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.

The Relationship between Stream Chemistry and Watershed Land Cover Data in the Mid-Atlantic Region, U.S.

Abstract: In order to investigate the relationship between stream chemistry and watershed land cover at the regional scale, we analyzed data from 368 wadeable streams sampled in the mid-Atlantic region of the U.S. during spring 1993–1994. Study sites were selected using a probability sample and the digitized version of the 1:100,000 scale USGS map stream network as the sample population. Both classified Thematic Mapper (TM) and USGS Land Use/Land Cover (LULC) data were used to quantify land cover in the study watersheds. On average, the most common land cover was forest (77%) followed by agriculture (20%), and urban (1%). Multiple regression analysis showed that concentrations of Cl−, nutrients, acid neutralization capacity, and base cations were the analytes most strongly related to watershed land cover. Despite large differences in resolution and age of the TM and LULC data sources, similar results were obtained with the two sources. Using a greater number of land cover subclasses did not greatly improve the land cover-chemistry relationships. Ecoregions with predominantly forested land cover had weaker relationships than ecoregions with more agricultural and/or urban land cover. In studies or databases without land cover information, Cl− concentration is a good surrogate indicator for general human disturbance in the watershed.

Spatial patterns of aboveground production and mortality of woody biomass for eastern u.s. forests

Abstract: We developed maps of aboveground production and mortality of woody biomass for forests of the eastern United States based on data collected from an extensive network of permanent plots remeasured by the U.S. Forest Service Forest Inventory and Analysis units (FIA). Forest volume inventory data for growth and mortality were converted to units of aboveground biomass at the county level for hardwood and softwood forest types. Aboveground production of woody biomass (APWB) for hardwood forests ranged from 0.6 to 28 Mg·ha−1·yr−1 and averaged 5.2 Mg·ha−1·yr−1. For softwood forests, APWB ranged from 0.2 to 31 Mg·ha−1·yr−1 and averaged 4.9 Mg·ha−1·yr−1. Aboveground production of woody biomass was generally highest in southeastern and southern counties, mostly along an arc from southern Virginia to Louisiana and eastern Texas. Although this pattern is generally the result we would expect from the general climatic gradients of the region, it was confounded by the effects of different forest management intensities. ...

Effects of ELF (1–120 Hz) and modulated (50 Hz) RF fields on the efflux of calcium ions from brain tissue in vitro

Abstract: We have previously shown that 16-Hz, sinusoidal electromagnetic fields can cause enhanced efflux of calcium ions from chick brain tissue, in vitro, in two intensity regions centered on 6 and 40 Vp-p/m. Alternatively, 1-Hz and 30-Hz fields at 40 Vp-p/m did not cause enhanced efflux. We now demonstrate that although there is no enhanced efflux associated with a 42-Hz field at 30, 40, 50, or 60 Vp-p/m, a 45-Hz field causes enhanced efflux in an intensity range around 40 Vp-p/m that is essentially identical to the response observed for 16-Hz fields. Fields at 50 Hz induce enhanced efflux in a narrower intensity region between 45 and 50 Vp-p/m, while radiofrequency carrier waves, amplitude modulated at 50 Hz, also display enhanced efflux over a narrow power density range. Electromagnetic fields at 60 Hz cause enhanced efflux only at 35 and 40 Vp-p/m, intensities slightly lower than those that are effective at 50 Hz. Finally, exposures over a series of frequencies at 42.5 Vp-p/m reveal two frequency regions that elicit enhanced efflux--one centered on 15 Hz, the other extending from 45 to 105 Hz.

Ecosystem services altered by human changes in the nitrogen cycle: a new perspective for US decision making.

Abstract: Human alteration of the nitrogen (N) cycle has produced benefits for health and well-being, but excess N has altered many ecosystems and degraded air and water quality. US regulations mandate protection of the environment in terms that directly connect to ecosystem services. Here, we review the science quantifying effects of N on key ecosystem services, and compare the costs of N-related impacts or mitigation using the metric of cost per unit of N. Damage costs to the provision of clean air, reflected by impaired human respiratory health, are well characterized and fairly high (e.g. costs of ozone and particulate damages of $28 per kg NO(x)-N). Damage to services associated with productivity, biodiversity, recreation and clean water are less certain and although generally lower, these costs are quite variable (<$2.2-56 per kg N). In the current Chesapeake Bay restoration effort, for example, the collection of available damage costs clearly exceeds the projected abatement costs to reduce N loads to the Bay ($8-15 per kg N). Explicit consideration and accounting of effects on multiple ecosystem services provides decision-makers an integrated view of N sources, damages and abatement costs to address the significant challenges associated with reducing N pollution.

Distinguishing androgen receptor agonists and antagonists: distinct mechanisms of activation by medroxyprogesterone acetate and dihydrotestosterone.

Abstract: Natural and pharmacological androgen receptor (AR) ligands were tested for their ability to induce the AR NH2-terminal and carboxyl-terminal (N/C) interaction in a two-hybrid protein assay to determine whether N/C complex formation distinguishes in vivo AR agonists from antagonists. High-affinity agonists such as dihydrotestosterone, mibolerone, testosterone, and methyltrienolone at concentrations between 0.1 and 1 nm induce the N/C interaction more than 40-fold. The lower affinity anabolic steroids, oxandrolone and fluoxymesterone, require concentrations of 10–100 nm for up to 23-fold induction of the N/C interaction. However no N/C interaction was detected in the presence of the antagonists, hydroxyflutamide, cyproterone acetate, or RU56187, at concentrations up to 1 μm, or with 1μ m estradiol, progesterone, or medroxyprogesterone acetate; each of these steroids at 1–500 nm inhibited the dihydrotestosterone-induced N/C interaction, with medroxyprogesterone acetate being the most effective. In transient ...