MEMORANDUM

To: Margaret Sheppard , U.S. EPA

CC: Yaidi Cancel, U.S EPA

From: Emily Herzog, Ed Carr, Kara Altshuler, Veronica Kennedy, Mark Wagner, ICF International 

Date: May 25, 2010

Re: Revised Assessment of the Potential Impacts of HFO-1234yf and the Associated Production of 

TFA on Aquatic Communities, Soil and Plants, and Local Air Quality (Deliverable under EPA 

Contract Number EP-W-06-008 Task Order 038, Task 06)

Please find attached a revised version of a paper that examines the emissions of HFO-1234yf and the 

associated production of TFA under several scenarios. The assessment has been revised to reflect a 

revised approach to analyzing impacts of HFO-1234yf emissions. This approach used EPA’s CMAQ 

model version 4.7 with the chemical mechanism incorporating chemistry and reaction rates for HFO1234yf transformation to TFA. The results from this analysis confirm our previous conclusions that 

projected emissions of HFO-1234yf should not result in a significant risk to aquatic communities, soil and 

plants, or local air quality.

Please contact Mark Wagner at 202-862-1155 with any questions or comments.
Assessment of the Potential Impacts of 

HFO-1234yf and the Associated Production of TFA 

on Aquatic Communities, Soil and Plants, and

Local Air Quality

Prepared for:

Stratospheric Protection Division

Office of Atmospheric Programs

U.S. Environmental Protection Agency

1310 L Street, NW

Washington, DC 20005

Prepared by:

ICF International 

1725 Eye Street, NW, Suite 1000

Washington, DC 20006

May 25, 2010
 TFA Assessment

Table of Contents

Foreword ............................................................................................................................... i

Executive Summary ............................................................................................................... 1

1. Introduction ................................................................................................................... 1

2. Production and Environmental Fate of Trifluoroacetic acid (TFA)..................................... 3

3. Toxicity of Trifluoroacetic Acid (TFA)............................................................................... 4

3.1. Aquatic and Environmental Toxicity .............................................................................................4

3.2. Human and Animal Toxicity ..........................................................................................................8

4. Assessment of Potential HFO-1234yf Emissions............................................................. 10

4.1. Scenarios of HFO-1234yf Market Penetration............................................................................10

4.2. HFO-1234yf Emission Assumptions ............................................................................................11

4.3. Estimated Emissions of HFO-1234yf...........................................................................................11

5. Assessment of Potential Impacts of HFO-1234yf and TFA .............................................. 13

5.1. TFA Rainwater Concentrations ...................................................................................................13

5.2. TFA Dry Deposition .....................................................................................................................14

5.3. Ground Level Ozone Concentrations..........................................................................................15

6. Discussion of Results .................................................................................................... 16

6.1. Summary of Findings...................................................................................................................17

6.2. Limitations of this Analysis..........................................................................................................17

7. References ................................................................................................................... 20
 TFA Assessment

i

Foreword

In a previous analysis conducted in the Spring/Summer of 2009, ICF International assessed the potential 

impacts of HFO-1234yf emissions and the associated production of TFA on aquatic communities and 

local air quality.1 Using the research and resources available at the time, ICF made numerous 

conservative assumptions regarding the potential emissions and atmospheric reactivity of HFO-1234yf. 

Specifically, in the earlier assessment, ICF scaled emissions of SO2 proportionately to the projected 

emissions of HFO-1234yf based on the understanding that the lifetime cycle for SO2 to sulfate 

conversion and removal in cloud droplets is similar to that of HFO-1234yf to TFA removal in cloud 

droplets. ICF then applied EPA’s three-dimensional community multiscale air quality model (CMAQ) 

using emissions of SO2 only from the Los Angeles and Houston air basins to determine the dry sulfate 

deposition and sulfate rainwater concentrations for a typical one-year (2001) period using hourly 

meteorological data.2 The sulfate concentrations were then scaled on an emissions molar adjusted 

basis to estimate the maximum potential concentration of TFA in rainwater and dry deposition both on 

an annual basis, as well as for the maximum month downwind deposition for both Houston and Los 

Angeles. To account for the minor difference in lifetime for sulfate and for TFA (3 days vs. 5 days) due to 

in-cloud removal, a log-log adjustment was also made to the output of the model to estimate TFA 

concentrations in rainwater.

The results from the earlier analysis estimated the highest monthly average TFA concentration in 

rainwater to be 1.8 mg/L in 2050 located downwind of Los Angeles, and only 0.008 mg/L downwind of 

Houston for the same year. The maximum concentrations in both annual and monthly rainwater for 

Houston were well below the 0.12 mg/L no observed effect concentration (NOEC) reported for the most 

sensitive freshwater green algae species tested at the time. However, Los Angeles showed the 

potential for concentrations to exceed the no effect levels for this algae species starting in 2020 for the 

monthly maximum concentration and 2025 for the annual average maximum. In addition, beginning 

sometime between 2025 and 2030, it was estimated that the rainwater concentrations could exceed the 

NOEC of 1 mg/L for vernal pool plant species in vernal pools near Los Angeles during the month of July. 

However, the maximum annual average of 0.29 mg/L in rainwater downwind of Los Angeles in 2050 and 

both the maximum annual and monthly averages for Houston were estimated to be significantly below 

the NOECs for all vernal pool species. 

In regards to dry deposition of TFA, ICF found that the monthly peak dry deposition occurred in March 

for Los Angeles and in July for Houston. The modeling results indicated that projected maximum annual 

average deposition of TFA will be greater after 2015 than what has been measured in vernal pools in the 

last decade in Northern California. However, current toxicity data on ecological receptors indicated that 

TFA has low toxicity for most aquatic microbial, plant, and animal species; does not bioconcentrate; and 

does not appear to have effects on germination on those species tested. .

 

1

ICF International. 2009. Assessment of the Potential Impacts of HFO-1234yf and the Associated Production of 

Trifluoroacetic Acid (TFA) on Aquatic Communities and Local Air Quality. Prepared by ICF International for U.S. EPA. 

July 31, 2009. Available online at www.regulations.gov in docket ID: EPA-HQ-OAR-2008-0664-0037.

2 More information is available on the CMAQ model at http://cmascenter.org/.
 TFA Assessment

ii

To estimate potential impacts on local air quality, ICF assumed the ozone creation from the release of 

HFO-1234yf to be similar to that of the volatile organic compound (VOC) ethylene, as described by 

Papadimitriou et al. (2008). The Houston-Galveston region and the South Coast Air Basin in California 

were again examined to analyze the potential impacts of using HFO-1234yf on ground level ozone, 

assuming business as usual emissions of NOx and VOC. For Houston, data were taken from the Post1999 Rate of Progress and Attainment Demonstration SIP to predict future emissions of NOx and VOC 

(Texas Natural Resource Commission, 2000) up to the 2019 ozone attainment year based on model 

simulations during the summer ozone season. Data for the South Coast region were taken from the 

2007 Air Quality Plan, which predicts future emissions of NOx and VOC for attaining the ozone standards 

for 2017 and 2023 (South Coast, 2007), again based on modeling during the summer ozone season. 

Data for future year projections after 2023 for both Houston-Galveston and the South Coast were 

estimated based on a need for continued reduction in emissions due to increased temperatures from 

global warming. Climate change impacts reported in the IPCC’s 4th Assessment Report (IPCC, 2007) 

predict that by 2050 global warming will increase average daily ozone levels across the eastern U.S. by 

3.7 ppb based on likely emission levels. It was assumed that the regional air quality plan would be 

adjusted accordingly to compensate for this expected increase. Thus, the Houston-Galveston regional 

emissions of both NOx and VOCs were proportionately reduced to maintain attainment of the current 8-

hour ground level ozone standard of 75 ppb. While less specific data is available for the South Coast, 

IPCC projections report significant increase in the frequency and magnitude of ground level 

temperature, which leads to higher ozone concentrations. Thus, it was assumed that the same level of 

increase in background ozone concentration would be seen for the South Coast region as projected for 

the eastern United States. As a result, regional emissions for the South Coast after 2023 were also

proportionately reduced to account for the expected 3.7 ppb increase in ozone due to global warming.

Results from this earlier analysis showed that for Houston-Galveston ground level ozone potentially 

could increase by less than 1%, assuming a VOC-limited environment, or an environment where ozone 

formation is limited by the availability of VOC (not the availability of NOx). For the South Coast (i.e., 

around Los Angeles), ground level ozone was expected to increase by about 1.4%. These percentage 

increases in ozone suggest how much ground level ozone could potentially increase as a result of the use 

of HFO-1234yf, relative to the projected emissions of NOx and VOC over time. For other areas of the 

United States that were not examined in the analysis, a similar conclusion was drawn: HFO-1234yf 

emissions have the potential to increase ground level ozone; however, the percent increase is expected 

to impact other regions to a much lesser extent. 

Given the limitations and conservative nature of this earlier analysis, ICF concluded that (a) projected 

levels of TFA in rainwater should not result in a significant risk of ecotoxicity; (b) dry deposition is 

somewhat of a concern, however more research is needed to fully understand the impacts of dry 

deposition on soil, plants, and aquatic communities; and (c) non-attainment resulting from HFO-1234yf 

emissions is not likely to be a major concern for local air quality in most locations.

Since the completion of the analysis, new information and findings have been brought to the attention 

of ICF. As a result, the analysis has been revised and is described in the remainder of this paper.
 TFA Assessment

1

 100-year GWPs of Selected HCFCs and HFCs 

Gas

IPCC Second 

Assessment 

Report (SAR)

IPCC Fourth 

Assessment 

Report (AR4)

HCFC-22 1,500 1,810

HCFC-123 90 77

HCFC-124 470 609

HCFC-141b 600 725

HCFC-142b 1800 2,310

HFC-23 11,700 14,800

HFC-32 650 675

HFC-125 2,800 3,500

HFC-134a 1,300 1,430

HFC-143a 3,800 4,470

HFC-152a 140 124

HFC-227ea 2,900 3,220

HFC-236fa 6,300 9,810

HFC-245fa NA 1,030

HFC-365mfc 860 794

Source: IPCC (1996), IPCC (2007)

Executive Summary

HFO-1234yf is a chemical under development for use in motor vehicle air conditioning (MVACs) and has 

the potential to be used more broadly in other end use sectors. Although HFO-1234yf has a low global 

warming potential (GWP) and is thus a desirable alternative to commonly used hydrofluorocarbons 

(HFCs), there is concern that use of HFO-1234yf could negatively impact both local air quality and 

aquatic communities. HFO-1234yf has a reactivity that could potentially lead to increased levels of 

ground-level ozone. Additionally, there is concern associated with the atmospheric degradation of HFO1234yf, which results in the production of trifluoroacetic acid (TFA). TFA has the potential to 

accumulate on soil, on plants, and in aquatic ecosystems over time and to impact the supported plant 

and animal communities. The following paper describes the production and fate of TFA, provides an indepth discussion of the toxicity of TFA, discusses the scenarios developed for this analysis, and discusses 

the potential impacts HFO-1234yf could have on aquatic ecosystems, soil, plants, and local air quality. 

The scenarios developed for this analysis project HFO-1234yf emissions and subsequent production of 

TFA up to 2050 based on market penetrations in the domestic market. In conjunction with three 

dimensional air quality modeling conducted using EPA’s Community Multiscale Air Quality (CMAQ) 

model (CMAQ - Byun, D. W., and J. K. S. Ching. 1999) these projections were used to estimate the 

maximum potential concentration of TFA in rainwater, the maximum amount of dry deposited TFA, and 

the potential increase in ground level ozone. From this analysis, it was concluded that the projected 

maximum concentration of TFA in rainwater and the amount of TFA dry deposited should not result in a 

significant risk of ecotoxicity, and that non-attainment resulting from HFO-1234yf emissions is unlikely 

to be a major concern for local air quality in most locations.

1. Introduction 

Since the inception of the Significant New 

Alternatives Policy (SNAP) program, a large number 

of substitutes have been reviewed in support of the 

development and commercialization of viable 

replacements for ozone depleting substances (ODS) 

across all of the end use sectors that have 

traditionally used ODS. Approved substitutes have 

included hydrochlorofluorocarbons (HCFCs), 

hydrofluorocarbons (HFCs), blends, hydrocarbons, 

and not-in-kind alternatives. The HFCs have been a 

significant alternative for many sectors because of 

their non-ozone depleting nature, but due to the high 

global warming potential (GWPs) of HFCs, new lowGWP alternatives are being developed. In particular, 

HFO-1234yf is a chemical under development for use 

in motor vehicle air conditioning (MVACs) and has the 

potential to be used more broadly in the 

refrigeration/air conditioning end use sectors. 

HFO-1234yf is proposed to replace HFC-134a in 
 TFA Assessment

2

Sources of TFA

Species Global TFA 

Production (t yr-1)

Halothane 520

Isoflurane 280

HCFC-123 266

HCFC-124 4440

HFC-134a 4560

Fluoropolymers 200

TFA (lab use etc) Negligible

Total 10,266

Source: IPCC/TEAP 2005

MVACs and has a particularly low GWP of 4.4 compared to the HFCs and HCFCs currently in use (as 

shown in the text box above). HFO-1234yf has the potential to significantly reduce the climate impacts 

of MVACs as well as that of other sectors (Papadimitriou et al., 2008).

Although the use of HFO-1234yf could potentially mitigate greenhouse gas emissions, it could also 

potentially contribute to increased levels of ground level ozone. While the maximum incremental 

reactivity of HFO-1234yf is expected to be similar to that of ethane (Carter 2009), it is possible that in 

some locations the reactivity could be considerable higher depending on regional conditions. Therefore, 

HFO-1234yf may pose a risk to local air quality, if emitted in sufficient quantities.

There is additional concern associated with the atmospheric 

degradation of HFO-1234yf which results in the production of 

trifluoroacetic acid (TFA). TFA is a well-known environmental 

contaminant that results from the degradation of halothane (an 

anesthetic introduced clinically in 1956), isoflurane, and 

fluoropolymers as well as HFC-134a, HCFC-123, and HCFC-124. 

In its 2006 report on Environmental Effects of Ozone Depletion 

and Its Interactions with Climate Change, the United National 

Environment Programme (UNEP) stated that risks to humans 

and the environment from TFA and other degradation products 

of HCFCs and HFCs “are considered minimal.” HFO-1234yf was 

not considered in the basket of HFCs at the time that UNEP 

prepared its 2006 report. 

At the current rate of production from atmospheric degradation of HFCs and HCFCs, the level of TFA is 

projected to reach close to 0.0001 mg/L in 2020 in rainwater, about 1,000 times lower than the lowest 

reported no observed effect concentration of 0.12 mg/L (Boutonnet et al. 1999). However, the rate of 

production of TFA from HFO-1234yf is significantly higher than that associated with HFC-134a. With the 

anticipated use (and associated emissions) of HFO-1234yf, TFA has the potential to accumulate in 

seasonal wetlands, which have both little to no outflow and high evaporation rates (e.g., vernal pools, 

playa lakes), over time and may impact the supported plant and animal communities in those wetlands. 

This paper examines the emissions of HFO-1234yf and the associated production of TFA under several 

scenarios and assesses the potential impacts of HFO-1234yf and TFA on aquatic communities and local 

air quality. The remainder of the document is organized as follows:

 Section 2 describes the production and fate of TFA;

 Section 3 provides an in-depth discussion of the toxicity of TFA;

 Section 4 discusses the scenarios developed for this analysis and the resulting emissions of HFO1234yf; 

 Section 5 discusses the results of this analysis and presents an assessment of the potential 

impacts on aquatic ecosystems and local air quality; and

 Section 6 discusses the results and identifies the limitations of the analysis.
 TFA Assessment

3

Chemical and Physical Properties of TFA

Molecular Formula CF3C(O)OH

Molecular Weight 114.02

Vapor Pressure 1.10 x 102 mm Hg

Boiling Point 72.4  ̊C

Melting Point -15.4  ̊C

Log Kow 0.50

pKa 0.25-0.5

Koc 3

Henry’s Law Constant 1.11 x 10-7 atm-m3/mol

Solubility Miscible in water at 20  ̊C

Source: Hazardous Substance Data Bank

2. Production and Environmental Fate of Trifluoroacetic acid (TFA)

Trifluoroacetic acid (TFA) is produced during the atmospheric breakdown of many fluorocarbons (e.g., 

CFC replacements), including HFO-1234yf. The process is initiated by the gaseous reaction of these 

fluorocarbons with hydroxyl (OH) radicals, eventually resulting in carbonyl products. These halogenated 

carbonyl compounds remain in the atmosphere for 11 days on average before they are encapsulated 

into water droplets and hydrolyzed to TFA (Papadimitriou et al., 2008).

Due to the re-evaporation of cloud droplets, TFA may also re-evaporate to the gas phase. A small 

portion (at most 5%) of gas phase TFA is estimated to react with OH and be dry-deposited to the earth’s 

surface (Kotamarthi et al. 1998). However, TFA is considered highly soluble and is instead expected to 

reincorporate into cloud and rainwater, eventually being wet-deposited to the oceans and land surfaces

(Kotamarthi et al. 1998). After deposition, TFA enters aquatic environments. 

TFA is a strong acid with a reported pKa range of ~0.25-0.5; 

therefore, it is expected to completely ionize at any pH that 

occurs naturally (Boutonnet et al. 1999; HSDB 2008; 

Kotamarthi et al. 1998). Due to its high solubility, 

volatilization from aqueous solution is not considered to be 

a significant transport pathway. In the aqueous phase, TFA 

does not absorb light at wavelengths greater than 250-290 

nm (Boutonnet et al. 1999; HSDB 2008), thus excluding 

photolysis as a degradation pathway. 

There are few studies available that provide information on 

the movement of TFA in solid and liquid media. Based on a 

low Henry’s Law constant and a low Kow (n-octanol/water 

partition coefficient) (Franklin 1993), it has been predicted 

that TFA would partition predominantly in water (Bowden et al. 1996; 1998). However, studies of TFA 

adsorption in soils have been performed in both upland forest and forest wetland environments in the 

Hubbard Brook Experimental Forest in New Hampshire, with varying results (Likens et al. 1997; Richey et 

al. 1997). These studies indicate that TFA is measurably retained in soils in those environments, with 

wetland systems retaining more applied TFA than the forest system. For example, within 1-3 weeks, 

applied TFA moved through the forest soil profile with drainage water, and more than 70% of the TFA 

exited the upland forest in drainage water. The authors suggested that TFA would likely be leached 

from the soil and enter drainage waters over approximately 2 years until the TFA concentrations 

returned to pre-application levels. In the case of the forest wetland, TFA did not move readily with 

water, and <5% of the applied TFA moved out of the wetland in drainage water. Interestingly, the 

authors did not see an increased concentration of TFA in drainage waters following dry spells and the 

drying of the wetland, indicating that the compound was not concentrating due to evaporation. The 

authors interpreted these data to indicate the compound was being retained in the vegetation (20-50%) 

and forest wetland soils (20-60%). 

A separate study investigated the properties of soils that affect TFA retention (Richey et al. 1997). The 

data indicate that soils with greater amounts of organic matter preferentially retain TFA compared to 

well-drained, aerobic soils, with organic soils from wetlands, peatlands, and a boreal forest showing the 
 TFA Assessment

4

greatest retention of the compound. Further, TFA was retained to a greater extent in lower pH 

environments, but was not retained in the presence of high concentrations of fluoride, chloride, and 

sulfate ions. As mentioned before, TFA is a strong acid; these data suggest that soils impacted by acid 

rain may be further impacted by the deposition of TFA, because of its acidity, although the presence of 

SO4

-

(currently a primary component of acid rain) in large quantities will inhibit TFA retention. Studies 

evaluating effects of TFA deposition/adsorption on soil or sediment chemistry have not been identified. 

Effects of TFA on soil microbial communities are described below.

Studies show that TFA is extremely persistent in aquatic environments. The estimated half-life for 

degradation of TFA in typical environmental conditions via reaction with hydroxyl radicals in water 

would be 100 years (Ellis et al. 2001). Further, data provided by Alternative Fluorocarbons 

Environmental Acceptability Study (AFEAS) indicates that TFA is resistant to oxidative and reductive 

degradation and biodegradation (Franklin 1993; Berends et al. 1999; Boutonnet et al. 1999). This is 

supported by recent independent data by Emptage et al. (1997) showing that TFA is not degraded by 

methanogenic bacteria from various environmental sources (freshwater sediments, marine sediments, 

rumen, and an anaerobic digestor sample). More recently, however, Kim et al. (2000) demonstrated 

cometabolic biodegradation of low concentrations (≤30 mg F/L) over the span of 100 weeks in small (10 

L) fermentation batches of a mixture of unidentified bacteria. The issue of environmental degradation 

of TFA is a subject of continuing research and the data currently do not allow one to predict whether 

this environmental sink will moderate TFA loading in the future.

3. Toxicity of Trifluoroacetic Acid (TFA)

3.1. Aquatic and Environmental Toxicity3

TFA is mildly toxic to plant life (i.e., phytotoxic). In certain environmental conditions, TFA might reach 

concentrations in the future that may be toxic to surrounding plant life. For example, studies show that 

as seasonal wetlands evaporate, the remaining TFA is concentrated; TFA in these standing pools can be 

retained for years, adding to long-term accumulation of TFA in wetlands (Cahill et al. 2001). Increased 

concentrations of TFA can inhibit growth in the most sensitive plants and may affect the survival of 

endangered and endemic plant species (Cahill et al. 2001). Lower aquatic life forms, such as bacteria, 

certain aquatic plant species, small invertebrates, and segmented worms (such as earthworms), do not 

accumulate large quantities of TFA, and are not significantly impacted by the compound (Berends et al. 

1999; Boutonnet et al. 1999). According to a study on the aquatic toxicity of TFA, systems exposed to a 

concentration of 0.10 mg/L are expected to experience no adverse effects (Berends et al. 1999), 

although many organisms show no toxic effects at much higher concentrations of the compound (see 

Table 1 below). 

Lowest observed effect concentrations (LOEC) and no observed effect concentrations (NOEC), as 

summarized by Boutonnet et al. (1999),4 are shown in Table 1. Note that values are listed both for the 

 

3 The toxicity of TFA has been evaluated in algae, microbial benthic organisms, fish, and freshwater plants. 

Terrestrial plant, laboratory animal, and human study data are not reviewed in this section.

4 Research sponsored by the Alternative Fluorocarbons Environmental Acceptability Study (AFEAS) and conducted 

by independent scientists at universities, private research organizations, and government laboratories.
 TFA Assessment

5

sodium salt of TFA (NaTFA) and estimated equivalent TFA, in parentheses. Boutonnet et al. (1999) 

measured NaTFA, because the free acid itself is not likely to be present at high concentrations in 

environmental media.

Table 1: Summary of Studies on the Aquatic Toxicity of Sodium Trifluoroacetate (mg/L) 

Aquatic Organisms EC50a LOECb NOECc

Selenastrum capricornutum 

(freshwater green alga) 

(new name: Pseudokirchneriella subcapitata)

4.8 (4.0)d

>1.2 (1.0) 0.36 (0.30)e <0.36 (0.30)

0.12 (0.1)

Anabaena flos-aquae 

(blue-green alga) 2400 (2011) 1200 (1000) 600 (500)

Navicula pelliculosa 

(freshwater diatom) 1200 (1000) 1200 (1000) 600 (500)

Skeletonema costatum 

(marine diatom) --- --- 2400 (2011)

Chlorella vulgaris

(freshwater green alga) --- --- 1200 (1000)

Chlamydomonas reinhardtii

(freshwater green alga) --- --- >120 (>100)

Microcystis aeruginosa 

(blue-green alga) --- --- >117 (98)

Phaeodactylum tricornutum 

(marine alga) --- --- >117 (98)

Dunaliella tertiolecta

(marine alga) --- --- >124 (104)

Euglena gracilis 

(freshwater alga) --- --- >112 (94)

Daphnia magna

(crustacea) --- --- 1200 (1000)

Brachydanio rerio 

(Zebra fish) --- --- 1200 (1000)

Lemna gibba 

(duckweed) --- vegetative growth 1100 (920) 600 (500) 300 (250)

a EC50 = test concentration resulting in an effect in 50% of the organisms tested; the table lists EC50 for biomass 

integral (adverse effects on growth)

b

LOEC = lowest observed effect concentration 

c NOEC = no observed effect concentration (defined as the lowest concentration for which the effects were not 

statistically different from the controls)

dValues provided in parentheses represent the data normalized to TFA, mg/L

e At this concentration, the inhibition of the biomass integral was 11%.

Source: Boutonnet et al. 1999

In general, high concentrations of NaTFA (≥300 mg/L; ca. 250 mg TFA/L) did not result in adverse effects 

in the fish, crustacean, and diatom species tested, and most of the algal species tested. In duckweed, 

mild negative growth effects were seen on frond and weight increase at 600 mg/L; no effects were 

noted at 300 mg/L. Toxicity tests conducted with select species of algae shown above are taken from a 

study by Berends et al. (1999) who found that, for ten of the eleven species tested, the effect 

concentration for 50% of the test organisms (EC50) was >100 mg/L NaTFA (ca 84 mg TFA/L). The lowest 

threshold for effects was observed for the unicellular alga, Pseudokirchneriella subcapitata (formerly S. 

capricornutum), which is commonly used as an indicator species in ecotoxicity screening tests. Toxicity
 TFA Assessment

6

results varied among the different labs testing P. subcapitata as reported by these authors (Berends et 

al. 1999); the authors state that responses at the low range of test concentrations were generally 

consistent, however, and they consider 0.12 mg NaTFA/L (0.10 mg TFA/L) to be the threshold for toxicity 

(e.g., no effects on growth were noted at this concentration). However, at higher concentrations TFA 

did not have an algicidal effect, but rather an algistatic (e.g., slowing growth) effect on this species, as 

growth resumed three days after the TFA was removed (Berends et al. 1999).

Environmental receptors in seasonal wetlands vary with geography, and are established in unique 

ecosystem niches. Plant species tend to be annuals, as perennials are not adapted to the seasonality of 

the rainfall. Animal species, such as the freshwater fairy shrimp (Branchinecta lynchi) and tadpole 

shrimp (Lepidurus packardi), which are found only in California, are obligate vernal pool species that 

define these wetlands. They are adapted to inconsistent levels of rainfall year to year, and varying pH 

and salinity gradients, and typically mature from egg to reproductive-age adult in a matter of weeks. As 

TFA exposure studies with these species are unavailable, there is no definite information regarding 

what, if any, effects increasing TFA concentrations would have on the life cycle of these niche organisms 

or others. Existing data on other similar organisms, however, indicate no cause for concern. 

Additional data taken from more recent articles relative to the toxicity of TFA in fish, aquatic plants, and 

freshwater benthic microbial communities are shown in Table 2. They indicate that TFA exhibits low 

toxicity in these receptors. 

Table 2: Summary of Additional Toxicity Studies of Trifluoroacetate (mg/L)

Aquatic Organisms EC50/LC50a LOECb NOECb

Brachydanio rerio (Zebra fish) 

(Wiegand et al., 2000) ---

1,000 (1,200)c

(low elevation of 

GST activity)

4,000 (4,770)

(no acute effects)

Myriophyllum sibiricum, Myriophyllum spicatum (aquatic plants) 

(exposure to trichloroacetic acid and TFA mixture for 49 days) 

(Hanson et al., 2002)

--- --- 10 

Lemna gibba, Myriophyllum sibiricum, Myriophyllum spicatum 

(aquatic plants [macrophytes]) 

(Hanson and Solomon, 2004a)

EC50 range:

222.1 - 10,000 

(265-12,000)

M. sib.: 300 (360)

M. spic.: 100 (120)

L. gibba: 100 (120) 

M. sib.: 100 (120)

M. spic.: 30 (36)

L. gibba: 30 (36)

Pimephales promelas (Fathead minnow) (Geiger et al., 1988, as 

cited in ECOTOX)

7.79 - 1.28 

(9.3-1.5) --- ---

Freshwater benthic microbial communities in stream sediments 

(Bott and Standley, 1998)

--- ---

0.00002 to 0.2 

(0.000024 to 0.24)(no 

effect on acetate 

metabolism)

a EC50 = test concentration resulting in an effect in 50% of the organisms tested; the table lists EC50 for biomass 

integral (adverse effects on growth); LC50 = lethal concentration for 50% of the tested organisms

b

LOEC = lowest observed effect concentration; NOEC = no observed effect concentration

c Glutathione S-transferase

The combined impact of TFA and other haloacetic acids in the environment is unlikely to create a 

significant impact on exposed species. Hanson et al. (2002) tested two aquatic plant species with a 

mixture of trichloroacetic acid (TCA) and TFA at concentrations up to 10 mg/L, and observed reversible 

effects on pigment concentrations at the start of the study, but no adverse effects thereafter. The 

authors conclude that, based on the lack of morphological or biochemical effects on these aquatic 

macrophytes, it is unlikely that the TCA/TFA mixture causes toxicity at the currently measured 
 TFA Assessment

7

environmental concentrations, which they report as 0.01 mg/L. Hanson and Solomon (2004a) tested the 

toxicity of TFA and other haloacetic acids (HAA) in the laboratory with three aquatic plants; mass and 

root measures, such as root number and root length, tended to be the most sensitive indicators of HAA 

toxicity. The results of this study were used in an ecological risk assessment for macrophytes (aquatic 

plants) and HAA (Hanson and Solomon, 2004b). The authors compare the thresholds of toxicity for the 

species tested to measured concentrations of HAAs in the environment from Canada, Europe, and Africa 

to calculate hazard quotients. The Hazard Quotient, as defined by Hanson and coworkers, is the ratio of 

the highest expected environmental concentration of HAA (EEC) and the toxicological benchmark 

concentration (TBC); HQ = EEC/TBC. 

An HQ of greater than 1 indicates a “potential for toxic effects to occur” while those less than 1 

essentially indicate no risk (“effects are unlikely”). The calculated hazard quotients are extremely low 

(those for TFA with the three macrophytes were all ≤0.000088 or lower), indicating that HAAs do not 

pose a significant risk to freshwater macrophytes at current environmental concentrations for both 

single compound and mixture exposures. The thresholds for toxicity in these calculations ranged from 

4.1 mg/L to 45.9 mg/L, concentrations which are 400-4500-fold greater than those currently detected in 

the environment (Cahill et al. 2001). Therefore, these data indicate that even in the event of increased 

environmental concentrations of TFA, which might result from increased use of HFO-1234yf, the risk to 

environmental receptors is expected to be small.

The potential for bioconcentration in aquatic organisms is low (HSDB 2008), based on one classification 

scheme (Franke et al. 1994). An estimated bioconcentration factor (BCF) of 3 for TFA was calculated in 

fish, using an estimated log Kow of 0.50 (Meylan and Howard 1995) and a regression-derived equation 

(Meylan et al. 1999). Boutonnet et al. (1999) conclude that TFA does not accumulate significantly in 

lower aquatic life forms such as bacteria based on results from Bott and Standley (1994, as cited in 

Boutonnet et al. 1999) in which incorporation of radiolabeled TFA increased over 2.5 years from 0.005% 

of total counts to 0.024% of total counts, and based on low BCFs derived in studies with green algae 

(BCF of approximately 10; van Dijk 1996, as cited in Boutonnet et al. 1999) and duckweed (BCF of 1.0 to 

1.6; Smyth et al. 1993, as cited in Boutonnet et al., 1999). 

As seasonal wetlands evaporate, TFA can remain in place and could concentrate over time, resulting in 

long-term accumulation. However, vernal pools have varying levels of seepage due to lateral movement 

of sub-surface ground water flow, or because of weak or broken hardpans at the bottom of the pools 

(Sefchick et al. 1994, as quoted in Boutonnet et al. 1999; Hanes, 1998). TFA accumulation is not 

expected in pools exhibiting seepage. Of course, as these wetlands go dry, any TFA salt present would 

be adsorbed to soil particles on the ground surface, and would be subject to other transport 

mechanisms, such as removal by wind, etc. Potential TFA accumulation may be linked to increased 

concentrations of TFA in plants in these wetlands, but again, plants in seasonal wetlands are heavily 

represented by annual grasses and similar species and TFA has been shown not to affect seed 

production for future propagation in these ecosystems. 

Studies in animals following long-term exposure to TFA have not been done to date. In one study, the 

highest TFA concentrations in water, which occurred just prior to the pools drying up, were in the 0.002

to 0.01 mg/L range. This concentration range is 10- to 60-fold lower than the lowest reported NOEC of 

0.12 mg/L for the most sensitive species of freshwater green algae (P. subcapitata). Plants exposed to 

high aqueous concentrations of TFA within the seasonal pools had elevated TFA concentrations with a 

median concentration of 279 ng/g dry weight in their tissues, as compared to 33 ng/g for species 
 TFA Assessment

8

growing outside the pools (Cahill et al. 2001). A study of the effects of TFA on vernal pool soil microbial 

and plant communities indicated that, at the test concentrations, TFA will not adversely affect the 

development of soil microbial communities and vernal pool plant species. Microbial respiration was not 

affected by TFA exposures up to 10 mg/L, and microbial degradation of TFA was not observed in soils 

incubated for three months. In addition, no adverse physiological responses were observed in wetland 

plants exposed to 0.1 and 1 mg/L TFA. TFA did accumulate in the foliar tissue of wetland plants as a 

function of root exposure concentration, but the concentrations in foliar tissue leveled off and/or 

declined with time (Benesch et al. 2002). Thus, the test concentration of 1 mg/L is a NOEC for plant 

species in vernal pools.

Studies of stomatal uptake in plants following dry deposition are limited. For TFA that is dry deposited, 

ponderosa pines were shown to take up TFA through their foliage (stomatal uptake) at concentrations of 

0.0015 and 0.01 mg/L for four months (Benesch and Gustin 2002). The study authors prevented misted 

TFA from reaching the roots of the trees to ensure they evaluated only foliar uptake. Although TFA 

concentrations were shown to increase in the pine needles over the course of the study, no visual 

morphological or photosynthetic effects were noted at either concentration. No NOEC values have been 

identified based solely on dry deposition of TFA, or on a combined wet/dry deposition model. 

In conclusion, NOECs from the published literature for the most sensitive species were:

 0.12 mg/L for freshwater green algae

 1200 mg/L for a fish species

 No observed adverse effects at up to 10 mg/L for vernal pool microbial species and up to 1 mg/L 

for vernal pool plant species

Current risk assessments indicate that vernal pool species would not be negatively impacted with 

current and predicted published estimates of TFA loading in the environment.

3.2. Human and Animal Toxicity

TFA has low inhalation toxicity, moderate oral toxicity, and the irritation threshold for humans is 54 ppm 

(Boutonnet et al. 1999). The free acid is considered a strong skin and eye irritant. TFA is not 

significantly metabolized by mammals. The sodium salt of TFA (NaTFA) has a much lower toxicity than 

the free acid and will be the focus of this section, as the free acid is not likely to be present at high 

concentrations in environmental media. Animal studies show that the target organ of TFA and its 

sodium salt is the liver. Single doses of up to 2000 mg/kg NaTFA in male mice resulted in fatty liver 

changes, accompanied by increases in glycogen and vacuolization (Rosenberg and Wahlstrom 1971, as 

cited in Boutonnet et al. 1999). 

Repeated oral dosing of male rats with NaTFA at up to 150 mg/kg-day resulted in significantly increased 

relative liver weights with decreased liver glycogen content (Stier et al. 1972, as cited in Boutonnet et al. 

1999), and doses of up to 500 mg/kg-day of trifluoroacetate caused increased liver cell size with 

peroxisomal proliferation (Just et al., 1989, as cited in Boutonnet et al.; 1999). The peroxisomal 

proliferation is unique to the rat, as this effect was not observed in dosed guinea pigs. Single doses of 

10 mg/kg (ip) or 25 mg/kg (oral) TFA in male rats resulted in no adverse testicular effects. Neither TFA 

nor its salts have been studied in reproductive or developmental assays; TFA was present in the 

amniotic fluid of halothane-dosed pregnant rats, but no fetal effects were observed (Ghantous et al. 
 TFA Assessment

9

1986, as cited in Boutonnet et al. 1999). TFA has also been identified in the milk of lactating rats (5-23% 

following saponification) after the administration of HCFC-123 (Buschmann 1996, as cited in Boutonnet 

et al. 1999). TFA has also been reported to be non-mutagenic in bacterial studies (Blake et al. 1981 and 

Waskell 1978, both cited in Boutonnet et al. 1999); studies have not been conducted to determine its 

carcinogenic potential. 
 TFA Assessment

10

4. Assessment of Potential HFO-1234yf Emissions 

This analysis is intended as a screening exercise to develop a reasonable worst-case estimate of HFO1234yf emissions under various use scenarios. The remainder of this section describes the assumptions 

used for this analysis to determine potential emissions of HFO-1234yf. A discussion on the limitations of 

the emission projections of HFO-1234yf can be found in section 6.1 of this paper.

4.1. Scenarios of HFO-1234yf Market Penetration

For this analysis, two scenarios were developed. These scenarios provide reasonable worst-case 

assumptions for the potential market penetration of HFO-1234yf in the domestic market only. Both 

scenarios assume that HFO-1234yf is used as a drop-in replacement for HFC-134a,5 with a replacement 

ratio of 1:1 HFC-134a to HFO-1234yf.6 The market penetration scenarios are described below and 

summarized in Table 3.

 Scenario 1: HFO-1234yf is used in the United States as a new car refrigerant in the MVAC sector. 

HFO-1234yf begins penetrating the market in 2016 reaching 100 percent market penetration by 

2020, as described in Table 3 below. 

 Scenario 2: HFO-1234yf is used in the United States as a new car refrigerant in MVAC systems, 

refrigeration, and stationary AC systems. Similar to scenario 1, by 2020, HFO-1234yf is used in all 

new MVAC systems. For refrigeration and stationary AC systems, HFO-1234yf enters the market 

in 2010, reaches 30 percent penetration of the market in 2015, and 100 percent by 2020. 

Table 3: Summary of Assumed Penetration of HFO1234yf in Scenarios Used in Analysis*

Sectors 2010 2015 2020

Scenario 1

MVACs 0% 0% 100%

Scenario 2

MVACs 0% 0% 100%

Refrigeration 6% 30% 100%

Stationary Air Conditioning 6% 30% 100%

*The dates of introduction of HFO-1234yf are consistent with the earlier analysis, conducted in 2009 and explained 

in the foreword of this document. 

The specific dates of introduction are used as a demonstration of how HFO-1234yf might be phased in; 

actual dates may differ by several years. Examining the period from initial introduction of the 

refrigerant to market saturation allows the analysis to consider potential impacts of HFO-1234yf in the 

near-term (i.e., 10 - 15 years), during which time there are already specific State goals for ground-level 

ozone impacts. In addition, the analysis considers the potential longer term impacts of HFO-1234yf after 

the refrigerant has saturated the market, assuming continued growth in motor vehicle use.

 

5

In all scenarios, HFO-1234yf replaces only pure HFC-134a, not any blends with HFC-134a as a component.

6 The ratio of HFC-134a to HFO-1234yf has been estimated at 1:0.9, however a 1:1 ratio was used to provide a 

worst case estimate.
 TFA Assessment

11

4.2. HFO-1234yf Emission Assumptions

ICF assumed that emissions of HFO-1234yf will be equivalent to emissions of HFC-134a. Emission 

assumptions from the MVAC sector for this analysis are summarized below in 

Table 4.

Table 4: Refrigerant Loss Assumptions from the MVAC Sector

Assumption Emissions Ratea

Leak Rate 8%

Servicing Leaks (annualized) 10%

End-of-life Loss Rate 42.5%

a HFC-134a MVAC assumptions from the U.S. EPA Vintaging Model, Version VM IO File v4.4_12-16-09. 

Emissions of refrigerant due to servicing motor vehicle air conditioning systems were expected to be 

higher during the spring and summer, with up to 80% of emissions due to repairs occurring from April 

through August.7 Furthermore, refrigerant emissions from servicing motor vehicle air conditioning 

systems were estimated at 47% of annual refrigerant emissions from motor vehicles.8 As a result, the 

analysis assumes that 59.5% of annual emissions of HFO-1234yf would occur from April through August, 

with 11.9% of annual emissions occurring during each of those five months. The remaining 40.5% of 

annual emissions was modeled to occur from September through March, with 5.8% of annual emissions 

occurring during each of those seven months. This assumption was also applied to stationary AC end 

uses based on the assumption that similar patterns of seasonal emissions would be attributable to this 

end-use.

4.3. Estimated Emissions of HFO-1234yf

Using EPA’s Vintaging Model, ICF estimated emissions of HFO-1234yf for both scenarios. These 

estimates are summarized in Table 5 while estimated monthly emission estimates of HFO-1234yf for the 

year 2050 are provided in Table 6. Estimated annual HFO-1234yf emissions under each scenario are also 

graphically depicted in Figure 1 and Figure 2. A complete table with estimated annual emissions can be 

found in Annex A. 

Table 5: Summary of Estimated Emissions of HFO-1234yf (MT)*

Scenarios 2020 2030 2040 2050

Scenario 1 6,244 28,327 33,093 35,851

Scenario 2 10,501 43,296 55,070 60,616

* ICF projected emissions of HFO-1234yf using special scenarios designed specifically for this analysis and run on 

the U.S. EPA Vintaging Model, Version VM IO File v4.4_12-16-09. 

Table 6: Summary of Estimated Monthly Emissions of HFO-1234yf in 2050 (MT)

Scenarios Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Scenario 1 2,074 2,074 2,074 4,266 4,266 4,266 4,266 4,266 2,074 2,074 2,074 2,074

Scenario 2 4,025 4,025 4,025 6,489 6,489 6,489 6,489 6,489 4,025 4,025 4,025 4,025

 

7 Hoffpauir, Elvis. 2009. Email to Karen Thundiyil, 10 March.

8 U.S. EPA Vintaging Model, Version VM IO File v4.2 10-07-08
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Figure 1: Estimated Emissions of HFO-1234yf by End-Use Sector under Scenario 1 (MT)

Figure 2: Estimated Emissions of HFO-1234yf by End-Use Sector under Scenario 2 (MT)
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5. Assessment of Potential Impacts of HFO-1234yf and TFA

This section uses the projected emissions of HFO-1234yf described in section 4 to predict impacts on 

aquatic communities, soils and plants, and local air quality. Emissions from each scenario for the year 

2050 were scaled from the national emissions estimates according to population for Houston and Los 

Angles regions to determine reasonable worst-case impacts. These regions were chosen based on the 

potential presence of vernal pools, their susceptibility to high TFA deposition concentrations, and their 

continuing and chronic problem with high levels of ground level ozone.

Using EPA’s CMAQ model version 4.7, a one-year simulation was performed using 2001 meteorological 

data to project maximum monthly TFA rainwater concentrations, monthly maximum dry deposition of 

TFA, and maximum 8-hr ozone concentrations for the Los Angeles and Houston regions resulting from 

emissions of HFO-1234yf from those regions only. The model used the extended version of the carbon 

bond five chemical mechanism as developed by Luecken et al. (2010), which incorporates the gaseous 

and aqueous chemistry of HFO-1234yf and its products. The results from this analysis are described in 

the remainder of this section.

5.1. TFA Rainwater Concentrations

Monthly maximum average TFA rainwater concentrations for each region under each scenario are 

summarized in Table 7.

Table 7: Summary of Estimated Monthly Average TFA Rainwater Concentrations in 2050 (ng/L)

Region Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Scenario 1

Los Angeles 90 32 166 167. 969 1116 707 944 170 120 196 94

Houston 18 21 32 34 50 75 106 59 54 19 16 27

Scenario 2

Los Angeles 174 63 322 322 1475 1700 1077 1438 319 232 380 182

Houston 35 40 61 51 76 114 161 90 85 37 30 51

Under scenario 1, the results indicate that the maximum monthly average TFA rainwater concentration 

in the Los Angeles region in 2050 is 1,116 ng/L, while the maximum monthly average TFA rainwater 

concentration in the Houston region in 2050 is 106 ng/L. Under scenario 2, the results indicate that the 

maximum monthly average TFA rainwater concentration in the Los Angeles region in 2050 is 1,700 ng/L, 

while the maximum monthly average TFA rainwater concentration in the Houston region in 2050 is 161 

ng/L. 

For Los Angeles, June represents the month with the highest projected monthly average TFA rainwater 

concentration, while for Houston, July represents the month with the highest projected monthly 

average TFA rainwater concentration. The monthly average maximum TFA rainwater concentrations for 

these two peak months are geographically depicted below in Figure 3 and Figure 4, for both scenarios, 

for Los Angeles and Houston, respectively. 
 TFA Assessment

14

Figure 3: June 2050 Los Angeles Scenario 1 and Scenario 2 Results 

 

Figure 4: July 2050 Houston Scenario 1 and Scenario 2 Results 

 

5.2. TFA Dry Deposition

Table 8 presents the results of both the maximum annual and monthly maximum TFA deposition

expressed on an annual basis. 

Table 8: Summary of Estimated TFA Dry Deposition in 2050 

Notes: Formula weight of TFA is 114 g/mole.

a Maximum concentration occurred in May for Los Angeles and in July for Houston. Results are expressed on 

annual basis using the peak monthly deposition rate times 12. 

Annualized TFA Maximum 

Monthly Average Flux Ratea

TFA Maximum 

Annual Average Flux Rate

nmole/m2-yr g/m2-yr nmole/m2-yr g/m2-yr

Scenario 1

Los Angeles 15,252 566 3,838 143

Houston 2,556 95 934 35

Scenario 2

Los Angeles 23,232 863 6,393 237

Houston 3,912 145 1,551 58
 TFA Assessment

15

Dry deposition of TFA is likely more of a concern in central and southern California than is wet 

deposition due to the lower rainfall in this part of the state compared to other geographical areas of the 

United States. For comparison, measured TFA flux rates from two vernal pool systems outside of 

Sacramento, California are presented in Table 9 (Cahill et al. 2001; data taken in 1998 and 1999).

Table 9: TFA Measurements in California Vernal Pools, 1998-1999

Observed Year Flux Rate Values Measured in California Vernal Pools

ng/m2-day g/m2

-yr

1998-1999 134* 49

1998-1999 110** 40

1998-1999 152*** 56

Notes: Values of g/m2-yr = ng/m2-day * 365 days/1000.

*Time-weighted average of values measured in Davis, CA Jan 1-May 16, 1998.

**Time-weighted average of values measured in Davis, CA Nov 26, 1998-Apr 2, 1999.

***Time-weighted average of values measured in Yolo Country Grasslands Regional Park, CA Jan 6-May 6, 1999.

The values above indicate that projected maximum annual average deposition of TFA will be somewhat 

greater than what has been measured in vernal pools in the last decade in Northern California. For 

Southern California, measured values in vernal pools would be expected to be somewhat higher than 

those reported owing to the reduced rainfall compared to Northern California. 

5.3. Ground Level Ozone Concentrations

Under scenario 1, results for the Los Angeles region show a maximum increase in the 8-hr ozone 

concentration of 0.053 ppb, while results for the Houston region show a maximum increase in the 8-hr 

ozone concentration of 0.014 ppb. Under scenario 2, results for the Los Angeles region show a 

maximum increase in the 8-hr ozone concentration of 0.080 ppb, while results for the Houston region 

show a maximum increase in the 8-hr ozone concentration of 0.021 ppb. Maximum increases in 8-hr 

ozone concentrations under each scenario are geographically depicted in 

Figure 5 and 
 TFA Assessment

16

Figure 6 below.

Figure 5: LA May 22, 2050 Scenario 1 and Scenario 2 Results

 
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Figure 6: Houston June 11, 2050 Scenario 1 and Scenario 2 Results

 

Figure 5: LA May 22, 2050 Scenario 1 and Scenario 2 Results

 
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Figure 6: Houston June 11, 2050 Scenario 1 and Scenario 2 Results

 

6. Discussion of Results

The following section provides a summary of the findings described in section 5 and additionally 

provides an overview of the limitations of this analysis.

In section 3.1 of this paper, based on available studies, it was concluded that the NOEC is 0.12 mg/L 

(120,000 ng/L) for freshwater green algae, 10 mg/L (10,000,000 ng/L) for vernal pool microbial species,

and 1 mg/L (1,000,000 ng/L) for vernal pool plant species. Relative to these levels, in the worst case 

scenario, TFA rainwater concentrations are expected to reach 1,116 ng/L in 2050, well below the NOEC 

of 1,000,000 ng/L for vernal pool species. The measured concentration of TFA in rainwater is only ten 

times greater than the 2020 level of TFA in rainwater projected from the current rate of production from 

atmospheric degradation of HFCs and HCFCs, which is estimated to be almost 0.0001 mg/L or 100 ng/L 

(Berends et al. 1999), but still 1,000 times lower than the NOEC for tested vernal pool species.

NOECs are compared to rainwater TFA concentrations because for most water bodies, it is difficult to 

predict what the actual TFA concentration will be. This is because concentrations of environmental 

contaminants in most fresh water bodies fluctuate widely due to varying inputs and outputs to most 

ponds, lakes, and streams. Comparison of NOECs to rainwater concentrations of TFA is actually more 

conservative because TFA is expected to be diluted in most freshwater bodies. The exception to this is 

that less dilution is expected in vernal pools and similar seasonal water bodies that have no significant 

outflow capacity. 

Although dry deposition of TFA in vernal pools has been projected to potentially be almost five times 

greater than concentrations measured in 1998-1999, studies indicate that vernal pools species are 

unlikely to be harmed because plant and animal species tested to date do not bioconcentrate TFA and 

the compound has not been shown to affect plant germination rates. It is noted that no NOEC values 

have been identified based solely on dry deposition of TFA, or on a combined wet/dry deposition model, 

but it is not expected that there will be adverse impacts based on the lack of reported bioconcentration 

and germination effects.
 TFA Assessment

19

In regards to ground level ozone formation, based on the findings described in section 5.3 and assuming 

an 8-hr ozone standard of 75 ppb, HFO-1234yf is projected to contribute to a maximum of roughly 

0.07% - 0.1% and 0.02% - 0.03% of total ground-level ozone in Los Angeles and Houston, respectively. 

These percentage increases are presented relative to the proposed 75 ppb standard for ozone, although 

it is unclear what the standard will be in the future with possible changes in standards for emissions of 

criteria pollutants, VOCs, and NOx. 

6.1. Summary of Findings

Based on results presented above, certain preliminary conclusions concerning the potential impacts of 

HFO-1234yf and the associated production of TFA can be made:

 Projected levels of TFA in rainwater should not result in a significant risk of ecotoxicity. After 

taking into account the nature of HFO-1234yf degradation and the resulting TFA concentration in 

rainwater; regional precipitation patterns; the geology of closed aquatic systems; and no 

observed effect concentrations (NOEC) for TFA, TFA production resulting from HFO-1234yf 

emissions is not expected to pose significant harm to aquatic communities in the near future. 

Future research is necessary to determine if significant TFA loading is occurring in vernal pools 

near major population centers as there are insufficient data to determine whether TFA would 

impact these environments significantly.

 Dry deposition is a potential concern; however, more research is needed to fully understand the 

impacts of dry deposition on soil, plants, and aquatic communities. Only two studies were 

identified which investigated the effects of dry deposition in plants. While one study showed 

measured effects on photosynthesis, the other did not. It is unclear what impact current and 

future loading of TFA will have in vernal pool ecosystems. Current tests on freshwater plants and 

animal species that might be found in vernal pools show that only one species of algae might be 

affected at predicted concentrations of deposited TFA. However, it is not possible to know

without further research, whether increased TFA loading might affect other obligate vernal pool 

species. Current risk assessments, though, indicate this is not a significant concern. 

 Non-attainment resulting from HFO-1234yf emissions is not likely to be a concern for local air 

quality in all locations. HFO-1234yf could potentially increase ground level ozone by up to 0.1% 

in the most extreme case. Given the expected photochemical reactivity of HFO-1234yf, 

emissions of HFO-1234yf are not expected to significantly result in ground level ozone formation.

6.2. Limitations of this Analysis

The analysis described above is based on numerous assumptions and projections that cannot be known 

with certainty at this time. The following discussion recognizes these uncertainties and indicates various 

factors that have potential to impact and change the results of this analysis. 

Market Modeling

 The market penetration assumptions used for this analysis assume HFO-1234yf will be the sole 

replacement for HFC-134a. However, the introduction of additional substitutes could 
 TFA Assessment

20

potentially lower the penetration of HFO-1234yf into the market, thus decreasing the emissions 

and impacts of HFO-1234yf and TFA.

 Even though EPA’s Vintaging Model, used to calculate emissions for both scenarios, provides 

output up to 2050, the assumptions used in the model are based only on current data and 

expert opinions regarding the near future. Since it is not possible to predict with certainty 

changes that will occur in the distant future (post 2020), the assumptions in the model are not 

adjusted for additional unpredictable changes that will likely take place.

 EPA’s Vintaging Model does not account for reductions in emissions that may occur as a result 

of using HFO-1234yf as a replacement for HFC-134a. Factors such as refrigerant price and 

advancements in leak-tightness of MVAC systems are not adjusted for in the modeling. 

Consequently, HFO-1234yf emission projections are considered to be conservative.

Aquatic and Soil Impacts

 A significant source of uncertainty in the analysis of aquatic toxicity is the receptor species used 

in the analysis. For example, in the cited studies, researchers used widely accepted and 

standardized species of freshwater and marine flora and fauna in the screening tests. These 

plant and animal species, however, with the possible exception of Daphnia magna, and some 

algal species, are not typical of specialized vernal pool species in California such as meadow 

foam, Downingia, Navarettia, fairy shrimp, tadpole shrimp, and tiger salamanders. Of course, 

one reason for this is that many of these species are endangered and/or protected, and it is not 

possible to conduct toxicity studies on them. Nevertheless, lack of knowledge regarding the 

susceptibility and/or resistance to TFA or similar compounds by these species affects the ability 

to more accurately quantify aquatic impacts from TFA deposition in certain geographical areas. 

However, one study (Benesch et al. 2002) did look at vernal pool microbial and plant species and 

found that predicted TFA concentrations would not adversely affect these receptors. Further, 

current and predicted TFA concentrations are well below effect levels in many related ecological 

receptors, and lower aquatic life forms do not bioconcentrate TFA. These data indicate that 

despite full knowledge of the effects of TFA on vernal pool species, adverse ecological effects 

are not anticipated.

 The ecology considered in this analysis is a highly specialized one that is vital to many species, 

including migratory birds. In addition, regional areas that contain the geology necessary for 

vernal pool formation are subject to modification via many means, including residential and 

commercial development, mining, agriculture, and in California, earthquakes. These activities 

also produce environmental contamination that affects species adapted to vernal pool ecology. 

It is not possible to predict the impact of these external effects on aquatic toxicity of vernal 

pools, nor how TFA concentrations, in concert with these other effects, might change the 

estimated results presented here.

Air Quality 

 Improvements in the understanding of the reactivity of HFO-1234yf and resulting production of 

TFA and ozone formation have potential to change the estimates made in this analysis. 
 TFA Assessment

21

 Further global warming impacts will result in region-specific changes that may, for example,

increase local cloud cover leading to decreases in local photolysis rates resulting in reduced 

ozone production.

 The changes in standards for other pollutants such as air toxics or criteria pollutants could affect 

the precursor ozone emissions. For example, EPA recently finalized a rule for a new 1-hour NO2

standard in the range between 80 to 100 ppb. In order to meet future standards, significant 

emission reductions may be required, thus impacting the potential production of ground level 

ozone.

 The ozone air quality standard may be lowered in the future (historically the standard has been 

lowered a number of times) and would require additional reductions of ozone precursor 

emissions, which would increase the importance of HFO-1234yf to the production rate for 

ozone.
 TFA Assessment

22

7. References

1234yf OEM Group. 2008. MAC Summit 2008. Available at 

<http://www.epa.gov/cppd/mac/HFO1234YF%20EXPERT%20CONSENSUS%20GROUP.ppt>

Abstracts: South African Association of Botanists – Annual meeting 2006. South African Journal of 

Botany 72:313-347

Benesch JA, MS Gustin, GR Cramer, and TM Cahill. 2002. Investigation of effects of trifluoroacetate on 

vernal pool ecosystems. Environ Toxicol and Chem. 21(3):640-47.

Berends, AG, JC Boutonnet, C de Rooij, and RS Thompson. 1999. Toxicity of Trifluoroacetate to Aquatic 

Systems. Environ Toxicol Chem. 18(5):1053–1059. 

Bott, TL and LJ Standley. 1994. The effect of TFA on biological processes in streams. Proceedings of a 

Workshop on the Enviornmental Fate of Trifluoroacetic Acid. March 3-4, 1994, Miami Beach, FL. 

Published by AFEAS, Washington, DC. Cited in Boutonnet et al., 1999.

Bott, TL and LJ Standley. 1998. Effects of trifluoroacetate, and atmospheric breakdown product of 

hydrofluorocarbon refrigerants, on acetate metabolism by freshwater benthic microbial communities. 

Bull. Environ. Contam. Toxicol. 60(3):472-79.

Bott, TL and LJ Standley. 1999. Incorporation of trifluoroacetate, a hydrofluorocarbon decomposition 

byproduct, by freshwater benthic microbial communities. Water Research. 33(6):1538-44.

Boutonnet, JC, P Bingham, D Calamari, C de Rooij, J Franklin, T Kawano, J-M Libre, A McCulloch, G 

Malinverno, JM Odom, GM Rusch, K Smythe, I Sobolev, R Thompson, and JM Tiedje. 1999. 

Environmental Risk Assessment of Trifluoroacetic Acid. Human Ecolog Risk Assessment. 5(1):59-124.

Bowden DJ, SL Clegg, andP Brimblecombe. 1996. The Henry’s Law constant of trifluoroacetic acid and 

its partitioning into liquid water in the atmosphere. Chemosphere. 32(2):405-420.

Bowden DJ, SL Clegg, and P Brimblecombe. 1998. The Henry’s law constant of the haloacetic acids. J. 

Atmos. Chem 29(1):85-107.

Byun, DW and JKS Ching. 1999. Science Algorithms of the EPA Models-3 Community Multiscale Air 

Quality (CMAQ) Modeling System. U.S. EPA Office of Research and Development, Washington, D.C. 

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Annex A: Annual HFO-1234yf Emissions Estimated under each Scenario for the

Years 2010 through 2050 (MT)*

Year

Scenario 1 Scenario 2

MVACs MVACs Refrigeration Stationary AC TOTAL

2010 - - 39 7 46

2011 - - 111 20 132

2012 - - 218 40 258

2013 - - 361 66 426

2014 - - 541 98 640

2015 - - 762 138 900

2016 407 407 1,093 196 1,696

2017 1,229 1,229 1,541 273 3,043

2018 2,472 2,472 2,110 369 4,951

2019 4,143 4,143 2,807 485 7,435

2020 6,244 6,244 3,636 620 10,501

2021 8,332 8,332 4,487 766 13,585

2022 10,413 10,413 5,389 916 16,718

2023 12,513 12,513 6,278 1,066 19,857

2024 14,644 14,644 7,209 1,216 23,069

2025 16,812 16,812 8,128 1,367 26,307

2026 19,003 19,003 9,043 1,516 29,561

2027 21,203 21,203 9,953 1,678 32,834

2028 23,962 23,962 10,914 1,848 36,724

2029 26,335 26,335 11,817 2,017 40,170

2030 28,327 28,327 12,748 2,221 43,296

2031 29,926 29,926 13,591 2,412 45,929

2032 31,118 31,118 14,348 2,577 48,043

2033 31,295 31,295 14,918 2,720 48,932

2034 31,514 31,514 15,479 2,861 49,854

2035 31,791 31,791 15,924 3,010 50,725

2036 32,084 32,084 16,382 3,213 51,678

2037 32,374 32,374 16,824 3,408 52,606

2038 32,627 32,627 17,249 3,592 53,468

2039 32,857 32,857 17,656 3,767 54,280

2040 33,093 33,093 18,046 3,931 55,070

2041 33,345 33,345 18,371 4,008 55,724

2042 33,637 33,637 18,668 4,080 56,385

2043 33,906 33,906 18,921 4,151 56,977

2044 34,177 34,177 19,156 4,217 57,549

2045 34,450 34,450 19,374 4,278 58,102

2046 34,726 34,726 19,566 4,315 58,606

2047 35,004 35,004 19,756 4,351 59,110

2048 35,284 35,284 19,944 4,383 59,611

2049 35,566 35,566 20,132 4,415 60,112

2050 35,851 35,851 20,318 4,447 60,616

* ICF projected emissions of HFO-1234yf using special scenarios designed specifically for this analysis and run on 

the U.S. EPA Vintaging Model, Version VM IO file v4.4_12-16-09.