EPA released an update of its National-Scale Air Toxics Assessment on June 24, 2009.
The results indicate that almost every person in the US lives in an area where the cancer risk exceeds 10 in 1 million after a lifetime of exposure to selected air toxics, well in excess of EPA’s general target of 1 in 1 million. For 2 million people, the risk is far worse, exceeding 100 in 1 million. The average risk is 36 in 1 million.
For noncancer respiratory risks, nearly everyone in the country lives in an area where the hazard index was higher than EPA’s target of 1.0, and the index was 10 or higher for more than 22 million people. The news was better for noncancer neurological risks, but about 350,000 people still live in areas exceeding the EPA target hazard index of 1.0.
For all three types of health effects evaluated, there are large risk differences between census tracts, between counties, between states, and between regions.
Although the latest version is limited by its use of 7-year-old data, it’s a slight upgrade from the old version based on 1999 data that addressed 177 of the 187 substances designated as toxics in the Clean Air Act, as well as diesel particulate matter. The new version includes 180 substances, and still includes diesel particulate matter.
However, the risk estimates are based on just 124 of the 180 substances, due to a lack of chronic exposure health data for the others, and there still is no cancer risk estimate for diesel, due to a lack of consensus on the risk posed. In the past few years, some scientists and public health officials and agencies have concluded that diesel emissions alone account for about 70% of all risk from air toxics.
Other limitations are that the risk estimates rely on a series of assumptions, any one of which could have some degree of error; they have yet to include dioxins, one of the most toxic classes of substances known; they don’t account for synergistic effects, or many potential changes to the emitted substances via chemical reactions once they are airborne; they don’t account for added risk posed by other air pollutants that are tracked under different categories, such as the 6 criteria air pollutants, or hundreds of other pollutants monitored through the Toxics Release Inventory (TRI), or from any substances in the ground or water; and the baseline data provided by each state for air emissions from stationary and mobile sources may be unreliable in some cases.
Nonetheless, the NATA information is likely somewhat better than having information on just the total mass or volume of pollutants released, as occurs with TRI, because there is at least some effort to translate these numbers to a degree of relative risk. Factors such as this have made this data of wide interest to many audiences, including various interest groups, as well as state and local jurisdictions that can use it to focus their risk reduction efforts.
The lag until the next update is expected to be much shorter than it was under the Bush administration, with an assessment based on 2005 data due for release in late 2009 or early 2010.
The latest findings are available for the overall US, and by state (and Puerto Rico and the Virgin Islands), county, and census tract (although some of the data is difficult to use as posted; contact EPA’s Ted Palma  or Dennis Pagano  if your computer can’t download it in a useful format).
There is a risk estimate for each substance, and three separate combined assessments – for cancer risk from 80 substances, for noncancer risk for respiratory effects from 68 substances, and for noncancer risk for neurological effects from the same 68 substances.