Methane-making plants in Inner Mongolian steppe Zhi-Ping Wang
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hen, nearly 2 years ago, a study first suggested that plants emit methane, scientists received the news with a flurry of excitement, a dash of skepticism, and hasty speculations on plants’ contribution to global warming. A new study published in ES&T (pp 62–68) is the first to confirm that plants do indeed make this potent greenhouse gas. But it also finds that the methanemaking ability varies among types of plants and, at least in the grasslands of Inner Mongolia, is limited to woody shrubs. Until recently, scientists thought they had all the sources of methane figured out. They knew that anaerobic bacteria living in swamps, rice paddies, and the stomachs of ruminating animals produce it. The rest is known to come from human activities like burning of fossil fuels, fires, and waste management. In the original study, published in January 2006, Frank Keppler of the Max Planck Institute for Nuclear Physics (Germany) tested 30 temperate and tropical trees and grasses. He found them burping tiny amounts of methane, which added up to global emissions of 62–236 million metric tons per year (Mt/yr), larger than emissions from wetlands—the biggest known source of methane. Subsequent studies by other groups reduced the estimates to 20–60 Mt/yr. In April 2007, Thomas Dueck of Wageningen University (The Netherlands) cast a shadow of doubt on the validity of Keppler’s findings. Unlike Keppler, who used detached leaves, Dueck used intact plants and failed to find biologically significant levels of emissions. Using detached leaves is faulty methodology, says Dueck, because
Two-thirds of shrubs but no herbs in the Inner Mongolian grasslands emit methane.
it doesn’t rule out the possibility of background methane diffusing out of leaves. In the current ES&T study, lead author Zhi-Ping Wang of the Chinese Academy of Sciences and his team took a “landscape approach” instead of randomly picking plants as done in previous studies. The team wanted to know whether methane emissions from plants could be important across a vast landscape such as that of Inner Mongolia, says coauthor Jay Gulledge of the Pew Center on Global Climate Change. The researchers tested 34 upland plants—25 herbs and 9 shrubs—from the Inner Mongolian steppe. None of the herbs showed any sign of methane production, whereas seven of the shrubs emitted methane at levels that varied among the species. And unlike Keppler’s work, this study found a carbon isotope fingerprint that explicitly marked the methane as of plant and not microbial origin. However, the total amount of the gas released was insufficient
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to make a dent in the grasslands’ huge carbon-absorbing ability. The findings suggest that methane is likely to be “very important in some ecosystems and not in all others,” says Gulledge. “This is a nice piece of work,” says Keppler, referring to the ES&T study. “It also shows how complex plants are—that is, release rates of methane from plants are varying tremendously between species.” And even the skeptical Dueck is impressed. He admits that he may have failed to detect methane in his experiments because he tested only herbs. And he is more convinced by Wang’s methods than by Keppler’s, because chopping up the leaves, as Wang did, would have released any background methane from them. Although the study provides “some support” for Keppler’s discovery, “the possibility of methane diffusion from plant tissues has not been entirely ruled out by this work,” says Michael Keller, chief of sciences at the National Earth Observatory Network (NEON). The © 2008 American Chemical Society
results “provide interesting circumstantial evidence but not absolute proof” that the source of the methane is indeed a chemical process in the plant. Gulledge understands the skepticism. He says the biggest problem with his and Wang’s findings, and with those of Keppler, is that the potential physiological mechanism behind their observations
remains a mystery. “Until you explain the pathway, you can’t be entirely sure what’s going on here,” he says. Keppler’s group is trying to solve this mechanistic mystery. “We have found specific carbon moieties in plants as precursors that are able to form methane under aerobic conditions,” Keppler adds, referring to some of his unpublished results.
As for estimating global methane contributions from plants, it is still too early to extrapolate. For now, the fact that plants can indeed synthesize methane in the presence of oxygen is “just very, very huge, from a biological perspective,” says Gulledge. “From an environmental perspective, it’s probably a less major discovery.” —RHITU CHATTERJEE
Two new research papers in ES&T, one published (pp 31–36) and the other in press (DOI 10.1021/ es0710104), document that the commonly used flame retardant Dechlorane Plus (DP) is found in the atmosphere of Europe and Asia, as well as North America, and present the first evidence that it is breaking down in the environment. DP is manufactured by OxyChem, and the U.S. EPA lists it as a high-production-volume (HPV) chemical. Although DP has been used for more than 40 years, little toxicity data is available on it. Its structure is similar to that of banned organochlorine pesticides such as heptachlor, chlordane, and mirex, but its large molecular size is thought to hinder its bioavailability. Xinghua Qiu and Ron Hites of Indiana University’s School of Public and Environmental Affairs used tree bark samples to provide the first data on DP’s prevalence in the atmosphere outside the Great Lakes region. Tree bark is an effective passive sampler for airborne pollutants, Hites says. In addition to being highly porous, bark contains relatively high concentrations of lipids, “so it soaks up [the lipophilic compounds] we want to measure,” he explains. Hites helped pioneer the
Jing Fu
New data on a widely used flame retardant
Xinghua Qiu of Indiana University collected bark samples from pine trees in the midwestern and northeastern U.S. and analyzed them for Dechlorane Plus.
technique of using bark from trees such as oaks, maples, and pines for this purpose 20 years ago (Environ. Sci. Technol. 1987, 21, 709–712). The new research shows that atmospheric concentrations of DP near its only known manufacturing site, in Niagara Falls, N.Y., are 1–3 orders of magnitude higher than elsewhere in the U.S. The researchers found relatively high DP concentrations in bark samples
from Korea and China, suggesting that the compound may also be manufactured in Asia, Hites says. Hites and Qiu document that the compound is found at low levels in European trees, but they did not find it in northern Canada. The paper presents further evidence of tree bark’s utility as a passive sampler and its ability to identify point sources of pollution, says Staci Simonich of Oregon State University. Although the OxyChem plant is clearly a major source, DP’s presence in household products such as electrical wire coatings and computer connectors suggests that indoor air also may be a significant source to the outdoor environment, adds Tom Harner, a research scientist at Environment Canada. In the second paper, a team of Canadian researchers led by Ed Sverko, the head of organic analysis at Environment Canada’s National Laboratory for Environmental Testing, looked at concentrations of DP in Great Lakes sediments. They documented that the concentrations of DP in sediments from Lake Ontario, where the water discharged from OxyChem’s Niagara Falls plant ends up, were up to 60 times higher than those in nearby Lake Erie sediments. The Canadian researchers analyzed the relative abundance of DP’s two isomers in the sediment samples. They were surprised to
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find that the syn isomer varied significantly from the commercial formulation in the sediment samples taken from sites closest to OxyChem’s Niagara Falls manufacturing facility. Samples from farther away, such as Lake Erie, tended to have isomeric profiles more similar to those of the commercial mixture. The researchers speculate that isomer-specific microbial degradation may be taking place. Previous research has shown that Great Lakes fish, especially those at the top of the food chain, are more likely to take up the antiisomer (Environ. Sci. Technol. 2007, 41, 2249–2254), points out Gregg Tomy, a research scientist in the Arctic Aquatic Research Division of Fisheries and Oceans Canada.
In contrast, the Indiana University scientists’ work shows that DP’s isomer ratios in the atmosphere are very close to those of the commercial formulation. Sverko, who is conducting his research at McMaster University (Canada), acknowledges that he and his colleagues stumbled upon DP degradation products in the environment “by mistake.” When he was analyzing the compound, he did not notice that the glass liner on his gas chromatography/mass spectrometry system was dirty. Eventually, he and his colleagues realized that something in the impurities attacked the DP molecules to produce degradation products with fewer chlorine atoms. When they looked for these degradates in
the environment, they found them in sediments from the Niagara River near the OxyChem plant. The smaller compounds that form as the DP molecule loses chlorine atoms are likely to be more bioaccumulative, Sverko says. Sverko and colleagues are currently conducting studies to determine whether the degradates can be found in fish. “Based on all the information we have seen and cooperative efforts with the EPA, we continue to believe that [DP] is a safe and effective product,” says Richard S. Kline, vice president of communications and public affairs for Occidental Petroleum Corp., OxyChem’s parent company. —KELLYN BETTS
per liter (ng/L). The researchers spiked natural waters from several sources across the U.S. with 36 difTrace concentrations of endocrine(AwwaRF), which funded the study ferent EDCs and PPCPs, including disrupting compounds (EDCs), and is the research arm of the those known to occur or likely to household chemicals, and phardrinking-water industry. occur in source waters, and subjectmaceuticals and personal-care The report, Removal of EDCs ed the waters to various treatment products (PPCPs) are showing up and Pharmaceuticals in Drinking methods. They also analyzed raw in streams and other water sources Water and Reuse Treatment Proand treated drinking water from 20 all over the world. So the potential cesses, evaluates physical, chemical, full-scale drinking-water utilities for these contaminants to and 6 water-reuse plants. reach drinking-water taps “No single process is high, especially because was able to remove abtreatment plants weren’t solutely every chemical,” designed to remove them. says Shane Snyder, an enHowever, a recent onevironmental toxicologist of-a-kind report on the at the Southern Nevada effectiveness of current Water Authority and lead drinking-water treatment author of the study. “The technologies—spanning findings demonstrate, conventional to advanced though, that certain proprocesses—offers some cesses can greatly rereassurance to utility ofduce the concentration of ficials grappling with this many classes of contamiissue. nants, while others have “The findings are enlittle impact on removal.” couraging because they For example, convenUV disinfection kills microbial pathogens such as Cryptosporid ium, and, when combined with hydrogen peroxide, it also reshow that supply waters tional coagulation, flocmoves endocrine disrupters. aren’t as contaminated culation, and filtration as we thought, and when removed few of the target these compounds are there, many and biological treatment methcompounds when used at full scale. are removed by our existing treatods at both bench and pilot scales Magnetic ion exchange also had litment processes,” says Djanette to determine removal potential at tle effect. Chlorine disinfection proKhiari, a project manager with environmentally relevant concencesses, on the other hand, removed the Awwa Research Foundation trations of less than 100 nanograms roughly half of the compounds. Cl ark Count y Water Recl amation District
Removing emerging contaminants
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Ozone, another disinfectant, proved extremely effective, removing most of the compounds even at relatively low ozone doses. Ultraviolet (UV) disinfection at typical drinking-water dosages was largely ineffective. However, when UV was combined with hydrogen peroxide for advanced oxidation, it offered the same removal rates as ozone. Similarly, granular activated carbon provided good removal as long as it was replaced or regenerated regularly. Reverse-osmosis membranes and nanofiltration membranes removed all of the target analytes, with reporting limits of 1–10 ng/L, whereas ultrafiltration and microfiltration membranes did not. Currently, only a handful of drinking-water utilities use membrane and advanced oxidation treatment processes. For those considering upgrades, the report “gives them a better understanding of what chemicals they can expect to remove with these processes,” Snyder says. Although several studies have
investigated the fate of trace EDCs and PPCPs through water treatment processes, “this is the first really comprehensive study,” says Jörg Drewes, an environmental engineer at the Colorado School of Mines. It provides drinking-water utilities with a great foundation and reassurance about the effectiveness of certain treatment processes, he says. Mic Stewart, water-quality manager at the Metropolitan Water District of Southern California, agrees. His utility is putting in ozone treatment to control disinfection byproducts. “It’s nice to know that an incidental benefit of that is control of these other compounds,” he says. What’s still missing, Snyder acknowledges, is information about just how important these compounds are to human health. He notes that the study finds the insect repellent N,N-diethyl-m-toluamide (DEET) in 90% of treated water samples. Several pharmaceuticals, including the tranquilizer meprobamate, the antiepileptic
Environmental Magna Carta under siege Environmental assessment in the U.S. was enshrined in law for the first time when President Richard Nixon signed the National Environmental Policy Act (NEPA) on January 1, 1970. Since then, however, the U.S. has slowly cast aside its role as a leader in the field of environmental assessments, as successive administrations have chipped away at the scope of NEPA, experts say. The cuts have reached a crescendo with President George W. Bush’s administration, and proponents of these assessments worry that pressure to develop natural resources with little oversight of the consequences will lead to an unsustainable future for the U.S. NEPA was born shortly after the news coverage in 1969 of the Santa Barbara, Calif., oil spill and Ohio’s Cuyahoga River on fire. The two
events captured the public’s attention and inspired Congress to create tough federal laws, says Bob Dreher, an attorney with Defenders of Wildlife, an environmental group. The idea behind NEPA, also known as the Magna Carta of U.S. environmental policy, is simple: federal agencies should evaluate and disclose the environmental impacts of major projects before they are launched. Steps to whittle away NEPA’s protections have been taken by Congress as well as by federal agencies that have issued rules, says Nick Yost, who served from 1977 to 1981 as general counsel at the White House Council on Environmental Quality (CEQ), which administers NEPA. Yost was also lead author of the NEPA regulations. For example, the U.S. De-
phenytoin, the anti-inflammatory ibuprofen, and the X-ray contrast medium iopromide, occurred in more than 65% of the treated samples, although rarely at concentrations greater than 10 ng/L. Atrazine, a widely used herbicide and known EDC, occurred at the highest concentrations of any contaminant tested (up to 430 ng/L), but still far below the U.S. EPA’s maximum contaminant level of 3 micrograms per liter. Hormones, which garner the greatest amount of concern for public health, occurred infrequently or not at all, Snyder notes. “Until we have toxicologically based health limits, utilities have no real treatment goal,” Snyder notes. “So until we chase down what it all means to public health, we’re just running after analytical detection limits.” AwwaRF released the report to its members early last fall and made it publicly available in November through the American Water Works Association. —KRIS CHRISTEN
partment of Homeland Security recently invoked Section 102 of the Real ID Act of 2005 to waive NEPA regulations for construction of the U.S.–Mexico border fence. The 10–15-foot-high metal wall will run through sensitive habitats such as the San Pedro Riparian National Conservation Area in Arizona, plugging up seasonal streams and wildlife corridors, Dreher explains. Defenders of Wildlife and the Sierra Club oppose waiving NEPA and other environmental laws to build the border fence and have filed a lawsuit in U.S. district court challenging it as unconstitutional. From 2003 to 2007, several other laws have been passed that allow agencies to waive NEPA regulations, expand categorical exclusions, or eliminate the consideration of alternatives. These include the 2003 Healthy Forests Restoration Act and the Energy Policy Act of 2005. By exempting some types of tree cut-
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tailed environmental impact statement (EIS), which includes a list of alternative approaches, such as a new project location or construction changes. NEPA also requires agencies to involve the public from the beginning of the process. “NEPA is revolutionary because it opened the door for the public into agencies in real time, and Mat t Cl ark /Defenders of Wildlife
ting and oil and gas development from NEPA review, these laws could boost growth of invasive species and erosion, among other environmental effects. In addition, former Rep. Richard Pombo (R-CA) led a very public attack on NEPA that was sidetracked once Pombo lost his re-election campaign in 2006, Yost adds.
With the help of Congress, the Bush Administration aims to waive all environmental laws, including NEPA, to construct this U.S.–Mexico border wall in the heart of sensitive desert habitats.
Federal actions such as these have dangerous long-term consequences, because as resources become scarcer, NEPA becomes more and more essential, says Oliver Houck, a professor of environmental law at Tulane University. “The fact is, the attack on NEPA has come, chronically, from a relatively small group of commodity users— timber companies, highway builders—who simply oppose having the public and environmentalists get in the way of their plans and programs,” Houck maintains. For major federal projects such as dams, highways, and oil and gas wells, NEPA requires a brief assessment of environmental impacts. If a project’s impacts are significant, agencies must produce a more de-
that’s why more than 100 countries around the world adopted the process,” says Bob Smythe, a CEQ administrator during the administration of President Gerald Ford. Improved federal decision making under NEPA led the U.S. Department of Energy (DOE) to cancel new reactors that would produce tritium. The EIS allowed DOE to evaluate alternative technologies, such as particle acceleration and the use of existing commercial reactors, leading the department to avoid building enormously expensive new tritium reactors at its Savannah River Site in Aiken, S.C., in the early 1990s, Dreher says. NEPA-driven improvements in a land management plan for the Los Alamos National Labo-
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ratory helped to prevent the release of radiation when the nuclear lab was swept by wildfire in May 2000, he adds. But NEPA requirements can consume inordinate amounts of time and money for certain industries and sometimes delay beneficial projects, says John Martin, a lawyer at Patton Boggs, a law firm representing industry clients. An EIS takes at least 3.5 years to complete and can run up to several thousand pages. However, NEPA regulations suggest a 150-page limit for an EIS, which normally consumes only 0.5–1.5% of project costs, Smythe says. “The current Bush Administration has really gone after NEPA in an effort to avoid the inconvenient and time-consuming responsibility for consulting with the public before they do things,” charges Smythe. Further legislative assaults on NEPA aren’t possible in today’s Democrat-controlled Congress, according to a spokesperson for Rep. Raúl Grijalva (D-AZ). This leaves the White House to focus on intensifying the use of categorical exclusions, which exempt broad categories of action from NEPA, such as the August 26 Bureau of Land Management announcement that grazing permits and some oil and gas activities are excluded from NEPA. Plans are afoot in Congress to reverse the weakening of NEPA and prevent it from being undermined further, Grijalva’s spokesperson says. But close observers of NEPA remain concerned that the law is vulnerable to thoughtless efforts in Congress to streamline it. When drafting the law in 1969, Congress urged the government to act in a way that preserves natural resources. “Unfortunately, the reasons why Congress originally adopted NEPA have been forgotten, so that most members of the public, and even most policy makers, fail to appreciate what is at stake when restrictions are proposed,” Dreher says. —JANET PELLEY
