POLLUTION LOCATOR|Using a Screening Level Risk Assessment to Assign Risk Scores

This website's risk scoring system is based on Toxic Equivalency Potentials (TEPs), which are calculated using CalTOX, an environmental fate and exposure model used by California regulatory agencies and highly regarded in the scientific community. The CalTOX model has been evaluated by the Integrated Human Exposure Committee of U.S. EPA's Science Advisory Board and described as "potentially the most advanced of all of the models reviewed."

THE CALTOX MODEL
CalTOX utilizes data on a pollutant's physical-chemical properties and the landscape characteristics of the environment receiving a release to model how that chemical will be distributed among seven connected environmental compartments (e.g., soil, water, air). CalTOX predicts the chemical concentrations in these compartments which will result from a continuous release of a pollutant, taking into account transport and transformation processes that affect the pollutant. CalTOX applies a multi-pathway exposure assessment model to these ambient concentrations to estimate the total chemical dose people may receive from a release. CalTOX produces an estimate of the average daily dose that is associated with a unit release of a chemical to air or water in a model environment, expressed in milligrams of a chemical per kilogram of body weight.

CalTOX was then used to combine estimated doses with Scorecard's risk assessment values to conduct screening-level risk assessments of releases of one pound of a chemical to air or water. In many cases, risk assessment values are available for only one of the three exposure routes CalTOX considers (ingestion, inhalation, and dermal contact). As a general rule, any available risk assessment value is applied to other routes of exposure lacking toxicity data , unless there is a clear toxicological rationale against making this assumption. This assumption of cross-route applicability is made to avoid treating chemicals as if they pose no health risk at all if exposures occur via a route that lacks data.

CalTOX characterizes potential cancer and noncancer risks using standard regulatory and scientific assumptions. For carcinogens, the increased risk of cancer associated with exposure is:

Added Lifetime Cancer Risk = Average Daily Dose from Exposure x Cancer Potency Value

For non-carcinogens, risks are characterized using a hazard index:

Hazard Index = Average Daily Dose from Exposure/Reference Dose

For chemicals that possess the physical-chemical and toxicity data required to run CalTOX, this method yields a set of up to four health risk estimates associated with a unit release of a chemical. This set can include cancer and/or noncancer risks posed by a unit release to air, and cancer and/or noncancer risks posed by a unit release to water.

CALCULATING TEPS USING THE RISK ESTIMATES FROM THE CALTOX MODEL
Once CalTOX has produced estimates of the health risks posed by a unit release of a chemical to air or water, these can be used to calculate TEPs for a chemical. TEPs are simply the ratio of the risk posed by a one pound release of chemical X to the risk posed by a one pound release of a reference compound. Separate TEPs are calculated for chemical releases to air and water.

For carcinogens, TEPs are expressed as pounds of benzene-equivalents:

TEP = [Added Cancer Risk/Unit Release of Chemical X]/[Added Cancer Risk/Unit Release of Benzene]

For noncarcinogens, TEPs are expressed as pounds of toluene-equivalents:

TEP = [Hazard Index/Unit Release of Chemical X]/[Hazard Index/Unit Release of Toluene]

MORE
On the assumptions made to deal with data gaps and modeling issues.

Technical details of how media and health endpoint-specific TEPs are calculated:
Cancer Risk Score - Air Releases
Cancer Risk Score - Water Releases
Noncancer Risk Score - Air Releases
Noncancer Risk Score - Water Releases

REFERENCES
Hertwich, E.G., S. Mateles, W.S. Pease, and T. McKone. Human toxicity potentials for life cycle assessment and Toxics Release Inventory risk screening. Environmental Toxicology and Chemistry 20(4):928-939. 2001.

Hertwich, E.G. and T.E. McKone. The spatial scale of pollutants in multimedia models and its implications for the potential dose. Environmental Science & Technology 35(1):142-148. 2001.

Hertwich, E.G., T.E. McKone, and W.S. Pease. A systematic uncertainty analysis of an evaluative fate and exposure model, Risk Analysis 20(4):437-452. 2000.

Hertwich, E.G. Toxic Equivalency: Addressing Human Health Effects in Life Cycle Impact Assessment. A dissertation submitted for the degree of Doctor of Philosophy in Energy and Resources in the Graduate Division of the University of California, Berkeley. 1999. http://www.is4ie.org/dynamic/listing.php?id=21
http://www.tev.ntnu.no/edgar.hertwich/CV.html

Hertwich, E.G., T.E. McKone, and W.S Pease. Parameter uncertainty and variability in evaluative fate and exposure models. Risk Analysis 19(6):1193-1204. 1999.

Hertwich, E.G., W.S. Pease, and T.E. McKone. Evaluating Toxic Impact Assessment Methods: What Works Best? Environmental Science & Technology 32(5): 138A -145A. 1998.

Science Advisory Board, U.S. Environmental Protection Agency. Human Exposure Assessment: A Guide to Risk Ranking, Risk Reduction and Research Planning. EPA/SAB/IAQC-95-005. Government Printing Office, Washington, DC. 1997.

McKone, T.E. CalTOX, A Multimedia Total Exposure Model for Hazardous-Waste Sites UCRL-CR-111456PtI-IV, U.S. Department of Energy, Lawrence Livermore National Laboratory, Government Printing Office, Washington, DC. 1993.

CalTOX Resources