Modelling of TFA from HFO-1234ze(E) released by prospective pressurised metered-dose inhaler

HFO-1234ze(E) has an ultra-low global warming potential (AR6 value, 1.37) and has been developed as a propellant for use in pressurised metered-dose inhalers (pMDIs). To quantify the contribution of TFA formed from prospective HFO-1234ze(E)-based pMDIs, a global atmospheric model coupled with detailed watershed modelling has been applied by Tewari et al. [1]. The atmospheric model incorporates the master chemical mechanism for HFO-1234ze(E) and assumes pMDIs as its sole emission source. Based on global pMDI volume-sales data for a single year (2022), the authors estimated HFO-1234ze(E) emissions at 4736 tonnes/year.  The state-of-the-art study coupled global chemical transport modelling with TFA surface fate and transport modelling to estimate surface water, sediment, and surface soil concentrations of TFA over a period of 30 years due to continued, global sales of prospective pMDIs using only HFO-1234ze(E) as the medical propellant. The authors chose the Hudson River (USA), Rhine River (Germany), and Cauvery River (India) as three representative watersheds, also known as drainage basins or catchment areas and applied a fate-and-transport model to estimate TFA concentrations in surface water, soil, and sediments over 30 years.

Atmospheric and watershed modelling predicts that future use of pMDIs may lead to TFA concentrations between 0.8 and 19.3 ng/L in surface waters, 2.3 and 8.8 ng/ kg in surface soils, and 0.2 and 4.8 ng/kg in surface sediments across the three studied watersheds. The authors explain that these modelled concentrations are more than 100 times below the Netherlands’ most recent drinking water guideline of 2200 ng/L, derived based on precautionary potency factors for PFAS. When placed in ecological context, the maximum TFA level estimated in surface water is over 6000 times below the frequently cited no observed-effect concentration (NOEC) of 120,000 ng/L for sensitive freshwater algae, indicating negligible risk to aquatic biota. For soils, predicted TFA loadings from pMDI emissions remain at least 90 000 times lower than the REACH long-term NOEC of 830,000 ng/kg for plant health.

The authors conclude that taken together, their findings indicate that even if HFO-1234ze(E) were to become the sole medical propellant in future pMDIs of all manufacturers, its continual atmospheric release would be expected to lead to only very low additional quantities of TFA in surface waters and soils in the assessed basins at levels orders of magnitude below available human health or ecological risk thresholds. The maximum TFA concentrations projected here are lower than all currently relevant drinking water, aquatic, and agro-environmental benchmarks considered for these regions. The authors note that their conclusion that model-predicted TFA levels do not pose a threat to human health, or the environment is based on currently known safety thresholds and pMDI-use emissions inventories (magnitude and spatiotemporal pattern). The authors state that annual global TFA deposition due to future pMDI usage represents less than 0.5% of current annual global emissions of TFA.

[1] S. G. Tewari, K. Vijayaraghavan, K. Zhao, L. M. David, K. Tuite, F. Kristanovich et al., Atmospheric and watershed modelling of trifluoroacetic acid from oxidation of HFO-1234ze(E) released by prospective pressurised metered-dose inhaler use in three major river basins. Atmos. Chem. Phys., 25, 15469–15486, 2025, https://doi.org/10.5194/acp-25-15469-2025