RESEARCH WATCH
GREEN CHEMISTRY Chitosan films Chitosan is a chemically modified form of chitin, the major component of the exoskeletons of insects and shells of crustaceans. Chitosan has a number of potential applications as a biodegradable polymer, especially when processed into either a film or a fiber. Xu and associates report that acylation can dramatically enhance the biodegradability of chitosan films. They acylated chitosan films and evaluated biodegradation in laboratory-scale aerobic thermophilic compost reactors. Acylation results in formation of discrete outer layers of chitin and an unreacted chitosan interior. The thickness of each layer depended on reaction time. Films 0.045 mm thick acylated for 3 h showed 100% weight loss after 28 days in the reactor. Unmodified chitosan films showed no significant weight loss after 35 days. [Macromolecules 1996, 29, 3436-440)
GROUNDWATER Nitrate leaching Elevated C0 2 levels associated with global climate could alter plant growth, carbon and nitrogen cycling in the soil, and leaching of nitrate to groundwater. Yet researchers have devoted little attention to the potential effects of elevated atmospheric C0 2 on groundwater quality in "agroecosystems." H. A. Torbert and colleagues examined these effects in field chambers in which they grew a legume (soybean) and a nonlegume (sorghum) in C0 2 concentrations twice those of ambient levels. The high COz increased plant biomass and decreased soil nitrate concentrations below the root zone. The decrease was attributed to higher carbon/nitrogen ratios in residues and soil organic matter, which reduced mineralization of soil nitro-
Colloid transport in pollutant migration Researchers have long surmised that solid particles and pollutants sorbed to them migrate slowly in porous soils and aquifers, posing no contamination risks at distant locations. Recent studies, however, have suggested that mobile, colloidal particles might be the dominant transport mechanism for strongly sorbing pollutants. D. Grolimund and co-workers provide experimental evidence to support this idea. They simulated field conditions in a laboratory column with lead sorbed to a noncalcerous soil. Soils loaded with 2 mg of Pb/g released colloids containing 7 mg Pb/g. A classic transport model underestimated both the concentration of Pb in the column effluent and the travel velocity by several orders of magnitude. The authors recommend that colloid-facilitated transport be considered in risk assessment of subsurface contaminants. [Environ. Sci. Techno!., 1996, 30(10), 3118-23)
gen. The authors speculated that increased atmospheric C0 2 could result in reduced nitrate concentrations in groundwater below agroecosystems. (/. Environ. Qual. 1996, 25, 720-26)
during refueling showed that the procedure had a limit of detection of 0.02 ug/m3. The data are modeled to estimate half-lives in two physiological compartments giving values of 2.9 and 34 min. The model also allows an estimation of the total amount of MTBE eliminated through breath by each individual following exposure. (J- Air Waste Manage. Assoc. 1996, 46(7), 676-82)
Pesticides in groundwater Automated techniques offer many advantages in the monitoring of trace amounts of pesticides in groundwater. S. Lacorte and D. Barcelo report on a method for determining part-per-trillion levels of organophosphorus pesticides. They used automated liquid-solid extraction with LC and atmospheric pressure chemical ionization mass spectrometry (APCI/MS) for detection. An acidified 100-mL water sample was concentrated and eluted through an LC column into an APCI source operated in either the positive ion or negative ion mode. In a selective ion monitoring [AU: positive ion?] mode the limits of quantitation for 12 pesticides ranged from 5 to 37 ng/L with a repeatability of 17-25%. The procedure had an average recovery of greater than 95%. {Anal. Chem. 1996, 68(15), 2464-70)
VOC sampling bag losses MEASUREMENTS MTBE breath test Wide use of methyl-ferr-butyl ether (MTBE) as a gasoline additive has created the need for methods to assess human exposure. A. B. Lindstrom and J. D. Pleil report on a method for determining MTBE in breath for measuring exposure during motor vehicle refueling. Breath samples collected in stainless steel canisters are analyzed with gas chromatography/mass spectrometry. Tests on two individuals exposed
0013-936X/96/0930-469AS12.00/0 © 1996 American Chemical Society
Tedlar bags are widely used to store samples in the determination of VOCs. T S. Raihala and colleagues report that these bags can cause significant losses of VOCs. They studied sorption of VOCs by commercial bags, modified commercial bags, and homemade bags. Losses of trichloroethylene, 1,2-dichloroethane, and toluene ranged from 15 to 25% in 24 h. VOC losses occurred rapidly but decreased with time, consistent with losses to a finite number of sorption sites. Their results showed that the majority of sorptive sites are in the hose valve
VOL. 30, NO. 11, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 4 6 9 A
