The widespread environmental occurrence of chemical pollutants presents an ongoing threat to human and ecosystem health. This challenge is compounded by the diversity of chemicals used in industry, commerce, agriculture and medicine, which results in a spectrum of potential fates and exposure profiles upon their inevitable release into the environment. This, in turn, confounds risk assessment, where challenges persist in accurate determination of concentrations levels, as well as spatial and temporal distributions, of pollutants in environmental media (e.g., water, air, soil and sediments).
Passive sampling technologies continue to gain acceptance as a means for simplifying environmental occurrence studies and, ultimately, improving the quality of chemical risk assessment. Passive samplers rely on the accumulation of a target analyte into a matrix via molecular diffusion, which is driven by the difference in chemical potential between the analyte in the environment and the sampling media (e.g., sorbent phase). After deployment, the target analyte can be extracted from the sampling media and quantified, providing an integrated, time-weighted average pollutant concentration via a cost-effective platform that requires little energy or manpower when compared to active (e.g., grab) sampling approaches. While a promising, maturing technology, however, limitations exist in current commercially available passive samplers; they are typically limited in the types of chemicals that can be targeted effectively, can require long deployment times to accumulate sufficient chemical for analysis, and struggle with charged analytes.
In this dissertation, we have designed a next-generation, nanofiber sorbent as a passive sampling device for routine monitoring of both legacy and emerging organic pollutant classes in water and sediment. The polymer nanofiber networks fabricated herein exhibit a high surface area to volume ratio (SA/V values) which shortens the deployment time. Uptake studies of these polymer nanofiber samplers suggest that field deployment could be shortened to less than one day for surface water analysis, effectively operating as an equilibrium passives sampling device, and twenty days for pore water analysis in soil and sediment studies. By comparison, most commercially available passive sampler models generally require at least a month of deployment before comparable analyses may be made.
Another highlight of the nanofiber materials produced herein is their broad target application range. We demonstrate that both hydrophobic (e.g., persistent organic pollutants, or POPs, like PCBs and dioxin) and hydrophilic (e.g., emerging pollutant classes including pesticides, pharmaceuticals and personal care products) targets can be rapidly accumulated with our optimal nanofibers formulations. This suggests that one of our devices could potentially replace multiple commercial passive sampling devices, which often exhibit a more limited range of analyte targets.
We also present several approaches for tailoring nanofiber physical and chemical properties to specifically target particular high priority pollutant classes (e.g., PFAS). Three promising modification approaches validated herein include: (i) fabricating carbon nanotube-polymer composites to capture polar compounds; (ii) introducing surface-segregating cationic surfactants to target anionic pollutants (e.g., the pesticide 2,4-D and perfluorooctanoic acid or PFOA); and (iii) use of leachable surfactants as porogens to increase nanofiber pore volume and surface area to increase material capacity.
Collectively, outcomes of this work will guide the future development of next generation passive samplers by establishing broadly generalizable structure-activity relationships. All told, we present data related to the influence on the rate and extent of pollutant uptake in polymer nanofiber matrices as a function of both physical (specific surface area, pore volume, and diameter) and chemical (e.g., bulk and surface composition, nanofiber wettability, surface charge) nanofiber properties. We also present modeling results describing sampler operation that can be used to assess and predict passive sampler performance prior to field deployment.
The electrospun nanofiber mats (ENMs) developed as passive sampling devices herein provide greater functionality and allow for customizable products for application to a wide range of chemical diverse organic pollutants. Combined with advances in and expansion of the nanotechnology sector, we envision this product could be made commercially available so as to expand the use and improve the performance of passive sampling technologies in environmental monitoring studies.