This website uses a scoring system to help identify environmental releases of toxic chemicals that are likely to pose the greatest risk to human health. This system adjusts the amount of a chemical that is released (in pounds) using a weighting factor (a chemical's "toxic equivalency potential"), so that chemical releases can be compared on a common scale that takes into account differences in toxicity and exposure potential.
The risk scoring system was developed by Drs. Edgar Hertwich and William Pease, in collaboration with colleagues at the School of Public Health at the University of California at Berkeley. Similar scoring systems are used by Minnesota's Pollution Control Agency, major chemical manufacturers like ICI, and national environmental agencies in Europe.
WHAT ARE TOXIC EQUIVALENCY POTENTIALS?
Toxic Equivalency Potentials (TEPs) indicate the relative human health risk associated with a release of one pound of a chemical, compared to the risk posed by release of a reference chemical. Information about the toxicity of a chemical (how much of it is required to cause harm) and its exposure potential (how much of it people are exposed to) are used to make this comparison. TEPs are based on a screening-level risk assessment that estimates the cancer and/or noncancer health risks associated with the total dose of a chemical that people will receive if one pound of that chemical is released to air or water in a model environment.
A reference compound is used to create a common denominator for chemicals that may cause cancer or noncancer chronic health effects. In this risk scoring system, all releases of carcinogens are converted to pounds of benzene-equivalents; all releases of chemicals that cause noncancer health effects are converted to pounds of toluene-equivalents.
TEPs for different chemicals vary tremendously, with values ranging over many orders-of-magnitude. The chemicals with the highest TEPs exhibit extreme toxicity and have physical/chemical characteristics that result in very high exposure potential. For example, a chemical like aldrin is a potent carcinogen (very small doses can increase cancer risks significantly). When released into the environment, it end up in plant produce and meat that people eat, resulting in a relatively high cumulative dose. As a result, releasing one pound of aldrin to air poses a comparable level of cancer risk to releasing 2,500 pounds of benzene.
HOW ARE RISK SCORES CALCULATED?
Risk scores are calculated for reported TRI releases to air or water by multiplying each chemicals' release quantity (in pounds) by the appropriate chemical-specific TEP. The resulting pounds of benzene-equivalents or toluene-equivalents are then summed to yield the overall cancer and noncancer risk scores. These scores provide a better indicator of the potential health risk posed by environmental releases than simply focusing on the total pounds of chemicals, because they take into account large differences in toxicity and exposure potential across chemicals.
THE LIMITS OF RISK SCORING USING TOXIC EQUIVALENCY POTENTIALS
TEPs are a tool for screening the potential human health impacts of environmental releases. TEPs are based on risk assessment values and environmental fate and exposure modeling that incorporate a number of assumptions that must be made to deal with scientific uncertainties. Scoring systems based on other assumptions (or focused on other environmental health concerns like acute toxicity to humans or ecotoxicity) would produce different rankings.
TEPs have been developed to support risk scoring in the absence of the extensive local data that are required to conduct a comprehensive risk assessment of a specific facility's environmental releases. TEPs do not address all the toxicity, environmental fate and transport and exposure factors that will affect the level of human health risks posed by chemical releases. In some situations, exposure routes that are responsible for high risk scores may not be relevant for a specific site (e.g., if there is no local consumption of fish contaminated by a chemical is surface water). Each chemical's TEP explanation page identifies the most significant exposure routes contributing to a substance's risk scores.
TEP-weighted releases do not characterize the estimated increase in health risk associated with a chemical exposure, and they cannot be combined with information about an exposed population to predict the incidence of adverse effects.
MORE ON RISK SCORING AND TEPS
Similar risk scoring systems
General introduction to how TEPs are calculated
Ongoing efforts to extend and improve TEPs
Recent changes to TEP values
HOW CAN I GET A COMPLETE LIST OF RISK SCORES?
Toxic equivalence potentials are available in a CSV file, which contains chemical name, CAS number, and TEP values (for cancer and noncancer risks from air and water releases).
CSV files can be easily opened by most word processing, spreadsheet or database applications (just be sure to let your application know you're opening a text file that is in comma-separated value format).