Environmental
Fate of the Next Generation Refrigerant
2,3,3,3-Tetrafluoropropene (HFO-1234yf)
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Abstract
The
hydrofluoroolefin 2,3,3,3-tetrafluoropropene (HFO-1234yf) has
been introduced to replace 1,1,1,2-tetrafluoroethane (HFC-134a) as
refrigerant in mobile, including vehicle, air conditioning systems
because of its lower global warming potential. HFO-1234yf is volatile
at ambient temperatures; however, high production volumes and widespread
handling are expected to release this fluorocarbon into terrestrial
and aquatic environments, including groundwater. Laboratory experiments
explored HFO-1234yf degradation by (i) microbial processes under oxic
and anoxic conditions, (ii) abiotic processes mediated by reactive
mineral phases and zerovalent iron (Fe<sup>0</sup>, ZVI), and (iii)
cobalamin-catalyzed biomimetic transformation. These investigations
demonstrated that HFO-1234yf was recalcitrant to microbial (co)metabolism
and no transformation was observed in incubations with ZVI, makinawite
(FeS), sulfate green rust (GR<sub>SO4</sub>), magnetite (Fe<sub>3</sub>O<sub>4</sub>), and manganese oxide (MnO<sub>2</sub>). Sequential
reductive defluorination of HFO-1234yf to 3,3,3-trifluoropropene and
3,3-dichloropropene with concomitant stoichiometric release of fluoride
occurred in incubations with reduced cobalamins (e.g., vitamin B<sub>12</sub>) indicating that biomolecules can transform HFO-1234yf at
circumneutral pH and at ambient temperature. Taken together, these
findings suggest that HFO-1234yf recalcitrance in aquifers should
be expected; however, HFO-1234yf is not inert and a biomolecule may
mediate reductive transformation in low redox environments, albeit
at low rates