning, consistent with ΝΕΡΑ re­quirements. Bounding analyses should be used more widely and are preferable to vague, qualitative fore­casts that do not advance the pur­poses of ΝΕΡΑ, they conclude. (Envi­ron. Prof. 1994, 16, 285-91)

BIODEGRADATIOn Biofilm on plastics Biodégradation techniques that treat groundwater contaminated with low concentrations of benzene, toluene, ethylbenzene, and xylene (BTEX) are important for effective bioremedia-tion 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)

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 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 hy­drocarbons. The oleophilic fertilizer also introduces nitrogen and phos­phorus. Both surfactants increased dispersion, emulsification, and min­eralization of hexadecane and octa-decane. In all cases, the oleophilic fertilizer was more effective than the rhamnolipid. Less mineralization occurred with aromatic hydrocar­bons (toluene and 2-methylnaphtha-

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 com­pounds (VOCs) in water and wastewa­ter are needed to comply with envi­ronmental regulations. S. Bauer and D. Solyom report on a membrane in­troduction mass spectrometry (MIMS) system that should prove useful for such monitoring. Their system cou­ples a direct insertion capillary mem­brane to an ion trap mass spectrome­ter. For the VOCs listed in EPA method 524.2 (purge and trap GC/MS), detec­tion limits with 1 inL of sample were <1 ppb. An analysis for total triha-lomethanes could be conducted every six minutes with detection limits of 100 pptr. {Anal. Chem. 1994, 66(24), 4422-31)

Solid-phase microextraction Solid-phase microextraction (SPME), a useful new technique in environ­mental analysis, has been improved to allow for the quantitative transfer of volatile organic compounds from the sample matrix to the polymeric coated capillary. Z. Zhang and J. Pawliszyn describe an SPME device in which the polymeric coating is cooled by liquid carbon dioxide while the sample matrix is heated. The heated matrix enhances analyte volatilization, whereas the tempera­ture difference between the matrix and coating greatly magnifies the partition coefficient. This procedure allows quantitative transfer of the analyte, which, in turn, allows for lower detection limits in the subse­quent thermal desorption GC/MS analysis of the coated capillary. Re­sults are shown in which benzene, toluene, ethylbenzene, and xylene (BTEX) are completely recovered from 2 grams of clay or sand in 5

1 6 0 A • VOL. 29, NO. 4, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY