The mussel Mytilus edulis as a bio-assay organism for mercury in seawater

Surveys of natural populations of mussels have identified areas of mercury contamination in the Firth of Forth, Scotland. A field bio-assay technique has been devised which accurately reflects the mean total mercury concentration in the surrounding seawater. The detection limit of the technique is estimated at 5–20 ng Hg l.^?1, and consequently the method can detect comparatively small enhancements over background mercury concentrations in estuarine and sea water.     

Dose-dependent response of a benthic system to biodeposition from suspended blue mussel (Mytilus edulis) culture

This study reports the results of a field experiment using benthic mesocosms that examined dose-dependent effects of mussel biodeposition on the benthic environment. Mesocosms were placed in the natural sea bottom and subjected to one of eight levels of biodeposition (from 0 to 1400 mussels m^?2). Most analyses indicated non-linear (i.e., threshold) effects. Sediment characteristics changed significantly between 200 and 400 mussels m^?2 as did multivariate community structure. Community structure effects were characterised by changes in abundances of species that are very sensitive or tolerant to organic loading. The multivariate AZTI Marine Biotic Index (M-AMBI) indicated that the benthic status changed from High to Good in all mesocosms receiving biodeposits. Sediments acted as a sink for oxygen (O₂), but results suggest O₂ sediment demand was not sensitive enough to evaluate organic loading impacts. Results from this and improved experiments can be used to determine the environmental carrying capacity of sites for bivalve culture.     

Embryotoxicity of the antifouling biocide zinc pyrithione to sea urchin (Paracentrotus lividus) and mussel (Mytilus edulis)

The effects of the new antifouling compound zinc pyrithione (Zpt) on the embryonic development of sea urchin (Paracentrotus lividus) and mussel (Mytilus edulis) were investigated in laboratory toxicity tests. The median effective concentrations (EC50) were 7.7 nM for sea urchin embryos and 8 nM for mussel embryos. Toxic effects of Zpt on the larval growth of the sea urchin were detected at 0.5 nM. Predicted environmental concentrations of Zpt in pleasure craft harbours are higher than the predicted no effect concentrations for sea urchin and mussel embryos, indicating that Zpt may pose a threat to those species from exposure in the field.     

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.     

Monitoring chemical contamination levels in the Mediterranean based on the use of mussel caging

Within the framework of the biointegrator network (RINBIO), 92 man-made cages containing mussels (Mytilus galloprovincialis), distributed over 1800 km of the French Mediterranean coast, made it possible to assess chemical contamination by heavy metals (Cd, Hg, Zn, Pb, Cu, Ni, Cr, As) and organic compounds (DDT, PCBs, HAP). The caging technique was adopted to compensate for the scarcity of natural shellfish stocks in the Mediterranean and to enable comparison of the sites regardless of their physicochemical and trophic characteristics. Models linking a biometric parameter (the condition index) to pollutant levels make it possible to adjust raw data on contamination for a reference individual, by making a clear distinction between physiological factors (growth) and environmental ones. The results demonstrate significant levels of pollutants in sites heretofore unsampled; the pollution occurs at limited areas, and the sources have been identified. Moreover, average contamination levels are comparable to those measured in wild species and in other areas. Overall, the research demonstrates the reliability of this methodological approach for monitoring marine pollution, especially in the Mediterranean.     

Histopathology alterations and histochemistry measurements in mussel, Mytilus edulis collected offshore from an aluminium smelter industry (Norway)

Histopathological characteristics of specific organs express condition, and represent time-integrated impacts on the organism stemming from alterations at lower levels of biological organisation. As integrative parameters, histochemical investigations have proved to be sensitive tools to detect effects of chemical compounds. The objective of this study was to determine changes in the tissues of mussels collected at a PAH contaminated site compared to a reference site using histopathological and histochemical parameters: lipofuscin (LF) accumulation in mussel digestive gland, and lysosomal membrane stability (LMS), and using additional information provided by body burden analysis to compare the sensitivity of these parameters. The histochemical measurements for both LF and LMS gave a clear indication of a high level of stress in animals from the PAH contaminated site. This LF accumulation in lysosomes is the result of peroxidation of autophagocytosed proteins associated with protein aggregates and oxidatively damaged organelles. These measurements were able to detect the effects of PAHs, and showed a strong relationship with the body burden results.     

Laboratory and field studies of the accumulation of inorganic mercury by the mussel Mytilus edulis (L.)

Laboratory and field experiments have been used to indicate the relative importance of mercury in dissolved and particulate phases as sources of mercury to mussels in a contaminated estuary. Laboratory experiments have demonstrated that mussels can accumulate inorganic mercury from sea-water, phytoplankton, and suspended sediment. Following exposure, concentrations were normally higher in the gills, digestive gland, and kidneys than in the adductor muscle, mantle, and foot, and the distribution of mercury between organs varied according to source. The relative bioavailabilities of inorganic mercury in water, phytoplankton, and sediment are estimated to be in the ratios 10:5:1. Mussels exposed for four weeks in a mercury-contaminated estuary accumulated primarily inorganic mercury from suspended sediment at the seaward end of the estuary, but further upstream uptake from solution and of methylmercury compounds were more important.     

Histopathology alterations and histochemistry measurements in mussel,Mytilus edulis collected offshore from an aluminium smelter industry (Norway)

Histopathological characteristics of specific organs express condition, and represent time-integrated impacts on the organism stemming from alterations at lower levels of biological organisation. As integrative parameters, histochemical investigations have proved to be sensitive tools to detect effects of chemical compounds.The objective of this study was to determine changes in the tissues of mussels collected at a PAH contaminated site compared to a reference site using histopathological and histochemical parameters: lipofuscin (LF) accumulation in mussel digestive gland, and lysosomal membrane stability (LMS), and using additional information provided by body burden analysis to compare the sensitivity of these parameters.The histochemical measurements for both LF and LMS gave a clear indication of a high level of stress in animals from the PAH contaminated site. This LF accumulation in lysosomes is the result of peroxidation of autophagocytosed proteins associated with protein aggregates and oxidatively damaged organelles. These measurements were able to detect the effects of PAHs, and showed a strong relationship with the body burden results.     

Cellular energy allocation in mussels (Mytilus galloprovincialis) from the stratified estuary as a physiological biomarker

This study demonstrates the usefulness of cellular energy allocation (CEA) evaluations as a physiological biomarker to infer the occurrence of natural stress in native populations of mussels inhabiting the stratified estuary (Krka River estuary, Croatia). Sampling sites were selected based on their differences in the salinity and temperature. The CEA value was calculated as a ratio between available energy (E_a) and energy consumption (E_c). Generally, higher values of E_a were recorded in June than in November, which were especially evident in the storage components (carbohydrates and lipids), while the constitutive component (proteins) remained relatively constant. The highest E_c was recorded in mussels at estuarine site compared to coastal site, which may be caused by the energetically costly maintenance of osmotic balance. Decrease in CEA recorded in estuarine mussels may ultimately result in a lower amount of energy available for growth, reproduction, or defence against other stresses (e.g. pollution).     

Sexual maturation as a source of variation in the relationship between cadmium concentration and body weight of Mytilus edulis L.

In order to refine the utilization of Mytilus edulis as a pollution indicator species, the relationship between cadmium concentration and mussel body weight was investigated at different sites in the Estuary and Gulf of the St. Lawrence. Our data show that the regression coefficients become considerably more variable when animals enter adulthood and that the variations are probably related to biochemical changes occurring during the sexual cycle. A substantial improvement of the applicability of mussels for monitoring marine pollution can be achieved by using only immature animals. This should reduce the influence of metabolism on the metal content of mussels and thereby give a more precise indication of ambiant pollution levels.     

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.     

Assessment of sacrificial anode impact by aluminum accumulation in mussel Mytilus edulis: a large-scale laboratory test

Since the early 1960s, the application of aluminum alloy sacrificial anodes to mitigate marine corrosion has been well known. The aim of this work was to study aluminum bioconcentration in Mytilus edulis by an in vitro test performed in two tanks: the first containing non-contaminated water (NCW) and the second containing aluminum-contaminated water (CW) (530 μg L⁻¹) released by sacrificial anode. The mussels were collected and examined over a period of 8 weeks. A comparison between the aluminum concentrations in the digestive glands of mussels from the CW and NCW tanks shows that the highest value (1700 mg/kg d.w.) was found in the CW mussels collected after 13 days. In NCW, the mean aluminum concentration in digestive glands during the test was 281 mg/kg d.w. The rapid concentration decrease in digestive glands is probably due to the inhibition of filtering activity due to valve closure at the high concentration as well as the induction of the detoxification response.     

Antioxidants in the black mussel (Mytilus galloprovincialis) as an indicator of Black Sea coastal pollution

The biologically active compounds, antioxidant activities, and free radical scavenging effects of black mussel dry matter (Mytilus galloprovincialis)--(BMDM) were investigated. The extract from BMDM with absolute methanol (BMDMAMet) showed the strongest inhibition of lipid peroxidation as a function of its concentration, and was comparable to the antioxidant activity of butylated hydroxyanisole, at the same concentration of 0.2 mg/ml. The extract with 50%methanol/water (BMDM50%Met) had the weakest antioxidant activity, whereas other extracts such as 1.2 M HCl in 50%methanol/water (BMDM50%Met/HCl) exhibited an average inhibition of lipid peroxidation. BMDMAMet extract showed marked activities in free radical scavenging determined by beta-carotene bleaching (beta-carotene), nitric oxide (NO*) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) radical cation (ABTS*+ methods. The antioxidant activities of BMDMAMet extract determined beta-carotene, NO* and ABTS*+ methods showed the highest correlation coefficients (R2) such as 0.998, 0.9976 and 0.6103, respectively, with the presence of total polyphenols. BMDM50%Met had lower antioxidant ability than BMDM50%Met/HCl in different scavenging methods, indicating that the major antioxidant components in these extracts must be derived from the polyphenols. Correlation between proteins and antioxidants was very low (0.0318 and 0.0433). The mussel extracts from polluted areas have shown by all using methods higher antioxidant activity than from the clean ones. The results presented in this report indicate that the antioxidant activities of mussel extracts could possibly be an additional index of pollution characterization.     

Integrated biomarker assessment of the effects exerted by treated produced water from an onshore natural gas processing plant in the North Sea on the mussel Mytilus edulis

The biological impact of a treated produced water (PW) was investigated under controlled laboratory conditions in the blue mussel, Mytilus edulis. Mussel health status was assessed using an integrated biomarker approach in combination with chemical analysis of both water (with SPMDs), and mussel tissues. Acyl-CoA oxidase activity, neutral lipid accumulation, catalase activity, micronuclei formation, lysosomal membrane stability in digestive cells and haemocytes, cell-type composition in digestive gland epithelium, and the integrity of the digestive gland tissue were measured after 5 week exposure to 0%, 0.01%, 0.1%, 0.5% and 1% PW. The suite of biomarkers employed were sensitive to treated PW exposure with significant sublethal responses found at 0.01-0.5% PW, even though individual chemical compounds of PW were at extremely low concentrations in both water and mussel tissues. The study highlights the benefits of an integrated biomarker approach for determining the potential effects of exposure to complex mixtures at low concentrations. Biomarkers were integrated in the Integrative Biological Response (IBR/n) index.     

Mussels (Mytilus edulis) as ‘point source’ indicators of trace metal pollution

Using X-ray Energy Spectroscopy trace metal concentrations including Pb, Cu and Zn were studied in the common blue mussel, Mytilus edulis. These organisms, sampled at intervals of only 1 km and less for a line transect study of the port of Vancouver, Canada, exhibited dramatic concentration variations. In particular, mussels only 30 m from a point source of lead displayed essentially base-line concentrations, representing a decline of two orders of magnitude.     

Concentration and distribution of 210Po in the tissues of the scallop Chlamys varia and the mussel Mytilus edulis from the coasts of Charente-Maritime (France)

Polonium-210 (210Po) has been analysed in the soft parts of two bivalves species, the scallop Chlamys varia and the common mussel Mytilus edulis, from the Bay of La Rochelle and Ré Island, on the French Atlantic coast. Between those sites, the highest 210Po concentrations have been found in whole scallop soft parts from La Rochelle, reaching 1,181 +/- 29 Bq kg(-1) dry weight (dwt), a size effect being related to the highest 210Po concentration in the smallest scallops. The results show a significant difference in concentrations for similar size individuals between species in each site (C. varia > M. edulis) and between sites for each species (Ré Island > Bay of La Rochelle). Very high 210Po concentrations have been found in the digestive gland of C varia, ranging 3,150-4,637 Bq kg(-1) dwt. Thus, the digestive gland contains up to 60% of the radionuclide. Subcellular investigations have shown that approximately 40% of the 210Po contained in the digestive gland is in the cytosolic fraction, suggesting a high bioavailability of the 210Po from this fraction to the trophic upper level. Calculations will show that approximately 4 kg of scallops flesh intake would be necessary to reach the annual incorporation limit of 1 mSv.     

PAH body burden and biomarker responses in mussels (Mytilus edulis) exposed to produced water from a North Sea oil field: laboratory and field assessments

In order to study the impact of produced water (PW) from a North Sea oil field on blue mussels (Mytilus edulis), chemical and biological markers were selected. A laboratory exposure (0.125%, 0.25% and 0.5% of PW) and a field study (6 stations 0.2-2 km from a PW discharge point) were conducted. In the laboratory study, PAH bioaccumulation increased in mussel soft tissue even at the lowest exposure dose. Micronuclei frequency demonstrated a dose-response pattern, whereas lysosomal membrane stability showed tendency towards a dose-response pattern. The same markers were assessed in the field study, biomarker analyses were consistent with the contamination level, as evaluated by mussel polycyclic aromatic hydrocarbons body burden. Overall, obtained results confirmed the value of an ecotoxicological approach for a scientifically sound characterisation of biological effects induced by offshore oilfield operational discharges.     

Gulfwatch: monitoring spatial and temporal patterns of trace metal and organic contaminants in the Gulf of Maine (1991-1997) with the blue mussel, Mytilus edulis L

Gulfwatch, established in 1991, is an international contaminant monitoring program in which the blue mussel, Mytilus edulis, is used as an indicator of the level and extent of contamination in the Gulf of Maine. Since 1991, trace metals, PAHs, PCBs, and OC pesticides have been measured in mussel tissues at 56 sites. The distribution of most metals was relatively uniform throughout the Gulf with the exception of Ag, Pb and Cr. However, the concentration of organic contaminants increased in a north-to-south direction. High concentrations of contaminants were correlated with large human population density and proximity to large rivers. Temporal analysis of five sites revealed that the majority of contaminant concentrations were either unchanged or decreasing. The concentrations of most contaminants were lower than the median of the National Status and Trends (NS & T) Mussel Watch with the exceptions of Cr, Hg, Pb and sigma PCB24. Hg concentrations at > 80% of the Gulfwatch sites exceeded the NS & T median +1 SD. Gulfwatch continues as a primary contaminant monitoring program in the Gulf of Maine.     

Experimental study on the bioaccumulation of oxytetracycline and oxolinic acid by the blue mussel (Mytilus edulis). An evaluation of its ability to bio-monitor antibiotics in the marine environment

The ability of blue mussel (Mytilus edulis) to act as a potential antibiotic bioindicator in marine waters was experimentally tested by the study of the kinetics of two veterinary antibiotics (oxolinic acid: OA and oxytetracycline: OTC). Antibiotic uptake was fast in the soft parts of the mussels. OA was quickly eliminated while OTC was released more slowly (half-life in viscera=3.9 days). OA and OTC were preferentially accumulated in gills and in viscera, respectively. Bio-accumulation factors were low (maximum: 2 for OTC in viscera) in accordance with the low K(ow)s. It was assumed that the higher OTC bioaccumulation pattern was related to its binding to mineral and organic compounds that led to its activity inhibition (62%). The antibiotics were persistent in shells (OTC half-life=8.3 days). Most veterinary and human antibiotics such as tetracyclines and sulphonamides have low log K(ow)(<2) and should weakly accumulate in mussel. This might limit the use of blue mussel to bio-monitor antibiotics in the marine environment.     

Metal exposure and biological responses in resident and transplanted blue mussels (Mytilus edulis) from the Scheldt estuary

The Western Scheldt river and estuary is known to be highly polluted as it receives industrial, agricultural and domestic effluents from one of the most populated and industrialised zones in Europe. Aquatic organisms are exposed to pollutants, specifically metals that are present in different environmental phases, e.g. dissolved, suspended material or sediment phases. The objective of this study was to study the relationship that exists between environmental metal levels, the degree of metal uptake by aquatic organisms with the concomitant biological responses. For this purpose the bivalve mollusk, Mytilus edulis, was selected as bioaccumulation indicator organism. Environmental (water and sediment) and mussel samples were collected during the late winter (March 2000) from sampling sites in the Scheldt estuary. Sites were selected to represent a salinity gradient from the mouth of the estuary to the furthest distribution area of mussels upstream in the system. Together with standard water quality parameters (e.g. salinity, dissolved oxygen, dissolved organic carbon, etc.) concentrations of twelve metals were analysed in the water (dissolved and suspended matter) and sediments. Levels of these metals were also measured in the soft tissue of M. edulis, together with concomitant biomarker responses in resident mussel populations at each site. The biomarkers that were included in this study were condition index, scope for growth, survival in air, cell membrane stability, DNA damage, and metallothioneins. Data were subjected to multivariate statistical analysis. The physico-chemical parameters and metals in the environmental samples clustered the sites to reflect the distribution based on the salinity gradient. Bioaccumulation results revealed increased metal uptake along a pollution gradient with the highest metal bioaccumulation occurring at the upstream most sites and therefore closest to the in the industrial activities. However, the biomarker responses clustered the sites in a manner that reflected the influence of combination of internal exposure (bioaccumulation) and external exposure (physico-chemical conditions). These differences in biomarker responses clearly demonstrated were attributed to abiotic factors other than metal pollution alone e.g. localized short-term increases in increased suspended sediment concentrations and decreased dissolved oxygen concentrations.