From Spill to Sequestration: The Molecular Journey of Contamination via Comprehensive Multiphase NMR

Abstract

Comprehensive multiphase NMR is a novel NMR technique that permits all components (solutions, gels, and solids) to be studied in unaltered natural samples. In this study a wide range of CMP-NMR interaction and editing-based experiments are combined to follow contaminants (pentafluorophenol (PFP) and perfluorooctanoic acid (PFOA)) from the solution state (after a spill) through the gel-state and finally into the true solid-state (sequestered) in an intact water-swollen soil. Kinetics experiments monitoring each phase illustrate PFOA rapidly transfers from solution to the solid phase while for PFP the process is slower with longer residence times in the solution and gel phase. Interaction-based experiments reveal that PFOA enters the soil via its hydrophobic tails and selectively binds to soil microbial protein. PFP sorption shows less specificity exhibiting interactions with a range of gel and solid soil components with a preference toward aromatics (mainly lignin). The results indicate that in addition to more traditional measurements such as Koc, other factors including the influence of the contaminant on the soil-water interface, specific biological interactions, soil composition (content of lignin, protein, etc.) and physical accessibility/swellability of soil organic components will likely be central to better explaining and predicting the true behavior of contaminants in soil.

In vivo comprehensive multiphase NMR

“…As such, it allows for the study of all components (liquids, gels, and solids) in complex multiphase samples. When combined with spectral editing approaches (discussed later), various phases can be studied and differentiated in situ allowing complex processes such as the transport of molecules across phases or swelling between phases to be monitored …”

“…In many ways, CMP NMR can be thought of as changing NMR technology to match natural samples, rather than changing the sample to match a specific NMR technique. CMP NMR has permitted the study of structural interactions and processes in unaltered heterogeneous samples, including soil, swelling of rubber by biofuels, intact plants, and to follow biological processes (seed growth) …”

Focusing on “the important” through targeted NMR experiments: an example of selective13C–12C bond detection in complex mixtures

“…", it would make sense that a researcher apply the highest resolution molecular tools available and try to evaluate what components make up the mixture as a whole in a nontargeted fashion. [16][17][18] Conversely, if the goal is to follow the fate of specific contaminants in soil, then having an NMR nucleus such as 19 F allows targeted monitoring of the contaminant and its interactions, providing information specific to the target of interest. 19 The study of Bell et al was successful in identifying novel structural units because the 13 C enrichment targeted the lignin components in the soil organic matter.…”

HRMAS NMR spectroscopy applications in agriculture

“…2) on the basis of HRMAS STDD results, which revealed the involvement of pesticides functional groups in the contaminant-soil associations and enabled a prediction of predominant sorption mechanisms. Recently, this study was extended by exploiting results from diffusion, relaxation, cross polarization, and saturation transfer difference NMR experiments, which permitted to follow the sequestration of contaminants from the liquid phase into the whole soil [32].…”