Chan E.A.W.,U.S. Environmental Protection Agency |
Buckley B.,National Center for Environmental Assessment |
Farraj A.K.,Health-U |
Pharmacology and Therapeutics | Year: 2016
Exposure to particulate matter air pollution has been causally linked to cardiovascular disease in humans. Several broad and overlapping hypotheses describing the biological mechanisms by which particulate matter exposure leads to cardiovascular disease have been explored, although linkage with specific factors or genes remains limited. These hypotheses may or may not also lead to particulate matter-induced cardiac dysfunction. Evidence pointing to autocrine/paracrine signaling systems as modulators of cardiac dysfunction has increased interest in the emerging role of endothelins as mediators of cardiac function following particulate matter exposure. Endothelin-1, a well-described small peptide expressed in the pulmonary and cardiovascular systems, is best known for its ability to constrict blood vessels, although it can also induce extravascular effects. Research on the role of endothelins in the context of air pollution has largely focused on vascular effects, with limited investigation of responses resulting from the direct effects of endothelins on cardiac tissue. This represents a significant knowledge gap in air pollution health effects research, given the abundance of endothelin receptors found on cardiac tissue and the ability of endothelin-1 to modulate cardiac contractility, heart rate, and rhythm. The plausibility of endothelin-1 as a mediator of particulate matter-induced cardiac dysfunction is further supported by the therapeutic utility of certain endothelin receptor antagonists. The present review examines the possibility that endothelin-1 release caused by exposure to PM directly modulates extravascular effects on the heart, deleteriously altering cardiac function. © 2016.
Meng Q.,Rutgers University |
Williams R.,National Exposure Research Laboratory |
Pinto J.P.,National Center for Environmental Assessment
Atmospheric Environment | Year: 2012
Personal total exposure (E t) is composed of exposure to pollutants of ambient origin (E a) and nonambient origin (E na), both of which are associated with health effects. However, E a is more relevant for estimating the health effects associated with ambient air pollutants. Associations between E a and ambient concentrations (C a) were examined for different subpopulations in the Detroit Exposure and Aerosol Research Study (DEARS). First, E a was estimated for PM 2.5, NO 2, and O 3. The associations between C a and E a were then characterized with mixed effect models. C a served as a good surrogate for E a for PM 2.5 in both summer (slope = 0.80) and winter (slope = 0.55), but only in summer for O 3 and NO 2 (slope = 0.13 for NO 2, and slope = 0.03 for O 3).The effects of exposure determinants on E a-C a associations were examined using mixed effect models. Exposure determinants examined include personal activities, building and household characteristics and ambient apparent temperature (AT). The strength of associations between C a and E a differed between that for the entire study population and different subpopulations, which in turn differed from each other. Personal activities and building characteristics significantly affected the E a-C a associations through modifying the air exchange rate (AER). C a was not a significant indicator of E a for O 3 and NO 2 for homes with central AC or with windows closed. Ambient AT affected the E a-C a associations through modifying both AER and personal activities. The fraction of daily time spent outdoors peaked (6%) at about 22 °C, and monotonically decreased when ambient AT departed from 22 °C. Adequate accounting for the effects of exposure determinants on the E a-C a associations will lead to a better understanding of the E a-C a associations and of the uncertainties associated with using ambient concentrations as surrogates for personal exposures of ambient origin. © 2012.
Buckley B.,National Center for Environmental Assessment |
Farraj A.,National Health and Environmental Effects Research Laboratory
Toxicology | Year: 2015
Air pollution consists of a complex mixture of particulate and gaseous components. Individual criteria and other hazardous air pollutants have been linked to adverse respiratory and cardiovascular health outcomes. However, assessing risk of air pollutant mixtures is difficult since components are present in different combinations and concentrations in ambient air. Recent mechanistic studies have limited utility because of the inability to link measured changes to adverse outcomes that are relevant to risk assessment. New approaches are needed to address this challenge. The purpose of this manuscript is to describe a conceptual model, based on the adverse outcome pathway approach, which connects initiating events at the cellular and molecular level to population-wide impacts. This may facilitate hazard assessment of air pollution mixtures. In the case reports presented here, airway hyperresponsiveness and endothelial dysfunction are measurable endpoints that serve to integrate the effects of individual criteria air pollutants found in inhaled mixtures. This approach incorporates information from experimental and observational studies into a sequential series of higher order effects.The proposed model has the potential to facilitate multipollutant risk assessment by providing a framework that can be used to converge the effects of air pollutants in light of common underlying mechanisms. This approach may provide a ready-to-use tool to facilitate evaluation of health effects resulting from exposure to air pollution mixtures. © 2015 Published by Elsevier Ireland Ltd.
Clark C.M.,National Center for Environmental Assessment |
Morefield P.E.,National Center for Environmental Assessment |
Gilliam F.S.,Marshall University |
Pardo L.H.,U.S. Department of Agriculture
Ecology | Year: 2013
Although nitrogen (N) deposition is a significant threat to herbaceous plant biodiversity worldwide, it is not a new stressor for many developed regions. Only recently has it become possible to estimate historical impacts nationally for the United States. We used 26 years (1985-2010) of deposition data, with ecosystem-specific functional responses from local field experiments and a national critical loads (CL) database, to generate scenario-based estimates of herbaceous species loss. Here we show that, in scenarios using the low end of the CL range, N deposition exceeded critical loads over 0.38, 6.5, 13.1, 88.6, and 222.1 million ha for the Mediterranean California, North American Desert, Northwestern Forested Mountains, Great Plains, and Eastern Forest ecoregions, respectively, with corresponding species losses ranging from <1% to 30%. When we ran scenarios assuming ecosystems were less sensitive (using a common CL of 10 kg·ha-1 yr-1, and the high end of the CL range) minimal losses were estimated. The large range in projected impacts among scenarios implies uncertainty as to whether current critical loads provide protection to terrestrial plant biodiversity nationally and urge greater research in refining critical loads for U.S. ecosystems. © 2013 by the Ecological Society of America.
Compton J.E.,U.S. Environmental Protection Agency |
Harrison J.A.,Washington State University |
Dennis R.L.,National Exposure Research Laboratory |
Greaver T.L.,National Center for Environmental Assessment |
And 4 more authors.
Ecology Letters | Year: 2011
Ecology Letters (2011) 14: 804-815 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 NOx-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. Published 2011. This article is a US Government work and is in the public domain in the USA.
Vanderhoof M.K.,U.S. Geological Survey |
Alexander L.C.,National Center for Environmental Assessment |
Todd M.J.,National Center for Environmental Assessment
Landscape Ecology | Year: 2016
Context: Quantifying variability in landscape-scale surface water connectivity can help improve our understanding of the multiple effects of wetlands on downstream waterways. Objectives: We examined how wetland merging and the coalescence of wetlands with streams varied both spatially (among ecoregions) and interannually (from drought to deluge) across parts of the Prairie Pothole Region. Methods: Wetland extent was derived over a time series (1990–2011) using Landsat imagery. Changes in landscape-scale connectivity, generated by the physical coalescence of wetlands with other surface water features, were quantified by fusing static wetland and stream datasets with Landsat-derived wetland extent maps, and related to multiple wetness indices. The usage of Landsat allows for decadal-scale analysis, but limits the types of surface water connections that can be detected. Results: Wetland extent correlated positively with the merging of wetlands and wetlands with streams. Wetness conditions, as defined by drought indices and runoff, were positively correlated with wetland extent, but less consistently correlated with measures of surface water connectivity. The degree of wetland–wetland merging was found to depend less on total wetland area or density, and more on climate conditions, as well as the threshold for how wetland/upland was defined. In contrast, the merging of wetlands with streams was positively correlated with stream density, and inversely related to wetland density. Conclusions: Characterizing the degree of surface water connectivity within the Prairie Pothole Region in North America requires consideration of (1) climate-driven variation in wetness conditions and (2) within-region variation in wetland and stream spatial arrangements. © 2015, The Author(s).
Johnson T.E.,National Center for Environmental Assessment |
Butcher J.B.,Tetra Tech Inc. |
Parker A.,Tetra Tech Inc. |
Weaver C.P.,National Center for Environmental Assessment
Journal of Water Resources Planning and Management | Year: 2012
The U.S. EPA's Global Change Research Program (GCRP) recently began an effort to address gaps in the current knowledge of the sensitivity of U.S. streamflow, nutrient (nitrogen and phosphorus), and sediment loading to potential future climate change, and the methodological challenges associated with integrating existing tools (e.g., climate models, land-use models, watershed models) and data sets to address these scientific questions. The study is based on watershed modeling in 20 large U.S. watersheds. The purpose of this paper is to describe the overall structure of this ongoing effort-methods, sites, models, and scenarios-and discuss preliminary results generated to date for a subset of the watersheds. Specifically, a representative set of modeling results are reviewed that encompass the full suite of sensitivity tests explored in this project. These results illustrate a number of key methodological issues, sensitivities, and uncertainties associated with carrying out these types of climate change/hydrologic impacts assessments, including: the sensitivity of simulated changes to the watershed model used; the sensitivity of simulated changes to climate model and downscaling approach used; and the interaction between climate change and other key forcing factors, specifically urbanization and change in atmospheric CO2 concentration. In addition, this suite of results provides an overview of the response to climate change in different geographic regions and the different sensitivities of a variety of flow and water quality end points. © 2012 American Society of Civil Engineers.
Sacks J.D.,National Center for Environmental Assessment |
Rappold A.G.,U.S. Environmental Protection Agency |
Allen Davis J.,National Center for Environmental Assessment |
Richardson D.B.,University of North Carolina at Chapel Hill |
And 2 more authors.
Environmental Health Perspectives | Year: 2014
Background: Air pollution epidemiologic studies, often conducted in large metropolitan areas because of proximity to regulatory monitors, are limited in their ability to examine potential associations between air pollution exposures and health effects in rural locations. Methods: Using a time-stratified case-crossover framework, we examined associations between asthma emergency department (ED) visits in North Carolina (2006-2008), collected by a surveillance system, and short-term ozone (O3) exposures using predicted concentrations from the Community Multiscale Air Quality (CMAQ) model. We estimated associations by county groupings based on four urbanicity classifications (representative of county size and urban proximity) and county health. Results: O3 was associated with asthma ED visits in all-year and warm season (April-October) analyses [odds ratio (OR) = 1.019; 95% CI: 0.998, 1.040; OR = 1.020; 95% CI: 0.997, 1.044, respectively, for a 20-ppb increase in lag 0-2 days O3]. The association was strongest in Less Urbanized counties, with no evidence of a positive association in Rural counties. Associations were similar when adjusted for fine particulate matter in copollutant models. Associations were stronger for children (5-17 years of age) compared with other age groups, and for individuals living in counties identified with poorer health status compared with counties that had the highest health rankings, although estimated associations for these subgroups had larger uncertainty. Conclusions: Associations between short-term O3 exposures and asthma ED visits differed by overall county health and urbanicity, with stronger associations in Less Urbanized counties, and no positive association in Rural counties. Results also suggest that children are at increased risk of O3-related respiratory effects.
Cho S.-H.,Rti International |
Richmond-Bryant J.,National Center for Environmental Assessment |
Thornburg J.,Rti International |
Portzer J.,Rti International |
And 3 more authors.
Atmospheric Environment | Year: 2011
The final 2008 lead (Pb) national ambient air quality standards (NAAQS) revision maintains Pb in total suspended particulate matter as the indicator. However, the final rule permits the use of low-volume PM10 (particulate matter sampled with a 50% cut-point of 10 μm) Federal Reference Method (FRM) monitors in lieu of total suspended particulate (TSP) monitors for some non-source-oriented monitoring. PM10 FRM monitors are known to provide more reliable concentration measurements than TSP samplers because they are omni-directional samplers and so are not biased by wind conditions. However, by design they exclude the upper tail of the particle size distribution. Hence, each monitor produces uncertainties about measured concentrations of Pb-bearing PM. Uncertainties in reported Pb data are also related to spatiotemporal variation of the concentration and size distribution of Pb-bearing PM. Therefore, a comprehensive literature review was performed to summarize the current knowledge regarding the concentration and size distribution of Pb particles in the atmosphere. The objectives of this review were to compile data that could shed light on these uncertainties, to provide insights useful during future Pb NAAQS reviews, and to identify areas where more research is needed.Results of this review indicated that Pb size distribution data are relatively limited and often outdated. Thirty-nine articles were found to have sufficiently detailed information regarding airborne Pb concentrations, study location, sample collection methods, and analytical techniques; only 16 of those papers reported Pb concentration data for multiple size fractions. For the most part, U.S. and European studies from the last forty years illustrate that the largest mode of the size distribution of airborne particle-bound Pb has shifted to larger sizes while airborne Pb concentrations have decreased in urban areas. This shift occurred as tetraethyl Pb additives in gasoline were phased out and industrial emissions and resuspended road dust became more important sources of Pb. Several studies also suggested the occurrence of long-range transport of Pb-bearing PM from industrial emissions. Uncertainties associated with these studies include influence of wind speed and direction on captured concentrations and variability in analytical techniques used to quantify Pb concentrations on the reported size distributions. © 2011.
Liu L.,National Center for Environmental Assessment |
Greaver T.L.,National Center for Environmental Assessment
Ecology Letters | Year: 2010
Nitrogen (N) effects on ecosystem carbon (C) budgets are critical to understand as C sequestration is considered as a mechanism to offset anthropogenic CO2 emissions. Interactions between aboveground C and N cycling are more clearly characterized than belowground processes. Through synthesizing data from multiple terrestrial ecosystems, we quantified the responses of belowground C cycling under N addition. We found that N addition increased litter input from aboveground (+20%) but not from fine root. N addition inhibited microbial activity as indicated by a reduction in microbial respiration (-8%) and microbial biomass carbon (-20%). Although soil respiration was not altered by N addition, dissolved organic carbon concentration was increased by 18%, suggesting C leaching loss may increase. N addition increased the C content of the organic layer (+17%) but not the mineral soil layer. Overall, our meta-analysis indicates that N addition will increase short term belowground C storage by increasing C content of organic layer. However, it is difficult to predict the response of long term C sequestration since there is no significant change in mineral soil C content. © 2010 Blackwell Publishing Ltd/CNRS.