Research AreasEnvironmental and Energy EconomicsCorporate Toxics Information ProjectToxic 100 Air Polluters IndexTechnical Notes

Technical Notes: Toxic 100 Air Polluters Index

The Toxics Release Inventory (TRI), compiled by the U.S. Environmental Protection Agency (EPA) in accordance with the Emergency Planning and Community Right-to-Know Act of 1986, annually reports the weight (in pounds) of each of approximately 600 toxic chemicals released into the environment by major industrial facilities in the United States.

Our analysis uses 2010 releases of toxic chemicals into air nationwide. We combine fugitive, stack, and post-incineration releases. In all, facilities reported to TRI the release of some 860 million pounds of toxic chemicals into the air in 2010. This is a substantial reduction from more than 1,300 million pounds in 2007 and more than 2,000 million pounds in 1999.

The EPA Office of Pollution Prevention and Toxics processes the raw TRI reports to create the Risk Screening Environmental Indicators (U.S. EPA RSEI version 2.3.1).  The EPA combines three variables to assess the human health risks posed by toxic releases:

  • fate and transport, or how the chemical spreads from the point of release to the surrounding area;
  • toxicity, or how dangerous the chemical is on a per-pound basis; and
  • population, or how many people live in the affected areas.

Each release begins at a smokestack, leaking valve, open canister, or other source within the facility or at the stack of an offsite incineration facility. Using the AERMOD fate-and-transport model, EPA combines data on local wind patterns, temperature, and topography with information on the smokestack height and the exit velocity of released gases and information about each chemical (molecular weight and rate of decay in sunlight and air) to determine the concentrations of releases in each 810 m by 810 m grid cell within 50 km around the release point.  For incinerator releases, the model computes the fraction of the chemical that escapes incineration.

EPA matches each chemical to a toxicity weight that expresses the relative toxicity of the chemical per pound or per unit of concentration. Although all TRI chemicals are hazardous, their toxicities vary greatly. At the extremes, just one pound of benzidine is equivalent, in terms of inhalation toxicity, to 3.4 billion pounds of the chemical chlorodifluoromethane (HCFC-22). The enormous variation in toxicity limits the usefulness of comparisons on the basis of the simple mass (pounds) of chemicals released. By multiplying the mass of each toxic release by its toxicity weight, EPA can compare the toxic significance of releases of different chemicals.

The EPA's toxicity-weighting system is based on peer-reviewed toxicity databases including those of the EPA's Integrated Risk Information System (IRIS), the EPA's Office of Pesticide Programs (OPP) Reference Dose Tracking Reports, the U.S. Department of Health and Human Services Agency for Toxic Substances and Disease Registry (ATSDR), the California Environmental Protection Agency (CalEPA) Office of Environmental Health Hazard and Assessment (OEHHA), and the EPA's Health Effects Assessment Tables (HEAST). For some of the chemicals listed in the TRI, no consensus has been reached regarding the appropriate toxicity weight, and these chemicals are excluded from the analysis. In the TRI data for the year 2010, chemicals with toxicity weights account for 99 percent of the reported pounds for all on-site air releases. Further details on the toxicity weights are available from the EPA (.pdf), or download a spreadsheet of the toxicity weights here (.xls).

After accounting for the quantity, dispersion, and toxicity of the release, EPA multiplies toxicity-weighted concentrations by the number of people living in each of the grid cell to measure the population health risk. (EPA slightly modifies the simple head count to account for differential uptake of chemicals depending on the age and sex composition of the exposed population.) A facility located in an urban area with high population density thus generates more risk than a facility with identical releases in a less populous rural area. To obtain the RSEI score for the facility, EPA aggregates the population-weighted, toxicity-weighted impacts for the entire area around the facility.

CTIP adjusts the TRI data so that they represent the most current available about the reporting year, in  case companies revise earlier TRI reporting.  In the case of downward revisions of the mass released,  RSEI scores are adjusted on the assumption of a linear relation between pounds released and that release's RSEI score. Upward revisions or new reports are noted but do not engender adjustments of the RSEI score.

Using information on company ownership of facilities from the TRI reports, Dun & Bradstreet's Million Dollar Database, Mergent Online, Hoover's, company websites, printed reports, and telephone calls, we matched each facility to its parent company. Individual facilities are assigned to corporate parents on the basis of the most recent available ownership structure. We then aggregated the RSEI scores for air releases of toxics by the facilities owned by each parent company, and ranked companies on this basis. The Toxic 100 reports the top polluters among the companies that appeared on any of the following lists of large US and foreign-owned corporations:

  • Forbes Global 2000, values calculated April 2012 (only first 500 companies)
  • Forbes America's Largest Private Companies, 2012 version
  • Fortune 500, 2012 version, issued May 21, 2012 (only first 500 companies)
  • Fortune Global 500, 2012 version, issued July 23, 2012
  • S&P 500 as of Jan 3, 2013.

We calculate environmental justice (EJ) ratios using geographical microdata generated by the RSEI model, which report impacts in individual grid cells. We match the RSEI grid cells to U.S. Bureau of the Census geography (as is done in the RSEI model to obtain population density), and link data on race, ethnicity, and poverty from the 2006-2010 American Community Survey 5-Year Estimates (U.S. Bureau of the Census).  In a small number of cases the match is incomplete, and this is noted. The minority EJ ratio is the percentage share of racial and ethnic minorities in the total RSEI score of the facility or firm; in the advanced data display, this is disaggregated into specific minority groups. Similarly, the poverty EJ ratio is the percentage people living below the Federal poverty line in the total RSEI score of the facility or firm, and near-poor refers to people living below 150 percent of the Federal poverty line. For comparison, the percentages of minorities and people living in poverty in the U.S. population as a whole in 2010 were 37% and 15%, respectively.  Further details on our methodology for calculating EJ ratios can be found in our 2009 report Justice in the Air.