Revisiting the Formula Presentation

Report
Revisiting the Formula
62-777 CTL Workgroup
Contaminated Media Forum
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Formula Changes since 2005 Revision
•
•
•
•
Exposure Routes
Mutagenic factors
Extrapolation of routes
Default values
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Exposure Routes: Inhalation
Soil
62-777:
– The inhalation exposure derived as a
chronic, daily “air intake” (mg/kg-day).
– Inhalation toxicity values were “converted”
into similar units for the risk quantification
step.
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62-777
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Exposure Routes: Inhalation
Soil
• EPA
– RAGS F recommends using the concentration of
the chemical in air as the exposure metric (e.g.,
mg/m3)
– If the exposure scenario of interest is less than 24
hours per day, the scenario specific exposure time
(ET) in hours per day can be used in the equations
and the averaging time will be in units of hours
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Figure from EPA Regional Screening Levels for a
Residential Scenario, Non Carcinogen
Figure from EPA Regional Screening Levels for a
Worker Scenario, Carcinogen (Calculator only)
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Exposure Routes: Inhalation
Groundwater
• 62-777
– Oral exposure route only
• EPA
– Screening levels include an inhalation exposure for
volatiles
– Use RAGS Part F Methodology
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• 62-777 :
–
–
Exposure Routes: Dermal
Soil
Included in SCTL to be inclusive and to address those chemicals
for which dermal absorption is a significant exposure
62-777 has default dermal absorption factors (DAFs) for
organics and inorganics
• EPA :
– RAGS E guidance suggested reduction in the number of
chemicals that receive a quantitative assessment. Dermal-soil
absorption values given for ten compounds are provided in this
guidance.
– Regional Guidance suggests retaining default DAFs and using
updated chemical-specific DAFs from RAGS E
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Exposure Route: Dermal
Groundwater
• 62-777
– uses oral route of exposure only
• EPA
– now considers a dermal route for showering/bathing
and swimming using RAGS F methodology
– Dermal absorbed dose (mg/cm2) is calculated to
describe the absorption process when the chemical is
(1) non-steady state and (2) once steady state is
reached.
– Inorganics and organics treated separately
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Mutagenic Factors
• For chemicals that act with a mutagenic mode of
action for carcinogenesis quantify risk by
– Age-dependent adjustment factors (ADAFs)
– Age-specific slope factor (i.e. vinyl chloride)
• A list of 16 chemicals are considered mutagenic
(including many PAHs)
• EPA suggests using the following ADAFs
– Children 0 < 2 years
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– Children 2 to < 16 years 3
– Adults 16 and older
1
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Extrapolation of Routes
• 62-777
– Uses route-to-route extrapolation for inhalation and
dermal exposure routes
• EPA
– Route-to-route extrapolation for inhalation route of
exposure has been discontinued due to uncertainty in
making those adjustments
• The inhalation guidance has evolved such that route-toroute extrapolation is not needed for inhalation risk
– Route-to-route extrapolation for dermal route
continues
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Default Values
• Since the last 62-777 update, a new version of
the Exposure Factors Handbook has been
released
• Examples of Changes
– Ranges of BW and Water Ingestion rates
– Exposure Duration (Lifetime, Upper Bound
Residence Time, etc)
– Surface Area
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