Mercury-induced chromosomal damage in wild fish (Dicentrarchus labrax L.) reflecting aquatic contamination in contrasting seasons

Toxicity Evaluation, Oxidative, and Immune Responses of Mercury on Nile Tilapia: Modulatory Role of Dietary Nannochloropsis oculata

The current study evaluated the potential ameliorative effect of a dietary immune modulator, Nannochloropsis oculata microalga, on the mercuric chloride (HgCl2)-induced toxicity of Nile tilapia. Nile tilapia (45-50 g) were fed a control diet or exposed to ¼ LC50 of HgCl2 (0.3 mg/L) and fed on a medicated feed supplemented with N. oculata (5% and 10% (50 or 100 g/kg dry feed)) for 21 days. Growth and somatic indices, Hg2+ bioaccumulation in muscles, and serum acetylcholinesterase (AChE) activity were investigated. Antioxidant and stress-related gene expression analyses were carried out in gills and intestines. Histopathological examinations of gills and intestines were performed to monitor the traits associated with Hg2+ toxicity or refer to detoxification. Hg2+ toxicity led to significant musculature bioaccumulation, inhibited AChE activity, downregulated genes related to antioxidants and stress, and elicited histopathological changes in the gills and intestine. Supplementation with N. oculata at 10% was able to upregulate the anti-oxidative-related genes while downregulated the stress apoptotic genes in gills and intestines compared to the unexposed group. In addition, minor to no histopathological traits were detected in the gills and intestines of the N. oculata-supplemented diets. Our data showed the benefit of dietary N. oculata in suppressing Hg2+ toxicity, which might support its efficacy as therapeutic/preventive agent to overcome environmental heavy metal pollution in aquatic habitats.

Mercury offloading in gametes and potential adverse effects of high mercury concentrations in blood and tissues of Atlantic Goliath Grouper Epinephelus itajara in the southeastern United States

Mercury (Hg) is a ubiquitous and non-essential heavy metal that is highly toxic to aquatic organisms. Few studies examine Hg and its effects on wild fish populations. Here, we investigated the potential effects of Hg exposure on a large and long-lived marine species of conservation concern, the vulnerable Atlantic Goliath Grouper Epinephelus itajara. Our objectives were (1) to measure Hg (methyl-Hg; and total Hg = combined methyl-Hg and inorganic-Hg) concentrations in whole blood (WB) and gametes (eggs and sperm); (2) to investigate the relationships between Hg concentrations in muscle and liver with WB and gametes; (3) to investigate the relationships between Hg concentrations in liver, muscle, and WB with hematological and plasma biochemical analytes; and (4) to investigate the relationship between liver Hg and pigmented macrophage aggregates in liver tissue sections. We found several lines of evidence for potential adverse effects on Goliath Grouper health and reproduction by high Hg concentrations in liver, muscle, WB, and gametes, including (1) Hg concentrations in all tissues and gametes were well above observable ranges of marine and freshwater fishes from experimental exposure studies; (2) gamete Hg concentrations were among the highest recorded in wild fishes, with seasonal patterns suggesting females offload significant amounts of Hg into their eggs during the spawning season; (3) Methyl-Hg was highest in muscle, followed by sperm, liver, eggs, and WB; (4) there were significant correlations between liver, muscle, and WB Hg concentrations with various blood analytes; (5) vitellogenin positively correlated with female liver methyl-Hg concentrations, and was abnormally high in males, suggesting direct endocrine effects; and (6) liver total Hg positively correlated with pigmented macrophage aggregate count and percent area. This work will help guide future research examining the potential adverse effects of Hg and its role as an additional stressor on wild fish populations.

Predictors of mitochondrial DNA copy number and damage in a mercury-exposed rural Peruvian population near artisanal and small-scale gold mining: An exploratory study

Mitochondrial DNA (mtDNA) copy number (CN) and damage in circulating white blood cells have been proposed as effect biomarkers for pollutant exposures. Studies have shown that mercury accumulates in mitochondria and affects mitochondrial function and integrity; however, these data are derived largely from experiments in model systems, rather than human population studies that evaluate the potential utility of mitochondrial exposure biomarkers. We measured mtDNA CN and damage in white blood cells (WBCs) from 83 residents of nine communities in the Madre de Dios region of the Peruvian Amazon that vary in proximity to artisanal and small-scale gold mining. Prior research from this region reported high levels of mercury in fish and a significant association between food consumption and human total hair mercury level of residents. We observed that mtDNA CN and damage were both associated with consumption of fruit and vegetables, higher diversity of fruit consumed, residential location, and health characteristics, suggesting common environmental drivers. Surprisingly, we observed negative associations of mtDNA damage with both obesity and age. We did not observe any association between total hair mercury or, in contrast to previous results, age, with either mtDNA damage or CN. The results of this exploratory study highlight the importance of combining epidemiological and laboratory research in studying the effects of stressors on mitochondria, suggesting that future work should incorporate nutritional and social characteristics, and caution should be taken when applying conclusions from epidemiological studies conducted in the developed world to other regions, as results may not be easily translated. Environ. Mol. Mutagen. 60: 197-210, 2019. © 2018 Wiley Periodicals, Inc.

Behavioural and brain biomarker responses in yellowfin bream (Acanthopagrus australis) after inorganic mercury ingestion

To assess the effects of inorganic mercury ingestion on fish general behaviour and brain biochemical markers (acetylcholinesterase - AChE; lipid peroxidation - LPO; glutathione S-transferase - GST; catalase - CAT), juvenile yellowfin bream (Acanthopagrus australis) were fed mercury dosed food (low = 0.7 mg kg^-1, medium = 2.4 mg kg^-1 and high = 6 mg kg^-1) or undosed food (control = 0.2 mg kg^-1) for up to 16 days (5 replicates per treatment). Behavioural indicators, LPO levels and GST activity significantly changed overtime, but were not affected by mercury concentration. In contrast, CAT activity was higher in exposed fish in comparison to controls after 4 days, but not after 8 and 16 days. An additional depuration treatment was evaluated and fish from this treatment were less active and had significantly lower LPO levels and CAT activity than fish constantly exposed to the medium treatment. Overall, results from the present study indicate that a diet containing inorganic mercury impaired yellowfin bream growth and initially affected fish brain CAT activity, however fish were able to recover even with continuous exposure.

Antigenotoxic effect of melatonin against mercuric chloride in human peripheral blood lymphocytes

Melatonin (MLT) is an extraordinary antioxidant, which plays an important role in reducing reactive oxygen species (ROS) by scavenging them directly or indirectly. Mercury (Hg) is a heavy metal, which induces cytogenetic alterations via various mechanisms, leading to genotoxicity. It induces genotoxicity by enhancing the ROS chiefly. In the present study, the antigenotoxic effect of MLT was evaluated against mercuric chloride (HgCl₂). All experiments were conducted in vitro in peripheral blood lymphocytes. Blood cultures were exposed to various concentrations of HgCl₂ (2.63, 6.57, and 10.52 microM) for 24 h to study a range of genotoxic parameters. MLT (0.2 mM) supplementation, alone and in combination with the high concentration of Hg, was administered to blood cultures for 24 h. Genotoxic parameters, such as chromosomal aberrations (CAs; structural aberrations (chromatid gaps and breaks, chromosomal gaps and breaks) and numerical aberrations), micronuclei (MNs), and comet assay, were evaluated and analyzed using suitable statistical analysis. Hg treatment revealed a significant increase in CAs, MNs, and comet length. Co-supplementation of MLT along with Hg showed marked protection of these genotoxic end points in treated cultures. In conclusion, our findings suggest that MLT protects against Hg-induced augmentation in genotoxic indices because of its antioxidant property.

Effects of oral exposure to inorganic mercury on the feeding behaviour and biochemical markers in yellowfin bream (Acanthopagrus australis)

Mercury is a known toxic metal, but studies on the effects of inorganic mercury ingestion in aquatic organisms are scarce. The present study aimed to investigate changes in feeding behaviour and biomarkers (lipid peroxidation, acetylcholinesterase, glutathione S-transferase and catalase activities) of yellowfin bream (Acanthopagrus australis) after ingestion of inorganic mercury (control: 0.2 mg kg^-1, low: 0.7 mg kg^-1, medium: 2.4 mg kg^-1 and high: 6 mg kg^-1) over 16 days. After 4 days, exposed fish attempted feeding more often, and showed a significantly lower eating success than controls. However, these differences became less notable with longer exposure periods. Most biochemical markers varied over time, regardless of mercury treatment. However, biomarker responses to mercury were also observed, mostly with increased exposure period and were dependant on the tissue analysed. This study showed that fish can recover from initial feeding behaviour effects of inorganic mercury, but showed delayed response in tissue biomarkers.

Addressing the impact of mercury estuarine contamination in the European eel (Anguilla anguilla L., 1758) - An early diagnosis in glass eel stage based on erythrocytic nuclear morphology

The decline of the European eel (Anguilla anguilla L., 1758) population throughout Europe has been partially attributed to pollution. As glass eel estuarine migration may represent a considerable threat, the impact of mercury (Hg) contamination at this stage was evaluated through an in situ experiment (7days). Total Hg (tHg) bioaccumulation was evaluated concomitantly with erythrocytic nuclear morphology alterations: erythrocytic nuclear abnormalities assay (ENA), frequency of immature erythrocytes (IE) and the erythrocytic maturity index (EMI). The ENA results suggested a genotoxic pressure at the most contaminated sites, in line with the tHg increase. The EMI data, together with IE frequency, showed that fish exposed to high levels of Hg exhibited alterations of haematological dynamics, translated into an erythropoiesis increment. Despite the presence of these compensatory mechanisms, the present findings suggest a harmful impact of Hg on genome integrity at this early development stage, potentially affecting eels' condition and ultimately the population sustainability.

Relationship between genotoxicity and oxidative stress induced by mercury on common carp (Cyprinus carpio) tissues

Mercury is one of the most toxic metals in aquatic systems since it is able to induce neurobehavioral disorders as well as renal and gastrointestinal tract damage. The common carp Cyprinus carpio is an important species from both an ecological and economic viewpoint as it is consumed in many countries, the top producers being Mexico, China, India and Japan. The present study aimed to evaluate the relation between Hg-induced oxidative stress and genotoxicity in diverse tissues of C. carpio. Specimens were exposed to 0.01mgHg/L (the maximum permissible limit for aquatic life protection), and lipid peroxidation, protein carbonyl content and the activity of antioxidant enzymes were evaluated at 96h. Micronuclei frequency and DNA damage by comet assay were determined at 12, 24, 48, 72 and 96h. Hg induced oxidative stress and genotoxicity on exposed fish, since inhibition of antioxidant enzymes activity and increases in lipid peroxidation, DNA damage and micronuclei frequency occurred. Blood, gill and liver were more susceptible to oxidative stress, while blood were more sensitive to genotoxicity. In conclusion, Hg at concentrations equal to the maximum permissible limit for aquatic life protection induced oxidative stress and genotoxicity on C. carpio, and these two effects prove to be correlated.

The sub-cellular fate of mercury in the liver of wild mullets (Liza aurata)--Contribution to the understanding of metal-induced cellular toxicity

Mercury is a recognized harmful pollutant in aquatic systems but still little is known about its sub-cellular partitioning in wild fish. Mercury concentrations in liver homogenate (whole organ load) and in six sub-cellular compartments were determined in wild Liza aurata from two areas - contaminated (LAR) and reference. Water and sediment contamination was also assessed. Fish from LAR displayed higher total mercury (tHg) organ load as well as in sub-cellular compartments than those from the reference area, reflecting environmental differences. However, spatial differences in percentage of tHg were only observed for mitochondria (Mit) and lysosomes plus microsomes (Lys+Mic). At LAR, Lys+Mic exhibited higher levels of tHg than the other fractions. Interestingly, tHg in Mit, granules (Gran) and heat-denaturable proteins was linearly correlated with the whole organ. Low tHg concentrations in heat stable proteins and Gran suggests that accumulated levels might be below the physiological threshold to activate those detoxification fractions.

Interference of the co-exposure of mercury with silica-coated iron oxide nanoparticles can modulate genotoxicity induced by their individual exposures--a paradox depicted in fish under in vitro conditions

The study aimed to assess the genotoxic potential of silica-coated iron oxide nanoparticle functionalized with dithiocarbamate groups (IONP, 100 nm) in vitro exposure alone or its interference with mercury (Hg) co-exposure in the blood of European eel (Anguilla anguilla L.) by evaluating 8-hydroxy-2'-deoxyguanosine (8-OHdG), lipid peroxidation (LPO), and erythrocytic nuclear abnormalities (ENA). Four groups were made: (i) 2 × 10(6) erythrocytes + Roswell Park Memorial Institute-1640 (RPMI-1640) (control), (ii) 2 × 10(6) erythrocytes + IONP (2.5 mg L(-1)), (iii) 2 × 10(6) erythrocytes + Hg (50 μg L(-1)), and (iv) 2 × 10(6) erythrocytes + IONP + Hg. Blood plasma was also processed following the previous exposure conditions. Samplings were performed at 0, 2, 4, 8, 16, 24, 48, and 72 h of exposure. The results revealed significant ENA increases at both early (2, 4, 8) and late (16, 24, 48, 72) hours of exposure to IONP alone. However, IONP exposure combined with Hg co-exposure revealed no ENA increase at 2 h, suggesting that IONP-Hg complex formation is efficient to eliminate the DNA damage induced by individual exposure to IONP or Hg at early hours. Hence, the initial occurrence of antagonism between IONP and Hg was perceptible; however, at late hours of exposure, IONP was unable to mitigate the mercury-accrued negative impacts. Plasma exposure to IONP alone displayed a significant increase in 8-OHdG levels at 2 and 48 h of exposure. However, IONP in combination with Hg co-exposure revealed an increase in 8-OHdG levels at all the exposure length (except 16 h), suggesting that both IONP and Hg independently oxidized DNA. In addition, an additive effect on 8-OHdG levels at both early and late hours, and on LPO only at late hours (except 24 h), suggested that DNA is more susceptible to peroxidative damage than lipid.