Correspondence/Rebuttal pubs.acs.org/est
Response to Comment on “Environmental Fate of the Next Generation Refrigerant 2,3,3,3-Tetrafluoropropene (HFO-1234yf)″.
T
Table 1. Key Physicochemical Properties of HFO-1234yf, HFC-134a, CFC-11, and CFC-113 and Their Reported Presence in Groundwatera
he refrigerant 2,3,3,3-tetrafluoropropene (HFO-1234yf) has been developed for use in mobile air conditioning systems to replace 1,1,1,2-tetrafluoroethane (HFC-134a), which has a much greater global warming potential. If HFO1234yf replaces the current refrigerant HFC-134a in mobile air conditioning systems as projected, high HFO-1234yf production volumes are anticipated and widespread handling will occur. At room temperature and atmospheric pressure, HFO1234yf is a gas (Henry’s Law constant of 1 × 10−3 M atm−1) with an aqueous solubility of about 200 ppm. HFO-1234yf leakages and emissions to the atmosphere have been estimated, and associated ecosystem effects in terms of ozone depletion and atmospheric trifluoroacetate formation were deemed insignificant.1 In 2013, the EPA ruled that HFO-1234yf should no longer be regulated as a volatile organic compound (VOC) under the Clean Air Act for the purpose of meeting the national ambient air quality standards for ozone (www.epa.gov/ airquality/ozonepollution/actions.html). While the benefits of the new refrigerant for the atmosphere have been documented, very limited information about the fate of HFO-1234yf in terrestrial and aquatic ecosystems is available. Im et al.2 explored the fate of 2,3,3,3-tetrafluoropropene (HFO-1234yf) in anoxic, aqueous batch reactors and concluded that rapid degradation in groundwater aquifers and freshwater sediments cannot be expected. Wallington and Anderson argue that it is “incorrect to claim that this compound could enter groundwater or other aqueous systems at appreciable concentrations”. Further, Wallington and Anderson reason that HFO-1234yf contamination of natural water systems is unlikely because the current refrigerant HFC-134a has not been recognized as a groundwater pollutant. We agree that the majority of HFO1234yf will be released to the atmosphere, and the atmosphere will not be a source for HFO-1234yf contamination of aquatic environments. However, we do not believe that HFO-1234yf physicochemical properties rule out possible groundwater contamination due to inappropriate handling and storage, as well as accidents during production, transportation, and use. Also, the meaning of “appreciable concentrations” is difficult to determine given the scarcity of long-term toxicological studies and the lack of science-based recommendations on maximum concentration and exposure limits. Since HFC-134a is not included in the EPA protocols commonly applied for groundwater VOC analysis, information about the prevalence of this compound in groundwater systems is vague. Halocarbons, including HFC-134a, have been used for groundwater dating indicating that pathways for these compounds into subsurface systems exist.3 Indeed, groundwater contamination with HFC-134a and CFC-113, both with comparable physicochemical properties than HFO-1234yf (Table 1), has been reported.4,5 The benefits of advanced refrigerants like HFO-1234yf with low global warming potential are obvious; however, a comprehensive environmental assessment is desirable so that risks can be recognized before environmental problems © XXXX American Chemical Society
compound
CAS registry number
HFO-1234yf HFC-134a CFC-11 CFC-113
754−12−1 811−97−2 75−69−4 76−13−1
Henry’s constant [M atm−1] 1.03 2.00 1.03 1.9
× × × ×
10−03 10−02 10−02 10−03
aqueous solubility [ppm]
groundwater contamination reported
198.2 2040 1100 170
Yes Yes Yes
a
Physicochemical data were obtained from the Syracuse Research Corporation database (http://esc.syrres.com/fatepointer/search.asp) and the HFO-1234yf safety data sheet (www51.honeywell.com/sm/ lgwp-it/common/documents/msds-documents/FP_LGWP_IT_ HFO-1234yf_it_MSDS.pdf). The Henry’s constant of HFO-1234yf was experimentally determined by Im et al.2
manifest. Too many examples exist where initially acceptable practices caused major groundwater problems. The gasoline additive methyl tert-butyl ether (MTBE) is an infamous example. We value the points raised by Wallington and Anderson, and agree that the atmosphere is a major sink for HFO-1234yf; however, we maintain our position that HFO1234yf can potentially penetrate aqueous environments (e.g., groundwater). Therefore, fate studies that include the hydrosphere are warranted so that comprehensive understanding of the risks (or lack thereof) associated with the transition to HFO-1234yf can be obtained. This form of scientific discourse is invaluable to reach conclusions for the best possible management and protection of human health and environmental resources.
Jeongdae Im†,‡ Gillian E. Walshe-Langford†,‡ Ji-Won Moon§ Frank E. Löffler*,†,‡,§,∥,⊥ †
Center for Environmental Biotechnology, University of Tennessee, Knoxville, Tennessee 37996, United States ‡ Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, United States § Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States ∥ University of Tennessee and Oak Ridge National Laboratory (UT-ORNL) Joint Institute for Biological Sciences (JIBS), Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States ⊥ Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States
A
DOI: 10.1021/acs.est.5b01970 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
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Correspondence/Rebuttal
AUTHOR INFORMATION
Corresponding Author
*Phone: +1-865-974-4933; fax: +1-865-974-4007; e-mail: frank. loeffl
[email protected]. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Luecken, D. J.; Waterland, R. L.; Papasavva, S.; Taddonio, K. N.; Hutzell, W. T.; Rugh, J. P.; Andersen, S. O. Ozone and TFA impacts in North America from degradation of 2,3,3,3-tetrafluoropropene (HFO1234yf), a potential greenhouse gas replacement. Environ. Sci. Technol. 2010, 44, 343−348. (2) Im, J.; Walshe-Langford, G. E.; Moon, J.; Löffler, F. E. Environmental fate of the next generation refrigerant 2,3,3,3tetrafluoropropene (HFO-1234yf). Environ. Sci. Technol. 2014, 48, 13181−13187. (3) Haase, K. B.; Busenberg, E.; Plummer, L. N.; Casile, G.; Sanford, W. E. Measurements of HFC-134a and HCFC-22 in groundwater and unsaturated-zone air: Implications for HFCs and HCFCs as dating tracers. Chem. Geol. 2014, 385, 117−128. (4) Semprini, L.; Hopkins, G. D.; McCarty, P. L.; Roberts, P. V. Insitu transformation of carbon tetrachloride and other halogenated compounds resulting from biostimulation under anoxic conditions. Environ. Sci. Technol. 1992, 26, 2454−2461. (5) Höhener, P.; Werner, D.; Balsiger, C.; Pasteris, G. Worldwide occurrence and fate of chlorofluorocarbons in groundwater. Crit. Rev. Environ. Sci. Technol. 2003, 33, 1−29.
B
DOI: 10.1021/acs.est.5b01970 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
