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Teflon offgas studies

Canaries in the Kitchen: Teflon offgas studies

May 15, 2003

Over the past five decades scientists from DuPont, government, and academia have published studies documenting temperatures at which non-stick cookware coatings begin to break apart, offgasing chemicals and particulate matter into the air. Dealing with multiple cases of polymer fume fever in their workers, DuPont scientists conducted a series of studies beginning in the 1950s to identify the toxic components from heated Teflon, killing birds and rats in efforts to understand the potency of the gases and particles.

Teflon Decomposition Products:

Studies show that thermal degradation of Teflon leads to the slow breakdown of the fluorinated polymer and the generation of a litany of toxic fumes including TFE (tetrafluoroethylene), HFP (hexafluoropropene), OFCB (octafluorocyclobutane), PFIB (perfluoroisobutane), carbonyl fluoride, CF4 (carbon tetrafluoride), TFA (trifluoroacetic acid), trifluoroacetic acid fluoride, perfluorobutane, SiF4 (silicon tetrafluoride), HF (hydrofluoric acid), and particulate matter. At least four of these gases are extremely toxic - PFIB, which is a chemical warfare agent 10 times more toxic than phosgene (COCl2, a chemical warfare agent used during World Wars I and II), carbonyl fluoride (COF2 which is the fluorine analog of phosgene), MFA (monofluoroacetic acid) which can kill people at low doses, and HF, a highly corrosive gas.

Many of the thermal degradation products are unmatched in their environmental persistence. Besides fire and heating, which are not considered normal methods of environmental degradation, some of these compounds have no known degradation methods, including four gaseous chemicals (TFA, PFOA, CF4, PFB) and some components of the particulate matter that are highly persistent. TFA and the other PFOA-like perfluorinated acids that have been detected in Teflon degradation studies have “no known significant loss mechanism” [1]. In addition, the perfluorinated alkene HFP, which makes up the bulk of the degradation products at temperatures above 680°F (360°C), will react with OH radicals in the troposphere to produce TFA with 100% conversion [2].

The lowest temperature at which nonstick coatings have been reported to kill birds in a peer-reviewed study is 396°F (202°C) [3]. In May 1998, poultry researchers at the University of Missouri recorded 52 percent mortality in 2400 chicks within three days of the birds being placed into floor pens with new PTFE-coated heat lamp bulbs. After ruling out bacterial infections like E. Coli and Salmonella, or toxic gases such as sulfur dioxide, carbon monoxide and carbon dioxide, the scientists finally linked the chick deaths to offgas products from the PTFE-coated bulbs. All of the chicks examined after death had lung lesions and moderate to severe pulmonary edema consistent with “PTFE toxicosis.”

The researchers also learned from a private communication with Dr. Bedros Nersessian that a duck research facility that used the same PTFE-coated heat lamps had 23.3 percent death in ducklings, over 400 ducklings in all, within five days [3]. In 1997, two English veterinarians reported a case in which eight raptor deaths over three months were attributed to PTFE coated heat lamps. This incident was described in a letter on PTFE toxicity in birds published in the journal Veterinary Record [4]. In addition, an inadvertent poisoning of pet birds has been reported when a Teflon-coated surface was heated to 325°F (163°C). | View Bird Death Diaries

These reports and personal accounts indicate that Teflon offgases toxic substances at temperatures as low as 396°F and 325°F. In 1991, a report by a collaborative team of DuPont and Louisiana State University scientists also addressed this issue. These scientists generated low molecular weight PTFE by heating Teflon to high temperatures and allowing the fumes to age for a few minutes; aging allowed the chemicals in the fumes to react to form small Teflon molecules. The scientists found that when this low molecular weight PTFE was reheated to 464°F two out of three exposed rats died. Evidence indicated that particulate matter was responsible for the rats’ death, and this particulate matter was composed of small molecules of Teflon [5].

Seidel and coworkers explain that “fumes generated at temperatures below 572°F (300°C) are formed exclusively by sublimation of a low MW (molecular weight) fraction already present in the polymer”[5]. From the Seidel study we can conclude that at low temperatures PTFE offgases particulate matter which is composed of small molecules of PTFE. We can also conclude that this particulate matter, which has been reported to cause bird deaths at temperatures below 500°F (260°C), is the result of the presence of low molecular weight PTFE.

This low molecular weight PTFE may be present in Teflon at the time of Teflon’s manufacture, or the PTFE may be created when a pan is heated repeatedly and the coating degrades as PTFE bonds break. PTFE particles have been measured in offgas products at temperatures as high as 1067°F (575°C).

According to Waritz's 1975 paper, particulate matter is emitted from Teflon pans between 554°F and 1067°F (290 and 575°C)[6]. These particles have been linked to bird deaths that can occur when an empty pan is heated on a burner. At these temperature the Teflon molecule breaks apart into smaller Teflon particles. When this occurs the carbon-carbon bonds of Teflon break, generating free radicals; these free radicals can then form alkenes, or they can react with oxygen to form carboxylic acids (forming PFOA, a chemical for which EPA is considering regulatory action, and PFOA-like compounds). The resulting particulate matter is thus a mixture of perfluorinated alkanes, perfluorinated alkenes, and perfluorinated acids [3, 7].

Many studies have established the toxicity of particulate matter generated at temperatures above 554°F (290°C). A study conducted by Zapp et al. in 1955 first indicated that particulate matter was implicated in the toxicity of PTFE [8]. In 1959, Clayton et al. found that PTFE resins will generate toxic products when heated in air. Clayton showed that the particulate matter is toxic when he demonstrated that the toxicity of the offgas products is removed when the PTFE offgas products are filtered to remove the particulate matter before animal exposure [9].

In 1968, DuPont scientists Waritz and Kwon showed that rats exposed to a 20 gram sample of PTFE heated to 842°F (450°C) produced death within four hours. The authors note that "exposures lasted four hours unless all rats exposed succumbed earlier," [10] but they failed to report the time to death among the rats. It was found that when the particulate matter was filtered from the offgas products before the rats were exposed, the mortality was reduced to zero; this provides evidence that the particulate matter is required for toxicity at 842°F. Based on the concentrations of particulate matter that caused rat death, Waritz and Kwon calculate that particulate matter is lethal at concentrations of only 1.4 parts per million (ppm) [10].

In a 1975 study by Waritz, Teflon breakdown products generated at lower temperatures were determined to cause death. Within four hours of exposure to a Teflon-coated pan heated to 536°F (280°C) parakeets died, and quail were killed when the pan was heated to 626°F or 330°C. These temperatures are easily accessible on a stovetop. Rats were killed within four hours when a Teflon pan was heated to between 797°F and 842°F (425 to 450°C). Once again, the DuPont scientist failed to report the time to death for the animals [6].

Many gases are also evolved when Teflon is heated. Heated to temperatures between 680 and 1112°F (360 to 600°C), Teflon generates TFE [1, 11]. This chemical is one of 174 chemicals that the National Toxicology Program considers to be reasonably anticipated human carcinogens [12]. Teflon heated to between 680 and 1202°F (360 and 650°C) will also generate HFP [1, 11]. Carbonyl fluoride, COF2, a toxic gas and the fluorinated cousin of the chemical warfare agent phosgene, is emitted from Teflon that is heated between 824°F and 1292°F (440 and 700°C) [6, 11]. PFIB, perfluoroisobutene, a chemical warfare agent that is ten times more toxic than phosgene, is detected when Teflon is heated in air between 887°F and 1004°F (475 and 540°C) [6]. Above 1202°F (650°C), carbon tetrafluoroide and carbon dioxide are the major products generated during the decomposition [7].

Other chemicals that have been detected in the offgas products of heated Teflon are trifluoroacetetic acid (TFA), difluoroacetic acid (DFA), and monofluoroacetic acid (MFA, also known as compound 1080, a pesticide and historical chemical warfare agent which has an LD50 of 0.7 – 2.1 mg/kg in men [13]), and various other perfluorinated acids with the general formula CF3(CF2)nCO2H; these acids were detected by University of Toronto scientists Ellis and Mabury (and coworkers) in a 2001 study in which Teflon was heated to 680°F (360°C) for 2 hours [1]. Finally, in the presence of glass (SiO2), SiF4 has been detected in the offgas products when teflon is heated to temperatures of 878°F (470°C)and higher [7, 11]; SiF4 is also a toxic gas and it has been reported that the presence of SiF4 enhances the toxicity of the other toxic Teflon offgas products [14].

In a recent PTFE rat toxicity study, Dr. Carl Johnston et al. found that neither the ultrafine particles or the gases produced by PTFE are toxic by themselves, but the two together are extremely toxic together [15]. The authors suggest the particles are acting as carriers for absorbed gas particles, allowing the gas particles to travel to the lower respiratory tract and cause severe damage. Alternatively, the particles could be generating toxic reactive groups on their surfaces. Also, the size of the particles matters. The most toxic particles are called ultrafine and are 16 nanometers in diameter. If the particles are able to coagulate and form larger particles, greater than 100 nm, they are not as acutely toxic to rats.

In one case of human polymer fume fever in the literature, the author reports a case in which a person developed polymer fume fever about one hour after a non-stick pan overheated. Five cockatiels in the house died within 30 minutes [16]. In another case, a healthy 26-year-old woman went to the hospital complaining of difficult breathing, chest tightness and cough after being exposed to toxic fumes coming from a defective microwave oven part: a melted and scorched Teflon block used as an axle for a rotating platform in the oven. At the hospital, doctors noted that her heart was racing, and she had high blood pressure, increased white blood cell count (leukocytosis) and was breathing heavily. An X-ray showed she had “diffuse pulmonary infiltrate.” Her lung function was still abnormal a month later. This woman's two pet parakeets died within minutes of being exposed to the Teflon fumes [17].

References:

[1] Ellis, DA., Mabury, SA., Martin, JW and Muir, DC. 2001. Thermolysis of fluoropolymers as a potential source of halogenated organic acids in the environment. Nature 412(6844): 321-4.

[2] Machino, M. 2000. Atmospheric chemistry of CF3CF=CF2: kinetics andmechanism of its reaction with OH radicals, chlorine atoms, and ozone. J. Phys. Chem. A 104: 7255-7260 (As cited in: Ellis, DA., Mabury, SA., Martin, JW and Muir, DC. 2001. Thermolysis of fluoropolymers as a potential source of halogenated organic acids in the environment. Nature 412(6844): 321-4).

[3] Boucher, M., Ehmler, TJ and Bermudez, AJ. 2000. Polytetrafluoroethylene gas intoxication in broiler chickens. Avian Dis 44(2): 449-53.

[4] Forbes, NA and Jones, D. 1997. PTFE toxicity in birds. Vet Rec 140(19): 512.

[5] Seidel, WC., Scherer, KV, Jr.., Cline, D, Jr.., Olson, AH., Bonesteel, JK., Church, DF., Nuggehalli, S and Pryor, WA. 1991. Chemical, physical, and toxicological characterization of fumes produced by heating tetrafluoroethene homopolymer and its copolymers with hexafluoropropene and perfluoro(propyl vinyl ether). Chem Res Toxicol 4(2): 229-36.

[6] Waritz, RS. 1975. An industrial approach to evaluation of pyrolysis and combustion hazards. Environ Health Perspect 11: 197-202.

[7] Coleman, WE., Scheel, LD and Gorski, CH. 1968. The particles resulting from polytetrafluoroethylene (PTFE) pyrolysis in air. Am Ind Hyg Assoc J 29(1): 54-60.

[8] Zapp, JA., Limperos, G and Brinker, KC. 1955. Toxicity of Pyrolysis Products of Teflon Tetrafluoroethylene Resin. Amer. Indust. Hyg. Assoc., Annual Meeting, May 1955. (As cited in: Waritz, RS and Kwon, BK. 1968. The inhalation toxicity of pyrolysis products of polytetrafluoroethylene heated below 500 degrees centigrade. Am Ind Hyg Assoc J 29(1): 19-26).

[9] Clayton, JW., Hood, DB and Raynes-Ford, GE. 1959. The Toxicty of the Pyrlysis Products of Teflon TFE-Fluorocoarbon Resins. Amer. Indust. Hyg. Assoc. Annual Meeting, May 1959. (As cited in: Waritz, RS and Kwon, BK. 1968. The inhalation toxicity of pyrolysis products of polytetrafluoroethylene heated below 500 degrees centigrade. Am Ind Hyg Assoc J 29(1): 19-26.

[10] Waritz, RS and Kwon, BK. 1968. The inhalation toxicity of pyrolysis products of polytetrafluoroethylene heated below 500 degrees centigrade. Am Ind Hyg Assoc J 29(1): 19-26.

[11] Arito, H and Soda, R. 1977. Pyrolysis products of polytetrafluoroethylene and polyfluoroethylenepropylene with reference to inhalation toxicity. Ann Occup Hyg 20(3): 247-55.

[12] National Toxicology Program (NTP). 2002. 10th Report on Carcinogens. http://ehp.niehs.nih.gov/roc/toc10.html.

[13] Key, BD., Howell, RD and Criddle, CS. 1997. Fluorinated organics in the biosphere. Environmental Science & Technology 31(9): 2445-2454.

[14] Scheel, LD., Lane, WC and Coleman, WE. 1968. The toxicity of polytetrafluoroethylene pyrolysis products including carbonyl fluoride and a reaction product, silicon tetrafluoride. Am Ind Hyg Assoc J 29(1): 41-8.

[15] Johnston, CJ., Finkelstein, JN., Mercer, P., Corson, N., Gelein, R and Oberdorster, G. 2000. Pulmonary effects induced by ultrafine PTFE particles. Toxicol Appl Pharmacol 168(3): 208-15.

[16] Blandford, TB., Seamon, PJ., Hughes, R., Pattison, M and Wilderspin, MP. 1975. A case of polytetrafluoroethylene poisoning in cockatiels accompanied by polymer fume fever in the owner. Vet Rec 96(8): 175-8.

[17] Zanen, AL and Rietveld, AP. 1993. Inhalation trauma due to overheating in a microwave oven. Thorax 48(3): 300-2.