The accumulation and tissue distribution of toxicants in aquatic biota can be determinative of their toxic impact to both exposed organisms and their potential human consumers. In the present study, accumulation of the trace metal thallium (Tl) in gill, muscle, plasma, and otoliths of rainbow trout (Oncorhynchus mykiss) following acute (96-h) and subchronic (28-day) waterborne exposures was investigated. Owing to known interactions between Tl and potassium ions (K+ ), plasma and muscle K+ concentrations were also determined. Branchial Tl accumulated in a dose-dependent manner in both acute and subchronic exposures, while plasma Tl was rapidly mobilized to tissues and accumulated only at exposure concentrations of 141 µg L-1 or higher. For muscle tissue, Tl concentrations at 28 days were markedly lower than those at 96 h at comparable exposure concentrations (0.9 µg L-1 ), indicating the presence of mechanisms that act to reduce Tl accumulation over time. However, after acute exposure, muscle Tl reached concentrations that, if consumed, would exceed acceptable daily intake values for this element, indicating some risk to human health from the consumption of fish from waters heavily contaminated with Tl. Otoliths showed Tl concentrations that reflected exposure concentration and length, confirming their capacity to provide insight into fish exposure history. No changes in tissue K+ concentrations were observed, suggesting that accumulation of Tl in rainbow trout plasma and muscle does not occur at the expense of K+ homeostasis. In addition to highlighting the capacity of rainbow trout to accumulate Tl to levels that exceed recommended dietary doses to human consumers, the present study provides the first data of tissue-specific Tl accumulation in an important regulatory species. Environ Toxicol Chem 2023;42:1553-1563. © 2023 SETAC.

The trace element thallium (Tl) exerts its toxic effects, at least in part, through its mimicry of potassium (K+) and subsequent impairment of K+ homeostasis. However, the specific nature of this effect remains poorly understood, especially in aquatic biota that are threatened by elevated concentrations of Tl associated with mining and refining effluents. In this study experiments were conducted to mechanistically examine the relationship between Tl and K+ in terms of uptake and toxicity in the regulatory model species Daphnia magna. In one set of experiments the effects of K+, the K+ analog rubidium (Rb+), and generalized K+ channel blocker cesium (Cs+) on Tl-induced acute toxicity were examined. The presence of increasing concentrations of K+ and Rb+ in exposure water reduced waterborne Tl toxicity, indicating that the actions of Tl were mediated at least in part through interactions with K+. However, in the presence of elevated water Cs+, the toxicity of Tl paradoxically increased. Pharmaceuticals with putative blocking actions on K+ channels failed to alter whole-body K+ of control organisms, but in the case of clozapine and chlorpropamide, whole-body K+ status was significantly elevated relative to exposures with Tl alone, which tended to reduce this metric. These data identify inwardly rectifying and voltage gated K+ channels as potential loci of Tl toxicity. Experiments using rubidium (Rb+) as a tracer of K+, showed that waterborne Tl affects the uptake of K+, but the magnitude of inhibition by Tl was not sufficient to explain the effect on whole-body K+. While these data indicate interactions between Tl and K occur at K+ transporters in D magna, they also indicate that environmental levels of K+ are likely to ameliorate toxicity in most natural waters.

The mechanisms of acute (96-hour) and subchronic (28-day) toxicity of the waterborne trace metal thallium (Tl) to rainbow trout (Oncorhynchus mykiss) were investigated. Specifically, effects on branchial and renal ionoregulatory enzymes (sodium/potassium adenosine triphosphatase [ATPase; NKA] and proton ATPase) and hepatic oxidative stress endpoints (protein carbonylation, glutathione content, and activities of catalase and glutathione peroxidase) were examined. Fish (19-55 g) were acutely exposed to 0 (control), 0.9 (regulatory limit), 2004 (half the acute median lethal concentration), or 4200 (acute median lethal concentration) µg Tl L-1 or subchronically exposed to 0, 0.9, or 141 (an elevated environmental concentration) µg Tl L-1 . The only effect following acute exposure was a stimulation of renal H+ -ATPase activity at the highest Tl exposure concentration. Similarly, the only significant effect of subchronic Tl exposure was an inhibition of branchial NKA activity at 141 µg Tl L-1 , an effect that may reflect the interaction of Tl with potassium ion handling. Despite significant literature evidence for effects of Tl on oxidative stress, there were no effects of Tl on any such endpoint in rainbow trout, regardless of exposure duration or exposure concentration. Elevated basal levels of antioxidant defenses may explain this finding. These data suggest that ionoregulatory perturbance is a more likely mechanism of Tl toxicity than oxidative stress in rainbow trout but is an endpoint of relevance only at elevated environmental Tl concentrations. Environ Toxicol Chem 2024;43:87-96. © 2023 SETAC.

Thallium (Tl) is a trace metal enriched in wastewaters associated with mining and smelting of base metals. The toxicity of Tl to aquatic biota is poorly understood, particularly with respect to its sublethal effects. In this study, phototactic behavioural responses of naïve (i.e. no previous exposure to Tl) Daphnia magna , a key regulatory freshwater crustacean species, were examined in waters containing Tl. Fed and fasted neonate daphnids (< 24 h old) and fed adults (10–15 days old) showed no significant response at any tested water Tl concentration. However, in fasted adults, an increase in the positive phototactic response (measured as a greater number of daphnids closer to the light source after a 5-min exposure) was seen at Tl concentrations of 917 and 2099 µg L −1 , values representative of extreme environmental Tl concentrations. The presence of Tl also decreased the swimming speed of adult Daphnia towards a light source. In the presence of cimetidine, a histamine receptor blocker, the increase in positive phototaxis induced by Tl disappeared, suggesting that Tl acts to perturb the phototaxis response through sensory inhibition. Conversely, although there was a trend towards enhanced activity, Tl had no significant effect on acetylcholinesterase, a marker of locomotor capacity.

There is limited information regarding the toxicity of the trace element thallium (Tl) to aquatic biota, most of which assesses acute toxicity and bioaccumulation. The relative lack of chronic Tl toxicity data compromises the establishment of water quality criteria for this trace metal. In the presented work, chronic toxicity endpoints (final body weight (a proxy measure of growth), survival, and reproduction) and Tl body burden were measured in the freshwater crustacean Daphnia magna during a 21-day exposure to dissolved Tl. Thallium caused complete mortality in daphnids between exposure concentrations of 424 and 702 mu g L-1. In contrast with previously published work examining acute Tl toxicity, exposure to Tl for 21 days was not associated with changes in whole-body potassium concentration. This was despite a 710-fold increase in Tl body burden in animals exposed to 424 mu g L-1 relative to the control. Median effect concentrations (EC50's) for growth and reproduction (total neonates produced), were 1.6 (95% confidence interval: 1.0-3.1) and 11.1 (95% confidence interval: 5.5-21.8) mu g Tl L-1, respectively. A no observable effect concentration (NOEC) of 0.9 mu g Tl L-1 for growth, and a NOEC range of 0.9-83 mu g Tl L-1 for a variety of reproductive metrics, was measured. A lowest observable effect concentration (LOEC) of 8.8 mu g Tl L-1 was determined for the effects of Tl on growth and most of the reproductive endpoints examined. These data indicate that under controlled laboratory conditions D. magna is significantly less sensitive to Tl than the species on which the current Canadian Council of Ministers of the Environment regulatory guideline value of 0.8 mu g L-1 is based. (C) 2020 Published by Elsevier Ltd.

Hydraulic fracturing of horizontal wells is a cost effective means for extracting oil and gas from low permeability formations. Hydraulic fracturing often produces considerable volumes of flowback and produced water (FPW). FPW associated with hydraulic fracturing has been shown to be a complex, often brackish mixture containing a variety of anthropogenic and geogenic compounds. In the present study, the risk of FPW releases to aquatic systems was studied using the model benthic invertebrate, Lumbriculus variegatus and field-collected FPW from a fractured well in Alberta. Acute, chronic, and pulse toxicity were evaluated to better understand the implications of accidental FPW releases to aquatic environments. Although L. variegatus is thought to have a high tolerance to many stressors, acute toxicity was significant at low concentrations (i.e. high dilutions) of FPW (48 h LC50: 4-5%). Chronic toxicity (28 d)of FPW in this species was even more pronounced with LC50s (survival/reproduction) and EC50s (total mass) at dilutions as low as 0.22% FPW. Investigations evaluating pulse toxicity (6 h and 48 h exposure) showed a significant amount of latent mortality occurring when compared to the acute results. Additionally, causality in acute and chronic bioassays differed as acute toxicity appeared to be primarily driven by salinity, which was not the case for chronic toxicity, as other stressors appear to be important as well. The findings of this study show the importance of evaluating multiple exposure regimes, the complexity of FPW, and also shows the potential aquatic risk posed by FPW releases. (C) 2020 Elsevier Ltd. All rights reserved.

The concentrations of trace elements (TEs) in large boreal rivers can fluctuate markedly due to changing water levels and flow rates associated with spring melt and variable contributions from tributaries and groundwaters, themselves having different compositions. These fluctuating and frequently high concentrations create regulatory challenges for protecting aquatic life. For example, water quality criteria do not account for changes in flow regimes that can result in TE levels that may exceed regulatory limits, and neither do they account for the markedly different lability and bioaccessibility of suspended solids. This review addresses the geochemical and biological processes that govern the lability and bioaccessibility of TEs in boreal rivers, with an emphasis on the challenges posed by the colloidal behaviour of many TEs, and their relationship to the dissolved fraction (i.e., <0.45 μm in size). After reviewing the processes and dynamics that give rise to the forms and behaviour of TEs in large boreal rivers, their relevance for aquatic organisms and the associated relationships between size and lability and bioaccessibility are discussed. The importance of biological variables and different forms of TEs for limiting lability and bioaccessibility are also addressed. Two case studies emphasize seasonal fluctuations and accompanying changes in the distribution of TE amongst different size fractions and associated colloidal species in large boreal rivers: the Northern Dvina and one of its tributaries, the Pinega River, both in Russia, and the Athabasca River in Alberta, Canada. Water quality in the Athabasca River is briefly discussed with respect to Canadian guidelines.

Thallium (Tl) is a trace element associated with base metal mining and processing, but little is known regarding how its toxicity is influenced by water chemistry. In the present study, the 48‐h median lethal concentration (LC50) of Tl to Daphnia magna was determined in a standard laboratory water, and toxicity was reassessed under conditions of varying cation (Ca, K, Na), anion (Cl, HCO–3), and dissolved organic matter (DOM) concentrations. The calculated 48‐h LC50 of 1.86mg Tl/L was consistent with previous work on Tl toxicity to D. magna. At the 48‐h LC50 concentration, changes in water chemistry had no statistically significant effect on mortality, although there was a trend toward lower Tl toxicity with elevated water K. Test waters containing 10mM CaCl2 did not support control survival. The measurement of Tl complexation with DOM using asymmetric flow field flow fractionation confirmed the outcomes of biogeochemical speciation modeling: Tl speciation was relatively unaffected by water chemistry, and the majority of Tl remained in the ionic form across all treatments. These data indicate that Tl toxicity is largely independent of speciation, a property that will greatly simplify risk assessments for this metal in freshwaters. Environ Toxicol Chem 2019;38:2472–2479. © 2019 SETAC

This study sought to develop non-invasive techniques to monitor glucocorticoids in captive Necturus as a means to correlate inter-renal gland function in relation to environmental and physiological changes. Six individually housed breeding pairs of captive Necturus beyeri were subjected to seasonal changes in water temperature (30°F temperature differential) to stimulate natural breeding, specifically spermatophore deposition and oviposition. An enzyme immunoassay was validated for the measurement of N. beyeri faecal corticosterone metabolites (fCMs) by exhibiting parallelism and accuracy to the standard curve. Longitudinal (December 2016-October 2017) assessment of fCM concentrations and pattern of excretion from samples collected from the six breeding pairs revealed a seasonal inter-renal effect with higher concentrations (P < 0.05) excreted during months (December-March) of the year associated with breeding activity and when water temperatures were lowest. Males from each pair produced spermatophores starting on 08 December 8 2016 and ending on 05 April 2017. Females from four of the six pairs went on to successfully oviposit eggs in mid-late April 2017. One clutch was fertile, and three were non-fertile. No differences (P > 0.05) were detected in fCM concentrations between pairs in which oviposition did or did not occur. In addition, a novel waterborne corticosterone metabolite (wCM) assay was validated to overcome challenges associated with faecal collection in a group-housed amphibian. An adrenocorticotropic hormone (ACTH) challenge performed in an adult male Necturus maculosus resulted in a 50-fold increase in wCM at 4 h post-injection and marked the first demonstration of a waterborne inter-renal response to ACTH in Necturus. This study not only provides insight into inter-renal function in an aquatic salamander that exhibits marked reproductive seasonality but also confirms utility of fCM and wCM measurements as non-invasive means of assessment.

Thallium (Tl) is a trace element associated with base metal mining and processing, but little is known regarding how its toxicity is influenced by water chemistry. In the present study, the 48-h median lethal concentration (LC50) of Tl to Daphnia magna was determined in a standard laboratory water, and toxicity was reassessed under conditions of varying cation (Ca2+, K+, Na+), anion (Cl-, HCO3-), and dissolved organic matter (DOM) concentrations. The calculated 48-h LC50 of 1.86 mg Tl/L was consistent with previous work on Tl toxicity to D. magna. At the 48-h LC50 concentration, changes in water chemistry had no statistically significant effect on mortality, although there was a trend toward lower Tl toxicity with elevated water K+. Test waters containing 10 mM CaCl2 did not support control survival. The measurement of Tl complexation with DOM using asymmetric flow field flow fractionation confirmed the outcomes of biogeochemical speciation modeling: Tl speciation was relatively unaffected by water chemistry, and the majority of Tl remained in the ionic form across all treatments. These data indicate that Tl toxicity is largely independent of speciation, a property that will greatly simplify risk assessments for this metal in freshwaters. Environ Toxicol Chem 2019;38:2472-2479. (c) 2019 SETAC

It has been suggested that open pit mining and upgrading of bitumen in northern Alberta releases Tl and other potentially toxic elements to the Athabasca River and its watershed. We examined Tl and other trace elements in otoliths of Trout-perch (Percopsis omiscomaycus), a non-migratory fish species, collected along the Athabasca River. Otoliths were analyzed using ICP-QMS, following acid digestion, in the metal-free, ultraclean SWAMP laboratory. Compared to their average abundance in the dissolved (<0.45 μm) fraction of Athabasca River, Tl showed the greatest enrichment in otoliths of any of the trace elements, with enrichments decreasing in the order Tl, Sr, Mn, Zn, Ba, Th, Ni, Rb, Fe, Al, Cr, Ni, Cu, Pb, Co, Li, Y, V, and Mo. Normalizing Tl in the otoliths to the concentrations of lithophile elements such as Li, Rb, Al or Y in the same tissue reveals average enrichments of 177, 22, 19 and 190 times, respectively, relative to the corresponding ratios in the water. None of the element concentrations (Tl, Li, Rb, Al, Y) or ratios were significantly greater downstream of industry compared to upstream. This natural bioaccumulation of Tl most likely reflects the similarity in geochemical and biological properties of Tl+ and K+. SUMMARY OF MAIN FINDINGS: Thallium is enriched in fish otoliths, relative to the chemical composition of the river, to the same degree both upstream and downstream of industry.