Toxicity of two heavy rare earth elements to freshwater mussels Dreissena polymorpha.

Rare earth elements (REE) are essential components of many electronic devices that could end-up in solid waste disposal sites and inadvertently released in the environment. The purpose of this study was to examine the toxicity of two heavy REEs, erbium (Er) and lutetium (Lu), in freshwater mussels Dreissena polymorpha. Mussels were exposed to 14 days to increasing concentration (10, 50, 250, and 1250 µg/L) of either Er and Lu at 15 °C and analyzed for gene expression in catalase (CAT), superoxide dismutase (SOD), metallothionein (MT), cytochrome c oxidase (CO1), and cyclin D for cell cycle. In addition, lipid peroxidation (LPO), DNA damage (DNAd), and arachidonate cyclooxygenase were also determined. The data revealed that mussels accumulated Er and Lu similarly and both REEs induced changes in mitochondrial COI activity. Er increased cell division, MT, and LPO, while Lu increased DNAd and decreased cell division. Tissue levels of Er were related to changes in MT (r = 0.7), LPO (r = 0.42), CO1 (r = 0.69), and CycD (r = 0.31). Lu tissue levels were related to changes in CO1 (r = 0.73), CycD (r = - 0.61), CAT (r = 0.31), DNAd (r = 0.43), and SOD (r = 0.34). Although the lethal threshold was similar between Er and Lu, the threshold response for LPO revealed that Er produced toxicity at concentrations 25 times lower than Lu suggesting that Er was more harmful than Lu in mussels. In conclusions, the data supports that the toxicity pattern differed between Er and Lu although they are accumulated in the same fashion.

Carbon Dioxide Toxicity to Zebra Mussels (Dreissena polymorpha) is Dependent on Water Chemistry.

Carbon dioxide (CO2) is gaining interest as a tool to combat aquatic invasive species, including zebra mussels (Dreissena polymorpha). However, the effects of water chemistry on CO2 efficacy are not well described. We conducted five trials in which we exposed adult zebra mussels to a range of CO2 in water with adjusted total hardness and specific conductance. We compared dose-responses and found differences in lethal concentration to 50% of organisms (LC50) estimates ranging from 108.3 to 179.3 mg/L CO2 and lethal concentration to 90% of organisms (LC90) estimates ranging from 163.7 to 216.6 mg/L CO2. We modeled LC50 and LC90 estimates with measured water chemistry variables from the trials. We found sodium (Na+) concentration to have the strongest correlation to changes in the LC50 and specific conductance to have the strongest correlation to changes in the LC90. Our results identify water chemistry as an important factor in considering efficacious CO2 concentrations for zebra mussel control. Additional research into the physiological responses of zebra mussels exposed to CO2 may be warranted to further explain mode of action and reported selectivity. Further study could likely develop a robust and relevant model to refine CO2 applications for a wider range of water chemistries. Environ Toxicol Chem 2024;43:1312-1319. Published 2024. This article is a U.S. Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Effects of diclofenac on sentinel species and aquatic communities in semi-natural conditions.

Due to the potential hazard of diclofenac on aquatic organisms and the lack of higher-tier ecotoxicological studies, a long-term freshwater mesocosm experiment was set up to study the effects of this substance on primary producers and consumers at environmentally realistic nominal concentrations 0.1, 1 and 10 µg/L (average effective concentrations 0.041, 0.44 and 3.82 µg/L). During the six-month exposure period, the biovolume of two macrophyte species (Nasturtium officinale and Callitriche platycarpa) significantly decreased at the highest treatment level. Subsequently, a decrease in dissolved oxygen levels was observed. High mortality rates, effects on immunity, and high genotoxicity were found for encaged zebra mussels (Dreissena polymorpha) in all treatments. In the highest treatment level, one month after the beginning of the exposure, mortality of adult fish (Gasterosteus aculeatus) caused effects on the final population structure. Total abundance of fish and the percentage of juveniles decreased whereas the percentage of adults increased. This led to an overall shift in the length frequency distribution of the F1 generation compared to the control. Consequently, indirect effects on the community structure of zooplankton and macroinvertebrates were observed in the highest treatment level. The No Observed Effect Concentration (NOEC) value at the individual level was < 0.1 µg/L and 1 µg/L at the population and community levels. Our study showed that in more natural conditions, diclofenac could cause more severe effects compared to those observed in laboratory conditions. The use of our results for regulatory matters is also discussed.

The geometry of the toxicity of silver nanoparticles to freshwater mussels.

The question about the influence of the geometry of silver nanoparticle (nAg) towards toxicity in aquatic organisms is largely unanswered. The purpose of this study was to examine if different geometries of nAg could initiate biophysical stress in the soft tissues of mussels. Freshwater Dreissenna bugensis mussels were exposed for 48 h at 15 °C to 10 and 50 µg/L of ionic Ag and to 3 forms of polyvinylpyrrolidone (PVP)-coated nAg of similar size: sphere, cube and prism. At the end of the exposure period, mussels were allowed to depurate overnight and the post-mitochondrial fraction of the soft tissues were analyzed for the levels of liquid crystals (LCs), changes in the activity and fractal dimensions of pyruvate kinase-lactate dehydrogenase (PK-LDH), F-actin and protein-ubiquitin (UB) levels. The data revealed that exposure to nAg forms lead to increased formation of LCs in increasing order of intensity: prismatic > cubic > spherical nAg. The activity in PK-LDH was decreased by all forms of nAg but not by ionic Ag+ (as with the following effects). Fractal kinetics of the PK-LDH system revealed that the nAg forms increased the spectral dimension (sD) in increasing order: spherical > cubic > prismatic nAg. A decrease in the fractal diffusion rate (fDR) with small changes in the fractal dimension (fD) was also obtained. The levels of F-actin and protein-UB were significantly affected for most forms of nAg and followed a pattern similar to LCs levels. In conclusion, the geometry of nAg could influence the formation of LCs, alter the fractal kinetics of the PK-LDH system, F-actin levels and protein damage in the soft tissues of freshwater mussels.

Effect of reproduction cycle stage on energy metabolism responses in a sentinel species (Dreissena polymorpha) exposed to cadmium: What consequences for biomonitoring?

Metal trace elements such as cadmium (Cd) are commonly present in ecosystems and could lead to impairment of mitochondrial functions and energy imbalance in aquatic organisms including molluscs. Combined exposure to increasing temperatures and Cd could enhance such an impact on animals. Seasonal fluctuations, such as temperature, and the corresponding reproduction cycle can affect biomarker responses. However, the reproduction cycle stage is rarely taken into account in ecotoxicological studies. Thus, this work aimed at understanding energy metabolism responses in a sentinel species, Dreissena polymorpha. Mussels were collected during the rest and the reproduction periods and were exposed to 10 µg.L-1 of cadmium (Cd) at two temperatures (in situ temperature and in situ temperature + 5°C) during 7 days. Energy metabolism was monitored by measuring reserves and energy nucleotides charge and by assessing aerobic and anaerobic metabolism markers, and upstream regulation pathways. Markers related to OXPHOS activity revealed seasonal variations under laboratory conditions. Conversely, adenylate nucleotides, glycogen, lipid and transcript levels of AMP-activated protein kinase, citrate synthase, ATP synthase and cytochrome b encoding genes remained steady after the acclimation period. No evident effect of Cd on energy metabolism markers was noticed for both exposures although the transcript level of succinate dehydrogenase and citrate synthase encoding genes decreased with Cd during the rest period. Cellular stress, revealed by lipid peroxidation and catalase mRNA levels, only occurred in Cd and warming co-exposed mussels during the reproduction period. These results suggest that contaminant impact might differ according to the reproduction cycle stage. The effect of confounding factors on biomarker variations should be further investigated to have a deeper knowledge of metabolism responses under laboratory conditions.

Temperature-Related Responses of an Invasive Mussel and 2 Unionid Mussels to Elevated Carbon Dioxide.

Zebra mussels (Dreissena polymorpha) have exacerbated the decline of native freshwater mussels (order Unionida) in North America since their arrival in the 1980s. Options for controlling invasive mussels, particularly in unionid mussel habitats, are limited. Previously, carbon dioxide (CO2 ) showed selective toxicity for zebra mussels, relative to unionids, when applied in cool water (12 °C). We first determined 96-h lethal concentrations of CO2 at 5 and 20 °C to zebra mussels and responses of juvenile plain pocketbook (Lampsilis cardium). Next, we compared the time to lethality for zebra mussels at 5, 12, and 20 °C during exposure to partial pressure of CO2 (PCO2 ) values of 110 to 120 atm (1 atm = 101.325 kPa) and responses of juvenile plain pocketbook and fragile papershell (Leptodea fragilis). We found efficacious CO2 treatment regimens at each temperature that were minimally lethal to unionids. At 5 °C, plain pocketbook survived 96-h exposure to the highest PCO2 treatment (139 atm). At 20 °C, the 96-h lethal concentration to 10% of animals (LC10) for plain pocketbook (173 atm PCO2 , 95% CI 147-198 atm) was higher than the LC99 for zebra mussels (118 atm PCO2 , 95% CI 109-127 atm). Lethal time to 99% mortality (LT99) of zebra mussels in 110 to 120 atm PCO2 ranged from 100 h at 20 °C to 300 h at 5 °C. Mean survival of both plain pocketbook and fragile papershell juveniles exceeded 85% in LT99 CO2 treatments at all temperatures. Short-term infusion of 100 to 200 atm PCO2 at a range of water temperatures could reduce biofouling by zebra mussels with limited adverse effects on unionid mussels. Environ Toxicol Chem 2020;39:1546-1557. Published 2020. This article is a U.S. Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

A new protocol for the simultaneous flow cytometric analysis of cytotoxicity and immunotoxicity on zebra mussel (Dreissena polymorpha) hemocytes.

Immunotoxicity analysis receives a strong interest in environmental a priori and a posteriori risk assessment procedures considering the direct involvement of the immune system in the health status of organisms, populations and thus ecosystems. The freshwater mussel Dreissena polymorpha is an invasive species widely used in ecotoxicology studies and biomonitoring surveys to evaluate the impacts of contaminants on aquatic fauna. Bivalve hemocytes are the immunocompetent cells circulating in the open circulatory system of the organism. However, there is nowadays no consensus on a protocol to evaluate the immunocompetent state of this particular cell type using flow cytometry. Wild species such as D. polymorpha present several technical barriers complicating their analyze including (i) the quality and the purity of the hemolymph sample, (ii) the controversial characterization of hemocyte subpopulations and their diversity, (iii) the quantity of biological material, and (iv) the high inter-individual variability of hemocyte responses. The present work proposes several technical and analytical improvements to control the above-mentioned issues. The inclusion of sedimentation and cell detachment steps in the pre-analytical phase of the protocol substantially ameliorate the quality of the hemolymph sample as well as the accuracy of the cytometric measurements, by selecting the analyzed cells on their adhesion ability and by increasing the concentration of the analyzed events. The development of an effective triple-labeling procedure including the cellular probe Hoechst® 33342, the membrane impermeant dye propidium iodide and yellow-green fluorescent microspheres allowed the simultaneous analysis of cytotoxicity and phagocytosis activity in hemocytes. It also significantly enhanced the accuracy of hemocyte endpoint measurements by eliminating non-target events from the analysis and allowing relevant gating strategies. Finally, the use of pooled samples of hemolymph noticeably reduced inter-sample variability while providing more plasticity in the experimental design and improving the discriminating potency between treatments. The developed protocol is suitable for ex vivo exposure of hemocyte in a chemical/environmental toxicity assessment as well as for in vivo exposure in the laboratory or in situ biomonitoring surveys with few adaptations.

Assessing relative sensitivity of marine and freshwater bivalves following exposure to copper: Application of classical and novel genotoxicological biomarkers.

Determination of relative sensitivity of biota following exposures to contaminants including metals is important for environmental protection. Copper (Cu), although biologically essential can be highly toxic to biota if present at higher concentrations in the natural environment. Given its ubiquitous presence within coastal and inland water bodies, we compared Cu-induced genotoxicity in two ecologically important mussel species, the freshwater Dreissena polymorpha (DP) and marine Mytilus galloprovincialis (MG), along with its tissue specific accumulation. Novel biomarker in terms of induction of gamma H2AX (γ-H2AX) foci, along with comet assay and induction of micronuclei (MN) were used to determine DNA damage response (DDR) in these two species following exposure to a range of Cu concentrations (18, 32, 56 µg L-1) for 10 days. Concentration-dependent increases in Cu concentration in gill tissue, as determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), were paralleled by a greater degree of genotoxicity. An induction of γ-H2AX foci was present in all Cu exposure concentrations, proving this technique to be a sensitive and suitable biomarker of genotoxicity in bivalves. The multi-biomarker approach adopted here suggests firstly that in parallel with MG, which is widely used to assess the health of marine and coastal environment, DP is also suitable representative of inland water bodies, and that there is a similar mechanism of action for the induction of genotoxicity between the two species, following exposure to Cu. Secondly, for genotoxicity assessment a battery of responses could simultaneously be assessed in these two bivalve species. Finally, for adequate protection of the environment it is vital to adopt a multi-biomarker, multi-species approach to determine adverse biological effects to gain a holistic understanding of the real threat posed by contaminants to hydrosphere.

The influence of surface waters on the bioavailability and toxicity of zinc oxide nanoparticles in freshwater mussels.

The release of engineered nanoparticles in the aquatic environment could pose a threat to the biota. The purpose of the study was to examine the influence of surface water characteristics on zinc oxide nanoparticles (nZnO) and ZnS04 toxicity to the freshwater mussel Dreissena polymorpha. Mussels were exposed to an equivalent concentration of 25 µg/L Zn as either nZnO or ZnSO4 for 96 h at 15 °C in 4 types of surface waters: green water (high conductivity and pH with low natural organic matter content), brown water (low conductivity and pH with high natural organic matter content), diluted municipal effluent (high conductivity and pH with high urban organic matter content) and aquarium water (treated green water with organic matter removed). After the exposure period, mussels were analyzed for air-time survival, total and labile Zn levels in tissues, lipid metabolism (phospholipase A2, triglycerides levels) and oxidative stress (glutathione S-transferase, arachidonate cyclooxygenase, lipid peroxidation). The data revealed that mussels exposed to ZnSO4 in controlled aquarium water accumulated more total and labile Zn tissues, decreased oxidative stress and triglycerides and increased air time survival. While nZnO had few effects in aquarium water, oxidative stress was enhanced and total Zn in tissues were decreased in brown water and diluted municipal effluent and triglycerides were higher in nZn-exposed mussels in brown water. Air-time survival was decreased in mussels kept in green water and nZnO. It was also decreased in mussels exposed to ZnSO4 in green water and diluted municipal effluent. In conclusion, the fate and toxic effects of Zn could be influenced by both the chemical form (nanoparticles or ionic Zn) and surface water properties in freshwater mussels.

Toxic effect and physiological disruption of sodium phosphate to the quagga mussel (Dreissena bugensis).

Phosphorous is an essential nutrient for all forms of life; however, the question of toxicity to aquatic species remains largely unanswered, despite many systems that exceed natural phosphorus loads. This study determined the ecotoxicological threshold concentration of phosphorus to the freshwater bivalve Dreissena bugensis using a 96-h bioassay. Sublethal, medial lethal, and lethal levels of sodium phosphate to D. bugensis were found to be 125, 260, and 476 ppm. Physiological biomarkers such as the oxygen consumption and filtration rate were estimated by exposing D. bugensis to five different sublethal concentrations (25, 50, 75, 100, and 125 ppm) of sodium phosphate for 96 h. Both oxygen consumption and filtration rate gradually declined with increasing exposure concentrations and durations, which was significant (α < 0.05) for 75, 100, and 125 ppm of sodium phosphate concentrations. Based on the feeding rate and oxygen consumption endpoints, the no-observed effect concentration and the low observed effect concentration were 25 and 75 ppm, respectively. Maximum acceptable toxicant concentration of sodium phosphate was 43.3 ppm. Measured environmental concentration (MEC) of total phosphorus (0.015 ppm; n = 6) was obtained from seasonal field assessments in Saginaw Bay during the years 2008 to 2010. An assessment factor of 1000 was used for calculating the predicted no effect concentration (PNEC) of 0.025 ppm. Risk quotient (RQ) of "0.6" was therefore established using MEC/PNEC (real risk) ratio. Binary ecological classification (RQ < 1) suggested that there is no appreciable risk of phosphorus to D. bungensis in the Saginaw Bay of Lake Huron of Laurentian Great Lakes.

Influence of cadmium on oxidative stress and NADH oscillations in mussel mitochondria.

Biological organisms evolved to take advantage of recurring environmental factors which enabled them to assimilate and process metabolic energy for survival. Mitochondria display non-linear oscillations in NADH levels (i.e. wave behavior) that result from the balance between NADH production (aerobic glycolysis) and oxidation for ATP synthesis. The purpose of this study was to examine the effects of cadmium (Cd) on mitochondrial NADH oscillations in quagga mussels Dreissena bugensis exposed to 50 and 100 µg/L CdCl2 for 7 days at 15 °C. Metallothionein (MT) levels, thioredoxin reductase (TrxR) activity and NADH oxidation rate were also determined, as were oscillations in NADH and the formation of dissipative structures (turbidity), in isolated mitochondria suspensions. The results show that exposure to Cd readily induced MT levels at both concentrations tested and that TrxR and NADH oxidase activity was induced at 100 µg/L Cd only. In control mussels, NADH levels oscillated in mitochondria suspensions with a natural period of 2 to 2.5 min for up to 40 min. Exposure to Cd increased the complexity of the frequency profile of NADH oscillations and reduced the amplitudes of the natural signal with a period of 2 to 2.5 min. The formation of dissipative structures decreased in response to a Cd concentration of 100 µg/L but increased at a level of 50 µg/L. The amplitudes at the natural frequency were significantly correlated with NADH oxidase activity (r = -0.91) and with the formation of dissipative structures (r = -0.59). We conclude that Cd could alter the natural frequency in oscillations of NADH in mitochondria, thereby contributing to an increase in NADH oxidation rate and disruption of the spatial organization of mitochondria in suspension. In conclusion, changes in the wave behavior of NADH in mitochondria are proposed as a novel biomarker of toxicity in aquatic organisms.

Bioaccumulation and metal-associated biomarker responses in a freshwater mussel, Dreissena polymorpha, following short-term platinum exposure.

Due to the increasing presence of platinum (Pt) in the environment, the caveat arises to identify its toxic potential in species at risk of being exposed - especially those found in aquatic environments where pollutants tend to accumulate. Comprehensive characterisation of possible adverse effects following exposure of aquatic organisms to Pt remains elusive. To address this, Zebra mussels (Dreissena polymorpha) were exposed to a range of Pt(IV) concentrations (0.1, 1, 10, 100 and 1000 µg/L) for one and four days, respectively, after which bioaccumulation was quantified and compared to alterations in biomarker profiles relevant to metal toxicity i.e. glutathione-S-transferase (GST) and catalase (CAT) activity, lipid peroxidation and metallothionein (MT) induction. Despite pre-conditioning of the tanks, Pt recovery in the exposure media was found to be 36% (0.1 µg/L), 42% (1 µg/L), 47% (10 µg/L), 68% (100 µg/L) and 111% (1000 µg/L) due to biological and non-biological processes. Pt concentrations in dried mussel soft tissue increased with exposure concentrations and were 20-153 times higher compared to quantified Pt concentrations in the exposure media. CAT activity was significantly increased in the tissue of mussels exposed to 0.1-100 µg/L Pt after Day 1 while the lowest effect concentration (LOC) for this response on both Day 1 and Day 4 was 0.1 µg/L. The effect on the GST activity was less pronounced but demonstrated a similar trend. However, enhanced lipid peroxidation was measured in the tissue of mussels exposed to ≥0.1 µg/L on Day 4. Bioaccumulation of Pt was also associated with a concentration-dependent increase in Pt-MT. Although these effects occurred at Pt levels higher than those present in the environment, it indicates that Pt has the ability to cause aberrancies in metal-associated biomarker profiles.

Neonicotinoid insecticides are potential substrates of the multixenobiotic resistance (MXR) mechanism in the non-target invertebrate, Dreissena sp.

Mussels are among the most frequently used invertebrate animals in aquatic toxicology to detect toxic exposure in the environment. The presence and activity of a cellular defence system, the multixenobiotic resistance (MXR) mechanism, was also established in these organisms. In isolated gill tissues of dreissenid mussels (D. bugensis) the MXR activity was assayed after treatment by commercially available insecticides (formulated products) which contain neonicotinoids as their active ingredients: Actara (thiamethoxam), Apacs (clothianidin), Calypso (thiacloprid) and Kohinor (imidacloprid), respectively. While applying the accumulation assay method, 0.5 µM rhodamine B was used as model substrate and 20 µM verapamil as model inhibitor of the MXR mechanism. In acute (in vitro) experiments when isolated gills were co-incubated in graded concentrations of insecticides and rhodamine B simultaneously, Calypso and Kohinor treatment resulted increasing rhodamine accumulation. Chemical analysis of gills in vitro incubated in insecticides demonstrated higher tissue concentrations of thiamethoxam, clothianidin and thiacloprid in the presence of verapamil suggesting that the active ingredients of Actara, Apacs and Calypso are potential substrates of the MXR mediated cellular efflux. In contrast, verapamil did significantly alter the accumulated imidacloprid concentrations in gills, suggesting that the active component of Kohinor is not transported by the MXR mechanism. Chronic (in vivo) exposures of the intact animals in lower, 1, 10 mg/L concentration of neonicotinoid products, resulted in a decreased level of both rhodamine accumulation and verapamil inhibition by the 12th-14th days of treatment. These results suggest an enhancement of MXR activity (chemostimulation), building up gradually in the animals exposed to Actara, Apacs and Kohinor, respectively. Neonicotinoid-type insecticides are generally considered as selective neurotoxins for insects, targeting the nicotinic type acetylcholine receptors (nAChRs) in their central nervous system. Our present results provide the first evidences that neonicotinoid insecticides are also able to alter the transmembrane transport mechanisms related to the MXR system.

Response of the freshwater mussel, Dreissena polymorpha to sub-lethal concentrations of samarium and yttrium after chronic exposure.

Samarium (Sm) and yttrium (Y) are commonly used rare earth elements (REEs) but there is a scarcity of information concerning their biological effects in non-target aquatic organisms. The purpose of this study was to determine the bioavailability of those REEs and their toxicity on Dreissena polymorpha after exposure to increasing concentration of Sm and Y for 28 days at 15 °C. At the end of the exposure period, the gene expression of superoxide dismutase (SOD), catalase (CAT), metallothionein (MT), glutathione-S-transferase (GST), cytochrome c oxidase 1 (CO1) and cyclin D (Cyc D) were analysed. In addition, we examined lipid peroxidation (LPO), DNA strand breaks (DSB), GST and prostaglandin cyclooxygenase (COX) activities. Results showed a concentration dependent increase in the level of the REEs accumulated in the soft tissue of mussels. Both REEs decreased CAT but did not significantly modulated SOD and MT expressions. Furthermore, Sm3+ up-regulated GST, CO1 and Cyc D, while Y3+ increased and decreased GST and CO1 transcripts levels, respectively. Biomarker activities showed no oxidative damage as evidenced by LPO, while COX activity was decreased and DNA strand breaks levels were changed suggesting that Sm and Y exhibit anti-inflammatory and genotoxic effects. Factorial analysis revealed that the major impacted biomarkers by Sm were LPO, CAT, CO1 and COX, while GST gene expression, COX, Cyc D and CAT as the major biomarkers affected by Y. We conclude that these REEs display different mode of action but further investigations are required in order to define the exact mechanism involved in their toxicity.

Genotoxic and Cytotoxic Effects on the Immune Cells of the Freshwater Bivalve Dreissena polymorpha Exposed to the Environmental Neurotoxin BMAA.

The environmental neurotoxin ß-N-Methylamino-l-alanine (BMAA) has been pointed out to be involved in human neurodegenerative diseases. This molecule is known to be bioaccumulated by bivalves. However, little data about its toxic effects on freshwater mussels is available, particularly on the hemolymphatic compartment and its hemocyte cells involved in various physiological processes such as immune defenses, digestion and excretion, tissue repair, and shell production. Here we exposed Dreissena polymorpha to dissolved BMAA, at the environmental concentration of 7.5 µg of /mussel/3 days, during 21 days followed by 14 days of depuration in clear water, with the objective of assessing the BMAA presence in the hemolymphatic compartment, as well as the impact of the hemocyte cells in terms of potential cytotoxicity, immunotoxicity, and genotoxiciy. Data showed that hemocytes were in contact with BMAA. The presence of BMAA in hemolymph did not induce significant effect on hemocytes phagocytosis activity. However, significant DNA damage on hemocytes occurred during the first week (days 3 and 8) of BMAA exposure, followed by an increase of hemocyte mortality after 2 weeks of exposure. Those effects might be an indirect consequence of the BMAA-induced oxidative stress in cells. However, DNA strand breaks and mortality did not persist during the entire exposure, despite the BMAA persistence in the hemolymph, suggesting potential induction of some DNA-repair mechanisms.

Toxicity of Potassium Chloride Compared to Sodium Chloride for Zebra Mussel Decontamination.

The use of chemicals to decontaminate watercraft and/or equipment after exposure to zebra mussels Dreissena polymorpha is one method of decontamination that has been recommended by multiple government agencies in the United States. The ideal chemical to be used for decontamination would be inexpensive and easily obtained, would have no or limited effect on nontarget species, and would be relatively environmentally friendly. Two chemicals that have been tested are potassium chloride (KCl) and sodium chloride (NaCl). The toxicity of each chemical to both adult zebra mussels and veliger larvae was examined. Sodium chloride was less effective at causing mortality than KCl within the exposure periods tested. Adult mussels required a 4× longer exposure period to exhibit complete mortality when exposed to NaCl at 30,000 mg/L (24 h) compared to KCl (6 h). At 10,000 mg/L, NaCl took 8× longer (96 h) than KCl (12 h) to cause 100% mortality of adult mussels. Veligers that were exposed to KCl at 1,250 mg/L required a 12-h exposure to attain complete mortality, while those exposed to NaCl at 10,000 mg/L required an 18-h exposure to exhibit the same result. To determine whether KCl is more advantageous as a decontamination chemical, the cost and chemical availability must be researched.

Differentiation of sympatric zebra and quagga mussels in ecotoxicological studies: A comparison of morphometric data, gene expression, and body metal concentrations.

The zebra mussel is among the best studied freshwater molluscs in ecotoxicology, but information on the quagga mussel is lacking. Considering its potential spread, we selected a river in France in which zebra and quagga mussels coexisted, and then we used genetic markers to differentiate the two species and compared morphological parameters. cDNA sequencing assays of ten genes already used in zebra mussels were performed on quagga mussels to obtain functional specific primers. Then we analyzed the expression of genes involved in cellular metabolic activities (Cytochrome-c-oxidase - cox, and ATP synthase - atp), detoxification processes (Glutathione-S-Transferase - gst), oxidative stress (Catalase - cat), and digestive functions (Amylase - amy) on the two species. Whereas morphometric analysis underlined similarities in shape between the two species, relative gene expression profiles and metal concentrations evidenced strong differences. Quagga mussels notably presented half as high concentrations in Cd and Pb, two particularly toxic elements, as zebra mussels. These results imply that i) particular attention should be paid to properly distinguish the two species considering their similar external appearance, and ii) zebra mussels cannot be replaced by quagga mussels in ecotoxicological studies without preliminary investigations on biomarker response patterns. To our knowledge, this study is the first to have undertaken such an approach in gene expression analysis in quagga mussels, and more generally to have compared such biomarker responses of zebra and quagga mussels in the field.

Differential tolerance to nickel between Dreissena polymorpha and Dreissena rostriformis bugensis populations.

Differential tolerance to stress is partly responsible for the heterogeneity of biomarker responses between populations of a sentinel species. Although currently used for freshwater biomonitoring, studies concerning inter-populational variability in tolerance to contaminants for the zebra mussel (Dreissena polymorpha) are scarce. Moreover, this well-known invader is currently replaced by another, the quagga mussel (Dreissena rostriformis bugensis). To evaluate the differential tolerance between dreissenids, several populations of both species were exposed to a high concentration of nickel. A LT50 (time when 50% of individuals were dead) was established for each population. Biomarker responses and internal nickel concentration were also measured, to link tolerance with physiological status. Results evidenced that D. polymorpha populations are more heterogeneous and more tolerant than D. r. bugensis ones. For D. polymorpha populations only, LT50 values were positively correlated with the nickel contamination in situ, with higher anti-oxidative defences and a higher Integrated Biomarker Response value in the field. Such findings may be explained by local adaptation and invasion dynamic within each species. The significance of this differential tolerance when using biomarker responses for biomonitoring purposes is thus discussed.

Cumulative effects of ibuprofen and air emersion in zebra mussels Dreissena polymorpha.

Municipal effluents are major source of pharmaceutical products in the environment. The purpose of this study was to examine the toxicity of a largely used drug, ibuprofen (Ibu), in Dresseina polymorpha mussels and its impact on air survival time. The mussels were exposed to increasing concentration of Ibu (0, 1, 10 and 100µg/L) for 96 at 15°C and a sub-group of mussels was maintain in air for another 96h. Post-exposure mussels (Ibu and Ibu+Air) were analyzed for weight loss, total triglycerides, neutral lipids, lipid peroxidation (LPO), arachidonate-dependent cyclooxygenase (COX) and glutathione S-transferase activity. Lipid extracts of mussel tissues were also analyzed by 1H-nuclear resonance spectroscopy. The data revealed that mussels exposed to Ibu had increased signs of lipid oxidation, neutral lipids and decreased triglycerides, LPO and GST activity. COX activity was significantly reduced by Ibu in keeping with mode of action of the drug. Following exposure to air, increased weight loss, neutral lipids (lipid degradation), were observed in mussels exposed to Ibu but no changes in COX activity were observed. Air stress limited the decrease in triglycerides and the increase in GST in mussels exposed to 100µg/L Ibu indicating decreased anti-oxidant response/phase II biotransformation and limited lipid metabolism. In conclusion, exposure to Ibu has some anti-inflammatory effects to mussels based on COX activity but resulted in increased oxidative damage and lipid catabolism. Exposure to air stress could enhance some of these responses and contribute to decreased resistance to air exposures.

Bioaccumulation of gadolinium in freshwater bivalves.

In this study, the presence of anthropogenic gadolinium (Gd) was evaluated in rivers, close to wastewater treatment plant outputs. Then, one site was selected for in situ experiments to assess the bioaccumulation of Gd in the digestive gland and in the gills of two bivalves (Dreissena rostriformis bugensis and Corbicula fluminea). For both organisms, the results suggested that the bioaccumulation of Gd can be observed when organisms are exposed in a geogenic and anthropogenic Gd mixture. In order to observe if Gd can bioaccumulate in tissues of bivalves when the ion is only present as the main anthropogenic speciation of Gd, i.e., Gd-contrast agents (Gd-CAs), the gadoteric acid was used for a laboratory experiment. In this case, the presence of Gd was clearly detected in a significant amount in the digestive glands of D. rostriformis bugensis and C. fluminea while low concentrations are measured in the gills. For the first time, these results clearly showed that Gd can bioaccumulate in bivalve tissues even when it is only present as Gd-CAs. Biochemical activities were measured in the digestive gland and in the gills of the bivalves to assess the effects of Gd-CA bioaccumulation. No significant variations were observed in the gills. Concerning the digestive gland, after 7 days of exposure at 10 µg L-1 of Gd as Gd-CA speciation, GST activity in D. rostriformis bugensis and lipid hydroperoxide and mitochondrial electron transfer system in C. fluminea had increased. The results suggest an acclimation of the organisms to the presence of Gd-CAs in the medium within less than 21 days.