Airborne transfer of per-and polyfluoroalkyl substances (PFAS) during hydrometallurgical leaching of electronic waste.

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals widely used in electronics manufacturing. PFAS monitoring in aquatic systems and soil surrounding electronic-waste (e-waste) recycling plants has gained significant attention due to their toxicological effects on human health and the environment.  While previous studies have demonstrated the aqueous-to-air transport of PFAS (predominantly perfluorooctanoic acid) at low pH while measuring acid-dissociation constants, atmospheric PFAS emissions remain understudied and the combined effect of low pH and temperature, and the role of PFAS physicochemical properties in governing atmospheric transfer of neutral PFAS have not been systematically investigated. Therefore, the key conditions (pH and temperature) controlling the airborne release of ionic PFAS (including new generation and legacy substances) from acidic aqueous solutions were investigated by focusing on the representative e-waste leaching conditions. Additionally, airborne PFAS emissions were characterised during the hydrometallurgical leaching of shredded e-waste materials.

Airborne PFAS releases were quantified from acidified aqueous solutions (pH < 1) spiked with  EPA 533PAR native PFAS standard mixture, containing 25 ionic PFAS compounds. Subsequently, the studies were extended to leaching experiments using the shredded e-waste materials. All the leaching experiments were conducted in an enclosed chamber, with air drawn through the chamber at a low flow rate to capture airborne PFAS on sorbent tubes. Post-sampling analysis was performed using online solid-phase extraction coupled with high-resolution LC-MS, following the workflow reported by Kourtchev et al., (2022).

Up to 50% by mass of airborne PFAS transfer from acidic solutions was observed for selected compounds with an initial PFAS load of 2500 pg. It was found that pH, temperature, and solution composition influenced the amount of PFAS transfer. Additionally, airborne PFAS transfer was found to be related to its physicochemical properties (e.g., functional group). In summary, the work demonstrated aqueous to air transport of PFAS under acidic conditions, which is governed by pH and PFAS molecular structure (e.g., PFAS headgroup). The work also confirmed that airborne PFAS emissions can occur during the leaching of shredded e-waste materials, signifying the need for routine PFAS monitoring and appropriate control measures to avoid potential human exposure.

Reference: 

Kourtchev, I., Hellebust, S., Heffernan, E., Wenger, J., Towers, S., Diapouli, E., & Eleftheriadis, K. (2022). A new on-line SPE LC-HRMS method for the analysis of Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) in PM2.5 and its application for screening atmospheric particulates from Dublin and Enniscorthy, Ireland. Science of The Total Environment, 835, 155496. doi:https://doi.org/10.1016/j.scitotenv.2022.155496