WATCH RESEARCH
BIODEGRADATION Surfactant additions Organic soil contaminants often are insoluble in the aqueous phase and readily adsorb to soil particles. Thus these contaminants are relatively inaccessible to soil microbes, inhibiting biodégradation. Introducing surfactants has been proposed as a way to increase biodégradation kinetics. F. Volkering and colleagues examined the effect of four surfactants, Triton X-100, Tergitol NPX, Brij 35, and Igepal CA-720, on the bioavailability and biodegradation of naphthalene and phenanthrene. Results indicated that the surfactants increased apparent solubilities and increased maximal rates of dissolution of crystalline naphthalene and phenanthrene. Biodegradation rates for both compounds in the dissolution-limited growth phases also were increased by surfactant addition. However, substrate collected in the micellar phase was not readily available for biodégradation. Because of this nonavailability, the authors contend that using surfactants for the bioremediation of contaminated soils requires careful study before applications are developed. (Appl. Environ. Microbiol. 1995, 67(5), 1699-1705)
Auto emissions increase with poor maintenance More than one million vehicles' exhaust emissions were analyzed in 22 cities around the world by Y. Zhang and co-workers, using remote sensing technology based on infrared spectroscopy. The researchers determined CO and hydrocarbon emissions from passing vehicles. Results were compared among cities and among cars of varying ages within the cities; hydrocarbon and CO emissions correlated with each other. In all cities, high emissions from relatively few vehicles dominated the city-wide average. Poor vehicle maintenance was the primary cause of the high emissions. Emissions increased with a vehicle's age, but the largest increases occurred from poorly maintained vehicles. (Environ. Sci. Technol., this issue, 2286-94)
alization at concentrations above the CMC. The authors conclude that surfactant sorption to sediment resulted in reduced toxicity to microorganisms and that surfactants might not be an effective method of removing contaminants from soilsediment systems. (Environ. Toxicol. Chem. 1995, 14(6), 953-59)
Surfactant inhibitors The sorption of polynuclear aromatic hydrocarbons (PAHs) to soils or sediments generally decreases biodégradation. Introducing nonionic surfactants at concentrations exceeding their critical micelle concentration (CMC) can increase the solubility of sorbed PAHs and enhance their bioavailabilty. However, some observations indicate that the presence of nonionic surfactants at concentrations above the CMC can inhibit PAH biodégradation. H. J. Tsomides and colleagues examined the effects of nonionic surfactants on phenanthrene biodégradation in a sediment-water slurry. Of seven surfactants tested, only Triton X-100 did not inhibit phenanthrene miner-
BIOREMEDIATION Fungal degradation Several recent studies describe contaminant degradation by the white rot fungus Phanerochaete chrysosporium, which invokes an extracellular ligninolytic system induced by limited nitrogen or carbon concentrations. Most studies used elevated oxygen concentrations or pure oxygen to offset limited oxygen availability in liquid cultures. N. Rothschild, Y. Hadar, and C. Dosoretz investigated inducement of the ligninolytic system in air. The fungus was immobilized on polyurethane foam cubes in a nonimmersed liquid culture system. Different carbon/ni-
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trogen ratios exposed to pure oxygen or air were evaluated. The authors measured lignin peroxidase, manganese peroxidase, and glyoxal oxidase activity. Results indicated that, with low carbon/nitrogen ratios, this culture system allowed substantial expression of all three ligninolytic enzymes in air. Because this study more closely mirrored natural growth conditions of the fungus, it may aid in the development of a more effective bioremediation system. (Appl. Environ. Microbiol. 1995, 61(5), 1833-38)
CLIMATE CHANGE Tree rings and climate The width and density of tree rings might provide information about past climate changes, if the type of variations recorded by each measurement are understood. G. C. Jacoby and R. D. d'Arrigo studied tree rings in central and northern Alaskan forests from data collected over the past three centuries. Analysis of the tree ring widths indicated that the warmest interval during the past 300 years occurred in the 1940s. Temperatures cooled throughout the 1950s and into the 1970s, but annual temperatures now are returning to the 1940 levels. The authors evaluated seasonal changes on temperatures by analyzing the density of tree rings. Their results indicate that recent summer temperatures are nearly comparable to maximum temperatures of the 300-year period. They conclude that recent temperature increases, coupled with drier years, may be altering the response of Alaskan and other boreal forests to global climate changes. (Global Biogeochem. Cycles 1995, 9(2), 227-34)
Radionuclides in the ocean An important aspect of global ocean circulation modeling involves the uncertainty in the uptake of fossil fuel C0 2 by the oceans. W. S. Broecker and colleagues developed a method to separate natural radiocarbon from radiocarbon and tritium
