Abstract:
The contamination of soils, particularly by organic pollutants at industrial sites, has
required the development of accurate methods of analysis to determine the nature and
concentration of the pollutants, thereby allowing appropriate risk assessments and
remedial strategies to be implemented. Conventional methods for site assessment
generally entail extensive sampling across the whole site, with subsequent sample
despatch to a centralised laboratory, where complex, solvent intensive procedures, such
as Soxhlet extraction and GC-MS analyses are performed. Since such processes are
laborious, expensive, and time-consuming, there has been an increasing demand for rapid
and reliable field-based analytical methods for the low-cost and efficient extraction and
analysis of organic pollutants from contaminated sites.
This thesis describes the development of a field-compatible supercritical fluid extraction
(SFE) device and method for extraction of organic contaminants from soil. SFE was
chosen due to its reported high extraction efficiency, selectivity and environmentally
friendly nature due to the usage of supercritical fluids as opposed to liquid solvents. A
compact 72(W)xS7(D)xSO(H) cm, easily-transportable and user-friendly device was
developed, based on the use of a reciprocating pump and back pressure regulator system.
The optimised method yielded an average extraction recovery of 80% for total polycyclic
aromatic hydrocarbons (PABs) when compared to the well-validated laboratory-based
Soxhlet extraction method. Tests were performed on a range of natural samples with
varying water content (0- 32% w/w) without any sample pre-treatment. In comparison,
the only commercially available competing field method, based on solvent shake
extraction, yielded recovery values of 20-70% coupled with poor precision.
The thesis then describes the optimisation of a field applicable method for analysis of the
SFE extracts, based on enzyme linked immunosorbent assays (ELISAs), a method
offering speed, low cost and low solvent consumption. Available as a test kit, it was
readily amenable to on-site usage requiring only simple equipment. Assay optimisation
using an EPA sanctioned P AH immunoassay test kit demonstrated that the kit could
function in methanolic SFE extracts diluted in buffer, hence allowing the direct analysis
of total P ABs in SFE extracts with minimum sample preparation. Cross-reactivity from
parent compounds was found to be an issue for the generation of quantitative data.
Nevertheless, the method served as a reliable semi-quantitative technique for rapid
screening of P AH levels in the SFE extracts of natural samples obtained from field-based
tests. Poor performance of the solvent-shake extraction method linked to immunoassay
further vindicated usage of the newly developed field-based SFEI immunoassay method.
The thesis concludes by reporting on the successful field-based trials of the coupled
SFE/immunoassay method. The SFE system shows promise as a valid tool for the rapid
and efficient on-site monitoring of organic contaminants in soil matrices, providing an
innovative and alternative approach to the commonly deployed solvent shake extraction
method. The combined field-based SFElimmunoassay method is of benefit for the rapid
low cost assessment of site contamination, allowing site owners and consultants alike to
make rapid and informed decisions regarding site characterisation, monitoring and
remediation without recourse to expensive and time consuming laboratory analyses.