Date of Graduation

5-2023

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Fairey, Julian L.

Committee Member

Hale, W. Micah

Second Committee Member

Murray, Cameron D.

Keywords

Analyte elution; Environmental sampling; Experimental methods

Abstract

The United States (US) Environmental Protection Agency (EPA) issued a proposed National Primary Drinking Water Regulation in March 2023 for six per- and polyfluoroalkyl substances (PFAS), which included maximum contaminant levels (MCLs) of 4.0 ng•L−1 for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS). These MCLs were based on current method detection limits (MDLs) for aqueous-phase grab samples achievable at certified analytical labs throughout the US. In June 2022, the US EPA issued the interim lifetime health advisory levels for PFOA and PFOS of 0.004 ng•L−1 and 0.02 ng•L−1, respectively, which presently cannot be reliably quantified using existing PFAS methods. As a result, there is a pressing need to develop sampling protocols to quantify PFAS at sub-ng•L−1 levels. Diffusive gradients in thin-films (DGT) passive samplers can achieve lower MDLs compared to grab sampling as they accumulate analyte mass over time through an exposure window of area, Ap. Here, DGT passive samplers were used to measure time-weighted average analyte concentrations (CDGT) below the grab sample MDL of 50 µg•L−1-N for nitrate (NO3−). NO3− is an anion, like many PFAS, and was used as a PFAS surrogate compound for DGT method development. A DGT passive sampler carousel was designed, fabricated, and used in a batch reactor mode, equipped with nine DGT passive samplers to quantify NO3− spiked at 5.8 µg•L−1-N. Multiple DGT binding layers were aggregated to increase Ap for a 14-day deployment time. The NO3− mass recovered scaled linearly with the number of DGT binding layers, indicating the aggregation procedure could be used to achieve lower MDLs. CDGT for NO3− ranged from 1.6–7.1 µg•L−1-N following correction for a NO3− elution efficiency of 26.5% with 0.1 M NaOH. Three DGT passive samplers deployed for 14 days were capable of quantifying NO3− below the current grab sample MDL. This work directly informs the design of a future study to quantify CDGT of PFOA at sub-ng•L−1 levels.

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