MEMORANDUM

To:	Margaret Sheppard; U.S. EPA

Cc:	Monica Shimamura, Bella Maranion; U.S. EPA

From:	Neha Mukhi, Kara Altshuler, Reva Rubenstein, Mark Wagner; ICF
International

Date:	September 11, 2009

Re:	Recommendation for an Acceptable Exposure Limit for C6-
Perflouroketone

(EPA Contract EP-W-06-008, TO 038, Task 6)



This memorandum recommends Acceptable Exposure Limit (AEL) for C6-
Perflouroketone and summarizes toxicity information used to develop it. 

Please contact Mark Wagner (202) 862-1155 with questions or comments.

Development of AEL for C6-Perfluoroketone

ICF has developed a revised AEL for C6-perfluoroketone based on a review
of recent additional studies in the C6-perfluoroketone toxicity
database.  These studies are

Sub-chronic (13-week) inhalation toxicity study with MTDID 5789 in rats
(TNO, 2007)

Reproduction/ developmental toxicity screening text after inhalatory
exposure to MTDID 5789 in rats (TNO, 2007) 

In the subchronic inhalation study, groups of 10 each male and female
Wistar rats were exposed to 0, 300, 1000 or 3000 ppm (target
concentrations) C6-perfluoroketone for 6 hours/day, 5 days/week for 13
weeks.  In addition, two recovery groups of 10 each male and female rats
were exposed to 0 or 3000 ppm of the test compound as with the main
groups of the study and were allowed to recover for 28-days post
exposure.  This recovery period was intended to investigate the
reversibility of noted adverse effects.

The study evaluated typical parameters for subchronic toxicity studies
including clinical/cageside observations, food consumption/efficiency,
body weight changes, hematology/clinical chemistry, localized effects,
gross necropsy, organ changes, and organ histopathology.  No
exposure-related effects were noted in the following parameters:
clinical/cage side observations, food consumption/efficiency, body
weight, food consumption or opthalmoscopy.  In addition, no local
effects were noted.

C6 perfluoroketone did induce effects on the liver (either shown
directly or via changes in clinical chemistry endpoints) in male rats in
all exposure groups and in female rats in the high-concentration group. 
These effects included increased relative liver weight in all male
exposure groups, increased albumin/globulin ratio in all exposure groups
and the following effects in the mid- and  high-concentration groups: 
decreased plasma cholesterol, increased alkaline phosphatase, and
increased albumin content.  Females in the mid- and high-concentration
groups had increased albumin content, while those in the
high-concentration group alone had increased albumin/globulin ratio and
relative liver weight.  Histopathological changes observed in male rats
included accumulation of eosinophilic granules in hepatocytes in mid-
and high-concentration groups (one high-concentration male also showed
hypertrophy cell foci [enlargement of cell size], presumably as a result
of the increased metabolic response to the exposure compound).  These
results were accompanied by an increase in the activity of peroxisomal
oxidizing enzyme activity (acyl CoA-oxidase) related to peroxisomal
proliferation, predominantly in males at all exposure concentrations,
but also in females in the high-concentration group.   The liver effects
were not noted in recovery rats after 28 days post-exposure, with the
exception of the persistence of slight or very slight increased
eosinophilic granulation in 4/10 male rats at 3000 ppm.  The study
authors identified a NOEL of 1000 ppm for female rats, were unable to
define a NOEL for male rats, and identified a NOAEL/LOAEL of 300 ppm for
male rats.

The subchronic study essentially validated the results of the previous
28-day inhalation study in rats using C6-perfluoroketone, which
indicated that peroxisomal proliferation resulted from rat exposure to
concentrations of 1000 ppm and higher. 

As stated in the 13-week study report, peroxisomal proliferation is a
liver response observed in rodents, predominantly male rats, in response
to exposure to certain compounds.  Responses in humans are poor or
absent following exposure to peroxisomal proliferators, due to genetic
differences in the elements necessary to respond to these compounds. 
For this reason, peroxisomal proliferation is considered to be a
species-specific response with more limited application to humans.  For
this reason, ICF has chosen the 1000 ppm exposure concentration in the
13-week study as the point of departure for developing the AEL for
C6-perfluoroketone.

A revised AEL has been developed as follows:

	1000 ppm x 6 hours (exposure of rats)/8 hours (workday) = 750 ppm (HEC)

750/3 (UF) = 250 ppm (AEL)

One uncertainty factor of 3 has been applied to account for interspecies
differences between rats and humans.  No other UFs have been applied. 
The database is comprehensive, including a one-generation reproductive
and developmental toxicity study in rats which showed no adverse effects
at any concentration tested up to 3000 ppm.  Therefore, the original UF
of 10 applied for database limitations in the initial AEL development
has been removed.  

We are aware that we have chosen as a point of departure an exposure
concentration that results in liver effects in the male rat (e.g., 
histopathological changes in the liver and increased relative liver
weight).  Studies show that rats and mice appear to be more sensitive
than humans to peroxisomal proliferators.  That is not to say that
humans are not responsive; they are responsive, for example, to a
certain class of pharmaceuticals known as hypolipidemic fibrates, such
as clofibrate, via activation of the peroxisome proliferator activated
receptor (PPAR).  There has been concern in the past with peroxisomal
proliferation in compounds that induce liver cancer in rodents and the
possibility that cancer induction is a concern with regard to humans
(e.g., DEHP, TCE, etc.; Melnick, 2001; Keshava and Caldwell, 2006). 
However, these compounds are much less potent as PPAR receptor agonists
than the hypolipidemic fibrates.  Further, these agents also induce
biological effects in animal models that appear to occur independently
of peroxisome proliferation.  It does not appear that C6-perfluoroketone
induces any other relevant toxicological effects in the rat other than
peroxisome proliferation in the liver and its associated effects. 
Therefore, we feel that establishing the AEL for C6-perfluoroketone at a
maximum of 250 ppm is appropriate and supported by the science.

 

References

Keshava N and JC Caldwell (2006) Key issues in the role of peroxisome
proliferator-activated receptor agonism and cell signaling in
trichloroethylene toxicity.  Environ Health Perspect 114(9):1464-1470.

Melnick RL (2001) Is peroxisome proliferation an obligatory precursor
step in the carcinogenicity of di(2-ethylhexyl)phthalate (DEHP)? Environ
Health Perspect 109(5):437-442.

