Developmental patterns of copper bioaccumulation in a marine fish model Oryzias melastigma

Dietary exposure of potentially toxic elements to freshwater mammals in the Ganga river basin, India

The threatened Gangetic dolphin (Platanista gangetica) and smooth-coated otter (Lutrogale perspicillata) occuring in the Ganga River Basin (GRB), are experiencing a decline in their population and distribution range owing to multiple anthropogenic pressures, including pollution by Potentially Toxic Elements (PTEs). Apex predators primarily encounter contaminants through dietary exposure. Yet, notable gaps persist in our understanding of the risks associated with the ingestion of PTE-contaminated prey for Gangetic dolphins and smooth-coated otters. In this study, we examined the occurrence and spatial variation of PTEs in the prey (fish) of both these riverine mammals across three major rivers of the Basin, while also evaluating the associated risk of ingesting contaminated prey. Our assessment revealed no statistical variation in bioaccumulation profiles of PTEs across the three rivers, attributable to comparable land use patterns and PTE consumption within the catchment. Zn and Cu were the most dominant PTEs in the prey species. The major potential sources of pollution identified in the catchment include agricultural settlements, vehicular emissions, and the presence of metal-based additives in plastics. Zn, As and Hg accumulation vary with the trophic level whereas some PTEs show concentration (Hg) and dilution (As, Cr, Pb and Zn) with fish growth. The Risk Quotient (RQ), based on the dietary intake of contaminated prey calculated using Toxicity Reference Value was consistently below 1 indicating no significant risk to these riverine mammals. Conversely, with the exception of Co and Ni, the Reference Dose-based RQs for all other PTEs indicated a substantial risk for Gangetic dolphins and smooth-coated otters through dietary exposure. This study serves as a pivotal first step in assessing the risk of PTEs for two threatened riverine mammals in a densely populated river basin, highlighting the importance of their prioritization in regular monitoring to reinforce the ongoing conservation efforts.

Metal/metalloid bioconcentration dynamics in fish and the risk to human health due to water contamination with atmospheric particulate matter from a metallurgical industrial area

Settleable atmospheric particulate matter (SeAPM) containing a mixture of metals, including metallic nanoparticles, has increased throughout the world, and caused environmental and biota contamination. The metal bioconcentration pattern in Nile tilapia (Oreochromis niloticus) was evaluated during a 30-day exposure to 1 g L-1 SeAPM and assessed the human health risk from consuming fish fillets (muscle) based on the estimated daily intake (EDI). SeAPM was collected surrounding an iron ore processing and steel industrial complex in Vitória city (Espírito Santo, Brazil) area. Water samples were collected daily for physicochemical analyses, and every 3 days for multi-elemental analyses. Metal bioconcentrations were determined in the viscera and fillet of fish every 3 days. The elements B, Al, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Rb, Sr, Ag, Cd, Pb, Hg, Ba, Bi, W, Ti, Zr, Y, La, Nb, and Ce were analyzed in SeAPM, water, and fish using inductively coupled plasma mass spectrometry. The metal concentration in SeAPM-contaminated water was higher than in control water. Most metals bioconcentrated preferentially in the fish viscera, except for the Hg and Rb, which bioconcentrated mostly in the fillet. The bioconcentration pattern was Fe > Al > Mn > Pb > V > La > Ce > Y > Ni > Se > As > W > Bi in the viscera; it was higher than the controls throughout the 30-day exposure. Ti, Zr, Nb, Rb, Cd, Hg, B, and Cr showed different bioconcentration patterns. The Zn, Cu, Sr, Sn, Ag, and Ta did not differ from controls. The differences in metal bioconcentration were attributed to diverse metal bioavailability in water and the dissimilar ways fish can cope with each metal, including inefficient excretion mechanisms. The EDI calculation indicated that the consumption of the studied fish is not safe for children, because the concentrations of As, La, Zr, and Hg exceed the World Health Organization's acceptable daily intake for these elements.

Biomolecular modifications in the sacfry of Mogurnda adspersa in response to copper stress

Copper (Cu) is one of the most harmful contaminants in fresh-water systems. Fish larvae such as sacfry are particularly vulnerable to metals such as copper (Cu) due to a less-developed excretory organ system and permeable skin that can absorb metals directly from the water. However, the sublethal effects of metals on this life stage are not well understood. This study assessed the sublethal toxicity of Cu on purple-spotted gudgeon sacfry (PSG, Mogurnda adspersa). For this purpose, 96 h Cu toxicity bioassays were performed and toxic effects of Cu on PSG were measured at different levels of biological organization, from the individual (loss of equilibrium, wet weight), to tissue (chemical changes in retinal tissue composition) and molecular responses (whole body amino acid (AA) profiles). The EC₁₀ and EC₅₀ (ECx: effect concentration that affected X% of test organisms) were found to be 12 (9 - 15) µg Cu L^-1 and 22 (19 - 24) µg Cu L^-1, respectively. Copper stress caused a decrease in total amino acid content and changed the AA profile of PSG compared to the controls. Proton-induced X-ray emission (PIXE) mapping techniques showed accumulation of Cu in the retinal tissues disturbing the distribution of other elements such as zinc, sulfur, phosphorus and potassium. Fourier-transform infrared (FTIR) microspectroscopy of control and Cu treated eye tissues revealed a change in protein secondary structure in retinal tissues in response to Cu accumulation, as well as decreased levels of the molecular retinal, consistent with the degradation of rhodopsin, a key protein in the visual sensory system. This is the first study to demonstrate the multi-level responses of PSG arising from exposure to environmentally realistic Cu concentrations and suggests that AA profiling can serve as a useful tool to assess the impacts of metals on fresh-water organisms.

Functional significance and physiological regulation of essential trace metals in fish

Trace metals such as iron, copper, zinc and manganese play essential roles in various biological processes in fish, including development, energy metabolism and immune response. At embryonic stages, fish obtain essential metals primarily from the yolk, whereas in later life stages (i.e. juvenile and adult), the gastrointestine and the gill are the major sites for the acquisition of trace metals. On a molecular level, the absorption of metals is thought to occur at least in part via specific metal ion transporters, including the divalent metal transporter-1 (DMT1), copper transporter-1 (CTR1), and Zrt- and Irt-like proteins (ZIP). A variety of other proteins are also involved in maintaining cellular and systemic metal homeostasis. Interestingly, the expression and function of these metal transport- and metabolism-related proteins can be influenced by a range of trace metals and major ions. Increasing evidence also demonstrates an interplay between the gastrointestine and the gill for the regulation of trace metal absorption. Therefore, there is a complex network of regulatory and compensatory mechanisms involved in maintaining trace metal balance. Yet, an array of factors is known to influence metal metabolism in fish, such as hormonal status and environmental changes. In this Review, we summarize the physiological significance of iron, copper, zinc and manganese, and discuss the current state of knowledge on the mechanisms underlying transepithelial metal ion transport, metal-metal interactions, and cellular and systemic handling of these metals in fish. Finally, we identify knowledge gaps in the regulation of metal homeostasis and discuss potential future research directions.

Measuring Metal Uptake and Loss in Individual Organisms: A Novel Double Stable Isotope Method and its Application in Explaining Body Size Effects on Cadmium Concentration in Mussels

Interindividual variabilities in metal bioaccumulation confound our interpretation of the biomonitoring data. Measuring metal toxicokinetics in organism "individuals" may provide insights into the processes underlying the variabilities. Therefore, we developed a double stable isotope method that can simultaneously measure uptake and elimination of metals in individual organisms and thus the distribution of the toxicokinetic parameters. Specifically, we exposed organisms to both isotopes (¹¹³Cd and ¹¹⁴Cd; Cd = cadmium) during the first stage and to only one isotope (¹¹⁴Cd) during the second stage. Metal uptake and elimination rate constants (i.e., k_u and k_e) were simultaneously estimated from the content of the two isotopes measured in each organism at the end of the second stage. We applied the method to investigate the interindividual variability in Cd concentrations caused by body size in two marine mussel species. Cd concentrations are higher in larger Xenostrobus atratus but lower in smaller Perna viridis. Size-dependent Cd uptake is found to be responsible for size effects on Cd concentrations in the mussels and the interspecies differences in the relationship between Cd concentration and body size. Specifically, Cd k_u increases with size in X. atratus (0.057-0.297 L g^-1 d^-1) but decreases with size in P. viridis (0.155-0.351 L g^-1 d^-1). In contrast, Cd k_e is not influenced by body size (X. atratus: 0.002-0.060 d^-1; P. viridis: 0.008-0.060 d^-1). Overall, we extended the applicability of the stable isotope methods to measure metal toxicokinetics in "individual" organisms, providing a readily available tool for investigating problems related to metal bioaccumulation.

Toxicity of nickel and cobalt in Japanese flounder

Nickel and cobalt are essential elements that become toxic at high concentrations. Little is known about nickel and cobalt toxicity in aquatic animals. This study aimed to investigate acute and chronic toxicity of nickel and cobalt in Japanese flounder (Paralichthys olivaceous), with emphasis on oxidative stress reactions, histopathological changes, and differences in gene expression. The lethal concentration for 50% mortality (LC₅₀) in 3 and 8 cm Japanese flounder exposed to nickel for 96 h was found to be 86.2 ± 0.018 and 151.3 ± 0.039 mg/L; for cobalt exposure, LC₅₀ was 47.5 ± 0.015 and 180.4 ± 0.034 mg/L, respectively. Chronic nickel and cobalt exposure caused different degrees of oxidative enzyme activity changes in gill, liver, and muscle tissues. Erythrocyte deformations were detected after acute or chronic exposure to nickel and cobalt. the nickel and cobalt exposure also caused pathological changes such as spherical swelling over other gill patches, rod-like proliferations in the gill patch epithelial cell layer, and disorder in hepatocyte arrangement, cell swelling, and cytoplasm loosening. RNA-Seq indicated that there were 184 upregulated and 185 downregulated genes in the liver of Japanese flounder exposed to 15 mg/L nickel for 28 d. For cobalt, 920 upregulated and 457 downregulated genes were detected. Among these differentially expressed genes, 162 were shared by both nickel and cobalt exposure. In both nickel and cobalt, pathways including fatty acid elongation, steroid biosynthesis, unsaturated fatty acid biosynthesis, fatty acid metabolism, PPAR signaling, and ferroptosis were significantly enriched. Taken together, these results aided our understanding of the toxicity of nickel and cobalt in aquatic animals.

Sub-lethal effects of waterborne copper in early developmental stages of rainbow trout (Oncorhynchus mykiss)

The aim of this work was to study the impact of copper during a sub-chronic exposure to environmental concentrations in the early life stages of rainbow trout (Oncorhynchus mykiss). Eyed-stage embryos of rainbow trout, at 265 °D, were exposed in semi-static conditions to sub-lethal concentrations of CuSO₄ up to the larval stage (528 °D) under laboratory-controlled conditions. During 3 weeks, they were exposed to the environmentally-realistic concentration of 2 µg/L Cu and to a 10-fold higher concentration, 20 µg/L Cu. Several biological (survival, hatching success, malformation, growth) and behavioral (swimming activity) and molecular endpoints (genotoxicity and gene transcription) were studied. Exposure to 20 µg/L Cu had an inhibitory effect on hatching and increased half-hatched embryos (25%). At the end of the exposure, no significant differences were observed in growth of the larvae exposed to the highest Cu concentration. However, larvae exposed to 2 µg/L Cu exhibited increased growth in comparison with non-exposed larvae. The percentage of malformed larvae was significantly higher for both copper conditions, with skeletal malformations being the most observed. Expression of several genes was evaluated in whole larvae using quantitative real-time PCR. Genes involved in detoxification (gst, mt1 and mt2) and in cell cycle arrest (p53) were significantly repressed in both copper conditions when compared to control. In addition, potential genotoxic effects on larvae were investigated by the comet assay on blood cells, but this test did not demonstrate any significant DNA damage on larvae exposed to copper. This study confirms the adverse effects of copper on early life stages of rainbow trout even at the lowest environmentally relevant tested concentration.

Metals and elements in sardine and anchovy: Species specific differences and correlations with proximate composition and size

Species - specific differences in the levels of 26 metals and elements in sardine and anchovy are investigated and the factors of proximate composition (proteins, lipids, ash) and body size (length, weight) that may affect the metal and elemental concentrations in fish are explored. Statistical analysis revealed that levels of metals and elements in fish seem to strongly depend on species. Significantly higher levels of most of the metals and elements studied have been observed in anchovy compared to sardine at each of six different sites. The observed species-specific differences in metal content could be attributed to different proximate composition and size among other factors. The significant (positive or negative) correlations found between lipids, proteins, ash, weight, length and metals or elements, suggest that higher levels of most of the metals and elements studied can be associated with lower lipid content, greater protein and ash content and smaller size.

Linkages between the spatial toxicity of sediments and sediment dynamics in the Yangtze River Estuary and neighboring East China Sea

Anthropogenic activities are driving an increase in sediment contamination in coastal areas. This poses significant challenges for the management of estuarine ecosystems and their adjacent seas worldwide. However, few studies have been conducted on how dynamic mechanisms affect the sediment toxicity in the estuarine environment. This study was designed to investigate the linkages between sediment toxicity and hydrodynamics in the Yangtze River Estuary (YRE) area. High sediment toxicity was found in the Yangtze River mouth (Region I), the depocenter of the Yangtze River Delta (Region II), and the southeastern area of the adjacent sea (Region III), while low sediment toxicity was found in the northeastern offshore region (Region IV). A spatial comparison analysis and regression model indicated that the distributed pattern of sediment toxicity was likely related to hydrodynamics and circumfluence in the East China Sea (ECS) shelf. Specifically, high sediment toxicity in Region I may be affected by the Yangtze River Pump (YRP) and the low hydrodynamics there, and high toxicity in Region II can be influenced by the low sediment dynamics and fine sediment in the depocenter. The high sediment toxicity in Region III might be related to the combination of the YRP and Taiwan Warm Current, while the low toxicity in Region IV may be influenced by the local coarse-grained relict sand with strong sediment dynamics there. The present research results further suggest that it is necessary to link hydrodynamics and the spatial behavior of sediment and sediment-derived pollutants when assessing the pollution status of estuarine environments, especially for those mega-estuaries and their neighboring ocean environments with complex waves, tides and ocean currents.

The simultaneous uptake of dietary and waterborne Cd in gastrointestinal tracts of marine yellowstripe goby Mugilogobius chulae

Aquatic animals under waterborne metal exposure are also very likely exposed to elevated dietary metals. This study quantified the simultaneous uptake of dietary and waterborne Cd in gastrointestinal tracts (GT) of marine yellowstripe goby using a dual stable isotope tracer method. The Cd spiked diet (10-100 μg g^-1, ¹¹¹Cd as tracers) were fed to the fish as a single meal, and then the fish were exposed to waterborne Cd (0-500 μg L^-1, ¹¹³Cd as tracers) for 48 h, during which the time-course uptake of Cd in the stomach and intestine was determined. The findings revealed that the dietary Cd uptake mainly occurred within 12 h after feeding. The fish exposed to 500 μg L^-1 waterborne Cd showed significantly lower Cd assimilation efficiency (2.07%) than the control group (3.48%) at the dietary Cd of 100 μg g^-1. Moreover, during 4-12 h when there was chyme in the GT, the waterborne Cd uptake in the intestine was lowest but the stomach showed the highest waterborne Cd uptake rate. The uptake of dietary and waterborne Cd, and the relative importance of dietary vs waterborne Cd was positively correlated with the Cd concentration in the chyme. Overall, this research demonstrated that there was interaction between dietary and waterborne Cd uptake in the GT of marine fish. The simultaneous uptake of metal from two routes is far more complex than the situation of a single route of metal uptake, which should be evaluated in determining metal bioaccumulation and toxicity in both laboratory and field metal exposure scenario.

Modulatory effect of the exudates released by the brown kelp Lessonia spicata on the toxicity of copper in early developmental stages of ecologically related organisms

Lessonia spicata is a key dominant species along the Pacific coast of South America, providing a habitat for many organisms. However, this role can be affected by abiotic stress, such as metals. To counteract the toxic effect, L. spicata, among other seaweeds, releases exudates that bind metals. In this study, tolerances to copper of organisms related to the kelp forest (spores of Ulva lactuca (Chlorophyceae) and L. spicata (Phaeophyceae) and Zoea I of Taliepus dentatus (Milne-Edwards, Crustacea)) were studied; then, exudates are assessed by their protective effect. Exudates increase the 48-h 50% effective concentration (EC50) of the germination of spores from 8 to 23 μg Cu L-1 for U. lactuca and from 119 to 213 μg Cu L-1 for L. spicata and the survival of the larvae Zoea I 48-h 50% of lethal concentration (LC50) from 144 to 249 μg Cu L-1. Results indicated that exudates had a protective effect. Each species is specifically sensitive to copper. Crab larvae Zoea I were able to support higher doses, and exposure before hatching increased their tolerance.

Effects of salinity and copper co-exposure on copper bioaccumulation in marine rabbitfish Siganus oramin

Marine fish living in estuaries and coastal areas commonly encounter the stress of both salinity and metal pollution. In this study, euryhaline rabbitfish Siganus oramin were exposed to 50 μg L^-1 waterborne Cu or 300 μg g^-1 dry wt dietary Cu at salinity 33‰, 25‰, 20‰, 10‰, and 5‰ for 30 days. The Cu accumulation in the liver (>20-fold increase) and intestine (>5-fold increase) significantly increased after either waterborne or dietary Cu acclimation. Moreover, Cu accumulation was further enhanced in the liver, intestine, plasma, and whole body of Cu-exposed fish at lower salinities. Similarly, the waterborne Cu uptake rate constants (k_us) were stable in the control at different salinities but increased significantly (2-4 times higher) after waterborne Cu exposure. Conversely, the dietary Cu assimilation efficiencies (AEs) were significantly lower in the dietary Cu-exposed fish (3-5%) than in the control fish (8-16%) at different salinities, suggesting that dietary Cu acclimation partially alleviated the dietary Cu uptake from the high-Cu diet. The Cu efflux rate constants (k_es) were comparable among all treatments as 0.060-0.071 d^-1. The changes of Cu accumulation by different salinities and Cu exposure were well estimated by the biokinetic modeling. In summary, the present study indicates that rabbitfish can regulate Cu uptake and accumulation when acclimated to different salinities, but the Cu-exposed rabbitfish failed to prevent the elevation of Cu accumulation at low salinities. It therefore suggested that the concurrence of low salinity and high Cu exposure enhances the risks of Cu bioaccumulation and toxicity in rabbitfish.

Homeostatic regulation of copper in a marine fish simulated by a physiologically based pharmacokinetic model

Copper (Cu) is an essential yet potentially toxic metal, thus delicate homeostatic controls are developed in the fish. In this study, a physiologically based pharmacokinetic (PBPK) model was developed to simulate the homeostatic regulation of Cu in a marine fish (Terapon jarbua) under dietary and waterborne exposures. In this model, fish were schematized as a six-compartment model, with the intestine being divided into two sub-compartments (chyme and gut wall). The blood was assumed to be the "carrier" distributing Cu into different compartments. The transfer rates between different compartments were determined in fish during Cu exposure (20 d) and depuration (20 d). The differences in Cu transfer from chyme to gut wall between dietary and waterborne treatments suggested that the intestine regulated the dietary uptake and re-absorption of Cu from the chyme. The extremely low uptake rate constant (0.0013 d^-1) for gills under waterborne exposure indicated that gills strongly restricted Cu uptake from the ambient water. For both treatments, the liver had considerable input rate through the enterohepatic circulation and comparably high exchange rate with the blood, suggesting that the liver can efficiently accumulate newly absorbed Cu. The differences in Cu output from the liver between dietary and waterborne treatments suggested that it can effectively regulate the redistribution of Cu. All of these observations demonstrated that the liver played the central role in Cu homeostasis by serving as the main depository and distributing center. Modeling results also indicated that renal and branchial excretion was of minor importance, whereas biliary excretion combined with defecation played the most important role in whole-body Cu elimination in marine fish. The effective regulation by the "Blood-Liver-Intestine" cycle could be the main reason for the relatively low levels of Cu in fish.

The effects of subchronic exposure to copper in fat snook (Centropomus parallelus)

Anthropogenic processes affect different communities through the release of contaminated effluents into water bodies. Copper can be found in the effluents of most industrial processes and in other effluent types. The fat snook Centropomus parallelus, found from Florida in the United States to southern Brazil, is of great economic importance and is used as a food resource near the coast. This study aimed to determine the effects of copper on C. parallelus. The fish were exposed for 30 or 60 days to treatments of 0, 13 and 26μgCuL(-1). Genotoxic effects of copper were observed in the micronuclei, especially in individuals exposed to higher concentrations. Copper exposure also had a negative effect on the growth of fat snook individuals. Compared to the control group without the addition of metal, an accumulation of metal was observed in the gills of exposed fish, an effect that was not found in the muscle.