United States Environmental Protection Agency

About: United States Environmental Protection Agency is a government organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Population & Environmental exposure. The organization has 13873 authors who have published 26902 publications receiving 1191729 citations. The organization is also known as: EPA & Environmental Protection Agency.

Rare species in multivariate analysis for bioassessment: some considerations

Abstract: BRIDGES is a recurring feature of J-NABS intended to provide a forum for the interchange of ideas and information between basic and applied researchers in benthic science. Articles in this series will focus on topical research areas and linkages between basic and applied aspects of research, monitoring policy, and education. Readers with ideas for topics should contact Associate Editors, Nick Aumen and Marty Gurtz.Multivariate analyses are used commonly in bioassessment studies examining the degree of human impact on aquatic ecosystems. However, these analyses may have shortcomings with respect to how well they address the presence or absence of rare species. Researchers may delete rare species explicitly, or ignore them implicitly by the use of small sample sizes. The motivation for exclusion of rare species may be related to sampling or analytical resource limitations. The authors provide an overview of the importance of rare species, the sensitivity of the newer multivariate techniques to rare ...

Density fractionation of forest soils: methodological questions and interpretation of incubation results and turnover time in an ecosystem context

Abstract: Soil organic matter (SOM) is often separated by physical means to simplify a com- plex matrix into discrete fractions. A frequent approach to isolating two or more fractions is based on differing particle densities and uses a high density liquid such as sodium polytungstate (SPT). Soil density fractions are often interpreted as organic matter pools with different carbon (C) turnover times, ranging from years to decades or centuries, and with different functional roles for C and nutrient dynamics. In this paper, we discuss the development and mechanistic basis of common density-based methods for dividing soil into distinct organic matter fractions. Further, we directly address the potential effects of dispersing soil in a high density salt solution on the recov- ered fractions and implications for data inter- pretation. Soil collected from forested sites at H. J. Andrews Experimental Forest, Oregon and Bousson Experimental Forest, Pennsylvania was separated into light and heavy fractions by floa- tation in a 1.6 g cm -3 solution of SPT. Mass balance calculations revealed that between 17% and 26% of the original bulk soil C and N content was mobilized and subsequently discarded during density fractionation for both soils. In some cases, the light isotope was preferentially mobilized during density fractionation. During a year-long incubation, mathematically recombined density fractions respired ~40% less than the bulk soil at both sites and light fraction (LF) did not always decompose more than the heavy fraction (HF). Residual amounts of tungsten (W) present even in well-rinsed fractions were enough to reduce microbial respiration by 27% compared to the control in a 90-day incubation of Oa material. However, residual W was nearly eliminated by repeated leaching over the year-long incubation, and is not likely the primary cause of the difference in respiration between summed frac- tions and bulk soil. Light fraction at Bousson, a deciduous site developed on Alfisols, had a radiocarbon-based mean residence time (MRT)

Bacterial metabolism of naphthalene: construction and use of recombinant bacteria to study ring cleavage of 1,2-dihydroxynaphthalene and subsequent reactions.

Abstract: The reactions involved in the bacterial metabolism of naphthalene to salicylate have been reinvestigated by using recombinant bacteria carrying genes cloned from plasmid NAH7. When intact cells of Pseudomonas aeruginosa PAO1 carrying DNA fragments encoding the first three enzymes of the pathway were incubated with naphthalene, they formed products of the dioxygenase-catalyzed ring cleavage of 1,2-dihydroxynaphthalene. These products were separated by chromatography on Sephadex G-25 and were identified by 1H and 13C nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry as 2-hydroxychromene-2-carboxylate (HCCA) and trans-o-hydroxybenzylidenepyruvate (tHBPA). HCCA was detected as the first reaction product in these incubation mixtures by its characteristic UV spectrum, which slowly changed to a spectrum indicative of an equilibrium mixture of HCCA and tHBPA. Isomerization of either purified product occurred slowly and spontaneously to give an equilibrium mixture of essentially the same composition. tHBPA is also formed from HCCA by the action of an isomerase enzyme encoded by plasmid NAH7. The gene encoding this enzyme, nahD, was cloned on a 1.95-kb KpnI-BglII fragment. Extracts of Escherichia coli JM109 carrying this fragment catalyzed the rapid equilibration of HCCA and tHBPA. Metabolism of tHBPA to salicylaldehyde by hydration and aldol cleavage is catalyzed by a single enzyme encoded by a 1-kb MluI-StuI restriction fragment. A mechanism for the hydratase-aldolase-catalyzed reaction is proposed. The salicylaldehyde dehydrogenase gene, nahF, was cloned on a 2.75-kb BamHI fragment which also carries the naphthalene dihydrodiol dehydrogenase gene, nahB. On the basis of the identification of the enzymes encoded by various clones, the gene order for the nah operon was shown to be p, A, B, F, C, E, D.

The value of reducing risks of death: A note on new evidence

Abstract: Government agencies face difficult resource-allocation decisions when confronted with projects that will reduce risks of fatality. Evidence from individual behavior helps determine society's values for reducing risks. The most credible evidence is based on individuals' willingness to pay (or willingness to accept compensation) for small changes in risks. Studies of consumer behavior are limited, but more evidence is available relating wages to job risks. Contingent valuation studies reinforce the wage-risk implications, leading to a range of values that can be compared with the costs of proposals to reduce fatal risks.

Low emission, diesel-cycle engine

Abstract: A diesel-cycle engine (22) with a unique exhaust gas recirculation system includes a plurality of cylinders with fuel feed for each of the cylinders and an intake manifold (21) for distributing intake air to each of the cylinders for combustion of the fuel charges therein with generation of exhaust gas. The exhaust gas is discharged to ambient atmosphere through an exhaust line (15) with a gas turbine (27) therein. The gas turbine drives an intake compressor (19) which serves to compress the intake air. An engine controller controls a valve (14) regulating the amount of exhaust gas recirculation responsive to sensed concentration of an exhaust gas component.