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.

Reactive nitrogen in atmospheric emission inventories

Abstract: . Excess reactive Nitrogen (Nr) has become one of the most pressing environmental problems leading to air pollution, acidification and eutrophication of ecosystems, biodiversity impacts, leaching of nitrates into groundwater and global warming. This paper investigates how current inventories cover emissions of Nr to the atmosphere in Europe, the United States of America, and China. The focus is on anthropogenic sources, assessing the state-of-the-art of quantifying emissions of Ammonia (NH3), Nitrogen Oxides (NOx) and Nitrous Oxide (N2O), the different purposes for which inventories are compiled, and to which extent current inventories meet the needs of atmospheric dispersion modelling. The paper concludes with a discussion of uncertainties involved and a brief outlook on emerging trends in the three regions investigated is conducted. Key issues are substantial differences in the overall magnitude, but as well in the relative sectoral contribution of emissions in the inventories that have been assessed. While these can be explained by the use of different methodologies and underlying data (e.g. emission factors or activity rates), they may lead to quite different results when using the emission datasets to model ambient air quality or the deposition with atmospheric dispersion models. Hence, differences and uncertainties in emission inventories are not merely of academic interest, but can have direct policy implications when the development of policy actions is based on these model results. The level of uncertainty of emission estimates varies greatly between substances, regions and emission source sectors. This has implications for the direction of future research needs and indicates how existing gaps between modelled and measured concentration or deposition rates could be most efficiently addressed. The observed current trends in emissions display decreasing NOx emissions and only slight reductions for NH3 in both Europe and the US. However, in China projections indicate a steep increase of both.

Thyroid disrupting chemicals: mechanisms and mixtures.

Abstract: Environmental contaminants are known to act as thyroid disrupting chemicals (TDCs). Broadly defined, TDCs are xenobiotics that alter the structure or function of the thyroid gland, alter regulatory enzymes associated with thyroid hormone (TH) homeostasis or change circulating or tissue concentrations of THs. For THs, homeostasis is defined as the normal range of THs and TSH in circulation and tissues. TDCs include a wide range chemical structures that act through a variety of mechanisms. Concern about TDCs has increased because of the critical role that thyroid hormones play in brain development. A major uncertainty regarding the endocrine disrupting potential of environmental xenobiotics is the potential for additive, antagonistic or synergistic effects following exposure to mixtures. In addition, there are a number of uncertainties in both interpretation and extrapolation of results from studies of TDC mixtures. Extrapolation of data from laboratory animals to humans is tempered by uncertainty in how the mechanism(s)-of-action of the TDCs may differ between species. The variety of mechanisms by which TDCs alter thyroid homeostasis also yields a difficulty in determining at what level of biological organization to cumulate effects. Should it be at the molecular level, which could be chemical class specific or at the level of a downstream consequence (e.g. circulating hormone levels, brain biochemistry and behaviour) which would be mechanism-independent? To date, the limited data from TDC mixture studies suggest that dose addition is reasonably accurate in predicting the effects on serum T4 concentrations. Assessing the health risks of thyroid disruption by environmental xenobiotics will need to include an improved understanding of how divergent mechanisms alter THs and consequent adverse impacts on nervous system development.

Metals associated with both the water-soluble and insoluble fractions of an ambient air pollution particle catalyze an oxidative stress

Abstract: One potential mechanism of injury mediated by air pollution particles is through metal-catalyzed oxidant generation. In one emission source particle, soluble metals have been associated with biological effect and toxicity. However, a majority of metals in ambient air pollution particles can be associated with insoluble components. We tested the hypothesis that concentrations of catalytically active metal in ambient air pollution particles are not equivalent to the concentrations of water-soluble metal. Twelve filters collected from the North Provo, UT, monitoring station were agitated in deionized water. Both the aqueous extract and pellet were isolated, lyophilized, and defined as the water-soluble and insoluble fractions, respectively. The fractions were chemically characterized and ionizable concentrations of metals were measured using inductively coupled plasma emission spectroscopy. While the water-soluble fraction had significantly greater concentrations of ionizable metals per unit mass, the insoluble fraction also had measurable quantities. In vitro oxidant generation by the two fractions, measured as thiobarbituric acid-reactive-products of deoxyribose, corresponded to the concentrations of ionizable rather than total metals. The release of interleukin-8 by cultured respiratory epithelial cells after incubation with the two fractions also coincided with the ionizable metal concentrations. Finally, neutrophil influx and lavage protein levels 24 h after instillation of the two fractions in rats reflected the ionizable metal concentrations, in vitro oxidative stress, and mediator release. We conclude that catalytically active metals can be measured in both the soluble and insoluble fractions of an ambient air pollution particle. These metals corresponded to the biological activity of the two fractions. While in greater concentration in the water-soluble fraction, larger total quantities of catalytically and biologically active metals are likely to be associated with the insoluble fraction as a result of the abundance of the latter.