Step 4: Risk Characterization
Objective: Combine the intakes from the exposure assessment with the toxicity values from the toxicity assessment to identify contaminants of concern, pathways of concern, and media of concern for the receptor.
- Contaminants of Concern: These are contaminants for which the total cancer risk exceeds 1E-06 or the hazard quotient exceeds 1 across all exposure routes.
- Pathways of Concern: An exposure pathway is considered a pathway of concern if the cancer risk for that pathway exceeds 1E-06 or the hazard quotient exceeds 1 across all contaminants.
- Media of Concern: Environmental media are classified as media of concern when the total cancer risk for that medium exceeds 1E-06 or the hazard quotient exceeds 1 across all contaminants and pathways associated with the medium.
- Note: it is possible to have pathways of concern and media of concern without having a single contaminant of concern.
The risk characterization image presented below shows that the hazard quotient total for benzene in water is greater than 1 and the cancer risk is greater than 1E-06. Therefore, benzene is a contaminant of concern, water is a media of concern, and all exposure routes are pathways of concern. Xylene and acetone are not contaminants of concern for soil and air, respectively.
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