Species and life-stage specific differences in cadmium accumulation and cadmium induced oxidative stress, metallothionein and heat shock protein responses in white sturgeon and rainbow trout

Comparative subchronic toxicity of copper and a tertiary copper mixture to early life stage rainbow trout (Oncorhynchus mykiss): impacts on growth, development, and histopathology

This research aimed to characterize and compare the subchronic impacts of Cu to a Cu, Cd, and Zn mixture in early life stages of rainbow trout (Oncorhynchus mykiss) by examining uptake, survival, growth, development, and histopathology parameters. To accomplish this, rainbow trout were exposed for 31 days from eyed embryos to the swim-up fry life stage to waterborne Cu (31, 47, 70, and 104 μg/L) individually or as mixture containing Cd (4.1, 6.2, 9.3, and 14 μg/L) and Zn (385, 578, 867, and 1300 μg/L). Exposures elicited pronounced effects on survival when Cu was administered as a mixture (LC25 = 32.9 μg/L Cu) versus individually (LC25 = 46.3 μg/L Cu). Mixtures of Cu, Cd, and Zn also elicited more pronounced sublethal toxicity relative to equivalent Cu treatments with respect to reduced yolk sac resorption and increased incidence and/or severity of gill, liver, and kidney lesions. Our findings of reduced body weight (EC10, Cu = 55.0 μg/L Cu; EC10, Cu+Cd+Zn = 58.9 μg/L Cu), yolk sac resorption (LOECCu = 70 μg/L Cu; LOECCu+Cd+Zn = 70 μg/L Cu), coelomic fat (LOECCu = 47 μg/L Cu; LOECCu+Cd+Zn = 70 μg/L Cu), and increased hepatocellular cytoplasmic vacuolation (LOECCu = 70 μg/L Cu; LOECCu+Cd+Zn = 47 μg/L Cu) collectively indicate a complicated metabolic interference by metals in exposed fish. These lethal and sublethal effects observed in the laboratory could translate to reduced survival and fitness of wild salmonid populations inhabiting waterbodies receiving wastewater or runoff containing multiple metals at elevated concentrations.

Pesticides in a warmer world: Effects of glyphosate and warming across insect life stages

Glyphosate (GLY) is a broad-spectrum herbicide that is the most commonly applied pesticide in terrestrial ecosystems in the U.S. and, potentially, worldwide. However, the combined effects of warming associated with climate change and exposure to GLY and GLY-based formulations (GBFs) on terrestrial animals are poorly understood. Animals progress through several life stages (e.g., embryonic, larval, and juvenile stages) that may exhibit different sensitivities to stressors. Therefore, we factorially manipulated temperature and GLY/GBF exposure in the variable field cricket (Gryllus lineaticeps) during two life stages-nymphal development and adulthood-and examined key animal traits, such as developmental rate, body size, food consumption, reproductive investment, and lifespan. A thermal environment simulating future climate warming obligated several costs to fitness-related traits. For example, warming experienced during nymphal development reduced survival, adult body mass and size, and investment into flight capacity and reproduction. Warming experienced by adults reduced lifespan and growth rate. Alternatively, the effects of GBF exposure were more subtle, often context-dependent (e.g., effects were only detected in one sex or temperature regime), and were stronger during adult exposure relative to exposure during development. There was evidence of additive costs of warming and GBF exposure to rates of feeding and growth in adults. Yet, the negative effect of GBF exposure to adult lifespan did not occur in warming conditions, suggesting that ongoing climate change may obscure some of the costs of GBFs to non-target organisms. The effects of GLY alone (i.e., in the absence of proprietary surfactants found in commercial formulations) were non-existent. Animals will be increasingly exposed to warming and GBFs, and our results indicate that GBF exposure and warming can entail additive costs for an animal taxon (insects) that plays critical roles in terrestrial ecosystems.

Oxidative stress and metal homeostasis alterations in Danio rerio (zebrafish) under single and combined carbamazepine, acetamiprid and cadmium exposures

Contaminants of emerging concern (CEC) are routinely detected in aquatic environments, especially pharmaceuticals, such as carbamazepine (CBZ), and neonicotinoid pesticides, like acetamiprid (ACT). CECs can interact with each other and with other legislated contaminants like Cd, resulting in unknown effects. Most studies evaluate only the effects of single contaminant exposures on aquatic biota. Therefore, the aim of the present study was to assess the effects of both single and combined CBZ, ACT and Cd exposures on zebrafish brain and liver oxidative stress parameters and metal homeostasis. The biomarkers catalase (CAT), glutathione-S-transferase (GST), total thiols (TOT), metallothionein (MT) and malondialdehyde (MDA) and the essential elements Ca, Cu, K, Na, Mg, Mn and Zn were evaluated after 96-hour static exposures. CBZ, ACT and Cd single (brain and liver) and combined (liver) treatments resulted in oxidative effects in both fish organs, also leading to metal (Ca, Mg, K, Mn, Zn and Cu) homeostasis alterations. ACT exposure resulted in the greatest adverse effects in the brain, while CBZ was the cause of major element homeostasis and oxidative stress alterations in the liver. Lower LPO levels were observed in the combined treatments compared to single treatments, suggesting interactions and contaminant effect attenuation. This study is the first to evaluate the initial effects of combined CBZ, ACT and Cd exposures in zebrafish, paving the way for further investigations concerning other biomarkers during longer exposure times.

Protective effects of different concentrations of selenium nanoparticles on rainbow trout (Oncorhynchus mykiss) primary hepatocytes under heat stress

Heat stress leads to altered expression of associated heat shock proteins (HSPs), which are critical molecular chaperones related to cellular function in living organisms. Selenium nanoparticles (SeNPs), a nanocomposite form of Se, have a protective effect against heat stress-induced cellular damage. In this study, primary rainbow trout hepatocytes were isolated to identify the protective function of SeNPs in rainbow trout hepatocytes. Experiments were divided into five groups and SeNPs were added at concentrations of 0, 2.0, 3.0, 5.0 and 8.0 μg/mL and incubated at 18 ℃ for 4, 8, 12, 24 and 48 h respectively. Hepatocyte viability, GSH-Px and SOD activity were enhanced and MDA content was reduced following the addition of SeNPs. Expression of GSH-P1 and genes related to HSPs (including HSP70a, HSP60, HSP90β, HSP10 and HSP47) were significantly increased and the optimal concentration of SeNPs for adding to hepatocytes was identified as 5.0 µg/mL. Adding 5.0 µg/mL SeNPs following heat stress (24 ℃) increased hepatocyte viability, GSH-Px and SOD activity, while MDA levels first decreased and then increased. Expression of GSH-P1 and genes related to HSPs (including HSP70a, HSP60, HSP90β, HSP10 and HSP47) were significantly higher than controls. In summary, SeNPs and slight heat stress synergistically enhanced the expression of GSH-P1 and HSPs and protected hepatocytes from heat stress damage, suggesting that SeNPs is a potential hepatocyte protective therapeutic agent.

Acute Cd Toxicity, Metal Accumulation, and Ion Loss in Southern Catfish (Silurus meridionalis Chen)

The amounts of cadmium in multiple organs and the amounts of Na⁺ and Ca²⁺ in the carcass were measured in dead and surviving southern catfish exposed to different concentrations of Cd. The 96 h median lethal concentration was 6.85 mg/L. The Cd content and Cd accumulation rate were positively correlated with Cd exposure concentrations, and there were significant differences between dead and surviving individuals, indicating that both Cd content in tissues and Cd accumulation rates were correlated with mortality. Cd levels in the liver of dead fish were saturated. A lethal threshold for Cd concentration in the whole fish was obtained. Bioconcentration factors for Cd did not decrease with increasing exposure. Acute exposure to waterborne Cd caused a significant decrease in the ion content of the fish carcass. There was a significant difference between the Na⁺ content of the carcass of dead fish (34.54 μmol/g wet weight) and surviving fish (59.34 μmol/g wet weight), which was not the case with the Ca²⁺ content, indicating that the lethal toxicity of Cd was probably related to the decrease in Na⁺ content. Collectively, these results suggest that whole-fish Cd concentration and carcass Na⁺ content can be useful indicators of fish acutely exposed to Cd.

Differences in the subcellular distribution of cadmium and copper in the gills and liver of white sturgeon (Acipenser transmontanus) and rainbow trout (Oncorhynchus mykiss)

Recent studies have shown that white sturgeon (Acipenser transmontanus) are more resistant to cadmium (Cd) compared to rainbow trout (Oncorhynchus mykiss), whereas they are more sensitive than rainbow trout when exposed to copper (Cu). Differences in the subcellular distribution of metals among species could be one of the factors responsible for the differences in the sensitivity to metals. Although, subcellular distribution has been studied extensively in many species with many metals, its direct role in species-specific differences in the sensitivity has not been well studied. The objective of this study was to evaluate the role of subcellular distribution of metals in species-specific differences in the sensitivity to metals between sturgeon and trout. We compared the subcellular distribution of metals Cd and Cu in the cellular debris, heat-stable proteins, heat-denatured fraction, metal-rich granules, and organelles fractions from the gills and liver after exposure of juveniles of both species to 1.25 and 20 μg/L Cd and Cu for 8 days, respectively. Sturgeon diverted a higher amount of Cd towards biologically inactive metal pool (BIM) and a lower amount towards the biologically active metal pool (BAM) compared to trout in both tissues. This explained why sturgeon are able to tolerate a relatively higher exposure level to Cd compared to trout. For Cu, there was no statistically significant species-specific differences in the amounts diverted towards either BAM or BIM; hence, white sturgeon's greater sensitivity to Cu was not explained by its subcellular distribution strategies.

Chronic exposure to environmental cadmium affects growth and survival, cellular stress, and glucose metabolism in juvenile channel catfish (Ictalurus punctatus)

Anthropogenic activities have led to the enrichment of cadmium in freshwater systems where it is a contaminant of concern for fisheries and aquaculture as it has no known biological function and is toxic at trace concentrations. Yet, knowledge gaps remain regarding effects of chronic exposure to environmentally relevant concentrations on freshwater fish. Thus, the objectives of the current study were to assess chronic impacts of cadmium on channel catfish (Ictalurus punctatus) including how tissue-specific bioaccumulation patterns relate to functions of those tissues over time. We focused on liver and kidneys, and expression of genes related to cellular stress, glucose metabolism, and steroidogenesis. Catfish were exposed to concentrations of 0.5 (control), 2 (low), and 6 (high) μg L^-1 Cd from fertilization to six months. Cadmium exposure negatively impacted channel catfish growth and was linked to bioaccumulation of tissue Cd, which followed a dose-related response, where concentrations in trunk kidney > liver = head kidney >> muscle. Differences in tissue Ca, Cu, Fe, and Zn concentrations were also observed between treatments. Following 3 months of exposure, expression of metallothionein (MT) and heat shock proteins (HSP) 70 & 90 increased relative to controls; however, no differences were detected at 6 months, suggesting compensation. Conversely, there were no differences in expression patterns for key genes in steroidogenesis, steroidogenic factor 1 (SF1), steroidogenic acute regulatory protein (StAR), and cytochrome P450scc (P450), which supports the observation that Cd did not affect the secondary stress response, evaluated via plasma cortisol and glucose concentrations following a low water stress event. As a function of length and weight, the high Cd treatment yielded fish that were significantly smaller than controls. In addition to the cellular responses in MT and HSPs noted, reduced growth in the high Cd treatment was likely due, at least in part, to elevated energetic demands. This is supported by observations of the upregulation of genes necessary for glucose metabolism. Hexokinase (HK), glucose-6-phosphatase (G6P), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were significantly elevated in the high treatment relative to controls at 3 months of exposure. Over the study period, exposure also reduced survival of channel catfish from 3 to 6 months. Reduced fitness, as a consequence of cadmium exposure, could be visible at the population level through altered life histories and growth patterns.

Immunity and health of two wild marine fishes naturally exposed to anthropogenic pollution

There are increasing global concerns of the alarming pollution impacts on marine life, thus it is becoming essential to generate reliable tools to monitor and understand the effects of these impacts on aquatic organisms. We performed a field study assessing how exposure to anthropogenic pollution impacts immunological and health-state parameters and parasite infection of a wild marine fish, the Brazilian sandperch Pinguipes brasilianus. Then we compared this information to previously published data of a sympatric species, the Patagonian rockfish Sebastes oculatus inhabiting the same polluted and pristine areas. The field study revealed that exposed P. brasilianus showed chronic stress, poor immune condition and higher prevalence and abundance of acanthocephalan parasites. By comparing these former results with already published in S. oculatus, we concluded that, although both species exhibited physiological alterations associate to inhabiting sites exposed to pollution, their specific immunological and health-state responses differed. Our results demonstrate that Patagonian reef-fish assemblages inhabiting sites exposed to pollutant are being affected in their immune and heath condition, which could potentially result in higher susceptibility to disease and in turn population decline. These findings highlight the necessity of more studies incorporating interspecific comparisons to assess variation in fish susceptibility in an ecoimmunotoxicological context and get a more profound understanding of anthropogenic impacts on wildlife.

Heat shock pretreatment induced cadmium resistance in the nematode Caenorhabditis elegans is depend on transcription factors DAF-16 and HSF-1

Cadmium (Cd) exposure poses a serious environmental problem due to the metal's bioaccumulation and difficult to eliminate from body. Understanding the mechanisms of Cd detoxification and resistance can provide insights into methods to protect against the damaging effects of the heavy metal. In the present study, we found that heat shock (HS) pretreatment increased Cd resistance of the nematode Caenorhabditis elegans by reducing the bagging phenotype and protecting the integrity of the intestinal barrier. HS pretreatment increased the expression of heat shock protein-16.2 (HSP-16.2) prior to Cd exposure, and HS-induced Cd resistance was absent in worms with hsp-16.2 loss-of-function mutation. Worm strain with daf-2(e1370) mutation presented enhanced HS-induced Cd resistance, which was eliminated in worm strains of daf-16(mu86) and hsf-1(sy441). HS pretreatment increased DAF-16 nuclear localization and HSF-1 granule formation prior to Cd exposure. DAF-16 and HSF-1 was essential in reducing bagging formation and protecting the integrity of intestinal barrier after HS pretreatment. In conclusion, the present study demonstrated that HS-induced Cd resistance in C. elegans is regulated by the DAF-16/FOXO and HSF-1 pathways through regulation of HSP-16.2 expression.

Two sigma and two mu class genes of glutathione S-transferase in the waterflea Daphnia pulex: Molecular characterization and transcriptional response to nanoplastic exposure

Two isoforms of Glutathione S-Transferase (GST) genes, belonging to mu (Dp-GSTm1 and Dp-GSTm2) and sigma (Dp-GSTs1 and Dp-GSTs2) classes, were cloned and characterised in the freshwater Daphnia pulex. No signal peptide was found in any of the four GST proteins, indicating that they were cytosolic GST. A highly conserved glutathione (GSH) binding site (G-site) occurred in the N-terminal sequence, and a substrate binding site (H-site), interacting non-specifically with the second hydrophobic substrate, was present in the C-terminal. A Tyr residue, for the stabilization of GSH, was found to be conserved in the analysed sequences. The secondary and tertiary structures indicated that these genes possess the typical cytosolic GST structure, including a conserved N-terminal domain with a βαβαββα motif. The μ loop (NVGPAPDYDR and NFIGAEWDR in Dp-GSTm1 and Dp-GSTm2, respectively) was identified between the βαβ (β1α1β2) and αββα motifs (α2β3β4α3) in the N-terminal domain. The expressions of Dp-GSTs1, Dp-GSTs2, and Dp-GSTm1 were higher in other age groups compared to the newly-born neonates (1 d); however, the expression of Dp-GSTm2 first increased and then decreased with age. Gene expression was significantly reduced by high concentration (1 and 2 mg/L) of 75 nm polystyrene nanoplastic. However, nanoplastic exposure at the predicted environmental concentration (1 μg/L) had a low effect. Exposure of mothers to nanoplastic (1 μg/L) elevated the Dp-GSTs2 level in their neonates. These results improve our understanding on the response of different types of Daphnid GST to environmental contaminants, especially nanoplastic.

Effect of sublethal gradient concentrations of nickel on postlarvae of Penaeus monodon, Perna viridis and Terapon jarbua: Enzyme activities and histopathological changes

The present study evaluates the enzyme activities and histopathological changes in the post larvae (PL) of shrimp (Penaeus monodon), green mussel (Perna viridis) and fingerlings of crescent perch (Terapon jarbua) exposed to sublethal gradient concentrations of Nickel (Ni). The median lethal concentration (LC₅₀) values were 2.49, 66.03 and 43.92 mg Ni L^-1 derived for the PL of shrimp, green mussel and fish fingerlings respectively. No Observed Effect Concentration (NOEC), Lowest Observed Effect Concentration (LOEC) and chronic values of the PL of shrimp were 46.5, 73.0 and 58.3 μg Ni L^-1 derived for the 21-d survival endpoint. The NOEC, LOEC and chronic values for the 30-d survival endpoint of the green mussels and fish fingerlings were 4.6, 6.32, 5.4 and 1.95, 2.6, 2.25 mg Ni L^-1 respectively. The isoforms of esterase, superoxide dismutase and malate dehydrogenase activities in the whole body tissues of test organisms were studied by native polyacrylamide gel electrophoresis after exposure to Ni. Histological examination of compound eye sections of shrimp revealed deformation, compression, fusion and detachement in the corneal cells from the corneal facet of the ommatidia indicating cellular anomalies due to Ni toxicity. Gill sections of the green mussel witnessed reduced haemolymph in sinuses of gill filaments, degenerative changes in interfilamentous junction and necrosis of frontal ciliated epithelial cells with vacuoles after exposure to Ni. Nickel affects the vision of shrimp and fish fingerlings, gills and byssus of green mussels.

Toxicological Potential of Cadmium Impact on Rainbow Trout (Oncorhynchus mykiss) in Early Development

Cadmium (Cd) is a toxic element widely distributed in the aquatic environment and producing a wide variety of harmful effects. In this study, the acute toxicity (96 h LC50) of Cd to rainbow trout Oncorhynchus mykiss embryos and larvae was determined. The obtained results showed that hatched larvae were the most sensitive to Cd exposure. After 4 days of exposure, embryos were found to have accumulated greater concentrations of Cd than larvae. Exposure to Cd at sublethal concentrations produced deleterious, exposure duration-related effects on biological parameters (mortality, heart rate and gill ventilation frequency) of larvae. Cd induced a significant elevation of all the studied geno- and cytotoxicity endpoints in larval erythroblasts.