Guidance for Conducting Risk Assessments and Related Risk ...

Equation 1. A single chemical within a single exposure route:
HQ i =
CDIi
RfDi
where: HQi
CDIi
RfDi
Equation 2. All chemicals within a single exposure route:
HI
n
p = ∑ HQi
i=
1
where: HIp
HQi
Equation 3. All chemicals over all exposure routes:
HI
= ∑
=
n
total HIp
p 1
where: HItotal
HIp
Equation 4. A single chemical within a single exposure route:
ELCR i = CDIi
× SFi
where: ELCRi
CDII
SFi
Equation 5. All chemicals within a single exposure route:
ELCR
n
p = ∑ ELCRi
i=
1
where: ELCRp
ELCRi
Equation 6. All chemicals over all exposure routes:
ELCR
n where: ELCRtotal
total = ∑ ELCRp
p=
1
ELCRp
=
=
=
=
=
=
=
=
=
=
=
=
=
=
The hazard quotient, an estimate of the systemic
toxicity posed by a single chemical.
The estimate of chronic daily intake (or absorbed dose
for some exposure routes) from the exposure
assessment.
The chronic reference dose for administered or
absorbed dose, as appropriate.
The pathway hazard index, an estimate of the systemic
toxicity posed by all chemicals within a single exposure
route.
The individual chemical hazard quotients for chemicals
reaching the receptor through a single exposure route
(from Eq.1).
The total hazard index, an estimate of the systemic
toxicity posed by all chemicals over all routes.
The pathway hazard indices from Eq.2
The chemical-specific excess cancer incidence.
The estimate of chronic daily intake (or absorbed dose)
from the exposure assessment.
The slope factor for administered or absorbed dose.
The pathway-specific excess cancer incidence.
The chemical-specific excess cancer incidence from Eq.
4.
The total excess cancer incidence posed by all
chemicals over all routes.
The pathway-specific excess cancer incidence.
4.4.1 Selecting Scenarios, Pathways, and Chemicals of Concern (COCs)
The selection of scenarios, pathways, and COCs follows the guidelines outlined by the EPA Region
IV in Office of Technical Services Supplemental Guidance to RAGS: Region 4 Bulletins (EPA 1996).
These guidelines are outlined below.
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