Page 1 of 9 **UNITED STA TES ENVIRONMENTA**  **L PROTECTION A GENCY**  WA SHINGTON, 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 ( 7403 M ) 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 Background: ................................ ................................ ................................ ................................ .............. 1 Discussion and Conclusions: ................................ ................................ ................................ .................... 2 Area Under the Curve Assessment ................................ ................................ ................................ ....... 2 Concentration Dependent Risk Assessment ................................ ................................ ......................... 3 Conclusions ................................ ................................ ................................ ................................ ........... 3 Hazard Assessment from Single Exposures: ................................ ................................ ............................ 3 Exposure Assessment from Single Exposures in Do - It - Yourself (DIY) Secenarios: ............................... 4 Highest TWA ................................ ................................ ................................ ................................ ........ 5 Highest peak exposures ................................ ................................ ................................ ......................... 6 Refer ences: ................................ ................................ ................................ ................................ ................ 7 APPENDECES: ................................ ................................ ................................ ................................ ........ 8 APPENDIX 1. Review of rabbit one hour inhalation study . ................................ ................................ 8 Background: O ne of the use scenarios for HFO - 1234yf is from Do - It - Yourself (DIY) individuals charging their vehicle air conditioning s ys tem. In order to assess this risk, data on short duration exposures related to this scenario are required from both toxicology and e xposure studies. The hazard assessment OFFICE OF CHEMICAL SAFETY AND POL L UTION

PREVENTIONPage 2 of 9

section below discusses the relevant toxicity stud ies 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 Conc lusions: It is important to note that this assessment is valid ONLY FOR SI NGLE, 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. Ty picall y the a ssumption 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 act ion 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, narco sis 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 resul t in a toxic effect. Ty

pically 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 exposur e 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 e xposures were tested, it is unknown whether toxicity would be observed before hy p oxia from l ow levels of ox ygen 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 anal ys is 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 we re 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/107,3 40 ppm - min = 106. For this mode of action and chemical the recommended MOE is 30. Ty pically 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 susc eptibility . 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 ofPage 3 of 9

the interspecies uncertainty is known, and th e 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 . T he assessment is inherentl y conservative because no toxicity was identified at the highest dose te sted ; 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 h ypox ia set in. Concentration	Dependent	Risk	Assessment For HFO - 1234yf there are no identified concentration dependent modes of action. HFO - 1234y f is in a class of chemicals that sometimes cause cardiac sensitization. It is replacing HVC - 134a which is a card iac 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 hy poxic 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 Honey

well, 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 Honey well, 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 E xposures: This discussion will focus on the one hour acute toxicity study in rabbits (Honey

well, 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 obs ervation 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, Honey well, 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 day s post exposure and histopathology performed on heart, kidney s, 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. Itis int eresting 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.Page 4 of 9

Exposure Assessment from Single Exposures in Do - It - Yourself (DIY) Secenarios: Honey well, 2012 conducted experiments with HFC - 134a to determine exposure levels in the event a DIY user did not properl y connect the refrigerant can and the entire contents were release d in a short period of time. This section will di scuss the data used for the risk assessment. The validity of the study is determined b y 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.Page 5 of 9

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 leve ls.Page 6 of 9 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.” Inthis case two cans were released within a minute of each other giving two peaks with maximum conce ntrations 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 Un der 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.Page 7 of 9

References: DuPont. 2010. Material Safety Data Sheet. ,23,3,3 - Tetrafluoro - 1 - propene (Research Sample). http://msds.dupont.com/msds/pdfs/EN/PEN_09004a2f806513e4.pdf Honey well. 2011. HFO - 1234yf: A 2 -phase inhalation screening study and single exposure study in rabbits via whole -body inha lation exposure (GLP) . Honey well. 201 2 . Refrigerant exposure to service personnel or DIYers due to leakage of 12 oz charging cans or “small cans”. Experiments Conducted at Honey well’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.Page 8 of 9

APPENDECES: APPENDIX	1.	Review	of	rabbit	one	hour	inhalation	study. Reviewer: Ernest V. Falke April 18, 2011 Reference/Report: H FO - 1234yf: A 2 - PHASE INHALATION SCREENING STUDY AND SINGLE EXPOSURE STUDY IN RABBITS VIA WHOLE - BODY INHALATION EXPOSURE (GLP) Study Ty pe: 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: Honey well 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 unlikel y, the outcome of leth ality 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 day s post exposure. Anal yt ica l concentrations for male/female were 0/0; 45,000/47,000; and 100,000/102,000 respectivel y. Five males and 6 pregnant females were exposed at each dose. Five non - pregnant females were exposed at 0 and 100,000 ppm.Page 9 of 9

No mortality

was observed for an y condi tion 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 anal yz ed 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.