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Ammonium Perfluorooctanoate (C-8
EPA OPPT Draft Risk Assessment (Jan. 2005): This risk assessment did not calculate
RfD, RfC, or cancer slope factors. Calculated a number of margin of exposures (MOEs) -
the ratio of the NOAEL or LOAEL for a specific endpoint to the estimated human
exposure level. Based estimated human exposure levels on serum levels of C8 from
human biomonitoring studies.
Cancer: "Suggestive evidence of carcinogenicity, but not sufficient to assess human
carcinogenicity."
EPA's SAB (Feb 2005)• Reviewed EPA's Draft Risk Assessment — A draft report is
available (June 2005), but no final report. The majority of panel members concluded that
the experimental weight of evidence with respect to the carcinogenicity of C-8 was
stronger than in the draft document and suggested that C-8 is a "likely carcinogen in
humans." However, they would not calculate a slope factor for C-8.
West Vir ig nia: In 2002, West Virginia prepared a C-8 Assessment of Toxicity Team
(GATT) Report, resulting from a consent decree between the WV Environmental
Protection Agency and Du Pont as a result of finding C-8 in Lubeck, WV. This report
used a team of 10 expert toxicologists from TERA (a non-profit consulting firm) to
determine human health provisional risk factors for the oral and inhalation routes of
exposure and calculated risk -based human health protective screening levels (SLs) based
on EPA Region 9's standard methodology. This report summarizes all the relevant
studies and the methodology used to develop the following numbers:
• RfD: 0.004 mg/kg-day (based on York, 2002 two -generation
reproductive/developmental study in rats, used a benchmark dose level of 0.42
mg/kg-day divided by an uncertainty factor of 100).
• RfC: 1 µg/m3 (based on Kennedy et al., 1986 2-week inhalation study in rats,
used a benchmark concentration level of 0.33 mg/m3 divided by an uncertainty
factor of 300).
• Cancer assessment: An oral cancer slope factor of 0.31 per mg/kg-day was
developed for Leydig cell tumors, however the panel agreed that the RfD
should be the basis for the water and soil screening levels since they had low
confidence in the cancer value, high confidence in the RfD, and felt that the
RfD would be protective against the possible cancer effects (liver tumors) in
humans.
• SL (water): 150 ppb (p.34 of CATT report for equation used)
• SL (soil): 240 ppb (p.34 of CATT report for equation used)
• SL (air): 1 µg/m3 (p.34 of CATT report for equation used)
Minnesota: 3M produced C-8 and other perfluorochemicals at Cottage Grove, MN from
the late 1940s until 2002. The facility was used for a variety of industrial operations and
also includes a permitted hazardous waste incinerator. The Minnesota Pollution Control
Agency has been overseeing the site and entered into a consent decree with 3M in 1985
requesting that they conduct environmental monitoring and other activities. 3M found
groundwater contaminated with C-8 and also conducted medical monitoring of its
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employees. In 2002, the Minnesota Dept. of Health developed a Health -Based Value
(HBV) for drinking water and a Soil Reference Value (SRV) for C-8 as follows:
• HBV (drinking water) = 7 ppb (based on RfD of 0.001 mg/kg-day from
Thomford et al. 2001, 26 week study in monkeys showed liver effects, p.3 of
MDH memo for equation used to calculate HBV)
• Residential SRV = 30 mg/kg; Industrial SRV = 200 mg/kg (based on RfD of
0.001 mg/kg-day (as above), RfC of 2E-5 mg/m3 (based on 3 M generic
exposure guidelines for chemicals found to be carcinogenic in animals but with
unknown relevance to humans) and dermal absorption of 10% (Minnesota's
default for organic compounds). They did not present the equations they used to
derive the SRVs from the RfD, RfC, and dermal absorption factor.
In 2005, an ATSDR health consultation was prepared for the Minnesota Dept. of Health
at the Cottage Grove site. This health consultation summarized the available exposure
and health information on C-8, as well as the HBV of 7 ppb and SRV values. The
summary of this report states that the potential health impacts from C-8 releases cannot
be fully assessed at this time and additional investigation is needed.
Ohio: Ohio EPA has posted a letter on their website stating that C-8 was detected in some
water supplies in Ohio and cited the West Virginia preliminary action level of 150 ppb.
They stated that they are relying on the U.S. EPA to study C-8. They also stated that all
their detections of C-8 were below the West Virginia action level; however DuPont has
agreed to finance a program to provide bottled water to customers of the water system
that had the highest levels of C-8 detected.
New Jersey: No information was given on the New Jersey web site about C-8.
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More on Ammonium Perfluorooetanoate (C-8)
The Environmental Working_Group (EWG): I have reviewed the EWG's criticisms of the
West Virginia C-8 numbers. Their concerns are as follows:
• They believe that the West Virginia RfD does not contain an adequate safety
factor. They obtained a preliminary draft of provisional RfDs and Screening
Levels done by West Virginia that EWP posted on their website. In this draft, a
different study and a much larger safety factor were used in the calculations than
that used in the final RfD. The EWG does not take issue with the different study
or the basic safety factor used in the final RfD; their criticism centers on the fact
that in the calculations of the provisional RfD, an additional safety factor (called
a modifying factor) of 3 was applied to the RfD because C-8 has a long half-life
and the potential to bioaccumulate in humans. The EWP says that this additional
factor of 3 should have been applied, resulting in an allowable level of C-8 in
drinking water of 50 ppb, not 150 ppb.
Response: In December, 2002, EPA's Risk Assessment Forum completed its
"Review of the Reference Dose and Reference Concentration Processes" and the
panel recommended that the use of the modifying factor be discontinued, since
the purpose of the modifying factor is covered by the other uncertainty factors.
Thus, I do not believe that this criticism by the EWG is valid at this time.
They state that West Virginia ignored substantial background exposure from
contamination in air and food. They cite EPA's standard assumption that 20% of
a contaminant comes from drinking water and 80% comes from other sources,
and they state that had West Virginia used this assumption the allowable amount
of C8 in tap water would be 30 ppb, instead of 150 ppb.
Response: This is not an easy issue. It is true that, in the absence of better data,
EPA's Office of Water uses a standard assumption that 20% of a contaminant
comes from drinking water and 80% from other sources, in developing their
drinking water health advisories and other health levels. Also, Minnesota used a
20% source contribution from drinking water in their calculation of the Ground
water health -based value (HBV) from the RfD. However, West Virginia based
their water screening level on EPA Region 9 guidance. on deriving risk based
concentrations which used a different equation that did not factor in a 20% source
contribution. I have not been able to verify this guidance. I have searched EPA's
website and cannot find this guidance posted; however I have e-mailed the
consulting firm that was responsible for preparing West Virginia's guidance and
hopefully they will be able to direct me to it. However, at this point, I would
agree with the EWG that 20% is generally used by the EPA in these types of
calculations.
• Their last point is that West Virginia failed to set a protective level for infants
exposed. They say that a C-8 level protective of bottle-fed infants would
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incorporate 3 more safety factors, giving an allowable level for C-8 in water of
1.5 ppb.
Response: It is true that West Virginia did not set a level specifically protective of
children or infants. However, in EPA's "Review of the Reference Dose and
Reference Concentration Processes" (the same document cited above), the panel
stated that in order to be protective of children, they recommended that
developmental toxicity data be used, whenever possible, to set the RfD. In the
absence of such data, they recommended that the extra uncertainty factor for
database deficiencies should be applied, which they felt would be protective of
children. Since the C-8 RfD, as calculated by West Virginia, was based on a
developmental toxicity study which should be protective for children, I do not
recommend calculating a separate number for children. As stated by the EWG, it is
true that bottle-fed infants receive the highest dose of all drinking water
contaminants, pound -for -pound compared to any other segment of the population.
However, EPA generally only sets health based numbers for infants in particular
situations where this sensitive subpopulation is known to be significantly affected.
New Jersey: According to the September 8 letter from DuPont, New Jersey has
adopted an "Interim Guidance Criteria" of 5 ppb for C-8. This value is not based on a
risk assessment but comes from guidance for the New Jersey Ground Water Quality
Standards which state that in situations where no specific criterion exists for a
synthetic organic chemical, the State of New Jersey should establish an interim
criterion of 5 ppb for compounds identified as "having evidence of carcinogenicity".
Since C-8 has been shown to be carcinogenic in rats, New Jersey has set the interim
criterion at 5 ppb. DuPont states in their letter that they do not believe that these
findings are relevant to humans; however New Jersey has used the potential
carcinogenicity of the compound as the basis for setting their number.
Recommendation for C-8 Number: I believe that the C-8 RfD calculated by the State
of West Virginia of 0.004 mg/kg-day is a good number based on the state of -the -art
in risk assessment. It was calculated by a panel of scientists using EPA's latest
guidance. In addition, another Rf) (0.007 mg/kg-day) calculated by the West
Virginia panel based on a different study, as well as Minnesota's RfD (0.001 mg/kg-
day), are both in the same general range, further adding to my level of confidence in
this number.
However, I do not have the same level of confidence in West Virginia's screening
level for water of 150 ppb. As I said previously, I cannot find the guidance that it was
based on on EPA's website. One option (and the one that I favor) is to recalculate a
screening level, using the EPA method that was used by Minnesota to calculate their
Health -Based Value, and is also used by the EPA to calculate their Health Advisories
and other water health levels. The following is the formula and calculation:
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(RfD mpg -day) (relative source contribution) (1000 jig/mg)
Intake Rate (2 liters per day)/70 kg)
(0.004 mg/kg-day) (0.2) (1000 µ mg) = 27.6 µg/L or 28 ppb
0.029 L/kg/day
A second option is to use Minnesota's Health -Based Value of 7 ppb. I prefer this
number over West Virginia's because it is more conservative and it incorporates the
20% relative source contribution factor. In addition, ATSDR cites this value in their
February, 2005 health consultation for the 3M facility in Cottage Grove, Minnesota.
Although Minnesota's RfD was calculated based on an older study compared with
West Virginia's, the final RfD of the two states, 0.001 mg/kg-day for Minnesota, and
0.004 mg/kg-day for West Virginia, are very close to each other.
A third option is to use West Virginia's screening level of 150 ppb. This is my 3ra
choice because of the reasons outlined above. However, this number does have one
advantage over the others: it was calculated by a panel of experts and went through
review and comment. Thus, it does have a degree of support behind it that would not
be there using the number I calculated (even though the number I calculated does use
West Virginia's RfD) or Minnesota's value.
A fourth and final option is to use New Jersey's 5 ppb interim criteria. This is my last
choice because the number was not based on science; it is a default value that New
Jersey uses in the absence of chemical -specific standards. However, this is the most
conservative value and could be supported on this basis.
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