Friday, November 22, 2013

EPA Study: Nitrogen Dioxide Pollution Seems More Dangerous -- Even Deadly -- Than Previously Known

The U.S. EPA has quietly published a draft new report which warns that nitrogen dioxide pollution, chiefly from traffic and construction equipment, appears to be more dangerous -- even more deadly -- than previously thought. 

These tentative conclusions are contained in a new draft "Integrated Science Assessment" of the pollutant.  Collecting the science is part of the process the EPA goes through as it reviews whether national health standards are adequate. The study is available for download here          

You may recall that in 2009, Clean Air Watch joined health advocates in calling for much tougher new standards   .  EPA eventually set a standard not as tough as we would have preferred   though it did call for more road-side monitors so the public can know just how dirty the air is in high-exposure areas.  These monitors are only now beginning to be put in place.

The EPA notes that:

Overall, findings from recent studies strengthen the conclusions from the previous NAAQS review, which was completed in 2010. Results from recent studies strengthen the body of evidence indicating that short-term exposure to NO2 can cause respiratory effects, in particular, effects related to asthma exacerbations. Recent results also strengthen the evidence that the respiratory effects of NO2 are independent of the effects of many other traffic-related pollutants. And finally, recent results expand on previous results supporting relationships between short-term exposure to NO2 and cardiovascular effects and premature mortality. There is now stronger evidence for a relationship between long-term exposure to NO2 and respiratory effects, particularly in children.

EPA is taking comments on the new study, which is noted in today's Federal Register.  Here are some of its key conclusions:           

Based on the 2008 National Emissions Inventory, the major NOX emissions source categories in the U.S. are highway and off-highway vehicles and fuel combustion by electric utilities. Ambient concentrations of NO2, NO, and NOX show spatial and temporal heterogeneity at multiple scales and have been shown to be 30% to 200% higher  at locations within 15 m of a roadway (averaged over hours to weeks) compared with  locations farther away from the road. Emissions of NOX and ambient concentrations of  NO2 have decreased over the past 20 years in the U.S. Relationships between NO2  concentrations obtained from ambient monitors and personal exposures vary in the population, and exposure measurement error resulting from the use of ambient concentrations has been shown to reduce epidemiologic associations observed with health effects.

Recent studies, most of which are epidemiologic, expand on findings reported in the 2008  ISA for Oxides of Nitrogen and previous assessments. The consistency, coherence, and biological plausibility of evidence integrated across scientific disciplines and outcomes related to asthma exacerbations indicate that there is a causal relationship between short-term exposure to NO2 and respiratory effects. Evidence indicates there is likely to be a causal relationship between short-term exposure to NO2 and cardiovascular effects as well as total mortality. There is likely to be a causal relationship between long-term NO2 exposure and respiratory effects based strongly on findings in children for asthma incidence and decreases in lung function. Evidence is suggestive of a causal relationship between long-term NO2 exposure and cardiovascular effects, reproductive and developmental effects, total mortality, and cancer.

A major uncertainty in the 2008 ISA for Oxides of Nitrogen was the extent to which evidence indicated that NO2 has effects on health that are independent of effects of  another traffic-related pollutant or mixture. For respiratory effects, cardiovascular effects,  and total mortality related to short-term exposure and respiratory effects related to long-term exposure, recent epidemiologic studies reduce this uncertainty with additional  results for associations with NO2 that remain positive in copollutant models. However,  analysis of confounding by the array of potentially correlated copollutants, in particular CO, UFP, EC, and BC, which also are emitted from vehicles, is limited. Therefore, other  lines of evidence that inform biological plausibility are key in addressing limitations of  the epidemiologic evidence. For cardiovascular effects and total mortality related to  short-term exposure and respiratory effects related to long-term exposure, biological  plausibility is limited, and evidence is not sufficient to conclusively demonstrate effects of NO2 exposure that are independent of those of other traffic-related pollutants. November 2013 lxxxi DRAFT: Do Not Cite or Quote

There is adequate evidence that children (ages 0-14 years) and older adults (ages 65 years and older) have increased risk for NO2-related health effects. A large proportion of the population lives near major roads; thus, the potential for elevated exposures to oxides of nitrogen, relative to people living 500 meters or more from roads, is large. There is suggestive evidence that the risk of NO2-related health effects differs by pre-existing asthma, pre-existing COPD, genetic variants for oxidative metabolism enzymes, dietary antioxidant intake, sex, and SES. Daily average and 1-h max NO2 concentrations as well as concentrations averaged over 30 minutes to a few hours are associated with health effects. For many respiratory outcomes, larger effects are estimated for multiday averages of ambient NO2 concentrations than single-day concentrations. For long-term exposure, respiratory effects are associated with 6-month average NO2 and NO2 averaged over 1 year to 10 (representing lifetime exposure) years. The concentration-response relationship for associations of short-term ambient NO2 exposure with respiratory-related ED visits and total mortality is found to be linear, and results do not identify a threshold for effects.

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