Elliptio Complanata Research Articles

Responses of freshwater mussel (Elliptio complanata) hemocytes exposed in vitro to crude extracts of Microcystis aeruginosa and Lyngbya wollei

Lyngbya wollei is a benthic filamentous cyanobacterium that produces a toxin analogous to the neurotoxic saxitoxin known as lyngbyatoxin (LYNGTX). Microcystis aeruginosa form blooms in the pelagic area of eutrophic lakes and produce a series of potent hepatotoxins-microcystins (MCYST). The aim of this study in vitro study was to examine the difference between the crude extracts of either M. aeruginosa or L. wollei toward the immune system of Elliptio complanata mussels. Freshly isolated hemolymph was plated and exposed to the crude extract of each species at LYNGTX or MCYST equivalent concentrations of 5, 10 and 25μg/L for 18h. Immunocompetence was characterized by following changes in hemocyte numbers, metabolic activity (viability), and phagocytosis. Hemocyte counts were not affected, indicating no turnover of hemocytes. Hemocyte metabolic activity was higher in cells exposed to crude extracts of L. wollei. Exposure to L. wollei extracts led to decreased pro-inflammatory precursors such as reactive oxygen species (ROS) and cyclooxygenase (COX) activities. Phagocytosis increased at 25μg/L for both types of crude extracts. However, hemocytes exposed to crude extracts of M. aeruginosa produced more ROS and COX compared to hemocytes exposed to crude extracts of L. wollei. In conclusion, the data suggest that the crude extract of M. aeruginosa was more toxic than crude extract of L. wollei to mussel hemocytes.

Burrowing in the Freshwater Mussel Elliptio complanata is Sexually Dimorphic and Feminized by Low Levels of Atrazine

The widely used herbicide atrazine (ATR) may have endocrine-associated adverse effects, including on behavior. In this study, 120 adult freshwater mussels, Elliptio complanata, were exposed to ATR at the environmentally relevant concentrations of 1.5, 15, or 150 μg/L. Burrowing depth was evaluated hourly for 6 h and at sacrifice animals were sexed by gonad smear. Female controls burrowed overall approximately 30% less than males, the first report of sexual dimorphism in this behavior. Atrazine at 15 μg/L feminized burrowing in both sexes, in that exposed animals burrowed 20% less than their same-sex controls. Males treated with 1.5 μg /L ATR displayed approximately 20-fold higher vitellogenin (VTG) levels than same-sex controls. Higher concentrations of ATR were not associated with increasing effects. A scatterplot showed a weak binomial curve associating low burrowing with high VTG levels. Taken together, these data suggest a nonlinear dose response in behavioral and physiological feminization produced by ATR and support the need to reconsider the widespread use of this compound.

Monitoring fitness of caged mussels (Elliptio complanata) to assess and prioritize streams for restoration

ABSTRACT Freshwater mussels (order: Unionidae) are among the most endangered aquatic organisms in North America. Conservationists and resource managers within the United States are increasingly advocating restoration of these animals to preserve biodiversity and boost ecosystem services in the nation's waterways. Historically, restoration methods have yielded less than optimal survival rates due in part to an inability to identify suitable habitat for these organisms. Through the use of caged mussels as bioindicators, a method was developed to test prospective restoration sites for their ability to support mussel fitness before beginning restoration so that investments are strategic. Mussels (Elliptio complanata) from a healthy population were caged and deployed to candidate streams. Their survivorship, condition, and proximate biochemical composition (protein, carbohydrate, lipid) was then monitored for 1 year. Streams that supported mussel fitness as well as or better than their source stream were considered to be suitable for restoration. Four of five candidate streams were found to support mussel fitness. In addition, reciprocal transfers between two source populations showed that the seasonal patterns of tissue biochemical composition responded to ambient stream conditions, indicating that this species is diagnostic as a bioindicator of stream quality and habitat suitability. Copyright © 2013 John Wiley & Sons, Ltd.

A Stable Isotope Tracer (δ13C) Study ofEscherichia coliRetention in Two Freshwater Bivalves (Corbicula flumineaandElliptio complanata) (Corbiculidae and Unionidae)

Bacteria are ingested by suspension feeding bivalves and can be an important component of their diet. This study evaluated whether a common bacterium of vertebrate enteric origin, Escherichia coli (Migula, 1895), is retained in the stomach or gill by two different freshwater bivalve species, Corbicula fluminea (Müller, 1974) and Elliptio complanata (Lightfoot, 1786). A series of diet treatment experiments were conducted comparing each anatomical section using a δ13C label and E. coli cells grown from stock cultures. A significant difference in δ13C values was related to anatomic structure among all treatment groups during a 7-day feeding experiment (24 jars, df = 140; F = 4.88; P < 0.001). A key finding was that in gill tissue, a significant difference was observed among <δ13C-labeled and unlabeled treatment combinations for both C. fluminea and E. complanata (F = 13.57; df = 31; P < 0.0001). The results suggest that water column E. coli are likely retained on gill tissue and to a lesser degree in the stomach in both E. complanata and C. fluminea. This study serves to validate the hypothesis that E. coli may be initially more abundant in gill tissue during sorting processes before being transferred to the stomach.

Bioavailability and Immunotoxicity of Silver Nanoparticles to The Freshwater Mussel Elliptio complanata

The purpose of this study was to examine the effects of Ag nanoparticles (nAg) of two different sizes (20 and 80 nm) and Ag+ on the immune system of the freshwater mussel Elliptio complanata. Mussels were exposed to increasing concentrations of nAg and dissolved Ag (AgNO3) for 48 h at 15°C and concentration of 0, 0.8, 4, or 20 μg/L. Immunocompetence was determined by hemocyte viability, phagocytosis, and cell cytotoxicity. Ag tissue loadings and levels of metallothioneins (MT), lipid peroxidation (LPO), and labile zinc (Zn) were also determined. Results revealed first that 20- and 80-nm nAg readily formed aggregates in freshwater. Ag was detected in soft tissues with each form of Ag with bioconcentration factors of 20, 9, and 7 for Ag+, 20-nm nAg, and 80-nm nAg, respectively. Significant induction in phagocytosis and decreased cell cytotoxicity were observed. All forms of Ag were able to induce LPO in gills and digestive glands at concentrations below those from the initial fraction of dissolved Ag. The effects of nAg on MT levels in mussels were not discernible from those of dissolved Ag, but the 80-nm was 25-fold more potent than 20-nm nAg in inducing MT. Multivariate analysis revealed that the global responses of the 20- and 80-nm nAg were generally similar to those of dissolved Ag. Data also demonstrated that nAg are bioavailable for mussels where the immune system is a target during early exposure to nanoparticles.

Polybrominated diphenyl ethers in sediment and caged mussels (Elliptio complanata) deployed in the Niagara River

Polybrominated diphenyl ethers (PBDEs) were detected in caged mussels (Elliptio complanata), deployed in the Niagara River for 3weeks in 2003, 2004 and 2006 and in sediment collected from the river and tributaries. The highest concentrations (measured as the sum of 17 BDE congeners) were in mussels deployed within tributaries to the American side of the River (Cayuga Creek: 11.5ngg−1 wet wt.; Two Mile Creek 9.5ngg−1; and Gill Creek: 5.8ngg−1). In addition to contributions from the atmosphere, each urban tributary has multiple potential sources of PBDEs which include storm sewers, sewage treatment plants and industries located upstream of the sampling sites. Total PBDE concentrations in sediment ranged from 0.25 to 188ngg−1. In general, mean mussel tissue concentrations were positively correlated with sediment BDE concentrations. Total PBDE concentrations were higher in mussels deployed at most sites in the Tonawanda Channel which is highly industrialised, compared with mussels deployed on the Canadian side of the upper Niagara River where the surrounding area is generally rural. The sum of BDE-47, -99, -100, -153, -154 and -209 contributed between 92% and 96% of the total BDE concentrations in all of the mussel samples. BDE-209 represented between 39% and 100% of the total BDE in sediment samples. BSAFs in mussels ranged from 1 to 18 depending on the sampling station. Ratios of BDE-47/99 and BDE-100/99 and congener patterns in mussels and sediment were suggestive of the penta formulation as the historical source.

The effects of zinc oxide nanoparticles on the metallome in freshwater mussels

The use of zinc oxide nanoparticles (nanoZnO) as sunscreens has raised concerns about their safety and release in the aquatic environment through swimming activities and within municipally treated wastewaters. This study's purpose was to examine the effects of nanoZnO on the elemental composition (metallome) in exposed freshwater mussels, Elliptio complanata. Mussels were exposed for 21days to an environmentally realistic (low) concentration (2μg/L) of nanoZnO and zinc chloride. The mussels were also exposed to a physically and chemically treated municipal effluent (ME), both alone and in the presence of both forms of Zn. The metallome profile was characterized by the following 15 elements in gills, digestive gland and gonad tissues: Ag, Al, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Se, V and Zn. The levels of metallothioneins (MT) and lipid peroxidation (LPO) in the digestive gland were also measured as biomarkers of toxic effects. The data revealed that exposure to nanoZnO increased the total levels of Zn, MT and LPO in the digestive gland. Discriminate function analysis revealed that the digestive gland responded the most to exposure to either nanoZnO or Zn2+. For nanoZnO, the observed changes in Al, As and Mo in the digestive gland offered the best discrimination from dissolved Zn2+. Co-exposure of nanoZnO with the ME changed the metallome profile closer to dissolved Zn2+, suggesting a common interaction site within the ME. This was observed in changes in Ni, Cu, Se and Zn in the digestive gland of exposed mussels. Canonical analysis of essential and non-essential elements revealed that exposure to nanoZnO increased the relationships between LPO and the sum of essential elements in the digestive gland. Conversely, exposure to dissolved Zn2+ and the ME decreased the relationship between the sum of non-essential elements and LPO and MT. In conclusion, the use of a “metallomic” approach was used to discriminate changes following exposure to nanoZnO and dissolved Zn in freshwater mussels and provided insights into the interaction of forms of Zn in ME towards mussels.

Sublethal Effects of Silver Nanoparticles and Dissolved Silver in Freshwater Mussels

The increasing application of silver nanoparticles (nAg) in various consumer products has raised concerns regarding toxicological impacts in the environment. It is unclear at present whether the toxicity of nAg is mainly the result of the release of ionic Ag+ in mussels. The freshwater mussel Elliptio complanata was exposed to increasing concentrations of 20-nm nAg, 80-nm nAg, and dissolved Ag+ for 48 h at 15°C. The following biomarkers were used to determine the mode of action of nAg-induced adverse effects: metallothioneins (MT) (ionic Ag+ release), lipid peroxidation (LPO) (ionic Ag+ and nanosurface interactions), heat-shock proteins (HSP) (size-related effects), protein-ubiquitin levels (size-related effects), and DNA strand breaks (ionic Ag+ and size effects). Results revealed that the response pattern of 80 nm nAg was more closely related to ionic Ag+ than 20 nm nAg, suggesting a more important release of dissolved Ag from 80 nm nAg. Data showed that all forms of Ag were able to increase the levels of MT and LPO, which suggests the presence of ionic Ag+ leads to oxidative stress. However, nanoparticles were also able to induce changes in protein-ubiquitin and to a lesser extent actinomyosin-ATPase, MT, and DNA strand breaks in the digestive gland in a manner different from Ag+, which permitted discrimination of the forms of Ag. Moreover, LPO was closely associated with DNA strand breaks in the digestive gland and was not entirely explained by induction of MT, suggesting another type of toxic interaction. It was concluded that the presence of nAg not only increases the toxic loadings of released Ag ions but also generates other and perhaps cumulative effects of nanoparticle-induced toxicity related to size and surface properties.

Non-target trials with Pseudomonas fluorescens strain CL145A, a lethal control agent of dreissenid mussels (Bivalvia: Dreissenidae)

In an effort to develop an efficacious and environmentally safe method for managing zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena rostriformis bugensis), we initiated a research project investigating the potential use of bacteria and their natural metabolic products as biocontrol agents. This project resulted in the discovery of an environmental isolate lethal to dreissenid mussels, Pseudomonas fluorescens strain CL145A (Pf-CL145A). In previous published reports we have demonstrated that: 1) Pf-CL145A’s mode of action is intoxication (not infection); 2) natural product within ingested bacterial cells lyse digestive tract epithelial cells leading to dreissenid death; and 3) high dreissenid kill rates (>90%) are achievable following treatment with Pf-CL145A cells, irrespective of whether the bacterial cells are dead or alive. Investigating the environmental safety of Pf-CL145A was also a key element in our research efforts, and herein, we report the results of non-target trials demonstrating Pf-CL145A’s high specificity to dreissenids. These acute toxicity trials were typically single-dose, short-term (24-72 h) exposures to Pf-CL145A cells under aerated conditions at concentrations highly lethal to dreissenids (100 or 200 mg/L). These trials produced no evidence of mortality among the ciliate Colpidium colpoda, the cladoceran Daphnia magna, three fish species (Pimephales promelas, Salmo trutta, and Lepomis macrochirus), and seven bivalve species (Mytilus edulis, Pyganodon grandis, Pyganodon cataracta, Lasmigona compressa, Strophitus undulatus, Lampsilis radiata, and Elliptio complanata). Low mortality (3-27%) was recorded in the amphipod Hyalella azteca, but additional trials suggested that most, if not all, of the mortality could be attributed to some other unidentified factor (e.g., possibly particle load or a water quality issue) rather than Pf-CL145A’s dreissenidkilling natural product. In terms of potential environmental safety, the results of these invertebrate and vertebrate non-target trials are encouraging, but it would be unrealistic to think that dreissenids are the only aquatic organisms sensitive to Pf-CL145A’s dreissenid-killing natural product. Additional testing is needed to better define Pf-CL145A’s margin of safety by identifying the sensitivity of other susceptible organisms. The results of these non-target safety trials – in combination with equally promising mussel control efficacy data – have now led to Pf-CL145A’s commercialization under the product name Zequanox ® , with dead cells as the product’s active ingredient. The commercial availability of only dead-cell Zequanox formulations will eliminate the risk of any possible non-target infection by Pf-CL145A, further reducing environmental concerns. During the non-target project reported herein, the limited quantities of Pf-CL145A cells that we were able to culture severely restricted the number and size of our trials. In contrast, the availability of Zequanox will now greatly expand the opportunities for non-target testing. The trials reported herein – exposing non-target organisms under aerated conditions to unformulated, laboratory-cultured cells – clearly point to Pf-CL145A’s potential for high host specificity, but non-target trials with Zequanox – using PfCL145A cells cultured, killed, and formulated using industrial-scale protocols – will be even more important as they will define the nontarget safety limits of the actual commercial products under a wide range of environmental conditions.

Size distribution effects of cadmium tellurium quantum dots (CdS/CdTe) immunotoxicity on aquatic organisms

The increasing use of products derived from nanotechnology has raised concern about their potential toxicity to aquatic life. This study sought to examine the comparative immunotoxicity of capped cadmium sulphide/cadmium telluride (CdS/CdTe) quantum dots (QDs) and possible impact of particle/aggregate size on two bivalves (Mytilus edulis and Elliptio complanata) and a fish (Oncorhynchus mykiss). The QDs were dispersed in sterile water and fractionated using a series of micro/ultrafiltration membranes of decreasing pore size: 450 nm, 100 nm, 50 nm, 25 nm, 100 kDa (6.8 nm), 30 kDa (4.6 nm), 10 kDa (3.2 nm) and 1 kDa (1.5 nm). The total concentrations of cadmium and tellurium were determined for the filtered material and for that retained on the filters (retentate). The immunotoxicity was determined by measuring cell viability and phagocytosis. Results revealed that nanoparticles retained on the ultrafilters had a higher Cd/Te ratio compared to the permeate fraction (ratio of 5 and 2 respectively) which could indicate that the CdS core was not associated with the permeable fraction of Cd. Our results demonstrate that the toxicity of CdS/CdTe QDs was concentration and size dependent. Large CdS/CdTe QD aggregates (25 nm < size < 100 nm) reduced phagocytosis more than did smaller nanoparticles (<25 nm). Moreover, our results revealed that the different species responded differently to these fractions. Mytilus edulis hemocytes were less sensitive to CdS/CdTe QDs than the Oncorhynchus mykiss macrophage and Elliptio complanata hemocytes.

Short-Term Effects of Small Dam Removal on a Freshwater Mussel Assemblage

Dam removal is increasingly used to restore lotic habitat and biota, but its effects on freshwater mussels (family Unionidae) are not well known. We conducted a four-year study to assess short-term effects on mussels after removal of a small hydropower dam on the Deep River (Cape Fear River drainage), North Carolina, USA, in 2006. We conducted annual pre- and post-removal monitoring of mussel density, richness, and survival (post removal only) with transect surveys and quadrat excavation, and assessed changes in substrate composition at two impact sites (tailrace and impoundment) and two reference sites. Before-after-control-impact (BACI) analyses of variance did not detect a significant change in mussel density (total or individually for the three most abundant species), spe cies richness, Eastern Elliptio (Elliptio complanata) mean length, or substrate composition in the tailrace or drained impoundment following dam removal. Apparent annual survival estimates of Eastern Elliptio at the tailrace site did not differ among sampling periods and were similar to control sites. We observed minimal mussel mortality from stranding in the dewatered reservoir. These results demonstrate that adverse short-term impacts of dam removal on downstream mussel assemblages can be minimized with appropriate planning, timing, and removal techniques, but additional monitoring is warranted to determine long-term effects on mussels within the restored river reach.

Newly Documented Host Fishes for the Eastern Elliptio Mussel Elliptio complanata

Abstract The eastern elliptio Elliptio complanata is a common, abundant, and ecologically important freshwater mussel that occurs throughout the Atlantic Slope drainage in the United States and Canada. Previous research has shown E. complanata glochidia to be host fish generalists, parasitizing yellow perch Perca flavescens, banded killifish Fundulus diaphanus, banded sculpin Cottus carolinae, and seven centrarchid species. Past laboratory studies have been conducted in the Midwest; however, glochidia used in these studies were obtained from adult mussels in the Great Lakes or St. Lawrence River basins, or glochidia sources were not reported. The objective of this study was to identify host fishes for E. complanata from streams in the Mid-Atlantic region. We used artificial laboratory infections to test host suitability of 38 fish and 2 amphibian species with E. complanata glochidia from the Chesapeake Bay drainage. Glochidia successfully metamorphosed into juvenile mussels on five fish species: American eel Anguilla rostrata, brook trout Salvelinus fontinalis, lake trout Salvelinus namaycush, mottled sculpin Cottus bairdii, and slimy sculpin Cottus cognatus. American eel was the most effective host, yielding the highest overall metamorphosis success (percentage of attached glochidia that transformed into juvenile mussels; ≥0.90) and producing 13.2 juveniles per fish overall. No juvenile E. complanata metamorphosed on other fish or amphibian species tested, including many previously identified host fishes that appear in the literature. Reasons for discrepancies in published host fish could include geographic variation in host use across the species' range, differences in host use between lentic and lotic populations, or poorly resolved taxonomy within the genus Elliptio.

Genotoxic Response of Unionid Mussel Hemolymph to Hydrogen Peroxide and Polycyclic Aromatic Hydrocarbons

The single cell gel electrophoresis or comet assay is widely used to detect DNA damage in isolated cells following exposure to genotoxic compounds. This assay, although commonly used with marine bivalve tissue and circulatory fluid, has received little use or demonstration in freshwater mussels of the order Unionida. Because such a large proportion (>70%) of this faunal group is globally imperiled and is being adversely impacted by environmental contaminants, including many genotoxicants, the aim of this study was to assess the applicability of the comet assay in unionid mussel hemolymph sampled non-lethally with a reference genotoxicant, hydrogen peroxide (H2O2) and polycyclic aromatic hydrocarbons (PAHs), a class of common environmental pollutants of genotoxic action. DNA damage was evaluated in samples of hemolymph from Elliptio complanata in both in vitro and in vivo exposures and quantified using the endpoints % tail DNA, or the percentage of DNA in the comet tail and OTM or olive tail moment, the product of the fraction of DNA in the tail and tail length. Hemocytes were isolated and the comet assay was performed on control, 160 µM H2O2, and PAH treated cells. From the in vitro exposures, 160 µM H2O2, as well as the 50 and 100 µg/L total PAH treatments yielded statistically significant (p < 0.05) levels of DNA damage, with the H2O2 yielding an average of 39.7 % tail DNA and 13.3 OTM and the two PAH treatments yielding 40.7 % and 38.6 % tail DNA, and 12.4 and 11.0 OTM, respectively. An in vivo PAH exposure with adult E. complanata did not detect a similar genotoxic response to that detected with in vitro exposure, indicating that additional research and evaluation may be necessary before implementing the widespread use of a non-lethal, unionid mussel hemolymph based genotoxicity screening tool for environmental biomonitoring.

Causes of recruitment failure in freshwater mussel populations in southeastern New York

Populations of freshwater mussels (Unionoida) are declining or disappearing from many waters around the world. In many declining populations, recruitment fails before adult mortality occurs, resulting in relict populations that can persist for decades. We tested whether recruitment failure in populations of the freshwater mussel Elliptio complanata was associated with invasion of nonnative crayfish, loss of a primary fish host (American eel Anguilla rostrata), excessive inputs of fine sediments, or unfavorable interstitial water chemistry (too little dissolved oxygen or too much un-ionized ammonia). We sampled mussel populations, crayfish populations, and environmental conditions at 14 sites on wadeable streams in southeastern New York. Five of the mussel populations had little or no recent recruitment. We found no association between recruitment failure and crayfish, American eels, fine sediments, or interstitial dissolved oxygen. In contrast, recruitment failure was strongly associated with high concentrations (>0.2 microg N/L) of un-ionized ammonia. This threshold is much lower than thresholds for acute ammonia toxicity identified in laboratory studies. We suggest that excessive concentrations of interstitial un-ionized ammonia may be responsible for widespread declines of freshwater mussel populations, especially in agricultural areas.

Sediment accumulation predicts the distribution of a unionid mussel (Elliptio complanata) in nearshore areas of a Canadian Shield lake

Summary1. The importance of native freshwater mussels for ecosystem processes depends on their density, size distribution and activity. In lakes, many of the factors that affect mussels (fish hosts, habitat, food) could be directly or indirectly related to wind‐driven physical processes.2. We tested whether the abundance and size of Elliptio complanata in the shallow, nearshore areas of a medium‐sized lake were related to site exposure, substratum type and fish distribution. To disentangle some of the correlated variables known to affect mussel distribution, we used paired exposed and sheltered sampling sites along the 7‐km fetch of the lake basin.3. The distribution of sediment characteristics in nearshore areas was highly predictable. The mean depth of accumulated soft sediments decreased with increasing fetch at wind‐exposed sites, but increased with increasing fetch at sheltered sites. Sediments were deeper along the main shoreline than around islands. Deeper sediments tended to be finer and higher in silt content and organic fraction.4. The density and proportion of juvenile mussels along the main shoreline varied in a unimodal way with sediment depth. These results suggest that wind‐driven physical forces affect the transport of young juveniles to sediment depositional areas and create sediment conditions that influence their growth and survival. In contrast, the proportion of juvenile mussels around islands was not related to sediment characteristics, but decreased with remoteness of the island, suggesting that the distribution of juvenile mussels may be limited by fish movements. These results are tentative since they do not include buried juvenile mussels.5. We also found a unimodal relationship between total mussel density (juveniles and adults) and sediment depth but, in contrast to the relationship for juveniles only, it applied to all sites with soft sediments, including islands. We conclude that factors related to sediment depth affect the growth and survival of adult mussels around islands and that these factors are strong enough to modify the pattern of distribution established via dispersal during earlier life stages.6. The mean shell length of adults at different sites within the lake basin ranged from 60 to 85 mm. Mussel shell length decreased with increasing fetch at sites exposed to the prevalent winds, but was relatively constant on the sheltered side of peninsulas and islands. The size of unionid mussels in different parts of the lake seems to be determined both by their exposure to physical forces and by sediments.7. The local distribution of E. complanata is determined, directly and indirectly, by wind‐driven forces. These processes are likely to be important for other benthic organisms affected by similar habitat conditions (e.g. sediment characteristics, physical disturbance).

In vitro immunotoxicity of environmentally representative antibiotics to the freshwater mussel Elliptio complanata

The separate and combined in vitro toxic effects of antibiotics (ciprofloxacin, erythromycin, novobiocin, oxytetracycline, sulfamethazole and trimethoprim) commonly found in urban wastewater effluents were assessed on the immune parameters of Elliptio complanata at environmentally relevant concentrations. The observed responses were then compared to those produced by the physicochemical-treated wastewater effluent of a major city before and after the removal of microorganisms. Most of the selected antibiotics, separately and as mixture, induced changes in immune responses. The removal of microorganisms and fine particles from the effluent increased or decreased the resulting immunotoxic effects, depending of the observed parameter. The immunotoxic effects of erythromycin, sulfamethoxazole and trimethoprim were closely associated to the antibiotic mixture and the filtered effluent. In conclusion, the data revealed that the removal of fine particles and microorganisms from municipal effluents can alter the toxic nature of the effluent that is closely associated with the cumulative effects of antibiotics.

Toxic Effects of Copper, Cadmium, and Methoxychlor Shown by Neutral Red Retention Assay in Two Species of Freshwater Molluscs

We used neutral red retention assay in lysosomes of digestive gland cells as an indicator for stress effects by the environmental contaminants Cu, Cd, and the pesticide methoxychlor in two freshwater molluscs, the unionid mussel, Elliptio complanata (Lightfoot) and the ramshorn snail Helisoma trivolvis (Say). Mussels and snails were exposed for 7 and 14 days to Cu and Cd each at nominal concentrations of 2.5 µg/L, 5.0 µg/L, and 10.0 µg/L, and to methoxychlor concentrations of 1.0 µg/L, 10.0µg/L, and 100.0 µg/L. Both mussels and snails exposed to Cu showed a significant increase in the percent of destabilized lysosomes compared with lab control and freshly-collected (field control) mussels at both 7 and 14 days exposure for all concentrations. Cd-exposed mussels did not show a significant difference with either of the controls at 7 days, but at 14 days exposure, Cd significantly increased the percent of destabilized lysosomes at all concentrations compared to field control mussels. Compared to laboratory controls, Cd increased lysosomal destabilization at 5.0 µg/L and 10.0 µg/L. Snails exposed to Cd for 7 days had a significantly higher percentage of lysosomal destabilization than both lab and field controls but at 14 days, significant differences were only seen at the two highest Cd concentrations. Methoxychlor-exposed mussels showed no significant lysosomal destabilization at 7 days compared to controls. But at 14 days exposure, the pesticide increased the percentage of lysosomal destabilization at 10.0µg/L compared to lab controls, and increased at both 10.0µg/L and 100.0µg/L compared to field control mussels. Methoxychlor-exposed snails had a higher percentage of lysosomal destabilization at 7 and 14 days at all concentrations compared to both controls with the exception of the 1.0 µg/L -7 day exposure group. Snails were more sensitive to Cd and to methoxychlor than were mussels possibly because they lack an operculum and are thus completely exposed to the environment. The lowest observed effect concentration (LOEC) for Cd was 2.5 µg/L (14 days) for Elliptio and 2.5 µg/L (7 and 14 days) for Helisoma. For methoxychlor, the LOEC was 10.0 µg/L (14 days) for Elliptio and 10.0 and 1.0 µg/L (7 and 14 days, respectively) for Helisoma. The LOEC for Cu was 2.5 µg/L (7 and 14 day exposure) for both Elliptio and Helisoma. These results show that lysosomal destabilization as indicated by neutral red retention is a reliable indicator of stress from heavy metals and a pesticide in freshwater molluscs, including a taxon that is endangered or threatened in North America.

Recent thermal history influences thermal tolerance in freshwater mussel species (Bivalvia:Unionoida)

AbstractUnderstanding species’ temperature tolerances in the context of concurrent environmental stressors is critical because thermal regimes of freshwater ecosystems are changing. We evaluated the critical thermal maximum (CTM) of 3 freshwater mussel species (Alasmidonta varicosa, Elliptio complanata, and Strophitus undulatus) acclimated to 2 temperatures (15 and 25°C) and exposed to 2 aeration treatments (aerated vs unaerated) during CTM testing. Responses varied by species, but mussels acclimated to 25°C generally had a higher CTM than mussels acclimated to 15°C. For E. complanata, the effects of acclimation temperature and aeration were interactive, such that CTM was highest at 15°C but only under aerated conditions. Our results indicate that recent thermal history affects thermal tolerance, combinations of environmental stressors may influence thermal tolerance, and such responses vary among species.

Short-term physiological effects of a xenobiotic mixture on the freshwater mussel Elliptio complanata exposed to municipal effluents

The aim of this study was to investigate the short-term effects of tertiary-treated municipal effluents on the freshwater mussel Elliptio complanata. Caged mussels were immersed during 2 weeks in a river located North of Montreal Island, upstream/downstream the outfall and in one reference site located at the beginning of the Rivière des Prairies. A selection of biomarkers was analyzed to depict changes on various physiological systems: general physiology (mussel viability, condition index and gonado-somatic index), immune status (hemocyte viability, cellularity, phagocytosis efficiency, NK-like cytotoxic activity and lysozyme activity), inflammation (cyclo-oxygenase activity), detoxification (glutathione-S-transferases activity) and vitellogenesis (alkali-labile phosphate level). The analysis of total and fecal coliform counts in water and of heterotrophic bacteria levels in mussel tissues showed that the bacteriological quality of the water strongly decreased from the reference site to the downstream site. This was correlated with a significant loss of weight and an increase of mussel mortality. Cellularity and phagocytosis efficiency were significantly increased in the downstream site compared to the reference site. Though not statistically significant, lysozyme activity was also increased. NK-like cytotoxicity, activity of the pro-inflammatory enzyme COX and the levels of ALP and MT were not significantly changed. Conversely, the municipal effluents induced a significant increase of GST activity in downstream site, indicating a stimulation of detoxification metabolism. Altogether, these results confirm that a short-term exposure to a mixture of bacterial and chemical compounds released by the wastewater treatment plant La Pinière induces adverse physiological effects in E. complanata, as observed with the modulation of immune response and induction of detoxification metabolism.

QSAR studies on the depuration rates of polycyclic aromatic hydrocarbons, polybrominated diphenyl ethers and polychlorinated biphenyls in mussels (Elliptio complanata)

Based on the mechanism of action, a quantitative structure–activity relationship (QSAR) model for the depuration rate constants (k d) of 28 PAHs, 8 PBDEs and 28 PCBs in mussels (Elliptio complanata) was constructed by partial least squares (PLS) regression, following the guidelines for development and validation of QSAR models. For the training set of the QSAR model, r 2 = 0.953, the cross-validated regression coefficient () was 0.947. The predicted log k d values for the validation set were consistent with the observed values, with a standard error (SE) of 0.160 log units and a squared correlation coefficient () of 0.892. Comparatively, the developed QSAR model had good robustness, predictive ability and extended applicability domain. The electrophilicity index (ω), molecular polarizability (α), the averages of the negative potentials on the molecular surface () and the balance parameter of surface potential (τ) were the key parameters governing the log k d values in the QSAR model, which indicated that the log k d value was mainly related to the partition ability, electrostatic interactions, and van der Waals interactions of compounds.