September 27, 2011

Significant New Alternatives Policy Program

Solvent Cleaning Sector

Risk Screen on Substitutes for CFC-113 in Electronics, Metal, and Precision 

Cleaning and Drying Applications

Substitute: Perfluorobutyl Iodide (Capstone® 4-I)

 This risk screen does not contain Clean Air Act (CAA) Confidential Business 

Information (CBI) and, therefore, may be disclosed to the public.

1. Introduction

Ozone-depleting substances (ODSs) are being phased out of production in response to a series of 

diplomatic and legislative efforts that have taken place over the past few years, including the Montreal 

Protocol and the Clean Air Act Amendments of 1990 (CAAA). The U.S. Environmental Protection 

Agency (EPA), as authorized by Section 612 of the CAAA, administers the Significant New Alternatives 

Policy (SNAP) Program, which identifies acceptable and unacceptable substitutes for ODS in specific 

end-uses based on assessment of their health and environmental impacts.

EPA's decision on the acceptability of a substitute is based largely on the findings of a screening 

assessment of potential human health and environmental risks posed by the substitute in specific 

applications. EPA has already screened a large number of substitutes in many end-use applications within 

all of the major ODS-using sectors, including refrigeration and air conditioning; solvent cleaning; foam 

blowing; aerosols; fire extinguishing; adhesives, coatings and inks; and sterilization. The results of these 

risk screens are presented in a series of Background Documents that are available in EPA’s docket.

The purpose of this risk screen is to supplement EPA's Background Document on the solvent cleaning 

sector (EPA 1994) (hereinafter referred to as the Background Document). This risk screen discusses 

potential human health and environmental risks posed by perfluorobutyl iodide (PFBI) when used as a 

replacement for CFC-113 in electronics, metal, and precision cleaning and drying applications.

PFBI was submitted under the trade name, Capstone® 4-I, as a potential substitute for CFC-113 in 

electronics, metal, and precision cleaning and drying applications, with primary application in the 

flushing of oxygen supply lines on aircraft. In addition, the substitute is nonflammable and may therefore 

serve as a replacement for CFC-113 in vapor degreasing applications. Based on information from the 

submitter, Capstone® 4-I is expected to gain only a small portion of the solvent cleaning market. Table 1 

provides the composition of Capstone® 4-I. The formulation proposed by the submitter consists of 

impurities which total at most one percent of the formulation. In addition to PFBI, this risk screen also 

discusses the risks associated with use the of the PFBI impurities indicated in the Capstone® 4-I

formulation.
September 27, 2011

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Table 1: Composition of Capstone® 4-I

Component Chemical Formula CAS No. Weight Percent (%)

Perfluorobutyl Iodide C4F9I 423-39-2 99-100

Potential Impurities

Perfluoroethyl Iodide C2F5I 354-64-3 0 - 0.5

Perfluorohexyl Iodide C6F13I 355-43-1 0 - 0.4

Iodine I2 7553-56-2 0 - 0.1

The potential risks associated with use of substitutes in solvent cleaning have been examined at length in 

the Background Document. The reader is referred to this reference for a detailed discussion of the 

methodologies used to conduct this risk screen. Occupational and general population exposure modeling 

was performed in this risk screen to ensure that use of the proposed substitute did not pose unacceptable 

risk to workers. 

Section 2 of this report summarizes the results of the risk screen for the proposed substitute. The 

remainder of the report is organized into the following sections:

 Section 3: Atmospheric Assessment

 Section 4: Flammability Assessment

 Section 5: Occupational Exposure Assessment

 Section 6: General Population Assessment 

 Section 7: Volatile Organic Compound Assessment

 Section 8: References

2. Summary of Results

PFBI (as well as Capstone® 4-I) is recommended for SNAP approval for electronics, metal, and precision 

cleaning and drying applications, provided that proper disposal procedures and appropriate personal 

protective equipment (PPE), such as gloves and goggles, are used (see Section 5 and Section 6). EPA’s 

risk screen indicates that the use of the proposed substitute will be less harmful to the atmosphere than the 

continued use of CFC-113. No significant toxicity risks to the general population are expected. In 

addition, the characteristics of the substitute indicate that flammability is not a concern at end-use. 

3. Atmospheric Assessment

This section presents an assessment of the potential risks to atmospheric integrity posed by the use of 

PFBI, as well as the remaining constituents of Capstone® 4-I, in electronics, metal, and precision 

cleaning and drying applications. The ozone depletion potential (ODP), global warming potential (GWP), 

and atmospheric lifetime (ALT) of the proposed substitute are presented in Table 2.
September 27, 2011

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Table 2: Atmospheric Impacts of PFBI and the Remaining Constituents of Capstone® 4-I

Compared to CFC-113

Chemical ODPa GWP (relative to CO2)

100 Year

ALT

PFBI <0.005b <5

b ~daysb

Perfluoroethyl Iodide NA <5

c NA

Perfluorohexyl Iodide NA NA NA

Iodine NA NA ~minutesd

CFC-113 0.8e 4,800f 85f

aODPs for these compounds are expected to vary by location of release, based on their very short lifetimes. 

b Confidential submitter 2011. The ALT for PFBI is estimated to be a few days.

c The GWP value for perfluoroethyl iodide is assumed to be roughly equal to the calculated GWP value of PFBI (ICF estimate 

developed through consultation with Dr. Don Wuebbles).

dThe ALT value for iodine is expected to be very short, on the order of a few minutes (ICF estimate developed through 

consultation with Dr. Don Wuebbles).

eMontreal Protocol and available at: http://www.epa.gov/ozone/ods.html.

f

IPCC 4th Assessment Report (Forster et al. 2007).

NA – Not Available. In the case of perfluorhexyl iodide, the values are not publicly available. 

PFBI (including the Capstone® 4-I formulation) presents a viable alternative to CFC-113. The GWP and 

ODP of PFBI are estimated to be less than 5 and less than 0.005, respectively, significantly lower than 

these for CFC-113 and comparable to or lower than other alternatives for CFC-113 in this end use. Even 

though the Capstone® 4-I formulation possesses no Class I or Class II ozone-depleting substances, it is 

expected to have a non-zero ODP. The three remaining constituents of Capstone® 4-I (perfluorohexyl 

iodide, perfluoroethyl iodide, and iodine), which comprise a maximum 1% of the formulation, do not 

have reported atmospheric values. However, because of the chemical similarities of the remaining 

constituents to PFBI, the ODP and GWP values are expected be roughly on the same order of magnitude 

as PFBI. Moreover, because of the small percentage of the three remaining constituents in the 

formulation, the overall GWP and ODP of the Capstone formulation is not expected to vary significantly. 

Therefore, the use of PFBI, including the Capstone® 4-I formulation, is expected to be less harmful to the 

ozone layer than the continued use of CFC-113. 

4. Flammability Assessment

As indicated in the substitute’s MSDS, the substitute is non-flammable and thus not expected to pose 

flammability concerns. 

5. Occupational Exposure Assessment

This section presents an assessment of potential health risks to workers exposed to PFBI during end-use

application. 

5.1 Toxicity of the Substitute

For this occupational exposure analysis, potential risks from worker exposure were evaluated by 

comparing estimated exposure concentrations to the available occupational exposure limit, which is listed 

in Table 4. EPA’s approach for identifying or developing these values is discussed in Chapter 3 of the 

Background Document.
September 27, 2011

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Current information regarding the decomposition of the substitute indicates that breakdown products, 

including perfluorooctane, iodine, carbon dioxide, carbon monoxide, and hydrofluoric acid, can form 

when the substitute is exposed to ultraviolet (UV) light or temperatures above 250°C. When exposed to 

UV light, a maximum concentration of 0.1% per byproduct may be generated, although generation of 

hydrofluoric acid is not likely. In addition, degradation during fire conditions may generate unspecified 

concentrations of byproduct. However, the submitter has also noted that hydrofluoric acid is not expected 

to form during normal use of the substitute. 

5.2 Occupational Exposure during End-Use 

Occupational exposure modeling was performed for the proposed substitute to ensure that its use does not 

pose an unacceptable risk to workers during solvent cleaning applications. For end-uses, the submitter has 

indicated that the proposed substitute will be used primarily for flushing of oxygen supply lines used in 

aircraft. In addition, the substitute may be used in shallow dipping pans, open top vapor degreasers, or for 

use with wipe cloths and in hand-pump bottles for assorted cleaning applications. To minimize potential

exposures, the submitter has indicated that open top degreasers will be used under ventilation controls.

Because actual worker exposure data for this proposed substitute is generally unavailable, potential 

exposures were estimated using the surrogate method. The methodology used for this screening 

assessment is based on the one used in the occupational exposure and hazard analysis described in 

Chapter 5 of the Background Document. Using this method, the potential occupational exposures to PFBI

range from 23.0 to 83.3 ppm. As summarized in Table 4, the maximum exposure is almost five times 

lower than the recommended exposure limit for PFBI, 375 ppm. Since the maximum occupational 

exposure to the proposed substitute during end-use is significantly below the acceptable exposure limit 

(AEL), the proposed substitute is not considered a significant toxicity threat. However, to ensure that 

exposures to PFBI remain below the recommended AEL, EPA recommends that workers wear 

appropriate PPE (e.g., goggles, gloves) and that proper ventilation controls be established when using the 

proposed substitute for solvent cleaning applications. Section VIII of the Occupational Safety & Health 

Administration (OSHA) Technical Manual (OSHA 1999) should be consulted for information on 

selecting the appropriate types of PPE to be worn by personnel involved during use of PFBI. 

Table 3: PFBI Occupational Exposure Assessment

Maximum Calculated Exposure 

Concentration AEL

83.3 ppm 375 ppm1

1See Attachment 1. ICF International, 2010. “Determination of an AEL for 

Perfluorobutyl Iodide.”

6. General Population Exposure Assessment

This section screens potential risks to the general population from exposure to releases of PFBI to 

ambient air, surface water, and solid waste. When the proper safety and disposal precautions, as listed in 

the remainder of this section, are followed, PFBI is not expected to cause a significant threat to the 

environment and human health in the general population when manufactured or used for electronics, 

metal, and precision cleaning and drying applications. 
September 27, 2011

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6.1 Ambient Air

If the accidental release measures, handling and storage, engineering controls, and waste disposal are 

followed per the substitute’s MSDS, significant releases to air are not expected to occur. According to the 

submitter, releases to the air of Capstone® 4-I are expected to occur during precision cleaning uses in 

aircraft and estimated to be 1-2 kg per day. Other releases to the air during precision, electronics, and 

metal cleaning and drying applications are expected to occur indoors, and therefore not expected to cause 

exposure to the general population. Because of the minimal releases of PFBI to the air, use of PFBI is not 

expected to generate concentrations of concern to the health of the general population. 

6.2 Surface Water 

High concentrations of PFBI in surface water could pose a concern to the environment as an LC50 of 2.3 

mg/L was estimated for fathead minnow in a study performed to assess the acute aquatic toxicity of PFBI.

However, due to PFBI’s high vapor pressure (114.3 mm Hg) and high percent volatiles (>98% WT), 

PFBI is not likely to accumulate in surface water at concentrations high enough to be considered toxic to 

aquatic organisms. In addition, the submitter estimates that 1-10 kg/day of spent Capstone® 4-I will be 

collected as wastewater when the substitute is used for precision cleaning. For electronics and metal 

cleaning, the product will be handled indoors with wastes scrubbed through ventilation systems and

primarily collected as wastewater, estimated to be 10-20 kg per day of the spent solvent. 

For facilities which collect the wastewater for treatment, the wastewater must be sent to an onsite 

industrial wastewater treatment facility that employs sufficient controls in order to remove halogenated 

materials. Domestic (sanitary) wastewater treatment facilities do not meet these requirements. EPA 

believes that treated wastewater which meets the discharge concentration requirements of an industrial 

treatment facility is sufficient to control human health and environmental risks, and thus recommends that 

all spent solvent collected as wastewater be sent to an industrial treatment facility. 

6.3 Solid Waste

The Capstone® 4-I PFBI formulation is estimated to be used at less than 100 sites; where the spent 

solvent can be collected, the spent solvent can also be reclaimed through distillation. EPA recommends 

that reclamation of the substitute through distillation be performed to the extent feasible. Residuals from 

the distillation process and spent solvent collected in containers (and therefore not collected as wastewater 

and sent to an onsite wastewater treatment facility) are generally considered to be a RCRA hazardous 

waste (40 CFR Part 261.31). However, not all applications of Capstone® 4-I may generate hazardous 

wastes. Although the constituents of Capstone® 4-I are not listed as RCRA hazardous wastes, solvents 

used for electronics, metal, and precision cleaning applications generally pick up metals and other 

chemical compounds during the process, which causes the spent solvent to display characteristics of 

hazardous waste (ignitability, corrosivity, reactivity, or toxicity); any solid waste displaying these 

characteristics or having a specific waste code (e.g., F001) is considered to be a hazardous waste (40 CFR 

Part 261). Waste regulated as RCRA hazardous wastes is subject to the requirements of the Subtitle C 

program (including storage, treatment, and disposal requirements), which EPA believes are sufficient to 

control human health and environmental risks. 
September 27, 2011

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7. Volatile Organic Compound Assessment 

PFBI is considered to be a VOC for purposes of local air quality. In addition, perfluoroethyl iodide and

perfluorohexyl iodide, of the remaining constituents of Capstone® 4-I, are also considered to be VOCs. In 

general, VOC emissions should be sufficiently controlled through regulations and standard industry 

practices. Analysis shows that even if all Capstone® 4-I produced by the submitter in one year at market 

penetration were to be released to the atmosphere over the course of the year (extremely unlikely), the 

resulting annual VOC emissions would be approximately 1.3x10-3percent of all VOC emissions from all 

solvent uses, and moreover, only 3.5x10-4percent of all annual anthropogenic VOC emissions.1 As these 

emissions of Capstone® 4-I are several orders of magnitude less than other anthropogenic emissions, the 

environmental impacts of these VOCs are not considered a threat. 

8. References

Confidential submitter. 2011. Follow-up Data for Significant New Alternatives Policy Program

Submission to the United States Environmental Protection Agency for Capstone® 4-I. 

September 22, 2011.

Confidential submitter. 2010a. Significant New Alternatives Policy Program Submission to the United 

States Evironmental Protection Agency for Capstone® 4-I. January 20, 2010.

Confidential submitter. 2010b. Follow-up Data for Significant New Alternatives Policy Program 

Submission to the United States Evironmental Protection Agency for Capstone® 4-I. April 24, 

2010.

Confidential submitter. 2010c. Follow-up Data for Significant New Alternatives Policy Program 

Submission to the United States Evironmental Protection Agency for Capstone® 4-I. April 16, 

2010.

EPA. 2009. 2008 National Emissions Inventory Air Pollutant Emissions Trends Data. Last updated 09 

June 2009. Available online at <http://www.epa.gov/ttn/chief/trends/index.html#tables>.

EPA. 1994. Risk Screen on the Use of Substitutes for Class I Ozone-Depleting Substances: Solvent 

Cleaning. Stratospheric Protection Division. February 1994. 

ICF International. 2010. “Determination of an AEL for Perfluorobutyl Iodide.” Prepared by Mukhi, N., 

Prusiewicz, C., Rubenstein, R., and Wagner, M. under EPA Contract No. EP-W-06-008 Task 

Order 038, Task 06.

IPCC/TEAP. 2001. Third Assessment Report: Climate Change: Working Group I: The Scientific Basis. 

Chapter 6: Radiative Forcing of Climate Change. Cambridge University Press, UK. 

 

1

Based on 2010 projections calculated using 2008 EPA annual VOC emissions data (EPA 2009) and ICF 

assumptions.
September 27, 2011

7

IPCC/TEAP. 1995. Second Assessment Report: Climate Change: Working Group I: The Science of 

Climate Change. Chapter 2: Radiative Forcing of Climate Change. Cambridge University Press, 

UK. 

OSHA. 1999. OSHA Technical Manual. Department of Labor. Occupational Safety and Health 

Administration. January 20, 1999. Available online at 

http://www.osha.gov/dts/osta/otm/otm_toc.html

Salamone, J. 1996. Polymeric Materials Encyclopedia. Volume 10 Q-S. CRC Press. 1996. 

Solomon, S., Burkholder, J. B., Ravishankara, A. R., and Garcia, R. R. 1994. Ozone Depletion and Global 

Warming Potentials of CF3I. Journal of Geophysical Research. Vol. 99, pp. 20929-20935. 

October 20, 1994.

Youn, D., Patten, K.O., Wuebbles, D.J., Lee, H., So, C.W.. 2010. Potential impact of iodinated 

replacement compounds CF3I and CH3I on atmospheric ozone: A three-dimensional modeling 

study. Atmospheric Chemistry and Physics Discussions. July 2, 2010. 

WMO (World Meteorological Organization). 2003. Scientific Assessment of Ozone Depletion: 2002, 

Global Ozone Research and Monitoring Project—Report No. 47, 498 pp., Geneva, 2003.
September 26, 2010

Appendix A: Determination of an AEL for Perfluorobutyl Iodide

AEL Derivation

Recommended AEL: 375 ppm (8-hour Time Weighted Average)

Basis and

Endpoints: NOAEL 1,500ppm (no body weight changes were noted at this exposure 

concentration)

Study: A 13-week nose-only inhalation toxicity study in rats with a 4-week 

recovery period

Protocol: Nose-only inhalation, 6 hours/day, 5 days/week for 13 weeks 

Concentrations: 0; 500; 1,500; 5,000 ppm

NOAEL: 1,500 ppm

Uncertainty Factors: 3 (interspecies extrapolation)

AEL 375 ppm (= 1,500 * 6 hours (exposure of rats)/8 hours (workday))* 

(1/3))

I. Introduction

The compound, perfluoro-n-butyl iodide (PFBI) has been proposed for use as a solvent for precision 

cleaning, electronics cleaning, metals cleaning, and associated drying end uses. Several studies have been 

performed for this compound including an acute, 4-week, and 13-week series of inhalation studies in rats, 

a cardiac sensitization study in beagle dogs, pharmacokinetic studies, and genotoxicity studies in bacteria 

and human cells in culture. The results of these studies are discussed in the following sections to inform 

an assessment of the potential health risks from human exposure in the intended end uses.

II. Summary of Toxicity Studies

Acute Toxicity

In a published article summarizing the series of toxicity studies, Dodd and coauthors (2004) report the 

findings of an acute toxicity study performed in Fischer 344 rats. Young adult rats (5/sex/group) were 

exposed (nose-only) to 0, 10,000, 20,000, 35,000, and 100,000 ppm of vaporized study compound for 4 

hours. The rats were kept and observed for 14-days post-exposure; toxicity measurements were taken pre-

, post-, and during exposure, and during the 2-week post-exposure period. Body weights were obtained 

prior to exposure and then weekly during the observation period. Gross necropsy was performed on any 

animals dying prematurely, and at scheduled sacrifice. 

No mortality was observed at 10,000 ppm; however, all animals at 20,000, 35,000, and 100,000 ppm died 

prematurely, before the end of the 4-hour exposure. Symptoms observed in rats during or immediately 

after exposure included clear or red nasal discharge, chromodacryorrhea (red tears), and labored 

breathing; recovery by the rats was noted within 48 hours post-exposure. The exposure did not induce any 
September 26, 2011

changes in weight gain in the lowest concentration group, and did not cause any organ effects identifiable 

by gross necropsy. The combined sex LC50 was calculated as 14,000 ppm.

Cardiac Sensitization 

Six pure-bred beagle dogs were exposed to increasing concentrations of PFBI following an individualized 

epinephrine dose (ranging from 2-12 μg/kg) that had been previously determined optimal. A positive 

response was identified as the appearance of a burst of multifocal ventricular ectopic activity or 

ventricular fibrillation (tachycardia alone was not sufficient to signal a positive response). None of the 

dogs exhibited a positive response at 900 or 3,900 ppm PFBI, but 2/6 dogs exhibited a positive response 

at 6,200 ppm. The LOAEL for cardiac sensitization was thus identified as 6,200 ppm. 

Four-Week Inhalation Toxicity

Five rats per sex per group were exposed to the following concentrations of vaporized PFBI: 0, 100, 

1,000, or 10,000 ppm. Exposures were nose-only, for 6 hours/day, 5 days/week. The animals were 

observed for clinical signs of toxicity (e.g., straining/twisting against the exposure apparatus) during 

exposures. Animals were also inspected for signs of toxicity twice prior to exposure and weekly after 

exposure started. Body weights and food consumption were measured similarly, before exposure began 

and weekly thereafter. Body weights were measured and blood samples were taken just prior to scheduled 

sacrifice; standard hematology and clinical chemistry analyses, as well as determination of circulating 

thyroid hormone levels, were performed on the blood samples. Urine samples were taken prior to 

sacrifice for iodide analysis. Select organs (adrenal glands, brain, kidneys, liver, lungs with bronchi, 

testes with epididymides, and thyroid/parathyroids) were weighed at terminal sacrifice. Tissues preserved 

for histopathology included all the weighed tissues, as well as esophagus, heart, larynx, nasopharyngeal 

tissue, ovaries, spleen, trachea, urinary bladder, and any tissues exhibiting abnormalities on gross 

necropsy. Histopathology was performed on the control and 10,000 ppm groups, and adrenal glands, 

liver, and testes were examined histologically in the 100- and 1,000-ppm groups. Means and standard 

deviations were determined for all measurements; statistical analyses of the data were performed 

appropriately.

The only clinical sign observed during treatment was reduced activity in the 10,000-ppm group. No 

mortalities occurred in any treatment group during the four-week study. Body weight gains were 

significantly decreased in males, but not females, at the end of each week of the study (weight gain at the 

end of week 4 in high-concentration males was just over 50% of control weight gain). Food consumption 

was unaffected. 

According to the study authors, hematology parameters were unaffected by exposure; the data were not 

published in the reference for confirmation. Triglycerides were significantly increased in males at the top 

two concentrations, and in females at 10,000 ppm. Urinary iodide levels were significantly increased in 

males and females at 10,000 ppm, and in males at 1,000 ppm. Interestingly, males excreted greater 

concentrations of iodide via the urine than did the females at all concentrations.

Although serum triglycerides were increased in mid- and high-concentration males and highconcentration females, other parameters of liver disruption/damage, including serum levels of liver 

enzymes, namely aspartate and alanine transaminases; ALT and AST, respectively were unchanged and 

there was no notable liver histopathology. 

Significant thyroid hormone changes were limited to increases in T4 levels only; these changes were 

noted in males at each exposure concentration and in females at the 1,000 and 10,000 ppm concentrations. 
September 26, 2011

T3 levels in females show a decline of the same general magnitude across all exposure concentrations, but 

the differences did not reach statistical significance. These changes are shown in Table 1 below.

Table 1. Changes in Serum Thyroid Hormone Levels Following 4-Week PFBI Exposure

Hormone Exposure Group, ppm#

0 100 1,000 10,000

TSH

males 0.60±0.08 0.62±0.35 0.74±0.19 0.72±0.09

females 0.52±0.18 0.79±0.45 0.58±0.12 0.77±0.25

T3

males 61.4±11.5 60.9±5.3 72.5±2.8 55.0±9.5

females 59.5±13.4 50.0±5.9 49.5±1.2 48.2±9.2

T4

males 2.95±0.44 6.07±0.52* (206%)^ 8.78±0.72* (298%)^ 7.86±1.10* (266%)^

females 2.47±0.56 3.38±0.46 (137%)^ 4.07±0.22* (165%)^ 5.60±0.95* (227%)^

#mean±SD; n=5/sex/group; *, statistically significant (p≤0.01); ^, percent increase over controls

Subchronic (13-week exposure) Toxicity

In this study, male (15/group) and female (10/group) were exposed 6 hr/day, 5 days/week for 13 weeks 

(nose-only) to the following concentrations of PFBI: 0, 500 (low), 1,500 (mid), or 5,000 (high) ppm. Ten 

male and female rats were sacrificed for necropsy at the end of the exposure period; the remaining 5 

males/group were maintained for a 4-week recovery period involving no exposure to the test compound. 

During exposures the following endpoints were measured: mortality and clinical observations, 

ophthalmology (pre exposure and at sacrifice), weekly food consumption and body weights, clinical 

pathology, neurotoxicity as determined by a functional observational battery (13th week only), motor 

activity (13th week only), thyroid function (serum TSH [thyroid stimulating hormone], triiodothyronine 

[T3]2, and thyroxine [T4] levels), organ weights and gross necropsy and histopathology. 

A Functional Observational Battery (FOB) was performed on 10 main study animals/sex/exposure group 

and consisted of the following analyses:

 Home cage evaluations

 Handling evaluations

 Open field evaluations

 Reflex assessments

 Grip strength

 Landing foot splay

 Proprioception

 Air righting ability

 Body temperature

 Body weight

Statistical analyses were performed on the following parameters: 

 

2

T3 and T4 are the primary iodine-containing hormones responsible for mediating several functions, including 

metabolism, within the body. T4 is deiodinated in the body to form T3, which is the active form of the hormone. 

TSH, thyroid stimulating hormone, stimulates thyroid cells to take up iodine and begin the iodine organification 

process.
September 26, 2011

 Weekly body weights/body weight changes

 Food consumption

 Hematology

 Coagulation

 Clinical chemistry

 Organ weights

 Forelimb and hindlimb grip strength measurements

 Landing foot splay measurements

 Body temperature and body weights for FOB evaluations

Results for Subchronic Toxicity

Atmospheric Exposure Concentrations

Measured concentrations of PFBI were very close to nominal concentrations 0.00±0.00, 500±22, 

1,489±83, and 4,931±359 ppm, for the control, low-, mid-, and high-concentration groups, respectively. 

Analyses indicated that the test compound was completely vaporized during the exposures. 

Mortality, Clinical Effects, Eye Effects, Food Consumption, Body Weights

One control male died on Day 29 during loading into the inhalation tube; all other animals survived to 

scheduled sacrifice. Clinical effects were generally absent with the exception of increased ano-genital 

staining in high-concentration rats during the final few weeks of exposure; this effect was not present 

during the recovery period in males. Ophthalmoscopy revealed no adverse exposure-related effects on the 

eyes. 

No exposure related effects in food consumption were noted throughout the study; any changes in food 

consumption were minor and transient. Body weights in the control, low- and mid-concentration males 

and females, and high-concentration females were unaffected by treatment, but the high-concentration 

males exhibited a 9.4% decrease in mean absolute body weight compared to controls at the end of the 

exposure period. Statistically decreased body weight gains and absolute body weights were evident as 

early as week 3 and 4, respectively in high-concentration males, and these changes persisted until the end 

of exposure. However, for most measurements in the first 8 weeks of the study, the differences in 

absolute body weight were around 5-6%. Body weights of all males during the recovery period were 

comparable, indicating that weight gain resumed to normal within the first week after exposure ceased.

Functional Observational Battery

Endpoints measured in the FOB were not significantly different in treated animals compared to controls, 

with the exception of group effect for male rats; however, because subsequent comparisons between 

treated groups and controls were not significant, the difference was not considered biologically relevant. 

Increases in motor activity were noted in the low-and mid-concentration rats compared to controls, but 

these increases were not statistically significant until combined. Because the changes were not doseresponsive, they were not considered biologically relevant.

Hematology/Clinical Chemistry

There were also no treatment-related effects in measured hematology parameters that were clinically 

significant. Dose-related and statistically significant decreases in prothrombin time (up to 1.3 seconds) 

were not considered relevant because they did not exceed 3 seconds difference from controls. Treated 

males and females at all concentrations had increased hemoglobin levels; the increases were only 10% 

and were consistent across exposure levels, they were not considered adverse or clinically relevant. 
September 26, 2011

Decreases in aspartate and alanine transaminases (ALT/AST) and alkaline phosphatase (ALP) levels and 

a non-dose-related increase in serum phosphorus concentrations in males in all exposed groups and in 

females in the mid- and high-concentration groups were not deemed clinically relevant. There were no 

clinical chemistry results that were indicative of potential liver or kidney damage. Other changes in 

clinical chemistry values (e.g., decreases in glucose, blood urea nitrogen, creatinine and cholesterol) were 

small or were only noted in one sex, and thus, were not considered significant. 

Thyroid Function

The thyroid, as well as some other organs/tissues, possesses an enzyme known as the sodium iodide 

symporter (NIS), which is responsible for taking up iodine, a necessary element for thyroid function. 

Because of this, it is expected that the thyroid will respond to the excess presence of free iodide in the 

body, or the disruption of thyroid hormone stasis, either at the histopathological level, or in the production 

of hormones that incorporate the iodine. Exposure to PFBI for 13 weeks did affect the levels of 

circulating thyroid hormones in both male and female rats. The results are shown in Table 2 below. In the 

absence of detail in the original study, it was assumed that the hormone levels were bound hormone, not 

free hormone. Only free hormone is biologically active (again, only T3 activates other biological 

processes), and therefore, most circulating hormone is bound with some protein (in the case of rats, this 

protein is albumin). TSH was increased in females only at concentrations ≥500 ppm, while T3 and T4 

levels were increased in both sexes at all exposure concentrations. T4 levels were affected the most, and 

the effect was most evident in male rats. It is of note that T4 levels were comparably elevated at all 

exposure concentrations in male rats, and that TSH levels did not increase in exposed males, similar to the 

response in the 28-day study. Again, as with the 28-day study, the male rats were more sensitive to 

thyroid hormone changes.

Table 2. Changes in Serum Thyroid Hormone Levels Following PFBI Exposure

Hormone Exposure Concentration, ppm

500 1,500 5,000

Male Female Male Female Male Female

TSH +6% +32%* +11% +42%* +10% +53%*

T3 -- +27%* +20%* +31%* +33%* +31%*

T4 +270%* +65%* +300%* +97%* +310%* +210%*

Percent increases were relative to control values; *, statistically significant

The hormone levels in exposed male rats were comparable to those of control rats at the end of the 

recovery period, indicating that the changes were transient and a result of thyroid responding to increased 

iodine load in the body. The study authors did not consider the effects as necessarily adverse.

Organ Weights

Slight decreases, some statistically significant, in select absolute organ weights were noted in males at 

5,000 ppm compared to controls, most likely as a result of the slight decrease in overall body weights of 

these animals. These included brain, epididymides, heart, kidneys, prostate, seminal vesicles, spleen, and 

thymus. Exceptions to this were absolute adrenal weights, which were increased in both mid- and high 

concentration males (the latter exhibited a 24% increase relative to controls). The absolute weights of 

adrenal glands were also significantly increased in females at 1,500 and 5,000 ppm, as were the kidneys; 

no other organs showed any dose response. 

Relative adrenal gland weights were increased in males and females at 1,500 and 5,000 ppm, and relative 

kidney, liver, seminal vesicle and testes weights were increased in males at 5,000 ppm. Relative kidney 
September 26, 2011

weights were increased in all treated females. In the recovery group of males, absolute organ weights 

were unchanged relative to control animals, with the exception of the prostate, which was increased in 

1,500-ppm males, the thyroid/parathyroid gland, which was significantly increased in 500- and 5,000-

ppm males, but not in 1500-ppm males, and the liver and spleen, which were increased in 5,000-ppm 

males only. The increased relative liver weight in the 5,000-ppm males was the only persistent change in 

organ weight following cessation of exposure. 

Gross Necropsy and Histopathology

There were no notable gross findings in any organs/tissue systems of any of the treated groups at 

necropsy. The only remarkable histopathological finding was a minimal level of follicular cell 

hypertrophy with/without minimal hyperplasia in 6/10, 6/10, and 7/10 male rats at 500-, 1,500-, and 

5,000-ppm, respectively, and in 1/10 female rats at 5,000 ppm only. This finding was not observed in any 

of the treated males in the recovery group at sacrifice, indicating the effect was completely reversible. It 

also did not result in an increase in thyroid weight. No effects were noted in any other tissue/organ that 

has NIS but does not engage in iodide organification (e.g., mammary tissue, uterine tissue, etc.). There 

were no notable histopathological findings in any of the organs with absolute or relative weight changes 

in the study, indicating that the organ weight changes may have been related to stress of exposure or body 

weight changes, and not the test compound itself.

Pharmacokinetic Studies

As a complement to the 13-week inhalation toxicity study, Mattie and coworkers at the Air Force 

Research Laboratory (2010) evaluated in vitro partition coefficients of PFBI using blood, fat, and liver 

samples from ten previously unexposed Fischer 344 rats. Blood:air partition coefficients for PFBI were 

evaluated also using human blood samples obtained from excess blood samples provided by a local 

hospital. The partition coefficients are provided below in Table 3.

Table 3. In Vitro Partition Coefficients for Rats and Humans

Rat Human

Blood:air Liver:air Fat:air Blood:air

0.95±0.45 (16*) 0.44±0.31 (12*) 41±3.9 (12*; 16 hrs#)

41±6.0 (15*; 24 hrs#)

0.67±0.34 (18*)

* Number of samples tested; #equilibrium of fat samples tested at 16 & 24 hrs

As shown above, the blood:air partition coefficient for PFBI was 42% greater in the rat than the human, 

indicating that inhaled PFBI will partition more readily into the blood of a rat than in the blood of a 

human. 

Genotoxicity 

PFBI was tested in an Ames bacterial reversion assay in Salmonella typhimurium (S. typhimurium) strains 

TA98, TA100, TA1535, TA1537, and E. coli strain WP2 uvrA (measuring either base pair or frame shift 

mutations) in the presence and absence of S9 fraction from induced rat livers (metabolizing enzymes 

including mixed function oxidases) at concentrations ranging from 313 to 5,000 μg/plate (5000 ug is the 

maximum recommended by harmonized guidelines for this assay published by OPPTS). Appropriate 

negative and positive controls were analyzed in the same assays. The number of mutants induced by PFBI 

did not reach the criteria for a positive response in this assay (e.g., a dose of study compound should 

induce a 2-fold increase in the numbers of revertants over controls and a dose-response should be seen), 

indicating that PFBI does not cause either base pair exchange mutations or frame shift mutations in 
September 26, 2011

bacterial cells either in the presence or absence of activating enzymes.

The clastogenicity of PFBI was tested by culturing human lymphocytes with increasing concentrations of 

PFBI; concentrations tested in Experiments 1 and 2, -S93, were 39-5,000 μg/mL, and 20-500 μg/mL; 

concentrations used in both experiments, +S9 were 39-313 μg/mL. Cultures were incubated for either 21 

hours (experiments 1 and 2) or 45 hours (experiment 2). 

Concentrations ≥625 μg/mL PFBI, -S9, were highly toxic to the cultured cells. Concentrations ranging 

from 39-200 μg/mL were selected for metaphase analysis, for which 39 μg/mL was the highest non-toxic 

concentration. In the presence of S9, PFBI was toxic at 313 μg/mL, prompting metaphase analysis at 

dose levels of 78-263 μg/mL. No increases in chromosomal aberrations were observed at any of the 

analyzed dose levels.

III. Disruptions in Iodide Homeostasis—Potential Differences in Sensitivity between 

Humans and Rats

There are distinct differences between animal species in thyroid hormone economy and metabolism. For 

example, T3 and T4 in serum have much shorter half-lives in rats than humans and other primates (Capen 

1994) as a result of differences in the type of proteins with which these enzymes bind and how tightly 

they bind. In rats, T3 and T4 only have albumin with which to bind; in human and monkey serum, by 

contrast, T4 and T3 can bind to albumin, as well as T4- and T3-binding globulins. Binding to 

thyroglobulin by T3 and T4 is stronger than binding to albumin, which increases the half-life of these 

hormones in the human, and means that they are under tighter control following perturbations in iodine 

homeostasis. Also, T3 is bound less tightly to thyroglobulin than T4, resulting in faster turnover and 

shorter half-life in most species evaluated (Capen 1994). 

There are also species-specific differences in sensitivity of the thyroperoxidase enzyme to therapeutic 

agents and other toxicants (Capen 1994). Thyroperoxidase is responsible for oxidizing iodide, which is 

the predominant form of iodine to which humans are exposed, to elemental iodine, which can then be 

added to the tyrosine residues of the thyroglobulin in a process called iodine organification, which results 

in thyroxine (T4), and triiodothyronine (T3). Studies show that thyroperoxidase from the rat, mouse, and 

dog is more susceptible to inhibition by toxicants than the same enzyme from the human, monkey, guinea 

pig, or chicken (Capen 1994).

Studies also show that TSH levels are naturally higher in male rats than female rats, and that male rats are 

more sensitive to disruptions in thyroid hormone economy/homeostasis. The toxicity studies currently 

under consideration support this finding.

More recently, the human and rat NIS (sodium iodide symporter) genes have been identified, isolated, and 

transfected into varying tumor cell types to determine if they can be useful in chemotherapy. For example, 

Heltemes and coworkers (2003) determined the abilities of the two symporters to concentrate radiolabeled 

 

3

S9 fraction is the supernatant fraction of homogenized liver that has been centrifuged at 9000xg--the supernatant 

contains cytosol and microsomes which contain metabolic enzymes from the liver, such as cytochrome P450 and 

others responsible for metabolizing toxicants. In this specific case, the S9 was isolated from male rats induced with 

Aroclor 1254 (dissolved in Arachis oil) 5 days prior to liver isolation and supernatant preparation. The S9 fraction 

was tested for efficacy using two mutagenic polycyclic aromatic hydrocarbons. ‘+S9’ indicates that experiments 

were undertaken with the fraction and ‘–S9’ indicates without the fraction.
September 26, 2011

iodine into varying tumor cell lines. They found that 7 human cancer and one monkey cancer cell lines 

transfected with and positively expressing the rat NIS gene took up 125I consistently better than those 

transfected with and expressing the human variant (uptake ratios of cells with rat NIS to those with 

human NIS ranged from 1.9 to 3.4, e.g., 190% to 340% more uptake with the rat symporter than the 

human symporter). 

Comparison of the thyroid hormone changes in the 4-week and the 13-week study indicate that T4 was 

more susceptible to change, and that these changes occurred even at the lowest exposure concentration 

used (100 ppm) and at the shortest exposure duration (28 days). TSH and T3 levels changed slightly, but 

not significantly, in exposed males and females in the 28-day study, but the trends were inconsistent. 

It is not possible to determine without additional study what cellular mechanisms in the PFBI-exposed 

rats in the 13-week study may be causing the increased values of TSH in female rats, and T4 and T3 in 

male and female rats. Increased release of stored T3 and T4 is possible but unlikely, given that 

histopathology of the thyroid did not indicate any notable degradation of the colloid within the thyroid 

that would be necessary for hormone release. Hepatic microsomal enzymes play a significant role in 

thyroid hormone regulation, since they are involved in turnover and excretion of both T3 and T4. 

However, the data do not indicate that increased excretion of thyroid hormones is responsible, as there 

was no reported increase in hepatic microsomal enzymes in the histopathology tables provided in the 

study. Disruption of the deiodination of T4 (to form T3) is a possible cause of the changes noted, but 

cannot be confirmed without additional mechanistic studies, which are not warranted at this time.

Taken together, the data do indicate that the rodent model is not the most appropriate one for trying to 

determine what effects on iodine homeostasis might be induced by exposure to PFBI. They also indicate 

that the human is likely to be less sensitive than the rat to excess iodide intake, and suggest that an 

uncertainty factor for intraspecies extrapolation (protection for sensitive subpopulations) is overly 

conservative. 

IV. Development of the AEL for PFBI

A NOAEL (point of departure) of 1,500 ppm from the 13-week inhalation study was chosen because at 

this exposure concentration, no body weight changes were noted. Thyroid histopathology and hormone 

changes observed at this level were completely resolved after exposure cessation and were considered 

adaptive, rather than adverse effects.

The AEL was calculated in the following manner:

1,500 x (6/8) ÷ 3 = 375 ppm

A human equivalent concentration (HEC) was determined by adjusting the NOAEL of 1,500 ppm by the 

ratio of rat exposure duration per day to that of an occupational worker (6 hours/8 hours). The guidelines 

for developing Reference Concentration (RfC) values (EPA 1994) were generally followed, which 

suggest the use of a combined uncertainty factor of 10 for interspecies extrapolation (3 for 

pharmacokinetic [PK] differences, and 3 for pharmacodynamic [PD] differences). Because the rat 

blood:air partition coefficient is larger than that of a human, and because the rat sodium iodide symporter 

is more effective at uptake than that of the human, a UF of 1 was used for PK differences, and a UF of 3 

was used for PD differences. An intraspecies UF was deemed not necessary because thyroid effects are 

specific to existing iodine status which varies significantly between individuals, and because the effects 
September 26, 2011

are adaptive and reversible. Because subchronic studies are typically used to develop AEL values, no 

additional UF has been added to account for study duration. Similarly, the database is considered 

comprehensive, and no additional UF has been added to account for database limitations. 
September 26, 2011

References

Capen CC. 1994. Mechanisms of Chemical Injury of Thyroid Gland. In Receptor-Mediated Biological 

Processes: Implications for Evaluating Carcinogenesis, eds. HL Spitzer, TJ Slaga, WF Greenlee, 

and M McClain. Hoboken, NJ: Wiley-Liss, Inc. pp. 173-191.

Dodd DE, Hoffmann GM, and Hardy CJ. 2004. Perfluoro-n-butyl iodide: Acute toxicity, subchronic 

toxicity and genotoxicity evaluations. Int J Toxicol 23:249-258. 

Heltemes LM, Hagan CR, Mitrofanova EE, et al. 2003. The rat sodium iodide symporter gene permits 

more effective radioisotope concentration than the human sodium iodide symporter gene in 

human and rodent cancer cells. Cancer Gene Ther 10:14-22.

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inhalation toxicity study in rats with a 4-week recovery period. Air Force Research Laboratory, 

Wright Patterson AFB, OH, September 2006.

Mattie D, G Hoffman, L Narayanan, et al. 2010. A 13-week nose-only inhalation toxicity study for 

perfluoro-n-butyl iodide (PFBI) in rats with recommended occupational exposure levels. 

Inhalation Toxicology 22 (10): 847-860. August 2010.

U.S. EPA. 1994. Methods for Derivation of Inhalation Reference Concentrations (RfCs) and Application 

of Inhalation Dosimetry. Office of Research and Development. EPA/600-8-90/066F. October 

1994.