Research AreasEnvironmental and Energy EconomicsCorporate Toxics Information ProjectToxic 100 Water PollutersToxic 100 Water Polluters Technical Notes

Technical Notes: Toxic 100 Water 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 year 2009 releases of toxic chemicals into surface water nationwide. We combine direct surface-water and post-sewage-treatment releases. In all, TRI-reporting facilities released almost 220 million pounds of toxic chemicals into water in 2009.

 The EPA Office of Pollution Prevention and Toxics has developed a method called Risk Screening Environmental Indicators (RSEI) to make the TRI reports more useful to the public. The EPA provides additional information to assess the human health hazard posed by toxic releases: 

  • toxicity, or how dangerous the chemical is on a per-pound basis; and
  • removal efficiency, or how much of the chemical is prevented from entering surface water following transfers for sewage treatment at POTW’s.

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. For example, the toxicity weight for ingesting the chemical zinc is about 3 while the toxicity weight for ingesting mercury is 10,000. It is roughly than 3,000 times more potentially harmful to ingest mercury as it is to ingest an equal quantity of zinc. The chemicals reported in the Toxics Release Inventory vary by ten orders of magnitude in their oral toxicity weights (from 0.02 to 500,000,000). 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 2009, chemicals with toxicity weights account for more than 98% of the reported pounds for all releases. Further details on the toxicity weights are available from the EPA at:
or download a spreadsheet of the toxicity weights here.

For many chemicals in the TRI, the US EPA Risk Reduction Engineering Laboratory estimates the removal efficiency, or how successfully sewage treatment removes toxic chemicals from wastes that are transferred for treatment based on the technology used and the type of influent. Toxic chemicals that are not removed are released into surface water with other effluents post-treatment: 

The product of the toxicity weight and the quantity released, including both direct and estimated post-treatment releases, is called the RSEI Hazard and represents potential human chronic-health hazard from water releases of the toxic chemicals. The extent of risk also depends on other determinants of exposure, including dilution and sedimentation in waterways, fish consumption from and recreation in contaminated waters, the location of drinking-water intakes, and the effectiveness of drinking-water treatment in achieving safe levels for regulated contaminants, and the number of persons affected.

The Corporate Toxics Information Project (CTIP) at UMass Amherst adjusts the RSEI Hazard data so that they use the most current TRI information available about the reporting year, in case companies revise earlier TRI reporting. In the case of downward revisions of pounds released, RSEI Hazards are adjusted based on the linear relation between pounds released and that release's RSEI Hazard. Upward revisions or new reports are noted but do not engender adjustments of the RSEI Hazard.

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, CTIP matches each facility to its parent company. Individual facilities are assigned to corporate parents on the basis of the most recent available ownership structure. CTIP then aggregates the RSEI scores for water releases of toxics by the facilities owned by each parent company, and ranked companies on this basis. The Toxic 100 Water Polluters Index reports the top polluters by company.