A Comparative Study on the Relative Terrestrial Toxicity of Two Gas-To-Liquid (GTL) Base Oils to a Low Toxicity Mineral Oil (LTMO), a Diesel, and a Biodiesel
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Until now however, there has been little to no research on the relative terrestrial toxicity and of GTLs. The goal of this thesis was to bridge this gap in GTL knowledge. To achieve this goal, the relative terrestrial toxicities of four base oils (GTL-1, GTL-2, LTMO, Diesel) were compared. This research included freshly spiked soils and oil-spiked soils that had been previously weathered 90 days at climates (10oC and 30oC) similar to those of popular drilling locations. First the weathering of soils spiked with these four base oils was investigated. There were two different weathering studies and a soil microbial respiration assay that compared the four base oils. Additionally, the accuracy of the modified method (Total Petroleum Hydrocarbons) used to monitor the oil content was also confirmed. Follwing these studies, the four base oils and their relative toxicity were compared in freshly spiked soils and in weathered soils (previously weathered for 90 days at 10oC and 30oC) through a series of toxicity assays. An acute toxicity assay of earthworms (Eisenia fetida) was performed where the toxic endpoint was their mortality. Phytotoxicity assays which included alfalfa (Medicago stavia), thick spike wheatgrass (Elymus lanceolatus), and fourwing saltbrush (Atriplex canescens) were also performed. The toxic endpoints included lack of germination and affected biomass. Another acute toxicity assay of springtails (Folsomia candida) was performed where the toxic endpoint was their mortality. Additionally, the terrestrial toxicity of these two GTLs were were further investigated in a LC50 earthworm assay and an EC50 thickspike wheatgrass assay. In the LC50 and EC50 the GTLs were compared against LTMO, Diesel, and a biodiesel. Overall the GTLs illustrated less toxicity when compared to LTMO and Diesel. GLT-spiked soils performed better in the earthworm acute toxicity study, the alfalfa germination and biomass study, and the saltbrush germination study. Additionally, during observations of activity, springtails in GTL-spiked soils survived better than in other oil-spiked soils. In the LC50 and EC50 assays, GTL base oils performed better than Diesel and LTMO. In the earthworm LC50 study, GTLs showed similar toxicity to the biodiesel. In some cases the other oils performed better than the GTLs. In the EC50, the biodiesel had much less toxicity than the other oils. Freshly spiked Diesel was determined to be less toxic then freshly spiked GTL-2 in both the thickspike wheatgrass and saltbrush germination assays, and GTL-1 freshly spiked soils had a significant toxic response towards germination of thickspike wheatgrass. When comparing GTL-1 to GTL-2, GTL-1 was less toxic than GTL-2 in freshly spiked soil (earthworms, LC50, alfalfa biomass, and saltbrush germination). In other cases, GTL-2 was less toxic than GTL-1 in freshly spiked soil (alfalfa germination, wheatgrass germination, EC50, and possibly springtails). The relative GTL-1 and GTL-2 toxicities varied according to the temperature and weathering of soils.