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.

Sensitivity of multiple life stages of 2 freshwater mussel species (Unionidae) to various pesticides detected in Ontario (Canada) surface waters.

Freshwater mussels contribute important ecological functions to aquatic systems. The water filtered by mussel assemblages can improve water quality, and the mixing of sediments by burrowing mussels can improve oxygen content and release nutrients. However, nearly 70% of North American freshwater mussel species are listed as either endangered, threatened, or in decline. In Ontario, 28 species are in decline or in need of protection. Even though freshwater mussels have a heightened sensitivity to some contaminants, few studies have investigated the risks that various pesticide classes pose to one freshwater mussel species or among life stages. Lampsilis siliquoidea and Villosa iris were the focus of the present study, with the latter currently listed as of "special concern" in Canada. A potential risk to the recovery of freshwater mussel species is the presence and persistence of pesticides in Ontario surface waters. Acute (48 h) toxicity tests were performed with V. iris glochidia to determine the effect on viability (surrogate for survival) following exposure to 4 fungicides (azoxystrobin, boscalid, metalaxyl, and myclobutanil), 3 neonicotinoids (clothianidin, imidacloprid, and thiamethoxam), 2 carbamates (carbaryl and malathion), 1 organophosphate (chlorpyrifos), and 1 butenolide (flupyradifurone). Juvenile and adult L. siliquoidea were also exposed to azoxystrobin, clothianidin, imidacloprid (juvenile only), and carbaryl (adult only). Our study found in general that all life stages were insensitive to the pesticides tested, with median effect and lethal concentrations >161 µg/L. The pesticides tested likely represent a minimal risk (hazard quotients <5.4 × 10-3 ) to freshwater mussel viability and survival in acute (48 h) and subchronic (28 d) exposures, respectively, in Ontario streams where pesticide concentrations were considerably lower than those tested in the present study. Environ Toxicol Chem 2018;37:2871-2880. © 2018 SETAC.

Toxicity of naphthenic acids to invertebrates: Extracts from oil sands process-affected water versus commercial mixtures.

The toxicity of oil sands process-affected water (OSPW) has been primarily attributed to polar organic constituents, including naphthenic acid fraction components (NAFCs). Our objective was to assess the toxicity of NAFCs derived from fresh and aged OSPW, as well as commercial naphthenic acid (NA) mixtures. Exposures were conducted with three aquatic species: Hyalella azteca (freshwater amphipod), Vibrio fischeri (marine bacterium, Microtox® assay), and Lampsilis cardium (freshwater mussel larvae (glochidia)). Commercial NAs were more toxic than NAFCs, with differences of up to 30-, 4-, and 120-fold for H. azteca, V. fischeri, and L. cardium, respectively, demonstrating that commercial NAs are not reliable surrogates for assessing the toxicity of NAFCs. Differences in toxicity between species were striking for both commercial NAs and NAFCs. Overall, V. fischeri was the least sensitive and H. azteca was the most sensitive organism. Responses of V. fischeri and H. azteca to NAFC exposures were consistent (< 2-fold difference) regardless of source and age of OSPW; however, effects on L. cardium ranged 17-fold between NAFCs. NAFCs derived from fresh OSPW sources were similarly or less toxic to those from aged OSPW. Our results support the need to better characterize the complex mixtures associated with bitumen-influenced waters, both chemically and toxicologically.

Sensitivity of walleye (Sander vitreus) and fathead minnow (Pimephales promelas) early-life stages to naphthenic acid fraction components extracted from fresh oil sands process-affected waters.

Unconventional oil production in Alberta's oil sands generates oil sands process-affected water (OSPW), which contains toxic constituents such as naphthenic acid fraction components (NAFCs). There have been few studies examining effects of NAFC exposure over long periods of early-life stage development in fish. Here we examined the effects of NAFCs extracted from OSPW to embryo-larval fathead minnow, exposed for 21 days. We compared the sensitivity of fathead minnow to walleye reared to 7 days post-hatch (18-20 days total). EC50s for hatch success, including deformities, and total survival were lower for walleye (10-11 mg/L) than fathead minnow (22-25 mg/L), with little post-hatch mortality observed in either species. NAFC exposure affected larval growth at concentrations below the EC50 in fathead minnow (total mass IC10 14-17 mg/L). These data contribute to an understanding of the developmental stages targeted by oil sands NAFCs, as well as their toxicity in a greater range of relevant taxa.

Toxicity of naphthenic acid fraction components extracted from fresh and aged oil sands process-affected waters, and commercial naphthenic acid mixtures, to fathead minnow (Pimephales promelas) embryos.

Naphthenic acids (NAs) are constituents of oil sands process-affected water (OSPW). These compounds can be both toxic and persistent and thus are a primary concern for the ultimate remediation of tailings ponds in northern Alberta's oil sands regions. Recent research has focused on the toxicity of NAs to the highly vulnerable early life-stages of fish. Here we examined fathead minnow embryonic survival, growth and deformities after exposure to extracted NA fraction components (NAFCs), from fresh and aged oil sands process-affected water (OSPW), as well as commercially available NA mixtures. Commercial NA mixtures were dominated by acyclic O2 species, while NAFCs from OSPW were dominated by bi- and tricyclic O2 species. Fathead minnow embryos less than 24h old were reared in tissue culture plates terminating at hatch. Both NAFC and commercial NA mixtures reduced hatch success, although NAFCs from OSPW were less toxic (EC50=5-12mg/L, nominal concentrations) than commercial NAs (2mg/L, nominal concentrations). The toxicities of NAFCs from aged and fresh OSPW were similar. Embryonic heart rates at 2 days post-fertilization (dpf) declined with increasing NAFC exposure, paralleling patterns of hatch success and rates of cardiovascular abnormalities (e.g., pericardial edemas) at hatch. Finfold deformities increased in exposures to commercial NA mixtures, not NAFCs. Thus, commercial NA mixtures are not appropriate surrogates for NAFC toxicity. Further work clarifying the mechanisms of action of NAFCs in OSPW, as well as comparisons with additional aged sources of OSPW, is merited.

Cadmium transport by the gut and Malpighian tubules of Chironomus riparius.

Many aquatic insects are very insensitive to cadmium in short-term laboratory studies. LC50 values for larvae of the midge Chironomus riparius are over 25,000 times the Criterion Maximum Concentration in the United States Environmental Protection Agency (U.S. EPA (2000)) species sensitivity distribution (SSD). Excretion or sequestration of cadmium may contribute to insensitivity and we have therefore examined cadmium transport by isolated guts and renal tissues of C. riparius larvae. Regional differences of Cd transport along the gut were identified using a Cd(2+)-selective microelectrode in conjunction with the Scanning Ion-Selective Electrode Technique (SIET). Cd is transported into the anterior midgut (AMG) cells from the lumen and out of the cells into the hemolymph. The transport of Cd from the gut lumen to the hemolymph exposes other tissues such as the nervous system and muscles to Cd. The gut segments which remove Cd from the hemolymph at the highest rate are the posterior midgut (PMG) and the ileum. In addition, assays using an isolated Malpighian (renal) tubule preparation have shown that the Malpighian tubules (MT) both sequester and secrete Cd. For larvae bathed in 10 micromol l(-1) Cd, the tubules can secrete the entire hemolymph burden of Cd in approximately 15 h.

Investigating a potential mechanism of Cd resistance in Chironomus riparius larvae using kinetic analysis of calcium and cadmium uptake.

The uptake kinetics of waterborne Ca and Cd, both independently and in combination, were examined in C. riparius larvae, which are extremely Cd tolerant. Larvae exposed to Ca (100-2500 micromol L(-1)), exhibited classic Michaelis-Menten saturation kinetics for Ca influx, measured using (45)Ca as a radio-tracer. The maximum rate of Ca influx (J(max)(Ca)) was 0.39 micromol g(-1)h(-1), and the Ca concentration where the carrier reached half saturation (K(M)(Ca)) was 289 micromol L(-1). Cd influx was measured using (109)Cd as a radio-tracer in larvae exposed to Cd (0-1400 micromol L(-1)) while the Ca concentration was set to the K(M)(Ca). This revealed a J(max)(Cd) (2.26 micromol g(-1)h(-1)) which was nearly 6-fold higher that of Ca. This unusually high capacity for Cd uptake is in accordance with the huge tissue Cd burdens that chironomid larvae are able to accumulate during high level exposures. The apparent K(M)(Cd) (1133 micromol Cd L(-1)), when recalculated to account for the background Ca level, was still high (567 micromol Cd L(-1)), suggesting that this organism has a low affinity for Cd relative to most aquatic animals, indeed lower or comparable to its affinity for Ca. In consequence, even well above environmentally relevant Cd exposures, C. riparius does not accumulate Cd at the expense of Ca, thereby avoiding internal hypocalcaemia, in contrast to most other organisms which are much more sensitive to Cd. However, Ca influx was significantly reduced when 1200 micromol Cd L(-1) was added to Ca exposures (96-2410 micromol L(-1)). Michaelis-Menten analysis revealed a similar J(max)(Ca) in Cd-exposed and control larvae (i.e. exposed only to Ca), but that the apparent K(M)(Ca) was many-fold higher in larvae which were simultaneously exposed to Ca and Cd. Conversely, increasing Ca concentrations (96-2410 micromol L(-1)) progressively inhibited Cd uptake from a Cd exposure concentration (1200 micromol L(-1)), providing additional support for a common transport system. These results suggest that the interaction of Cd and Ca in C. riparius is one of simple competitive interaction, and that the unusual Cd transport kinetics (low affinity, high capacity) relative to fairly standard Ca transport kinetics help explain the unusual tolerance that this organism has to acute Cd exposure.

The effect of extreme waterborne cadmium exposure on the internal concentrations of cadmium, calcium, and sodium in Chironomus riparius larvae.

Chironomus riparius larvae (3rd-4th instar) were extremely resistant to waterborne Cd with 48h LC50s of 331 mg Cd/L in soft water (10 mg/L Ca CO(3)) and 1106 mg Cd/L in moderately hard (140 mg CaCO(3)/L) water. Unexposed larvae had whole body Ca and Na concentrations of 11.2(0.3) and 84.5(3.0) micromol/g, respectively. The larvae exposed through acute toxicity tests accumulated massive amounts of Cd, reaching >50 micromol/g in larvae exposed to 437 mg Cd/L, though burdens were lower at higher exposure concentrations. These Cd burdens were approximately fivefold greater than whole-body Ca concentrations. Cd exposure also had a significant negative effect on internal Ca: whole-body Ca declined by over 70% in larvae exposed to Cd above the LC50 concentration. The effect of Cd exposure on whole-body Na was much less dramatic as levels dropped by 10-28% in the acutely exposed larvae. Time series exposures (up to 72h) across a range of Cd concentrations (0.1-865 mg/L) revealed that internal Ca dropped within the first hour of exposure regardless of the concentration of Cd. In all but the highest (865 mg Cd/L) exposure, internal Ca eventually recovered to the control level. Cd resistance in C. riparius may lie in its ability to maintain internal Ca balance even when exposed to extreme (>100 mg/L) levels of Cd, coupled with remarkable capacities for storage-detoxification and excretion of Cd.

Uptake and depuration of cadmium, nickel, and lead in laboratory-exposed Tubifex tubifex and corresponding changes in the concentration of a metallothionein-like protein.

Based on weight loss in water, 24 h is recommended for Tubifex tubifex gut clearance. Biota-to-sediment accumulation factors (BSAFs) in gut-cleared T. tubifex following six weeks of exposure to Cd-, Ni-, and Pb-spiked sediment were 12.4, 3.0, and 19.0, respectively. Tissue Ni concentrations peaked after 12 h, whereas Cd and Pb were accumulated for the duration of the exposure. Tubifex tubifex were transferred to either water (24 h) or sediment (10 weeks) to monitor changes in internal metal concentrations. After 24 h in water, only Ni concentration had declined significantly (p < 0.05), suggesting that the majority of Ni was associated with the gut content, while Cd and Pb were accumulated in the tissues. Metal depuration in sediment was described with two-compartment, first-order kinetic models (r2 = 0.7-0.8; p < 0.001), indicating that T. tubifex has both a quickly depurated and a more tightly bound pool of accumulated metal. Tubifex tubifex were also exposed to sediment spiked with just Cd (3.66 micromol/g). Cadmium uptake and induction of metallothionein-like protein (MTLP) were rapid; both parameters were significantly elevated within 24 h of exposure. Metallothionein-like protein (8.7 +/- 1.8 nmol/g) and Cd (60.8 +/- 11.0 micromol/g) reached maximum concentrations after 96 h and four weeks, respectively.

Cadmium-induced production of a metallothioneinlike protein in Tubifex tubifex (Oligochaeta) and Chironomus riparius (Diptera): correlation with reproduction and growth.

Laboratory-cultured Chironomus riparius and Tubifex tubifex were exposed to sediments artificially enriched with a range of cadmium (Cd) concentrations. Both species accumulated Cd in a concentration-dependent manner. The concentration of a metallothioneinlike protein (MTLP), as measured by a mercury saturation assay, increased with increasing Cd exposure. After reaching a threshold of Cd exposure, the whole-body endpoints of reproductive output in T. tubifex and growth in C. riparius declined significantly. The threshold effect concentrations for T. tubifex and C. riparius were 2.68 and 0.134 micromol Cd/g dry sediment, respectively. Metallothioneinlike protein and Cd tissue concentrations were more sensitive indicators of exposure than the whole-body endpoints. For T. tubifex, the concentrations of MTLP and tissue Cd were significantly elevated above control levels after exposure to the 0.67 micromol Cd/g dry sediment treatment. In C. riparius, MTLP concentration and tissue Cd concentration were both significantly elevated above control levels after exposure to the 3.8 x 10(-3) micromol Cd/g dry sediment treatment. Analysis of these data suggests that MTLP and tissue Cd concentrations are sensitive subcellular endpoints, which can be used to predict exposure to and the effects of metals at the individual or population level.