The influence of surface coatings on the toxicity of silver nanoparticle in rainbow trout.

Silver nanoparticles (nAg) are often produced with different coatings that could influence bioavailability and toxicity in aquatic organisms. The purpose of this study was to examine the influence of 4 surface coatings of nAg of the same core size towards bioavailability and toxicity in juvenile rainbow trout (Oncorhynchus mykiss). Juveniles were exposed to 50 µg/L of 50 nm diameter nAg for 96 h at 15 °C with the following coatings: branched polyethylenimine (bPEI), citrate, polyvinylpyrrolidone (PVP) and silicate (Si). The data revealed that the coatings influenced hepatic Ag loadings in the following trend PVP > citrate > bPEI and Si with estimated bioavailability factors of 28, 18, 6 and 2 L/kg respectively. Hepatic Ag levels were significantly associated with DNA damage and inflammation as determined by arachidonate cyclooxygenase activity. The bPEI and citrate-coated nAg consistently produced the observed effects above in addition to increased mitochondrial electron transport activity and glutathione S-transferase activity. The absence of metallothionein and lipid peroxidation suggests that mechanisms other than the liberation of Ag+ were at play. In conclusion, surface coatings were shown to significantly influence bioavailability and toxic properties of nAg to rainbow trout juveniles.

Gene expression changes and toxicity of selected rare earth elements in rainbow trout juveniles.

Rare earth elements (REEs) are increasingly used in electronics industry and other areas of our economy and questions were raised about their impacts to the environment. The purpose of this study was to examine the lethal and sublethal toxicity of REEs in juvenile rainbow (Oncorhynchus mykiss) trout. The fish were exposed to increasing concentrations (0.064, 0.32, 1.6, 8 and 40 mg/L) of the following 7 REEs for 96 h at 15 °C: cerium (CeCl3), erbium (ErCl3), gadolinium (GdCl3), lanthanum (LaCl3), neodymium (NdCl3), samarium (SmCl3) and yttrium (YCl3). The mortality were determined and in the surviving fish, 10 target gene transcripts were measured in the liver to track changes in oxidative stress, DNA repair, tissue growth/proliferation, protein chaperoning, xenobiotic biotransformation and ammonia metabolism. The data revealed that Y, Sm, Er and Gd formed a distinct group based on toxicity (mortality) and gene expression changes. Electronegativity was significantly correlated (r = -0.8, p < 0.01) with the lethal concentration (LC50). Gene expression changes occurred at concentration circa 120 times lower than the LC50 and the following transcripts in protein chaperoning (heat shock proteins), DNA repair (growth arrest DNA Damage) and CYP1A1 gene expression involved in the metabolism of coplanar aromatic hydrocarbons were involved. In conclusion, the study revealed that the more electronegative REEs were the most toxic to trout juveniles and produced sublethal effects at concentrations 2 orders of magnitude lower than the lethal concentrations. The toxicity of REEs depends on the elements were toxicity involves specific pathways at the gene expression level.

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.

Metal bioaccumulation and biomarkers of effects in caged mussels exposed in the Athabasca oil sands area.

The Athabasca oil sands deposit is the world's largest known reservoir of crude bitumen and the third-largest proven crude oil reserve. Mining activity is known to release contaminants, including metals, and to potentially impact the aquatic environment. The purpose of this study was to determine the impacts of oil sands mining on water quality and metal bioaccumulation in mussels from the Fort McMurray area in northern Alberta, Canada. The study presents two consecutive years of contrasting mussel exposure conditions (low and high flows). Native freshwater mussels (Pyganodon grandis) were placed in cages and exposed in situ in the Athabasca River for four weeks. Metals and inorganic elements were then analyzed in water and in mussel gills and digestive glands to evaluate bioaccumulation, estimate the bioconcentration factor (BCF), and determine the effects of exposure by measuring stress biomarkers. This study shows a potential environmental risk to aquatic life from metal exposure associated with oil sands development along with the release of wastewater from a municipal treatment plant nearby. Increased bioaccumulation of Be, V, Ni and Pb was observed in mussel digestive glands in the Steepbank River, which flows directly through the oil sands mining area. Increased bioaccumulation of Al, V, Cr, Co, Ni, Mo and Ni was also observed in mussel gills from the Steepbank River. These metals are naturally present in oil sands and generally concentrate and increase with the extraction process. The results also showed different pathways of exposure (particulate or dissolved forms) for V and Ni resulting from different river water flows, distribution coefficient (Kd) and BCF. Increasing metal exposure downstream of the oil sands mining area had an impact on metallothionein and lipid peroxidation in mussels, posing a potential environmental risk to aquatic life. These results confirm the bioavailability of some metals in mussel tissues associated with detoxification of metals (metallothionein levels), and oxidative stress in mussels located downstream of the oil sands mining area. These results highlight a potential ecotoxicological risk to biota and to the aquatic environment downstream of the oil sands mining area, even at low metal exposure levels.

An investigation of the immunotoxicity of oil sands processed water and leachates in trout leukocytes.

Increased oil sands (OS) mining activity has raised concerns about impacts on aquatic organisms. This study sought to examine the effects of single representative compounds from OS (benzo(a)pyrene, naphthalene), a mixture of naphthenic acids (NAs), OS-processed water (OSPW) and OS leachate (OSL) extracts on rainbow trout leukocytes. Primary cultures of trout leukocytes were exposed to increasing concentrations of benzo(a)pyrene, naphthalene, NAs, OSPW and OSL for 48h at 18°C. Immunocompetence was followed by measuring changes in lymphocyte and macrophage viability and phagocytosis. Changes in the expression of 10 transcripts were also followed: interleukin 1, 2 and 6 (Il-1, Il-2 and Il-6), calreticulin (CRT), caspase 9 (Cas9), aryl hydrocarbon receptor (AhR), cyclooxygenase-2 (COX2), glutathione S-transferase (GST), catalase (CAT) and p53 tumor suppressor. The results revealed that exposure to OSPW extracts decreased the capacity of macrophages to engulf three beads or more, while the other compounds generally increased phagocytosis activity. Lymphocyte apoptosis was increased by all compounds and mixtures except naphthalene. Both OSPW and OSL induced apoptosis in macrophages. At the gene expression level, Cas9, CRT, Il-1 (inhibition) and Il-2 were specifically influenced by OSPW, while CAT, p53, COX2 and Il-1 (induction) transcripts were specifically expressed by OSL. Leukocyte exposure to OSPW produced characteristic changes in immunocompetence and genes involved in proinflammatory, apoptosis and protein damage (CRT) pathways which could not be explained by OSL, benzo(a)pyrene, naphthalene and NA mixture.

Elemental profiles of freshwater mussels treated with silver nanoparticles: A metallomic approach.

Nanoparticles released into the environment could pose a risk to resident organisms that feed on suspended particles in aquatic ecosystems. The purpose of this study was to examine the effects of silver nanoparticles (nanoAg) of different sizes in freshwater mussels using a multi-elemental (metallomic) approach in order to determine signature effects of nanoparticulate and ionic Ag. Mussels were exposed to three concentrations (0.8, 4 and 20µg/L) of 20-nm and 80-nm nanoAg and AgNO3 for 48h at 15°C. After the exposure period, mussels were placed in clean, aerated water for a depuration step and analyzed for the following total elements in gill, digestive gland and gonad tissues: Al, Ag, As, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Pb, Na, Ni, Se, Sr, Th, U, V and Zn. Metallothioneins (MT; digestive gland only) and lipid peroxidation (LPO) were also determined in gills, digestive glands and gonads. The 20-nm-diameter nanoAg was detected in all three tissues at 20µg/L, while the 80-nm nanoAg was detected more strongly in the digestive gland. Ionic Ag was found at higher levels in gills than in other tissues. Correlation analysis revealed that gonad Ag levels were significantly correlated with Al (r=0.28), V (r=0.28), Cr (r=0.31), Co (r=0.32), Se (r=0.34) and MT levels (r=0.28). Indeed, the MT levels in the digestive gland were significantly increased by 20-nm nanoAg (20µg/L) and 80-nm nanoAg (4µg/L) and AgNO3 (<0.8µg/L). LPO was observed in gills, digestive glands and even gonads for all Ag forms. Discriminant function analysis revealed that all forms of Ag differed from each other and from unexposed mussels, where ionic Ag was more closely related to the 80-nm-diameter nanoAg. Factorial analysis revealed that Ba, Ca, Co, Mn, Sr, U and Zn had consistently high factorial weights in all tissues; that explained 80% of the total variance. Moreover, the following elements showed strong correlations (r>0.7) with each other: Sr, Ba, Zn, Ca, Mg Cr, Mn and U. Comparisons of these elements with other elements showing low or no correlations (e.g., transition elements) revealed that these elements had significantly lower standard reduction potential and electronegativity, suggesting that stronger reducing elements were most influenced by the oxidizing effects of nanoAg and ionic Ag in tissues. Indeed, tissues with oxidative stress (LPO) had decreased levels for most of these reducing elements. We conclude that exposure to Ag nanoparticles produces a characteristic change in the elemental composition of gills, digestive gland and gonad tissues in freshwater mussels. Elements most responsive to oxidative stress were more influenced by both nanoAg and ionic Ag. Sr and Ba were readily decreased by Ag and appeared to respond more sensitively to nanoAg than to ionic Ag. The metallomic approach could contribute in the understanding of fundamental mode of action of nanoparticles in mussels.

Fate of silver nanoparticles in wastewater and immunotoxic effects on rainbow trout.

Silver nanoparticles (AgNPs) are currently used in technology, medicine and consumer products, even though the fate and the ecotoxicological risks on aquatic organisms of these new materials are not well known. The purpose of this study was to investigate the fate, bioavailability of AgNPs and their effects on fish in presence of municipal effluents. Juvenile rainbow trout were exposed for 96h to 40µg/L of AgNPs or 4µg/L of dissolved silver (AgNO3) in diluted (10%) municipal wastewater. Silver (Ag) concentrations were measured both on water samples and fish tissues (liver and gills). Toxicity was investigated by following immunological parameters in the pronephros (viability, phagocytosis) and biomarkers in liver and gills (cyclooxygenase activity, lipid peroxidation, glutathione-S-transferase, metallothioneins, DNA strand breaks and labile zinc). Results indicated that AgNPs appeared as small non-charged aggregates in wastewaters (11.7±1.4nm). In gills, the exposure to AgNPs induced morphological modifications without visible nanoparticle bioaccumulation. Dissolved Ag(+) was bioavailable in diluted effluent and induced oxidative stress (lipid peroxidation), labile zinc and a marginal decrease in superoxide dismutase in fish gills. Ag(+) also increased significantly metallothionein levels and inhibited the DNA repair activity in the liver. Finally, the two silver forms were found in liver and induced immunosuppression and inflammation (increase in cyclooxygenase activity). This study demonstrated that both forms of Ag produced harmful effects and AgNPs in wastewater were bioavailable to fish despite of their formation of aggregates.

Impacts of municipal wastewater oxidative treatments: changes in metal physical speciation and bioavailability.

The environmental repercussions of the discharge of disinfected effluents are still poorly understood. This study assessed the impact of ozonation and UV oxidative treatment processes on metal forms - particulate, colloidal and permeable fractions - and bioavailability in disinfected wastewaters. In addition to wastewater analyses, mussels were placed in continuous flow-through aquaria and exposed for 4wk to wastewater, then metals in their tissues were analysed in parallel with exposure biomarkers. Metal size distribution was affected by oxidative processes; results showed that ozonation treatment generally increases the permeable fraction of some metals, particularly Cd and Cu, in treated waters, whereas UV treatment fosters the formation of permeable Zn. Ozone treatment of wastewater generally increased the bioavailability of specific metals. Metal bioaccumulation was in most cases significantly higher in mussels exposed to ozone-treated effluent compared to the UV treatment: 58%, 32%, 42% and 47% higher, respectively, for Ag, Cd, Cr and Cu. Physical metal speciation in these wastewaters comparatively measured the permeable fraction of metals to relate them to the bioaccumulation results for the exposed mussels. The levels of lipid peroxidation were significantly increased in gills but not in the digestive gland. The levels of metallothionein in the digestive gland were also significantly reduced suggest decreased input of particulate metals. Results of bioaccumulation in mussels suggested that metal bioavailability can be modified by the different oxidative processes. Despite this disadvantage, ozonation still represents a great choice of treatment considering the overall environmental benefits.

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.

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.

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.

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 21 days to an environmentally realistic (low) concentration (2 µg/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 Zn(2+). For nanoZnO, the observed changes in Al, As and Mo in the digestive gland offered the best discrimination from dissolved Zn(2+). Co-exposure of nanoZnO with the ME changed the metallome profile closer to dissolved Zn(2+), 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 Zn(2+) 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.

A comparative toxicogenomic investigation of oil sand water and processed water in rainbow trout hepatocytes.

The purpose of this study was to compare the expression of gene transcripts involved in toxic stress in rainbow trout hepatocytes exposed to oil sand water (OSW), lixiviate (OSLW), and processed water (OSPW). We pose the hypothesis that the changes in gene expression responses in cells exposed to a simulated oil sand extraction procedure (OSPW) differ from the gene expression responses of OSLW and OS. Rainbow trout hepatocytes were exposed to increasing concentrations of OSW, OSLW, and OSPW for 48 h at 15 °C. Cell viability was assessed by measuring membrane permeability, total RNA levels, and gene expression using an array of 16 genes involved in xenobiotic biotransformation (GST, CYP1A1, CYP3A4, MDR), metal homeostasis and oxidative stress (MT, SOD, and CAT), estrogenicity (VTG, ERß), DNA repair (LIG, APEX, UNG, and OGG), cell growth (GADD45 and PCNA), and glycolysis (GAPDH). The results showed that the toxicogenomic properties of OSPW differed from those of OSLW and OSW. Gene transcripts that were influenced by OSW and OSLW, and strongly expressed in OSPW, were MT, CAT, GST (induction), CYP1A1, VTG, UNG/OGG, and PCNA. These genes are therefore considered not entirely specific to OSPW but to water in contact with OS. We also found gene transcripts that responded only with OSPW: SOD, GST (inhibition), MDR (inhibition), CYP3A4, GAPDH, GADD45, and APEX. Of these gene transcripts, the ones strongly associated with toxicity (loss of cell viability and RNA levels) were CYP3A4, GST, and GAPDH. Genes involved in DNA repair were also strongly related to the loss of cell viability but responded to both OSLW and OSPW. The observed changes in cell toxicity and gene expression therefore support the hypothesis that OSPW has a distinct toxic fingerprint from OSLW and OSW.

Screening test of silver nanoparticles in biological samples by graphite furnace-atomic absorption spectrometry.

A simple, rapid and inexpensive screening test is presented to determine the presence of silver (Ag) nanoparticles in biological samples. The method is based on graphite furnace-atomic absorption spectrometry (Zeeman background correction) where an increase in the atomization temperature is observed with an increase in the particle size of Ag. The method is able to determine the presence of Ag ions from the presence of nano-Ag of 20, 60 and 80 nm, but the methodology was less apt to resolve nanoparticles between 20 and 60 nm. The proposed methodology was capable of determining the presence of dissolved Ag(+) from 20 nm in prepared mixtures, and in the liver of rainbow trout exposed to either dissolved or 20-nm nano-Ag.

Toxicity of silver nanoparticles to rainbow trout: a toxicogenomic approach.

Silver (Ag) nanoparticles are used as antimicrobial adjuvant in various products such as clothes and medical devices where the release of nano-Ag could contaminate the environment and harm wildlife. The purpose of this study was to examine the sublethal effects of nano-Ag and dissolved Ag on Oncorhynchus mykiss rainbow trout. Hepatic Ag contents and changes in gene expression were monitored to provide insights on bioavailability and mode of action of both forms of silver. Fish were exposed to increasing concentrations (0.06, 0.6 and 6 µg L(-1)) of nano-Ag (20 nm) and silver nitrate (AgNO(3)) for 96 h at 15°C. A gene expression analysis was performed in the liver using a DNA microarray of 207 stress-related genes followed by a quantitative polymerase chain reaction on a selection of genes for validation. The biochemical markers consisted of the determination of labile zinc, metallothioneins, DNA strand breaks, lipid peroxidation (LPO) and vitellogenin-like proteins. The analysis of total Ag in the aquarium water revealed that nano-Ag was mostly aggregated, with 1% of the total Ag being dissolved. Nevertheless, hepatic Ag content was significantly increased in exposed fish. Indeed, dissolved Ag was significantly more bioavailable than nano-Ag only at the highest concentration with 38 ± 10 and 11 ± 3 ng Ag mg(-1) proteins for dissolved and nano-Ag respectively. Exposure to both forms of Ag led to significant changes in gene expression for 13% of tested gene targets. About 12% of genes responded specifically to nano-Ag, while 10% of total gene targets responded specifically to dissolved Ag. The levels of vitellogenin-like proteins and DNA strand breaks were significantly reduced by both forms of Ag, but DNA break levels were lower with nano-Ag and could not be explained by the presence of ionic Ag. Labile zinc and the oxidized fraction of metallothioneins were increased by both forms of Ag, but LPO was significantly induced by nano-Ag only. A discriminant function analysis revealed that the responses obtained by biochemical markers and a selection of ten target genes were able to discriminate completely (100%) the effects of both forms of Ag. Exposure to nano-Ag involved genes in inflammation and dissolved Ag involved oxidative stress and protein stability. Hence, the toxicity of Ag will differ depending on the presence of Ag nanoparticles and aggregates.

Ecotoxicological impacts of effluents generated by oil sands bitumen extraction and oil sands lixiviation on Pseudokirchneriella subcapitata.

The exploitation of Athabasca oil sands deposits in northern Alberta has known an intense development in recent years. This development has raised concern about the ecotoxicological risk of such industrial activities adjacent to the Athabasca River. Indeed, bitumen extraction generated large amounts of oil sands process-affected water (OSPW) which are discharged in tailing ponds in the Athabasca River watershed. This study sought to evaluate and compare the toxicity of OSPW and oil sands lixiviate water (OSLW) with a baseline (oil sands exposed to water; OSW) on a microalgae, Pseudokirchneriella subcapitata, at different concentrations (1.9, 5.5, 12.25, 25 and 37.5%, v/v). Chemical analyses of water-soluble contaminants showed that OSPW and OSLW were enriched in different elements such as vanadium (enrichment factor, EF=66 and 12, respectively), aluminum (EF=64 and 15, respectively), iron (EF=52.5 and 17.1, respectively) and chromium (39 and 10, respectively). The toxicity of OSPW on cells with optimal intracellular esterase activity and chlorophyll autofluorescence (viable cells) (72h-IC 50%<1.9%) was 20 times higher than the one of OSW (72h-IC 50%>37.5%, v/v). OSLW was 4.4 times less toxic (IC 50%=8.5%, v/v) than OSPW and 4.5 times more toxic than OSW. The inhibition of viable cell growth was significantly and highly correlated (<-0.7) with the increase of arsenic, beryllium, chromium, copper, lead, molybdenum and vanadium concentrations. The specific photosynthetic responses studied with JIP-test (rapid and polyphasic chlorophyll a fluorescence emission) showed a stimulation of the different functional parameters (efficiency of PSII to absorb energy from photons, size of effective PSII antenna and vitality of photosynthetic apparatus for energy conversion) in cultures exposed to OSPW and OSLW. To our knowledge, our study highlights the first evidence of physiological effects of OSPW and OSLW on microalgae.

Ecotoxicity of CdTe quantum dots to freshwater mussels: impacts on immune system, oxidative stress and genotoxicity.

The purpose of this study was to examine the toxic effects of cadmium-telluride (CdTe) quantum dots on freshwater mussels. Elliption complanata mussels were exposed to increasing concentrations of CdTe (0, 1.6, 4 and 8 mg/L) and cadmium sulfate (CdSO(4), 0.5mg/L) for 24h at 15 degrees C. After the exposure period, they were removed for assessments of immunocompetence, oxidative stress (lipid peroxidation) and genotoxicity (DNA strand breaks). Preliminary experiments revealed that CdTe dissolved in aquarium water tended to aggregate in the particulate phase (85%) while 15% of CdTe was found in the dissolved phase. Immunotoxicity was characterized by a significant decrease in the number of hemocytes capable of ingesting fluorescent beads, and hemocyte viability. The cytotoxic capacity of hemocytes to lyse mammalian K-562 cells was significantly increased, but the number of circulating hemocytes remained unchanged. Lipid peroxidation was significantly increased at a threshold concentration of 5.6 mg/L in gills and significantly reduced in digestive glands at a threshold concentration <1.6 mg/L CdTe. The levels of DNA strand breaks were significantly reduced in gills at <1.6 mg/L CdTe. In digestive glands, a transient but marginal increase in DNA strand breaks occurred at the lowest concentration and dropped significantly at the higher concentrations. A multivariate analysis revealed that the various response patterns differed based on the concentration of CdTe, thus permitting the identification of biomarkers associated with the form (colloidal vs. molecular) of cadmium.

Changes in metallothionein levels in freshwater mussels exposed to urban wastewaters: effects from exposure to heavy metals?

Municipal effluents are complex mixtures of compounds such as heavy metals, aromatic and aliphatic hydrocarbons, and micro-organisms and are released in aquatic ecosystems. The purpose of this study was to verify whether changes in metallothioneins (MT) were associated with the accumulation of labile metals in tissue of freshwater mussels exposed to the dispersion plume of a major municipal effluent. Mussels were placed in experimental cages deployed at sites 1.5 km upstream, 8 km downstream and 12 km downstream of the outfall of a major, primary-treated municipal effluent in the St. Lawrence River (Québec, Canada). Mussels were analysed for MT and labile zinc levels in their gonads, gills and digestive glands. Lipogenic enzyme (isocitrate and glucose-6-phosphate dehydrogenase) and arachidonic acid cyclooxygenase (COX) activities were also measured in gonad and gill tissues. Although MT was induced in all the tissues examined, the results showed that labile zinc levels were significantly reduced in gill and gonad tissues, with an increase observed only at the 12 km downstream site in the digestive gland. COX activity was readily induced in gills and gonads. Glucose-6-phosphate dehydrogenase activity was reduced at both downstream sites, but isocitrate dehydrogenase activity was significantly induced at the farthest (12 km) site. Analysis of covariance revealed that MT levels in gills were more influenced by COX activity than with distance in the dispersion plume and was negatively correlated with labile zinc levels. In conclusion, MT induction was inversely related to the levels of labile zinc but positively so with the inflammation biomarker COX. Hence, the induction of MT in mussels exposed to the municipal effluent of a large city appears to be associated with either inflammatory processes or as compensation for the loss of labile essential metals. We propose that the simple and complimentary parameters of labile zinc and COX evaluations be used to link MT induction with divalent heavy metal exposure in environmental studies dealing with various type of contaminants in such complex contaminant mixture effluents.

Toxicity evaluation of organic sediment extracts resolved by size exclusion chromatography using rainbow trout hepatocytes.

The (geno)toxicity of sediment dichloromethane extracts and fractions obtained by size exclusion chromatography were evaluated to investigate effects based on size fractionation. In this study, three sediments were selected according to their incremental contamination in PAHs and in PCBs: Hamilton harbour, Toronto bay and lake St. Clair sediments. Heavy metals, total sulfur and elemental sulfur (S8) were also determined in the (un)fractionated sediment extracts. The liver cells were exposed to concentrations of sediment extracts and fractionated samples for 24 h at 15 degrees C, afterwhich cell viability, cytochrome P4501A1 activity, available free Zn, DNA damage and oxidative stress were determined. The results showed that the sediment extracts contained high levels of sulfur most of which was found in the low molecular weight (LMW) region, i.e., the 2000-50 atomic mass unit (amu) fraction. Elemental sulfur (S8) accounted for 14-41% of extractable sulfur and were found to elute in the post-column volume (PCV) fraction despite its molecular weight of 256 amu. Heavy metals were found mainly in the HMW (i.e. the > 2000 amu) fraction and LMW fractions and very few or none were observed in the PCV fractions. In sediment extracts, sublethal effects were present principally by the HMW and LMW fractions suggesting that some chemicals were also associated with high molecular weight compounds of extractable organic matter. Less toxicity or effect was sometimes found in the extract indicating an antagonistic effect of the contaminants. We found that cell viability and genotoxicity evaluations could be performed on the unfractionated extracts while EROD, available Zn and oxidative stress measurements should be performed on the LMW fractions because of possible antagonist or shielding effects. Considering the cytotoxic responses, the best toxicity ranking in respect to contaminant levels in sediment extract was obtained with the LMW and PCV fractions which accounted for most of the toxic responses in the chromatographic fractions. Moreover, the shielding effect could be explained, in part, by the association of LMW contaminants to large macromolecules.