Approximately 20% of the aquatic species in the Hudson River basin are exotics, that is, species introduced from outside the United States. That figure emerges from a two-year study of the region, w h i c h w a s discussed by Cornell University's Edward Mills at the International Zebra Mussel Conference in March. "In both the Great Lakes a n d the Hudson River basin, about one exotic species has become established per year since 1840," said Mills. " T h e difference between the two ecosystems is that the rate of introduction has increased during the past 30 years in the Great Lakes, while it has d i m i n i s h e d in the H u d s o n River." Exotics pose a danger to biodiversity by competing with native species and altering ecosystems. For instance, in Oneida Lake, NY, 5 0 % of the native clam species have perished since zebra mussels entered the waters in 1991, said Mills. Many of the exotics in the H u d s o n River were probably introduced through ship ballast. Before 1900, most ships relied on a ballast of m u d and rocks, w h i c h provided a med i u m for plants. Since then, w a t e r has become the preferred ballast, w h i c h could account for the drop in exotic introductions in the region. For the United States as a w h o l e , the level of exotics is estimated at 2 % to 8%. The dramatic shrinking of the Aral Sea in Central Asia and the subsequent changes in landscape have changed the region's weather, according to a National Center for Atmospheric Research study by geographer David Smith. Speaking at the Association of American Geographers meeting in March, Smith reported that summers have become hotter a n d winters colder as a result of the changing landscape a n d ecosystem. " A n y changes in regional climate w o u l d affect the regional hydrologic character of rivers a n d deltas a n d t h u s may entail particularly high economic a n d social costs," warns Smith. The diversion of fresh water from the Aral Sea began in the 1960s u n d e r the old Soviet regime. Because the water flowed into interior regions, there was no return to rivers that feed the basin. As a result, rivers and fertile deltas have dried u p , and the climate has became more " c o n t i n e n t a l " as the shrinking sea loses its moderating effect. 254 A
Environ. Sci. Techno)., Vol. 28, No. 6, 1
"MA,-
\
Yi Birds prefer old-growth forests to second-growth sites, according to a report prepared by researchers from P u r d u e University and the U.S. National Park Service. The report discusses a study conducted in six areas of old-growth, h a r d w o o d forests in the Great Smoky M o u n t a i n s National Park, w h i c h w e r e compared w i t h nearby second-growth sections w i t h trees about 60 years old. The old-growth section contained u p to 5 0 % more songbird species and 5 0 % more individual birds than the second-growth stands. "Because old-growth sites are a primary habitat for migratory songbirds, disturbance or reduction of the few remaining old-growth forests may a d d to an already critical decline in bird p o p u l a t i o n s , " said P u r d u e biologist Kerry Rabenold. Great Smoky Mountain National Park contains the largest remaining tract of protected eastern deciduous forest in North America. Similar observations have been m a d e in studies in Indiana. Data from the U.S. Fish a n d Wildlife Service indicate that over the past decade the n u m b e r of birds migrating through North to Central a n d South America has declined by as m u c h as 3 0 % .
TECHNOLOGY A newly patented biological treatment process for wastewater significantly reduces phosphorus levels, claim its developers Piedm o n t Olsen Hensley (Raleigh, NC). The system has been operating since July 1992 at a wastewater treatment plant in Wilson, NC, that processes 12 million gallons per day. During its first year of operation, the system lowered p h o s p h o r u s to an average of 0.27 mg/L w i t h o u t chemical addition. To reach these levels three indep e n d e n t processes are p u t into operation: a mainstream, activat-
ed-sludge process that uses aeration and solids separation zones; a side stream that treats some of the activated sludge u n d e r anoxic conditions to remove nitrates, then places it in anaerobic conditions to allow selection of desired microorganisms for removing p h o s p h o r u s ; a n d a second side stream that ferments organic material into volatile acids a n d other products that satisfy the metabolic needs of the desired microorganisms. Bradtec (Roswell, GA), in conjunction with the Department of Energy, has been testing a unique remediation process that selectively b i n d s magnetic particles to soil contaminants such as actinides and heavy metal elements. The heart of the MAG*SEP system is 1 to 10 micrometer-sized magnetic particles coated w i t h either a functionalized polymer (e.g., amidoxime resin) or an absorbing " s e e d " (e.g., KCoFe(CN) 6 ). These specially prepared particles are injected into the soil w h e r e they bind with the radioisotopes or heavy metals. Clean water flushes the particles out so that they can be magnetically separated from the w a s h stream. The contaminants can then be reclaimed and the particles recycled. Bradtec claims that the system can reduce metals in process water d o w n to p p b levels. Metal-enhanced reductive dehalogenation (MERD), a simple, passive technology for reductive dehalogenation of organics, is undergoing pilot testing. Developed by EnviroMetal Technologies, Inc., and the University of Waterloo (both in Ontario, Canada), MERD will be evaluated this s u m m e r at Utah's Hill Air Force Base for both in situ a n d surface treatment of groundwater contaminated w i t h trichloroethylene (TCE). The system relies on granular iron mixed with sand to reduce the TCE to safer byproducts. For in situ remediation, groundwater is funneled through impermeable sheet piles or slurry walls into a reactive cell—a slotted steel caisson filled with the sand—iron mixture. The cell is placed in the path of the groundwater p l u m e , and the water migrates at natural flow rates. Because this is a passive system, it should require little maintenance. In laboratory tests, MERD rapidly degraded
TCE from initial concentrations of more than 3000 ug/L d o w n to 116 ug/L.
MEASUREMENTS A new analytical method for measuring gas-phase H 2 0 2 , hydroxymefhyl hydroperoxide, and methyl hydroperoxide in the field is described in this m o n t h ' s ES&T (p. 1180). The approach, developed by researchers at Brookhaven National Laboratory (Upton, NY) and the State University of N e w York at Old Westbury, is based on the hydroxylation of benzoic acid by Fenton reagent to form fluorescent hydroxybenzoic acid. The authors have incorporated this technique into a 3-channel sampling device, a n d report on potential interferences a n d field studies with their apparatus. The development of a radically new type of solid-state laser with potential applications for environmental monitoring has been announced by AT&T Bell Laboratories (Murray Hill, NJ). The quantum cascade (QC) semiconductor laser can be tailored to emit light at specific wavelengths over a wide range of the mid- to far-IR spectrum by simply varying the thickness of the layers. Development of the QC laser culminates a 30-year effort, say AT&T
physicists. Compared with current semiconductor lasers, the n e w QC lasers should be less sensitive to temperature variation, p r o d u c e a narrower linewidth, a n d display a different frequency response. In conventional diode lasers, the photon's wavelength is determined by the bandgap or energy difference between the electron in a conduction b a n d and the " h o l e " or positive charge in a valence band. Thus, the wavelength is a fundamental property of the semiconductor material; to significantly change the wavelength requires a different composition. QC lasers d e p e n d on electrons jumping between two energy levels in the conduction b a n d of the active layers (or q u a n t u m wells). However, that energy difference is controlled by the thickness of the active layer. The AT&T QC laser emits 4.25-pm light at temperatures u p to 125 K w i t h 5 m W of power.
typical 10-year-old unit. " U p until now, there hasn't been a compressor that could operate with a chlorine-free refrigerant," said Carrier North American president John Lord. "The n e w compressor works just as efficiently—and potentially better—with a chlorinefree refrigerant than what is presently available." With the impending phase-out of CFCs and, eventually, hydrochlorofluorocarbons, manufacturers are under the gun to produce commercial products that run on acceptable alternatives.
BUSINESS What is claimed to be the world's first chlorine-free, non-ozonedepleting residential air conditioner w a s unveiled by Carrier Corporation in April. The WeatherMaker 134a operates w i t h hydrofluorocarbon 134a (CF 3 CH 2 F) and, says the manufacturer, is 50% more energy efficient than a
Some Washington, DC, taxicabs took on a new look in March after Green Seal (Washington, DC) slapped its label on a fleet of "environmentally friendly" cabs. The Clean Air Cab c o m p a n y operates a small fleet of automobiles in the District that run on compressed natural gas, a lower polluting fuel.
Microwaves for detecting t r a c e gases? BY A L A N
A
NEWMAN
lthough not usually considered a routine analytical tool, Fourier transform (FT) microwave spectrometry is being developed by researchers at the National Institute of Standards a n d Technology (NIST, Gaithersburg, MD) for detecting and quantifying species in the gas phase (2). According to NIST chemist Richard Suenram, "basically, we can measure d o w n to 10 to 100 p p b for any volatile organic or inorganic c o m p o u n d with a permanent dipole." Such a system could be used for monitoring automotive exhaust emissions, smokestack fumes, or indoor air quality. Unlike its better k n o w n cousin FT-infrared spectrometry (see May ESS-T, p . 224A), FT-microwave spectrometry can reliably identify analytes on the basis of a
single transition which, typically, has linewidths of < 10 kHz. Moreover, the NIST instrument uses a specially designed nozzle that cools the sample to about 1 K, leaving only the lowest rotational levels populated. T h u s , say the NIST researchers, peak overlap problems are virtually eliminated a n d even large molecules can be detected. (NIST also has collected rotational spectra into a database that could form the core of a computer library). The NIST scientists estimate that they can detect acrolein d o w n to about 3 p p b using an average of 100 repetitive scans. However, this result is based on studies of acrolein diluted in neon. Nitrogen or air can work as a carrier gas, but w i t h a significant loss of signal-to-noise ratio caused by the less efficient cooling of diatomic gases. Suenram estimates that the cur-
rent NIST instrument costs about $100,000. The NIST FT-microwave spectrometer pulses the sample into an evacuated chamber containing two movable alum i n u m microwave mirrors that form a Fabry—Perot cavity. The mirrors are tuned to the exact frequency of interest, a n d the sample is excited with a weak microwave pulse of about 1 m W for several microseconds. The microwave pulse generates Fourier components that p u m p the rotational transition to the higher energy, and the emission signal is detected, amplified, a n d eventually Fourier transformed. Samples enter the cavity through a sample inlet nozzle set in one of the microwave mirrors. The gas stream can be pulsed into the chamber at an 8-Hz repetition rate, limited only by the vacuum p u m p i n g speed. The pulsed nozzle also serves to cool the gas by Environ. Sci. Technol., Vol. 28, No. 6, 1994
255 A
