Research▼Watch One of the lesser known consequences of scenarios outlined in the Intergovernmental Panel on Climate Change is that most models predict that tropospheric ozone as well as CO2 levels will rise worldwide in the coming years (Environ. Sci. Technol. 2002, 36, 379A–382A). In a new study, 25 authors from 16 institutions scattered across Europe, the United States, and Japan evaluate six scenarios for ozone over the next 100 years, reporting that five predict near-surface increases of as much as 20 ppb; one calculates a drop of 4 ppb. Because many urban areas in developed countries already face high ozone levels and days with values above air quality standards, even small increases could endanger current efforts to regulate this pollutant. Large increases would threaten air quality over much of the northern hemisphere. Tropospheric ozone in urban areas arises from reactions of NOx, CO, and volatile organic compounds, which are emitted by vehicles and industries. Ozone exacerbates numerous respiratory conditions, such as asthma, and damages crops and ecosystems. All six scenarios in this study also predict a short-term increase in ozone, so that by 2030, average pollutant levels could increase by 2 to 7 ppb. However, the authors acknowledge that the predictions could change significantly if global warming alters the dynamics, temperature, and humidity of the troposphere. (Geophys. Res. Lett. 2003, 30, 10.1029/2002 GL016285)
Pest resistance to Bt cotton Researchers have identified mutations in field populations of a major pest—the pink bollworm—that confer resistance to genetically modified (GM) cotton. The findings may spur the development of DNA-based resistance screening tests that are 1000fold more sensitive than current
Unstable mercury reservoir
bioassays. Such screening tests are needed to assess whether strategies to delay pest resistance, such as the refuge strategy mandated by the U.S. EPA, in which farmers are required to grow refuges of non-GM cotton next to GM cotton fields, are successful. PEGGY GREB, USDA/ARS
Climate change and ozone
Pink bollworms are beginning to show signs of resistance to Bt toxins in genetically modified cotton.
Transgenic crops engineered to produce Bacillus thuringiensis (Bt) toxins are grown on millions of hectares. The economic success of Bt crops is threatened, however, by the evolution of resistant pests. So far, no field outbreaks of pesticide resistance to Bt crops have been observed, although many pests have been found to develop resistance to Bt toxins in the laboratory. Bruce Tabashnik and colleagues at the University of Arizona–Tucson, Clemson University, and the University of Melbourne in Australia have now unravelled the genetic basis of resistance to Bt toxins. In field populations of the pink bollworm (Pectinophora gossypiella) they have identified three different mutations, which all disrupt one gene encoding a cadherin-like protein. The function of cadherins in insect larvae is not well known. Insect cadherins are located in the gut membrane, where their interactions with the Bt toxins result in the death of the larvae. Mutations in this gene reduce both overwintering survival and survival on non-Bt cotton, underlining the importance of EPA’s refuge strategy. (Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 5004–5009)
More than 40% of the mercury that accumulates in snow is transferred back into the atmosphere within 24 hours, according to a new study by researchers at Université du Québec in Canada. The findings suggest that total mercury concentrations in snow should not be considered as a net input of mercury to terrestrial and aquatic systems. Snow is a major reservoir of atmospheric pollutants in boreal and polar regions. Atmospheric mercury, in particular, which is primarily Hg 0, has been shown to be oxidized to Hg(II) by bromine oxide radicals and deposited in snow. Many scientists are concerned about Hg(II) readily accumulating in snow, because when the snow melts, a large pulse of Hg(II), which is the biologically available form of mercury, could end up in lakes and bioaccumulate in fish. In the new study, Janick Lalonde and colleagues help to ease some of those concerns by confirming earlier observations that Hg(II) in snow is relatively short lived. In previous work conducted in a suburban area, where mercury levels are typically higher than snow in pristine locations, the researchers observed the photochemical reduction of Hg(II) in snow and subsequent transfer of Hg 0 to the atmosphere (Environ. Sci. Technol. 2002, 36, 174–178). Now, they have shown that Hg(II) is also quickly reduced in snow in remote areas. In the presence of chloride, however, the researchers observed both the reduction of Hg(II) in snow and the oxidation of Hg 0. The two processes apparently compete with each other, slowing the snow-to-air mercury transfer. This is particularly important in coastal regions where the snowpack contains high concentrations of chloride but is unlikely to have a large effect in areas with minimal marine influences. (J. Geophys. Res. 2003, 108, 10.1029/2001JD001 534)
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Revised estimates of Agent Orange use Agent Orange use in Vietnam between 1961 and 1971 was significantly underestimated, suggests a new data analysis performed by J. M. Stellman of Columbia University and colleagues. According to the reanalysis, which was conducted under contract to the U.S. National Academy of Sciences (NAS), large numbers of American troops, along with 2–5 million Vietnamese people, were likely exposed to the herbicide mixture.
supplies. The herbicides were banned by the United States in 1970 from most domestic uses because of their evident teratogenicity. The Agent Orange Act of 1991 empowered NAS to reconstruct and reevaluate the potential for herbicide exposure in Vietnam. So far, there has been no large epidemiological study of herbicides and the health of the Vietnamese population or war veterans. The authors suggest that the areas sprayed may be of particular interest for follow-up studies. (Nature 2003, 422, 681–687)
Organochlorine pesticides and breast cancer
Figure Not Available for Use on the Web
Compared with a previous NAS study conducted in 1974, which relied on the flight path coordinates of spraying missions, called the HERBS file, the new analysis used a more complete data set that included specific military herbicide targets. The reanalysis suggests that spraying was more extensive and that the amount of dioxin sprayed was almost twice as much as previously estimated. Agent Orange, and others such as Agent Purple, nicknamed by the colored identification bands painted on storage barrels, contained 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) contaminated with varying amounts of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The U.S. military used these herbicides as defoliants to clear the perimeters of military installations and to decrease enemy food
Breast cancer in women is strongly correlated with high levels of two organochlorine pesticides—p,p′-DDE and hexachlorobenzene (HCB)—in blood, according to a new study by researchers in Belgium. Although previous studies have demonstrated that organochlorine pesticides in blood and fat tissue can promote growth of estrogen-related tumors in animals, conflicting results have also been published. The new results add to the growing evidence that breast cancer patients have elevated levels of some persistent pollutants in their blood compared with healthy women. In this study, Charles Charlier and colleagues at Sart Tilman Hospital in Liege, Belgium, examined the blood of 159 women diagnosed with breast cancer and of 250 presumably healthy controls. p,p′-DDE, a metabolite of the pesticide DDT, which was banned in 1972 but is still used in developing countries, appeared in blood samples from 84% of the women with breast cancer, and HCB, which has been used as a pesticide and often appears as a byproduct from pesticide manufacturing, appeared in 18% of the cancer patients. Twenty-four percent of the 250 participants in the healthy control group had no pesticide residues in their blood, whereas only 2.5% of the women with breast cancer were pesticide-free. The average age of all subjects was 54, and demographics were relatively balanced with respect to smoking habits, living environment, and breastfeeding. The researchers are reluctant to establish the pesticides as a direct cause of breast cancer, because even
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though the patients were tested shortly after diagnosis, cancer is known to alter metabolism and body weight, which were not accounted for in this study. The data, they say, warrant further analysis and consideration of exposure routes and dietary intake. (Occup. Environ. Med. 2003, 60, 348–351)
Satellite data reanalysis shows warming trend A new look at satellite data from 1979 to 2001 indicates a tropospheric warming trend of 0.1 °C per decade, in contrast to earlier analyses of the same data, which showed almost no change in tropospheric temperature. Skeptics of global warming have used these previous analyses to argue that the troposphere has not warmed, putting human-induced climate change in question. The new results continue to fuel the climate-change controversy, by suggesting that humans have indeed influenced the earth’s climate over the past two decades. To obtain temperature trends from the raw satellite data, Ben Santer of the Lawrence Livermore National Laboratory and colleagues made a series of adjustments and corrections, such as accounting for heating of the radiation sensor and drifting of the satellites’ orbits. These satellite data uncertainties were not addressed in previous analyses. The results fit well with four computer-model climate simulations developed by researchers at the National Center for Atmospheric Research and the Los Alamos National Laboratory, and they are in good agreement with observed surface warming data, unlike the previously derived satellite-based temperature trends. To further analyze the satellite data, the researchers investigated regional patterns. By using a statistical technique, they looked for underlying fingerprints of climate change. For example, rates of warming tend to vary from north to south, which was evident in both the models and the new satellite data analysis. The findings suggest that inconsistencies between models, satellite tropospheric temperature data, and surface data are likely due to data uncertainties that were not accounted for in the past. (Science 2003, 300, 1280–1284)
