RESEARCH WATCH
AIR Pigeons as biomarkers Vehicle tailpipe emissions contain carcinogens and mutagens, but the long latency period before development of cancer makes it difficult to determine whether exhaust poses a cancer risk for humans. P. Schilderman and colleagues studied whether wild city pigeons could be used as biological indicators of air pollution. Pigeons caught from four areas with different levels of traffic density were analyzed for PAHDNA adducts, DNA damage, and heavy-metal levels. PAH-DNA adduct levels similar in pigeons from 3.11 four circss Heavy-metal levels and DNA damage were ciated with higher traffic densitv The results indicate that wild pigeons may be a useful biological marker of heaw-metal air pollutants and their potential carcinogenicity (Environ Heallh Pprmect 1997 705 322-30)
Carbon pools Understanding the movement of carbon among terrestrial, marine, and atmospheric reservoirs is critical for understanding how humans affect global climate change. C. A. Boyle and L. Lavkulich evaluated changes in the carbon pool caused by human activity in a 828,000-ha area of British Columbia from 1827 to 1990. Major losses of biomass carbon were from soils (43%), logged forests (42%), and wetlands (14%). Old-growth forest, which covered only 19% of the area, still contained 20% of the region's carbon. TllC 3.U.thors estimated that the equivalent of 870 Mt of carbon dioxide released to the atmosphere during the study period The results emphasize the need to protect forests in developed countries which act as huge carbon pools i'ust as rainforests in developing countries should be preserved {Environ Manaee 1997 21 443-55)
Particulate transport of PAHs into the aquatic environment The hydrophobic polycyclic aromatic hydrocarbon, pyrene, enhances water solubility in the presence of humic acid. Masami Fukushima and colleagues found that in the presence of activated carbon (as a model adsorbent), there was a nonlinear relationship between the concentration of humic acid and the water solubility of pyrene. A micelle-like partitioning model, which included readsorption of humic acid-pyrene moieties on the activated carbon, could explain the experimental data, the researchers point out. At pH 6, the water solubility of pyrene was 6 x 10"9 M; in the presence of 100 mg HA L ', this was increased to 5 x 10~7 M. The system was slow to reach equilibrium; measurements were taken after 48 h. The results have implications for the fate and mobility of hydrophobic pollutants in aquatic systems. (Environ. Sci. Techno!., ,his iisue, pp. 2218-22)
BIODEGRADATION Atrazine-degrading enzyme Atrazine is an herbicide that causes significant groundwater and surface water contamination. A strain of rhizobium, PAIR, was isolated from agricultural soil and found to actively degrade atrazine. C. Bouquard and colleagues investigated PATR's activity in atrazine degradation using 30 mg/L liquid cultures of atrazine that were rapidly dechlorinated. Hydroxyatrazine was the only metabolite detected after eight days. No mineralization occurred. The authors reported partial purification and characterization of the enzyme rc~ sponsible for the hydroxylation. It was an atrazine hydrolase consisting of 50-kDa subunits with similarities to atrazine chlorohydrolase AtzA produced by a strain of pseudomonas The authors conclude that PATR and related organisms probably play an important role in biodegradation of atrazine in soils (Arml Environ Microbiol 1997 63 862-66)
How white rot works Soil organopollutants such as methoxychlor are degraded by the white rot fungus (P. chrysosporium) )ven though they lack structural features that would make them susceptible to its peroxidase enzymes. In an effort to understand this action, M. Grifoll and K. E. Hammel investigated the early
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steps in the metabolism of methoxychlor by P. chyrsosporium. Cultures were spiked with methoxychlor and incubated at 39 °C. Results indicated that methoxychlor was mineralized and metabolized to a variety of products. Three major metabolites were mineralized and were likely intermediates in the degradation. The authors could not yet explain the mechanisms involved in methoxychlor removal from contaminated soil, but they predict that they do not involve direct action by fungal peroxidase enzymes. (Appl. Environ. Microbiol. 1997, 63, 1175-77)
Breaking down nylon Nylon generally is regarded as nonbiodegradable, even though its main molecular chain contains the amide bond (CONH), which in natural polymers is easily hydrolyzed by proteolytic enzymes in the environment. T. Deguchi and co-workers report the first evidence of nylon biodegradation by the white rot fungus IZU-154. Nylon-66 membranes were placed on agar media and incubated for 20 days at 30 °C with IZU-154. Results showed significant degradation of nylon-66 by the fungus. Nuclear magnetic resonance analysis suggested thcit n.ylon~66 W3.s degraded oxidatively The authors also report that addition of manganese as MnS0 accelerated nylon biodegradation bv the fungus (Awl Environ Microbiol .197 63 329-31)
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