Characterizing toxicity and chemical profile of acidic,basic and neutral fractions of oil sands process affected water
Date
2018-09-27
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ORCID
Type
Thesis
Degree Level
Doctoral
Abstract
There is concern about toxicity of Oil Sands-Affected Process Water (OSPW). Results of previous studies have shown that toxicity is caused primarily by organic chemicals in the aqueous phase. Most research has focused on acute and chronic toxicity of the acid-extractable organic fraction to aquatic organisms. It has been shown that acute toxicity is caused by organic acids commonly known as naphthenic acids (NAs) as well as other sulfur- and nitrogen-containing compounds. Also, chemical analyses of OSPW have been focused only on the acid extractable fraction, however, little is known about sub-lethal effects and chemical profiles of species of chemicals other than NAs or the “acid-extractable organics (AEOs)” extracted from OSPW.
The aim of this research was to evaluate effects of acidic and non-acidic compounds in OSPW. First, a comprehensive chemical extraction method was developed to simultaneously isolate acidic, basic and neutral fractions from an end-pit lake known as Base Mine Lake (BML-OSPW; fresh OSPW) and an experimental reclamation pond known as Pond 9 or Tailings Pond Water (P9-OSPW or aged OSPW). Second, these fractions were analysed using ultrahigh resolution mass spectrometry (Orbitrap), which possess high resolution and superior selectivity and covered an extensive range of chemical components. Third, these fractions, which contain structurally different chemicals, were assessed for acute and sub-lethal toxicity of aquatic species with respect to functions and expression of genes for ABC transporter proteins as well as modulation of toxic potencies of polycyclic aromatic hydrocarbons (PAHs).
The acidic fraction of BML but not P9-OSPW was acutely toxic to larvae of Japanese medaka. However, there is a lack of information about the reasons for lesser toxic potency of P9-OSPW. Profiles of relative proportions of organic chemicals in the acidic fractions of BML and P9-OSPW were investigated in detail, by use of ultrahigh resolution mass spectrometry (Chapter 2). In both ionization modes, mass spectra were similar between the acidic fractions of BML and P9 extracts. However, relative abundances of chemicals between the two fractions were different. The profile of homologs containing heteroatoms in each fraction revealed that the profile of nitrogen, sulfur, and oxygen (NSO) containing chemicals was not very different. Acidic fractions were dominated by Ox chemicals. Sulfur and nitrogen-containing chemicals were detected in the acid fraction with high abundances in ESI+.
The ATP-binding cassette (ABC) superfamily of transporter proteins are essential for detoxification of xenobiotic. Effects of acidic, basic and neutral compounds from BML-OSPW and P9-OSPW on activities of ABC transporters in Japanese medaka (Oryzias latipes) at the fry stage of development were investigated (Chapter 3). The neutral and basic fractions, but not the acidic fraction, of BML-OSPW, and neither fraction of P9-OSPW, caused inhibition of ABC proteins in fry of Japanese medaka. Neutral and basic fractions of BML-OSPW contained relatively greater amounts of several oxygen-, sulfur, and nitrogen-containing chemical species. Naphthenic acids (O2−), which were dominant in the acidic fraction, did not appear to be the cause of inhibition.
Solubility, bioavailability, and toxicity of PAHs might be modulated in the presence of surfactants. Effects of organic compounds extracted from BML-OSPW or P9-OSPW on toxicity of the model alkyl-PAH, retene, to early life-stages of Japanese medaka was determined (Chapter 4). Effects of retene were greater when larvae were co-exposed to OSPW compared to retene alone. However, those effects would not be expected to occur at current concentrations of OSPW and is attenuated by aging of OSPW.
Detailed studies on effects of OSPW on functions of ABC transporters (specifically P-gp) were performed in vitro by use of Caco-2 cells, and in vivo with larvae of Japanese medaka (Chapter 5). Neutral and basic fractions of BML-OSPW inhibited activity of ATP binding cassette protein ABCB1 (permeability-glycoprotein, P-gp) in Caco-2 cells, while the acidic fraction had the least effect. Co-exposure to chlorpyrifos (a substrate of P-gp), but not malathion (not a substrate of P-gp) and an extract of OSPW containing basic and neutral compounds reduced survival of larvae, increased the internal concentration, bioconcentration and terminal elimination half-life compared to survival of larvae exposed only to chlorpyrifos.
Effects of acidic, basic and neutral compounds from BML-OSPW on expression of genes encoding biotransformation enzymes and proteins were quantified (Chapter 6). Abundances of transcripts of phase I, II and III genes were significantly different in larvae of medaka exposed to basic and neutral compounds compared to acidic compounds. Changes in abundance of transcripts in response to the pooled sample and the acidic fraction were correlated, whereas changes in abundance of transcripts in larvae exposed to the basic fraction and the neutral fraction were correlated.
From results presented in this thesis, it can be concluded that besides acute toxicities of acidic compounds (i.e. NAs) in OSPW, other compounds in basic and neutral fractions from OSPW can have adverse effects at sub-lethal levels, and may interact with the different molecular target in fish that can cause specific endpoints of toxicity. These results provide new insights into the sub lethal effects of non-acidic compounds regarding the detoxification mechanisms such as ABC transporters, which can decrease the effective protection mechanism against xenobiotic in aquatic species. Also, the toxicity of PAHs is expected to increase in the presence of OSPW, however, aging of OSPW was shown to be effective in attenuating the adverse effects of not only the acutely toxic acidic fraction but also the effects of non-acutely toxic basic and neutral fractions. This thesis explores new concepts, methods and approaches that contribute to the risk assessment of OSPW.
Description
Keywords
oil sands process affected water, ABC transporters
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Toxicology Centre
Program
Toxicology