Environ. Sci. Technol. 2007, 41, 1180-1185
Quantitation of Gas-Phase Perfluoroalkyl Surfactants and Fluorotelomer Alcohols Released from Nonstick Cookware and Microwave Popcorn Bags EWAN SINCLAIR,† SEUNG KYU KIM,† HENRY B. AKINLEYE,‡ AND K U R U N T H A C H A L A M K A N N A N * ,† Wadsworth Center, New York State Department of Health, and Department of Environmental Health Sciences, State University of New York at Albany, Albany, New York 12201-0509, and Consumers Union, 101 Truman Avenue, Yonkers, New York 10703
Fluoropolymer dispersions are used for coating certain cookware products and food-contact packaging to impart oil and water repellency. Since salts of perfluorooctanoic acid (PFOA) are used as a processing aid in the manufacture of many fluoropolymers, it is necessary to determine if these compounds are still present as residuals after the process used to coat nonstick cookware or packaging, and could be released during typical cooking conditions. In this study, we identified and measured perfluoroalkyl carboxylates (PFCAs), particularly PFOA, and fluorotelomer alcohols (FTOHs; 6:2 FTOH and 8:2 FTOH), released from nonstick cookware into the gas phase under normal cooking temperatures (179 to 233 °C surface temperature). PFOA was released into the gas phase at 7-337 ng (11-503 pg/cm2) per pan from four brands of nonstick frying pans. 6:2 FTOH and 8:2 FTOH were found in the gas phase of four brands of frying pans, and the sources of FTOHs released from nonstick cookware are under investigation. We observed a significant decrease in gas-phase PFOA following repeated use of one brand of pan, whereas the other brand did not show a significant reduction in PFOA release following multiple uses. PFOA was found at >5 ng during the fourth use of both brands of pans. FTOHs were not found after the second use of either brand of pans. PFOA was found at 5-34 ng in the vapors produced from a prepacked microwave popcorn bag. PFOA was not found in the vapors produced from plain white corn kernels popped in a polypropylene container. 6:2 FTOH and 8:2 FTOH were measured in the vapors produced from one brand of prepacked microwave popcorn at 223 ( 37 ng and 258 ( 36 ng per bag, respectively, but not measured at >20 ng (LOQ) in the other two brands. On the packaging surface of one brand of microwave popcorn several PFCAs, including C5-C12, 6:2 FTOH, and 8:2 FTOH, were found at concentrations in the order of 0.56.0 ng/cm2. This study suggests that residual PFOA is not completely removed during the fabrication process of * Corresponding author phone: 518-474-0015; fax: 518-473-2895; e-mail:
[email protected]. † Wadsworth Center and SUNY at Albany. ‡ Consumers Union. 1180
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the nonstick coating for cookware. They remain as residuals on the surface and may be off-gassed when heated at normal cooking temperatures.
Introduction Perfluoroalkyl carboxylates (PFCAs) are a class of fluorochemicals manufactured for their unique chemical stability and surface-tension lowering properties (1). Following several decades of commercial use, PFCAs have been discovered to be globally distributed and persistent environmental contaminants (2-4). Several studies have reported the occurrence of PFCAs, such as perfluorooctanoic acid (PFOA), in the blood of general populations worldwide (5, 6). Furthermore, there is evidence that PFOA can cause developmental toxicity and carcinogenicity in rats (7). Therefore, there is a need to identify the sources of exposure of PFCAs to the general population. Ammonium salt of PFOA is used as an emulsifier in the production of polytetrafluoroethylene (PTFE)-based fluoropolymers. Some of these fluoropolymers have unique oil and water repellent properties and are commonly used as a nonstick coating for stovetop cookware. Certain fluoropolymers have been shown to thermally degrade to produce PFCAs (8). Ammonium salt of PFOA has been shown to degrade at temperatures (350-400 °C) often used to melt fluoropolymers (9). However, the temperatures at which the thermal degradation occurs are greater than those reached during normal cookware use. Residual PFOA has been measured at ng/g concentrations in the surface coating of nonstick cookware (10). However, no earlier studies have measured gas-phase release of perfluorochemicals upon heating nonstick cookware. Off-gassing of such residual emulsifier, under normal cooking temperature conditions, provides a potential source of human exposure to PFOA. In this study, we measured gas-phase release and concentrations of PFOA, 6:2 FTOH, and 8:2 FTOH from nonstick frying pans and microwave popcorn bags. Studies have shown that fluorotelomer alcohols (FTOHs) may be atmospherically or metabolically degraded to PFCAs (11, 12). FTOHs are used as surface active agents in domestic products such as carpet treatments, paints, and cleaning agents (13). In addition, FTOHs are used in surface protection products for food-contact coatings such as those used in some brands of microwave popcorn bags (10). Off-gassing of residual FTOHs from fluorotelomer-based products has recently been characterized (13). There is potential for residual FTOHs to be released from the coated surface of popcorn bags during cooking, and either transferred to the popcorn or to the gas phase. The vapor pressures of FTOHs increase with increasing temperature (14) and therefore, under cooking conditions, FTOHs are expected to partition to gas phase. In this study, gas-phase concentrations of PFOA, 6:2 FTOH, and 8:2 FTOH released from nonstick cookware under normal cooking conditions were quantified. We also measured concentrations of PFOA and FTOHs transferred from cookware to boiled water. The effect of multiple uses of cookware on residual fluorochemical release was investigated. Finally, we measured the presence of PFCAs, 6:2 FTOH, and 8:2 FTOH in microwave popcorn food-contact surfaces and the release of these fluorochemicals to the gas phase.
Materials and Methods Standards and Reagents. Perfluorooctanoic acid (PFOA) was purchased from Strem Chemicals, Inc. (Newburyport, MA). 10.1021/es062377w CCC: $37.00
2007 American Chemical Society Published on Web 01/10/2007
1,2 13C-labeled PFOA was obtained from Perkin-Elmer (Boston, MA). Perfluorobutanoic acid (PFBA), perfluorononanoic acid (PFNA), and pentadecafluoro-1-octanol (7:1 FTOH) were purchased from Avocado Research Chemicals, Ltd. (Heysham, Lancashire, UK). Perfluoropentanoic acid (PFPeA), perfluoroheptanoic acid (PFHpA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), and perfluorododecanoic acid (PFDoDA) were purchased from Fluorochem Ltd. (Glossop, Derbyshire, UK). 1-Hydroxyethane2-perfluorohexane (6:2 FTOH) and 1-hydroxyethane-2-perfluorooctane (8:2 FTOH) were purchased from Oakwood Products, Inc. (West Columbia, SC). 2-Perfluorooctyl-[1,1-H-2H2][1,2-13C2]-ethanol (13C2,2H2-8:2 FTOH) was purchased from Wellington Laboratories (Guelph, Ontario, Canada). Purified XAD-2 resin (Amberlite) was obtained from Supelco (Bellefonte, PA). All of the analytical standards were of g95% purity. Samples. Four brands of nonstick coated frying pan and one brand of stainless steel frying pan were investigated. Three to five replicate samples of domestic and imported brands were purchased from retail stores in New York City in 2005. Two brands of microwave popcorn and one brand of plain white popcorn kernels were also analyzed. The white popcorn kernels were packaged in polyethylene bags and were used as control. Headspace Analysis. The pans used for headspace analysis were new and unused. Certain pans were selected for repeat use experiments. All frying pans were pre-cleaned using hot soapy water, rinsed with Milli-Q water, and dried using a hand towel. A commercial brand dishwashing soap was used. Schematic illustration of the gas-phase sampling procedure is shown in the Supporting information (Figure SF1). Headspace vapors from frying pans were collected using two, 6-in. long (1-in. diameter) glass tubes filled with purified XAD-2 (Amberlite) resins. The tubes were attached in series at ground glass joints using clamps. The first tube was packed with 2 g of XAD-2 resin and the following tube was packed with 4 g of XAD-2 resin. These tubes were fitted and sealed using rubber O-rings at the center of a stainless-steel lid. The lid was placed over the sample frying pan during extraction. A GAST vacuum pump (Benton Harbor, MI) was set to draw air through the XAD-2 tubes at 32 L/min. The lid was not allowed to seal tight to avoid creation of vacuum inside the sample pan; lab air was allowed to flow over the pan and through the XAD-2 packing. Control experiments were performed every day to check for contamination from lab air and sampling apparatus. Control experiments involved using stainless steel, noncoated pans heated and tested using the same experimental procedures as those reported for nonstick pans. Laboratory air was drawn through XAD-2 cartridges as discussed above at 32 L/min for 20 min to check for contamination of PFCAs and FTOHs. A Corning PC-600 hot plate (Acton, MA) was heated to a plate temperature of 250 °C, as measured using a Hanna HI 9063 thermometer (Woonsocket, RI) with a surface probe. A frying pan sample was placed on the hot plate that had reached 250 °C and the extraction lid was placed over the top of the pan. The vacuum was immediately turned on and headspace air was collected for 20 min. The frying pan sample was spiked with 10 ng of 13C-PFOA, 100 ng of 7:1 FTOH, and 100 ng of 13C2,2H2-8:2 FTOH (internal standards in methanol) using a syringe inserted into the lid through a small, predrilled hole, immediately after placing the pan on the heated surface. After extraction the glass tubes were removed and allowed to cool. The surface temperature of the heated pan was recorded. The XAD-2 packed tubes were attached and sealed to a pre-cleaned polypropylene tap. Analytes were eluted from XAD-2 with 50 mL of methanol into a pre-cleaned round-bottom flask. Care was taken to allow for a slow and even elution (5 mL/min), and the glass tubes were tapped gently to remove bubbles and prevent eddying.
This extract was concentrated to approximately 6 mL by using a rotary evaporator, and further concentrated to 1 mL under a gentle stream of nitrogen. The extract was never evaporated to dryness as this was found to result in loss of FTOHs. The extract was then centrifuged to remove particles (if any) before analysis by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Headspace extraction of popcorn bags was carried out using the XAD-2 packed tubes described above. Internal standards 13C-PFOA (10 ng) and 13C2,2H2-8:2 FTOH (100 ng) were spiked directly into the 2 g XAD-2 packed tube. The popcorn bag was cooked in a microwave oven for 3 min. The bag was then removed and the glass tubes were inserted into the opening at the top of the bag. Air was drawn through the tubes for 5 min to collect all vapors from the popcorn bag. The analytes were eluted and concentrated as described above. Breakthrough Experiments. Breakthrough of target analytes from the XAD-2 tubes was tested by attaching a third glass tube packed with 4 g of XAD-2 in series to the extraction setup described above. The first XAD-2 packing was spiked with 10 ng of each of the PFCAs and 100 ng of each of the FTOHs. The extraction apparatus was placed over a 250 °C hotplate and air was drawn through the XAD-2 packed tubes for 20 min. Each XAD-2 packed tube was eluted and analyzed separately for PFCAs and FTOHs. Average PFCA recovery in the first XAD-2 tube ranged from 76% to 105%, while no PFCAs were found at >1 ng in either the second or third XAD-2 tubes (Supplementary Table S1). FTOHs were recovered in the first XAD-2 tube at 42% to 48% (mean) and in the second XAD-2 tube from 26% to 28% (mean). FTOHs were not found in the third XAD-2 tube. Thus, the total recovery of FTOHs ranged from 68% to 76%. Reported concentrations were not corrected for the recoveries of the internal standards, but were based on extracted calibration curves as described below. The observed loss of 24% to 32% FTOHs in the analytical procedure may be due to volatilization during solvent concentration. Water Analysis. The hotplate was preheated to 250 °C. A new (cleaned with soapy water) frying pan sample was then placed on top and 250 mL of Milli-Q water was poured into the pan. The water was allowed to boil for 10 min and then cooled. The water was then spiked with 10 ng of 13C-PFOA and 100 ng of 7:1 FTOH and extracted using solid-phase extraction (SPE). The SPE method used has been previously described (15). Briefly, water samples were passed through Oasis HLB (60 mg, 3 cm3) cartridges (Waters Corporation, Milford, MA) preconditioned with methanol and Milli-Q water. A flow rate of 1 mL/sec was maintained through the cartridges. The cartridges were then washed with 20% methanol in water, and were dried completely under vacuum. The target compounds were eluted in 10 mL of methanol into a polypropylene tube and were concentrated under nitrogen to a final volume of 1 mL. The extract was then centrifuged and analyzed by HPLC-MS/MS. Popcorn Packaging Analysis. Popcorn packaging was extracted for PFCA and FTOH analysis both before and after cooking. A 1 in. × 2 in. undyed section of the packaging was cut from the side of the popcorn bag. This section was placed in a 50 mL polypropylene tube and spiked with 13C-PFOA (10 ng). Methanol (20 mL) was added and the sample was shaken for 30 min. A duplicate sample was taken and spiked with 13C ,2H -8:2 FTOH (100 ng) internal standard. Ethyl acetate 2 2 (20 mL) was added and the sample was shaken for 30 min. Extracts were centrifuged and the supernatant was transferred to a pre-cleaned round-bottomed flask. Extracts were concentrated to 1 mL. FTOH analysis of the ethyl acetate extract was carried out by gas chromatography-mass spectrometry (GC-MS) and PFCA analysis was carried out by HPLC-MS/MS. VOL. 41, NO. 4, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Mean Masses (ng) and Concentrations (pg/cm2) of Gas-Phase Perfluorooctanoate (PFOA) and Fluorotelomer Alcohols (FTOHs) Released from Nonstick Frying Pansa
sample brand
surface temp (°C)
pan area (cm2)
n
PFOA (ng)
PFOA (pg/cm2)
6:2 FTOH (ng)
6:2 FTOH (pg/cm2)
8:2 FTOH (ng)
8:2 FTOH (pg/cm2)
pan 4 pan 13 pan 32 pan 39 blank stainless steel
180 (1) 229 (2) 190 (3) 205 (3) 200 (2) 230 (1)
640 477 670 659 640 670
3 3 3 3 3 3
12 (5) 32 (12) 192 (148) 40 (8) ND
