Abstract
The study of dissolved organic matter (DOM) has advanced rapidly in the last decade, primarily due to the advances in resolution and accuracy of high-resolution mass spectrometry (HRMS). However, the anthropogenic contributions to DOM are not widely understood as such compounds can be at low concentrations in freshwater but may cause long-lasting harm to aquatic life. This thesis uses direct-infusion high-resolution mass spectrometry (DI-HRMS) coupled with untargeted analysis and multivariate statistics to characterise samples from waste water treatment plants WWTPs collected by grab sampling and passively by a novel polar organic chemical integrative sampler (POCIS).Baseline bulk DOC concentrations determined by total organic carbon analysis (TOC) showed the POCIS was capable of capturing episodic pollution events through accumulation of organic matter onto the sorbent, which was supported by principal component analysis (PCA). DI-HRMS on the Orbitrap ID-X proved successful at characterising the molecular fingerprint of both “natural” DOM and anthropogenic DOM. Anthropogenic compounds were tentatively identified using both positive and negative mode electrospray ionisation (ESI). These included the confident identification of a range of polypropylene glycol (PPG) oligomers in positive mode and linear alkylbenzene sulfonates (LAS) and sulfophenyl carboxylic acids (SPC) in negative mode. Untargeted characterisation was made possible through the use of the “xcms” package in R and online spectral databases. The identification of suspect compounds was partially aided through the use of tandem MS/MS. However, the ability to make comprehensive identifications using online databases is limited by their poor compound coverage. The link between polarity and ESI response proved to be inversely correlated, although this link was stronger in the positive than negative ion mode. The quantification of PPG showed similar quantities were detected as compared to previous studies carried out on water collected out at WWTPs.
While grab sampling combined with DI-HRMS revealed a higher amount of DOC and greater variety of compounds, the POCIS provided more information on the impact of WWTPs on natural DOM, with large influxes of PPG reflected in the greater amount of DOC quantified. Therefore, pre-treatment of the POCIS before deployment could increase the range of compounds it is able to detect and enhance its use alongside grab sampling for identification of the greatest number of anthropogenic compounds to be identified.
| Date of Award | 21 Mar 2023 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Richard P Evershed (Supervisor) & Matthew P Crump (Supervisor) |