Environmental Health Perspectives
`Vol. 21, pp. 255-267, 1977
`
`Toxicology of the Fluoroalkenes:
`Review and Research Needs
`
`by J. Wesley Clayton*
`
`In this review of the published literature on the toxicology of fluoroalkenes several features emerge and
`research needs are evident. The fluoroalkenes vary widely in acute inhalation toxicity. Those, such as
`perfluoroisobutylene, PFIB, the most highly toxic member, attacks the pulmonary epithelium of rats
`eventuating in edema and death after a delay of about one day. Other fluoroalkenes, such as hexafluoro-
`propylene (HFP) or chlorotrifluoroethylene (CTFE), also cause pulmonary injury but at lower concentra-
`tions produce concentration dependent changes in the renal concentrating mechanism of the rat. Changes
`in the CNS of rats and rabbits have also been reported for CTFE. CTFE, in repeated exposures, has
`produced blood pressure changes in dogs, CNS effects and changes in the erythropoietic system. This
`variety of responses indicates the need for investigation. Chronic effects have not been sufficiently studied
`for PFIB and HFP. Thus pointing up the desirability for study. Mechanisms of action research for
`fluoroalkenes is an important area of need. While several ideas have been suggested, there are no data to
`support them. The nucleophilic sensitivity of the fluoroalkenes and the potential carcinogenic effects
`stemming therefrom suggests a need field for investigation. We also can readily perceive the needs for the
`evaluation of effects on reproduction (including mutagenesis and teratogenesis), metabolism pulmonary
`functions, cellular function and structure. Epidemiologic studies on occupationally exposed populations
`are desirable in order to adequately define human health hazard from these fluorocarbons.
`
`Introduction
`
`Because of legitimate concern about the tox-
`icologic and environmental effects of widely used
`fluoroalkane propellants such as dichlorodi-
`fluoromethane (fluorocarbon I2),
`trichloro-
`fluoromethane (fluorocarbon 11) and others which
`have been in commercial use for decades, other
`fluorocarbons such as the fluoroalkenes, have only
`been cursorily evaluated for toxic and other
`hazards. It is the purpose of this paper to review the
`relevant published literature on the toxicology of
`several fluoroalkenes and to define areas of need for
`future toxicologic research.
`That fluoroalkenes are important in toxicologic
`evaluation, has been pointed out by Krespan (1).
`He points out that it was recognized more than 40
`years ago that fluoroalkenes such as tetra-
`fluoroethylene and chlorotrifluoroethylene could be
`polymerized by free-radical catalysis. This de-
`velopment led naturally to a preparation of several
`kinds of fluoropolymers formed from the variety of
`fluoroalkenes which were subsequently synthe-
`
`*Toxicology Program, University of Arizona, Tucson,
`Arizona 85721.
`
`insofar as health
`sized. Thus, fluoroalkenes,
`hazards were concerned, were treated mainly as in-
`dustrial chemicals, prepared by the manufacturer,
`subjected to appropriate toxicity evaluation, and
`handled with the caution considered their due.
`
`Consequently, they rarely if ever came in contact
`with the public as the fluoroalkanes have. How-
`ever,
`isolated accidental exposures in industry
`brought the toxic potential of the fluoroalkenes
`dramatically to our attention. It would seem that
`the industrial controls requisite to the safe manufac-
`ture and handling of these chemicals precluded sig-
`nificant health hazards. Accordingly,
`little tox-
`icologic research beyond single and shortterm re-
`peated inhalation exposures has been available in
`the published literature.
`
`Chemistry
`
`Fluoroalkenes differ from their hydrocarbon
`counterparts in that the area of the double bond
`tends not to be rich, but deficient in electrons be-
`cause of the strong electronegativity of the fluorine
`atoms attached to adjacent carbons. Thus fluoroal-
`kenes are subject
`to nucleophilic attack and are
`prey for bases or other nucleophiles, e.g., fluoride,
`
`December 1977
`
`Page 1 of 13
`
`255
`
`Arkema Exhibit 1141
`
`Page 1 of 13
`
`Arkema Exhibit 1141
`
`

`
`OH or NH2. Krespan (I) shows how the fluoride
`ion (F_) is related to the chemistry of the fluoroal-
`kenes in the same way as the proton (H+) is related
`to the alkene hydrocarbons:
`
`H" + c+H,=cHcH,cH, = CH,,C*HCH,CH3
`
`: CH3CH = CHCH3 + H+
`
`(1)
`
`F‘ + cF,=CFcF,cF, = cF,c-FcF,cF,
`
`= CF,CF=CFCF3+ F-
`
`(2)
`
`In reaction (2), migration of the double bond is ac-
`complished by the movement of the nucleophile F‘
`into the double-bond electrophilic center with sub-
`sequent leaving of F‘ to proceed down the chain.
`The same event for the alkene hydrocarbons is
`shown in Eq. (1). In alkene hydrocarbons, the area
`of the double bond is electron rich thus attracting an
`electrophilic proton.
`Where a locus of the type present in the double
`bond area of the fluoroalkenes exerts a major influ-
`ence on its electronic properties,
`it would seem
`likely that biological activity would be largely influ-
`enced by the area of low electron density between
`adjacent carbons and the consequent susceptibility
`to nucleophilic attack. According to Chambers and
`Mobbs (2) and Cook and Pierce (3), susceptibility
`of fluoroalkenes to nucleophilic attack is in the fol-
`lowing order:
`
`(CF3)2—C——-CF, > CF2=CFCF3 > CF2=CF2
`
`The inhalation toxicity is in the same order per-
`fluoroisobutylene > hexafluoropropylene > tetra-
`fluoroethylene (Table 1). However, experimental
`data bearing on this potential relationship are lack-
`ing, as is information on the biologic or toxicologic
`mechanisms of action among the fluoroalkenes. For
`example, Danishevskii and Kochanov (4) claim that
`the high toxicity of perfluoroisobutylene (PFIB)
`stems from in vivo carbonyl fluoride formation.
`Against this view, however, COF2 is lower in acute
`inhalation toxicity than PFIB (5), and it produces
`different biologic sequelae. The picture of COF2
`toxicity is that of hydrogen fluoride. The approxi-
`mate lethal concentration (ALC) of COF2 (4-hr ex-
`posures in rats) is 100 ppm, which would corre-
`spond to 200 ppm of HF, a concentration in the
`lethal range. It is only conjecture, but the suscepti-
`bility of PFIB to nucleophilic attack might consti-
`tute the basis for its high toxicity.
`
`256
`
`Page 2 of 13
`
`Acute Inhalation Toxicity
`
`Summaries of acute inhalation toxicity of several
`fluoroalkenes are found in Tables 1 and 2. A wide
`
`range of toxicity is readily apparent in Table l. and
`while it may seem that toxicity in this class is in-
`versely related to the number of fluorine atoms, in-
`adequate knowledge of toxic mechanisms at present
`obviates any such conclusion. It is more likely that
`some biological action related to the double bond,
`as postulated above, is predominantly responsible
`for the high toxicity of PFIB, rather than its com-
`plement of eight fluorine atoms. The toxic
`mechanism however remains to be demonstrated.
`
`Table 1. Inhalation toxicity of several fluoroalkenes.“
`
`Structure
`CH,=CHF
`CF2=CH,
`
`No. F
`atoms
`1
`2
`
`Acute toxicity for rats”
`ALC,
`LC5.,
`ppm
`ppm
`>800,000"
`—
`128,000
`—
`>800,000°
`—
`—
`40,000
`—
`3,000
`0.5, 0.76“
`—
`
`4
`6
`8
`
`CF,=CF,
`CF,CF=CF,
`((;}=3),c=cF2
`"Data of Clayton (5).
`"4-hr exposures except where noted.
`‘80% CH2=CHF, 20% O2; 12.5-hr exposure.
`480% CH2=CF,, 20% 0,; 19-hr exposure.
`90.5 ppm exposure was 6 hr; the 0.76 ppm exposure was 4 hr.
`
`Table 2. Inhalation toxicity of several halogenated alkenes.“
`
`Structure
`CCl,=CH2
`CHCl=CCl,
`CCl,=CCl,
`CCl,=CF,
`CClF=CF,
`
`No. F No. Cl
`atoms
`atoms
`0
`2
`0
`3
`0
`4
`2
`2
`3
`I
`
`Acute toxicity for rats”
`ALC,
`LC,-,0
`ppm
`ppm
`32,000
`—
`8,000
`—
`4,000
`—
`1,000
`—
`—-
`1000
`
`“Data of Clayton (5).
`“All 4-hr exposures.
`
`Generally, fluorinated alkenes are less toxic than
`chlorinated alkenes. Table 3 brings together three
`homologous pairs illustrating this point. A direct
`relationship between toxicity and number of
`chlorine atoms is illustrated by the sequence sig-
`nifying acute inhalation toxicity of these chlorinated
`alkenes as judged by animal inhalation exposures.
`In order of decreasing toxicity we have:
`
`CCl,=CCl, > CI-ICl=CCI, > CI-I,=CCI, > CH,=CI-ICl
`
`Illustrative of fluoroalkenes of relatively low tox-
`icity are vinyl fluoride (VF) (CH2=CHF) and vin-
`ylidene fluoride (VF2) (CH2=CF2). As indicated
`
`Environmental Health Perspectives
`
`Page 2 of 13
`
`

`
`Table 3. Toxicity comparisons among some
`halogenated alkenes (rats).“
`
`Structure
`CH,=CHCl
`CHg=*CI-IF
`CH2=CCl,
`
`CH2=CF,
`CCl2=CCl,
`CF,=CF,
`
`Acute inhalation toxicity, ALC,
`ppm (by volume)”
`>250,000‘
`>800,000"
`32,000
`128,000
`>800,000‘
`4,000
`40,000
`
`“Data of Clayton (5).
`"All 4-hr exposures except where noted.
`‘Guinea pigs, 8-hr exposure.
`"80% CH2=CHF, 20% 0,; 12.5 hr exposure.
`980% CH,=CF,, 20% 0,; 19-hr exposure.
`
`by Table 3, high concentrations were not lethal for
`rats exposed to either VF or VF2 for 12.5 and 19 hr,
`respectively. In the work by Lester and Greenberg
`(6) there was no organ damage reported. Limperos
`(7) conducted repeated exposures with male and
`female rats inhaling 100,000 ppm VF 7 hr/day, 5
`days/week, for 30 exposures. There were no
`fatalities; rats gained weight normally, showed no
`obvious behavioral changes, or tissue damage, as
`evaluated by microscopic examination.
`Fluoroalkenes of moderate to slight toxicity may
`be exemplified by tetrafluoroethylene (TFE), hexa-
`fluoropropylene (HFP), and chlorotrifluoro-
`ethylene (CTFE). These compounds are irritating to
`the respiratory tract and lungs in lethal concen-
`trations as judged by animal exposures, but in addi-
`tion they also can cause kidney injury (8-10). Single
`exposures of rats to varying concentrations of CTFE
`have produced evidence of kidney dysfunction.
`Radford (11), as reported by Zapp (8) demonstrated
`that laboratory rats ingesting a dry diet ad libitum
`voluntarily limited their water intake and conse-
`quently excreted a maximally concentrated urine.
`Tracking the water intake, urine volume, and solute
`concentration of several rats, Radford found a high
`degree of uniformity in the response of individual
`rats for these variables. This suggested an exquisite
`response system relating to the concentrating
`mechanism of the renal tubular cells in the rat. When
`this mechanism was disturbed, water intake and
`urine volume increased while solute concentration
`decreased. In order to determine possible “dose”
`relationships, Radford exposed groups of male rats
`for 4 hr in an inhalation chamber to 125, 240, 340, or
`460 ppm of chlorotrifluoroethylene (CTFE). Work
`reported by Hood et al. (10) had disclosed kidney
`injury in rats inhaling CTFE. In Radford’s work,
`half of the rats inhaling 460 ppm died within one
`week after exposure. The remaining animals sur-
`vived and were observed for signs of renal dysfi1nc-
`
`December 1977
`
`Page 3 of 13
`
`tion for 39 days. Figure 1 depicts the effects of the
`various levels of CTFE on the rat’s ability to con-
`centrate its urine. Of the three variables shown,
`body weight was the least sensitive to CTFE. Rats
`inhaling 460 ppm showed weight depression as com-
`pared to the pre-exposure values. At 340, 240, and
`125 ppm,
`it is debatable whether or not the body
`weight curves show a weight depresssion related to
`CTFE exposure because food consumption was also
`down slightly. Variables reflecting renal function
`were the most sensitive indices of effects. All treat-
`ment levels exerted an effect on the renal concentrat-
`ing mechanism, and this effect varied in a dose-
`related fashion.
`
`M
`’°°
`4
`
`|
`I
`
`am;vow:ml/layFOODIIIYAIEooovWEIGHT9-0-/ur.3S.=asis9a8
`
`
`
`
`nolll
`IIIICOI¢IYRA‘Il0I
`
`
`250 no mun: Yemin -I on
`.;.g.4.;.g.:oIzscsc1I9noI
`
`DAYS AFTER EXPOSURE
`
`($365110;
`
`FIGURE 1. Effects of single exposure of chlorotrifluoroethylene:
`(
`) 125 ppm; (A) 240 ppm; (o) 340 ppm; (9) 460 ppm. Mean
`values for groups of six male rats.
`
`Figure 2 illustrates the dose dose/concentration re-
`lationships derived from the foregoing CTFE expo-,
`’ sures and several doses administered by subcutane-
`ous injections of mercuric chloride, a comparative
`control. Functional impairment of the kidney can
`therefore be expressed as a decline of urine solute
`concentration and increased water intake with in-
`
`257
`
`Page 3 of 13
`
`

`
`ZIOO
`
`PrI~
`Exposurc
`Range
`
`mOs/liver
`
`
`
`MINIMUMURINESOLUTECONCENTRATION
`
`500
`
`15(1)
`nooo
`NOMINAL concsmnmons (ppm, val)
`
`2000
`
`FIGURE 3. Effects of hexafluoropropylene on rat renal concen-
`tration for 4 hr exposure.
`
`of the renal tubules. Clayton conducted kidney func-
`tion studies on these rats and showed that sublethal
`concentrations caused increased urine volume which
`reached a high point 2 to 4 days after exposure and
`gradually returned to lower volumes in the 14-day
`observation period following exposure. These find-
`ings agree with those observed by Radford. We need
`now to study this post-exposure phase in more de-
`tail. It would be important to follow the anatomical
`changes (light and electron microscopy) occurring at
`several points along the curves plotted in Figure 2
`describing renal function changes. Of particular sig-
`nificance is the so-called recovery phase. Is it in fact
`“recovery?” What is the significance of these events
`for humans accidentally exposed to these fluoroal-
`kenes?
`
`Kochanov (12) exposed groups of rats and rabbits
`for 2 hr each to various concentrations of CTFE.
`The LC5o for both rats and rabbits was determined as
`5,040 ppm. The concentrations resulting in death of
`,all animals from the 2-hr exposure were 5544 ppm
`and 7560 ppm for rabbits and rats, respectively. The
`animals became first excited, apathetic, then dys-
`pneic and inactive during exposure. There was also
`impairment of coordination at the highest concen-
`tration of approximately 10,000 ppm. Deaths oc-
`curred during the first few days after exposure. His-
`tology of animals that died disclosed congestion of
`intemal organs, changes in the brain, and necrosis of
`
`Environmental Health Perspectives
`
`me met, me.
`FIGURE 2. Efiects of (X) I-IgCl, and (o) CTFE on rat kidneys.
`
`creasing CTFE concentrations. The threshold con-
`centration for this effect appears to be around 100
`ppm, approximately one tenth the 4-hr, rat LC5o of
`1000 ppm (5). Hexafluoropropylene (HFP) and tet-
`rafluoroethylene (TFE) provoked similar responses
`in the rat kidney, but these were both less active in
`this regard than CTFE. For HFP the 4-hr rat LC50
`was found to be 3000 ppm, and the threshold con-
`centration for impairment of the rat renal concentrat-
`ing function was approximately 400 ppm (Fig. 3)
`about one tenth the LC5o, as with CTFE. For TFE
`these values were 40,000 ppm and 500 ppm respec-
`tively (5). These findings in rats suggests a physiolog-
`ical basis for setting workplace standards for the
`fluoroalkenes, but it is clear that detailed studies, say
`on isolated renal tubules and electron microscopy,
`are needed to elucidate the finer aspects of the
`phenomenon just described. Furthermore, other
`fluoroalkenes, e.g., VF, VF2, dichlorohexa-
`fluorobutene, hexafluorocyclobutene, and per-
`fluoroisobutene need to be subjected to evaluation
`of effects on renal function. In addition, long-term,
`repeated, low level exposures are needed.
`Microscopic examination of tissues from male rats
`exposed to 800, 900, 1000, or 1200 ppm of CTFE for
`4 hr was reported by Hood et al. (10). The LC5., was
`calculated as 1000 ppm. Death occurred 1-11 days
`after the inhalation exposure. Pathology revealed
`pulmonary edema, pleural effusion and degeneration
`
`258
`
`Page 4 of 13
`
`Page 4 of 13
`
`

`
`the kidney tubules. The authors did not report on the
`histology of animals that survived exposure. Neither
`did they describe any changes in the water intake or
`volume of urine excreted. It is also notable that the
`
`LCT50 of 10,000 ppm-hours reported by Kochanov
`(I2) is about 2.5 times that of 4000 ppm-hours deter-
`mined by Hood et al. (10). This raises the question of
`sample identity. Neither of the two groups reported
`on the composition of their samples or the contami-
`« nants .
`
`Paulet and Desbrousses (I3) exposed Swiss mice
`and Wistar rats to hexafluoropropylene for time
`periods of 0.5-8 hr. The results of the experiments of
`these authors are summarized in Table 4. The lowest
`lethal concentrations for the 8-hr exposures were 400
`ppm for mice and 2000 ppm for rats. Deaths
`occurred during the succeeding 10 days follow-
`ing exposures. At the high levels deaths occurred
`within one day.
`
`Table 4. Acute inhalation toxicity of hexalluoropropylene.“
`
`Duration of
`exposure, hr
`lé
`2
`4
`6
`8
`
`Mice
`3000
`1200
`750
`680
`600
`
`LC’“’’ ppm
`
`Rats
`15,750
`4,000
`2,800
`2,350
`2,400
`
`“Data of Paulet and Desbrousses (I3).
`
`Danishevskii and Kochanov (4) report studies on
`rats exposed to hexafluoropropylene,
`tetra-
`fluoroethylene and chlorotrifluoroethylene. The fol-
`lowing lethal levels were reported for 2-hr expo-
`sures: hexafluoropropylene, 3,240—13,365 ppm; tet-
`rafluoroethylene,
`25,000
`ppm;
`chlorotri-
`fluoroethylene, 7,560 ppm. Histology of rats which
`died after exposure to these three fluoroalkenes
`showed pulmonary congestion and edema with de-
`generative changes in liver and kidney. These levels
`would be expected to be lethal on the grounds of
`previously described studies. Changes that might
`have occurred in urine volume and water intake
`
`were not reported.
`Investigating the toxicity of tetrafluoroethylene,
`Zhemerdei (I4) exposed rats and rabbits for 2 hr
`each to concentrations in the range of 5000 to
`100,000 ppm by volume. The lowest lethal concen-
`tration for the rats exposed was 25,000 ppm. The
`time of death of the rats was in direct proportion to
`the concentration and varied from 3 hr after expo-
`sure to 16 days and more. Rats exposed to 50()0 ppm
`showed no signs of toxicity. At higher concentra-
`tions, there was inactivity, rapid respiration and
`somnolence. After exposure ended, there was de-
`pression, slow respiration, inactivity and occasional
`
`December 1977
`
`Page 5 of 13
`
`tetanic convulsions elicited by external stimuli. For
`rabbits, the lowest lethal concentration was 40,000
`ppm. At 10,000 ppm there were no signs of toxicity;
`above 10,000 ppm, there was inactivity and a de-
`crease in respiration rate. After exposure, the rab-
`bits appeared apathetic, lost appetite, and the rate
`of respiration increased. Rabbits which succumbed
`experienced a convulsion before death. Pathology
`of rats and rabbits disclosed congestion of organs,
`especially the brain, hemorrhage of the lungs and
`spleen, and degenerative changes in the kidneys.
`Considering probable differences in the kind and
`quantity of contaminants in the various samples,
`the work reported by Danishevskii and Kochanov
`(4) and Zhermerdei (14) reveals the same order of
`toxicity for the several fluoroalkenes as reported
`earlier.
`
`Referring to Table I, perfluoroisobutylene
`(PFIB) is by far the most toxic fluoroalkene known.
`Clayton (15) reported the acute inhalation of PFIB.
`Table 5 summarizes the data from the exposures,
`and Figure 4 discloses time/concentration relation-
`ships with mortality. Rats succumbing to PFIB
`showed progressively severe tachypnea and
`cyanosis and died as a result of pulmonary edema
`with no effects discernible in other organ systems.
`From these data and similar animal experiments
`with phosgene, PFIB (LCT5o = 3 ppm-hr) is about
`ten times as toxic as phosgene (LCT50 = 25 to 40
`ppm-hr). The acute toxic action of these two irri-
`tants appears to be directed solely at the lung.
`Longer-term exposures to PFIB at levels without
`deleterious effects on the lung could exert other
`actions—possibly on the kidney, as has been re-
`ported for CTFE and HFP.
`Exposures of rats and mice to PFIB are reported
`by Danishevskii and Kochanov (4). In 2-hr expo-
`sures all rats succumbed to a concentration of 1.8
`
`ppm (vol) (3.7 ppm-hr), and the maximum tolerated
`concentration was 1.6 ppm. Mice tolerated a con-
`centration of 0.6 ppm while 1.2 ppm (2.4 ppm-hr)
`and 1.8 ppm (3.7 ppm-hr) were the minimum lethal
`and absolute lethal concentrations, respectively.
`Histology disclosed pulmonary hemorrhages and
`edema and degenerative changes in the kidney,
`viz., albuminous, granular dystrophy and plas-
`molysis [sic] of the cells of tubules. Degenerative
`changes, sometimes fatty, in the liver were also re-
`ported. A relationship between the degree of the
`histologic reaction and the level of exposure is not
`delineated by these authors. This work is in agree-
`ment with that already summarized with respect to
`lung changes. Changes in other organs however are
`not consistent.
`
`With the exception of Kochanov’s work on
`CTFE (12), Russian investigations of the toxicity of
`
`259
`
`Page 5 of 13
`
`

`
`Table 5. Summary of single exposures of rats to perfluoroisobutylene.“
`
`Mortality ratio,
`Time of
`Nominal concn,
`exposure,
`(no. dead/no.
`Clinical signs
`Pathological
`
`ppm (by vol.)
`hr
`exposed)
`changes
`1.0
`4.25
`2/2
`Acute pulmonary
`5.33
`edema
`6.00
`Acute pulmonary
`edema
`
`0.5
`
`2/2
`
`Dyspnea, cyanosis, gasp-
`ing convulsions
`Slight dyspnea after ex-
`posure. Both died over-
`night
`None during exposure.
`Slight increase in respi-
`ration rate and weight
`loss next day. Recov-
`ered thereafter
`
`
`0.3
`
`6.00
`
`0/2
`
`None observed
`9 days after
`exposure
`
`“Data of Haskell Laboratory, unpublished.
`
`RANGE
`
` LETHAL
`
`NON- LETHAL
`RANGE
`
`CONCENTRATIONOFPFIB,ppm(volI
`
`+EXPOSURE TIME - mmuies
`
`:l__J I;
`no
`200300
`
`FIGURE 4. Rat mortality from inhaled perfluoroisobutene.
`
`CTFE, TFE, HFP, and PFIB disclose the same
`order of toxicity that American authors report.
`However, the histologic changes appeared to differ
`somewhat; these need to be clarified.
`In their studies on fluoride ion excretion by rats
`inhaling fluoroalkenes, Dilley et al. (16) found that
`hexafluoropropene (30 min exposure at 2600 ppm)
`produced increased urine excretion as well as in-
`creased fluoride excretion. The eiuretic effect was
`most pronounced and lasted longer with H FP com-
`pared to the other fluorocarbons investigated. Rats A
`inhaling HFP displayed histologic changes in the
`kidneys which were described as dilation and ne-
`crosis of the proximal
`tubules, cytoplasmic
`eosinophila, and sloughing into the intraluminal
`areas. The authors conclude that the fluoroalkenes
`
`260
`
`Page 6 of 13
`
`or a metabolite thereof caused the increase in urine
`volumes observed. Because only one concentration
`was used,
`it
`is not possible to determine the
`threshold levels of these fluorocarbons. However,
`the work is in agreement with those previously cited
`which demonstrated renal toxicity for the fluoroal-
`kenes studied.
`
`Dilley et al. (16) also studied the effects of tetra-
`fluoroethylene (TFE), trifluoroethylene, vinylidene
`fluoride, vinyl fluoride, and hexafluoroethane.
`Changes like those reported for HFP were ob-
`served, however, the extent of these were not as
`marked as those noted for HFP. It is likely that the
`changes would be dose-related and that experi-
`ments at additional levels would reveal this.
`
`Repeated Inhalation Toxicity
`
`Few studies of the effects of repeated animal ex-
`posures to fluoroalkenes have been reported, yet
`these fluorocarbons possess the greatest potential
`for biological effects.
`
`Chlorotrifluoroethylene (CTFE),
`Repeated Exposures
`
`After Hood et al. (10) had determined the LC5o
`for CTFE in rats, viz., 1000 ppm, these inves-
`tigators went on to study the effects of repeated
`exposures, Phases I and II.
`In Phase 1, three dogs, male and female rats,
`male guinea pigs, and male rabbits were exposed to
`300 ppm CTFE, 4 hr per day, 5 days per week.
`Eighteen exposures were actually conducted. Rats
`showed a slight weight loss but no other signs of
`toxic action. There were changes in the renal
`tubules. In the guinea pigs there was one death after
`the sixth exposure, loss of body weight, and normal
`histology. Rabbits showed two deaths after the fourth
`and fifth exposures, loss of body weight, normal
`
`Environmental Health Perspectives
`
`Page 6 of 13
`
`

`
`histology. In dogs, blood pressure and heart rate
`were normal;
`there was mild leucopenia and
`granulocytopenia during the second and third day of
`each week. Mild encephalopathy was seen in two
`dogs. A third dog was not sacrificed but exposed as
`follows: 300 ppm,
`three times; 400 ppm, seven
`times; 500 ppm, two times; 600 ppm, one time; 800
`ppm, three times; and 1000 ppm, one time. At each
`of these steps there was temporary leucopenia.
`After recovery of the white cell count, the concen-
`tration of CTFE was raised to the next level. An
`increase in the red blood cell count was detected
`
`during the 400 ppm exposure; plasma cholesterol
`rose slightly.
`Following the exposure to 1000 ppm, the dog was
`subjected by Clayton, as reported by Hood (10) to
`the additional stress of exercise using a treadmill,
`the objective being an attempt to simulate a real-life
`problem where accidental exposure could be as-
`sociated with considerable muscular exertion by the
`individual. Heart rate was the parameter chosen to
`assess this potential problem. Upon exercise, the
`dog became weak and was unable to complete a
`standard exercise pattern that his cohorts had no
`difficulty in completing. Heart rate was signifi-
`cantly elevated to 200 beats/min. No changes in
`cardiac rhythm were detected even though a high,
`endogenous epinephrine level was probably
`reached. After his exercise period, recovery to base
`line heart rate was slowed.
`
`In order to segregate the effects of the parade of
`exposures which had preceded the final one at 1000
`ppm, a fourth dog was exposed once, for 4 hr, to
`1000 ppm. Effects on this animal were not nearly as
`dramatic. No acute toxic effects were reported, and
`there was a transient drop in the white cell count
`from 7100 to 2200 in the day following the exposure.
`Pathologic examination revealed degenerative
`neural changes which were not pronounced in the
`dog which had received multiple exposures than in
`the dog which had been exposed once to 1000 ppm.
`Short-tenn, repeated exposures in dogs therefore
`cause transient leucopenia, an adaptive component
`('2), persistent erythrocytosis, a slight rise in plasma
`cholesterol, and encephalopathy without clinically
`detectable neurological abnormalities.
`These findings strongly indicated that long-term,
`repeated exposures could ultimately damage the
`adaptive competence of the dog and provoke clini-
`cally observable neurological changes to accom-
`pany the encephalopathy. Accordingly, in Phase II,
`a long-term investigation was carried out by these
`workers. Rats, rabbits, guinea pigs, and dogs were
`exposed to CTFE concentrations beginning at 15
`ppm (38 exposures) and raised progressively to 30
`ppm (28 exposures), 50 ppm (93 exposures), 100
`
`December 1977
`
`Page 7 of 13
`
`ppm (56 exposures), and 150 ppm (104 exposures).
`The exposures lasted 6 hr each day (excepting holi-
`days) and were conducted 5 days per week for 14
`months. Guinea pigs and rabbits were not affected,
`clinically or anatomically by the exposure regimen.
`Rats developed degenerative changes in the renal
`tubules which were discovered at the end of the 14
`
`months of exposure. It is not known from the report
`of this work when or at what concentration of those
`
`named above the kidney response occurred. From
`Radford’s data previously cited, one would expect
`the change to occur at the beginning of the 100-150
`ppm exposure series and progressively worsen for
`the remainder of the 14 months.
`
`In the group of dogs in this experiment, overt
`signs of toxicity were not noticeable through the
`exposures up to 150 ppm. At this level, neurological
`disturbances were observed in two dogs after 27 or
`64 exposures. Changes in blood pressure became
`statistically significant shortly after the 100 ppm
`series was begun (Fig. 5). There was some hint of
`these changes near the finish of the 50 ppm series. It
`is probable that extending the 50 ppm level beyond
`the 93 exposures would have gradually increased
`the departure of the blood pressure parameters
`from control limits.
`
`Hematological evidence of changes attributable
`to CTFE was also picked up during the 50 ppm
`series and became statistically significant at the
`higher levels. These responses were consistent with
`changes in hematologic measurements made during
`Phase II, viz., leucopenia, erythrocytosis (RBC,
`Hemoglobin, Hematocrit), granulocytopenia, and a
`slight elevation in plasma cholesterol in two dogs.
`Pathologic examination of the dogs revealed
`muscle atrophy and degenerative changes in the
`brain, spinal cord, spinal and peripheral nerves. On
`the grounds of these data, the authors suggest that
`20 ppm would be a safe “ceiling” concentration for
`workers potentially exposed 8 hr/day. Human data
`were evidently not available for entry into this
`judgement. Accidental human exposure has not
`been reported. Therefore the mode of toxic action
`ofCTFE in humans is, at present, not known. Until
`this point is delineated, those who might be exposed
`to CTFE or supervise those who might, could, from
`the animal data just discussed, anticipate almost
`any organ system to be affected—respiratory,
`nervous, renal or hematopoietic.
`The Russian investigator, Kochanov has pub-
`lished results of chronic animal toxicity experi-
`ments on CTFE (12). In this study, seven rabbits
`were exposed 4 hr daily except Sundays and holi-
`days for 58 days to 500 ppm of CTFE. Three rab-
`bits died during this sequence at days 16, 29, and 30.
`The concentration of CTFE was lowered on ex-
`
`261
`
`Page 7 of 13
`
`

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`FIGURE 5. Vital signs in dog on long-term exposure to chlorotrifluoroethylenc.
`
`posure number 59_ to 250 ppm with 6-hr exposures
`conducted. Rabbits experienced a reduction in
`motor activity and respiratory rate. Although var-
`ied. the CTFE group showed a decrease in rate of
`body weight gained as compared to the control
`group. Alkaline phosphatase values dropped stead-
`ily throughout the 81 to I30 day exposure period.
`Cholinesterase activity was increased 2 to I0 times
`by CTFE exposures. No significant differences in
`organ to body weight ratios were noted. His-
`topathologic examination revealed a widespread
`congestion of liver. spleen. and kidneys.
`On comparing Kochanov‘s results (12) with those
`of Hood et al. (10), a noteworthy similarity
`emerges. Hood and co-workers exposed three rab-
`bits at a lower concentration (300 ppm, Phase I and
`50-150 ppm, Phase 11). Neither of these proved in-
`jurious to the rabbits, although it is not given in
`their report whether or not they included some of
`the same clinical tests (alkaline phosphatase
`cholinesterase) employed by Kochanov. Hood
`et al. detected no depression in growth rate or
`pathologic change whereas, presumably because of
`the higher CTFE concentration, Kochanov did,
`and cites nonspecific congestive changes in some
`organs, but without a significant decline in body
`weight values.
`A second chronic toxicity study (12) was under-
`taken by Kochanov, using rats and rabbits exposed
`
`262
`
`Page 8 of 13
`
`to 250 ppm CTFE, 6 hr/day over a period of 70 to
`110 days. Only rabbits showed a decline in growth,
`as was true of the first series Kochanov conducted.
`
`Rat growth lagged only slightly behind that of con-
`trols. Rabbits displayed an increase in heart rate
`when held in an upright position and a slowed heart
`rate recovery period. Hematology of the rabbits
`disclosed a hypochromic anemia. reduction of the
`hemoglobin concentration, and number of erythro-
`cytes; he also saw leucopenia. Hood et al. did not
`report hematologic changes in rabbits, but
`leucopenia was observed by them in dogs.
`Kochanov's rats displayed a considerable reduc-
`tion in their ability to integrate subliminal impulses,
`and oxygen consumption was increased.
`What do these experiments of Hood et al. (10)
`and Kochanov (12) mean with regard to biologic
`activity and health hazards of the fluoroalkenes?
`Much! CTFE, for example, emerges as a com-
`pound of widespread biologic activity capable of
`provoking changes in the central nervous. respira-
`tory, hematopoietic, and renal systems.
`
`Perfluoroisobutylene (PFIB), Repeated
`Exposures
`
`Clayton (5) has reported the repeated exposure
`toxicity of PFIB. This was a short experiment.
`
`Environmental Health Perspectives
`
`

`
`considering the extreme toxicity of this compound
`and thus the need to evaluate its toxicity. Rats were
`exposed to 0.1 ppm for 4 hr/day for 10 days. None
`of the four rats died. During the exposures the rats
`were occasionally restless and developed
`tachypnea. Two of the four rats showed moist rales
`and all appeared cyanotic occasionally. Some body
`weight losses occurred but not of sufficient mag-
`nitude to depress the growth curve. At the end of
`the 2-we