Effects of Naphthenic Acids and Acid Extractable Organic Mixtures on Development of The Frog Silurana (Xenopus) Tropicalis

Title: Effects of Naphthenic Acids and Acid Extractable Organic Mixtures on Development of The Frog Silurana (Xenopus) Tropicalis
Authors: Gutierrez Villagomez, Juan Manuel
Date: 2018-05-16
Embargo: 2020-05-16
Abstract: Naphthenic acids (NAs) are oil-derived mixtures of carboxylic acids and are aquatic contaminants of emerging concern. The objective of the research presented in this thesis was to investigate the toxicity of NAs in tadpoles of the frog Silurana (Xenopus) tropicalis. Using electrospray ionization high-resolution mass spectrometry (ESI-HRMS), I determined that the proportions of O2 (presumably carboxylic acid moiety) species were 98.8, 98.9 and 58.6% respectively, for two commercial extracts (S1 and S2), and acid extractable organics (AEOs) from oil sands process-affected water (OSPW). The rank order potency based on the lethal concentration fifty (LC50) and effect concentration fifty (EC50) with and without normalization for the quantity of O2 species was S1 > S2 > AEO. The main effects observed were reduced body size, edema, and cranial, cardiac, gut and ocular abnormalities. Oligonucleotide microarray technology was used to determine the transcriptomic responses in developing S. tropicalis embryos following exposure to S1 and S2 at a sub-lethal concentration of 2 mg/L. Some of the significantly enriched pathways (p < 0.05) included metabolism and cell membrane depolarization, and some were related to observed abnormalities including edema, gastrointestinal system, and cartilage differentiation. I established and validated a derivatization method for NAs using pentafluorobenzyl bromide (PFBBr) prior to gas chromatography-electron impact mass spectrometry (GC-EIMS) to increase chromatographic resolution, and sensitivity, compared to boron trifluoride-methanol (BF3/MeOH) and N-tert-Butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA). Solid-phase microextraction of volatiles originating from S1, S2, Merichem NAs and an AEO mixture led to the identification of 54, 56, 40 and 4 compounds, respectively. The compounds identified in the mixtures included aliphatic and cyclic hydrocarbons, carboxylic acids, alkyl-benzenes, phenols, naphthalene and alkyl-naphthalene, and decalin compounds. To determine the chemical nature of the toxic compounds in NA mixtures, the S2 and AEOs preparations were fractionated using open column chromatography. A non-polar and a polar fraction were obtained from S2. Overall, the toxicity of the polar fraction was not significantly different from whole S2 (p > 0.05). Six fractions of AEOs were obtained, however because of limited material, only the toxicities of F3 and F4 were assessed. The toxicity of F3 was significantly lower than AEOs (p < 0.05) and F4 was not toxic for S. tropicalis (p > 0.05). These results suggest that during fractionation, toxic compounds were lost or that the toxicity of AEOs results from the combined effects of the compounds present in the whole extract. The toxicological dose descriptors, morphometric, transcriptomic and chemical analysis herein presented may contribute to the development of environmental guidelines for NAs and AEOs.
URL: http://hdl.handle.net/10393/37707
CollectionThèses - Embargo // Theses - Embargo