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Petroleum Hydrocarbon Persistence and Toxicity to Soil Dwelling Organisms in Canadian Soils



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Petroleum hydrocarbon contamination remains a major environmental issue in Canadian soils. Site-specific risk assessments provide unique opportunities to investigate both toxicity and persistence of the contaminant, and to include the latest advances in ecotoxicology such as new test species or accounting for mixture toxicity. The main objectives of this thesis were to investigate the persistence and toxicity of a medium fraction petroleum hydrocarbon (PHC) product (lubricating oil) to soil-dwelling organisms in both standardized and Canadian field soils. First, the toxicity of PHC-contaminated soils to a suite of standardized soil invertebrate test organisms was investigated in a standardized test soil. Acute and chronic toxicity tests were conducted on the following test organisms exposed to soil contaminated with a medium fraction PHC mixure: Eisenia fetida, Lumbricus terrestris, Enchytraeus crypticus, Folsomia candida, Oppia nitens and Hypoaspis aculeifer. Mortality and inhibition of reproduction occurred in all test species exposed to PHC-contaminated soils, with the exception of lethality to E. crypticus. Interspecies differences in toxic responses were reflected in unique traits. In regard to mixture toxicity, both reference models (concentration addition and independent action) provided the best fit, however, concentration addition provided superior predictions of the individual fraction effective concentrations. Following the investigation into toxic effects of PHC-contaminated soils on soil invertebrate mortality and reproduction, the toxic effects to plants and impacts on soil invertebrates’ behaviour were assessed. Two tree species (Pinus banksiana and Picea glauca) were included in testing along with the more common garden (Lactuca sativa and Raphanus sativus) and agronomic (Elymus lanceolatus and Medicago sativa) species. Behavioural responses to PHC-contaminated soils were tested in five soil invertebrate test species (E. fetida, E. crypticus, F. candida, O. nitens and H. aculeifer) in an avoidance test system. The key finding from this study was soil invertebrate avoidance of PHC-contaminated soil was in a similar range of toxicity values for growth endpoints of plant species sensitive to PHC-contaminated soils. The third chapter represents a synthesis of the previous chapters as well as laboratory testing of persistence and toxicity of PHCs to soil dwelling organisms in Canadian field soils. The study explored numerous themes. The primary objective explored the impact of guidelines protective of soil-dwelling organisms on two soil invertebrates (F. candida and O. nitens) in a range of field soils. The study findings indicated that current approaches to establishing guidelines in Canada provided low levels of protection to soil invertebrates in soils lacking organic matter. The study investigated an alternative option to overcome this flaw; through the incorporation of organic carbon normalization into soil invertebrate and plant PHC toxicity data. Organic carbon normalization reduced variability in PHC toxicity data as well as provided greater protection to soil-dwelling organisms in low organic matter soils. The compilation of these findings highlights how Canadian regulations on deriving soil guidelines for PHC-contaminated soils protective of soil dwelling organisms should be revisited and consider incorporating soil organic carbon content as a modification option. The last chapter of this thesis details one of the first studies to assess the juvenile avoidance response of soil invertebrates to contaminated soils. The differences in avoidance response to sodium chloride, phenanthrene and copper-contaminated soils in three (E. fetida, E. crypticus, F. candida) adult and juvenile soil invertebrates was investigated. The study had variable and inconsistent results; the juvenile’s avoidance response could be more sensitive, less sensitive and the same as the adult’s avoidance response, depending on the contaminant and test species. The major finding was the assumptions that juveniles are the most sensitive individuals in a population cannot be assumed for behavioral responses to contaminated soils. In addition, sodium chloride proved to be an ideal reference toxicant for avoidance tests.



soil ecotoxicology, petroleum hydrocarbon, ecological risk assessments



Doctor of Philosophy (Ph.D.)


Soil Science




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