Application of volatile organic compounds (VOCs) in characterising anthropogenic and natural matrices

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Volatile organic compounds (VOCs) are emitted by various sources such as plants and microbes,
posses diverse functions and are recognised as secondary metabolites. However, little research
has been conducted on the applications of VOCs as potential biomarkers for specific processes
or materials. This work aims to increase our understanding of the significance and practical
utilisation of VOCs as rapid indicators of organic materials in the field of archaeological
and agricultural science. VOC compositions were determined by solid-phase microextraction
(SPME), and gas chromatography (GC) linked to high resolution accurate mass (HRAM)
mass spectrometry (MS). The results are statistically interrogated and classified to identify
compounds of interest associated with distinct attributes.
Initial work concerned the use of VOCs to characterise coprolites from the Paisley Caves, USA.
It was conducted to distinguish between coprolites and non-faecal deposits by analysing their
volatile profiles and identifying their sources (carnivores, herbivores, or humans). The results
indicate a clear separation between coprolites of carnivorous origin and those originating from
herbivores and humans. Even though herbivores and humans are more closely related, they can
still be largely differentiated from each other. The same approach was used to assess differences
in the embalming material utilised in the production of ancient Egyptian mummies, namely
plant oil/animal fats, beeswax, natural resins and bitumen. It further illustrated the utilisation
of VOC analysis as a non-destructive analytical procedure which provided valuable information
for the sensitive determination of archaeological materials. The variations in the composition
of the mummy-derived VOCs were also investigated to differentiate between mummies that
originated from distinct historical periods and different sample types.
Following the application of VOCs in the archaeological field, the focus shifed to agricultural
science. The SPME method was developed further by incorporating compound specific 13C
stable isotope probing, which enabled soil volatilome profile shifts during root degradation
to be studied, tracking carbon dynamics together with phospholipid fatty acid (PLFA) and
genomics analysis to assess the activities of the soil microbial community. Different agricultural
management practices can induce distinct volatile profiles, with the temporal effect being more
pronounced. The composition of actively decomposing microbes varies depending on time and
the extent of root disturbance caused by agricultural management practices. Over the long-term,
reduced root disturbance dramatically increases carbon incorporation by soil microorganisms.
The results of this dissertation highlight the potential of VOCs as a novel and non-destructive
analytical approach, enabling fast screening and sensitive determination of organic materials,
while also underpinning substanstial further avenues of investigations.
Date of Award7 May 2024
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorIan D Bull (Supervisor) & Richard P Evershed (Supervisor)

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