IMPORTANT NOTE
Risk estimates are calculations based on models - they are useful for ranking purposes but are not necessarily predictive of any actual individual's risk of getting cancer or other diseases.
SCORECARD'S RISK ASSESSMENT METHODS
Scorecard utilizes conventional risk assessment methods to estimate the potential health risk associated with reported air releases from manufacturing facilities. In general, Scorecard's methods are in accordance with EPA's Cancer Risk Guidelines and California's AB 2588 Health Risk Assessment Guidelines. To generate screening-level health risk estimates, Scorecard combines its risk assessment values with chemical doses estimated from ambient air concentrations using standard exposure assessment assumptions.
Cancer risks are assessed for each pollutant identified as a suspected or recognized carcinogen by multiplying the estimated dose of a chemical that a average individual would receive from its predicted concentration by its cancer potency to derive an upper bound estimate of added cancer risk. Cancer risks for each hazardous air pollutant were assumed to be additive and were summed together to derive an estimate of total added lifetime cancer risk.
ASSUMPTIONS AND CAVEATS
Conventional health risk assessment involves a number of important uncertainties. Risk assessment methods rely on the use of assumptions to address gaps in scientific understanding and data, which can lead to mis-estimation of health risks. Some assumptions err on the side of health protection and may result in overestimation (e.g., presuming animal carcinogens are potential human carcinogens). Other assumptions may result in underestimated health risk (e.g., presuming all people have equal susceptibility to toxicants).
Scorecard's risk estimates assume that a large population with a standard distribution of age and other demographic factors is exposed for a lifetime. Because the actual demographic features and exposure duration for a particular population may vary significantly from these assumptions, it is not appropriate to use these figures to make projections of the numbers of additional cancer cases that a particular local population will experience. Scorecard's risk estimates provide a screening-level perspective on the potential magnitude of public health impacts from a facility, which are useful for comparative purposes. They are not necessarily predictive of any one actual person's risk of getting cancer.
Several important caveats apply to Scorecard's estimates of cancer risks from manufacturing facilities:
1) Scorecard's rely on U.S. EPA estimates of exposures to the chemicals in question, which are based on computer models rather than direct measurements.
2) Facility risk estimates driven by metals or metal compounds are subject to greater uncertainty because Toxic Release Inventory reporting data do not reflect the specific chemical identify of metal compounds. Certain metals are only carcinogenic if present in a specific valence state (for example, hexavalent chromium vs. trivalent chromium) or as specific compounds (for example, nickel). In these cases, Scorecard utilizes the best available risk assessment value (for example, a cancer potency value for chromium compounds). In order to accurately characterize cancer risks from metals, it is necessary to obtain additional information from a facility regarding the chemical nature of the metals and metal compounds it releases.
3) Facility risk estimates assume that reported TRI chemical releases to air and resulting ambient concentrations remain constant over an exposed individual's 70 year lifespan. If chemical releases are reduced in the future, cancer risks attributable to a specific facility will be lower than predicted. If an individual moves from a polluted to a cleaner area, cancer risks will also be lower than predicted.
4) Facility risk estimates do not address the following environmental health concerns: noncancer health effects, acute health effects associated with short-term, periodic exposures to higher levels of modeled chemicals, and ecological effects.
