The development of a field-deployable system that could screen groundwater samples for per- and polyfluoroalkyl substances (PFAS) simultaneously and quickly would improve site characterization, site remediation efforts, and routine, long-term monitoring of PFAS-impacted sites.  

The overall objective of the work is to evaluate the potential to use the direct nuclear techniques called particle-induced gamma-ray emission (PIGE) as a rapid screening method to count all the ¹⁹F fluorine present in groundwater samples. This work is being conducted in two phases. Specific technical objectives associated with Phase I included:

1. Determining the beam-energy dependence of ¹⁹F signal for proton beam over 2—5MeV range.
2. Optimizing and determining method detection limits (MDL) achievable for PFAS with sampling methods suitable for PIGE.
3. Determining requirements for field deployable PIGE unit for PIGE rapid PFAS screening.

The results from Phase I can be found in the Final Report and are summarized below. 

In Phase II of this project, the objective is to validate the rapid screening method for PFAS quantification, risk assessment, and on-site decision-making for Department of Defense (DoD) site characterization and monitoring by:

1. Transitioning to a field demonstration unit with small business lead, university technology transfer, and environmental end-user engagement with DoD-affected PFAS sites.
2. Building a technology readiness levels (TRL) 6-7 prototype, field deployable PIGE system based on Phase I and prior Defense Advanced Research Projects Agency investment in compact accelerator technology (i.e., Starfire’s Centurion® system).
3. Testing the system in two ways: (i) comparing groundwater samples and laboratory standards against traditional laboratory techniques for PFAS and total F measurements; and (ii) deploying the PIGE system by van to several active characterization and/or remediation sites to demonstrate portability, ease of use, and speed of analysis with field team.
4. Validating the utility of the PIGE approach for rapid screening and publishing results to create transition opportunities.

The current state-of-the-art detection method for aqueous solutions of PFAS is the Liquid Chromatography – Tandem Mass Spectrometer (LC-MS/MS). It can achieve part-per-trillion (ppt) sensitivity and identify which specific PFAS are present. However, because of the nature of preparing each sample for multiple PFAS standards, and the chromatographic separation steps required to identify the individual PFAS, any LC-MS/MS method are inherently slow. In addition, LC-MS/MS techniques require a library of known compounds for comparison, which means that although it is very sensitive, it is blind to most PFAS precursors that may subsequently degrade into known chemicals. Other total fluorine measurements exist; however, they do not have sufficient sensitivity to be useful for environmental samples, are too cumbersome, or require large facilities.

PIGE is a well-established laboratory technique using charged particles (protons) that are accelerated to MeV-level energies into a material sample (i.e., groundwater filter cartridge). Protons directly interact with ¹⁹F present in the sample producing characteristic gamma rays at specific energies that can be quantified to determine the presence of very low concentrations that could be attributable for PFAS.

The work performed during Phase I of this project consisted of de-risking efforts to measure the ¹⁹F abundance as a function of proton energy over an accessible range of energies for modern particle accelerators, to evaluate different groundwater sampling techniques that were suitable for interrogation from the proton beam, and to generate requirements for a portable system to be developed in Phase II. The Phase II program will build an ultra-compact proton accelerator, compare groundwater samples in both a laboratory and field environment with comparisons with traditional quantification techniques, and publish utility findings from PFAS-impacted DoD field sites. 

Phase I Results

The PIGE technique for ¹⁹F detection and quantification was de-risked under Phase I using a 50nA Van de Graaf accelerator at the University of Notre Dame. The Final Report contains graphs and details showing ~1 ppb MDL with small wax aliquots and ~300 ppt level with commercial-off-the-shelf GAC-felt in-line filters for solid-phase extraction from 1L groundwater samples. MDL scale linearly with water volume and proton current from the accelerator. 

Phase I provided sufficient technical basis with an immediate pathway to achieve a TRL 6-7, high-fidelity, cargo-van mobile, PFAS rapid screening tool in Phase II using the more powerful Centurion® linac. A system accelerator design at 4MeV was selected for greater proton penetration into the sample media for ¹⁹F excitation while minimizing carbon gamma-ray emissions. Increasing flow from 1à10L for solid-phase extraction and increasing proton current from 50à5,000nA can improve MDL to sub-ppt levels. This is more sensitive than the current health advisory limits for specific PFAS and can detect both identified and precursors that are typically unidentified. 

PIGE cannot distinguish between specific PFAS compounds – it is a total F method that is quantitative with respect to fluorine only, but because hundreds of samples can be run per day per accelerator, it is an ideal screening tool. If there is significant fluorine measured, the sample can be shipped to any Environmental Laboratory Accreditation Program-accredited LC-MS/MS laboratory and analyzed to identify which specific PFAS are present.

PIGE would also be advantageous in monitoring efforts of extracted water treatment systems by simply measuring the total fluorine content quickly and inexpensively each week and doing a full LC-MS/MS characterization annually rather than doing a full LC-MS/MS characterization regularly. Rapid field quantification is the goal of this method. Thus, PIGE emerges as a technique that could be applied to hundreds of samples per day per instrument if the technique is brought to the field. (Anticipated Phase II Completion - 2026)

Tighe, M., Y. Jin, H.D. Whitehead, K. Hayes, M. Lieberman, M. Pannu, M.H. Plumlee, and G.F. Peaslee. 2021. Screening for Per-and Polyfluoroalkyl Substances in Water with Particle Induced Gamma-Ray Emission Spectroscopy. ACS ES&T Water, 1(12):2477-2484.

Wilkinson, J.T., S.R. McGuinness, and G.F. Peaslee. 2020. External Beam Normalization Using Atmospheric Argon Gamma Rays. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 484:1-4.