Protective effects of selenium on mercury-induced DNA damage in mussel haemocytes

Integrated transcriptomics and metabolomics reveal the toxic mechanisms of mercury exposure to an endangered species Tachypleus tridentatus

Mercury (Hg) pollution is threatening the health of endangered Tachypleus tridentatus whereas the toxic mechanism is still unclear. This study combined transcriptomic and metabolomics technology to reveal the toxic mechanisms of mercury (Hg 2+, 0.025 mg/L) exposing to T. tridentatus larvae for 15 days. Mercury induced cellular toxicity and cardiovascular dysfunction by dysregulating the genes related to endocrine system, such as polyubiquitin-A, cathepsin B, atrial natriuretic peptide, etc. Mercury induced lipid metabolic disorder with the abnormal increase of lysoPC, leukotriene D4, and prostaglandin E2. Cytochrome P450 pathway was activated to produce anti-inflammatory substances to reconstruct the homeostasis. Mercury also inhibited arginine generation, which may affect the development of T. tridentatus by disrupting the crucial signaling pathway. The mercury methylation caused enhancement of S-adenosylmethionine to meet the need of methyl donor. The mechanisms described in present study provide new insight into the risk assessment of mercury exposure to T. tridentatus.

The toxicity of selenium and mercury in Suaeda salsa after 7-days exposure

Mercury is one of the major pollutants in the ocean, selenium causes toxicity beyond a certain limit, but there are few comparative toxic studies between them in halophytes. The study was to investigate the toxic effects of selenium (Se⁴⁺) and mercury (Hg²⁺) in halophyte Suaeda salsa at the level of genes, proteins and metabolites after exposure for 7 days. By integrating the results of proteomics and metabolomics, the pathway changed under different treatments were revealed. In Se⁴⁺-treated group, the changed 3 proteins and 10 metabolites participated in the process of substance metabolism (amino acid, pyrimidine), citrate cycle, pentose phosphate pathway, photosynthesis, energy, and protein biosynthesis. In Hg²⁺-treated group, the changed 10 proteins and 10 metabolites were related to photosynthesis, glycolysis, substance metabolism (cysteine and methionine, amino acid, pyrimidine), ATP synthesis and binding, tolerance, sugar-phosphatase activity, and citrate cycle. In Se⁴⁺+ Hg²⁺-treated group, the changed 5 proteins an 12 metabolites involved in stress defence, iron ion binding, mitochondrial respiratory chain, structural constituent of ribosome, citrate cycle, and amino acid metabolism. Furthermore, the separate and combined selenium and mercury both inhibited growth of S. salsa, enhanced activity of antioxidant enzymes (superoxide dismutase, peroxidase and catalase), and disturbed osmotic regulation through the genes of choline monoxygenase and betaine aldehyde dehydrogenase. Our experiments also showed selenium could induce synergistic effects in S. salsa. In all, we successfully characterized the effects of selenium and mercury in plant which was helpful to evaluate the toxicity and interaction of marine pollutants.

The threshold effect between the soil bioavailable molar Se:Cd ratio and the accumulation of Cd in corn (Zea mays L.) from natural Se-Cd rich soils

There is little available information about the important interactions between selenium and cadmium (Se-Cd) in crops grown on natural Se-Cd rich soils. We investigated their interactive effects on the translocation and uptake of Se and Cd from soils to crops. Corn (Zea mays L.) roots, stems, leaves, and grains, and their corresponding rhizosphere soils were collected from naturally Se-Cd rich areas in Wumeng Mountain, Guizhou, China. The Se and Cd levels were determined in the soils, roots, stems, leaves, and grains. Soil bioavailable Se and Cd were also determined. The low soil bioavailable molar ratios for Se and Cd (Se:Cd) (≤0.7) improved Cd accumulation in the plants. However, relatively high Se:Cd molar ratios (>0.7) in the soils prevented Cd from entering the plants, but the effect of the soil Se:Cd on Se accumulation in corn was not significant. The strong anion exchange-high performance liquid chromatography-inductively coupled plasma mass spectroscopy (SAX-HPLC-ICP-MS) chromatograms showed that Se-Cd complexes occurred in the leaves, which likely indicated that direct interactions between Se and Cd happened there. The results suggested that thresholds for soil bioavailable Se:Cd molar ratios played a role in the interaction between Se and Cd in corn under natural conditions.

The Protective Role of Selenium Against AFB1-Induced Liver Apoptosis by Death Receptor Pathway in Broilers

Aflatoxin B1 (AFB₁) is the most toxic among the mycotoxins and causes detrimental health effects on the liver of human and animals. Selenium (Se) plays an important role in protection of various animal species against numerous notorious toxic agents. The present study is designed to explore the protective effects of Se against AFB₁-induced liver pathogenesis by the methods of histopathology, flow cytometry, quantitative real-time polymerase chain reaction (qRT-PCR), and biochemical analysis. A total of 312, 1-day-old healthy Cobb-500 broilers were randomly divided into four groups and fed with basal diet (control group), 0.6 mg/kg AFB₁ (AFB₁ group), 0.4 mg/kg Se (+ Se group), and 0.6 mg/kg AFB₁ + 0.4 mg/kg Se (AFB₁ + Se group) for 21 days, respectively. Our results showed that 0.4 mg/kg Se supplement in broiler's diets could alleviate the AFB₁-induced histological lesions in the liver. The apoptosis analysis by flow cytometry showed that 0.4 mg/kg Se ameliorated the AFB₁-induced apoptosis in the liver. Moreover, the mRNA expression levels of Fas, TNF-α, FAS-associated death domain, TNF receptor-associated death domain, TNF receptor-associated factor 2, caspase 10, caspase 8, B cell lymphoma 2, IκB kinase, X-linked inhibitor of apoptosis protein, caspase 9, and caspase 3 analyzed by qRT-PCR demonstrated that 0.4 mg/kg Se could relieve the impact caused by AFB₁ to these parameters. The biochemical analyses of activities of CAT, GSH-Px and SOD, hydroxyl ion scavenging and contents of MDA and GSH in liver cells also indicated that 0.4 mg/kg Se has positive effect on AFB₁-induced oxidative stress in the liver. In conclusion, Se could relieve AFB₁-induced apoptosis by the molecular regulation of death receptors pathway in the liver of broilers. The outcomes from the present study may lead to a better understanding of the nature of selenium's essentiality and its protective roles against AFB₁.

Comet assay in ecogenotoxicology: Applications in Mytilus sp

The comet assay is a sensitive technique to detect DNA damage caused by exposure to genotoxic chemical and physical agents and is widely used in ecotoxicology. The assay has been applied in aquatic species, mainly fish and bivalves, in field biomonitoring programs and in experimental studies. The aim of the present study was to retrieve and review the published evidence to define the role of the comet assay in the assessment of genotoxic pollutants. The study focused on the application of the test in Mytilus sp, used as a sentinel organism. Twenty-one biomonitoring studies, carried out in wild and in transplanted mussels, were evaluated. An increase of the comet parameters in animals from polluted areas with respect to the controls was observed in the majority of the studies with a large variability (frequency ratio:1.2-14.5) associated with types and extent of exposure to pollutants. Three studies out of 21 reported a lack of response. Heavy metals, polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB) and pesticides were the main types of chemicals detected in sediments and/or mussel tissues from polluted areas. Twenty-nine laboratory studies were retrieved showing the sensitivity of the comet assay in detecting DNA damage in mussels exposed to the most relevant pollutants and mixtures of relevant contaminants, such as pharmaceuticals, anti-fouling agents or crude oil. The comet test also appeared to be a suitable approach to detect the genotoxic effects of nanoparticles. In some studies problems in the interpretation of data or discrepancies between the results from different laboratories were noted. Critical steps in experimental protocol and characterization of pollution, environmental variables such as temperature, salinity, food availability, physiological and pathological status of the animals are important factors which should be controlled and considered in the analysis of the results.

Effects of Selenium on Mercury Bioaccumulation in a Terrestrial food Chain from an Abandoned Mercury Mining Region

Few reports of the relationship exist between mercury (Hg) and selenium (Se) from locations of severe Hg contamination in terrestrial environments. Here, we report the concentrations of Hg and Se as well as Se:Hg molar ratios in biotic samples collected from a region with a long history of Hg mining. Nitrogen isotopes (δ¹⁵N) were analyzed to confirm the trophic levels. Results showed that bird feathers at the top trophic level exhibited the highest Hg concentrations, while the lowest concentrations were found in herbivorous insects, demonstrating a significant biomagnification across the food chain. In contrast, herbivorous insects of different types (generalists vs. specialized rice pests) exhibited both the highest and the lowest concentrations of Se, indicating a lack of biomagnification. Indeed, Se was correlated positively with Hg when Se:Hg ratios were greater than one, suggesting Se:Hg molar ratios can be a controlling influence on Hg in terrestrial organisms.

Application of a new targeted low density microarray and conventional biomarkers to evaluate the health status of marine mussels: A field study in Sardinian coast, Italy

In the present study, we investigated the health status of marine mussels (Mytilus galloprovincialis) caged and deployed at three different sites on the Sardinian coastline characterized by different levels of contamination: Fornelli (F, the reference site), Cala Real (CR), and Porto Torres (PT). A new low density oligonucleotide microarray was used to investigate global gene expression in the digestive gland of mussels. Target genes were selected to cover most of the biological processes involved in the stress response in bivalve mollusks (e.g. DNA metabolism, translation, immune response, cytoskeleton organization). A battery of classical biomarkers was also employed to complement the gene expression analyses. Chemical analysis revealed higher loads of heavy metals (Pb and Cu) and total polycyclic aromatic hydrocarbons (PAHs) at PT compared to the other sites. In mussels deployed at CR, functional genomics analysis of the microarray data rendered 78 differentially expressed genes (DEGs) involved in 11 biological processes. Animals exposed at PT had 105 DEGs that were characterized by the regulation of 14 biological processes, including mitochondrial activity, adhesion to substrate, DNA metabolism, translation, metal resistance, and cytoskeleton organization. Biomarker data (lysosomal membrane stability, lysosomal/cytoplasm volume ratio, lipofuscin accumulation, metallothionein content, micronucleus frequency, and cytoskeleton alteration) were in trend with transcriptomic output. Biomarker data were integrated using the Mussel Expert System (MES), allowing defining the area in which the presence of chemicals is toxic for mussels. Our study provides the opportunity to adopt a new approach of integrating transcriptomic (microarray) results with classical biomarkers to assess the impact of pollutants on marine mussels in biomonitoring programs.

Association of textile industry effluent with mutagenicity and its toxic health implications upon acute and sub-chronic exposure

Complex industrial discharges pose certain risks to the ecosystem. This study was aimed at identifying acute and sub-chronic toxicological effects of the textile industry wastewater. The textile wastewater was evaluated for the metals and organic pollutants by atomic absorption spectrophotometer and GC-MS respectively. In vitro genotoxicity and mutagenicity were assessed by Comet assay in peripheral lymphocytes isolated from Ovis aries and Ames test in Salmonella typhimurium strains TA-100 and 102 respectively. Physiological and behavioral changes along with systemic toxicity were determined in Rattus norvegicus albinus following acute and sub-chronic exposure. High amount of heavy metals such as Cr, Pb, Hg, As, and Cd were detected in textile wastewater. Organic pollutants such as 25-deacetoxy cucurbitacin-b, E-14-Hexadecenal, 11-Tricosene, and phthalates were also found. In vitro genotoxicity assessment in lymphocytes showed statistically significant DNA damaging potential of textile wastewater. Textile wastewater also showed significantly higher (p˂ 0.05) mutagenic potential in Salmonella TA-100 and TA-102 strains than sodium azide and 2-amino anthracycline. Acute exposure of textile wastewater to Rattus norvegicus was associated with several physiological changes and behavioral symptoms. Sub-chronic exposure of textile wastewater in Rattus norvegicus instigated the degeneration and necrosis of epithelial cells in renal tubules, hydropic degeneration and necrosis of hepatocytes, peri-bronchiolar infiltration and emphysema of the alveoli, and the degradation of myocardial cells. This study concludes that the textile wastewater may cause genotoxicity and mutagenicity, result in physiological and behavioral changes upon acute exposure, and inflict various pathological lesions upon sub-chronic exposure.

Mercury (II) impairs nucleotide excision repair (NER) in zebrafish (Danio rerio) embryos by targeting primarily at the stage of DNA incision

Mercuric ion (Hg²⁺) is the most prevalent form of inorganic Hg found in polluted aquatic environment. As inhibition of DNA damage repair has been proposed as one of the mechanisms of Hg²⁺-induced genotoxicity in aquatic animals and mammalian cells, this study explored the susceptibility of different stages of nucleotide excision repair (NER) in zebrafish (Danio rerio) embryos to Hg²⁺ using UV-damaged DNA as the repair substrate. Exposure of embryos at 1h post fertilization (hpf) to HgCl₂ at 0.1-2.5μM for 9h caused a concentration-dependent inhibition of NER capacity monitored by a transcription-based DNA repair assay. The extracts of embryos exposed to 2.5μM Hg²⁺ almost failed to up-regulate UV-suppressed marker cDNA transcription. No inhibition of ATP production was observed in all Hg²⁺-exposed embryos. Hg²⁺ exposure imposed either weak inhibitory or stimulating effects on the gene expression of NER factors, while band shift assay showed the inhibition of photolesion binding activities to about 40% of control in embryos treated with 1-2.5μM HgCl₂. The damage incision stage of NER in zebrafish embryos was found to be more sensitive to Hg²⁺ than photolesion binding capacity due to the complete loss of damage incision activity in the extracts of embryos exposed to 1-2.5μM Hg²⁺. NER-related DNA incision was induced in UV-irradiated embryos based on the production of short DNA fragments matching the sizes of excision products generated by eukaryotic NER. Pre-exposure of embryos to Hg²⁺ at 0.1-2.5μM all suppressed DNA incision/excision in UV-irradiated embryos, reflecting a high sensitivity of DNA damage incision/excision to Hg²⁺. Our results showed the potential of Hg²⁺ at environmental relevant levels to disturb NER in zebrafish embryos by targeting primarily at the stage of DNA incision/excision.

DNA double-strand breaks in incubating female common eiders (Somateria mollissima): Comparison between a low and a high polluted area

Alterations in the genetic material may have severe consequences for individuals and populations. Hence, genotoxic effects of environmental exposure to pollutants are of great concern. We assessed the impact of blood concentrations of persistent organic pollutants (POPs) and mercury (Hg) on DNA double-strand break (DSB) frequency, in blood cells of a high-exposed Baltic, and lower exposed Arctic population of common eiders (Somateria mollissima). Furthermore, we examined whether the genotoxic response was influenced by antioxidant concentration (plasma total glutathione (tGSH) and total antioxidant capacity) and female body mass. The DNA DSB frequency did not differ between the two populations. We found significant positive relationships between Hg and DNA DSB frequency in Baltic, but not in Arctic eiders. Although both p,p'-DDE and PCB 118 had a lesser effect than Hg, they exhibited a positive association with DNA DSB frequency in Baltic eiders. Antioxidant levels were not important for the genotoxic effect, suggesting alternative mechanisms other than GSH depletion for the relationship between Hg and DNA DSBs. Hence, the Baltic population, which is considered to be endangered and is under the influence of several environmental stressors, may be more susceptible to genotoxic effects of environmental exposure to Hg than the Arctic population.

The interactive effects of mercury and selenium on metabolic profiles, gene expression and antioxidant enzymes in halophyte Suaeda salsa

Suaeda salsa is the pioneer halophyte in the Yellow River Delta and was consumed as a popular vegetable. Mercury has become a highly risky contaminant in the sediment of intertidal zones of the Yellow River Delta. In this work, we investigated the interactive effects of mercury and selenium in S. salsa on the basis of metabolic profiling, antioxidant enzyme activities and gene expression quantification. Our results showed that mercury exposure (20 μg L(-1)) inhibited plant growth of S. salsa and induced significant metabolic responses and altered expression levels of INPS, CMO, and MDH in S. salsa samples, together with the increased activities of antioxidant enzymes including SOD and POD. Overall, these results indicated osmotic and oxidative stresses, disturbed protein degradation and energy metabolism change in S. salsa after mercury exposures. Additionally, the addition of selenium could induce both antagonistic and synergistic effects including alleviating protein degradation and aggravating osmotic stress caused by mercury.

Evaluation of the toxic potential of calcium carbide in the third instar larvae of transgenic Drosophila melanogaster (hsp70-lacZ)Bg(9)

In the present study the toxic potential of calcium carbide (CaC2) was studied on the third instar larvae of transgenic Drosophila melanogaster (hsp70-lacZ)Bg(9). The third instar larvae were exposed to 2, 4, 8, 16 and 32×10(-3)g/ml of CaC2 in diet for 24h. The results reveal that the dose 2×10(-3)g/ml was not toxic but the remaining doses showed a dose dependent significant increase in the hsp70 expression, β-galactosidase activity, tissue damage, oxidative stress markers (lipid peroxidation and protein carbonyl content), glutathione-S-transferase activity, expression of Caspase 3 and 9, apoptotic index and DNA damage (midgut cells). A significant reduction as compared to control group in total protein, glutathione content and acetylcholinesterase activity was also observed. The Inductively Coupled Plasma Atomic Emission Spectroscopy analysis (ICPAES) reveals the presence of copper, iron, sodium, aluminium, manganese, calcium, nickel and mercury. The toxic effects of CaC2 in the present study may be attributed to the impurities present in it.

Investigation of olive mill wastewater (OMW) ozonation efficiency with the use of a battery of selected ecotoxicity and human toxicity assays

The effects of olive mill wastewater (OMW) on a battery of biological assays, before and during the ozonation process, were investigated in order to assess ozone's efficiency in removing phenolic compounds from OMW and decreasing the concomitant OMW toxicity. Specifically, ozonated-OMW held for 0, 60, 120, 300, 420, 540min in a glass bubble reactor, showed a drastic reduction of OMW total phenols (almost 50%) after 300min of ozonation with a concomitant decrease of OMW toxicity. In particular, the acute toxicity test primarily performed in the fairy shrimp Thamnocephalus platyurus (Thamnotoxkit F™ screening toxicity test) showed a significant attenuation of OMW-induced toxic effects, after ozonation for a period of 120 and in a lesser extent 300min, while further treatment resulted in a significant enhancement of ozonated-OMW toxic effects. Furthermore, ozonated-OMW-treated mussel hemocytes showed a significant attenuation of the ability of OMW to cause cytotoxic (obtained by the use of NRRT assay) effects already after an ozonation period of 120 and to a lesser extent 300min. In accordance with the latter, OMW-mediated oxidative (enhanced levels of superoxide anions and lipid peroxidation by-products) and genotoxic (induction of DNA damage) effects were diminished after OMW ozonation for the aforementioned periods of time. The latter was also revealed by the use of cytokinesis block micronucleus (CBMN) assay in human lymphocytes exposed to different concentrations of both raw- and ozonated-OMW for 60, 120 and 300min. Those findings revealed for a first time the existence of a critical time point during the OMW ozonation process that could be fundamentally used for evaluating OMW ozonation as a pretreatment method of OMW.

Genotoxic potency of mercuric chloride in gill cells of marine gastropod Planaxis sulcatus using comet assay

In vivo and in vitro exposures were used to investigate the genotoxicity of mercuric chloride (HgCl2) to the marine snail, Planaxis sulcatus. The comet assay protocol was validated on gill cells exposed in vitro to hydrogen peroxide (H2O2, 0-50 μM). Snails were exposed in vivo for 96 h to HgCl2 (10, 20, 50, and 100 μg/l). Our results showed significant concentration-dependent increase in the tail DNA (TDNA) and olive tail moment (OTM) in exposed snails for all doses compared with controls. In vitro exposure to HgCl2 (10-100 μg/l) resulted in significantly higher values for TDNA at all concentrations. Our results showed that DNA damage increased in the gill cell with increasing exposure time. This study demonstrates the usefulness of comet assay for detection of DNA damage after exposure to HgCl2 and the sensitivity of marine snail P. sulcatus as a good candidate species for metal pollution.

Applications of biological tools or biomarkers in aquatic biota: A case study of the Tamar estuary, South West England

Biological systems are the ultimate recipients of pollutant-induced damage. Consequently, our traditional reliance on analytical tools is not enough to assess ecosystem health. Biological responses or biomarkers are therefore also considered to be important tools for environmental hazard and risk assessments. Due to historical mining, other anthropogenic activities, and its conservational importance (e.g. NATURA sites, SACs), the Tamar estuary in South West England is an ideal environment in which to examine applications of such biological tools. This review presents a thorough and critical evaluation of the different biological tools used in the Tamar estuary thus far, while also discussing future perspectives for biomarker studies from a global perspective. In particular, we focus on the challenges which hinder applications of biological tools from being more readily incorporated into regulatory frameworks, with the aim of enabling both policymakers and primary stakeholders to maximise the environmental relevance and regulatory usefulness of such tools.

Combined chemical and toxicological evaluation of leachate from municipal solid waste landfill sites of Delhi, India

In the present study, landfill leachate of three landfill sites of Delhi, India, was toxico-chemically analyzed for human risk assessment. Raw leachate samples were collected from the municipal solid waste (MSW) landfills of Delhi lacking liner systems. Samples were characterized with relatively low concentrations of heavy metals while the organic component exceeded the upper permissible limit by up to 158 times. Qualitative analysis showed the presence of numerous xenobiotics belonging to the group of halogenated aliphatic and aromatic compounds, polycyclic aromatic hydrocarbons (PAHs), phthalate esters, and other emerging contaminants. Quantitative analysis of PAHs showed that the benzo(a)pyrene-toxic equivalence quotient (BaP-TEQ) ranged from 41.22 to 285.557 ng L(-1). The human risk assessment methodology employed to evaluate the potential adverse effects of PAHs showed that the cancer risk level was lower than the designated acceptable risk of 10(-6). However, significant cytotoxic and genotoxic effects of leachates on HepG2 cell line was observed with MTT EC50 value ranging from 11.58 to 20.44 % and statistically significant DNA damage. Thus, although the leachates contained low concentrations of PAHs with proven carcinogenic potential, but the mixture of contaminants present in leachates are toxic enough to cause synergistic or additive cytotoxicity and genotoxicity and affect human health.

Mercury levels assessment in hair of riverside inhabitants of the Tapajós River, Pará State, Amazon, Brazil: fish consumption as a possible route of exposure

The study present evaluated the levels of mercury (Hg) and methylmercury (MeHg) in hair samples of people from Barreiras community, riverside inhabitants of the Tapajós River (Pará, Brazil), an area impacted by clandestine gold mining, as well as we analyzed the levels of Hg and Se (selenium) in nine fish species (carnivores and non-carnivorous) from the Tapajós River, which stand out as the main species consumed by riverside inhabitants, to evaluate a relationship between frequency of fish consumption and Hg concentration, and also to evaluate possible mechanisms of fish protection (or non-protection) to Hg exposure by Se. Furthermore we analyze the water quality to evaluate the environmental trophic state, fact responsible by creating conditions that can potentiate the effects of toxic mercury. Concentrations of Hg and MeHg were analyzed in hair samples of 141 volunteers in different age band. Of those, 84.40% of samples present values above the threshold for biological tolerance, which is 6.00μgg(-1) of total Hg in hair. Total Hg, in men there was a variation of 2.07-24.93μgg(-1), while for women the variation was 4.84-27.02μgg(-1). Consequently, the level of MeHg in men presented a variation of 1.49-19.57μgg(-1), with an average of 11.68μgg(-1), while with women the variation was from 3.73 to 22.35μgg(-1), with an average of 10.38μgg(-1). In fish species, Hg concentrations in carnivorous species had an average of 0.66μgg(-1), higher than that permitted by current legislation, ranging from 0.30 to 0.98μgg(-1), while the non-carnivorous species have values below the recommended by the legislation averaging 0.09μgg(-1), ranging between 0.02 and 0.44μgg(-1). For Se in fish, show that among carnivores, the contents of Se ranged between 0.18 and 0.54μgg(-1) with a mean of 0.34μgg(-1), while for non-carnivores these values were of the order of 0.16-0.56μgg(-1), with an average of 0.32μgg(-1). In surface water quality variables at the sampling points all showed values in accordance with the range established by current legislation. In this regard, the results provided by this study, while not conclusive, are strong indicators that despite not having been shown the relationship between the concentration of mercury in hair and feeding habits along the Tapajós River basin communities showed that a plausible correlation exists between levels of mercury and selenium in fish. This fact may serve as a subsidy to research human health, because in the Amazon, there is still a lot to examine with regards to the full understanding of the Se cycle.

Comparison of intermittent and continuous exposures to inorganic mercury in the mussel, Mytilus edulis: accumulation and sub-lethal physiological effects

Aquatic organisms are often subject to intermittent exposure to pollutants in real ecosystems. This study aimed to compare mercury accumulation and the physiological responses of mussels, Mytilus edulis during continuous and intermittent exposure to the metal. Mussels were treated in a semi-static, triplicated design to either a control (no added Hg) or 50 µg l(-1) Hg as HgCl2 in continuous (daily) or intermittent (2 day exposure, 2 days in clean seawater alternately) exposure for 14 days. A time-dependent increase in Hg accumulation was observed in the continuous exposure, while the intermittent treatment showed step-wise changes in Hg concentrations with the exposure profile, especially in the gills. At the end of the experiment, tissue Hg concentrations were significantly increased in the continuous compared to the intermittent exposure for digestive gland (4 fold), gonad and remaining soft tissue (>2 fold), but not for the gill and adductor muscle. There was no observed oxidative damage at the end of the experiment as measured by the thiobarbituric acid reactive substances (TBARS) concentrations in tissues from all treatments. However, total glutathione was significantly decreased in the gill and digestive gland of both the continuous and intermittent exposure by the end of the experiment. The neutral red retention ability of the haemocytes was not affected, but total haemocyte counts were significantly decreased (<2 fold) in the intermittent compared to the continuous exposure. Histopathological examinations showed less pathology in the gill, but more inflammation in the digestive gland of mussels for the intermittent compared to the continuous exposure. Overall, the results showed that Hg accumulation from intermittent exposure was less than that of the continuous exposure regime, but the sub-lethal responses are sometimes more severe than expected in the former.

Environmental and human risk assessment of landfill leachate: an integrated approach with the use of cytotoxic and genotoxic stress indices in mussel and human cells

The present study investigates leachate hazardous effects on marine biota and human cells, with the use of a battery of assays, both under in vivo and in vitro conditions. According to the results, mussels exposed for 4 days to 0.01 and 0.1% (v/v) of leachate showed increased levels of DNA damage and micronuclei (MN) frequencies in their hemocytes. Similarly, enhanced levels of DNA damage were also observed in hemocytes treated in vitro with relevant concentrations of leachate, followed by a significant enhancement of both superoxide anions (O₂(-)) and lipid peroxidation products (malondialdehyde/MDA). On the other hand, human lymphocyte cultures treated with such a low concentrations of leachate (0.1, 0.2 and 1%, v/v), showed increased frequencies of MN formation and large MN size ratio, as well as decreased cell proliferation, as indicated by the use of the cytokinesis block micronucleus (CBMN) assay and Cytokinesis Block Proliferation Index (CBPI) respectively. These findings showed the clear-cut genotoxic and cytotoxic effects of leachate on both cellular types, as well as its potential aneugenic activity in human lymphocytes.

Monitoring of DNA damage in haemocytes of freshwater mussel Sinanodonta woodiana sampled from the Velika Morava River in Serbia with the comet assay

This study was undertaken to investigate the potential of the freshwater mussel Sinanodonta woodiana for detection of genotoxic pollution of the environment. Study was performed at two sites in the Velika Morava River, from May 2010 to February 2011. The alkaline comet assay on haemocytes was used, and the olive tail moment (OTM) was chosen as a measure of DNA damage. The specimens held on acclimation under controlled laboratory conditions for 10d were used as a control. Chemical analysis revealed the presence of phosphates and increased concentrations of zinc, copper and nickel at both sites during the entire sampling period. The values of OTM in mussels collected from the environment, significantly correlated with the concentration of zinc (r=0.6248), temperature (r=0.7006) and dissolved oxygen (r=0.7738). Seasonal variations in genotoxic response were observed, with the highest OTM values obtained during summer months. Preliminary results of the in vitro study indicated the effect of water temperature on genotoxic response to zinc and cadmium in S. woodiana suggesting that the presence of genotoxic pollutants during months with lower temperature could be under-estimated. Obtained results indicate that S. woodiana could be a valuable tool for active biomonitoring of aquatic environments and emphasizes the importance of seasonal genotoxic monitoring with this organism.

Effects of selenium supplemented diets on growth and condition indexes in juvenile red swamp crayfish, Procambarus clarkii

Effects of selenium diets (Se, 0.3 and 1.2mgkg(-1)) on juvenile red swamp crayfish Procambarus clarkii were observed for eight weeks. Growth, condition factors and Se levels in exoskeleton and hepatopancreas for both sexes and diets were evaluated at three endpoints. The specific growth rate (SGR) showed a faster, but not statistically significant growth in Se exposed specimens. Se levels were higher in exoskeleton and hepatopancreas of both Se exposed males and females, when compared to controls. The abdomen-total weight relationship (Tw/B) showed no significant differences between Se exposed and control groups. A constant decline of HI values was recorded in both Se exposed sexes and the same trend was observed in control males. Se exposed females evidenced lower HI after 4 and 8 weeks when compared to controls. Therefore, evident reductions of the health indicator values HI suggested that selenium can deplete the hepatopancreas energy reserves, mainly in juvenile male crayfish.

Selenium inhibits the phytotoxicity of mercury in garlic (Allium sativum)

To investigate the influence of selenium on mercury phytotoxicity, the levels of selenium and mercury were analyzed with inductively coupled plasma-mass spectrometry (ICP-MS) in garlic tissues upon exposure to different dosages of inorganic mercury (Hg(2+)) and selenite (SeO3(2-)) or selenate (SeO4(2-)). The distributions of selenium and mercury were examined with micro-synchrotron radiation X-ray fluorescence (μ-SRXRF), and the mercury speciation was investigated with micro-X-ray absorption near edge structure (μ-XANES). The results show that Se at higher exposure levels (>1mg/L of SeO3(2-) or SeO4(2-)) would significantly inhibit the absorption and transportation of Hg when Hg(2+) levels are higher than 1mg/L in culture media. SeO3(2-) and SeO4(2-) were found to be equally effective in reducing Hg accumulation in garlic. The inhibition of Hg uptake by Se correlates well with the influence of Se on Hg phytotoxicity as indicated by the growth inhibition factor. Elemental imaging using μ-SRXRF also shows that Se could inhibit the accumulation and translocation of Hg in garlic. μ-XANES analysis shows that Hg is mainly present in the forms of Hg-S bonding as Hg(GSH)2 and Hg(Met)2. Se exposure elicited decrease of Hg-S bonding in the form of Hg(GSH)2, together with Se-mediated alteration of Hg absorption, transportation and accumulation, may account for attenuated Hg phytotoxicity by Se in garlic.

Protective and antioxidant role of selenium on arsenic trioxide-induced oxidative stress and genotoxicity in the fish hepatoma cell line PLHC-1

In vitro models are useful tools for rapid screening for toxicity, elucidation of mechanisms of toxicity, and understanding complex interactions among environmental toxicants. These evaluations may provide useful information for ecological evaluations if the relationship between in vitro and in vivo effects is established. The present study was undertaken to evaluate the protective effect of selenium on arsenic trioxide (As(2) O(3) )-induced cytotoxicity, DNA damage, and apoptosis. N-acetylcysteine (NAC), a free radical scavenger, was used to determine the involvement of reactive oxygen species (ROS) in As(2) O(3) -induced DNA damage and apoptosis. Poeciliopsis lucida hepatocellular carcinoma line 1 (PLHC-1) cells were pretreated with selenium (1, 5, and 10 µM) and NAC (50 and 100 µM) for 2 h. After pretreatment, cells were exposed to 100 µM of As(2) O(3) for 10-, 20-, and 40-h intervals. The As(2) O(3) exposure promoted extensive DNA damage and apoptosis compared to control, while selenium- and NAC-pretreated cells improved cell survival rate against As(2) O(3) -induced cell death. Improved survival likely resulted from increasing glutathione peroxidase activity and reduction of ROS formation, reduction of mitochondrial membrane potential damage, DNA damage, and caspase-3 activity. During As(2) O(3) exposure, selenium played the same role as NAC. The authors conclude that As(2) O(3) -induced DNA damage and apoptosis are mediated by oxidative stress and selenium and that, although toxic at higher concentrations, selenium provides significant protection against As(2) O(3) effects in PLHC-1 cells.

Organic selenium supplementation increases mercury excretion and decreases oxidative damage in long-term mercury-exposed residents from Wanshan, China

Due to a long history of extensive mercury mining and smelting activities, local residents in Wanshan, China, are suffering from elevated mercury exposure. The objective of the present study was to study the effects of oral supplementation with selenium-enriched yeast in these long-term mercury-exposed populations. One hundred and three volunteers from Wanshan area were recruited and 53 of them were supplemented with 100 μg of organic selenium daily as selenium-enriched yeast while 50 of them were supplemented with the nonselenium-enriched yeast for 3 months. The effects of selenium supplementation on urinary mercury, selenium, and oxidative stress-related biomarkers including malondialdehyde and 8-hydroxy-2-deoxyguanosine were assessed. This 3-month selenium supplementation trial indicated that organic selenium supplementation could increase mercury excretion and decrease urinary malondialdehyde and 8-hydroxy-2-deoxyguanosine levels in local residents.

Fluctuating estuarine conditions are not confounding factors for the Comet assay assessment of DNA damage in the mussel Mytilus edulis

The Comet assay is finding increasing application as a biomarker assay for the genotoxic potential of contaminants in field transplantation experiments involving mussels. Especially in estuaries, habitats that are of particular concern, environmental variables, such as salinity, can vary significantly. Although hinted at in the literature, there is a lack of clarification as to whether changes in salinity or emersion-induced hypoxia have the potential to alter background DNA damage in mussels, thus masking the extent of potential genotoxic effects following exposure to environmental contaminants. The present study exposed Mytilus edulis in the laboratory to static salinities (25, 50, 75, and 100 %) for 72 h. Mussels were also subjected to simulated tidal cycles, including periods of emersion, for 72 h. None of these treatments resulted in a significant change in the level of DNA damage expressed as % tail DNA. These experiments demonstrate that salinity, within the limits of the concentrations tested, and temporary emersion are not confounding factors for Comet assay data derived from M. edulis.

Interspecific and intraspecific variation in selenium:mercury molar ratios in saltwater fish from the Aleutians: potential protection on mercury toxicity by selenium

A number of factors affect the consumption risk from mercury in fish, including mercury levels, seasonal patterns of mercury concentrations, human consumption patterns, and sensitive populations (e.g. pregnant women, fetuses, young children, and yet unknown genetic factors). Recently the protective effects of selenium on methylmercury toxicity have been publicized, particularly for saltwater fish. We examine levels of mercury and selenium in several species of fish and seabirds from the Aleutians (Alaska), determine selenium:mercury molar ratios, and examine species-specific and individual variation in the ratios as a means of exploring the use of the ratio in risk assessment and risk management. Variation among species was similar for mercury and selenium. There was significant interspecific and intraspecific variation in selenium:mercury molar ratios for fish, and for birds. The mean selenium:mercury molar ratios for all fish and bird species were above 1, meaning there was an excess of selenium relative to mercury. It has been suggested that an excess of selenium confers some protective advantage for salt water fish, although the degree of excess necessary is unclear. The selenium:mercury molar ratio was significantly correlated negatively with total length for most fish species, but not for dolly varden. Some individuals of Pacific cod, yellow irish lord, rock greenling, Pacific halibut, dolly varden, and to a lesser extent, flathead sole, had selenium:mercury ratios below 1. No bird muscle had an excess of mercury (ratio below 1), and only glaucous-winged gull and pigeon guillemot had ratios between 1 and 5. There was a great deal of variation in selenium:mercury molar ratios within fish species, and within bird species, making it difficult and impractical to use these ratios in risk assessment or management, for fish advisories, or for consumers, particularly given the difficulty of interpreting the ratios.

Merging nano-genotoxicology with eco-genotoxicology: an integrated approach to determine interactive genotoxic and sub-lethal toxic effects of C(60) fullerenes and fluoranthene in marine mussels, Mytilus sp

Whilst there is growing concern over the potential detrimental impact of engineered nanoparticles (ENPs) on the natural environment, little is known about their interactions with other contaminants. In the present study, marine mussels (Mytilus sp.) were exposed for 3 days to C(60) fullerenes (C(60); 0.10-1 mg l(-1)) and a model polycyclic aromatic hydrocarbon (PAH), fluoranthene (32-100 μg l(-1)), either alone or in combination. The first two experiments were conducted by exposing the organisms to different concentrations of C(60) and fluoranthene alone, in order to determine the effects on total glutathione levels (as a measure of generic oxidative stress), genotoxicity (DNA strand breaks using Comet assay in haemocytes), DNA adduct analyses (using (32)P-postlabelling method) in different organs, histopathological changes in different tissues (i.e. adductor muscle, digestive gland and gills) and physiological effects (feeding or clearance rate). Subsequently, in the third experiment, a combined exposure of C(60) plus fluoranthene (0.10 mg l(-1) and 32 μg l(-1), respectively) was carried out to evaluate all endpoints mentioned above. Both fluoranthene and C(60) on their own caused concentration-dependent increases in DNA strand breaks as determined by the Comet assay. Formation of DNA adducts however could not be detected for any exposure conditions. Combined exposure to C(60) and fluoranthene additively enhanced the levels of DNA strand breaks along with a 2-fold increase in the total glutathione content. In addition, significant accumulation of C(60) was observed in all organs, with highest levels in digestive gland (24.90 ± 4.91μg C(60) g(-1) ww). Interestingly, clear signs of abnormalities in adductor muscle, digestive gland and gills were observed by histopathology. Clearance rates indicated significant differences compared to the control with exposure to C(60), and C(60)/fluoranthene combined treatments, but not after fluoranthene exposure alone. This study demonstrated that at the selected concentrations, both C(60) and fluoranthene evoke toxic responses and genetic damage. The combined exposure produced enhanced damage with additive rather than synergistic effects.

Oxidative stress, genotoxicity and histopathology biomarker responses in mullet (Mugil cephalus) and sea bass (Dicentrarchus labrax) liver from Bizerte Lagoon (Tunisia)

The aim of the study was to evaluate the impact of environmental contaminants on oxidative stress, genotoxic and histopathologic biomarkers in liver of mullet (Mugil cephalus) and sea bass (Dicentrarchus labrax) collected from a polluted coastal lagoon (Bizerte Lagoon) in comparison to a reference site (the Mediterranean Sea). Antioxidant enzyme activities were lower in fish from the polluted site compared with fish from the reference site, suggesting deficiency of the antioxidant system to compensate for oxidative stress. DNA damage was higher in both fish species from the contaminated site indicating genotoxic effects. The liver histopathological analysis revealed alterations in fish from Bizerte Lagoon. Hepatocytes from both fish species featured extensive lipid-type vacuolation and membrane disruption. Results suggest that the selected biomarkers in both fish species are useful for the assessment of pollution impacts in coastal environments influenced by multiple pollution sources.

Chemical and toxicological characterization of the bricks produced from clay/sewage sludge mixture

The present study aimed to characterize chemical properties of clay bricks containing 20 % of sewage sludge. After detection of potentially hazardous metals, we simulated precipitation exposure of such material to determine the amount of heavy metals that could leach out of the bricks. Metals, such as copper, zinc, nickel, cobalt, chromium, etc., were detected in leachate in low concentrations. Moreover, human peripheral blood lymphocytes were exposed to brick leachate for 24 h in order to evaluate its possible negative impact on human cells and genome in vitro. Cytotoxicity tests showed no effect on human peripheral blood lymphocytes viability after exposure to brick's leachate. On the contrary, the alkaline comet assay showed slight but significant increase in DNA damage with all three parameters tested. As we might predict, interactions of several heavy metals in low concentrations could be responsible for DNA damaging effect. In that manner, our findings suggest that leachates from sewage sludge-produced bricks may lead to adverse effects on the exposed human population, and that more stabile bricks should be developed to minimize leaching of heavy metals into the environment. Bricks with lower percentage of the sludge may be one of the solutions to reduce the toxic effect of the final product.

Tissue-specific expression of p53 and ras genes in response to the environmental genotoxicant benzo(α)pyrene in marine mussels

Marine mussels can develop hemeic and gonadal neoplasia in the natural environment. Associated with these diseases are the tumor suppressor (TS) p53 and the proto-oncogene ras coded proteins, both of which are highly conserved among molluscs and vertebrates. We report, for the first time, tissue-specific expression analysis of p53 and ras genes in Mytilus edulis by means of quantitative RT-PCR. A tissue-specific response was observed after 6 and 12 days exposure to a sublethal concentration of a model Polycyclic Aromatic Hydrocarbon (PAH), benzo(α)pyrene (B(α)P). This sublethal concentration (56 μg/L) was selected based on an integrated biomarker analysis carried out prior to gene expression analysis, which included a 'clearance rate' assay, histopathological analysis, and DNA strand break measurements. The results indicated that the selected concentration of B(α)P can lead to the induction of DNA strand breaks, tissue damage, and expression of tumor-regulating genes. Both p53 and ras are expressed in a tissue-specific manner, which collaborate with tissue-specific function in response to genotoxic stress. The integrated biological responses in Mytilus edulis strengthen the use of this organism to investigate the fundamental mechanism of development of malignancy in invertebrate which could be translated to other organisms including humans.

DNA damage in Gammarus fossarum sperm as a biomarker of genotoxic pressure: intrinsic variability and reference level

In the perspective of a biomonitoring application for assessing genotoxicity of freshwater ecosystems, the Comet assay has recently been developed on spermatozoa in the amphipod Gammarus fossarum, in order to propose a sensitive and reliable genotoxicity biomarker in an ecologically relevant freshwater species. The appropriate use of a genotoxicity biomarker requires good knowledge of its basal level and its natural variability related to intrinsic biotic and environmental abiotic factors. We propose a procedure for which the lowest biomarker variability related to methodological and intrinsic biotic factors is obtained and a reference value of biomarker basal response taking into account its spatio-temporal changes has been defined. A strong impact of spermatogenesis status and exposure time on the response to genotoxicant pressure was observed. These reports led us to select a standard organism, i.e., the mature male gammarid in precopula. No effect of temperature and conductivity on baseline DNA damage was observed in the laboratory for the tested range (6-24 °C and 300/600 μS cm⁻¹). Similarly, no spatio-temporal change relative to season or the physico-chemical characteristics of the water was recorded during the field survey. On the basis of these results, a reference level with maximal threshold values has been proposed for the standard gammarid.

Olive oil mill wastewater toxicity in the marine environment: alterations of stress indices in tissues of mussel Mytilus galloprovincialis

This study investigated the impact of olive mill wastewater (OMW) as a pollutant of the marine environment, via the detection of stress indice alterations in mussels Mytilus galloprovincialis. Due to the absence of data concerning the levels of OMW in the receiving waters, mortality test (96h) was first performed in order to estimate the range of OMW concentration where no mortality occurs. OMW concentrations ranging from 0.01 to 0.1% (v/v) showed no increased mortality and thus were used for the determination of pre-pathological alterations in tissues of mussels. In particular, mussels exposed to either 0.1 or 0.01% (v/v) OMW for 5 days showed significant alterations of stress indices in their tissues. Specifically, decreased neutral red retention (NRR) assay time values, inhibition of acetylcholinesterase (AChE) activity, as well as a significant increase of micronucleus (MN) frequency and DNA damage were detected in haemolymph/haemocytes and gills, compared with values measured in tissues of control mussels. The results of the present study showed that OMW disposal into the marine environment could induce pre-pathological alterations in marine organisms, before severe disturbances, such as disease, mortality, or population changes occur.

Selenium in water enhances antioxidant defenses and protects against copper-induced DNA damage in the blue mussel Mytilus edulis

Selenium and copper are naturally occurring elements in the environment that have important roles in cellular function. Selenium is known for its role in antioxidant defense, whereas copper is a redox-active metal capable of acting as a pro-oxidant. We investigated the effects of short term selenium (Na(2)SeO(3)) supplementation (4 μg/L for 3 days) on antioxidant parameters of the blue mussel, Mytilus edulis, and its possible protective effects against a subsequent copper (CuSO(4)) exposure (56 μg/L for 3 days). Selenium supplementation caused a 4-fold increase in glutathione levels in gills. The activity of selenium-dependent glutathione peroxidase was modulated by selenium in gills (2-fold increase) and also in cell-free haemolymph (40% increase). Copper exposure produced decreases in protein thiol levels (35%) and in thioredoxin reductase activity (60%) in gills and induced an increase in DNA damage in haemocytes (70% increase in % tail DNA observed using the comet assay). The decrease in thioredoxin reductase activity may constitute a mechanism of copper toxicity in bivalves, warranting further investigation. Pre-treatment with selenium largely prevented these deleterious effects of copper on protein thiols, thioredoxin reductase activity and DNA damage. The results suggest that induction of key antioxidant defenses such as glutathione and selenium-dependent glutathione peroxidase, as a result of selenium supplementation, may play an important role in protection of aquatic organisms against oxidative stress.

Golden grey mullet and sea bass oxidative DNA damage and clastogenic/aneugenic responses in a contaminated coastal lagoon

Several xenobiotics or their metabolites have redox-cycling properties and potential to induce oxidative stress and DNA damage. The current work aimed to study, under environmental conditions, oxidative DNA damage (8-hydroxy-2'-deoxyguanosine (8-OHdG)) and its association with chromosomal damage measured as erythrocytic nuclear abnormalities (ENAs), in Liza aurata and Dicentrarchus labrax, caught at a costal lagoon (Ria de Aveiro, Portugal) having sites with different contamination profiles. The quantified parameters were also used to assess the lagoon's environmental status. Five critical sites were assessed comparing to a reference site. L. aurata displayed higher 8-OHdG levels and ENAs frequency, respectively, at Laranjo and Vagos. D. labrax 8-OHdG levels were higher at the sites where quantification was possible whereas no differences were found in terms of ENAs. No correlation was found in both species between 8-OHdG and ENAs. Despite no direct linkage between the two biomarkers was found, this study demonstrates species and site dependent genotoxic responses.

Trace element accumulation in bivalve mussels Anodonta woodiana from Taihu Lake, China

Data are presented for 13 trace metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Ag, Cd, and Pb) in 38 bivalve mussels Anodonta woodiana from four separate sites (Huzhou, Dapu, Sansandao, and Manshan) around the Taihu Lake of China. All elemental concentrations generally ranked in decreasing order, Mn > Fe > Zn > As ≈ Cu ≈ Cd ≈ Se > Pb > Mo ≈ Ag, except that Cr, Co, and Ni were not detected. Anodonta woodiana was able to bioaccumulate essential Mn and toxic Cd to the extremely high level of 19,240 and 53 mg/kg dry weight, respectively. Geographical differences in the concentrations of trace elements were usually significant between sampling sites except for As and Pb, and the mussels from Sanshandao site had mostly accumulated or were contaminated with essential and toxic elements. The residue level of Cd in A. woodiana from the Sanshandao and Manshan sites appeared to be even higher than those of the essential elements Cu and Se, and exceeded the corresponding maximum residue limits of China. The present study provides the most recent information on trace element bioaccumulation or contamination in Taihu Lake and, further, suggests that A. woodiana can be used as a suitable bioindicator for inland water environmental monitoring.

DNA damage and metal accumulation in four tissues of feral Octopus vulgaris from two coastal areas in Portugal

The alkaline comet assay has been employed for the first time to estimate the basal DNA damage in the digestive gland, gills, kidney and gonads of Octopus vulgaris. Octopuses were captured in two coastal areas adjacent to the cities of Matosinhos (N) and Olhão (S), Portugal. The area of Matosinhos is influenced by discharges of the Douro River, city of Porto, industries and intensive agriculture, while Olhão is an important fisheries port. Previous works point to contrasting metal availability in the two coastal areas. Among the analysed tissues digestive gland presented the highest levels of Zn, Cu, Cd and Pb. Tissues of specimens from Matosinhos exhibited high levels of Cd and from Olhão enhanced Pb concentrations. The DNA damages in digestive gland, gills and kidney were more accentuated in specimens from Matosinhos than from Olhão, suggesting a stronger effect of contaminants. Elevated strand breakages were registered in digestive gland, recognised for its ability to store and detoxify accumulated metals. The DNA damages in kidney, gills and gonads were lower, reflecting reduced metal accumulation or efficient detoxification. The broad variability of damages in the three tissues may also mirror tissue function, specific defences to genotoxicants and cell-cycle turnover.

Involvement of Na+/H+ exchanger and respiratory burst enzymes NADPH oxidase and NO synthase, in Cd-induced lipid peroxidation and DNA damage in haemocytes of mussels

This study investigated cadmium-induced oxidative and genotoxic effects, such as lipid peroxidation and disturbance of DNA integrity (DNA damage) in haemocytes of mussel Mytilus galloprovincialis and the possible involvement of Na+/H+ exchanger (NHE), and/or the main enzymes of respiratory burst, NADPH oxidase and nitric oxide (NO) synthase, in the induction of Cd toxic effects. In order to verify the role of either NHE, or NADPH oxidase and NO synthase in Cd-mediated toxicity, inhibitors such as ethyl-N-isopropyl-amiloride (EIPA), diphenyleneiodonium chloride (DPI) and NG-nitro-L-arginine methyl ester (L-NAME) were used in each case. Moreover, phorbol-myristate acetate (PMA), a well-known protein kinase C (PKC)-mediated NADPH oxidase and NO synthase stimulator, as well as hydrogen peroxide (H2O2), a well-known genotoxic agent, was also used for elucidating the modulation of signaling molecules within cells, thus leading to the induction of lipid peroxidation and DNA damage. The results of the present study showed that micromolar concentrations of Cd (0.05-50 microM) could enhance both lipid peroxidation and DNA damage, possible via a PKC-mediated signaling pathway with the involvement of NHE, thus leading to the induction of NADPH oxidase and NO synthase activity, since inhibition of either NHE, or NADPH oxidase and NO synthase activity, significantly attenuates Cd-induced toxic effects in each case.

Contamination of bivalve haemolymph samples by adductor muscle components: implications for biomarker studies

Haemolymph samples and haemocytes collected via the adductor muscles of bivalve molluscs are extensively used in ecotoxicological studies. Withdrawal of haemolymph from mussels, Mytilus edulis, via the posterior adductor muscle, may lead to contamination with the intracellular contents of adductor myocytes. Lysopine dehydrogenase (LyDH) activity, an adductor myocyte marker, was used to investigate the impact of this potential contamination on levels of total glutathione, glutathione peroxidase (GPx) and acetylcholinesterase (AChE) measured in cell-free haemolymph. The mean glutathione content of cell-free haemolymph from 28 mussels was 3.2 +/- 1.8 microM (mean +/- SD). There was a linear relationship (slope = 0.28 +/- 0.03 min; mean +/- SE; P < 0.0001, n = 28) with haemolymph LyDH levels suggesting that at least some of the glutathione measured in cell-free haemolymph had arisen from contamination. Haemolymph LyDH activity was significantly higher in samples extracted using larger diameter needles, and also in samples where there had been some difficulty in the extraction. Exposure of mussels to oxidative stress using 40 microg l(-1) Cu for 5 days resulted in a 1.7 fold increase in glutathione (P = 0.033), but no increase (P = 0.810) in LyDH activity in adductor muscle. This was reflected in a similar increase in the slope of a plot of cell-free haemolymph glutathione versus LyDH activity (P = 0.011), consistent with both of these having originated from the adductor muscle. Cell-free haemolymph GPx and AChE activities also correlated with LyDH activity (Spearman rank correlation coefficients of 0.531 (P = 0.0068) and 0.537 (P = 0.0062), respectively, n = 27) suggesting that these also arise from contamination of the haemolymph. For GPx there was a significant linear relationship (P = 0.025) with haemolymph LyDH levels consistent with both enzymes originating from the myocytes. However, there was hyperbolic relationship (P = 0.0004) between haemolymph AChE and LyDH activities. It appears that this is because the AChE originates from a different compartment to the LyDH, i.e. cholinergic neuromuscular junctions in the adductor muscle. We conclude that it would be prudent, when considering the possibility of using a biomarker in cell-free haemolymph from bivalve molluscs, to check whether contamination could be an issue.