Correlations between metal uptake in the soft tissue of Perna perna and gill filament pathology after exposure to mercury

Metallic nanoparticles affect uptake of polycyclic aromatic hydrocarbons and impacts in the Mediterranean mussels Mytilus galloprovincialis

The impact of metallic nanoparticles (NPs) on the uptake and toxicity of persistent organic pollutants by marine bivalves was assessed through a comparative laboratory study by exposing mussels to polycyclic aromatic hydrocarbon (PAHs), in the presence and absence of ZnO and TiO₂ NPs. PAHs and NPs concentration was analyzed after 14 days of exposure in mussels by GC/MS and ICP/AES. Furthermore, impact on the physiology and neurotoxicity of PAHs and NPs acting alone or in mixtures were also determined. Our results confirmed the bio-uptake of PAHs and NPs by mussels. In addition, the exposure NPs-PAHs resulted in different bio-uptake profile to that of PAHs alone. The NPs and accumulation of PAHs led to disturbance of essential metals concentration and to different impact profiles in the filtration and respiration capacities as well as in the acetylcholinesterase activity. Antagonist interactions between NPs and PAHs could occur after exposure.

Metals and co-presence of other pollutants in mussels (Perna perna) around Algoa Bay: Human consumption safety concerns

Elevated metal concentrations can become harmful to marine organisms and to humans that consume them. Metal concentrations at multiple sites around Algoa Bay, South Africa, were last investigated in the 1980s. We collected wild brown mussels (Perna perna) from seven sites around Algoa Bay, and quantified metallic elements using ICPMS. Metallic element concentrations differed significantly among the sampling sites and correlated with pollution sources at specific sites. The concentration of Pb in mussels at one site slightly exceeded South African limits. Based on the South African estimated daily intake, the target hazard quotient, and South African metal limits, mussels from Algoa Bay are safe for human consumption, except possibly from one site. However, combined with data on bisphenols and benzophenone UV filters in P. perna from the same sites, we suggest a possible health concern to consumers.

How does the brown mussel Perna perna respond to environmental pollution? A review on pollution biomarkers

The brown mussel Perna perna (Linnaeus, 1758) is a valuable resource for aquaculture in tropical and subtropical coastal regions. It presents desirable characteristics for biomonitoring, including being sessile, widely distributed and abundant, and is a filter-feeder able to accumulate several classes of pollutants (e.g., metals, hydrocarbons, among others). Mussels' biological responses to pollution exposure can be measured as biomarkers, which include alterations ranging from molecular to physiological levels, to estimate the degree of environmental contamination and its effects on biota. This full review compiles two decades (2000-2020) of literature concerning biological effects on P. perna mussel caused by environmental pollutants (i.e., metals, hydrocarbons, and emerging pollutants), considering environmental and farm-based biomonitoring. Biochemical markers related to mussels' oxidative status were efficient for the biomonitoring of metals (i.e., antioxidant enzymes associated with oxidative damage in biomolecules). Genotoxicity and cytotoxicity indicators (i.e., comet, micronucleus, and neutral red assays) provided a depiction of hydrocarbon contamination. The neutral red assay gave a time-concentration cytotoxic response to a wide range of pollutants, including emerging pollutants (e.g., pharmaceuticals and biocides) and hydrocarbons. Perna perna hemocyte parameters provided a useful approach for biocide biomonitoring. This paper summarizes useful biomarkers from molecular to physiological levels in this mussel species used to identify and quantify the degree of coastal pollution. An integrated biomarker analysis may provide a way to overcome possible biomarker variations and assess multi-polluted sites. Nevertheless, it is necessary to investigate biomarker variations according to natural factors (e.g., season and gonad maturation stage) to standardize them for trustworthy biomonitoring.

Metaplasia of respiratory and digestive tissues in the eastern oyster Crassostrea virginica associated with the Deepwater Horizon oil spill

Metaplasia is a well documented and deleterious effect of crude oil components on oysters. This reversible transformation of one cell type to another is a common response to petroleum-product exposure in molluscs. It has been shown experimentally in previous work that eastern oysters (Crassostrea virginica) exposed to petroleum products will exhibit metaplasia of digestive tissues. Here we document for the first time that wild adult oysters inhabiting coastal waters in the northern Gulf of Mexico during and in the aftermath of the Deepwater Horizon oil spill (2010) exhibited metaplasia in both ctenidial (respiratory and suspension feeding) and digestive tract tissues at significantly higher frequencies than geographic controls of C. virginica from Chesapeake Bay. Metaplasia included the loss of epithelial cilia, transformations of columnar epithelia, hyperplasia and reduction of ctenidial branches, and vacuolization of digestive tissues. Evidence for a reduction of metaplasia following the oil spill (2010-2013) is suggestive but equivocal.

Mercury interactions with algal and plastic microparticles: Comparative role as vectors of metals for the mussel, Mytilus galloprovincialis

The adsorption and desorption of Hg onto and from microplastics (MP) and microalgae (MA) were investigated, and fitted using pseudo-first-order and pseudo-second order kinetics models. Then, the potential role of MP as vector for the entrance and accumulation of Hg (MP-Hg) in comparison to natural pathways (via MA -MA-Hg-, and dissolved -WB-Hg-) was investigated in mussel. Mussels were exposed to a single dose of Hg (2375 ng ind^-1) for 4 h. Although the clearance of MP-Hg was relevant (82 %), it was lower than that of MA (95 %) and MA-Hg (94 %). The amount of the Hg accumulated and eliminated was higher in mussels exposed to MP-Hg (1417 ng Hg) than in those exposed to MA-Hg (882 ng Hg) and WB-Hg (1074 ng Hg). However, Hg accumulation was similar in the three mussel groups (≈800 ng Hg). This was related to the fast elimination of Hg still attached to MP by MP-Hg mussels. Hg was mainly accumulated in digestive gland in MA-Hg and MP-Hg mussels, and in gills in WB-Hg mussels. Overall, the results indicated that MP facilitated the entrance of Hg in mussel but also promoted Hg elimination, which could limit the toxicological risk of Hg adsorbed onto MP.

Application of Biomarker Tools Using Bivalve Models Toward the Development of Adverse Outcome Pathways for Contaminants of Emerging Concern

As contaminant exposures in aquatic ecosystems continue to increase, the need for streamlining research efforts in environmental toxicology using predictive frameworks also grows. One such framework is the adverse outcome pathway (AOP). An AOP framework organizes and utilizes toxicological information to connect measurable molecular endpoints to an adverse outcome of regulatory relevance via a series of events at different levels of biological organization. Molecular endpoints or biomarkers are essential to develop AOPs and are valuable early warning signs of the toxicity of pollutants, including contaminants of emerging concern. Ecological risk-assessment approaches using tools such as biomarkers and AOPs benefit from identification of molecular targets conserved across species. Bivalve models are useful in such approaches and integral to our understanding of ecological and human health risks associated with contaminant exposures. We discuss the value of using biomarker approaches in bivalve models to meet the demands of twenty-first-century toxicology. Environ Toxicol Chem 2020;39:1472-1484. © 2020 SETAC.

Cigarette butt leachate as a risk factor to the health of freshwater bivalve

The toxicity caused by smoking to human health has been demonstrated in several scientific studies. However, little attention has been given to damages caused to aquatic biota when cigarette butts (CB) are disposed of on water surface. Thus, the main aim of the current study is to evaluate the behavioural toxicity of cigarette butt leachates (CBL) in freshwater bivalve species Anodontites trapesialis exposed to different environmentally-relevant dilutions (CBL1x = 1.375%, CBL10x: 13.75%). There were significant CBL effects on the burrowing performance of the evaluated bivalves, after 14 exposure days. Animals exposed to CBL presented higher latency to foot emission and to start the burrowing process, as well as larger number of cycles required for burial. In addition, there were lower burrowing angle and burrowing rate index in CBL-exposed bivalves than in the unexposed ones. Chemical analyses performed on the muscle tissues of animals exposed to both CBL dilutions evidenced the bioaccumulation of several metals at high concentrations in CBL (Cr, Ni, Pb, Mn, Zn and Na); this outcome enabled associating these metals with behavioural changes observed in CBL-exposed groups. Thus, the current study firstly reports that even highly-diluted CBL concentrations can induce behavioural changes in freshwater bivalves, as well as that CBL extrapolation to natural environments can lead to several damages to the fitness of living organisms and to the dynamics of their population.

Examining the relationship between metal exposure (Cd and Hg), subcellular accumulation, and physiology of juvenile Crassostrea virginica

To assess the toxicity and accumulation (total and subcellular partitioning) of cadmium (Cd) and mercury (Hg), juvenile eastern oysters, Crassostrea virginica, were exposed for 4 weeks to a range of concentrations (Control, Low (1×), and High (4×)). Despite the 4-fold increase in metal concentrations, oysters from the High-Cd treatment (2.4 μM Cd) attained a body burden that was only 2.4-fold greater than that of the Low-Cd treatment (0.6 μM Cd), while oysters from the High-Hg treatment (0.056 μM Hg) accumulated 8.9-fold more Hg than those from the Low-Hg treatment (0.014 μM Hg). This fold difference in total Cd burdens was, in general, mirrored at the subcellular level, though binding to heat-denatured proteins in the High-Cd treatment was depressed (only 1.6-fold higher than the Low-Cd treatment). Mercury did not appear to appreciably partition to the subcellular fractions examined in this study, with the fold difference in accumulation between the Low- and High-Hg treatments ranging from 1.5-fold (heat-stable proteins) to 4.6-fold (organelles). Differences in toxicological impairments (reductions in condition index, protein content, and ETS activity) exhibited by oysters from the High-Cd treatment may be partially due to the nature of how different metals partition to subcellular components in the oysters, though exact mechanisms will require further examination.

Seawater acidification increases copper toxicity: A multi-biomarker approach with a key marine invertebrate, the Pacific Oyster Crassostrea gigas

Ocean acidification (OA) has been found to increase the release of free Cu²⁺ in seawater. However, only a handful of studies have investigated the influence of OA on Cu accumulation and cellular toxicity in bivalve species. In this study, Pacific oysters, Crassostrea gigas, were exposed to 25 μg/L Cu²⁺ at three pH levels (8.1, 7.8 and 7.6) for 14 and 28 days. Physiological and histopathological parameters [(clearance rate (CR), respiration rate (RR), histopathological damage and condition index (CI)), oxidative stress and neurotoxicity biomarkers [superoxide dismutase (SOD) and glutathione transferase (GST) activities, lipid peroxidation (LPO) and acetylcholinesterase (AChE) activity], combined with glycolytic enzyme activities [pyruvate kinase (PK) and hexokinase (HK)] were investigated in C. gigas. The bioconcentration of Cu was increased in soft tissues of Cu-exposed oysters under OA. Our results suggest that both OA and Cu could lead to physiological disturbance, oxidative stress, cellular damage, disturbance in energy metabolism and neurotoxicity in oysters. The inhibited CR, increased glycolytic enzymes activities and decreased CI suggested that the energy metabolism strategy adopted by oysters was not sustainable in the long term. Furthermore, integrated biomarker response (IBR) results found that OA and Cu exposure lead to severe stress to oysters, and co-exposure was the most stressful condition. Results from this study highlight the need to include OA in future environmental assessments of pollutants and hazardous materials to better elucidate the risks of those environmental perturbations.

Multiple-biomarker approach in the assessment of the health status of a novel sentinel mussel Brachidontes rodriguezii in a harbor area

The objective of this study is to analyze whether a combination of biomarkers at different levels of biological complexity could be used to assess the health status of a population of Brachidontes rodriguezii associated to a harbor area in Mar del Plata, Argentina. A battery of biomarkers of general stress was measured in mussels collected from impacted and non-impacted areas. This included: condition index; shell analysis; histopathological alterations; atrophy and integrity of the digestive gland tissue; changes in cell type composition of the digestive gland, and glycogen accumulation. The studied biomarkers were integrated into the Integrative Biological Response (IBR/n) index. Overall, the IBR/n indicated a higher level of stress in mussels located in the harbor area. Thus, this biomarker index is a sensitive analytical tool that could be used to classify the ecotoxicological risk in coastal sites.

Heavy metal pollution and its relation to the malformation of green mussels cultured in Muara Kamal waters, Jakarta Bay, Indonesia

Jakarta Bay has become contaminated by both organic and inorganic pollutants, including heavy metals. This study aimed to examine the effect of heavy metal pollution on green mussels cultured in Muara Kamal Waters, Jakarta Bay over seven months. In this research, the water quality was assessed, through measuring the concentrations of the heavy metals, Hg, Pb, Cd, Cr, and Sn in the water, and in the tissue of green mussels that had been cultured there for seven months. The percentage of congenital abnormalities (malformations) in the green mussels was analyzed descriptively and the relationship between the water quality, heavy metals, and green mussel malformation was studied through principal component analysis (PCA). The result showed that the heavy metals concentrations in the water and sediment exceeded the quality standard at Muara Kamal but that in other respects the water quality was quite good. The green mussels cultured there for seven months had accumulated high concentrations of heavy metals, and ±60% of them had malformations of their shells. Based on the heavy metal concentrations in their bodies, the main cause of malformations in green mussels was suspected to be Pb, Hg, and Sn. However, the result of PCA showed it was the interaction between nitrogen compounds, phosphate, turbidity, salinity, pH, as well as the heavy metals in the water that determined the green mussel abnormality.

Ultrastructural Alterations of Midgut Epithelium, But Not Greater Wing Fluctuating Asymmetry, in Paper Wasps (Polistes dominula) from Urban Environments

Polistes paper wasps can be used to monitor trace metal contaminants, but the effects of pollution on the health of these insects are still unknown. We evaluated, in a south-eastern area of Spain, whether workers of Polistes dominula collected at urban and rural sites differ in health of midgut tissue and in fluctuating asymmetry, an estimate of developmental noise. We found that wasps collected at the urban sites had abundant lead (Pb)-containing spherites, which were less visible in wasps from the rural sites. Evident ultrastructural alterations in the epithelium of the midgut of the wasps collected at the urban sites included broken and disorganized microvilli, a high amount and density of heterochromatin in the nucleus of epithelial cells, cytoplasmic vacuolization and mitochondrial disruptions. Altogether, these findings suggest a negative effect on the transmembrane transport and a less efficient transcription. On the contrary, a healthy epithelium was observed in wasps from the rural sites. These differences may be preliminarily linked with levels of lead pollution, given that wasps from urban sites had double the Pb concentrations of wasps from rural sites. Level of fluctuating asymmetry was unrelated to wasp origin, thus suggesting no link between developmental noise and Pb-driven pollution.

Detection of metal induced cytopathological alterations and DNA damage in the gills and hepatopancreas of green mussel Perna viridis from Ennore Estuary, Chennai, India

This study report the impact of heavy metals on cytopathology and DNA damage in the gills and hepatopancreas of Perna viridis collected from Ennore estuary and the Kovalam coastal waters. Principal Component Analysis (PCA) showed significant differences among all variables at the scale of plots. The ultrastructural alterations such as lack of microvilli, distorted mitochondria, electron dense particles and the presence of large mucous droplets were common in the gill and hepatopancreatic cells of mussels from Ennore estuary. However, the gill and hepatopancreatic cells of P. viridis from Kovalam revealed normal compartmentalization of cells. The percentage of tail DNA in the mussels from Ennore estuary was recorded as 12.44 and 10.14% in the gills and hepatopancreas respectively. Overall, it has been demonstrated that the Comet and cytopathological assays are useful biomarkers to assess the level of pollution and it provide reliable information on ecotoxicology and genotoxicology of coastal waters.

Assessing mercury contamination in a tropical coastal system using the mussel Perna perna and the sea anemone Bunodosoma caissarum

Total mercury concentrations in the mussel Perna perna and the sea anemone Bunodosoma caissarum were determined to assess Hg contamination in Guanabara Bay, Rio de Janeiro, Brazil, and an adjacent sea area. Concentrations in the tissues of these species were compared. Average total mercury concentrations ranged from 3.54 to 21.01 μg kg^-1 (wet wt.) in P. perna and from 4.51 to 23.19 μg kg^-1 (wet wt.) for B. caissarum. Concentrations varied according to the sampling stations. Distribution of concentrations for both species was similar along the sampling stations, and a significant correlation was observed. Results suggest that B. caissarum could be a suitable biomonitor species for mercury contamination in the study area and could be used as a complementary species for monitoring studies. Further research is, however, needed to assess how environmental conditions and other variables affect Hg concentrations in B. caissarum.

Biomarkers of environmental stress in gills of Pinna nobilis (Linnaeus 1758) from Balearic Island

In aquatic environments, bivalve molluscs are used as sentinel species for environmental biomonitoring. In this study Pinna nobilis specimens, the biggest Mediterranean bivalve, were collected in the Magaluf bay (Mallorca), a touristic location and in a pristine area of the Cabrera National Park as the control location. Histological and histochemical analysis in gills of specimens sampled from Magaluf exhibited evident tissue alterations with high presence of haemocytes. Lower acetylcholinesterase (AChE) activity and protein expression were also found in the gills of specimens collected from Magaluf compared with the control area. The determination of antioxidant enzyme activities, such as superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase, showed a higher activities of these antioxidant enzymes and total glutathione content in samples from Magaluf bay than in Cabrera. In conclusion, the present study demonstrated that human activities result in morphological tissue alterations and a reduced AChE activity in gills of P. nobilis. Moreover, these stressful environmental conditions induced an adaptive response in P. nobilis as evidenced by increased antioxidant defences and a decreased AChE activity.

CAPSULE

The human activities induce oxidative stress in P. nobilis as evidenced by increased antioxidant defences and a decreased acetylcholinesterase activity.

Neurotoxicological effects on marine mussel Mytilus galloprovincialis caged at petrochemical contaminated areas (eastern Sicily, Italy): ¹H NMR and immunohistochemical assays

The neurotoxicological potential of environmental pollution, mainly related to petrochemical activities, was investigated in marine mussel Mytilus galloprovincialis. Bivalve mollusks, particularly mussels, are widely used as sentinel organisms in biomonitoring studies for assessing the impact of anthropogenic contaminants. The gills, mainly involved in nutrient uptake, digestion, gas exchange and neuronal signaling, are the first organ to be affected by pollutants present in the external environment, and therefore were selected as the target organ for this study. Mussels from an aquaculture farm were caged at a highly polluted petrochemical area and a reference site along the Augusta coastline (eastern Sicily, Italy) for one month. A battery of biomarkers indicative of neuronal perturbations was applied on gills in order to investigate on the serotonergic (i.e. serotonin, 5-HT, and its receptor, 5-HT3R), cholinergic (i.e. acetylcholine, acetylcholinesterase, AChE, and choline acetyltransferase, ChAT), and dopaminergic systems (i.e. tyrosine and tyrosine hydroxylase, TH). Overall, impairment in the normal ciliary motility was found in mussels caged at the polluted site. Alterations in serotoninergic and cholinergic systems were revealed, with enhancement of dopaminergic neurotransmission resulting in a cilio-inhibitory effect. However, the over-expression in 5-HT3R and ChAT at cellular level may indicate an adaptive response of mussels to recover a regular physiological activity in gills. To our knowledge, this is the first study that uses (1)H NMR and immunohistochemical assays. Their concurrent use demonstrated to be sensitive and effective for assessing environmental influences on the health status of aquatic organisms, and thus suitable to be applied in ecotoxicological studies.

Impact of environmental pollution on caged mussels Mytilus galloprovincialis using NMR-based metabolomics

Metabolic responses to environmental pollution, mainly related to Hg and PAHs, were investigated in mussels. Specimens of Mytilus galloprovincialis, sedentary filter-feeders, were caged in anthropogenic-impacted and reference sites along the Augusta coastline (Sicily, Italy). The gills, mainly involved in nutrient uptake, digestion and gas exchange, were selected as target organ being the first organ to be affected by pollutants. Severe alterations in gill tissue were observed in mussels from the industrial area compared with control, while gill metabolic profiles, obtained by (1)H NMR spectroscopy and analyzed by multivariate statistics, exhibited significant changes in amino acids, energy metabolites, osmolytes and neurotransmitters. Overall, the morphological changes and metabolic disturbance detected in gill tissues may suggest that the mussels transplanted to the contaminated field site were suffering from adverse environmental condition. The concurrent morphological and metabolomic investigations as applied here result effective in assessing the environmental influences on health status of aquatic organisms.

Tissue-specific response of metallothionein and superoxide dismutase in the clam Mactra veneriformis under sublethal mercury exposure

To identify the relationship between mercury (Hg) and stress responses in the clam Mactra veneriformis, metallothionein (MT) and superoxide dismutase (SOD) mRNA expression in the digestive gland, gill, and mantle as well as MT protein content and SOD activity in the digestive gland were examined under sublethal Hg exposure at doses of 10, 20, and 40 μg/L for 21 days. The ranking of the tissues in decreasing order of their basal MvMT and MvSOD mRNA expression is as follows: digestive gland > mantle > gill > adductor muscle > foot and digestive gland > mantle > gill > foot > adductor muscle, respectively. Hg exposure significantly elevated MvMT and MvSOD mRNA transcripts in the digestive gland, gill, and mantle in a tissue-specific way. In the digestive gland, a dose-dependent increase of MvMT and MvSOD mRNA expression, stimulation of MT protein, and alteration of SOD activity were observed under Hg stress. MT protein responded later than MT mRNA to Hg exposure and no clear relationship was found between them, indicating the occurrence of posttranscriptional events. All of the results suggest that MT and SOD cooperate in resisting Hg toxicity and maintaining cellular metabolic homeostasis in M. veneriformis. MT and SOD mRNA expressions have great potential as biomarkers of Hg pollution in the aquatic environment for the studied species.

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.

Acute responses of brown mussel (Perna perna) exposed to sub-lethal copper levels: integration of physiological and cellular responses

This study examined the effect of sub-lethal copper levels on selected physiological and cellular responses of the marine bivalve Perna perna. Animals were exposed to five environmentally relevant concentrations of 12.5, 25.0, 37.5 and 50.0 μg L⁻¹ copper and metal accumulation was found to be significantly increased at the two higher copper concentrations after 24 h of exposure. Physiological responses found to increase during acute copper exposure included mucus secretion rate (at 25 and 50 μg L⁻¹ copper), nitrogen excretion rates and oxygen consumption rates (both at 25 and 50 μg L⁻¹ copper). Perna perna changed its substrate utilisation at 25, 37.5 and 50 μg L⁻¹ copper in favour of protein-based metabolism. A higher degree of ROS induced DNA damage was observed at acute exposure to 37.5 and 50 μg L⁻¹ copper. Filtration rate was unchanged during acute copper exposure. A model is proposed that integrates cellular and physiological responses to copper during short-term acute and long-term chronic exposures.

Toxicity of sodium arsenite in the gill of an economically important mollusc of India

Toxicity of arsenic was investigated in the gill of Lamellidens marginalis by exposing the animals to sublethal concentrations of sodium arsenite for a maximum period of 30 days in controlled laboratory conditions. Arsenite exposure inhibited the activities of acid phosphatase (ACP), alkaline phosphatase (ALP), glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT) and acetylcholinesterase (AChE) in a dose and time dependent manner. Depletion in cytotoxic molecule like nitric oxide (NO) and suppression of phenoloxidase (PO) activity suggests an immune compromise in the animal. Inhibition in the activities of glutathione-s-transferase (GST) and catalase (CAT) in the species indicate impairment of its vital detoxification process and elevated oxidative stress respectively. Histopathology of the gill indicates arsenite induced damage of the organ leading to its possible dysfunction. The toxic exposure ravaged the structure and impaired the functions of the gill of the animal which might restrict its proper gaseous exchange, filter feeding and elicitation of immune responses against pathogens.

Application of oxidative stress indices in natural populations of Perna viridis as biomarker of environmental pollution

Oxidative stress indices were measured in gills and digestive glands of Perna viridis collected from three coastal locations in Goa i.e., Bambolim, Marmugao Harbour and Malim. In addition to lipid peroxidation, the activities of antioxidant enzymes such as superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glutathione S-transferase and two non-enzymatic antioxidants (ascorbic acid and reduced glutathione) were investigated in order to understand their variation with respect to pollution status of the sampling locations. We observed a significant increase in lipid peroxidation and antioxidant enzymes of both the tissues at Mormugao Harbour and Malim, suggesting that the animals at these two locations are at higher level of oxidative stress as compared to those at Bambolim. Conversely, low levels of non-enzymatic antioxidants such as ascorbic acid and reduced glutathione, observed at Mormugao Harbour and Malim indicate that the animals may use these compounds to counteract stress in the tissues. This study shows that changes in lipid peroxidation, superoxide dismutase, catalase, glutathione reductase, glutathione S-transferase and reduced glutathione in tissues of P. viridis can be used as molecular biomarkers in environmental monitoring programs.

Modulation of antioxidant defences in digestive gland of Perna viridis (L.), on mercury exposures

Sub-lethal effects of mercury exposure (110th of LC(50), i.e. 0.045 mg l(-1)) for 5, 10 and 15 d was investigated on oxidative stress parameters and antioxidant defences in digestive gland of Perna viridis. In addition to this an in vitro effect of mercury single and supplemented with reduced glutathione on lipid peroxidation was studied. Increased lipid peroxidation (during first 10 days and also during in vitro exposures), protein carbonyl and hydrogen peroxides (from 5th till last day of exposure) indicate the resultant oxidative stress in the mercury exposed specimen. DNA damage (F-value) response although less distinct on 5th and 15th d, its low values on 10th d and significant correlation with hydrogen peroxide suggests the toxic role of free radicals towards DNA integrity. Superoxide dismutase, which remains low initially (5th d) and increases later suggests its immediate response against superoxide radical. Higher activities of catalase, glutathione peroxidase and glutathione reductase on 15th d and glutathione-S-tranferase from 10th d onwards suggests the adaptive behaviour of the tissue against oxyradicals. Increasing levels of non-enzymatic antioxidant molecules, such as reduced glutathione and ascorbic acid indicated its involvement in counteracting oxidative damage. Further role of reduced glutathione in reducing Hg toxicity is evident in in vitro experiments where lipid peroxidation remains low in mercury concentrations supplemented with reduced glutathione. The elevated levels of metallothionein from 5th to 10th d suggest involvement of this protein in detoxification of reactive oxygen species and toxic metal. The above results suggest that both enzymatic and non-enzymatic antioxidants play an important role in protecting cell against Hg toxicity, which can be used as a biomarker of metal contamination in aquatic environment.

Fine structure of Mytella falcata (Bivalvia) gill filaments

Bivalve filter feeders are sessile animals that live in constant contact with water and its pollutants. Their gill is an organ highly exposed to these conditions due to its large surface and its involvement in gas exchanges and feeding. The bivalve Mytella falcata is found in estuaries of Latin America, on the Atlantic as well as the Pacific Coast. It is commonly consumed, and sometimes is the only source of protein of low-income communities. In this study, gill filaments of M. falcata were characterized using histology, histochemistry and transmission electron microscopy for future comparative studies among animals exposed to environmental pollutants. Gill filaments may be divided into abfrontal, intermediate and frontal zones. Filaments are interconnected by ciliary discs. In the center of filaments, haemocytes circulate through a haemolymph vessel internally lined by an endothelium and supported by an acellular connective tissue rich in polysaccharides and collagen. The abfrontal zone contains cuboidal cells, while the intermediate zone consists of a simple squamous epithelium. The frontal zone is composed of five columnar cell types: one absorptive, mainly characterized by the presence of pinocytic vesicles in the apical region of the cell; one secretory, rarely observed; and three ciliated with abundant mitochondria. All cells lining the filament exhibit numerous microvilli and seem to absorb substances from the environment. PAS staining was observed in mucous cells in the frontal and abfrontal zones. Bromophenol blue allowed the distinction of haemocytes and detection of a glycoprotein secretion in the secretory cells of the frontal region. The characteristics of M. falcata gill filaments observed in this study were very similar to those of other bivalves, especially other Mytilidae, and are suitable for histopathological studies on the effect of water-soluble pollutants.

Trace metals in mussel shells and corresponding soft tissue samples: a validation experiment for the use of Perna perna shells in pollution monitoring

The uptake of Cr, Mn, Ni, Cu, Zn, Cd and Pb in soft tissue of Perna perna mussels and their shells has been studied in aquarium experiments in which mussels were exposed for 30 or 60 days to seawater spiked with different concentrations of these contaminants (125 and 500 microg L(-1)). Tissue samples were analyzed after acid digestion by conventional solution nebulization ICP-MS. Laser ablation ICP-MS was used for the quantitative determination of trace elements in different areas of the corresponding shells. With the exception of Mn and Zn, all other elements studied showed a significant concentration enhancements in soft tissue, with the magnitude of this enhancement following the order: Cr > Ni > Cd > Cu > Pb. A corresponding increase in most contaminants, although less pronounced, was also observed in the newly formed growth rings of mussel shells, contributing to the validation of Perna perna mussel shell as a bioindicator of toxic elements.

Valve movement response of the mussel mytilus galloprovincialis to metals (Cu, Hg, Cd and Zn) and phosphate industry effluents from Moroccan Atlantic coast

Valve activity was measured in the Mediterranean mussel Mytilus galloprovincialis in response to sublethal concentrations of four metals (Hg, Cu, Zn and Cd) and two phosphate industry effluents from the Atlantic coast of Morocco. Valve movements were monitored using a proximity inductive sensor which could display all activity figures from full closure to wide opening of the shell valves. In a 1 h exposure experiments, all metals induced a decrease in the time of normal opening and the appearance of sequences of stress behaviour, including enhanced valve adductions and complete closure at high concentrations. Mercury (tested from 5 to 75 microg Hg l(-1)) was the most toxic to the valve activity, with a threshold effective concentration at 10 microg Hg l(-1) and full valve closure occurring at 50 microg Hg l(-1). Copper (15-150 microg Cu l(-1)) showed a toxic effect starting at threshold concentration of 20 microg Cu l(-1) and induced full valve closure at 150 microg Cu l(-1). Zinc (100-500 microg Zn l(-1)) was effective in reducing the time of normal opening (threshold concentration at 100 microg Zn I(-1)) but no complete closure was recorded in any of the tested concentrations. For cadmium (1000-5000 microg Cd l(-1)), the valve activity was insensitive for exposures under 2000 microg Cd l(-1). Results for the testing of several samplings of the phosphate industry effluents (Safi and Jorf Lasfar) showed that their toxicity varied over the time. The effluent of the Jorf Lasfar plant (2-9.4%) was, however, more toxic than that of Safi (1-25%). In the light of these results, the sensitivity of the valve activity of Mytilus galloprovincialis to pollutants and its usefulness for in situ monitoring of coastal pollution in Morocco are discussed.

Proteome modifications of blue mussel (Mytilus edulis L.) gills as an effect of water pollution

The discharge of chemicals such as oil associated or not with derived products constitutes a real threat for the environment. We report here the differential expression of the blue mussel (Mytilus edulis) gill proteins corresponding to two contaminated environmental conditions: crude oil and offshore produced water. In order to evaluate and understand contaminants, effects and adaptive response of these organisms, we identified proteins using MS. The latter can be grouped into three main classes: proteins involved in the cellular structure, in metabolism, and in defence proteins.

Modulation of adenyl cyclase activity in the gills of Tapes philippinarum

Adenyl cyclase (AC) plays a pivotal role in cell signaling. The AC system of bivalves has received little attention so far, and our study has been addressed to the characterization of AC properties in the gills of T. philippinarum. The enzyme showed a Km value of 0.77 mM for ATP in the presence of 5 mM Mg2+; in the absence of agonists, it was poorly affected by GTP, while it was stimulated by GTPgammaS and GppNHp up to 14-fold and 4-fold, respectively. Similarly to other invertebrates, the enzyme activity was scarcely stimulated by forskolin. The receptor agonist serotonin (5-HT) significantly stimulated the AC activity, and the pharmacological profile of the 5-HT receptor/s was as follows: (+)butaclamol > dihydroergocryptine > methysergide > prazosin > yohimbine. The AC activity was assessed in vitro in the presence of tributyltin chloride and HgCl2, which reduced the AC activity only at the highest dose tested (10-100 microM). Our data indicate the presence of a membrane-bound AC in gill membranes of T. philippinarum, coupled to Gs proteins and to a specific class of 5-HT receptors. Such receptors show a pharmacological profile slightly different from that reported for 5-HT invertebrate receptors cloned so far.

Metal accumulation, filtration and O(2) uptake rates in the mussel Perna perna (Mollusca: Bivalvia) exposed to Hg(2+), Cu(2+) and Zn(2+)

Tissue metal concentrations, filtration and oxygen uptake rates were investigated for Perna perna (Bivalvia: Mollusca) during exposure to Hg(2+), Cu(2+) and Zn(2+) (50 microg/l for 24 days, and 24 days recovery with no metal). Hg and Cu tissue levels increased with exposure time, reaching maximum levels after 24 days (87.5 microg Hg/g dry mass and 45 microg Cu/g dry mass, respectively). Zn levels peaked after 4 days exposure (to 233 microg Zn/g dry mass) and stabilized thereafter. Accumulated metal was rapidly lost from tissues when mussels were returned to uncontaminated seawater, suggesting that tissue concentration data may be of limited use in biomonitoring situations where environmental metals fluctuate to low levels. Filtration rates fell below control rates during Hg(2+) exposure, and became elevated again during the recovery period. Cu(2+) and Zn(2+) exposure had little effect on filtration, but suppressed oxygen uptake. During recovery, oxygen uptake of Cu(2+) and Zn(2+) exposed mussels was elevated above the controls. Filtration and oxygen uptake rates were not correlated, but rather responded in different ways to metal pollution. While these physiological responses of P. perna may be of limited use in biomonitoring, they could indicate how populations may respond to marine pollution.