Metallothioneins in Arctic bivalves

Effects of an Endocrine Disruptor Triclosan on Ruditapes decussatus: Multimarker and Histological Approaches

The aim of this work was to study the ecotoxicological effects of an endocrine disruptor triclosan on the clam Ruditapes decussatus. The bivalves were exposed to three concentrations of this biocide (C1 = 100 ng/L, C2 = 200 ng/L and C3 = 500 ng/L) for three and seven days. The impact was assessed at the gills and digestive glands, through activities of an antioxidant defense biomarker (Gluthatione S-Transferase, GST), a damage biomarker (Malondialdehyde, MDA), and a neurotoxicity biomarker (Acetylcholinesterase, AChE). Furthermore, histological traits were approached in different organs to evaluate any possible alteration induced by triclosan. It appears from this study that both gills and digestive glands responded discernibly to triclosan and effects were concentration-dependent. The stressed clams showed a significant increase in their GST and MDA activities in gills and digestive glands compared to controls for both time slots considered. In turn, the AChE activity was clearly inhibited in both organs in a time dependent way. The histological study made it possible to observe several structural pathologies caused by triclosan in the gills and the digestive gland. These alterations consisted mainly of inflammatory reactions, malformations of the lamellae and fusion of the gill filaments, degeneration of the connective tissue, and the erosion of the gill cilia with the appearance of certain severe alterations (cell necrosis and apoptosis), which can thus cause a malfunction of the gills and eventually lead to a reduction in oxygen consumption and a disruption of the osmoregulation for bivalves. Alterations in the digestive gland have also been detected, mainly by epithelial alterations, thinning of the tubules, and alteration of the basal cell membrane which can impair the ability of clams to absorb food. At germinal cells, several damages were observed in the oocytes which probably disturbed the reproductive function and the fertility of the clams. The damages observed in female gonads were caused by the cytolysis of a large number of oocytes through autophagy and necrosis at 200 ng triclosan/L. Moreover, at 500 ng triclosan/L, hemocytic infiltration was observed in acini and apoptotic bodies reflected in the fragmentation of more than 90% of oocytes.

Nickel oxide nanoparticles induce genotoxicity and cellular alterations in the ground beetle Blaps polycresta (Coleoptera: Tenebrionidae)

Nickel nanoparticles (Ni-NPs) have advantageous applications in the industry; however, little is known of their adverse effects on biological tissues. In the present study, the ground beetle Blaps polycresta was employed as a sensitive indicator for nickel oxide nanoparticles (NiO-NPs) toxicity. Adult male beetles were injected with six dose levels of NiO-NPs (0.01, 0.02, 0.03, 0.04, 0.05, and 0.06 mg/g body weight). Mortality was reported daily over 30 days under laboratory conditions to establish an LD₅₀. Nickel was detected in the testicular tissues of the beetles using X-ray analysis and transmission electronic microscopy. Beetles treated with the sublethal dose of 0.02 mg/g were selected to observe molecular, cellular, and subcellular changes. Gene transcripts of HSP70, HSP90, and MT1 were found to be increased >2.5-, 1.5-, and 2-fold, respectively, in the treated group compared with the controls. Decreased gene expression of AcPC01, AcPC02, and AcPC04 (≤1.5-, ≤2-, and < 2.5-fold, respectively, vs. controls) also were reported in the treated group. Under light microscopy, various structural changes were observed in the testicular tissues of the treated beetles. Ultrastructure observations using scanning and transmission electron microscopy showed severe damage to the subcellular organelles as well as deformities of the heads and flagella of the spermatozoa. Therefore, the present study postulated the impact of NiO-NPs in an ecological model.

Seasonal variation of biomarker responses in Cantareus aspersus and physic-chemical properties of soils from Northeast Algeria

This study belongs to the biomonitoring program of soil qualities using a land snail, Cantareus aspersus, as bioindicator. The metal-soil contamination in some sites (National Park of El Kala (NPK), El Bouni, Sidi Amar, Nechmaya, and Guelma) located in Northeast Algeria were determined during two seasons (winter and spring 2015, 2016). Glutathione (GSH) content and acetylcholinesterase (AChE) activity were significantly decreased in snails collected during spring as compared with those noticed during winter under bioclimate change. In addition, a significant difference between various sites was observed, depending on the proximity to pollution sources. The significant variation of biomarker levels is a function of the physic-chemical properties of soils when they positively correlated with EC, H, and OM, and negatively correlated with all metallic elements. Moreover, Fe and Al₂O₃ are the most abundant in all the sites, and the most polluted site was found as that of El Bouni, followed by Sidi Amar, Nechmaya, and Guelma, since NPK is the less polluted site and considered a reference site. The tested biomarkers are sensitive oxidative parameters in snails exposed to pollution correlated significantly with the soil physic-chemical properties and metallic element contents in soil. Indeed, C. aspersus could be used as sentinel species in field monitoring of Mediterranean climate regions.

Acute Toxicity and Hazardous Concentrations of Zinc to Native Freshwater Organisms Under Different pH Values in China

Zinc bioavailability to aquatic organisms varies greatly under different pH values. In the present study, five native species in China and four common international test species were selected to investigate the influence of changing pH on acute zinc toxicity. The results showed that the higher trophic levels exhibited increasing sensitivity to zinc as pH decreased. However, when the pH value was between 8 and 11, the acute toxicity of zinc was relatively constant. In addition, by using a species-sensitivity distribution (SSD) method, the short-term hazardous concentrations of zinc at different pH values (based on the 5th percentiles of the pH-specific SSDs) were determined to be 17.26 µg/L (pH 4), 48.31 µg/L (pH 5), 80.34 µg/L (pH 6) and 230.6 µg/L (pH 7), respectively. The present study provides useful information for deriving water quality criteria and assessing the risks of metals in the near future.

A baseline study of the metallothioneins induction and its reversibility in Neohelice granulata from the Bahía Blanca Estuary (Argentina)

Contamination by heavy metals causes serious effects in marine systems. Nowadays, the combination of chemical and biological data is recommended in monitoring programs. Metallothioneins (MT) are early-warning signals of metal exposure and are widely used in biomonitoring. The present research evaluates the heavy metals levels in sediments and the MT synthesis in the crab Neohelice granulata from the Bahía Blanca Estuary (BBE). Then, the recovery capabilities of N. granulata followed by a depuration phase are assessed. Results demonstrate a slow decline in the level of metals in the study area. In relation to MT, female crabs showed elevated MT when compared to males. Furthermore, MT synthesis diminished after the depuration phase. These data constitute the first MT information in organisms from the BBE and may be considered as baseline for future studies in this matter. Although pollution level found was low, further biomonitoring considering both types of data is recommended.

Effect of metal accumulation on metallothionein level and condition of the periwinkle Littorina littorea along the Scheldt estuary (the Netherlands)

Metal (i.e. Ag, As, Ca, Cd, Co, Cu, Mn, Pb and Zn) and metallothionein (MT) concentrations in the soft tissue of Littorina littorea were measured along the heavily polluted Western Scheldt (WS) and relatively clean Eastern Scheldt (ES) estuary. Along the WS metal and MT levels in periwinkles reflected the known downstream decreasing pollution gradient. Surprisingly in ES animals As, Mn and Zn concentrations decreased from east to west reflecting past pollution. Compared to the WS metal concentrations of ES periwinkles were significantly lower and both estuaries were maximally discriminated from each other based on their Cd soft tissue concentration using a canonical discriminant analysis. Furthermore, no overall difference was found in MT levels among animals from both estuaries. Using previously obtained condition data (i.e. dry/wet weight ratio and lipid content) the relation between soft tissue metal concentration (i.e. Cd, Cu and Zn) and fitness indicators (i.e. MT and condition data) was examined using a canonical correlation analysis. Periwinkles with a high metal load (i.e. Cd and Zn) also had high MT levels but were in a relatively poor condition.

Comparison of bioaccumulation of metals and induction of metallothioneins in two marine bivalves (Mytilus edulis and Mya arenaria)

The St. Lawrence maritime estuary (Quebec, Canada) is subjected to mixed inputs of pollutants and the study of the induction of metallothionein in species of economic and ecologic importance such as Mytilus edulis and Mya arenaria was pertinent to assess the consequences of pollution in this northern estuary. Bivalves from an area devoid of anthropogenic influences but characterized by background metal contamination (Franquelin) were actively transplanted within this location and in a site contaminated by urban, industrial and endogenous pollutants, Baie-Comeau (Baie-des-Anglais). Spatial differences in metal concentrations were shown between sites. Cu and Zn concentrations were higher in mussels from Baie-des-Anglais at the beginning of the transfer and after 1 and 2 months. In clams, Zn concentrations were significantly higher in gills and digestive gland tissues for organisms transplanted in Baie-des-Anglais thus showing that spatio-temporal variations of metal concentrations were different between the two species studied. Mussels and clams partitioning of metals were shown to be different depending of the species, metal and/or tissue studied. In mussels, Cd and Cu concentrations decreased in both organs and both groups after the 3-month transfer in the polluted site. In mussels, total metal and metallothionein (MT) concentrations were positively correlated in digestive gland while in clams a positive correlation was only observed in gills.

In situ potential use of metallothionein as a biomarker of cadmium contamination in Ruditapes decussatus

Cadmium (Cd) and metallothionein (MT) concentrations were analysed in the gills and digestive gland of clams Ruditapes decussatus collected from two sites of the Gulf of Gabès (Tunisia) which differ by their degree of pollution. The effect of biotic (maturity stages, protein, sex and body mass) and abiotic factors (temperature, salinity, site and season) on Cd and MT concentrations showed that in the reference site "Bordj d'Ungha" physiological changes caused by gamete development and maturity contributed more to changes in MT concentrations than the bioavailable Cd concentrations; whereas, in the contaminated site "El Hofra", MT induction responded to raised Cd bioavailabilities rather than to physiological changes. With a view to using MTs as metal exposure biomarker in monitoring program, our results show that the analysis in the digestive gland seem to be more relevant than in gills, and that males appear as the most promising candidates compared to females in the determination of this biomarker.

New metallothionein assay in Scrobicularia plana: heating effect and correlation with other biomarkers

Metallothionein (MT) and other biomarker levels were measured in Scrobicularia plana clams to assess pollution of the Guadalquivir Estuary possibly affected by metals released from Aznalcóllar pyrite mine in 1998. After optimizing reagent concentrations for monobromobimane derivatization, MT levels were quantified by reversed-phase high-performance liquid chromatography coupled to fluorescence detection (RP-HPLC-FD) in heated or unheated digestive gland extracts and compared to those obtained by differential pulse polarography (DPP). MT content assayed by RP-HPLC-FD in unheated samples was higher than that obtained by DPP and correlated better with metals and anti-oxidant activities. MT assay by RP-HPLC-FD in unheated extracts would be preferable for assessing metal pollution, due to its greater sensitivity and specificity. In addition to MT induction, glyoxalase II inhibition was well correlated with metal contents. Our results suggest that metals at the estuary do not originate from Aznalcóllar spill, but from those carried along by the river and deposited at its concave bank.

Neuroendocrine disruption in Mya arenaria clams during gametogenesis at sites under pollution stress

This study examined the neuroendocrine status of clams on intertidal mud flats in the St. Lawrence Estuary and Saguenay Fjord areas during late gametogenesis. The impact of pollution was determined by a test battery of early stress markers (metallothioneins, heme levels, glutathione S-transferase activity), tissue damage (lipid peroxidation and DNA damage) and morphologic characteristics (age, soft-tissue weight ratio and growth index). Neuroendocrinal status was examined by tracking serotonin and dopamine metabolism, monoamine adenylate cyclase activity in synaptosomes, monoamine oxidase and arachidonate cyclooxygenase activities in relation to gametogenetic activity: pyrimidine synthesis, (aspartate transcarbamoylase activity or ATC), vitellogenin-like proteins and gonado-somatic index. The results show that clam soft tissue weights were reduced at sites close to harbours and higher at sites near domestic wastewater outfalls. The age-to-length ratio of clams was generally higher at impacted sites, suggesting reduced growth. The biomarkers of stress or damage confirmed that oxidative stress, DNA damage, metallothioneins and glutathione S-transferase activity were significantly increased at varying degrees, at the polluted sites. Vitellogenin-like proteins and gametogenetic activity were significantly increased at sites influenced by domestic wastewaters. Furthermore, the clams were still in active gametogenesis and not ready for spawning, as indicated by the concordance of the serotonin/dopamine ratio with vitellogenin-like proteins and pyrimidine synthesis. However, gonadal cyclooxygenase activity was increased at polluted sites and significantly correlated with most of the stress biomarkers, suggesting that the clams were in a state of inflammation rather than at the spawning stage. Finally, a multivariate analysis revealed that the sites were readily discriminated with high efficiency (>71%) and that both neuroendocrine physiological markers and stress responses were identified as the major components, thus explaining the global physiological response of the clams. We conclude that the effects of pollution compromise the clams' health status and that the initiation of gametogenesis in environments contaminated by municipal wastewaters or harbours contributes to the toxic effects of pollution.

Lysosomal responses and metallothionein induction in the blue mussel Mytilus edulis from the south-west coast of Iceland

It has recently been emphasized that high levels of inorganic and organic micropollutants (particularly organometals, POPs and PAHs) may be present in coastal waters at high latitudes, stressing the need to evaluate the effects of contaminants on marine organisms from sub-arctic zones. With this aim, specimens of the blue mussel Mytilus edulis were sampled in polluted and reference areas along the south-west coast of Iceland in July 2004. Samples were collected from the intertidal zone at three sites in Reykjavik harbour which are differently exposed to contaminants, and at three reference coastal sites, two located along the Reykjanes Peninsula and the third one on the northern part of Hvalfjordur fiord. Lipofuscin content, neutral lipid accumulation and lysosomal enlargement were evaluated in digestive cells from cryostat sections of the mussel hepatopancreas, and quantified by automated image analysis. Metallothionein induction was also determined in the same tissue. Results indicate that mussels from the inner part of Reykjavik harbour, which is the most sheltered and most influenced by extensive shipping traffic, were the worst affected, with the highest values in neutral lipids, lipofuscin and lysosomal swelling. At the other two harbour sites, mussels exhibited lower values, similar to those observed in organisms collected in Hvalfjordur fiord and in bay of Osar. Mussels from Kuagerdi had the lowest values.

Morphological and cytological responses of ammonia (foraminifera) to copper contamination: implication for the use of foraminifera as bioindicators of pollution

The effect of graded concentrations of copper was analyzed at morphological and cytological levels on two species of Ammonia (foraminifera) often found in polluted areas. The two species were sensitive to low concentration, but survived high concentration (threshold value<10 microg l(-1), lethal value>200 microg l(-1)), which gives them a high potential value as bioindicators. Increasing concentrations lead to (1) increasing delay before production of new chambers, explaining dwarfism in polluted areas; (2) increasing delay before reproduction and decreasing number of juveniles, explaining low density; and (3) increasing proportion of deformed tests. Cytological modifications occurred only in deformed specimens (thickening of the organic lining, proliferation of fibrillar and of large lipidic vesicles, increased number of residual bodies). They may be responsible for anomalies in biomineralization processes. The detection of sulfur in deformed specimens suggests that foraminifers may have a detoxification mechanism with production of a metallothionein-like protein.

Metal influence on metallothionein synthesis in the hydrothermal vent mussel Bathymodiolus thermophilus

The present study reports on the metallothionein expression in the hydrothermal vent mussel Bathymodiolus thermophilus. Metallothioneins (MT) are proteins involved in intracellular metal regulation and conserved throughout the animal kingdom. The hydrothermal vent environment presents peculiarities (high levels of sulfides and metals, low pH, anoxia) that may have driven associated species to develop original evolutionary ways to face these extreme living conditions. Mussels were exposed to different metal solutions at the atmospheric pressure. The MT mRNA levels and MT contents were measured in gills and mantles of each exposed mussel. The intracellular metal distribution was estimated in fractions obtained after the centrifugation of tissue homogenates. A few of the tested metals (Ag, Cu, Cd, Hg and Zn) were able to significantly induce MT mRNA levels. Silver was the only one that produced a significant increase of the MT protein level in both mantle and gills. The gills always presented higher MT protein levels than the mantle did, while their MT mRNA levels were similar. Our data show that MT mRNA and MT protein levels do not follow a clear relationship in the gills and mantle of B. thermophilus and we assume that a posttranscriptional control occurs in these mussels.

Metal bioaccumulation and metallothionein concentrations in larvae of Crassostrea gigas

Larval stages of bivalve molluscs are highly sensitive to pollutants. Oysters from a hatchery from Normandy (English Channel) were induced to spawn, and fertilized eggs were exposed to copper or cadmium for 24 h. Metal accumulation (from 0.125 to 5 microg Cu L(-1) and from 25 to 200 microg Cd L(-1)) and MT concentrations were measured in larvae. Compared to controls, larvae accumulated copper and cadmium with an increase in MT concentrations particularly with cadmium (i.e. 130.96 ng Cu (mg protein)(-1) and 12.69 microg MT (mg protein)(-1) at 1 microg Cu L(-1) versus 23.19 ng Cu (mg protein)(-1) and 8.92 microg MT (mg protein)(-1) in control larvae; 334.3 ng Cd (mg protein)(-1) and 11.70 microg MT (mg protein)(-1) at 200 microg Cd L(-1) versus 0.87 ng Cd (mg protein)(-1) and 4.60 microg MT (mg protein)(-1) in control larvae). Larvae were also obtained from oysters of a clean area (Arcachon Bay) and a polluted zone (Bidassoa estuary) and exposed to copper in the laboratory, their MT concentration was measured as well as biomarkers of oxidative stress. Biomarker responses and sensitivity to copper for the larvae from Arcachon oysters were higher than for those from Bidassoa.

Biomarker responses as indication of contaminant effects in blue mussel (Mytilus edulis) and female eelpout (Zoarces viviparus) from the southwestern Baltic Sea

During a field study performed in spring and autumn 2001 and 2002, blue mussels (Mytilus edulis) and female eelpout (Zoarces viviparus) were collected at three locations in the Wismar Bay (Baltic Sea), and several biomarkers of contaminant effects were analysed. Besides seasonal and inter-annual variations, biomarker signals were most pronounced at the location closest to Wismar Harbour (Wendorf) in both species. Lysosomal membrane stability (LMS) was lowest and acetylcholinesterase activity (AChE) was significantly reduced. Frequency of micronuclei (MN) was significantly higher (in blue mussels), indicating mutagenic effects. In eelpout elevated levels of DNA adducts, EROD induction and PAH-metabolites were measured. Metallothionein (MT), biomarker for trace metal exposure, showed a gradient only in spring. Organochlorine contaminant analyses (PCBs, DDTs) corresponded to the observed biomarker levels. The results obtained clearly demonstrate pollution effects in the southwestern Baltic Sea. Moreover, they show that a multibiomarker approach is also applicable in a brackish water environment.

Evaluation of the Mytilus galloprovincialis Lam. digestive gland metallothionein as a biomarker in a long-term field study: seasonal and spatial variability

A study was made of seasonal and spatial variability of metallothionein (MT) concentrations, determined spectrophotometrically in the soluble fraction of the digestive gland of mussels Mytilus galloprovincialis, collected between 1999 and 2001 from several coastal and estuarine locations along the central Eastern Adriatic coast (Croatia). The seasonal influence on the MT and metal concentrations (higher values in winter-spring season, than in summer-autumn season) is more pronounced than the local site-specific influence. Furthermore, within each season a significant site-specific dependence on the MT and trace metal variations can be detected. An inverse relationship of mussel condition index (CI) and temperature with MT and trace metals levels indicates the influence of food abundance and mussel annual reproductive cycle. Substantially higher concentrations of both MT and Cd were recorded in mussels inhabiting estuarine locations, possibly indicating a markedly higher Cd bioavailability at these locations. The positive correlations obtained between MT and Cd in all seasons except autumn support an argument for application of digestive gland MT as a biomarker of Cd exposure, providing evidence for assessing the most appropriate season for mussel sampling.

Small metallothionein MT-10 genes in coastal and hydrothermal mussels

Metallothioneins (MTs) are important proteins in the intracellular regulation of metals. In the Mytilidae family, which includes many economically important species, 2 major forms of MTs have been reported: MT-10 (10 kDa) and MT-20 (20 kDa). Many different MT-10 proteins have been isolated from the common species Mytilus edulis, which suggests that distinct MT-10 genes may occur in a single specimen. Some MT genes, involving 3 exons and 2 large introns, have been isolated in Mytilidae. Our aim was to determine whether intron-free forms of the MT-10 genes can exist, which could allow rapid transcription in response to exposure to metals. Our study focused on 2 species living under very different environmental conditions: Mytilus edulis (a coastal mussel) and Bathymodiolus thermophilus (a hydrothermal mussel). We report here the first description of small, intron-free MT-10 genes, possessing a correct open reading frame in these 2 species.

Seasonal variability in biomarkers in the bivalves Mytilus edulis and Macoma balthica from the northern Baltic Sea

Metallothionein level (MT), and acetylcholinesterase (AChE), catalase (CAT) and glutathione-S-transferase (GST) enzyme activities in the bivalves Mytilus edulis and Macoma balthica were investigated for seasonal variations from an inshore and an offshore site in the northern Baltic Sea. All the biomarkers showed variability, following mostly a similar pattern at both sites. Relationships between biomarkers and environmental factors and protein concentration and weight of target tissues were examined. In M. edulis, GST activity was related to Secchi depth, while in M. balthica a correlation with near-bottom oxygen saturation was observed. AChE activity correlated with the weight of the foot tissue of M. balthica. In both species, an integrated biomarker index indicated a stressed condition during the spring/early summer period. Strong seasonal variability in temperature and a concentrated period of food availability in spring-both governing the reproductive cycle of the bivalves-probably explains most of the observed natural variability in biomarkers in this sea area.

Is the digestive gland of Mytilus galloprovincialis a tissue of choice for estimating cadmium exposure by means of metallothioneins?

A study performed over 12 months with caged mussels Mytilus galloprovincialis in the coastal marine zone, which is under urban pressure, reveals a temporal variation of digestive gland mass, which causes "biological dilution" of cytosolic metallothionein (MT) and trace metal (Cd, Cu, Zn, Fe, Mn) concentrations. The dilution effect was corrected by expressing the cytosolic MT and metal concentrations as the tissue content. Consequently, the changes of the average digestive gland mass coincide with the changes of MT and trace metal contents. From February to June, MT contents are nearly twice and trace metal contents nearly three times higher than those of the other months. The period of increased average digestive gland mass, of MT and trace metal contents probably overlaps with the sexual maturation of mussels (gametogenesis) and enhanced food availability. Since natural factors contribute more to the MT content than the sublethal levels of Cd, the digestive gland of M. galloprovincialis is not considered as a tissue of choice for estimating Cd exposure by means of MTs.

Do organisms living around hydrothermal vent sites contain specific metallothioneins? The case of the genus Bathymodiolus (Bivalvia, Mytilidae)

The unusual characteristics of the hydrothermal vent environment (high pressure and metal concentrations, low pH, etc.) leads us to wonder how species living in this particular biotope have adjusted to these severe living conditions. To investigate the consequences of high metal concentrations, filter-feeding organisms are commonly used in ecotoxicological studies. Metallothioneins (MTs) are proteins conserved throughout the animal kingdom and involved in intracellular metal regulation. Therefore, we tried here to find out whether the metallothioneins of hydrothermal bivalves are different from those of coastal bivalves. The characterization of DNA sequences coding MTs from some of the most common hydrothermal bivalves, belonging to the genus Bathymodiolus (Mytilidae) was performed by reverse transcription polymerase chain reactions (RT-PCRs). The complementary DNAs (cDNAs) of MT-10 and MT-20 isoforms were obtained for the Atlantic and Pacific hydrothermal mussels (Bathymodiolus azoricus and Bathymodiolus thermophilus). The MT-10 transcripts were 222 nucleotides long and the MT-20 transcripts, 207 nucleotides. The polymorphism of the MT cDNAs in these two hydrothermal species is discussed. The comparison between metallothionein cDNA sequences of the Mytilus and the Bathymodiolus genera shows strong homologies among metallothioneins of coastal and hydrothermal mussels.

Abnormal features of Macoma balthica (Bivalvia) in the Baltic Sea: alerting symptoms of environmental adversity?

Recent studies of the Baltic clam Macoma balthica (L.) from the southern Baltic (the Gulf of Gdansk) have revealed striking morphological, histological and cytogenetic features. Strong deformation of the shell, including elongation of the posterior end and the appearance of an easily visible flexure in this part, has been recorded. The population contribution of the deformed blunt shelled ("irregular") clams ranged from 0% to 65% and tended to increase with depth. The morphologically "irregular" clams had higher accumulated tissue concentrations of trace metals (As, Ag, Cd, Pb, Cu and Zn), indicating a different metal handling ability. Adverse conditions in deeper water regions of the Gulf (e.g. hypoxia, hydrogen sulphide, elevated bioavailability of contaminants) have been suggested as inducers of the phenotypical changes (morphological deformation) in part of the population and, in parallel, of the specific physiological adaptations that result in higher metal accumulation in the "irregular" clams. Cytogenetic and histological analyses showed the presence of tumours in gill cells and digestive system of the affected clams, the prevalence of disseminated neoplasia ranging from 0% to 94% depending on the site. The disease was manifested by a modified karyotype (i.e. an abnormal number and morphology of chromosomes), a higher activity of nucleolar organizer regions (AgNORs), and tissue lesions (enlarged cells, actively proliferative with pleomorphic nuclei). Bottom sediments showed acute toxicity and have been proposed as a source of an initialising carcinogenic factor. However, none of the ecotoxicological studies provided was successful in the clear demonstration of a single (or multifactorial) agent that can account for the disseminated neoplasia.

Endocrine disruption and health effects of caged mussels, Elliptio complanata, placed downstream from a primary-treated municipal effluent plume for 1 year

Freshwater mussels, Elliptio complanata, were caged in special benthic pens and were immersed at one upstream (Ups) site and two downstream sites (8 and 11 km) of a primary-treated municipal effluent plume for 1 year. The levels of metallothionein-like proteins (MT), lipid peroxidation, protein-free DNA strands and glutathione S-transferase (GST) activity were assayed in digestive gland, gill and gonad tissues to evaluate biological effects and damage. The levels of monoamines (serotonin and dopamine) in nerve ganglia, ATP-dependent transport activity and monoamine oxidase (MAO) activity were also investigated in the homogenates, synaptosomes and mitochondria, respectively. Results showed that significant amounts of sediment accumulated in cages and 82% of mussels survived the yearlong exposure period at the downstream sites. MT-like proteins were induced in all tissues with the following response intensity: gill (3-fold), digestive gland (1.4-fold) and gonad tissues (1.3-fold). Lipid peroxidation decreased (2.5-fold) in digestive gland but increased in gill (1.6-fold) and in gonad tissues (1.5-fold). GST activity was readily increased in digestive gland (2.5-fold), suggesting the presence of organic contaminants in the plume. Levels of protein-free DNA strands did not vary significantly in digestive gland and gill tissues but were significantly reduced in gonad tissues (2.5-fold) relative to the upstream site. In visceral nerve ganglia, both serotonin and ATP-dependent serotonin transport decreased 1.7-fold with a 4-fold increase of 5-hydroxyindole acetate (5-HIAA, a serotonin metabolite) level relative to the upstream site. However, MAO activity was somewhat reduced at downstream sites (0.7- to 0.9-fold of the activity at the upstream site). Dopamine levels were found to be decreased (1.5-fold), but dopamine ATP-dependent transport activity was increased 1.8-fold, suggesting reduced dopaminergic activity. These results indicate that estrogenic chemicals are likely at play, and the increased dopamine and decreased serotonin ATP-dependent transport suggest that the municipal plume was serotonergic for mussels located at the downstream sites. Mussels exposed for 1 year display a complex but characteristic pattern of responses that could lead to harmful health effects including neuroendocrine disruption of reproduction.

Regulation of translation initiation in mussels (Mytilus galloprovincialis, lam.) following contamination stress

The use of mussels (Mytilus sp.) as bioindicators of the aquatic environment is a valuable approach to monitor environmental contamination. Applying batteries of biomarkers is an essential prerequisite, since the complexity of environmental contaminants can induce in mussels a variety of structural and functional responses, which are not necessarily correlated. In an attempt to correlate translation responses to contamination stress, the sedimentation profiles of runoff ribosomes isolated from digestive gland cells of control or contaminated Mediterranean mussels (Mytilus galloprovincialis, Lam.) were examined and the efficiency of these ribosomes to accomplish protein synthesis was determined. While the major species of ribosomal material was 80S monomers, native 60S and 40S ribosomal subunits were also detected independently of the contamination level in the surrounding waters. However, concomitant with the increase of contamination stress, the level of 80S ribosomes was reduced in favor of free ribosomal subunits. In addition, ribosomes isolated from contaminated mussels and programmed with poly(U) were less efficient to enzymatically bind AcPhe-tRNA, compared with ribosomes from control samples. These results suggest that the contamination stress causes stoichiometric aberrations in the ribosomal particle pool and reduction of translation machinery capability to initate protein synthesis. Data support the notion that downregulation of translation is an important component of the cellular stress response and may be exploited as a biomarker of environmental contamination.

Metallothionein concentrations in a population of Patella aspera: variation with size

The determination of metallothionein (MT) concentrations in species with different feeding habits is important from the ecotoxicological point of view because it provides a better understanding of the role of these proteins in metal uptake pathways. The main objective was study the variation of MT and metal (Cd, Cu and Zn) concentrations with size and weight in the limpets Patella aspera. In addition investigate the relationship between MT and metal concentrations in limpets from different metal load environments of the south coast of Portugal with the aim to use MT in P. aspera as a biomarker of metal exposure. MT concentrations in the whole soft tissues of P. aspera increased with size and weight while metals decrease with size and weight. MT concentrations showed no significant relationship with Cd or Cu concentrations in the limpets from the South Portuguese Coast. However, a negative exponential relationship detected between MT and Zn concentrations suggest that Zn bound to MT might be displaced by Cd or Cu ions. The ability of limpets to store both Cd and Cu bound to MT may be responsible for the tolerance of this species to contaminated environments. The relationship between MT concentrations and Zn indicates that MT seems to play a minor role in binding Zn in Patella species.

Metallothionein concentration in the mussel Mytilus galloprovincialis as a biomarker of response to metal contamination: validation in the field

Mussels were translocated from a shell-fish breeding area (Sète, on the French Mediterranean coast) to sites exposed to trace element inputs in April 2000. They were recovered 3 months later. Whole soft tissues from all of the sites (n = 97) were analysed for arsenic, cadmium, chromium, copper, mercury, nickel, lead and zinc. Metallothioneins (MTs) were also measured in the digestive gland and in the remaining tissues (allowing calculation of whole soft tissue concentrations) at 22 of the 97 sites. MT concentrations in the digestive gland and the whole soft tissues were strongly correlated. The condition index varied with food availability at different sites. This did not influenced MT concentrations in the whole soft tissues, whereas the condition index was negatively correlated to trace element concentrations. A model is proposed to minimize this influence of condition. Metal concentrations adjusted using this model showed significant correlations with MT levels for those metals (cadmium, copper, nickel and zinc) that are known to bind to this protein, with the exception of mercury. Even in moderately contaminated sites, measurement of the MT level in the soft tissues of mussels was generally able to discriminate between different levels of contamination, allowing the use of a simplified procedure compared with dissection of the digestive gland. It is recommended to avoid translocation and sampling during the reproductive period, which is well documented for commercial species such as Mytilus sp.

Use of metallothionein in gills from oysters (Crassostrea gigas) as a biomarker: seasonal and intersite fluctuations

The use of oyster gills for the analytical determination of metallothionein (MT) concentration as a biomarker of metal exposure was investigated. Temporal variations in MT and metal concentrations (which can interfere with inter-site differences) were examined over a 7 month period (from spring to autumn) in Japanese oysters from a clean site (Bay of Bourgneuf, France) and a metal-rich site (Gironde estuary, France) as well as in individuals translocated from the clean to the contaminated area. The ratio between the annual average of MT concentrations in specimens from the clean and the metal-rich sites was 1.3. During the last 3 months of the experiment, significant differences were no longer registered between transplants and residents from the Gironde estuary. Metals concentrations in oyster gills differed consistently between the clean and the metal-rich sites (annual average ratios of 1.5, 2.7 and 9.8, respectively, for zinc, copper and cadmium) and a fast increase in metal concentrations (over a few months) was observed in transplants, mainly for cadmium. MT and soluble metal concentrations were found to be positively and significantly correlated over the period of the study. This relationship is a positive argument for a possible use of gill MT concentration as a biomarker of metal pollution in contrast to previous findings on the digestive gland, there being a smaller amount of seasonal variability in the weight of oyster gills.

Cadmium accumulation and metallothionein synthesis in freshwater bivalves (Pyganodon grandis): relative influence of the metal exposure gradient versus limnological variability

The relative influence of limnological confounding factors on cadmium (Cd) bioaccumulation and metallothionein (MT) synthesis was quantified in natural populations of freshwater bivalves (Pyganodon grandis) living in lakes along a Cd concentration gradient. During the ice-free period, we measured 15 environmental variables in the water compartment and determined total concentrations of Cd and MT in the gills of bivalves at 37 littoral stations in 20 lakes distributed across the mining area of Rouyn-Noranda in northwestern Quebec. A multiple linear regression model including pH (+), dissolved Ca concentrations (-) and free Cd2+ concentrations at the sediment-water interface (+) explained 74% of the variability in Cd concentrations in the bivalve gills. Dissolved Ca (-) and free Cd2+ (+) together explained 62% of the variation in MT concentrations in the bivalve gills. Partial linear regression analyses indicated that the limnological factors' pure and shared effects together accounted for 48 and 45% of the total variation in Cd and MT concentrations in the gills, respectively. A lake selection procedure that could be applied in monitoring programs is proposed to minimise the relative influence of these confounding variables.

Comparison of metallothionein concentrations and tissue distribution of trace metals in crabs (Pachygrapsus marmoratus) from a metal-rich estuary, in and out of the reproductive season

Crabs, Pachygrapsus marmoratus, were sampled in June 1997 and February 1998 from two sites (at the mouth and 25 km upstream) in the metal-rich Gironde estuary, France. Gills and hepatopancreas were analysed for metal (Cd, Cu, Zn) and metallothionein (MT) contents, in order to examine the influence of both biological and environmental factors on the physico-chemical forms of detoxified metal storage in the crabs. The concentrations of MT and both cytosolic and insoluble metals were not greatly different between males and females, and the influence of organ weights was also minimal. Intersite differences were observed, probably resulting from the gradient of salinity in the estuary, which interacts with both the chemical speciation and bioavailability of metals, and the general protein metabolism of the crabs. Seasonal changes were also important, probably in interaction with the moult and reproductive cycles. In February, concentrations of insoluble metals were generally higher than in June, in both organs, suggesting that essential metals, particularly Zn, are stored during winter then remobilised during the breeding season. The natural variability in the concentrations of MT often concealed any relationship with accumulated metal concentrations. Thus MT in crabs cannot be considered as a useful biomarker of metal pollution.

Changes in metallothionein concentrations in response to variation in natural factors (salinity, sex, weight) and metal contamination in crabs from a metal-rich estuary

Intermoult male and female crabs Pachygrapsus marmoratus and Carcinus maenas were sampled from three sites between the mouth and 25 km upstream in the Gironde, the most Cd-contaminated estuary in France, in order to study the relative importance of natural factors (salinity, sex, weight) and accumulated metal concentrations on metallothionein (MT) concentrations. In the two species studied, higher metal, total protein and MT concentrations were observed in the hepatopancreas than in the gills. In P. marmoratus, MT concentrations were mainly related to changes in the natural factors even if MT and Zn concentrations were positively correlated in the hepatopancreas whereas in C. maenas, the main relationships were with accumulated metal levels. In the case of the natural factors, the most important ones were weight in gills of both crab species, and salinity changes in both hepatopancreas and gills of P. marmoratus. Cd and Cu concentrations in both organs of the two species were inversely related to salinity. The same observation was found for Zn concentrations in C. maenas but not in P. marmoratus. In the hepatopancreas of both species, the highest total protein concentrations were found in crabs from the site with the highest salinity, whereas there were no such differences in the gills. It seems that changes in MT concentrations are linked more to changes in general protein metabolism than to changes in metal accumulation. Thus it was important to examine the storage of metals in other tissue compartments, particularly the insoluble fraction which includes mineral granules which is known to also contribute to trace metal detoxification in invertebrates. In the gills of the crabs, Zn was present mainly in the insoluble fraction, whereas Cd was nearly equally distributed between soluble and insoluble fractions. In contrast, Cu in the gills and all three metals in the hepatopancreas of both species were mainly cytosolic, but this does not necessarily imply a predominant role for MT since the cytosolic fraction also includes other macromolecules which may be the target binding site for accumulated trace metals.