Environmental ▼ News 2-D isotope analysis deciphers anaerobic MTBE degradation
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UNFALLTECHNISCHER DIENST DER STADTPOLIZEI ZÜRICH (ACCIDENT TECHNICAL SERVICE OF THE ZURICH POLICE)
or the first time, two papers carbon and hydrogen. Bonds of the isotope analysis, we would never published in ES&T show that lighter stable isotopes are easier to have been able to characterize the 2-D stable isotope analysis can break, which causes an enrichment biodegradation pathway at a combe used to assess and quantify degof the heavier isotopes in the replex field site like that,” says Stefan radation of methyl-tert-butyl ether sidual substrate. On the other hand, Haderlein, corresponding author (MTBE) in the field. Moreover, one abiotic nondegrading processes, of the study and now professor of paper develops a method to elucisuch as sorption, dilution and volageochemistry at the University of date the reaction mechanism intilization, do not change the isotope Tübingen, Germany. Knowing the volved that could well set degradation pathway, the new standards for the field, authors were also able to say experts. calculate the extent of bioMTBE is widely used degradation at the site. as an additive to gasoline, Samples were obtained and it is one of the most frefrom numerous monitoring quently detected groundwells at the site and then taken water contaminants in to the laboratory for analyindustrialized countries sis. The goal was to find out because of leaking underwhether biodegradation ocground storage tanks, accurred at the site, which would cidental gasoline spills, and make natural attenuation a precipitation. Although potential alternative to the MTBE is rapidly mineralized current and costly removal of by aerobic bacteria, its degthe plume by pumping wells radation under the anaeroto keep MTBE from the adjabic conditions that prevail in cent wetlands. Accidental gasoline spills like the one caused by this demost plumes is much slowIn the second paper, rerailed train with tanker cars full of gasoline are significant er; this makes MTBE the searchers from the University sources for MTBE contamination in groundwater. most persistent of all gasoof Oklahoma, the U.S. EPA, ratio. While the aerobic biodegraline constituents. To find out whether and the Atlantic Richfield Co. used natural attenuation is an option for dation of MTBE is initiated through 2-D isotope analysis to investigate site remediation or whether the plume the cleavage of a C–H bond, the anMTBE degradation at nine field sites must be dug up to prevent the conaerobic biodegradation starts with in the United States and found antamination of drinking water, fast and the cleavage of a C–O bond. This aerobic biodegradation to be the marobust methods for determining the means that the isotope ratio shift is jor degradation process at each of the biodegradation of MTBE in situ are different for the two pathways, essites (Environ. Sci. Technol. 2005, 39, needed. Conventional approaches pecially for hydrogen. 213–220). “The method has a potento assess MTBE’s in situ degradation Analyzing a complex field site in tial to become a routine method for through mass balances are complicatBrazil, researchers from the Swiss assessing MTBE degradation,” says ed because the primary transformaFederal Institute for Environmental corresponding author Tomasz Kuder, tion product, tert-butyl alcohol, may Science and Technology (EAWAG) pointing out that it offers a cheaper be present at the site as one of the othand the Swiss Federal Institute of alternative to lengthy, labor-intener components of spilled gasoline and Technology Zurich (ETHZ) used sive microcosm studies. Because the because many sites have very complex combined stable carbon and hymethod is in an initial phase, there is geochemistry and hydrology. drogen isotope analysis to show some reluctance by industry to use Compound-specific isotope that the degradation of MTBE proit, says Kuder. However, an initiative analysis, a rather recently develceeds anaerobically rather than to introduce it into industry or EPA oped technique in environmental aerobically at that site in research guidance documents should overgeochemistry, identifies biodegpublished in this issue (pp 1018– come these reservations, he adds. radation by the shift in the stable 1029). “Based on conventional 1-D The paper by Haderlein and coisotope ratio of elements such as [such as just carbon or hydrogen] authors also gives more insight in78A ■ ENVIRONMENTAL SCIENCE & TECHNOLOGY / FEBRUARY 15, 2005
© 2005 American Chemical Society
to the exact anaerobic degradation mechanism of MTBE. This insight is made possible by a new physicochemical concept that transforms the empirical isotopic enrichment factors into universal constants by introducing a correction for carbon and hydrogen atoms at nonreacting positions on the investigated molecule. The general concept for the correction was adapted from isotope chemistry, says Haderlein. He adds that it was devised to allow comparisons of isotope enrichment between different compounds and also to enable predictions to be made about the expected fractionation once the degradation mechanism is known. “This correction is completely innovative and allows one to get much more quantitative values
and information about the reaction mechanisms. . . . It is also applicable to many other compounds, making this a really important step,” says Barbara Sherwood-Lollar, director of the Stable Isotope Laboratory at the University of Toronto, Canada. “These papers are a very good illustration of the direction the field [of isotope analysis] is in the process of moving,” says SherwoodLollar. “While the measurements so far have mainly been qualitative, one can now use the measurements in a quantitative way, getting out much more information.” Haderlein agrees and says that the method has gained new scientific rigor and should become the method of choice for analyzing bioremediation at complex geochemical sites. —ANKE SCHAEFER
PBDEs in dust and dryer lint Research published in this issue of ES&T (pp 925–931) provides the strongest hypothesis to date for the source of the very high levels of brominated flame retardants being found in the blood and breast milk of U.S. residents. Heather Stapleton of the National Institute of Standards and Technology says the study also shows that young children in the most contaminated homes may be ingesting enough polybrominated diphenyl ethers (PBDEs), which are suspected to be endocrine disrupters, from dust to raise public health concerns. Stapleton’s research shows that the dust in U.S. homes can contain very high levels of PBDEs. She found flame retardants in the dust of all 16 homes she tested in the Washington, D.C., metropolitan area, as well as in the one Charleston, S.C., home she sampled. Stapleton analyzed for 22 different PBDE compounds, or congeners, and found that the homes contained
780–30,100 nanograms (ng) of total PBDEs per gram of dry mass. As has been the case with human milk and blood, the levels of PBDEs in the U.S. dust were nearly an order of magnitude higher than the amounts measured in European homes. Stapleton’s results are similar to the levels that were reported by the Silent Spring Institute, an environmental nonprofit (Environ. Sci. Technol. 2003, 37, 407A–411A). Arnold Schecter of the University of Texas School of Public Health and colleagues also reported similar findings last summer at international meetings. The PBDE levels in the U.S. house dust are in line with what’s being found in dust in the 70 randomly selected Canadian homes that have already been analyzed for PBDEs in indoor air (Environ. Sci. Technol. 2004, 38, 386A–387A), says Tom Harner of the Meteorological Service of Canada. Taken together with Harner’s research into the levels of PBDEs in indoor air—which shows
News Briefs U.S. PM2.5 levels drop . . . Levels of fine particulate matter (PM2.5 ) in 2003 were the lowest since the U.S. EPA began monitoring them in 1999, according to an agency report released in December. These levels are declining alongside dropping amounts of sulfur dioxide and nitrogen dioxide emissions from coal-fired power plants, under the acid rain program established by the 1990 Clean Air Act. Although levels have dropped, fine particles remain EPA’s most pressing air pollution problem. Millions of people still live in areas where particle pollution exceeds levels set to protect public health, particularly busy urban areas, the agency notes. PM2.5 penetrates deeply into the lungs, and studies link fine particle exposure to an increased risk of heart attack, aggravation of asthma, and even premature death. The Particle Pollution Report: Current Understanding of Air Quality and Emissions through 2003 is available at www.epa.gov/airtrends.
. . . but not everywhere Thirty states meet the nation’s first standards for fine particulate matter (PM2.5 ), announced Michael Leavitt, the U.S. EPA administrator, in December. This means that 20 states, mostly along the East Coast, and the District of Columbia have not attained the country’s mass-based particle pollution standards. They have until early 2008 to submit plans that outline how they will meet the standards. The PM2.5 standards are part of the Clean Air Rules of 2004 implemented by the Bush Administration and include regulations for emissions from nonroad diesel equipment and power plants. For more information on particulate pollution, go to www.epa. gov/pmdesignations.
FEBRUARY 15, 2005 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 79A
New research suggests that the PBDEs used as flame retardants in consumer goods such as couches are escaping from the products they are used to protect. Children are at particularly high risk of taking up the chemicals, which are suspected to be endocrine disrupters, from house dust. PBDEs also appear to be attaching themselves to people’s clothes.
that air emissions cannot completely explain the highest levels in people—the dust studies confirm that “we need to consider indoor exposure as a route,” Stapleton says. “House dust could definitely be a source of exposure to PBDEs through inhalation, ingestion, and dermal uptake,” Birnbaum agrees. “Ingestion of dust is likely to be the dominant intake route for both [non-nursing] children and adults, compared to dietary intake,” Harner adds. Stapleton also found that the percentage of congeners associated with the Deca PBDE formulation, the only PBDEs that are being included in U.S. goods as of this year, varies to a “surprising” degree in the tested homes. This may reflect differing manufacturing practices for the electronic goods the Deca flame retardants are used to protect, such as computers, televisions, and stereo equipment, she says. “Smaller houses or apartments have more Deca in their dust,” she adds. By using EPA estimates of how much dust a toddler between the ages of 1 and 4 can be expected to take up, Stapleton and her colleagues determined that children in homes with high levels of PBDEs could be ingesting as much 1180 ng of PBDEs from dust each day. She warns that this is sufficiently
close to the levels that cause behavioral effects in laboratory animals to highlight the need for more data on indoor exposure to PBDEs. This is particularly true for children, because previous studies have revealed that nursing infants may already be consuming a high dose. PBDEs are slated for evaluation by the Children’s Environmental Exposure Research Study program, which is currently undergoing additional peer review (Environ. Sci. Technol. 2005, 39, 40A). Exactly how the PBDEs are escaping from consumer products remains unclear, but Stapleton attempted to glean more information about one potential route by looking for PBDEs in dryer lint. Stapleton was surprised by what she found. “The levels were higher than I expected to see,” she says. “If anything, those are low estimates, because we expect some to be taken off in the washing cycle before it even hits the dryer,” she says. She acknowledges that at least some dryers could contain Deca as a flame retardant, but the “fact that we see Penta and Deca levels in some of these dryer lint samples suggests that it’s most likely associated with the dust,” she says. —KELLYN BETTS
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News Briefs Growing biotech North America continues to be the leader in producing biotech crops, but China’s funding for biotech research ranks second in the world behind the United States, according to a report released by the Council for Biotechnology Information, a nonprofit group of biotech companies and trade associations. The United States, Argentina, China, Canada, and Brazil grow 98% of global biotech crops, but China has emerged as a major center for biotech research. China’s government has invested several hundred million dollars, and half of China’s farm fields could be growing genetically modified crops within 10 years, the report predicts. The report does not define trees as crops. Biotech crops are now being grown in 18 countries, while 45 additional countries are conducting related research, according to the report. The report’s authors found that the global commercial value of biotech crops grown in 2003 and 2004 totaled $44 billion. The Global Diffusion of Plant Biotechnology: International Adoption and Research in 2004 is at www.apec.umn.edu/faculty/frunge/ globalbiotech04.pdf.
Window into the Arctic To make it easy for scientists to find the latest data on the changes being observed in Arctic ecosystems, the U.S. National Oceanic and Atmospheric Administration (NOAA) has dedicated a website to presenting information collected from reputable scientific sources over the past three decades on the area’s ice, land, climate, marine ecosystem, and human effects. The changes being documented in “near real time” include warming spring temperatures, sea ice loss, and the conversion of tundra to wetlands and shrub areas. To see the site, go to www.arctic.noaa.gov/detect.
NOAA
KELLYN BETTS
Environmental▼ News
