UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

					April 4, 2012

MEMORANDUM

SUBJECT:	Risk Assessment of Single Exposures to HFO-1234yf (P-07-0601)

FROM:	Ernest V. Falke, Ph.D.

		Senior Scientist

		Risk Assessment Division (7403M)

		Office of Pollution Prevention and Toxics

THRU:	Oscar Hernandez, Acting Branch Chief

		Science Support Branch

		Risk Assessment Division (7403M)

		Office of Pollution Prevention and Toxics

TO:		Ken Moss

		New Chemicals Notice Management Branch

		Chemical Control Division (7405M)

		Office of Pollution Prevention and Toxics

Contents

  TOC \o "1-3" \h \z \u    HYPERLINK \l "_Toc320607205"  Background:	 
PAGEREF _Toc320607205 \h  1  

  HYPERLINK \l "_Toc320607206"  Discussion and Conclusions:	  PAGEREF
_Toc320607206 \h  2  

  HYPERLINK \l "_Toc320607207"  Area Under the Curve Assessment	 
PAGEREF _Toc320607207 \h  2  

  HYPERLINK \l "_Toc320607208"  Concentration Dependent Risk Assessment	
 PAGEREF _Toc320607208 \h  3  

  HYPERLINK \l "_Toc320607209"  Conclusions	  PAGEREF _Toc320607209 \h 
3  

  HYPERLINK \l "_Toc320607210"  Hazard Assessment from Single Exposures:
  PAGEREF _Toc320607210 \h  3  

  HYPERLINK \l "_Toc320607211"  Exposure Assessment from Single
Exposures in Do-It-Yourself (DIY) Secenarios:	  PAGEREF _Toc320607211 \h
 4  

  HYPERLINK \l "_Toc320607212"  Highest TWA	  PAGEREF _Toc320607212 \h 
5  

  HYPERLINK \l "_Toc320607213"  Highest peak exposures	  PAGEREF
_Toc320607213 \h  6  

  HYPERLINK \l "_Toc320607214"  References:	  PAGEREF _Toc320607214 \h 
7  

  HYPERLINK \l "_Toc320607215"  APPENDECES:	  PAGEREF _Toc320607215 \h 
8  

  HYPERLINK \l "_Toc320607216"  APPENDIX 1. Review of rabbit one hour
inhalation study.	  PAGEREF _Toc320607216 \h  8  

 

Background:

	One of the use scenarios for HFO-1234yf is from Do-It-Yourself (DIY)
individuals charging their vehicle air conditioning system.  In order to
assess this risk, data on short duration exposures related to this
scenario are required from both toxicology and exposure studies.  The
hazard assessment section below discusses the relevant toxicity studies
and presents a brief description of the exposure study.  The exposure
results are presumed to be accurate for the purpose of this assessment.

Discussion and Conclusions:

	It is important to note that this assessment is valid ONLY FOR SINGLE,
SHORT DURATION EXPOSURE SCENARIOS THAT DO NOT REPEAT OVER A NUMBER OF
DAYS.

	In assessing risk from different exposures one must consider the mode
of action.  Typically the assumption is made that the toxicity is based
upon the total dose delivered during a daily exposure.  This presumes
that the area under the curve (AUC) is the determining factor.  Such
toxicants follow Haber’s Rule where concentration x time = constant
(c*t=k).  In this case a high exposure for a short duration or a low
exposure for a long duration can have the same toxic result as long as
their products are the same.  This mode of action is presumed in the
time weighted approach (TWA) scenario discussed in the Exposure
Assessment section.

	A concentration dependent mode of action depends on exceeding a
specific level in the blood to exhibit toxicity.  One example would be
anesthetic agents.  As long as blood levels are below a threshold
concentration, narcosis will not occur, regardless of duration of
exposure.  Another example would be cardiac sensitization where short
duration exposures to high levels can cause cardiac sensitization within
minutes whereas the same dose averaged over an hour would not result in
a toxic effect.

	Typically the AUC mode of action is assumed when performing risk
assessments.  A concentration dependent mode of action may be utilized
where there are data to that effect.  For HFO-1234yf no toxicity was
seen in the one hour exposure of rabbits to 0, 50,000, and 100,000 ppm
discussed below.  The Human Equivalent Concentration of the 100,000 ppm
exposure in rabbits is 190,000 and will be utilized for this assessment.
 No effect was seen at 100,000 ppm exposure in rabbits.  If higher
exposures were tested, it is unknown whether toxicity would be observed
before hypoxia from low levels of oxygen occurred.  Since no toxicity
was observed, it is not possible to differentiate between a potential
AUC or concentration dependent mode of action so a worst case analysis
will be done for each mode of action.

Area Under the Curve Assessment

The No Observed Adverse Effect Level (NOAEL) HEC of the rabbit study is
190,000 ppm for 60 minutes of exposure.  This equates to an AUC of
11,400,000 ppm-min (190,000 ppm * 60 min).  The exposure in the exposure
scenario (“full, upright can (340 g) released at LS Service Port with
hood half open and condenser fan off” ) with the highest TWA for 30
minutes was 1,789 ppm.  Since Figure 17 showed exposure levels were
about the same from 3 to 60 minutes an exposure of 1,789 ppm will be
assumed for 60 minutes for a worst case scenario.  The cumulative
exposure AUC is 107,340 ppm-min (1,789 ppm * 60 min).  The MOE for the
worst case scenario is 11,400,000 ppm-min/107,340 ppm-min = 106.

For this mode of action and chemical the recommended MOE is 30. 
Typically an MOE of 100 is recommended; a factor of ten for potential
differences in species susceptibility and a factor of 10 for differences
between individual human susceptibility.  The factors of ten comprise
uncertainties due to differences in pharmacokinetics and
pharmacodynamics.  Since pharmacokinetic modeling was used to estimate
the HEC, the pharmacokinetic component of the interspecies uncertainty
is known, and the interspecies factor of 10 is reduced to 3.  This
results in a total MOE of 30.

The MOE of 106 is acceptable because it exceeds the recommended MOE of
30. The assessment is inherently conservative because no toxicity was
identified at the highest dose tested; it is unlikely that the user
would remain for an hour in the “Passenger side under the engine”
location after releasing a whole can of refrigerant; and it is unknown
whether higher exposures would have resulted in toxicity being observed
before hypoxia set in.

Concentration Dependent Risk Assessment

For HFO-1234yf there are no identified concentration dependent modes of
action.  HFO-1234yf is in a class of chemicals that sometimes cause
cardiac sensitization.  It is replacing HVC-134a which is a cardiac
sensitizer.  However, HFO-1234yf has been tested at 120,000 ppm and did
not cause cardiac sensitization.  It is considered negative in this
test.  For comparison, the HEC of this concentration is 228,000 ppm.

Conclusions

Toxicity studies of HFO-1234yf in rabbits and dogs did not show signs of
toxicity or cardiac sensitization at HEC exposure concentrations that
are borderline hypoxic in humans.  Using an AUC mode of action the
calculated MOE for worst case exposure scenarios is 106, higher than the
30 recommended.  There are no risk concerns identified for the exposure
scenarios presented in Honeywell, 2012.  The only potential for toxicity
due to short duration (on the order of one hour), single exposures is if
exposure levels reach high enough levels to deplete oxygen.  These
levels were not reached in the Honeywell, 2012 exposure scenarios.  IT
IS IMPORTANT TO NOTE THAT THIS ASSESSMENT ONLY ADDRESSES SHORT DURATION
EXPOSURES THAT ARE NOT REPEATED OVER A PERIOD OF DAYS.

Hazard Assessment from Single Exposures:

	This discussion will focus on the one hour acute toxicity study in
rabbits (Honeywell, 2011) because the rabbit is the most sensitive
species.  The full report on the study is included in Appendix 1.  The
reason to focus on the rabbit is the observation that repeated exposures
can cause cardiac histopathology and death in pregnant rabbits.  In
order to address the toxicity of HFO-1234yf from single short duration
exposures, Honeywell, 2011 exposed pregnant and non-pregnant female
rabbits as well as males to 0, 50,000, and 100,000 ppm for one hour. 
Animals were necropsied 14 days post-exposure and histopathology
performed on heart, kidneys, liver and lungs.   No treatment related
differences were noted between control and exposed animals.  The No
Observed Adverse Effect Level (NOAEL) for this study is 100,000 ppm
exposure for 1 hour.  The Human Equivalent Concentration (HEC) of the
NOAEL is the exposure level required to raise blood levels in humans to
those seen in the rabbit at 100,000 ppm. Based on earlier work the HEC
is 190,000 ppm.

	For this class of compounds, cardiac sensitization may be of concern. 
HFO-1234yf is not a cardiac sensitizer at the highest dose tested of
120,000 ppm (DuPont, 2010).  HFO-1234yf is replacing HFC-134a.  It is
interesting to note that HFC-134a is a cardiac sensitizer in dogs at
75,000 ppm but not 50,000 ppm (NRC, 2002).  Thus, for single high
exposure scenarios, HFC-134a is a greater risk than HFO-1234yf.

Exposure Assessment from Single Exposures in Do-It-Yourself (DIY)
Secenarios:

	Honeywell, 2012 conducted experiments with HFC-134a to determine
exposure levels in the event a DIY user did not properly connect the
refrigerant can and the entire contents were released in a short period
of time.  This section will discuss the data used for the risk
assessment.  The validity of the study is determined by the exposure
experts.

	For the purpose of this exposure assessment, two of the six test cases
will be considered.  They give either the highest time weighted average
(TWA) for 30 minutes or the highest peak exposures.  Exposure
concentrations were measured at eight locations.  Results below are
given for the highest concentration measured.

	Highest TWA

Test case #6-“full, upright can (340 g) released at LS Service Port
with hood half

open and condenser fan off.”  These test conditions gave the highest
30 minute TWA of 1,789 ppm at the Passenger Side Under Engine location
(see Figure 17 below from the report).  The highest peak concentration
was approximately 15,000 ppm, less than Test Case #4 discussed below. 
The peak was reached within approximately one minute, decreased to near
background levels within about 2 minutes and then increased to
approximately 2,000 ppm for about 60 minutes before falling to
background levels.

Highest peak exposures

Test case #4- “full, inverted cans (2 cans, 680 g) released at LS
Service Port with hood open half and condenser fan off.”  In this case
two cans were released within a minute of each other giving two peaks
with maximum concentrations being achieved within approximately 30
seconds of opening the can.  The maximum peaks were approximately 30,000
ppm each.  The exposure levels rapidly decreased to near background
levels after a total duration of 180 seconds at the Driver Side Under
Engine location (see Figure 15 below from the report).  The highest time
weighted average was 1,030 ppm, less than seen with test case #6.

References:

DuPont. 2010. Material Safety Data Sheet. ,23,3,3-Tetrafluoro-1-propene
(Research Sample).   HYPERLINK
"http://msds.dupont.com/msds/pdfs/EN/PEN_09004a2f806513e4.pdf" 
http://msds.dupont.com/msds/pdfs/EN/PEN_09004a2f806513e4.pdf 

Honeywell. 2011. HFO-1234yf: A 2-phase inhalation screening study and
single exposure study in rabbits via whole-body inhalation exposure
(GLP).

Honeywell. 2012. Refrigerant exposure to service personnel or DIYers due
to leakage of 12 oz charging cans or “small cans”. Experiments
Conducted at Honeywell’s Research Laboratory in Buffalo, NY USA. 14
pp.

NRC. 2002. Acute Exposure Guideline Levels for Selected Airborne
Chemicals. 1,1,1,2-Tetrafluoroethane. (HFC-134a) Acute Exposure
Guideline Levels.

APPENDECES:

APPENDIX 1. Review of rabbit one hour inhalation study.

Reviewer:

Ernest V. Falke

April 18, 2011

Reference/Report:

HFO-1234yf: A 2-PHASE INHALATION SCREENING STUDY AND SINGLE EXPOSURE
STUDY IN RABBITS VIA WHOLE-BODY INHALATION EXPOSURE (GLP)

Study Type:

	One hour inhalation study in pregnant rabbits.

Study Date:

	February 28, 2011

Test Material:

	Name:

		HFO-1234yf (2,3,3,3 – Tetrafluoropropene)

	CAS No:

		754-12-1

	Structure:

Test Material Composition:

	HFO-1234yf was administered as a gas and was 99.99% pure.

Sponsor:

Honeywell

101 Columbia Road

PO Box 2245R

Morristown, New Jersey 07962-1057

Test Lab:

Huntingdon Life Sciences

100 Mettlers Road

East Millstone, New Jersey 08875-2360

Materials Methods/Results

	In earlier developmental toxicity studies in rabbits, lethality of the
dams was observed after multiple exposures.  While deemed unlikely, the
outcome of lethality from a single exposure was not known.  This
experiment was designed to address that question.

	New Zealand White rabbits were exposed to target concentrations of 0;
50,000; and 100,000 ppm for 1 hour and observed for 14 days post
exposure.  Analytical concentrations for male/female were 0/0;
45,000/47,000; and 100,000/102,000 respectively.  Five males and 6
pregnant females were exposed at each dose.  Five non-pregnant females
were exposed at 0 and 100,000 ppm.

	No mortality was observed for any condition of the experiment.  No
differences in body weight over the experiment, gross pathology, and
histopathology (control and high dose) of heart, kidney, liver and lung
were observed.

	Metabolites were analyzed from urine samples taken at 12 hour intervals
after exposure up to 48 hours post-exposure.  Metabolite patterns were
similar in all exposed groups except an unidentified metabolite
approximately twice as much in females (both groups) as males.

	In conclusion, a single exposure of pregnant rabbits to high levels of
HFO-1234yf (100,000 ppm) will not cause lethality, changes in body
weight, or pathology and histopathology of major organs.  The cause of
lethality in dams exposed multiple time in developmental toxicity
studies remains unknown.

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