Relative sensitivity of two marine bivalves for detection of genotoxic and cytotoxic effects: a field assessment in the Tamar Estuary, South West England

Partitioning of metals in the tissues and cytosolic fraction of Cerastoderma edule

The concentrations of Cd, Cu and Zn have been determined in the tissues and the cytosolic fraction of the common cockle, Cerastoderma edule, collected from sediments in the Tamar, Plym and Avon estuaries (South West, England). Metal concentrations in the tissues of C. edule from the Avon were lower than those from the Tamar and Plym, except for Cu in the digestive gland. Significant statistical relationships were only obtained between the total sedimentary metal concentrations and Cd in the body of C. edule and Cu in the digestive gland. The cytosolic fraction was extracted from each of the tissues and separated for protein analysis thereby allowing determination of the metal contents in high molecular weight (HMW) compounds, metallothionein-like proteins (MTLP) and very low molecular weight (VLMW) compounds. The digestive glands of C. edule from the Avon had relatively low concentrations of MTLP, whereas MTLP concentrations in the digestive gland of cockles from the Tamar and Plym were higher. The cytosolic fraction of C. edule had relatively low total Cd and Cu concentrations associated with MTLP, whereas Zn was preferentially associated with the HMW and the VLMW components. The results are relevant to metal distributions in C. edule and the role of cytosols in the management of metals by C. edule and other invertebrates.

Composition of deposited sediment and its temporal variation in a disturbed tropical catchment in the Kelantan river basin, Peninsular Malaysia

Pristine tropical river systems are coming under increasing pressure from the development of economic resources such as forestry and mining for valuable elements. The Lebir catchment, north eastern Malaysia, is now under development as a result of unregulated tree felling and mining for essential and rare metals. Two sediment cores, one in the upstream reaches and the other from the downstream reaches, were taken from flood prone area of the Lebir River, Malaysia, and analysed for their elemental composition by XRF, specifically Al, Si, Fe, Ca, K, Mg, Mn, V, Cu, Ni, Pb, Cr, Zn, As, Th and U. Activities of fallout radionuclides, ¹³⁷Cs and ²¹⁰Pb were also determined to from a geochronological context. The elemental concentrations in the soils were assessed in terms of their enrichment factor and Si, Ca, K, Mg, Mn, V, Cu, Ni and Zn were found not to be enriched, whereas As, Th and U had elevated enrichment factors. The Th and U were particularly enriched in the downstream core indicating inputs from a tributary that drains a catchment with known deposits of Th and possibly U. The results suggest that the growth in economic development is fostering the transport of contaminants by the major rivers which, in turn, is contaminating the riverine floodplains. This points to the need for a more integrated and holistic approach to river basin management to maintain the environmental quality of these fragile aquatic systems.

Methylmercury, Trace Metals, Organotins and Their Effects on the Qatari Mangrove Shrimp, Palaemon khori

The Qatari mangroves of Al-Khor are being increasingly exposed to a wide variety of anthropogenic pollutants due to land reclamation and urban expansion. In this study, we evaluated the lethal and genotoxic effects of methylmercury, trace metals, and organotins, assessing mortality and aneuploidy levels (abnormal number of chromosomes) in the endemic shrimp Palaemon khori under laboratory conditions. In the experimental design, two different concentrations were used for each family of contaminant (single or combined): an environmental concentration equivalent to the maximum value reported in the environment and a value ten times higher, for a period of eight weeks. Survival decreased significantly when pollutants were administrated in combination, even at environmental concentrations (as shown by Cox proportional hazards ratios): similar levels of mortality would be reached by individual type of pollutants only at ten times the environmental concentration. This critical result, under controlled lab conditions, highlights the importance of monitoring mixtures of contaminant types over single ones in the marine environment. Aneuploidy was reported in all treatments and control ranging from 5% to 19% at week four and from 7% to 21% at week eight. All treatments presented significantly higher aneuploidy levels when compared to the control. However, no significant difference was observed between the two time periods, even though 30% of the treatments could not be assessed at week eight, as not enough animals were still alive. In conclusion, the use of endemic species should be considered a valuable tool to determine local perturbations, representing a regional bioindicator of multiple environmental stressors from the initial stages of contamination.

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.

Preliminary Assessment of Stress and Genotoxicity Biomarkers in Bivalve Molluscs from the Gulf of Annaba, Algeria

The aim of this work is to assess biomarker responses to stresses caused by pollution of the marine environment in the Gulf of Annaba, using the bivalve mollusc Donax trunculus and Mytilus galloprovincialis. Males and females were collected during the summer from site 1 considered to be far from pollution sources (SM1 and SD1), site 2 (SM2 and SD2) exposed to a mixture of contaminants, and site 3 (SM3 and SD3) receiving the untreated sewage. The whole body was used for the determination of malonaldehyde (MDA), reduced glutathione (GSH) and DNA damage. The MDA concentration from site 2 of both species has indicated significant augmentation. The two bivalves from S2 and S3 have recorded significant decrease of GSH level, with the highest number of Comet scores. A significant site and sex effect was measured for the level of GSH and MDA, accompanied with a significant site effect for DNA damage. The genotoxicity seems correlated with the stress biomarkers and dependent on the effluent types.

Genomic damage in Mugil curema (Actinopterygii: Mugilidae) reveals the effects of intense urbanization on estuaries in northeastern Brazil

The largest metropolitan centers in northeastern region of Brazil are all located near the coast, and industrial, tourist, and agro-industrial activities are the principal causes of water contamination due to discharges of untreated sewage. Adverse environmental conditions can often be detected by analyzing the genetic material of organisms exposed to pollutants, and furnish an overview of environmental quality. We evaluated possible damage to the DNA of one of the fish resources most widely consumed and commercialized by coastal communities in northeastern Brazil, Mugil curema ("tainha"). Erythrocytes from M. curema were analyzed by the presence of micronuclei and by comet assay (single cell gel electrophoresis, SCGE). Statistical comparisons to both tests revealed considerably greater genomic damage in polluted estuaries than in the control site (p < 0.05), suggesting strong genotoxic impacts on the specimens evaluated, principally among those taken near localities with dense demographic and industrial development.

Evaluation of the impact of bioaccumulation of PAH from the marine environment on DNA integrity and oxidative stress in marine rock oyster (Saccostrea cucullata) along the Arabian sea coast

Marine pollution due to oil spills is of great concern globally for their impact on the health of marine ecosystems. We assessed the genotoxic effects and oxidative stress due to genotoxic pollutants accumulated from the ambient marine environment in the tissues of marine rock oyster, Saccostrea cucullata along the Arabian Sea coast around Goa, India. The extent of DNA damage in S. cucullata was determined by comet assay as variation of comet parameter: mean % tail DNA along the coast with respect to that at the reference site (Tiracol, Goa, India). In addition, the oxidative stress responses of rock oysters exposed to marine pollutants such as polycyclic aromatic hydrocarbons (PAHs) were assessed as a function of variation in antioxidant enzyme activities such as glutathione-s-transferase (GST), catalase (CAT) and superoxide dismutase (SOD) along the coast. Spearman correlation analysis showed significant correlation between different components of PAHs (viz., 2-3-PAH, 4-6-PAH and oxy-PAH) in the tissues of the rock oysters and the antioxidant enzyme activities. The antioxidant enzyme activities in S. cucullata increased with increasing concentrations of PAHs in tissues in the following order of sampling sites: Tiracol < Arambol < Betul < Velsao. Among the PAHs, oxy-PAH was found to be most predominant in causing DNA damage in S. cucullata. These results provide an insight into environmental genotoxicity and oxidative stress induced by PAHs along the Arabian Sea coast, India.

Baseline and oxidative DNA damage in marine invertebrates

Anthropogenic pollutants produce oxidative stress in marine organisms, directly or following generation of reactive oxygen species (ROS), potentially resulting in increased accumulation of DNA strand breaks quantified. The aim of this study is to quantify baseline levels of DNA strand breaks in marine species from four phyla and to assess relative sensitivity to oxidative stress as well as ability to recover. DNA strand breaks were determined using a formamidopyrimidine DNA glycosylase (Fpg)-amended comet assay in circulating cells from blue mussel (Mytilus edulis), shore crab (Carcinus maenas), sea star (Asterias rubens), and vase tunicate (Ciona intestinalis). Lymphocytes from Atlantic cod (Gadus morhua) were used as a reference. In addition to immediate analysis, cells from all species were exposed ex vivo to two concentrations of hydrogen peroxide (H₂O₂) at 25 or 250 μM prior to assay. Mean baseline DNA strand breaks were highest for cells from sea star (34%) followed by crab (25%), mussel (22%), tunicate (17%), and cod (14%). Circulating cells from invertebrates were markedly more sensitive to oxidative stress compared to cod lymphocytes. DNA strand breaks exceeded 80% for sea star, crab, and mussel cells following exposure to the lowest H₂O₂ concentration. There was no recovery for cells from any species following 1 hr in buffer. This study provides an in-depth analysis of DNA integrity for ecologically important species representing 4 phyla. Data indicate that circulating cells from invertebrates are more sensitive to oxidative stress than cells from fish as evidenced by DNA strand breaks. Future studies need to address the extent to which DNA strand breaks may exert consequences for body maintenance costs in marine invertebrates.

Exposure to tritiated water at an elevated temperature: Genotoxic and transcriptomic effects in marine mussels (M. galloprovincialis)

Temperature is an abiotic factor of particular concern for assessing the potential impacts of radionuclides on marine species. This is particularly true for tritium, which is discharged as tritiated water (HTO) in the process of cooling nuclear institutions. Additionally, with sea surface temperatures forecast to rise 0.5-3.5 °C in the next 30-100 years, determining the interaction of elevated temperature with radiological exposure has never been more relevant. We assessed the tissue-specific accumulation, transcriptional expression of key genes, and genotoxicity of tritiated water to marine mussels at either 15 or 25 °C, over a 7 day time course with sampling after 1 h, 12 h, 3 d and 7d. The activity concentration used (15 MBq L^-1) resulted in tritium accumulation that varied with both time and temperature, but consistently produced dose rates (calculated using the ERICA tool) of <20 Gy h^-1, i.e. considerably below the recommended guidelines of the IAEA and EURATOM. Despite this, there was significant induction of DNA strand breaks (as measured by the comet assay), which also showed a temperature-dependent time shift. At 15 °C, DNA damage was only significantly elevated after 7 d, in contrast to 25 °C where a similar response was observed after only 3 d. The transcription profiles of two isoforms of hsp70, hsp90, mt20, p53 and rad51 indicated potential mechanisms behind this temperature-induced acceleration of genotoxicity, which may be the result of compromised defence. Specifically, genes involved in protein folding, DNA double strand break repair and cell cycle checkpoint control were upregulated after 3 d HTO exposure at 15 °C, but significantly downregulated when the same exposure occurred at 25 °C. This study is the first to investigate temperature effects on radiation-induced genotoxicity in an ecologically relevant marine invertebrate, Mytilus galloprovincialis. From an ecological perspective, our study suggests that mussels (or similar marine species) exposed to increased temperature and HTO may have a compromised ability to defend against genotoxic stress.

Histopathological and apoptotic changes on marine mussels Mytilus galloprovincialis (Lamark, 1819) following exposure to environmental pollutants

Marine bivalve mussels, especially Mytilus species are an earlywarning system used for determining of damage caused by the various aquatic pollutions. In the present study, Mytilus galloprovincialis L. (black mussel) have been utilised as a biomonitoring organism to reveal environmental pollution in the Aliaga, Foca and Urla where located along the Izmir Coast of Turkey. Mussels were collected at these areas and gill and hepatopancreas (digestive gland) tissues were excised. mRNA expressions of initiator (caspase-2 and -8) and executioner (caspase -3/7-1, -3/7-2, -3/7-3 and -3/7-4) caspases of mussels tissues in areas exposed to pollution agent have been observed. TUNEL immunoreactivity in paralel to histopathological changes in both Aliaga and Foca areas were compared with Urla. This study is the first report to reveal the pollution with apoptotic expression on mussels in the coast of Turkey.

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.

Lysosomal membrane stability of the mussel, Mytilus galloprovincialis (L.), as a biomarker of tributyltin exposure

The effect of tributyltin (TBT) on the stability of hemocytic lysosome membranes of the mussel, Mytilus galloprovincialis, and the use thereof as a biomarker of TBT-induced stress, was investigated. Mussels were exposed to 0.1 and 1.0 µg/L tributyltin respectively for 4 weeks. Lysosomal membrane stability of hemocytes was tested weekly by means of the neutral red retention time (NRRT) assay, after which the mussel samples were analyzed for TBT content. The two exposed groups exhibited significantly increased (p < 0.05) whole body TBT concentrations with concomitant significant decreases (p < 0.05) in NRRT (R(2) values of 0.85 and 0.971 for lower and higher exposure groups, respectively). The higher exposure group showed a typical dose-response curve. For the control, no TBT was detected and NRRT remained stable. It was concluded that the NRRT assay could be considered as a useful technique, and lysosomal membrane destabilization a useful early warning and cellular biomarker of stress due to TBT exposure in M. galloprovincialis.

Evaluation of γ-radiation-induced DNA damage in two species of bivalves and their relative sensitivity using comet assay

Ionizing radiation is known to induce genetic damage in diverse groups of organisms. Under accidental situations, large quantities of radioactive elements get released into the environment and radiation emitted from these radionuclides may adversely affect both the man and the non-human biota. The present study is aimed (a) to know the genotoxic effect of gamma radiation on aquatic fauna employing two species of selected bivalves, (b) to evaluate the possible use of 'Comet assay' for detecting genetic damage in haemocytes of bivalves as a biomarker for environmental biomonitoring and also (c) to compare the relative sensitivity of two species of bivalves viz. Paphia malabarica and Meretrix casta to gamma radiation. The comet assays was optimized and validated using different concentrations (18, 32 and 56 mg/L) of ethyl methanesulfonate (EMS), a direct-acting reference genotoxic agent, to which the bivalves were exposed for various times (24, 48 and 72 h). Bivalves were irradiated (single acute exposure) with 5 different doses (viz. 2, 4, 6, 8 and 10 Gy) of gamma radiation and their genotoxic effects on the haemocytes were studied using the comet assay. Haemolymph was collected from the adductor muscle at 24, 48 and 72 h of both EMS-exposed and irradiated bivalves and comet assay was carried out using standard protocol. A significant increase in DNA damage was observed as indicated by an increase in % tail DNA damage at different concentrations of EMS and all the doses of gamma radiation as compared to controls in both bivalve species. This showed a dose-dependent increase of genetic damage induced in bivalves by EMS as well as gamma radiation. Further, the highest DNA damage was observed at 24h. The damage gradually decreased with time, i.e. was smaller at 48 and 72 h than at 24h post irradiation in both species of bivalves. This may indicate repair of the damaged DNA and/or loss of heavily damaged cells as the post irradiation time advanced. The present study reveals that gamma radiation induces single strand breaks in DNA as measured by alkaline comet assay in bivalves and comet assay serves as a sensitive and rapid method to detect genotoxicity of gamma radiation. This study further indicates that both M. casta and P. malabarica exhibit almost identical sensitivity to gamma radiation as measured by DNA damage.

Genotoxicity in two bivalve species from a coastal lagoon in the south of Portugal

DNA damage was evaluated by comet assay in the haemolymph of two bivalve species Ruditapes decussatus and Mytilus galloprovincialis from the Ria Formosa lagoon (south Coast of Portugal). Clams and mussels were sampled from sites close to each other to determine interspecific responses to similar environmental conditions, considering also seasonal and gender differences. Coupled with genotoxic effect, another damage biomarker (lipid peroxidation) was analysed to verify if the conditions that instigate DNA damage can be related with injury to cell membranes. For both species, DNA damage was low, reflecting the low levels of genotoxic contaminants in the lagoon, and no interspecific differences were found. However, seasonal differences were established for both bivalve species, reflecting higher environmental stress in summer. Regarding gender susceptibility, only clams showed differences in percentage of Tail DNA, with females more sensitive to DNA damage than males. Additionally, results for clams point out that factors responsible for LPO may not be the same as those causing genotoxicity. This study demonstrated that DNA damage is a sensitive biomarker to discriminate spatial, temporal and gender differences, being an appropriate biomarker for genotoxicity evaluation even in places of low contamination, such as the Ria Formosa lagoon.