Date of Award
Doctor of Philosophy in Oceanography
Per- and polyfluorinated alkyl substances (PFAS) are a group of man-made chemicals of significant environmental and ecological concern. Several PFAS are classified as persistent organic pollutants, due to their long half-lives, ability to bioaccumulate, and human health impacts. Due to their ubiquity in the environment, development of a reliable and affordable detection tool for measuring PFAS in surface, ground, drinking, and waste waters is a priority. To address this concern, a design for a tube passive sampler has been modified and optimized for measuring PFAS in diverse aqueous environments using multiple different approaches to account for the diversity of PFAS compounds and contaminant dynamics.
The tube passive sampler design was calibrated for use with two different sorbents as the receiving phase. First, a hydrophilic-lipophilic balance sorbent (HLB) was investigated through laboratory, field, and numerical modeling experiments. Laboratory and model results displayed that the design was flow independent, accomplishing a major goal for integrative passive sampler that had been highlighted in literature. While the predictive ability of the model for generating passive sampler uptake rates was overall promising, it highlighted some key difficulties to address in PFAS passive sampling. Specifically, the high affinity of PFAS for the membrane of the tube sampler may have the potential to inhibit long term deployments through electrostatic repulsion as the non-polar tail of the PFAS binds to membrane leaving the charged headgroup facing outwards. This limited the application of the predictive numerical model to short term passive sampler deployments.
To improve upon this, a PFAS-specific receiving phase, made up of cyclodextrin with a positive surface charge on molecule cross linker, was investigated to try and enhance uptake by the sorbent over longer time periods. Field deployments showed that this cyclodextrin sorbent performed better in environmental waters than the previously studied HLB, in both fresh and saline conditions. Time trials also showed an improved duration of linear uptake, extending the deployment length for this design.
This tube passive sampler was then broadly applied to examine PFAS profiles and source dynamics in the field. First, the mass flux of PFAS to the Atlantic Ocean from local textile facilities was quantified during a yearlong study using passive samplers in the Pawcatuck River. The time weighted average concentration provided by passive samplers gave a broader scope of PFAS contamination and sources across 7 sites in the river compared to discrete grab samples and quantified a mean mass flux of 28 grams per month of each PFAS compound from sources with two distinct fingerprints, modern and historical textile mill effluent.
The specific interest in textile mills in Rhode Island was driven by the results of a study performed in the surrounding surface waters of Dhaka, Bangladesh. Air passive samplers of a different design were paired with water grabs to highlight that modern textile activity is a key source of specific replacement PFAS compounds and shorter chain perfluoro carboxylic acids that are likely reaching the environment through both wastewater discharges and deposition from smokestack releases of volatile PFAS. This textile activity in the highly populated hub of Dhaka was proposed as one of many large sources of PFAS downstream to the Bay of Bengal, and the coastal Indian Ocean.
Finally, to expand on these applications, field deployments in a highly contaminated watershed in Cape Cod were used to validate the use of the tube passive sampler for non-target PFAS methods, including predictably sampling total extractable organofluorine (EOF) and suspect PFAS compounds for which no analytical standards exist. By using a ratio approach, wherein the uncertainty in these novel measurements is equally distributed amongst the passive sampler and water grab results, sampling rates were calculated that cancelled out much of this uncertainty and showed how suspect PFAS precursors may act very similar to their targeted degradation products (for which we have standards) in the passive sampler and in complex environments including ground water, river water, and estuarine water. Overall, our understanding of PFAS passive sampling and their fate & transport in the environment has significantly improved and will guide impactful further studies, policy decisions in the state of Rhode Island, and greatly improve the ability for impacted communities to monitor PFAS levels in their local environments.
Dunn, Matthew, "CALIBRATION AND APPLICATION OF A TUBE PASSIVE SAMPLER FOR EVALUATING FATE AND TRANSPORT OF PER- AND POLYFLUORINATED ALKYL SUBSTANCES (PFAS)" (2023). Open Access Dissertations. Paper 1569.