Research▼Watch Methane linked to local air pollution Aggressive efforts to improve urban air quality could be undermined by rising levels of methane, a compound more closely linked to global warming than air pollution. Using a global model of tropospheric chemistry, researchers at Harvard University, Argonne National Laboratory, and the U.S. EPA determined that higher methane levels could increase ozone background levels worldwide, lead to a greater frequency of days with high ozone levels in the summer, and produce a longer “season” of ozone pollution days. Anthropogenic methane comes from many sources, including leaking pipelines and cattle herds. Because it has a lifetime of eight to nine years, effective methane reductions would require worldwide cooperation. Indeed, the researchers warn that efforts in Europe and North America to improve local air quality could be undermined by rising methane emissions in developing nations. The study used the GOES-CHEM model, which follows ozone, NOx, carbon monoxide (CO), and volatile organic compound (VOC) chemistry, to predict changes in the troposphere. The researchers simulated daily afternoon ozone levels during the months June through August, which typically have the most polluted days. It is already known that methane is a major source of worldwide tropospheric ozone background concentrations, and this study supports that finding. However, the surprise is that a 50% reduction in anthropogenic methane in their scenario is as effective as a 50% drop in anthropogenic NOx concentrations at lowering summer afternoon ozone levels over the United States. CO and VOCs in the presence of NOx are known to generate ozone in urban settings and have historically been the targets of air quality regulations.
Moreover, by taking a threshold value of 70 parts per billion by volume (ppbv) ozone as a pollution event, the researchers found that reducing methane by 50% decreased the number of high ozone days by 45%. By way of comparison, the ozone standard in many European countries is 55–65 ppbv versus 80 ppbv (8-hour average) in the United States. Finally, using a relatively pessimistic scenario for increasing methane, the researchers find that by 2030, the high ozone pollution season in the United States could begin as early as April. (Geophys. Res. Lett. 2002, 29, 10.1029/2002GL015601)
Characterizing aluminum flocs in polluted streams When aluminum-rich acid mine drainage mixes with near-neutral surface waters, fluffy aluminum oxyhy-
Figure not available for use on the Web.
that the flocs are formed from aggregation of the more toxic aqueous polyoxocation, AlO4Al12(OH)24 (H2O)127+ (Al13). The finding is important because Al13 is phytotoxic and is likely to be responsible for the declining fish populations in rivers polluted by acid mine drainage. The compound also has a high affinity for heavy-metal cations, such as Pb2+, Cu2+, and Zn2+, and is therefore likely to transport metals over long distances. Gerhard Furrer of the Institute of Terrestrial Ecology in Zürich, William Casey of the University of California– Davis, and colleagues examined flocs from nine streams polluted from acid mine drainage in Germany and California. Using 27Al magic-angle spinning NMR spectroscopy, they observed the presence of distinct Al(O)4 centers in the flocs. To confirm that the source of Al(O)4 is Al13, they performed experiments with solutions of GaO4Al12(OH)24(H2O)127+ (GaAl12), in which a Ga(O)4 is substituted for Al(O)4. As expected, they saw no signal for Al(O)4 when GaAl12 was aggregated, whereas they did see a signal for Al(O)4 when Al13 was aggregated. (Science 2002, 297, 2245–2247)
Global warming may harm agricultural crop quality
droxide flocs precipitate and move downstream as suspended solids, transporting adsorbed pollutants. Scientists previously thought that such flocs formed by aggregation of monomeric Al(OH)4– complexes into a Al6(OH)12(H2O)126+ multimer, even though such a multimer has never been found in nature. Now, researchers are challenging that belief with 27Al nuclear magnetic resonance (NMR) data, which suggest instead
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Increasing levels of carbon dioxide (CO2) in the environment may increase agricultural production at the expense of crop quality, according to a new analysis. Leanne Jablonski and her colleagues at Ohio State University and Indiana University−Purdue University say that their analysis represents the first comprehensive and statistically robust summary of plant reproduction in environments with enriched CO2. Although the studies show that increased CO2 concentrations markedly enhance fruit, flower, and seed production in domesticated crops, elevated CO2 also appears to
decrease the concentration of nitrogen in the seeds of both domesticated and wild plant species. On average, the nitrogen concentration dropped by 14% in the seeds of 79 species for which data are available on growth changes in environments with enhanced CO2. While both soybeans and rice were exceptions to this general trend, the effect was particularly pronounced on wheat seeds, which lost approximately 20% of their nitrogen concentrations. This means that people and animals would need to eat more of the crops with the reduced nitrogen content to get the same amount of nutrition. The researchers conclude that the trade-offs between quantity and quality need to be considered when the effects of rising CO2 levels on agriculture are calculated. The ecological consequences of reduced nitrogen concentrations in seeds could be extensive, they claim. Because the populations of pollinators, as well as creatures whose diets are dependent upon consuming fruit and insects, could be significantly altered, ecosystem functioning ultimately could be impacted. (New Phytologist 2002, 156, 9−26)
To obtain high fluoroquinolone recoveries, the researchers used two separate extraction procedures, accelerated solvent extraction and solid-phase extraction. When these sample preparation procedures were coupled with a known liquid chromatography fluorescence detection method, they report a limit of quantification of 0.45 and 0.18 milligrams per kilogram (mg/kg) of dry matter for sewage sludge and sludge-treated soils, respectively. To test the new method, the researchers analyzed both anaerobically treated and untreated sewage sludge from wastewater treatment plants near Zürich. Concentrations of ciprofloxacin and norfloxacin ranged from 1.40 to 2.42 mg/kg of dry matter. The researchers are confident that the new method will transfer to other similar antibiotics and environmental matrixes with little modification. (Anal. Chem. 2002, 74, 5455–5462)
Altered landscapes contribute to amphibian decline Forest fragmentation is likely to make it difficult for juvenile amphibians to move to new habitats, according to a
as more trees are cut and land use intensifies. To determine whether amphibians initially move in the direction of a particular habitat when they leave a breeding pond, the researchers added larvae of three amphibian species— spotted salamanders, small-mouthed salamanders, and American toads— to experimental pools situated on the edge between a forest and an open field. The experiments were performed in the midwestern United States, where much of the land around amphibian breeding sites is agricultural cropland or pasture. A circular drift fence surrounded the experimental pools, with pitfall traps and two enclosures that extended into forest and old-field habitats. Each morning the researchers collected the amphibians in the traps and documented whether they were found headed toward the forest or the open field, and how far they had traveled. The spotted salamander and American toad juveniles significantly avoided the open field habitats when leaving the pools, but the findings for the small-mouthed salamander were inconclusive. In addition, salamanders trapped in open fields showed signs of greater dehydration, which suggests
Antibacterial agents in sludge quantified Researchers investigating the fate and transport of pharmaceuticals in aquatic environments have previously reported surprisingly low levels of antibiotics in rivers and streams, despite their widespread usage. Because most antibiotics are hydrophobic, many researchers have speculated that the drugs accumulate in sewage sludge and sludge-treated agricultural soils, but until now analytical methods were not available for confirmation. Alfredo C. Adler and colleagues at the Swiss Federal Institute for Environmental Science and Technology (EAWAG) and the Swiss Federal Institute of Technology–Zürich have developed a method to quantify the two most prescribed human antibiotics in Switzerland, ciprofloxacin and norfloxacin, in sewage sludge and sludge-treated soil. They report that fluoroquinolone antibacterial agents persist in sewage sludge and are likely to accumulate in soil when sludge is applied to land as fertilizer.
Figure not available for use on the Web.
new study reported by Betsie Rothermel and Raymond Semlitsch of the University of Missouri–Columbia. Because such movement is crucial to maintaining gene flow and survivability of declining populations, the findings suggest that amphibian populations will continue to decline
that mortality is higher in fields than in forests. On the basis of these results, the researchers conclude that habitat fragmentation is likely to reduce the dispersal rates between populations of the three amphibian species and contribute to their decline. (Conserv. Biol. 2002, 16, 1324–1332)
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