Research▼Watch
For about a decade, researchers have linked sulfuric acid in the air above oceans with the formation of aerosols and cloud condensation nuclei (CCN) —nanometer-sized particles that help create clouds. Now, add iodocarbons as a possible second source of marine aerosols and CCN. Understanding the ocean’s role in generating aerosols and clouds is an important factor in models that predict a host of environmental effects, such as global warming and patterns of drought. Depending on their composition, aerosols can cool or warm the Earth’s surface, impair human health, and affect tropospheric chemistry; clouds add their own cooling effect. Marine sulfuric acid is generated by the oxidation of dimethylsulfide from algae. Colin O’Dowd of the National University of Ireland and colleagues stumbled upon the iodocarbon source after other results showed that the production of marine particles in coastal areas was independent of sulfuric acid concentration. Their focus turned to iodocarbons, which are produced by macroalgae in coastal waters, as the potential missing contributor. Using a smog chamber, the scientists found that a mixture of diiodomethane (CH2I2), ozone, and ultraviolet light led to the rapid formation of nuclei, even at CH2I2 concentrations as low as 0.015 parts-per-billion. Computer modeling predicts that combining iodocarbons with sulfuric acid increases the number and lifetime of condensation sites for CCN. (Nature 2002, 417, 632–636)
Benefits of organic farming Soils on organic farms are healthier, according to the most comprehensive study yet comparing farming practices. The 21-year study found that although crop yields are 20% lower, organic farming uses less fertilizer 314 A
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and energy than conventional methods and supports greater biodiversity. Paul Mäder of Switzerland’s Research Institute of Organic Agriculture and his colleagues compared the yield and ecological ramifications of growing potato, winter wheat, and grass/clover crops using four different farming techniques. The two conventional methods they evaluated relied upon synthetic pesticides and either only mineral fertilizers or a combination of mineral and manure fertilizers. The organic techniques used manure fertilizers and naturally derived pesticides. The researchers found that the organic farming methods used 26–53%
plants take up nutrients, than conventionally grown plants, and the organic soils contained 1.3–3.2 times more earthworms. Because healthy ecosystems are characterized by higher levels of biodiversity, the researchers conclude that the higher level of bioactivity and biodiversity associated with organic farming methods “is likely to provide a positive contribution toward the development of higher food web levels including birds and larger animals”. (Science 2002, 296, 1694–1697)
Utah salt flats release reactive halogens DIGITAL STOCK
New source of cloud-forming nuclei
Organic farms use less fertilizers and energy, and support greater biodiversity than conventional farms, according to a 21-year study in Switzerland.
less energy per unit of land and that the inputs of nitrogen, phosphorus, and potassium in the organic systems were 34–51% lower. They credit the higher microbial diversity observed in the soil of the organic plots for their more efficient utilization of soil resources. The highest level of microbial diversity was associated with the biodynamic organic farming technique, a less-popular approach which its adherents say uses “special plant, animal, and mineral preparations [to] stimulate and balance vital processes in soil and plants.” The soils in the organic plots were 10–60% more stable, the scientists found, which implies that they would be less prone to erosion. The organic plants had 40% more roots colonized by mycorrhizae fungi, which help
ENVIRONMENTAL SCIENCE & TECHNOLOGY / AUGUST 1, 2002
Salt flats surrounding Great Salt Lake, Utah, are a significant source of chlorine and bromine radicals, report scientists from the University of California–Los Angeles and Pacific Northwest National Laboratory. The reactive halogens are mobilized into the atmosphere, where they can destroy tropospheric ozone and convert elemental gaseous mercury into a more biologically available form. Using optical absorption spectroscopy, Jochen Stutz and colleagues observed chlorine oxide levels of up to 15 pmol/mol of air and bromine oxide levels of up to 6 pmol/mol of air in the lower troposphere near Great Salt Lake. The findings provide the first direct evidence of the presence of chlorine radicals in the lower troposphere and confirm a previous discovery of the presence of bromine radicals. The researchers believe that the large surface areas of salt deposits are acidified by dry and wet deposition of pollutants from nearby Salt Lake City, which makes them ideal surfaces on which heterogeneous reactions can take place. Such reactions have been shown to release reactive chlorine and bromine in laboratory studies. Although it is unclear whether all salt lakes and saline soils release halogen radicals, the scientists note that as arid and semiarid regions become saltier, they may become more important © 2002 American Chemical Society
sources of reactive halogens. Because these reactive halogens are strong oxidants, if the phenomenon turns out to be widespread, it could have important implications for the atmospheric chemistry of mercury and tropospheric oxidants. (Geophys. Res. Lett. 2002, 29, DOI 10.1029/2002GL014812)
Picogram PAH analysis of aerosol particles Using a home-built, two-step laser mass spectrometry (L2MS) system that is optimized for filter samples, Renato Zenobi and colleagues at the Swiss Federal Institute of Technology (ETH) in Zürich, have developed a method to quantify picogram levels of polycyclic aromatic hydrocarbons (PAHs) adsorbed on aerosol particles. L2MS has previously been used to analyze PAHs in air, but until now, only qualitative measurements of the relative abundance of different PAHs could be made using the technique. PAHs are emitted primarily by anthropogenic combustion, from sources like diesel and gasoline vehicles, biomass fires, tobacco smoke, home-heating oil, gas, and wood. Atmospheric concentrations are typically in the nanogram-per-cubicmeter range. Because PAHs are carcinogenic and mutagenic, they are often analyzed in air quality measurements. Conventional analysis methods, however, such as gas chromatography/mass spectrometry (GC/ MS), require intense sample collection and processing, making it difficult to obtain dynamic information about PAH emissions. L2MS offers 15-minute time resolution and almost no sample preparation. The two steps in L2MS refer to laser desorption and laser ionization. In the first step, a CO2 laser hits the filter sample and the aerosol particles are desorbed. A second laser then ionizes the particles for analysis in a time-of-flight mass spectrometer. To obtain quantitative results, the ETH researchers used di-isopropylnaphthalene (DIPN) as an internal standard, because its mass of 212 Da does not overlap with any PAHs. In addition, DIPN has a low vapor pressure, so it does not evaporate from the sample during MS analysis, and it is ionizable at the wavelength chosen for the analysis (in this case, 266 nm). Using the new L2MS method, the researchers obtained linear concen-
trations over two orders of magnitude for five PAHs—phenanthrene, pyrene, chrysene, benzo[e]pyrene, benzo[ghi]perylene—with detection limits for a single PAH in the 50–300-pg range. The results for benzo[e]pyrene were compared with GC/MS using model aerosols consisting of benzo[e]pyrene adsorbed on inorganic salt aerosol particles. In general, the results using GC/MS were 25% lower than those using L2MS. The researchers attribute the discrepancy to losses during sample preparation for the GC/MS measurements. (Anal. Chem. 2002, 74, 3492–3497)
Snowmobiles stress wildlife Hormone levels in wolves and elk increase in response to stress caused by snowmobile activity, according to a study performed in three U.S. National Parks. Although the Department of Interior’s proposal to ban snowmobiles in the parks has been disputed, the findings indicate that animals are indeed being affected by the recreational vehicles. Scott Creel and researchers at Montana State University and Michigan Technological University studied radiocollared wolf and elk populations in Yellowstone, Voyageurs, and Isle Royale National Parks. The researchers analyzed fecal samples collected over two winter seasons in order to monitor the animal’s glucocorticoid concentrations. Glucocorticoid levels rise when an animal feels stressed. The levels in each species increased with the number of snowmobiles in the parks. The relatively stable populations of wolves and elk, however, suggest that they are able to compensate for the physiological effects during the winter months. Although the results may not demonstrate an immediate threat, studies on captive animals have shown that prolonged elevation of glucocorticoid levels reduces survival and reproduction. (Conserv. Bio. 2002, 16, 809–814)
Less concern over antiseizure medications Carbamazepine, an antiepileptic drug for controlling seizures, has been detected in municipal sewage treatment effluents, but there have been few reports regarding its persistence in the environment and toxicity to aquatic
organisms. Researchers from Universita degli Studi di Napoli, in Italy, now have evidence that carbamazepine can break down rapidly in the presence of sunlight and can be removed from wastewaters using ozonation. In addition, they report that carbamazepine does not accumulate in algae or inhibit their growth, suggesting that it is not toxic to aquatic organisms at the levels found in environment. To assess the drug’s persistence in the environment, Roberto Andreozzi and colleagues conducted photodegradation and oxidation experiments with carbamazepine dissolved in both distilled water and water samples from the Liri River in Italy, at concentrations on the order of 10–6 mol/dm3, the level reported in German sewage effluent. The researchers exposed the solutions to sunlight during spring in Naples, Italy, and found that the concentration of carbamazepine decreased with increasing irradiation time. The presence of nitrates was found to enhance the rate of photolysis, whereas the presence of humic acids slowed down the rate. The results suggest that carbamazepine can be photochemically degraded, but the rate at which it is degraded is largely dependent on what other chemicals are in the water. The Italian researchers also subjected aqueous solutions of carbamazepine to ozone treatment, analogous to that used to treat drinking water, to determine whether the compound is capable of being oxidatively degraded. Complete degradation of carbamazepine was found in all cases, suggesting that the drug can be easily removed from water by ozonation. To investigate the toxicity of carbamazepine to aquatic organisms, the researchers exposed two species of algae, Ankistrodesmus braunii and Selenastrum capricornutum, to varying levels of the drug. After 96 hours, no inhibition of growth was found for either species, independent of algae and drug concentrations. In 60-day experiments, no differences were seen between the control groups and those treated with carbamazepine. The findings indicate that carbamazepine is not toxic toward these two particular algal species; however, further experiments are needed to determine whether this holds true for other aquatic organisms as well. (Water Res. 2002, 36, 2869–2877)
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