The acute toxicity of bitumen-influenced groundwaters from the oil sands region to aquatic organisms.

The extraction of surface mined bitumen from oil sands deposits in northern Alberta, Canada produces large quantities of liquid tailings waste, termed oil sands process-affected water (OSPW), which are stored in large tailings ponds. OSPW-derived chemicals from several tailings ponds migrating past containment structures and through groundwater systems pose a concern for surface water contamination. The present study investigated the toxicity of groundwater from near-field sites adjacent to a tailings pond with OPSW influence and far-field sites with only natural oil sands bitumen influence. The acute toxicity of unfractionated groundwater and isolated organic fractions was assessed using a suite of aquatic organisms (Pimephales promelas, Oryzias latipes, Daphnia magna, Hyalella azteca, Lampsilis spp., Ceriodaphnia dubia, Hexagenia spp., and Vibrio fischeri). Assessment of unfractionated groundwater demonstrated toxicity towards all invertebrates in at least one far-field sample, with both near-field and far-field samples with bitumen influence toxic towards P. promelas, while no toxicity was observed for O. latipes. When assessing the unfractionated groundwater and isolated organic fractions from near-field and far-field groundwater sites, P. promelas and H. azteca were the most sensitive to organic components, while D. magna and L. cardium were most sensitive to the inorganic components. Groundwater containing appreciable amounts of dissolved organics exhibited similar toxicities to sensitive species regardless of an OSPW or natural bitumen source. The lack of a clear distinction in relative acute toxicities between near-field and far-field samples indicates that the water-soluble chemicals associated with bitumen are acutely toxic to several aquatic organisms. This result, combined with the similarities in chemical profiles between bitumen-influenced groundwater originating from OSPW and/or natural sources, suggests that the industrial bitumen extraction processes corresponding to the tailings pond in this study are not contributing unique toxic substances to groundwater, relative to natural bitumen compounds present in groundwater flow systems.

Development of a Reduced-Volume Acute Lethality Toxicity Test for Hyalella azteca.

Effects-directed analysis (EDA) is used to identify the principal toxic components within a complex mixture using iterative steps of chemical fractionation guided by bioassay results. Bioassay selection can be limited in EDA because of the volume requirements for many standardized test methods, and therefore, a reduced-volume acute toxicity test that also provides whole-organism responses is beneficial. To address this need, a static, 7-d, water-only, reduced-volume method (50 mL, 10 organisms) was developed for Hyalella azteca that substantially decreases the volume requirements of standard-volume acute test exposures (200-500 mL of test solution, 15-20 organisms) while maintaining water quality and meeting control survival criteria. Standard- and reduced-volume methods were compared by conducting concurrent toxicity tests with 2 inorganic toxicants (KCl and CdCl2 ) and 2 organic mixtures of naphthenic acid fraction components (NAFCs) to evaluate test performance. There was no difference between methods when comparing the median lethal concentrations (LC50s) for KCl and both NAFC mixtures (p > 0.05). The LC50s for CdCl2 were statistically different (p = 0.0002); however, this was not considered biologically meaningful because the difference between LC50s was <2-fold. In conclusion, the reduced-volume H. azteca test method generated results comparable to standard-volume test methods and is suitable for use in situations where limited testing material is available, such as when conducting EDA. Environ Toxicol Chem 2020;39:2221-2227. © Her Majesty the Queen in Right of Canada 2020. Reproduced with the permission of the Minister of Environment and Climate Change Canada.

Effect of mixed occupancies on the thermoelectric properties of BaCu6-xSe1-yTe6+y polychalcogenides.

The title materials have been reported earlier to be p-type thermoelectrics when x = 0.1 and y = 0. Here, we studied the properties after varying the Cu and the Se/Te concentrations. At first, materials with the same nominal Cu concentration, 5.9 Cu per formula unit, and different Se/Te ratios were prepared. The different thermoelectric properties indicated that the Se/Te ratio strongly affected the Cu deficiency, which is directly responsible for the charge carrier concentration. Single crystal structure data revealed the Cu amount to be less than 5.8 per formula unit when y = 0.4; therefore a sample of nominal composition "BaCu5.74Se0.46Te6.54" was also studied. This sample exhibited an electrical conductivity of 685 Ω-1 cm-1 at room temperature, which is almost three times larger than in case of "BaCu5.9SeTe6", in accord with the lower Cu amount causing a larger hole concentration. The larger mass fluctuation on the Se/Te site resulted in a lower lattice thermal conductivity, but the decreased Seebeck coefficient mitigated a performance increase in form of a higher figure-of-merit. In contrast to other Cu chalcogenides, the data are reproducible under the measurement conditions.