Ion Exchange Membranes and Fibers as Passive Samplers for Chemically-diverse PFAS: ESTCP Project ER20-1073

Abstract

Project Number: ER20-1073 Project Title: Ion exchange membranes and fibers as passive samplers for chemically-diverse PFAS Lead Principal Investigator: Lee Blaney, PhD Lead Organization: University of Maryland Baltimore County (UMBC) Objective: The overall goal of this project was to develop ion-exchange membrane and fiber strategies for passive sampling of chemically diverse PFAS. The project was developed to address DoD’s needs with respect to measurement and remediation of PFAS. The specific objectives were as follows: (1) develop ion-exchange membrane and fiber passive samplers capable of concentrating short- and longchain PFAS with varying log D values; (2) establish selectivity coefficients for 19 PFAS of concern in the ion exchange-based samplers to quantitatively describe PFAS uptake and partitioning; (3) confirm that the ion-exchange materials are capable of effective deployment and performance in synthetic and real groundwater and surface water matrices; (4) investigate ion exchange-based passive samplers for cationic, zwitterionic, and anionic PFAS; (5) ensure consistent performance of the samplers in single- and multisorbate scenarios; (6) characterize effects of solution pH, ionic strength, background ions, temperature, and dissolved organic matter on the passive samplers; and, (7) deploy the passive samplers in laboratorybased mesocosms to confirm their ability to resolve spatiotemporal variations in PFAS concentration. Technical Approach: Ion-exchange membranes and fibers represent a paradigm shift in passive sampling strategies for organic contaminants and PFAS, in particular. This shift stems from the wideranging physicochemical properties of PFAS, which complicate traditional passive sampling strategies. The specific objectives were achieved through (i) batch sorption tests to identify selectivity coefficients, competitive effects, and impacts of interfering substances on PFAS uptake by the sampler and (ii) mesocosm studies using synthetic and real water matrices. The limited-scope portion of the project was focused on Objectives 1, 2, and 3. Results: Our findings indicated that PFAS uptake into the ion-exchange membranes was fairly rapid, namely 2-3 days under well-mixed conditions and 2-4 weeks under static conditions; furthermore, these results were confirmed in large-volume studies using a real groundwater and pond water. We confirmed through both sorption and desorption studies that ion exchange was the primary mechanism of uptake for short- and long-chain PFAS with different head groups. The uptake capacity, selectivity coefficients, and PFAS recovery (extraction) were measured for ten ion-exchange membranes and one set of ion-exchange fibers. Based on the aggregate results, the FAD-PET-75 membrane was selected as the optimal choice for follow-on work. The selectivity coefficients for PFAS over chloride ranged from 1.57 (PFBA) to 4.90 (PFOS), and 1-4 cm2 membrane coupons were able to accumulate enough PFAS for downstream analysis. The selectivity coefficients demonstrated trends with chain-length and head group. The total dissolved solids concentration (related to ionic strength) in real groundwater and pond water affected the observed selectivity coefficients, which increased with salt content, but these parameters were successfully corrected using Setschenow constants. The FAD-PET-75 membrane was effectively dissolved in methanol to achieve high recovery of short- and long-chain PFAS (e.g., 87% PFBA, 104% PFOA). We also developed prototype samplers that will continue to be refined for field deployments in the proposed follow-on work. Benefits: Given the increased importance of PFAS to ongoing cleanup and remediation efforts at DoD facilities, new strategies are required to enable monitoring of PFAS. The limit-scope portion of this project provided proof-of-concept evidence for ion exchange-based strategies, and follow-on work will continue to develop, evaluate, and test innovative ion exchange-based materials for passive sampling of PFAS. Due to the ion-exchange mechanism, the passive samplers offer robust solutions for the full range of PFAS of interest. The results of this project contributed new scientific understanding to the use of ionexchange passive samplers, which may also be useful for other DoD-relevant contaminants.