The effects of heavy metals on embryonic development of fish (a review)

Effects of Cu(Ⅱ) stress on embryonic development, oxidative stress response, cholinergic system and energy metabolism in the Sepiella maindroni

In order to investigate the causes of population degradation and resource decline, this thesis investigated the ecotoxicological effects of heavy metal Cu(Ⅱ) on the embryonic development of Sepiella maindroni. Results indicate significant effects of Cu(Ⅱ) concentrations on the developmental toxicity, teratogenicity, and lethality of S. maindroni embryos. Different concentrations of Cu(Ⅱ) caused varying degrees of malformations in embryos, altered developmental rates, reduced hatchability and hatchling quality, and increased malformation and mortality of hatchlings. At the same time, Cu(Ⅱ) exposure led to an increase in the content of the lipid peroxidation product malondialdehyde (MDA) and a significant decrease in the activity of antioxidant enzymes (superoxide dismutase [SOD], catalase [CAT]), energy-metabolizing enzymes (adenylate kinase [AK]), and cholinergic-related enzymes (acetylcholinesterase [AChE], choline acetyltransferase [ChAT]). In conclusion, when the concentration of Cu(Ⅱ) in the environment is ≥ 0.01 mg/L, it causes significant lethality toxicity, developmental toxicity and teratogenicity in S. maindroni embryos. These effects are likely related to Cu(Ⅱ)-induced stress impacting the antioxidant capacity, energy metabolism, and cholinergic system. Ultimately, these toxic effects may lead to population degradation and resource decline in fishery organisms by affecting the early replenishment process of fisheries.

Active biomonitoring of river pollution using an ex-situ exposure system with two model species

In the context of increasing pollution pressure on aquatic ecosystems, it is essential to improve our knowledge of habitat quality and its suitability for organisms. It is particularly relevant to better integrate early life stages of fish into pollution biomonitoring programs, as they are reliable indicators of ecosystem integrity and because of their high sensitivity to pollutants. To avoid the influence of environmental parameters on their development, a lab-on-field approach, called the ex-situ exposure method, was developed. Aquatic organisms were exposed to a continuous flux of water under semi-controlled temperature, oxygen, and photoperiod conditions to avoid the influence of these confounding factors when interpreting the results. To investigate the potential role of water contamination, this active biomonitoring method was applied to the Garonne River (Southwest France), where migratory fish populations have declined. Two model species from different taxa were used: embryos of the Japanese medaka (Oryzias latipes) and adults of the crustacean Gammarus fossarum. The results showed a significant impact of water quality on embryo mortality and early hatching in two separate experiments on Japanese medaka. In addition, an induction of feeding rate was observed in exposed gammarids, but no impact on their embryo survival, suggesting differences in sensitivity between the two species selected. Chemical and biological analyses did not identify trace metals, pesticides, or microorganisms as potential sources of toxicity in medaka embryos or G. fossarum. These results raise concerns about the quality of the water in the Garonne River and its toxicity to aquatic organisms.

The combined metabolism and transcriptome of tail muscles reveal the effects of antimony pulse exposure on swimming behavior of Pelophylax nigromaculatus tadpoles

Due to the periodic emission of pollutants, the exposure mode of contaminants in water bodies is mostly pulse exposure, and the toxic effects of fluctuating exposure on aquatic animals are not consistent with traditional toxicological experiments of constant exposure. The toxic effects of heavy metal antimony (Sb) on the swimming behavior of Pelophylax nigromaculatus tadpoles after pulse exposure (PESb) and continuous exposure (CESb) for 28 days were explored. The mechanisms were analyzed from the perspectives of tail muscle metabolism and transcriptomics. Compared to the control group, PESb and CESb decreased the average speed of P. nigromaculatus tadpoles by 25.72 % and 18.08 %, respectively. PESb and CESb led to changes in 70 and 24 metabolites of tail muscle, respectively. PESb led to alterations in metabolic pathways related to pyrimidine metabolism, arginine biosynthesis, and glycerophospholipid metabolism. In contrast, CESb altered metabolic pathways such as alanine, aspartate, and glutamate metabolism. Compared to the control, 1225 and 1139 DEGs were identified for PESb and CESb, respectively. These DEGs were mainly associated with functions such as immune response, DNA replication, protein digestion, and absorption. It can be seen that PESb and CESb can alter the metabolism and transcriptome of the tail muscle of P. nigromaculatus tadpoles, leading to differential expression of individual movements.

The role of chorion integrity on the bioaccumulation and toxicity of selenium nanoparticles in Japanese medaka (Oryzias latipes)

Selenium nanoparticles (nano-Se) have a wide range of biomedical and agricultural applications. However, there is little information on the potential toxicity of nano-Se once it enters the environment, particularly in fish. The first line of defense from contaminants that embryonic fish have is the chorion, but the degree to which the chorion protects the developing embryo is unknown. Japanese medaka (Oryzias latipes) embryos were exposed to nano-Se in a wide range of concentrations (0.1-400 µM). The importance of chorion integrity was evaluated by exposing embryos to 16 nm nano-Se under four degrees of dechorionation: intact, roughened, partially-dechorionated, fully-dechorionated. Then, effects of particle size on embryos and larvae were determined using four sizes of nano-Se particles (16, 25-50, 50, 100 nm). The results showed that nano-Se exposure reduced survival, development, and hatching. Nano-Se was observed to adsorb on the chorion, with the amount decreasing with increased degree of dechorionation. Toxicity increased with increasing degree of dechorionation, and smaller-sized nano-Se crossed intact chorion more readily and resulted in higher toxicity than larger ones. In larvae, nano-Se accumulated on the skin and was more toxic compared to embryos. This study demonstrated the importance of the chorion in protecting developing embryos and effects of nanoparticle size on its bioavailability and subsequent toxicity.

Effects of polluted groundwater on chum salmon (Oncorhynchus keta) survival and body size

This study reports the effect of spatial variation in hyporheic water, partially influenced by urban-polluted groundwater, on the early life stage of chum salmon (Oncorhynchus keta) in the Toyohira River, Northern Japan. We hypothesized that increased groundwater influence would reduce the survival rate and body size of O. keta due to the combined effects (i.e., growth retardation effects) of chemical toxicants, low dissolved oxygen (DO), and high winter temperatures. Experimental tests were conducted in field and laboratory conditions to address the difficulties associated with field observations of fry emergence during snowmelt floods in spring and to examine the independent effects of water pollution in groundwater in relation to temperature and DO. Artificially fertilized eyed eggs, alevins, and fry of O. keta were monitored for several months with varying exposure to groundwater from winter to early spring. We noted that groundwater affected the fish by reducing their size and weight by >10% and by increasing their mortality in both tests. Moreover, independent effects of water pollution were identified in the swim-up fry stage in laboratory experiments, along with growth-retarding effects from warmer groundwater temperatures. Not all factorial combinations of potentially confounding factors were tested rigorously, and the specific toxicants are unidentified, leaving questions about how groundwater pollution affects Salmonidae fish. Immediate concerns regarding the current water quality (including DO) of hyporheic water associated with groundwater influence are low because no detrimental effects on survival were detected in the field. Nevertheless, spawning grounds formed in areas with high exposures to polluted groundwater require continuous management attention due to potential risks associated with low DO levels. Additionally, pollution-induced growth patterns could pose a risk of size- or weight-dependent mortality at the swim-up fry stage and in early juveniles.

Impacts of paternal transmission of PCBs and global warming on the evolution of pace-of-life syndrome (POLS) during the early life stages of a cold stenothermic fish (Arctic charr)

In the context of strong historical and climate anthropological pressure, we studied the impact of paternal transmission of PCBs on offspring of the stenothermic salmonid, Artic charr. Indeed, the transgenerational effects of maternal transmission are widely studied, unlike the paternal effect, which is often limited to epigenetic impacts. The study aims to test the effects of temperature and PCBs on the Artic charr (Salvelinus alpinus), whose population within the perialpine lakes has remained low for about a decade. A previous study (Realis-Doyelle et al., 2023) on the effect of maternal transmission of PCB, coupled with an increase in temperature, showed a collapse in offspring survival as well as morpho-anatomic disorders in Salvelinus alpinus. This study follows on from the previous one, we contaminated 21 males with intra-peritoneal PCB injection at three levels of concentration one month before spawning. Each male fertilised a pool of 12 female oocytes not contaminated with PCBs. Each fertilized pond was separated in two and incubated at 4.5°C and 8.5°C, respectively. To explore the effects, we have relied on the POLS theories that suggest a co-variation of traits of life. The results show no population collapse (∼50 % survival), in contrast to the maternal contamination study (∼12 % survival). We may issue the hypothesis that this smaller importance of paternal transmission is due to the synergic impact of PCB and temperature on fewer parameters, in particular for survival than female transmission.

Singapore's urbanised coral reefs: Changes in heavy metal pollution between 1994 and 2021

The heavy metal load in coral reefs of Singapore has not been comprehensively assessed since 1994. Here, we repeated the surveys conducted 27 years ago to quantify the levels of Cd, Cu, Cr, Fe, Pb, Ti, Zn in sediment and the sea urchin Diadema setosum from seven reefs. Cu and Cd showed significant reductions, Pb and Cr remained stable, while Fe, Ti and Zn had increased significantly. Overall, based on the Pollution Load Index (PLI), Singapore's reefs would not be considered polluted. Nevertheless, elevated concentrations of Cu, Pb and Zn were detected in sediment, with Cu and Pb exceeding the Threshold Effect Level. The spatial distribution of metal loads between sediment and sea urchin tissues were decoupled, underscoring the complexity of metal uptake and bioavailability. We reveal a mixed temporal trend among the heavy metals examined, each presenting different toxicity potentials and hence risks to local marine assemblages.

Functionalization of Ti3C2 MXene with Diethylenetriamine for a Column-Based Solid-Phase Extraction of Heavy Metals

Transition metal carbides, nitrides, and carbonitrides, known as MXenes, are attracting attention for their potential application in trace detection of heavy metals. This study presents diethylenetriamine-functionalized Ti3C2 MXene for trace detection of cadmium and lead ions. Functionalization of Ti3C2 significantly improves the adsorption properties of MXenes by replacing native functional groups with silane moieties that contain three amine groups, offering higher affinity for heavy metals. We demonstrate the efficacy of this material as a solid-phase extractor in column-based solid-phase extraction for heavy metal analysis in various food samples. Diethylenetriamine-functionalized Ti3C2 coupled with the flame atomic absorption spectrometer exhibits exceptional analytical performance. While maintaining a robust stability for 15 adsorption-desorption cycles, the proposed method shows detection limits of 0.09 ng mL-1 for cadmium and 1.7 ng mL-1 for lead, with a linear dynamic range of 0.3-50 ng mL-1 for cadmium and 5-90 ng mL-1 for lead, and relative recoveries of 97.50-101.05 and 98.65-100.80% for cadmium and lead ions, respectively. Additionally, relative standard deviations and enrichment factors were calculated as 0.60-4.70% and 42.3 for cadmium ions and 0.65-1.24% and 44.2 for lead ions.

Soluble trehalase responds to heavy metal stimulation by regulating apoptosis in Neocaridina denticulata sinensis

Trehalase plays an important role in insect metabolism and development by hydrolyzing blood sugar trehalose, but it seems to perform primarily an immunomodulatory function in crustaceans whose blood sugar is glucose. Metal ions as pollutants seriously affecting crustacean health, but studies on trehalase in metal immunity are still limited. In this study, a soluble trehalase (NdTre1) that could bind to multiple metals was identified from Neocaridina denticulata sinensis for investigating metal resistance. Expression profiling revealed that NdTre1 was mainly expressed in the gill and was significantly decreased following stimulation with copper (Cu²⁺) and cadmium (Cd²⁺). Transcriptomic analysis of gills revealed an increase in ecdysone synthesis after interference with NdTre1. Increased ecdysone activated the endogenous mitochondrial pathway and the mitogen activated protein kinase (MAPK) pathway to further induced apoptosis. In vitro, Escherichia coli overexpressing recombinant NdTre1 had higher survival and faster growth rates to better adapted the metal-containing medium. Overall, NdTre1 exercises an important immune function in shrimp resistance to metal stimulation by regulating apoptosis and molting. Further investigation can further explore specific response mechanisms of NdTre1 to multiple metals.

Analysis of Differential Gene Expression under Acute Lead or Mercury Exposure in Larval Zebrafish Using RNA-Seq

This study was first conducted to investigate the effects of acute lead exposure on developing zebrafish embryos or larvae from 24 to 120 h post-fertilization (hpf). Our data showed that treatment with 50-200 μM lead significantly affected larval survivability and morphology compared to the respective control. Second, we chose 120 hpf larvae treated with 12.5 μM lead for RNA sequencing due to its exposure level being sufficient to produce toxic effects with minimum death and lead bioaccumulation in developing zebrafish. A total of 137.45 million raw reads were obtained, and more than 86% of clean data were mapped to the zebrafish reference genome. Differential expression profiles generated 116 up- and 34 down-regulated genes upon lead exposure. The most enriched GO terms for representative DEGs were ion transport and lipid metabolism. Third, a comparison with the dataset of mercury-regulated gene expression identified 94 genes (64 up-regulated and 30 down-regulated) for exposure specific to lead, as well as 422 genes (338 up-regulated and 84 down-regulated) for exposure specific to mercury. In addition, 56 genes were co-regulated by micromolar mercury and lead treatment, and the expression of thirteen genes, including mt2, ctssb.1, prdx1, txn, sqrdl, tmprss13a, socs3a, trpv6, abcb6a, gsr, hbz, fads2, and zgc:92590 were validated by qRT-PCR. These genes were mainly associated with metal ion binding, proteolysis, antioxidant activity, signal transduction, calcium ion or oxygen transport, the fatty acid biosynthetic process, and protein metabolism. Taken together, these findings help better understand the genome-wide responses of developing zebrafish to lead or mercury and provide potential biomarkers for acute exposure to toxic metals.

Baseline polycyclic aromatic hydrocarbon maternal transfer data in Lesser Numbfish Narcine brasiliensis (Elasmobranchii: Batoidea) from an impacted estuary in Southeastern Brazil

Maternal offloading of polycyclic aromatic hydrocarbons (PAHs) poses a significant exposure route for developing embryos, with implications for subsequent generations. Despite known developmental effects regarding fish physiology and behavior, maternal PAH transfer assessments in elasmobranchii are still lacking. This study investigated PAH contamination and maternal transfer in one female Lesser Numbfish (Narcine brasiliensis) electric ray and seven embryos for the first time. Naphthalene was identified as the predominant low molecular weight PAH, and dibenzo[a,h]anthracene was the most abundant high molecular weight compound. Most embryos exhibited some level of PAH exposure, with varying accumulation patterns potentially influenced by size, developmental stage, and yolk absorption rates. Further investigation is warranted to understand the impacts of PAH maternal offloading on elasmobranchii uterine contents and embryos.

Selenium toxicity in fishes: A current perspective

Anthropogenic activities have led to increased levels of contaminants that pose significant threats to aquatic organisms, particularly fishes. One such contaminant is Selenium (Se), a metalloid which is released by various industrial activities including mining and fossil fuel combustion. Selenium is crucial for various physiological functions, however it can bioaccumulate and become toxic at elevated concentrations. Given that fishes are key predators in aquatic ecosystems and a major protein source for humans, Se accumulation raises considerable ecological and food safety concerns. Selenium induces toxicity at the cellular level by disrupting the balance between reactive oxygen species (ROS) production and antioxidant capacity leading to oxidative damage. Chronic exposure to elevated Se impairs a wide range of critical physiological functions including metabolism, growth and reproduction. Selenium is also a potent teratogen and induces various types of adverse developmental effects in fishes, mainly due to its maternal transfer to the eggs. Moreover, that can persist across generations. Furthermore, Se-induced oxidative stress in the brain is a major driver of its neurotoxicity, which leads to impairment of several ecologically important behaviours in fishes including cognition and memory functions, social preference and interactions, and anxiety response. Our review provides an up-to-date and in-depth analysis of the various adverse physiological effects of Se in fishes, while identifying knowledge gaps that need to be addressed in future research for greater insights into the impact of Se in aquatic ecosystems.

Comparative effects of different metals on the Japanese medaka embryos and larvae

Rapid evaluation of the toxicity of metals using fish embryo acute toxicity is facilitative to ecological risk assessment of aquatic organisms. However, this approach has seldom been utilized for the comparative study on the effects of different metals to fish. In this study, acute and sub-chronic tests were used to compare the toxicity of Se(IV) and Cd in the embryos and larvae of Japanese medaka (Oryzias latipes). The embryos with different levels of dechorionation and/or pre-exposure were also exposed to Se(IV) and Cd at various concentrations. The results showed that the LC50-144 h of Cd was 1.3-5.2 folds higher than that of Se(IV) for the embryos. In contrast, LC50-96 h of Se(IV) were 200-400 folds higher than that of Cd for the larvae. Meanwhile, dechorionated embryos were more sensitive to both Se and Cd than the intact embryos. At elevated concentrations, both Se and Cd caused mortality and deformity in the embryos and larvae. In addition, pre-exposure to Cd at the embryonic stages enhanced the resistance to Cd in the larvae. However, pre-exposure to Se(IV) at the embryonic stages did not affect the toxicity of Se(IV) to the larvae. This study has distinguished the nuance differences in effects between Se(IV) and Cd after acute and sub-chronic exposures with/without chorion. The approach might have a potential in the comparative toxicology of metals (or other pollutants) and in the assessment of their risks to aquatic ecosystems.

Metal-contaminated sediment toxicity in a highly impacted Neotropical river: Insights from zebrafish embryo toxicity assays

The Fundão dam collapse was one of the largest mining-related disasters globally. It resulted in the release of mining tailings containing heavy metals, which contaminated the Doce River in southeastern Brazil. This study assessed the effects of acute exposure of Danio rerio embryos to sediments contaminated by mine tailings six years after the Fundão dam collapse. The study sites included P2, P3, and P4 in the upper Doce River, as well as site P1 on the Piranga River, an uncontaminated river. Sediment samples were analyzed for 10 metals/metalloid by atomic absorption spectrometry. In the assays, embryos were exposed to sediment from P1-P4 sites, and uncontaminated quartz was used as control sediment. Various biomarkers were applied to assess biological responses, and the integrated biomarker response (IBR) index was calculated for each site. Sediment samples revealed elevated levels of As, Cr, Cu, Hg, and Ni beyond Brazilian legislation limits. At 96-h exposure, embryo mortality rates exceeded 20% in P1, P2, and P3, higher than the control and P4 (p < 0.0001). Hatching rates ranged from 60 to 80% in P1, P2, and P3, lower than the control and P4 (p < 0.001). Larvae exposed to P2 sediment (closest to the Fundão dam) exhibited skeletal, physiological, and sensory malformations. Neurotoxicity was indicated by increased acetylcholinesterase activity and reduced spontaneous movements in embryos exposed to Doce River sediment. Contamination also increased metallothionein and heat shock protein 70 levels, along with changes in cell proliferation and apoptosis. Principal component analysis showed a good correlation between metals/metalloid in the sediment and larval morphometric endpoints. The IBR index highlighted suitable biomarkers for monitoring metal contamination in fish embryos. Overall, our findings suggest that sediment toxicity following the Fundão dam failure may compromise the sustainability of fish communities in the Doce River.

Long-term and combined heavy-metal contamination forms a unique microbiome and resistome: A case study in a Yellow River tributary sediments

Microorganisms have developed mechanisms to adapt to environmental stress, but how microbial communities adapt to long-term and combined heavy-metal contamination under natural environmental conditions remains unclear. Specifically, this study analyzed the characteristics of heavy metal composition, microbial community, and heavy metal resistance genes (MRGs) in sediments along Mang River, a tributary of the Yellow River, which has been heavily polluted by industrial production for more than 40 years. The results showed that the concentrations of Cr, Zn, Pb, Cu and As in most sediments were higher than the ambient background values. Bringing the heavy metals speciation and concentration into the risk evaluation method, two-thirds of the sediment samples were at or above the moderate risk level, and the ecological risk of combined heavy metals in the sediments decreased along the river stream. The high ecological risk of heavy metals affected the microbial community structure, metabolic pathways and MRG distribution. The formation of a HM-resistant microbiome possibly occurred through the spread of insertion sequences (ISs) carrying multiple MRGs, the types of ISs carrying MRGs outnumber those of plasmids, and the quantity of MRGs on ISs is also higher than that on plasmids. These findings could improve our understanding of the adaptation mechanism of microbial communities to long-term combined heavy metal contamination.

Common and inter-specific toxic effects in three wild fish species after chronic gamma irradiation of early stages

The objective of this study was to investigate the effects of gamma irradiation on the aquatic environment. We used three wild fish species to compare phenotypic responses with a fish model such as Danio rerio. We focused on embryonic development, a sensitive life stage to stressors like ionizing radiation, to evaluate the effects of exposure to 0.5 and 5 mGy h-1 on Arctic char, trout and stickleback embryos from fertilization to free-swimming larvae. Irradiation did not cause mortality but induced an acceleration of hatching in the three species. These new data on wild species, obtained under comparable irradiation conditions, did not go against the threshold values for the protection of freshwater aquatic ecosystems. Moreover, irradiation caused inter-specific sublethal effects, such as an increase in non-eyed egg proportion in Arctic char, an increase in the incubation period in trout and an acceleration of larval mortality in stickleback. The consequences of these early effects on the adult stage remain to be studied.

Molecular variations to the proteome of zebrafish larvae induced by environmentally relevant copper concentrations

Contaminants are increasingly accumulating in aquatic environments and biota, with potential adverse effects on individual organisms, communities and ecosystems. However, studies that explore the molecular changes in fish caused by environmentally relevant concentrations of metals, such as copper (Cu), are limited. This study uses embryos of the model organism zebrafish (Danio rerio) to investigate effect of Cu on the proteome and amino acid (AA) composition of fish. Wild-type embryos at 24 h post-fertilisation were exposed to Cu (2 µg L-1 to 120 µg L-1) for 96 h and the number of healthy larvae were determined based on larvae that had hatched and did not display loss of equilibrium (LOE). The effect concentrations where Cu caused a 10 % (EC10) or 50 % (EC50) decrease in the number of healthy larvae were calculated as 3.7 µg L-1 and 10.9 µg L-1, respectively. Proteomics analysis of embryos exposed to the EC10 and EC50 concentrations of Cu revealed the proteome to differ more strongly after 48 h than 96 h, suggesting the acclimatisation of some larvae. Exposure to excess Cu caused differentially expressed proteins (DEPs) involved in oxidative stress, mitochondrial respiration, and neural transduction as well as the modulation of the AAs (Proline, Glycine and Alanine). This is the first study to suggest that LOE displayed by Cu-stressed fish may involve the disruption to GABAergic proteins and the calcium-dependent inhibitory neurotransmitter GABA. Moreover, this study highlights that proteomics and AA analysis can be used to identify potential biomarkers for environmental monitoring.

UV aging may enhance adsorption capacity of Poly (butylene adipate-co-terephthalate) (PBAT) to heavy metals and toxicity to zebrafish

Compared with the fossil-based plastics, biodegradable plastics are more easily decomposed into small-sized particles (e.g., microplastics). However, the role of aged biodegradable plastics in being vector of co-existed pollutants and potential toxicological effects remain to be elucidated. The present study selected micro-sized biodegradable polymer Poly (butylene adipate-co-terephthalate) (PBAT) as the object, aiming to explore its aging process, environmental behavior with heavy metals (Cu and Pb), and the toxic effects on zebrafish. The results showed that distinct changes such as cracks and severe deformation can be observed on the surface of PBAT after 60 days of UV aging, and the functional groups changed consequently. The maximum adsorption capacity of aged PBAT for Cu and Pb reached 0.967 and 0.939 mg·g-1, which increased by 1.32 and 1.46 times, respectively. The results of 7-day acute toxicology experiments suggested that the adsorption behavior of aged PBAT may alleviate the toxic effects of heavy metals Cu and Pb on zebrafish in short-term exposure, however it could simultaneously cause a serious imbalance of intestinal microorganisms in zebrafish. As demonstrated, the coexistence of aged PBAT and heavy metals (Cu, Pb) can seriously reduce the intestinal microbial diversity and richness of zebrafish, which may induce more serious toxicity and disease in long-term exposure to pollutants. This study could provide fundamental data for better understanding on the adsorption behavior and ecological risk of aged biodegradable plastics with coexisted pollutants.

Assessment of the impact of chemical pollution on endangered migratory fish in two major rivers of France, including spawning grounds

Water pollution is a one of the most contributors to aquatic biodiversity decline. Consequently, ecological risk assessment methods have been developed to investigate the effects of existing stresses on the environment, including the toxic effects of chemicals. One of the existing approaches to quantify toxic risks is called "Potentially Affected Fraction of species" (PAF), which estimates the potential loss of species within a group of species studied. In this study, the PAF method was applied to the Garonne catchment (southwest France) due to the limited information available on the involvement of water pollution in the decline of diadromous fish populations. This approach was used to quantify the potential toxic risk associated with chemical contamination of water for fish species. The objectives were to quantify this risk (1) in the Garonne and Dordogne rivers and (2) in the spawning grounds of two endangered anadromous fish species: the allis shad and the European sturgeon during the development period of their early life stages. Environmental pollution data was provided for 21 sites within the Garonne catchment between 2007 and 2022, and toxicity data was obtained specifically from freshwater toxicity tests on fish species. Then, for each site and each year, the potential toxic risk for a single substance (ssPAF) and for a mixture of substances (msPAF) was calculated and classified as high (>5 %), moderate (>1 % and < 5 %) or low (<1 %). Potential toxic risks were mostly moderate and mainly associated with: metals > other industrial pollutants and hygiene and care products > agrochemicals. In summary, this study highlights the probable involvement of water contamination on the decline, fate and restoration of diadromous fish populations in the Garonne catchment, focusing notably on the toxic effects on early life stages, a previously understudied topic.

Spatio-temporal variability of potentially toxic elements' pollution in road-deposited sediments according to health risk thresholds: a meta-analysis

Road deposited sediments (RDS) are important sinks of potentially toxic elements (PTEs), which may have a significant impact on human health. A systematic review of published papers on the PTEs occurrence in RDS was carried out. The main goal was to assess the global RDS contamination by PTEs and human health risks linked with anthropogenic activities. A systematic search was made to collect information about the most cited PTEs in the published literature and perform a statistical analysis. Subsequently, health risks were assessed for 35 different areas worldwide. PTE concentrations showed high variability, and means were multiple times higher than the corresponding consensus-based threshold effect concentrations (5.2-, 10.3-, 5.3-, 3-, 7.3-, and 3.6-fold higher for Zn, Pb, Ni, Cr, Cu, and Cd, respectively). PTEs concentrations were ranked as Zn > Pb > Cu > Mn > Cr > Ni > Cd. Non carcinogenic risks followed the trend Pb > Cu > Zn > Cd. Lead is responsible for the highest significant non carcinogenic risk to human health. Unacceptable exposition to carcinogenic risks is present in most areas. The top carcinogenic risk areas were Singapore > Beijing > Yixing > Shanghai > Zhuzhou for adult male, Dresden > Singapore > Ulsan > Huludao for adult females, and Dresden > Singapore > Ulsan > Huludao for children. Highest chromium and nickel carcinogenic risks occurred in Singapore, Cd in Dresden, and Cu in Huludao. Highest RDS contamination was seen in industrial areas due to pollutants deposition. Highest Zn, Cu, Cd, and Pb concentrations occur in densely urbanized areas due to heavy-duty vehicular exhausts.

Sea cucumber physiological response to abiotic stress: Emergent contaminants and climate change

The ocean is facing a multitude of abiotic stresses due to factors such as climate change and pollution. Understanding how organisms in the ocean respond to these global changes is vital to better predicting consequences. Sea cucumbers are popular echinoderms with multiple ecological, nutritional, and pharmaceutical benefits. Here, we reviewed the effects of environmental change on an ecologically important echinoderm of the ocean, aiming to understand their response better, which could facilitate healthy culture programs under environmental changes and draw attention to knowledge gaps. After screening articles from the databases, 142 studies were included on the influence of emergent contaminants and climate variation on the early developmental stages and adults of sea cucumbers. We outlined the potential mechanism underlying the physiological response of sea cucumbers to emerging contaminants and climate change. It can be concluded that the physiological response of sea cucumbers to emergent contaminants differs from their response to climate change. Sea cucumbers could accumulate pollutants in their organs but are aestivated when exposed to extreme climate change. Research showed that the physiological response of sea cucumbers to pollutants indicates that these pollutants impair critical physiological processes, particularly during the more susceptible early phases of development compared to adults, and the accumulation of these pollutants in adults is often observed. For climate change, sea cucumbers showed gradual adaptation to the slight variation. However, sea cucumbers undergo aestivation under extreme conditions. Based on this review, critical suggestions for future research are presented, and we call for more efforts focusing on the co-occurrence of different stressors to extend the knowledge regarding the effects of environmental changes on these economically and ecologically important species.

Zinc modulates hypothalamo-pituitary-gonadal-liver axis to impair reproduction in female Mystus vittatus (Bloch, 1794)

The present study investigated the effects of zinc on the hypothalamo-pituitary-gonadal-liver (HPGL) axis of the bagrid catfish Mystus vittatus. Female fish (pre-ovulatory and ovulatory phases) were exposed to zinc sulphate at 1/10th of LC50 (5.62 mg/L) for 60 days and sacrificed at every 15-day interval to collect tissues. Zinc concentration in all tissues was significantly higher in the metal-exposed group at all exposure durations compared to control for both phases. Metallothionein (MT) levels increased in the brain, liver and ovary of fish from both phases with exposure duration. Reactive oxygen species (ROS) generation in the brain, liver and ovary tissues increased with exposure duration at both reproductive phases while serum cortisol levels in ovulatory fish increased significantly compared to pre-ovulatory. Condition factor, gonadosomatic index and hepatosomatic index decreased in Zn-exposed fish. Brain GnRH and kisspeptin levels decreased significantly in the Zn-exposed group for both phases. GnIH was significantly higher in Zn-exposed fish. Serum FSH levels in pre-ovulatory and LH levels in ovulatory fish decreased gradually with an increase in the duration of exposure. Zn exposure reduced vitellogenin (Vtg) and estradiol (E2) in the liver and ovary with an increase in duration from both phases. Ovary maturation-inducing hormone (MIH) levels showed a decrease with exposure duration in ovulatory fish. Moreover, Zn-exposed ovulatory fish showed a degenerated oocyte nucleus due to the disintegration of the nuclear membrane. It might be inferred that Zn altered the HPGL regulatory system of M. vittatus reproduction at both the pre-ovulatory and ovulatory phases.

Effect of Pb, Cu and Zn on development and Wnt/β-catenin signaling pathway genes expression of Ctenopharyngodon idella

Pollution of the aquatic environment with heavy metals is a serious environmental problem, since they accumulate in aquatic organisms and can affect their development and worsen their condition. According to the scheme of Fig. 1 zinc (Zn), copper (Cu) or lead (Pb) were studied when exposed to concentrations of: Zn (0.01; 0.1; 1 mg/L), Cu (0.001; 0.01; 0.1 mg/L), Pb (0.006; 0.06; 0.6 mg/L) for 144 h after fertilization (hpf) on the grass carp (Ctenopharyngodon idella), one of the important commercial fish species of Kazakhstan, the activity of superoxide dismutase (SOD) and the expression of genes of the Wnt/β-catenin signaling pathway involved in development. All metals significantly reduced survival, hatching rate, and changed biometric parameters and heart rate of cupid larvae. In addition, these metals (mainly Pb and Cu) inhibited superoxide dismutase (SOD) activity and mRNA transcription of genes encoding genes of the Wnt/β-catenin signaling pathway. These results showed that Pb, Cu and Zn not only affect the survival and development of fish at an early stage of life, but also cause oxidative stress and prevent fish detoxification.

Maternal transfer of trace elements to shark eggs and their dietary assimilation efficiencies

Dogfish (Scyliorhinus canicula) transferred trace elements (110Ag, 109Cd, 54Mn and 75Se) from their diet to eggs, and their components (yolk and embryo, case and jelly) at greatly varying rates. Trace element levels in eggs showed positive linear relationships (p < 0.001; r2-0.83-0.91) with their cumulative rates of maternal ingestion over 61 days (maternal-to-egg transfer rates: mTFs). These mTFs varied by 2-3 orders of magnitude, with 54Mn > 110Ag > 75Se > 109Cd, and their range encompassed those previously measured for 60Co, 65Zn, 241Am and 134Cs. For six of the eight trace elements, their mTFs were significantly influenced (p < 0.05; r2 = 0.72) by both their dietary assimilation efficiency and their location within the egg (case). In contrast, both 110Ag and 54Mn greatly exceeded the mTFs predicted by this multiple regression model by one and 2-3 orders of magnitude, respectively, and were predominantly transferred to the egg case. Among elements, contrasting rates of transfer and percentage distributions in egg components imply differing ecotoxicological and radiological detriments to the developing embryo.

Shedding Light on Heavy Metal Contamination: Fluorescein-Based Chemosensor for Selective Detection of Hg2+ in Water

This article discusses the design and analysis of a new chemical chemosensor for detecting mercury(II) ions. The chemosensor is a hydrazone made from 4-methylthiazole-5-carbaldehyde and fluorescein hydrazide. The structure of the chemosensor was confirmed using various methods, including nuclear magnetic resonance spectroscopy, infrared spectroscopy with Fourier transformation, mass spectroscopy, and quantum chemical calculations. The sensor's ability in the highly selective and sensitive discovery of Hg2+ ions in water was demonstrated. The detection limit for mercury(II) ions was determined to be 0.23 µM. The new chemosensor was also used to detect Hg2+ ions in real samples and living cells using fluorescence spectroscopy. Chemosensor 1 and its complex with Hg2+ demonstrate a significant tendency to enter and accumulate in cells even at very low concentrations.

Polystyrene microplastics effects on zebrafish embryological development: Comparison of two different sizes

Microplastics have become a great worldwide problem and it's therefore important to study their possible effects on human and environmental health. In this study, zebrafish embryos were used to compare two different sizes of polystyrene microplastics (PS-MPs), 1 µm and 3 µm respectively, at 0.01, 0.1, 1.0 and 10.0 mgL-1, and were monitored up to 72 h. Toxicity tests demonstrated that neither of the PS-MPs altered the embryos' survival and the normal hatching process. Instead, higher concentrations of both sizes caused an increase of the heart rate and phenotypic changes. The PS-MPs of both sizes entered and accumulated in the larvae at the concentration of 10.0 mgL-1 and the same concentration caused an increase of apoptotic processes correlated to redox homeostasis changes. The reported results give a realistic view of the negative effects of exposure to PS-MPs and provide new information on their toxicity, also considering their sizes.

Realistic microplastics harness bacterial presence and promote impairments in early zebrafish embryos: Behavioral, developmental, and transcriptomic approaches

The plastisphere is a newly recognized ecosystem. However, its interaction with early life stages of aquatic vertebrates is a multifaceted issue that requires further research. This study investigated the involvement of bacteria in shaping realistic microplastics hazards in zebrafish Danio rerio embryos. Fish were exposed to bottle micro-fragments (FR) and textile micro-fibers (FI) of polyethylene terephthalate (5-15 μm), concomitant with Aeromonas salmonicida achromogenes challenge from 2h post-fertilization for 3 days. Egg chorion showed affinity for FR and FI, inducing earlier embryo hatching. However, this effect was masked by biofilm invasion. Fragments were more detrimental than fibers on developmental parameters, while bacterial presence compromised body length, eye, and yolk sac surface area. In a further finding, MPs alone increased locomotor activity in zebrafish larvae, without synergistic effect when combined with bacteria. Data showed that realistic MPs had no significant effects except for downregulated sod and cyp1a gene expression, whereas bacterial challenge inhibited larval potency for most of the evaluated mRNA levels (mpx (immune system), apoeb (lipid metabolism), nfkb and tfa (inflammation), cyp and sod (oxidative stress)). This study provides new insights into realistic microplastic effects under relevant conditions when combined with environmental pathogen within the first life stages of aquatic vertebrates.

In-nest mortality and pathology of hawksbill sea turtle (Eretmochelys imbricata) embryos and hatchlings in St. Kitts and Nevis

Strategies to improve the hatch success and survival of critically endangered hawksbill turtles (Eretmochelys imbricata) require knowledge of threats to them including pathological conditions. The objective of this study was to describe the mortality and pathology of embryos and dead-in-nest hatchlings on St. Kitts and Nevis. Over the 2019/20 and 2020/21 nesting seasons, the combined mean (SD) hatch success for the two islands was 81.9% (13.2%) and deceased individuals within excavated nests were early-stage embryos (70.7%), late-stage embryos (17.7%), pipped-hatchlings (8.2%) or dead-in-nest hatchlings (3.4%). From 2017 to 2021, a post-mortem examination was performed on 183 turtles, including histology for 116. Anatomical malformations affected 77 (42.1%) examined turtles and included abnormal scute shape or number (22.4%), dysmelia (8.7%), schistosomus reflexus (7.7%) and compressed carapace (7.7%). Microscopic lesions were found in 49.1% of turtles and included tissue mineralization (26.7%, including renal, fetal membrane, liver, heart or muscle), chorioallantoitis (16.2%) and skeletal muscle degeneration and necrosis (10%). Inflammatory lesions associated with fungal or bacterial infections were in the skin (n = 3), chorioallantois (n = 4), lung (n = 3) or yolk sac (n = 1). These lesions may reflect non-specific terminal conditions but their presence in-nest helps explain some of the mortality and pathology documented in hatchlings that die during rehabilitative care. All of the gonads adequately represented for histological determination of sex were female (n = 62), supporting concern for feminization of Caribbean hawksbill turtle nests. The study identifies lesions that could affect hatch and emergence success. The high frequency of skeletal malformations indicates the need for investigations addressing regional impact and pathogenesis, especially genetic and environmental aetiologies including nest temperature. Immediate examination of live hatchlings on nest emergence is warranted to better determine the prevalence of non-fatal malformations that could impact fitness and population genetics.

Investigating seasonal metal impact on Stramonita haemastoma gastropod along the Algerian East Coast: Understanding through various pollution indicators

The main objective of this study was to assess the impact of environmental pollution on the gastropod Stramonita haemastoma by examining various physiological and biochemical parameters. Trace metal elements (TME) were measured in the snail's foot. Over a one-year period from 2013 to 2014, the study investigated the variations in reduced glutathione, malondialdehyde, metallothionein, glutathione S-transferase, acetylcholinesterase and catalase activities in the foot of the gastropod at three different sites. The results showed spatiotemporal fluctuations in biomarkers, physiological parameters and TME. This integrative approach, being the first of its kind in the region using S. haemastoma as a model organism, represents a means of environmental assessment accessible to all countries allowing the monitoring and conservation of coastal marine environments on a national and international scale and which could be used in marine biomonitoring programs to indicate the impact of pollution and assess the quality of the Algerian coastal marine environment.

Implications of biotic factors for toxicity testing in laboratory studies

There is an emerging call from scientists globally to advance the environmental relevance of laboratory studies, particularly within the field of ecotoxicology. To answer this call, we must carefully examine and elucidate the shortcomings of standardized toxicity testing methods that are used in the derivation of toxicity values and regulatory criteria. As a consequence of rapidly accelerating climate change, the inclusion of abiotic co-stressors are increasingly being incorporated into toxicity studies, with the goal of improving the representativeness of laboratory-derived toxicity values used in ecological risk assessments. However, much less attention has been paid to the influence of biotic factors that may just as meaningfully impact our capacity to evaluate and predict risks within impacted ecosystems. Therefore, the overarching goal is to highlight key biotic factors that should be taken into consideration during the experimental design and model selection phase. SYNOPSIS: Scientists are increasingly finding that lab reared results in toxicology might not be reflective of the external wild environment, we highlight in this review some key considerations when working between the lab and field.

Single and mixture toxicity of cadmium and copper to swim bladder in early life stages of Japanese medaka (Oryzias latipes)

Toxicity observed in aquatic ecosystems often cannot be explained by the action of a single pollutant. Likewise, evaluation standards formulated by a single effect cannot truly reflect the environmental quality requirements. The study of mixtures is needed to provide environmental relevance and knowledge of combined toxicity. In this study, the embryos of Japanese medaka (Oryzias latipes) were treated with individual and binary mixture of copper (Cu) and cadmium (Cd) until 12 days post-fertilization (dpf). Hatching, mortality, development, histology and gene expression were assessed. Our results showed that the highest concentration mixture of Cd (10 mg/L) and Cu (1 mg/L) affected survival, hatching time and hatching success. Occurrence of uninflated swim bladder was the highest (value) with exposure to 10 mg/L Cd. Swim bladder was commonly over-inflated in a mixture (0.1 mg/L Cd + 1.0 mg/L Cu) exposure. Individuals exposed to the mixture (0.1 Cd + 1.0 Cu mg/L) showed up to a 7.69% increase in swim bladder area compared to the control group. The mixtures containing 0.1 or 10 mg/L Cd, each with 1.0 mg/L Cu resulted in significantly increased of Pbx1b expression, higher than any Cd or Cu alone (p < 0.01). In the co-exposure group (0.1/10 Cd + 1.0 Cu mg/L), Pbx1b expression was found at 12 dpf but not 7 dpf in controls. Higher concentrations of Cd may progressively reduce Pbx1b expression, potentially explaining why 75% of individuals in the 10 mg/L Cd group failed to inflate their swim bladders. Additionally, the swim bladder proved to be a valuable bio-indicator for biological evaluation.

Effects of mercury chloride on antioxidant and inflammatory cytokines in zebrafish embryos

In this study, a zebrafish embryo toxicity model was employed, utilizing 24 h postfertilization (hpf) zebrafish embryos. These embryos were treated with varying concentrations of mercuric chloride for 96 h under static conditions. We assessed multiple parameters that reflected developmental abnormalities, behavioral alterations, morphological anomalies, antioxidant enzyme activities, including those of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and glutathione S-transferase (GST), immune messenger RNA transcription levels of key factors such as tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and cyclooxygenase 2 (COX-2), as well as protein expression of TNF-α. The results revealed that embryos exposed to higher concentrations of mercury exhibited reduced hatchability and increased rates of morphological abnormalities and mortality at 48, 72, and 96 hpf. In addition, a concentration-dependent increase in developmental abnormalities, including cardiac edema, reduced body length, yolk sac edema, scoliosis, and bent tails, was observed. Larval behaviors, such as touch-induced escape responses, startle reactions, and turning actions, were found to be diminished in a concentration-dependent manner. Additionally, the activities of various antioxidative enzymes, such as SOD, CAT, and GST, exhibited an increase at higher mercury concentrations, with the exception of GPX activity, which decreased significantly in a dose-dependent manner (p < 0.05). Pro-inflammatory cytokine transcription levels, specifically TNF-α, IL-1β, IL-6, and COX-2, were significantly upregulated in a dose-dependent manner in the mercuric (II) chloride (HgCl2 ) treatment group compared with the control group. TNF-α protein expression was notably elevated in the larvae group treated with 300 and 400 nM HgCl2 .

An experiment on the glucose metabolite, serum electrolytes, and somatic characteristics of the Levantine Barbel Luciobarbus pectoralis (Heckel, 1843) under the effect of heavy metals

Levantine Barbel (Luciobarbus pectoralis) is a benthopelagic, subtropical native fish living in the inland waters of the Mediterranean region in Türkiye and Syria. Even though it is widely consumed locally, experimental observations on how heavy metals [zinc (Zn), copper (Cu), cadmium (Cd), and lead (Pb)] and their mixtures affect the fish are lacking. Several bioindicators of the fish exposed to heavy metals are the focus of the current investigation. Initially, Fulton condition factor (K) and hepato-somatic index (HSI) were utilized in the somatic characteristics of L. pectoralis. Then, changes in the level of glucose metabolite and electrolytes [sodium (Na+), potassium (K+), and chloride (Cl-)] of blood were determined by Architect C-800 auto-analyzer after exposure durations. The results of the experiments demonstrated that heavy metals can rapidly have a negative impact on the regulation of blood and somatic characteristics of fish. It was observed that the K index decreased in all metal groups at 24 and 96 h, while considerably increased in the 24-h effect of cadmium only (P ≤ 0.05). Along with that, in the 96-h effect of metals, Cu indicated the highest decrease in the HSI value (19.33%, P ≤ 0.05). In general, all heavy metal exposures caused the fish's glucose metabolite level to rise compared to the control (P ≤ 0.05). Furthermore, sublethal effects of metals at both durations caused considerable changes in blood electrolytes of the fish compared to control (P ≤ 0.05). Additionally, putative biomarkers in both durations had the greatest difference in toxic similarity under the Cu impact compared to the control, according to Hierarchical clustering and Euclidean distance metrics. Although the applied concentrations of Zn, Cu, Cd, and Pb and their mixture studied were generally within the limits of the various organizations and the surface water regulations, changes in ecophysiological and somatic indices were nonetheless seen in fish.

Comparison of the accumulation and effects of copper pyrithione and copper sulphate on rainbow trout larvae

Copper pyrithione (CuPT) is used as a co-biocide in new antifouling paints but its toxicity remains little known. To compare the toxicity of copper-based compounds, rainbow trout (Oncorhynchus mykiss) larvae were exposed for 8-day to CuPT and CuSO4 at equivalent copper concentrations. CuPT exposure led to the greatest accumulation of Cu in larvae. Exposure to 10 µg.L-1 CuPT induced 99% larval mortality but only 4% for CuSO4-exposed larvae. The larval development and growth were affected by CuPT (from 0.5 µg.L-1 Cu) but not by CuSO4. Lipid peroxidation was not induced by either contaminant. The expression of genes involved in oxidative stress defence, detoxification and copper transport was induced in larvae exposed to CuSO4 and CuPT but at higher concentrations for CuPT. This study highlights the marked toxicity of CuPT for early life stages of fish and raises the question of the possible environmental risks of this antifouling compound.

Yeast vacuolar enzymes as novel hatching inhibitors for aquatic organisms, Daphnia magna and Danio rerio eggs

Concerns over the spread of non-native species in aquatic environments have led to the need for effective methods to prevent and control their spread while protecting native species. This study investigated the potential of yeast vacuolar enzymes as a natural hatching inhibitor for controlling aquatic organisms. Hatching experiments with Daphnia magna eggs demonstrated that exposure to yeast vacuole enzymes inhibited hatching in a concentration-dependent manner, suggesting their potential as an effective inhibitor of egg hatching in aquatic organisms. Interestingly, the protease used for comparative purposes did not inhibit hatching, but instead increased the mortality of hatched D. magna. Additionally, chorionic changes were observed in non-hatched D. magna eggs and zebrafish eggs exposed to yeast vacuole enzymes, suggesting that the enzyme can alter the chorion and interfere with hatching. These findings suggest that yeast vacuolar enzymes may be a promising and natural management tool for controlling the spread of harmful aquatic organisms, and further research is warranted to explore their potential for species-specific control.

Essential and toxic elements in juvenile migratory commercial fish species in the Paraná River alluvial valley (South America): an approach for aquatic environmental monitoring

The Paraná River is the sixth largest in the world, and the lower section of the river is one of the largest and most productive floodplain wetlands in South America. The alluvial plain is an important habitat for nursery and feeding areas for commercial fish; however, it has been heavily anthropized due to industries, agricultural activities, and the growth and expansion of metropolitan areas. The aim of this study was to determine element accumulation (As, Cd, Cr, Cu, Fe, Mn, Pb, and Zn) in young-of-the-year fish muscle from a floodplain lagoon of the lower Paraná River (Argentina) during summer and winter seasons, in relation with abiotic matrices (water and sediment). Four commercial fish species were assessed: sábalo (Prochilodus lineatus), boga (Megaleporinus obtusidens), dorado (Salminus brasiliensis), and pirapitá (Brycon orbignyanus). The concentrations of eight elements were detected by quadrupole inductively coupled plasma mass spectrometry. In water samples, Cd, Cr, Mn, Fe, and Zn levels were under the permissible limits for aquatic biota protection in both seasons, except for Pb (> 1 μg L-1) and Cu (> 2 μg L-1). In sediment, the average concentrations of all elements were under the limits set by national and international regulatory authorities. Differences in elemental concentrations between species and seasons were found. In general, the levels of elements in water were higher in summer than in winter, while in sediment, the lowest concentrations of elements were detected during the summer. The order of element concentration in fish muscle was Cd (0.01-0.04 μg g-1) < As (0.02-0.16 μg g-1) < Pb (0.03-0.23 μg g-1) < Mn (0.77-4.32 μg g-1) < Cu (1.01-4.07 μg g-1) < Cr (1.09-4.30 μg g-1) < Zn (15.8-31.7 μg g -1) < Fe (12.6-49.7 μg g-1). The accumulation assessment showed that the four fish species significantly accumulate Cr, Cu and Zn, and As and Zn from water and sediment, respectively. The correlation analysis showed a relationship between fish size and As, Cr, Cu, Fe, Mn, and Zn concentrations. Similarly, the highest values of element concentrations in muscle were detected during the summer when the fishes are early juveniles. The level of As, Cd, and Pb detected in B. orbignyanus, M. obtusidens, and P. lineatus juveniles suggested that these species had the potential to be used as biomarkers for assessing accumulation of toxic elements in the environment. Also, this study reveals that the accumulation patterns differ between size and fish species, which should be a considered insight at the moment of selecting a bioindicator to monitor pollution in the ecosystem.

Hexavalent Chromium Inhibited Zebrafish Embryo Development by Altering Apoptosis- and Antioxidant-Related Genes

This study aimed to assess the effects of hexavalent chromium on zebrafish (Danio rerio) embryo development. The zebrafish embryos were treated with solutions containing chromium at different concentrations (0.1, 1, 3.125, 6.25, 12.5, 50, and 100 µg/mL). The development of zebrafish embryos was estimated by the determination of survival rate, heart rate, and the measurement of larvae body length. Real time RT-PCR and Western blot were performed to assess the expression of apoptosis- and antioxidant-related genes. The results showed that the reduced survival rate of zebrafish embryos and larvae was associated with an increase in chromium concentration. The exposure of higher concentrations resulted in a decrease in body length of zebrafish larvae. In addition, a marked increase in heart rate was observed in the zebrafish larvae under chromium treatment, especially at high concentrations. The real-time RT-PCR analysis showed that the transcript expressions for cell-cycle-related genes (cdk4 and cdk6) and antioxidant-related genes (sod1 and sod2) were downregulated in the zebrafish embryos treated with chromium. Western blot analysis revealed the upregulation of Caspase 3 and Bax, while a downregulation was observed in Bcl2. These results indicated that hexavalent chromium induced changes in zebrafish embryo development by altering apoptosis- and antioxidant-related genes.

Spatial and temporal variations of geochemical processes and toxicity of water, sediments, and suspended solids in Sibuti River Estuary, NW Borneo

A comprehensive geochemical study was conducted in the Sibuti River estuary by considering water, suspended solids (SS), and sediment samples from 36 stations during southwest monsoon (SWM) and northeast monsoon (NEM). In this study, the distribution of in situ parameters, major ions, nutrients, trace metals, and isotopes (δD, δ18O) were analyzed in water samples, whereas sediments and SS were studied for trace metals. The distribution revealed that suspended solids were the major carrier of Cd, Zn, and Mn, whereas sediments worked as a major source of Co, Cr, Ba, Se, Cu, and Pb. Na-Cl water type and ion exchange dominated the lower part of the estuary during both seasons. However, the mixed mechanism of Ca-Cl, Ca-Mg-Cl, and higher weathering indicated reverse ion exchange in the intermediate and upper parts of the estuary. Isotopic signatures of δD and δ18O in estuarine water indicate that the precipitation over the Limbang area dominates during SWM, whereas higher evaporation was confirmed during NEM. The factor analysis revealed that seawater influence in the estuary majority controlled the water chemistry irrespective of seasons. Major ions were mainly regulated by the tidal influence during the low flow time of the river (SWM), whereas the mixing mechanism of weathering and seawater controlled the concentrations during NEM. Nutrients such as NO3, SO42-, NH3, and NH4+ mainly originated from the agricultural fields and nitrification along with ammonification were responsible for the recycling of such nutrients. Trace metals except Cd were found to be geogenic in nature and originating mainly from the oxidation of pyrites present in the sandstone and mudstones of the Sibuti Formation. Redox condition was catalyzed by microorganisms near the river mouth, whereas Al-oxyhydroxides and Fe-oxyhydroxides complexes in the intermediate and upper part under oxygenated conditions controlled the absorption of metals. Overall, the estuary was found to be absorptive in nature due to ideal pH conditions and was confirmed by the saturation index (SI) of minerals.

Exposure to manganese (II) chloride induces developmental toxicity, oxidative stress and inflammatory response in Marine medaka (Oryzias melastigma) embryos

Manganese (Mn) is an essential metal for organisms, but high levels can induce serious toxicity. To date, the toxic mechanism of Mn to marine fish is still poorly understood. In the present study, Oryzias melastigma embryos were exposed to different concentrations of MnCl₂ (0-152.00 mg/L) to investigate its effect on early development. The results showed that exposure to MnCl₂ caused developmental toxicity to embryos, including increased heart rate, delayed hatching time, decreased hatching rate and increased malformation rate. MnCl₂ exposure could induce oxidative stress in O. melastigma embryos, as indicated by increased the contents of malondialdehyde (MDA) and the activities of the antioxidant enzymes (superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT)). The heart might be an important target organ for MnCl₂ because of cardiac malformations and disruption in the expression of cardiac development-related genes (ATPase, epo, fg8g, cox1, cox2, bmp4 and gata4). In addition, the expression levels of stress- (omTERT and p53) and inflammation-related genes (TNFα and il1β) were significantly up-regulated, suggesting that MnCl₂ can trigger stress and inflammatory response in O. melastigma embryos. In conclusion, this study demonstrated that MnCl₂ exposure can induce developmental toxicity, oxidative stress and inflammatory response in O. melastigma embryos, providing insights into the toxic mechanism of Mn to the early development of marine fish.

Ovaries of guppies (Poecilia reticulata) investigated in pre-embryonic, embryonic and post-embryonic stages after exposure to maghemite nanoparticles (y-Fe2O3) associated with Roundup® and glyphosate, followed by recovery period evaluation

Iron oxide nanoparticles (IONP) are promising alternatives to environmental remediation, so this study investigates IONP single and associated to contaminants, in this case, glyphosate (GLY) and Roundup® (GBH) in Poecilia reticulata (guppy). The guppies have internal development, therefore this study analyzed female gonads to establish the developmental stages of P. reticulata and evaluate effects of exposure (7, 14 and 21 days) and post-exposure (same period) to the treatments with Iron ions 0.3mg Fe/L (IFe); IONP 0.3mg Fe/L; IONP 0.3 mgFe/L + GBH 0,65mgGLY/L (IONP+GBH1); IONP 0.3 mgFe/L + GBH 1.30 mgGLY/L (IONP+GBH2); and IONP 0.3 mgFe/L + GLY 0.65 mg/L (IONP+GLY). The development was organized in immature, development, and gestation phases. The damage in all treatments after 21 days of exposure was evident in reaction patterns regressive inflammatory, and circulatory including total histopathologic index of liver, nevertheless there was a damage recovery trend during post-exposure period.

Alterations to unionid transformation during agricultural and urban contaminants of emerging concern exposures

Highly imperiled unionids have a complex life cycle including the metamorphosis of an obligate parasite life stage, larval glochidia, to the juvenile stage. Despite the known vulnerabilities of both glochidia and juveniles to pollutants, little is known on how metamorphosis success may be affected by chemical stress. Disruption of the transformation process in which glochidia encyst on the gills of a host fish, could lead to lowered recruitment and population declines. Transformation rates of Lampsilis cardium on host fish Micropterus salmoides were empirically derived from experimental exposures to low, medium, or high concentrations of an agricultural or urban mixture of contaminants of emerging concern (CECs) over two exposure durations. Transformation was characterized by: (1) a zero-inflated Poisson general linear mixed effects model to compare difference in transformation between exposure durations and (2) time response curves to describe the transformation curve using long-term exposure data. Lampsilis cardium transformation was similar between exposure durations. When compared to controls, CEC stress significantly reduced juvenile production (p « 0.05) except for the agricultural medium treatment and tended to increased encapsulation duration which while statistically insignificant (p = 0.16) may have ecological relevancy. Combining the empirically derived reduction of transformation rates with parameters values from the literature, a Lefkovich stage-based population model predicted strong declines in population size of L. cardium for all treatments if these results hold in nature. Management focus on urban CECs may lead to best conservation efforts though agricultural CECs may also have a concentration dependent impact on transformation and therefore overall recruitment and conservation success.

Consequences of prenatal exposure to contaminants in elasmobranchs: Biochemical outcomes during the embryonic development of Pseudobatos horkelii

Coastal elasmobranchs are vulnerable to chemicals mostly due to their k-strategic life history characteristics and high trophic positions. Embryos might be particularly exposed through the maternal offloading of contaminants, possibly leading to disruptions during critical developmental phases. Yet, knowledge on biochemical outcomes of prenatal exposure in elasmobranchs is notably limited. Therefore, we aimed to investigate the effects of prenatal exposure to contaminants in embryos of the critically endangered Brazilian guitarfish, Pseudobatos horkelii. Polybrominated diphenyl ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), pharmaceuticals and personal care products, and metals were determined in embryos. Additionally, glutathione S-transferase activity (GST), glutathione (GSH), and metallothionein levels (MT) were analyzed. Finally, lipid peroxidation levels (LPO) and protein carbonyl groups (PCO) were assessed. Embryonic exposure depended on yolk consumption, which was conspicuous in earlier development. We observed a dilution effect of contaminants levels, potentially related to biotransformation of these compounds throughout the embryonic development. Nevertheless, GST was not correlated to contaminant concentrations. The multivariate relationship between antioxidant components (GSH and GST) and LPO and PCO was negative, suggesting the lack of efficient defense of these biomarkers in early development, leading to oxidative damage. In this context, our results indicate that prenatal exposure to contaminants might impact the redox status in embryos of P. horkelii, leading to oxidative damage. Furthermore, metal concentrations influenced MT levels, suggesting this as a potential detoxification pathway in this species.

Major, minor and trace element concentrations in the muscle and liver of a pregnant female Pacific sharpnose shark (Rhizoprionodon longurio) and its embryos

The Pacific sharpnose shark Rhizoprionodon longurio is an abundant shark consumed by human population in Mexico. This study aimed to determine and compare the concentrations of thirteen essential elements (K, S, P, Na, Ca, Mg, Fe, Zn, Se, Cu, Mn, Cr and Co) and eleven non-essential elements (As, Sr, Cd, V, Li, U, Tl, Ag, Sn, Sb and Pb) in the muscle and liver of a pregnant female, fished near the copper mine of Santa Rosalía, and their respective embryos. Major, minor and trace (essential and non-essential) elements were transferred during gestation to embryos. All major elements analyzed had significantly higher concentrations in embryos liver than the pregnant female, except for magnesium. Higher concentrations in embryo tissues than the pregnant female tissues were found for the non-essential trace elements of strontium, lithium, thallium and silver, which indicate an easy maternal transfer of these non-essential elements.

Assessing metal(loid)s concentrations and biomarkers in tilapia (Oreochromis niloticus) and largemouth bass (Micropterus salmoides) of three ecosystems of the Yaqui River Basin, Mexico

Aquatic ecosystems have been suffering deleterious effects due to the development of different economic activities. Metal(loid)s are one of the most persistent chemicals in environmental reservoirs, and may produce adverse effects on different organisms. Since fishes have been largely used in studies of metal(loid)s exposure, tilapia and largemouth bass were collected in three ecosystems from the Yaqui River Basin to measure the concentrations of metal(loid)s (chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), zinc (Zn) arsenic (As), mercury (Hg), and selenium (Se)) and some biomarkers (somatic indices, metallothionein expression and histopathological analysis) in tissues of both species. Metal(loid) concentrations varied seasonally among ecosystems in tissues of both species. The elements varied seasonally and spatially in tissues of both species, with a general distribution of liver > gills > gonads. Also, biomarkers showed variations indicative that the fish species were exposed to different environmental stressor conditions. The highest values of some biomarkers were in largemouth bass, possibly due to differences in their biological characteristics, mainly feeding habits. The multivariate analysis showed positive associations between metal(loid)s and biomarkers, which are usually associated to the use of these elements in metabolic and/or regulatory physiological processes. Both fish species presented histological damage at different levels, from SI types (changes that are reversible for organ structure) to SII types (changes that are more severe but may be repairable). Taken together, the results from this study suggest that the Yaqui River Basin is moderately impacted by metals and metalloids.

Toxicity of single and combined 4-epianhydrotetracycline and cadmium at environmentally relevant concentrations on the zebrafish embryos (Danio rerio)

The combined pollution of antibiotics and heavy metals has attracted a worldwide attention in the recent years. 4-epianhydrotetracycline (EATC) is the major degradation product of tetracycline (TC), which has been detected frequently in environment and its concentration is even higher than TC under some circumstances. Cadmium (Cd) is a common heavy metal contaminant and has highly toxic to organisms, plants and humans even at low doses. In the present study, zebrafish (Danio rerio) embryo toxicity test was performed to investigate the single and combined effects of EATC and Cd on aquatic organisms. Exposure to EATC and Cd at environmentally relevant concentrations had a series of hazardous impacts on the embryonic development, including lethality, hatching rate, heart rate and teratogenic effects. Compared to the contaminant existed alone, combined pollution produced stronger toxicity, which appeared as the decreasing of heart rate and hatching rate, and the increasing of malformation of zebrafish embryos. After 96 h exposure, the reactive oxygen species (ROS) levels in zebrafish embryos were increased significantly, revealing that EATC-Cd co-exposure resulted in potential oxidative stress-induced damage. Acridine orange (AO) staining showed that combined exposure resulted in stronger cell apoptosis. The potential health risks of the combined pollution of EATC and Cd should be paid more attention to higher level vertebrates and humans.

The effect of environmental stressors on growth in fish and its endocrine control

Fish body growth is a trait of major importance for individual survival and reproduction. It has implications in population, ecology, and evolution. Somatic growth is controlled by the GH/IGF endocrine axis and is influenced by nutrition, feeding, and reproductive-regulating hormones as well as abiotic factors such as temperature, oxygen levels, and salinity. Global climate change and anthropogenic pollutants will modify environmental conditions affecting directly or indirectly fish growth performance. In the present review, we offer an overview of somatic growth and its interplay with the feeding regulatory axis and summarize the effects of global warming and the main anthropogenic pollutants on these endocrine axes.

Assessments of some trace metals in water samples of nursery pond of Grass Carp (Ctenopharyngodon idella, Valenciennes, 1844) in Bannu Fish Hatchery of Khyber Pakhtunkhwa, Pakistan

Abstract The present investigation was aimed to examine the concentrations of trace metals including e.g copper (Cu), manganese (Mn), nickel (Ni), and zinc (Zn) in water samples collected from nursery pond of grass carp (Ctenopharyngodon idella) in Bannu Hatchery of Khyber Pakhtunkhwa during the period from April 2018 to January 2019. The temperature and pH of each water sample were measured for the whole study duration. The concentration of Copper (Cu), Manganese (Mn), Nickel (Ni), and Zinc (Zn) in collected water samples were measured in mg/liter by using Atomic Absorption Spectrophotometer. The blank and standard solutions for device calibration Standard solutions i.e., 2.0 mg, 4.0 mg, and 6.0 were used to measure the concentration of these metals in water samples to verify the measurements. The data was statistically analyzed on descriptive statistics (estimation of proportions and standard deviation) used to summarize mean concentration. The results obtained of both temperature and pH of water samples were found in ranged 10 to 36 0C and 7.0 to 8.44; whereas the size of fry stages was ranged from 4.0 to 56.0 mm in total length. The results of investigated metals found in pond water samples are in order of Zn>Mn>Ni>Cu, respectively. As optimum temperature and pH for grass carp were mostly between 15 0C and 30 0C and pH 6.5 to 8.0. It was concluded from obtained results that temperature, pH, and trace metals were found appropriate for the growth of Ctenopharyngodon idella from fry to fingerling stages, but the highest amount of zinc can cause its mortality. It is a preliminary study on grass carp culturing in Bannu fish hatchery so, it would provide useful information for model fish seed production unit in a hatchery.

Morphological Alterations in the Early Developmental Stages of Zebrafish (Danio rerio; Hamilton 1822) Induced by Exposure to Polystyrene Microparticles

Microplastics (MPs) are emerging pollutants of widespread concern in aquatic environments. The aim of this study was to evaluate the negative impact of pristine MPs of polystyrene of 100 μm on embryo and larvae of Danio rerio exposed to three environmentally relevant concentrations of polystyrene (3.84 × 10^- 6, 3.84 × 10^- 7, and 3.84 × 10^- 8 g/mL). The exposure effect was evaluated through the general morphology score, biometrics, and integrated biomarker response version 2 index. No mortality was observed but the anatomical structure of fishes was affected showing pigmentation deficiency and alterations in the head region as the main affected endpoints. The general morphology score and the integrated biomarker response values were highly sensitive to address the effect of the three concentrations of MPs used here. Our results provide solid evidence of the negative impact of 100 μm pristine polystyrene MPs exposure on early stages of zebrafish.

Copper and Zinc Treatments Alter the Thyroid Endocrine System in Zebrafish Embryos/Larvae

Copper (Cu²⁺) and zinc (Zn²⁺) are two kinds of heavy metals essential to living organisms. Cu²⁺ and Zn²⁺ at excessive concentrations can cause adverse effects on animals, but little is known about the thyroid-disrupting effects of these metals in fish, especially in the early developmental transition stage from embryos to larvae. Wild-type zebrafish embryos were used to expose to Cu²⁺ (0, 1.5, 15, and 150 μg/L) and Zn²⁺ (0, 20, 200, and 2000 μg/L) for 120 h. Thyroid hormone contents and transcriptional changes of the genes connected with the hypothalamic-pituitary-thyroid (HPT) axis were measured. Results showed that zebrafish embryos/larvae malformation rates were significantly increased in the Cu²⁺ and Zn²⁺ groups. Remarkably elevated thyroxine (T4) concentrations and reduced triiodothyronine (T3) concentrations were observed in Cu²⁺ and Zn²⁺ exposure fish. And the expression patterns of genes connected with the HPT axis were changed after Cu²⁺ and Zn²⁺ treatment. Based on principal component analysis (PCA) results, Zn²⁺ caused significant effects on the thyroid endocrine system at 200 μg/L, while Cu²⁺ resulted in thyroid disruption as low as 1.5 μg/L. In short, our study demonstrated that exposure to Cu²⁺ and Zn²⁺ induced developmental toxicity and thyroid disruption to zebrafish embryos/larvae.