ASSESSMENT OF PETROLEUM HYDROCARBON CONTAMINATION IN TERRESTRIAL ECOSYSTEMS USING CONVENTIONAL AND NOVEL APPROACHES

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Petroleum hydrocarbon , Ecotoxicology , Transcriptomic , Soil invertebrate , Risk Assessment
Abstract
Petroleum hydrocarbon (PHC) contamination has emerged as a pressing global concern, due to its impacts on human health and ecosystems, and presents a major challenge for remediation efforts. The heterogeneous nature of PHC mixtures and natural weathering processes that influence the bioavailability of individual compounds, make it difficult to predict the toxicity of PHC-contaminated sites. Despite their usefulness in accurately determining risks at PHC-contaminated sites, traditional toxicity tests are labourious and time-consuming. Hence, there is an urgent need to develop methods to predict PHC toxicity and modernize toxicity assessments to allow for high-throughput screening of impacted sites. The goals of this research were to assess the toxicity of weathered PHC-impacted soils to native organisms, improve the efficiency and accuracy of current toxicological tests, and identify molecular biomarkers in a model springtail species, Folsomia candida, suitable for high-throughput toxicity testing. Weathered PHC-contaminated soils from a Northwestern Canadian site were found to be non-toxic to native soil invertebrate and plant species despite exceeding federal PHC guidelines. Standard quantification methods of soil invertebrates following extraction from soils were deemed sub-optimal due to excessive invertebrate movement. Chill-coma induction and ethanol anesthesia methods were developed to temporarily immobilize soil invertebrates with no adverse affects, allowing for more precise quantification. Transcriptome analysis of F. candida exposed to PHCs linked reduced fecundity with diminished energy budgets caused by inhibition of carbohydrate metabolic processes and allocation of remaining energy to detoxify xenobiotics. These findings contribute to the understanding of weathered PHC-contaminated sites and have the potential to significantly impact decisions that land-owners and risk assessors make regarding contaminated sites. Additionally, ecotoxicological values (e.g., 50% lethal concentration [LC50]) derived in this study differed by a factor of six when comparing weathered vs fresh crude oil contamination, highlighting the shortcomings of generic PHC guidelines and the necessity of employing high-throughput toxicity assays to derive site-specific guidelines. The findings in this thesis demonstrate the potential for molecular biomarkers in ecological risk assessments based on their ability to provide novel insights into PHC toxicity and modes-of-action, with a much shorter exposure duration than traditional growth endpoints.
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