Research▼Watch Impact of land-use changes on climate
and in another, the hydrogen concentration was raised to 2.3 ppmv, which is about 4 times the current value. Land-use changes over the past 50 The researchers estimate that if all years are responsible for about 40% current gasoline and oil combustion of the earth’s surface warming trend, technologies were replaced by hydroaccording to research published in gen fuel cells, hydrogen emissions the May 29 issue of Nature. The rewould increase between a factor of 4 sults suggest that urbanization and and 8. agriculture have contributed almost The modeling results predict that as much as greenhouse gases to the a 4-fold increase in hydrogen conrise in global temperatures. centration will lead to an increase Two methods are commonly used in stratospheric water vapor levels, to estimate the effects of urbanization which would cause the lower stratosConsequences of a hydrogen on surface temperature trends—one phere to cool and would enhance the economy based on population data and the chemistry that destroys ozone. The other on satellite measurements of A hydrogen fuel-cell economy could result would be an ozone hole that night light. The two approaches, howhave unintended environmental imis deeper, larger in area, and longer ever, have yielded significantly differpacts, including delaying the recovery lasting in the spring. Increased hyent estimates (0.06 and 0.15 °C per of the stratospheric ozone layer, acdrogen emissions could therefore century, respectively). Using a new cording to modeling results published jeopardize efforts to recover the approach, meteorologists Eugenia in the June 13 issue of Science. The ozone layer through regulation of Kalnay and Ming Cai of the University new predictions point to the need for chlorofluorocarbons. of Maryland–College Park estimated a better understanding of emissions The model also predicts that a rise that land-use changes have caused from hydrogen-based technologies in hydrogen emissions could lead to the mean surface temperature to rise and possible hydrogen sinks. changes in tropospheric chemistry, by 0.27 °C per century. such as altering levels The new estimate shows of hydroxyl radicals, 0.0 –0.5 a larger effect, presummethane, and carbon 90° –1.0 ably because it covers monoxide. Because hy–1.5 60° –2.0 all land-use changes, drogen is a microbial –2.5 –3.0 not just the effects of nutrient, increased emis30° –3.5 –4.0 urbanization. sions could also have –4.5 0° In the new approach, unintended effects on –5.0 –5.5 the researchers commicroorganisms. Such –30° –6.0 Hotspots NonTotal –6.5 pared trends in observed emissions, however, hotspots –7.0 –60° –7.5 surface temperatures could be negligible if soil –8.0 taken at nearly 2000 turns out to be a domi–90° Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan weather stations across nant hydrogen sink. FurMonth the United States since ther research is needed the 1960s with a 50-year to determine how an inLatitudinal and seasonal distribution of ozone depletion (in %), assuming a reanalysis of satellite and 4-fold increase in anthropogenic hydrogen emissions. Adapted with permis- crease in hydrogen emisweather balloon data sions would impact the sion. Copyright 2003 American Association for the Advancement of Science. conducted by the Nationuptake of hydrogen by al Centers for Environmental PredicY. L. Yung and colleagues at the soil. (Science 2003, 300, 1740–1742) tion (NCEP) and the National Center California Institute of Technology for Atmospheric Research (NCAR). used an atmospheric chemistry and Atmospheric mercury trends Because the NCEP–NCAR data are not transport model called Caltech/JPL sensitive to surface observations, the 2-D to estimate the effects of increased Atmospheric mercury concentrations difference between the surface temhydrogen levels on temperatures and peaked in the 1980s, then declined perature trends and those derived water and ozone concentrations in until 1996, and have been relatively from the NCEP–NCAR reanalysis rethe stratosphere. In one case, the hyconstant ever since, according to reflects the effects of urbanization as drogen level was set equal to the cursearch published on May 22 in Geowell as other land-use changes. rent global surface concentration, physical Research Letters. The findings Latitude
The results suggest that converting undeveloped land into agricultural areas is just as important as urbanization and needs to be factored in when estimating the impact of land-use changes on climate. The researchers plan to expand their work beyond the continental United States to determine if their estimate of surface warming from land-use changes holds true on a global scale. (Nature 2003, 423, 528–531)
© 2003 American Chemical Society
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Airborne metals exacerbate asthma Heavy metals attached to fine airborne particles are likely to be important aggravators of allergic asthma, according to research published in the May 27 online version of Environmental Health Perspectives. The new study, in which mice are exposed to fine particulate matter (PM) from a heavily industrialized city in Germany, shows the importance of PM’s chemical composition in exacerbating respiratory problems. Although levels of common air pollutants, such as PM10 (particles less than 10 micrometers (µm) in diame-
Bioavailability of soil-bound atrazine
ter), ozone, and sulfur dioxide, have declined considerably in developed countries in the last 20 years, allergic asthma is considered an epidemic that afflicts 15 million people in the United States alone. The number of asthma cases, especially in children under five, has continued to rise since 1980, possibly indicating that PM’s physical and chemical properties have changed over time and are critical factors in the enhancement of preexisting allergic respiratory diseases. PHOTODISC
are inconsistent with inventories of anthropogenic mercury emissions and suggest that the contributions of mercury from both natural and anthropogenic sources need to be reevaluated. A team of international scientists, led by Franz Slemr of the Max-Planck Institut für Chemie in Mainz, Germany, reconstructed global atmospheric mercury trends using direct measurements taken during the period 1977–2001. The long-term measurements were obtained at six sites in the Northern Hemisphere, two sites in the Southern Hemisphere, and on eight cruises in the Atlantic Ocean. Total gaseous mercury concentrations in the Southern Hemisphere were approximately one-third lower than those in the Northern Hemisphere, but the same trends were observed in both hemispheres. Higher levels in the Northern Hemisphere are consistent with mercury sources being primarily in the north. Mercury trends derived from sediments, peat bogs, and ice cores show similar temporal profiles. Atmospheric mercury levels decreased during the period 1990–1996 by a larger amount than predicted in published inventories of natural and anthropogenic emissions. The researchers suggest that the discrepancy could be due to large temporal variations in natural emissions or a substantially underestimated ratio of anthropogenic to natural emissions. Because gaseous mercury concentrations have been constant since 1996, they believe that the latter explanation is more likely. (Geophys. Res. Lett. 2003, 30, doi:10.1029/2003GL016954)
Metals in polluted air may be the culprit behind increasing cases of asthma.
Stephen H. Gavett and colleagues at the U.S. EPA’s National Health and Environmental Effects Research Laboratory in Research Triangle Park, N.C., and the Research Center for Environment and Health (GSF) in Neuherberg, Germany, followed up a previous epidemiological study showing that children living in Hettstedt, a city in eastern Germany heavily impacted by industrial emissions, have higher rates of bronchitis and allergic diseases than children living in the less polluted neighboring city of Zerbst. In the new study, the researchers exposed mice to PM2.5 (particles less than 2.5 µm in diameter) collected in Hettstedt as well as to PM2.5 from Zerbst. Consistent with the human studies, mice exposed to the Hettstedt particles displayed stronger symptoms of pulmonary inflammation and developed stronger allergic responses than mice exposed to equal amounts of PM2.5 from Zerbst. Chemical analysis showed that PM2.5 from Hettstedt had several-fold higher concentrations of lead, copper, cadmium, tin, strontium, arsenic, and zinc than particles from Zerbst. This new link between human epidemiological data and animal data suggests that metals in soot are the primary cause of enhanced allergic asthma. (Environ. Health Perspect. 2003, doi:10.1289/ ehp.6300)
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Atrazine can be bioavailable to microorganisms even when it is sorbed to soil organic matter and clay minerals, according to research published in the June issue of Applied and Environmental Microbiology. The findings have implications for bioremediation of soils contaminated with the most commonly used herbicide in the United States. Most organic contaminants and pesticides that are bound to soil particles have been considered unavailable to microorganisms for biodegradation. To degrade soilsorbed pesticides, bacteria must either desorb the chemicals from the soil or somehow use the sorbed molecules directly. Yucheng Feng and colleagues at Auburn University and Michigan State University evaluated the bioavailability of sorbed atrazine using three different atrazine-degrading bacteria and six different soils. They performed sorption and desorption experiments and fit the data to a desorption, biodegradation, and mineralization (DBM) model, which accounted for sorption/desorption processes and biodegradation of dissolved, but not sorbed, atrazine. In 11 out of 18 cases, the data fit the DBM model, indicating that mineralization was limited to the amount of dissolved atrazine initially present plus any that was desorbed during the experiments. This suggests that sorbed atrazine was not bioavailable to the bacteria in most cases. In five cases, however, the data did not fit the model and indicated enhanced bioavailability, suggesting that in some cases, bacteria can use atrazine as a nitrogen source even when it is sorbed to soil. One explanation is that bacteria access localized regions where the atrazine is bound. For all three bacteria tested, enhanced bioavailability was observed for the soil with the highest organic carbon content. The results indicate that physicochemical properties of soils, such as organic carbon content, influence the bioavailability of sorbed atrazine. In addition, the researchers found evidence that bacterial cell characteristics, such as the way the cells attach to soil particles, also play an important role. (Appl. Environ. Microbiol. 2003, 69, 3288–3298)
