Category Archives: Environmental Toxicology and Chemistry

Effects of Acute and Sub‐Chronic Waterborne Thallium Exposure on Ionoregulatory Enzyme Activity and Oxidative Stress in Rainbow Trout (Oncorhynchus mykiss)

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ABSTRACT

The mechanisms of acute (96 h) and sub-chronic (28-d) 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 ATPase 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 sub-chronically 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 sub-chronic 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 defences 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.

Development and Validation of Multiple Linear Regression Models for Predicting Chronic Zinc Toxicity to Freshwater Microalgae

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Abstract

Multiple linear regression (MLR) models were developed for predicting chronic zinc toxicity to a freshwater microalga, Chlorella sp., using three toxicity modifying factors (TMF): pH, hardness, and dissolved organic carbon (DOC). The interactive effects between pH and hardness, and pH and DOC were also included. Models were developed at three different effect concentration (EC) levels, including the EC10, EC20 and EC50 level. Models were independently validated using six different zinc-spiked Australian natural waters with a range of water chemistries. Stepwise regression found hardness to be an influential TMF in model scenarios and was retained in all final models, while pH, DOC and interactive terms had variable influence and were only retained in some models. Autovalidation and residual analysis of all models indicated that models generally predicted toxicity and there was little bias based on individual TMF. The MLR models, at all effect levels, performed poorly when predicting toxicity in the zinc-spiked natural waters during independent validation, with models consistently overpredicting toxicity. This overprediction may be from another unaccounted for TMF that may be present across all natural waters. Alternatively, this consistent overprediction questions the underlying assumption that models developed from synthetic laboratory test waters can be directly applied to natural water samples. Further research into the suitability of applying synthetic laboratory water-based models to a greater range of natural waters is need.

Model‐Assisted Interpretation of 4,4′‐Methylene Dianiline Adsorption on Soils at Micromolar Concentrations

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Abstract

Adsorption kinetics and isotherms were determined for 4,4′-methylene dianiline (MDA) on five diverse soils at nominal concentrations of 0.01–1.0 mg L−1 (nominal soil loading 0.1–40 μg gs −1). The data were used to model the adsorption process based on the two-step mechanism that is characteristic of the adsorption of aromatic amines, consisting of a physical equilibrium between the aqueous phase and the soil organic matter and a chemical reaction between the adsorbed MDA and reactive sites in the soil organic matter. Generic parameters were determined that enabled application of the model to other soils, which was checked against previously published data for MDA adsorption. At the low concentrations evaluated, the adsorption process took place almost exclusively in the organic matter without the need to account for a separate ion exchange process with the soil mineral fraction. Physical adsorption was found to be mainly dependent on the protonation state of MDA and increased with decreasing pH of the soils. Because of the chemical reaction taking place, adsorption equilibrium constants (organic–carbon partition coefficient [K OC]) normalized to the organic carbon content in the soil gradually increased with time; and it was demonstrated that, at steady-state conditions, values of log K OC > 3.5 can be expected for most any soil at conservatively estimated potential environmental MDA concentrations. Environ Toxicol Chem 2023;00:1–9. © 2023 SETAC

Different Life‐Stage Exposure to Hexafluoropropylene Oxide Trimer Acid Induces Reproductive Toxicity in Adult Zebrafish (Danio rerio)

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Abstract

As a novel alternative to perfluorooctanoic acid (PFOA), hexafluoropropylene oxide trimer acid (HFPO-TA) has been widely used and has caused ubiquitous water pollution. However, its adverse effects on aquatic organisms are still not well known. In the present study, zebrafish at different life stages were exposed to 0, 5, 50, and 100 μg/L of HFPO-TA for 21 days to investigate reproductive toxicity in zebrafish. The results showed that HFPO-TA exposure significantly inhibited growth and induced reproductive toxicity in zebrafish, including a decrease of the condition factor, gonadosomatic index, and the average number of eggs. Histological section observation revealed that percentages of mature oocytes and spermatozoa were reduced, while those of primary oocytes and spermatocytes increased. In addition, exposure to HFPO-TA at three stages induced a significant decrease in the hatching rate, while the heart rate and normal growth rate of F1 offspring were only significantly inhibited for the exposure from fertilization to 21 days postfertilization (dpf). Compared with the exposure from 42 to 63 dpf, the reproductive toxicity induced by HFPO-TA was more significant for the exposure from fertilization to 21 dpf and from 21 to 42 dpf. Expression of the genes for cytochrome P450 A1A, vitellogenin 1, estrogen receptor alpha, and estrogen receptor 2b was significantly up-regulated in most cases after exposure to HFPO-TA, suggesting that HFPO-TA exhibited an estrogen effect similar to PFOA. Therefore, HFPO-TA might disturb the balance of sex steroid hormones and consequently induce reproductive toxicity in zebrafish. Taken together, the results demonstrate that exposure to HFPO-TA at different life stages could induce reproductive toxicity in zebrafish. However, the underlying mechanisms deserve further investigation. Environ Toxicol Chem 2023;00:1–11. © 2023 SETAC

Assessing the Toxicity of Sea Salt to Early Life Stages of Freshwater Mussels: Implications for Sea Level Rise in Coastal Rivers

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Abstract

Sea levels across the planet are rising, particularly along the eastern coast of the United States. Climate-induced sea level rise can result in the inundation and intrusion of seawater into freshwater drainages. This would alter salinity regimes and lead to the salinization of coastal freshwater ecosystems. Increased salinity levels in freshwater can negatively affect freshwater-dependent species, including native mussels belonging to the order Unionida, which are highly sensitive to changes in water quality. Sea salt is largely made up of sodium and chloride ions, forming sodium chloride, a known toxicant to freshwater mussels. However, sea salt is a mixture that also contains other major ions, including potassium, sulfate, calcium, strontium, and magnesium, among others. Freshwater mussels exposed to sea salt would be exposed to each of the sea salt ions at the same time, resulting in a mixture toxicity effect. The mixture toxicity of these ions on early life stages of freshwater mussels is largely unknown because most research to date has evaluated individual salt ions in relative isolation. Therefore, we conducted acute toxicity tests on early life stages (glochidia and juvenile) of three freshwater mussel species that inhabit Atlantic Slope drainages (nonsalinity-adapted Atlanticoncha ochracea, salinity-adapted A. ochracea, Sagittunio nasutus, and Utterbackiana implicata). Glochidia and juveniles of each species were exposed to a control and six concentrations of Instant Ocean® Sea Salt (IOSS), a synthetic sea salt that closely resembles the ionic composition of natural sea salt. Exposure concentrations were 1 part(s) per thousand (ppt), 2 ppt, 8.5 ppt, 12.5 ppt, 17 ppt, and 34 ppt. We calculated the median effect concentration (EC50) for each of the eight acute toxicity tests and found that glochidia were more sensitive than juveniles to IOSS. At hour 24 EC50s for the glochidia ranged from 0.38 to 3.6 ppt, with the most sensitive freshwater mussel being the nonsalinity-adapted A. ochracea, exhibiting an EC50 of 0.38 ppt (95% confidence interval [CI] 0.33–0.44). Juvenile freshwater mussels exhibited EC50s at hour 96 ranging from 5.0 to 10.4 ppt, with the least sensitive freshwater mussel being the nonsalinity-adapted A. ochracea, exhibiting an EC50 of 10.4 ppt (95% CI 9.1–12.0). Our results show that acute exposure to sea salt adversely affects freshwater mussel viability, particularly glochidia. This information can be used to enhance freshwater mussel conservation strategies in regions that are or will be impacted by climate-induced sea level rise and associated freshwater salinization. Environ Toxicol Chem 2023;00:1–12. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Divergent Temporal Trends of Mercury in Arctic Char from Paired Lakes Influenced by Climate‐related Drivers

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Abstract

Climate-driven changes including rising air temperatures, enhanced permafrost degradation, and altered precipitation patterns can have profound effects on contaminants, such as mercury (Hg), in High Arctic lakes. Two physically similar lakes, East Lake and West Lake at the Cape Bounty Arctic Watershed Observatory on Melville Island, Nunavut, Canada are being affected by climate change differently. Both lakes have experienced permafrost degradation in their catchments; however, West Lake has also undergone multiple underwater Mass Movement Events (MME; beginning in fall 2008), leading to a sustained 50-fold increase in turbidity. This provided the unique opportunity to understand the potential impacts of permafrost degradation and other climate-related effects on Hg concentrations and body condition of landlocked Arctic char (Salvelinus alpinus), an important sentinel species across the Circum-Arctic. The objectives of this work were to assess temporal trends in char Hg concentrations and to determine potential mechanisms driving the trends. There was a significant decrease in Hg concentrations in East Lake char averaging 6.5 %/y and 3.8 %/y for length-adjusted and age- adjusted means, respectively, from 2008 to 2019. Conversely, in West Lake there was a significant increase, averaging 7.9 %/y and 8.0 %/y for length-adjusted and age-adjusted mean Hg concentrations, respectively, for 2009 to 2017 (last year with sufficient sample size). The best predictors of length-adjusted Hg concentrations in West Lake were carbon and nitrogen stable isotope ratios, indicating a shift in diet including possible dietary starvation brought on by the profound increase in lake turbidity. This work provides an example of how increasing lake turbidity, a likely consequence of climate warming in Arctic lakes, may influence fish condition and Hg concentrations.

Oxidative Stress Contributes to Flumioxazin‐Induced Cardiotoxicity in Zebrafish Embryos

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ABSTRACT

Flumioxazin is a widely applicated herbicide in the control of aquatic plants. Current evidence suggested that flumioxazin could induce cardiac defects (ventricular septal defects) in vertebrates, but the underlining mechanisms remain unclear. Because of the inhibitory effect of flumioxazin on polyphenol oxidase (PPO), the assumption is made that flumioxazin-induced cardiotoxicity is caused by oxidative stress. The results show that flumioxazin induced cardiac malformations and abnormal gene expression associated with cardiac development. Cardiac malformations include pericardium edema, cardiac linearization, elongated heart, cardiomegaly, cardiac wall hypocellularity, myocardial cell atrophy into granular, and a significant gap between the myocardial intima and the adventitia. An increase in oxidative stress and apoptosis was observed in the cardiac region of zebrafish after exposure to flumioxazin. Antioxidant astaxanthin reversed the cardiac malformations, excessive ROS production and expression of genes for cardiac developmental and apoptosis regulation induced by flumioxazin. In addition, flumioxazin also activated AHR signaling pathway genes (ahr2, cyp1a1, and cyp1b1) and increased porphyrins concentration. In conclusion, the results suggest that excessive ROS production, which could be mediated through AHR, led to apoptosis, contributing to the cardiotoxicity of flumioxazin in zebrafish embryos.

INCREASED ENDOCRINE ACTIVITY OF XENOBIOTIC CHEMICALS AS MEDIATED BY METABOLIC ACTIVATION

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ABSTRACT

The US EPA is faced with long lists of chemicals that require hazard assessment. This research is part of a larger effort to develop in vitro assays and QSARs applicable to untested chemicals on US EPA inventories through study of estrogen receptor (ER) binding and estrogen mediated gene expression in fish. The current effort investigates metabolic activation of chemicals resulting in increased estrogenicity. Phenolphthalin (PLIN) was shown not to bind rainbow trout (Oncorhynchus mykiss) ER (rtER) in a competitive binding assay but vitellogenin (Vtg) expression was induced in trout liver slices exposed to 10-4 and 10-3.7 M PLIN. Phenolphthalein (PLEIN), metabolite of PLIN, was subsequently determined to be formed when slices were exposed to PLIN. PLEIN binds rtER with a relative binding affinity (RBA) to 17β-estradiol of 0.020%. Slices exposed to PLEIN expressed Vtg mRNA at 10-4.3, 10-4, and 10-3.7 M, with no detectable PLIN present. Thus, Vtg expression noted in PLIN slice exposures was explained by metabolism to PLEIN in trout liver slices. A second model chemical, 4,4’-methylenedianiline (MDA) was not shown to bind rtER but did induce Vtg mRNA production in tissue slices at 10-4.3, 10-4, and 10-3.7 M in amounts nearly equal to reference estradiol induction, thus indicating metabolic activation of MDA. A series of experiments were performed to identify a potential metabolite responsible for the observed increase in activity. Potential metabolites hydroxylamine-MDA, nitroso-MDA, azo-MDA, or azoxy-MDA were not observed. However, acetylated-MDA was observed and tested in both ER-binding and tissue slice Vtg induction assays.

Research Priorities for the Environmental Risk Assessment of Per‐ and Polyfluorinated Substances

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Abstract

Per- and polyfluorinated substances (PFAS) are a group of thousands of ubiquitously applied persistent industrial chemicals. The field of PFAS environmental research is developing rapidly, but suffers from substantial biases toward specific compounds, environmental compartments, and organisms. The aim of our study was therefore to highlight current developments and to identify knowledge gaps and subsequent research needs that would contribute to a comprehensive environmental risk assessment for PFAS. To this end, we consulted the open literature and databases and found that knowledge of the environmental fate of PFAS is based on the analysis of <1% of the compounds categorized as PFAS. Moreover, soils and suspended particulate matter remain largely understudied. The bioavailability, bioaccumulation, and food web transfer studies of PFAS also focus on a very limited number of compounds and are biased toward aquatic biota, predominantly fish, and less frequently aquatic invertebrates and macrophytes. The available ecotoxicity data revealed that only a few PFAS have been well studied for their environmental hazards, and that PFAS ecotoxicity data are also strongly biased toward aquatic organisms. Ecotoxicity studies in the terrestrial environment are needed, as well as chronic, multigenerational, and community ecotoxicity research, in light of the persistency and bioaccumulation of PFAS. Finally, we identified an urgent need to unravel the relationships among sorption, bioaccumulation, and ecotoxicity on the one hand and molecular descriptors of PFAS chemical structures and physicochemical properties on the other, to allow predictions of exposure, bioaccumulation, and toxicity. Environ Toxicol Chem 2023;00:1–15. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Trace Elements and Consequent Ecological Risks in Mining‐Influenced Streams of Appalachia

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Abstract

Appalachian (eastern USA) coal surface mines fracture geologic materials, causing release of both major ions and trace elements to water via accelerated weathering. When elevated above natural background, trace elements in streams may produce adverse effects on biota via direct exposure from water and sediment and via dietary exposure in food sources. Other studies have found elevated water concentrations of multiple trace elements in Appalachia's mining-influenced streams. Except for Se, trace-element concentrations in abiotic and biotic media of Appalachian mining-influenced streams are less well known. We analyzed environmental media of headwater streams receiving alkaline waters from Appalachian coal mines for eight trace elements (Al, As, Cd, Cu, Ni, Sr, V, and Zn) and assessed the potential consequent ecological risks. Streamwater, particulate media (sediment, biofilm, leaf detritus), and benthic macroinvertebrates (primary consumers, secondary consumers, crayfish) were sampled from six mining-influenced and three reference streams during low-flow conditions in two seasons. Dissolved Cu, Ni, and Sr were higher in mining-influenced streams than in reference streams; Ni, Sr, and Zn in fine sediments and Ni in macroinvertebrates were also elevated relative to reference-stream levels in samples from mining-influenced streams. Seasonal ratios of mining-influenced stream concentrations to maximum concentrations in reference streams also demonstrated mining-influenced increases for several elements in multiple media. In most media, concentrations of several elements including Ni were correlated positively. All water-column dissolved concentrations were below protective levels, but fine-sediment concentrations of Ni approached or exceeded threshold-effect concentrations in several streams. Further study is warranted for several elements (Cd, Ni, and Zn in biofilms, and V in macroinvertebrates) that approached or exceeded previously established dietary-risk levels. Environ Toxicol Chem 2023;00:1–15. © 2023 SETAC.