EPA's Report on the Environment: External Review Draft
Ambient Concentrations of Manganese Compounds in EPA Region 5
Note to reviewers of this draft revised ROE: This indicator reflects data through 2011. EPA anticipates updating this indicator in 2014.
Manganese is a naturally occurring metal that is ubiquitous in the environment. Exposure to low levels of manganese in the diet is considered to be nutritionally essential for people and animals (ATSDR, 2008). However, exposures to elevated concentrations of manganese are harmful to human health and have been associated with subtle neurological effects, such as slowed eye-hand coordination. Manganese compounds are hazardous air pollutants emitted by iron and steel production plants, power plants, coke ovens, and many smaller metal processing facilities. Manganese also may be contributed in border communities by vehicles using Canadian fuel with the additive methylcyclopentadienyl manganese tricarbonyl (MMT), though use of MMT in Canadian gasoline has decreased dramatically in recent years (ATSDR, 2008).
Although manganese compounds are air pollutants of concern nationwide, they are of special concern in EPA Region 5, which includes Illinois, Indiana, Michigan, Minnesota, Ohio, Wisconsin, and 35 tribes. For example, the 2002 National Emissions Inventory (NEI) showed that Region 5 had the highest manganese emissions of all EPA Regions, contributing 48 percent of all manganese compounds emitted nationwide (U.S. EPA, 2010a). Emissions from industrial sources in Region 5 occurred from various facilities, such as those that manufacture steel or process iron ores and alloys for steelmaking. Between 1988 and 2009, manganese emissions from point sources as reported to the Toxics Release Inventory declined both nationally and in EPA Region 5. During this 22-year period, national manganese emissions decreased 22.5 percent, or 1 percent per year, and Region 5 emissions declined 69.4 percent, or 3.3 percent per year (U.S. EPA, 2010b).
EPA’s National Air Toxics Assessment (NATA) is intended to provide a better understanding of the health risks resulting from inhalation exposure to air toxics. The 2005 NATA results (U.S. EPA, 2010c) identify manganese compounds as the largest contributor to neurological non-cancer health risk in the U.S. Based on the 2005 NATA, modeled estimates of ambient manganese compounds in all 3,222 U.S. counties show that among the 50 counties with the highest concentrations nationwide, 17 are located in EPA Region 5.
This indicator presents ambient concentrations of manganese compounds measured as total suspended particulates (TSP) by direct monitoring. This indicator addresses manganese in the TSP fraction (not PM10 or PM2.5) because it is the most complete dataset in EPA Region 5 in terms of geographic and temporal coverage. TSP metals data have been commonly used in human health risk assessments. EPA recommends PM10 as the most appropriate fraction for evaluating people’s exposure to toxic metals (U.S. EPA, 2002), but PM10 metals data are sparse at this time, both nationally and in EPA Region 5. Data from a limited number of sites in EPA’s Air Quality System (AQS) with collocated PM10 and TSP speciation monitors suggest that the proportion of manganese in PM10 versus TSP is about 50 percent at most sites and can be as high as 75 percent. TSP manganese data therefore should be considered a conservative estimate of PM10 manganese exposures. PM2.5 metals data are plentiful since the establishment of the Speciation Trends Network in 2000, but this size fraction is believed to underestimate human exposures.
Data were considered for 63 urban and suburban monitoring sites in EPA Region 5 that had a complete year of data reported to the AQS national database in 2011. Average manganese concentrations were calculated for each monitoring site. A concentration trend was determined using the 38 monitoring sites with nine or more complete years of data between 2000 and 2011. As annual average concentrations are representative of long-term inhalation exposures, the ambient monitoring data are displayed in comparison with the manganese reference concentration (RfC). The RfC is an estimate of a chronic inhalation exposure that is likely to be without appreciable risk of adverse non-cancer effects during a lifetime. The RfC for manganese is 0.05 micrograms per cubic meter (μg/m3), based on impairment of neurobehavioral function in people. At exposures increasingly greater than the RfC, the potential for harmful effects increases (ATSDR, 2008; U.S. EPA, 1999). Monitoring sites were classified into different categories based on land use as defined in AQS.
What the Data Show
In 2011, the median average annual ambient concentrations of manganese as TSP in EPA Region 5 were 0.014 µg/m3 at the 18 residential sites, 0.045 µg/m3 at the 12 sites in commercial or high-traffic areas, and 0.044 µg/m3 at the 33 industrial sites (Exhibit 1). The 90th percentile concentrations in 2011 were 0.136 µg/m3 at the commercial and high-traffic sites, 0.141 µg/m3 at the residential sites, and 0.176 µg/m3 at the predominantly industrial sites. In 2011, 26 of the 63 urban and suburban monitoring sites had annual average manganese concentrations higher than the RfC; 16 of these sites were categorized as industrial, six commercial or high-traffic, and four residential.
The average annual manganese concentration averaged across 38 trend sites showed a 43 percent decline between 2000 and 2011 (Exhibit 2). The trend sites had the following land use designations: commercial and high-traffic (10 sites), industrial (15 sites), residential (12 sites), and one site in an agricultural setting.
- AQS data represent several sites per state, but do not have full geographic or temporal coverage. Some emissions “hotspots” are included, while others may exist that have not been monitored.
- The land use categories are only generally indicative of the area represented by an ambient air monitor. For example, a site categorized as “industrial” may adjoin a densely populated community where many residents are exposed to ambient pollution.
Summary data in this indicator were provided by EPA Region 5, based on ambient air monitoring data for manganese compounds reported in EPA’s AQS (U.S. EPA, 2012) (http://www.epa.gov/ttn/airs/airsaqs/). Trends in this indicator are based on the subset of monitoring stations located in EPA Region 5 that have sufficient manganese concentration data to assess trends over the period of record.
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