|dc.description.abstract||Vanadium (V) is one of the most abundant trace elements in crude oils, making it an element of potential concern in aquatic ecosystems surrounding various industries, such as the Athabasca Oil Sands (AOS) industry in northeastern Alberta. When bitumen from the AOS region is upgraded to synthetic crude oil, V is removed and enriched at elevated concentrations (> 1000 mg V/kg) into the by-product petroleum coke. This coke is stored on-site of some major oil sands companies, until more practical ways of utilizing or storing it becomes available. Recently, coke has been evaluated as a treatment option for the removal of organic acids in oil sands process-affected water (OSPW) through adsorption processes. However, past studies have found coke to leach toxicologically relevant concentrations of V (> 1 mg/L) into solution upon contact with water, including OSPW. Thus, coke-leachates or coke-treated OSPW containing V could pose risks to aquatic organisms in nearby freshwater systems. Currently, a knowledge gap exists pertaining to the toxicity of V to aquatic organisms, which makes it difficult to assess how increased V in coke-treated OSPW could impact aquatic systems, if it were to be discharged into the surrounding freshwater environment. Thus, the overall goal of this research was to evaluate the toxicity of V (as vanadate oxyanions) to a diverse suite of aquatic organisms regionally-relevant to the AOS region to generate the data needed to derive sound V water quality benchmarks for this region. To achieve this goal, acute and chronic toxicity tests were conducted using comparable laboratory standard test-organisms and organisms more regionally-relevant to northern Alberta. Selected test-species included: four zooplankton species (Daphnia pulex, D. dentifera, Simocephalus serrulatus, and Ceriodaphnia quadrangula; 2-d and 8- to 21-d studies), two unicellular green algae species (Pseudokirchneriella subcapitata and Scenedesmus quadricauda; 72-h cell growth studies), two benthic invertebrates (Chironomus dilutus and C. riparius; 4-d and 30 to 40-d studies), and two freshwater fish species (Oncorhynchus mykiss and Pimephales promelas; 4-d and 28-d studies).
In short-term acute studies (≤ 4-d), the median lethal concentration (LC50) was the major endpoint reported and ranged from a low of 0.60 mg/L for C. quadrangula to a high of 63.2 mg/L for C. riparius. During longer-term chronic toxicity tests (≥ 4-d), effects (lethality and growth, reproductive, and adult emergence inhibition) occurred at concentrations greater than 0.1 mg V/L, and ranged upwards to concentrations of 37.3 mg V/L. When chronically exposed, V appeared to elicit toxicity directly through reduction of lifespan, with little to no effects on sublethal endpoints, such as cladoceran reproduction or fish growth. Sublethal toxicity was more evident in toxicity tests with benthic invertebrates. Here, V significantly impaired adult emergence of C. dilutus and C. riparius at concentrations ≥ 16.7 mg/L (31.6% reduction) and 8.3 mg/L (18.0% reduction), respectively. Overall, significant differences in V sensitivity among regionally-relevant green algal species and benthic invertebrate species and more commonly-used laboratory species were not observed in this research. One exception was the field-collected zooplankton species, D. dentifera, which was approximately 2- to 3-times more sensitive to acute and chronic V exposures than the comparable standard test species D. pulex. However, there were no significant differences in sensitivity of the field-collected cladocerans, S. serrulatus and C. quadrangula when compared to the standard test species, D. pulex and C. dubia, respectively. Similarly, P. promelas was 4 to 9 times more sensitive than the standard salmonid species, O. mykiss, in acute and chronic V tests, respectively.
The toxicity data generated in this research for V were combined with data from the peer-reviewed literature to construct acute (23 species) and chronic (21 species) species sensitivity distributions (SSDs). From these SSDs, the acute and chronic hazardous concentrations to 5% of species tested (HC5) were estimated as 0.64 and 0.09 mg V/L, respectively. Based on these SSDs and associated HC5 estimates, the most sensitive species to V were from the Cladocera (Daphnia and Ceriodaphnia species) and Cyprinidae (P. promelas). Toxicity threshold estimates for these species are < 1 mg V/L, and thus they could be adversely affected if V was elevated in future site-water or process-water discharges associated with Athabasca oil-sands operations. Many fish and unicellular green algae species were intermediate in their sensitivity to V, whereas benthic invertebrates were the least sensitive to acute and chronic exposures of V. These new toxicity data will not only supplement the current V toxicity database to ensure enough data are available to develop sound national water quality guidelines, but also to develop regional guidelines for the protection of aquatic communities near oil sands industries, and other industrial sites with V contamination. In conclusion, interim V acute and chronic effects benchmarks of 0.64 and 0.09 mg V/L, respectively, are proposed for freshwater environments to protect aquatic life from exposure to hazardous levels of V in local AOS environments and elsewhere in Canada.||