2009-05-19_REVISION - M1977416 ‎(29)‎

• Permit No: M1977416
• IBM Index Class Name: REVISION
• Doc Date: 5/19/2009
• Doc Name: EPP‎(AM-01)‎ Att 4: Bioavailability; Att 5: Water Bal; Att 6: Percolation; Att 7: Lab Rpts. ‎(part 4)‎
• From: Denison Mines
• To: DRMS
• Type & Sequence: AM1
• Email Name: RCO
• Media Type: D
• Archive: No

The site-specific relative bioavailability (RBA) can be used to adjust RMC screening values for a
site by modifying the reference dose (RfD) and/or oral slope factor (SFo) for arsenic to account •
for differences in absorption between arsenic ingested in soil as follows (EPA 1997):
HfAlefavir
1VREA and 5d1'Qadf ? S"defoulr X REA
Given that the RBA value is less than one, the adjusted RfD value will increase and the SFo will
decrease. Reviewing the noncarcinogenic and carcinogenic RMC calculations presented above,
it can be readily seen that the use of a site-specific bioavailability factor will adjust the RMC
values upward as discussed in the BLM guidance document (BLM 2004).
It should be noted that for arsenic, the IVBA test conditions have not yet been optimized.
Accordingly, EPA Region 8 recommends a weight-of-evidence approach that combines the in
vitro studies and geochemical speciation results (e.g., via use of an electron microscope) with
the in vivo and geochemical results from the library of in vivo studies on arsenic bioavailability
(ESTCP 2008). For example, if RBA for arsenic in site soils was observed to be 20 percent, and
electron microprobe analysis showed geochemistry consistent with low bioaccessibility, results
would strongly support downward adjustment of the bioavailability term, which would result
in increase RMC This approach was utilized to assess RBA for arsenic at the Sunday Mines
Group.
References
CDM Inc. (CDM). 2009. Telephone Conversation and Email, Mark Nelson (CDM) and Dr. Karl Ford
(BLM). January 6.
SERDP and ESTCP Expert Panel Workshop on Research and Development Needs for Understanding
and Assessing the Bioavailability of Contaminants in Soils and Sediments. November.
U.S. Bureau of Land Management (BLM). 2004. Rick Management Criteria for Metals at BLM
Mining Sites. Technical Note 390 Rev. October.
U.S. Environmental Protection Agency (EPA). 1997. Relative Bioavailability of Arsenic in Mining
Wastes, EPA Region 8 Document. December.
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