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Revisiting the Formula 62-777 CTL Workgroup Contaminated Media Forum 1.

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Presentation on theme: "Revisiting the Formula 62-777 CTL Workgroup Contaminated Media Forum 1."— Presentation transcript:

1 Revisiting the Formula 62-777 CTL Workgroup Contaminated Media Forum 1

2 Formula Changes since 2005 Revision Exposure Routes Mutagenic factors Extrapolation of routes Default values 2

3 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. 3

4 62-777 4

5 Exposure Routes: Inhalation Soil EPA – RAGS F recommends using the concentration of the chemical in air as the exposure metric (e.g., mg/m 3 ) – 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 5

6 Figure from EPA Regional Screening Levels for a Worker Scenario, Carcinogen (Calculator only) Figure from EPA Regional Screening Levels for a Residential Scenario, Non Carcinogen 6

7 Exposure Routes: Inhalation Groundwater 62-777 – Oral exposure route only EPA – Screening levels include an inhalation exposure for volatiles – Use RAGS Part F Methodology 7

8 Exposure Routes: Dermal Soil 62-777 : – 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 8

9 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/cm 2 ) 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 9

10 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 10 – Children 2 to < 16 years 3 – Adults 16 and older 1 10

11 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-to- route extrapolation is not needed for inhalation risk – Route-to-route extrapolation for dermal route continues 11

12 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 12

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