Temporal fluctuation of metallic trace elements concentrations in three morphotypes of floating holopelagic Sargassum from the Caribbean coast (Guadeloupe, French West Indies).

Since 2011, the Caribbean coasts have unprecedented stranding of a pelagic brown macroalgae Sargassum inducing damages for coastal ecosystems and economy. This study evaluated the temporal fluctuations of metallic trace elements (MTE) in Sargassum freshly arrived on the Caribbean coast. From May 2020 to September 2021, 12 floating samples of three morphotypes (S. fluitans III and S. natans I and VIII) were regularly collected in the Petit Cul-de-Sac Marin (Guadeloupe, French West Indies). Measured concentrations of 28 metal(loid)s trace elements reveal i) an absence of seasonal patterns in MTE concentrations except for metals Fe and Al during 2020 summer ii) a regular and high As content during the entire survey iii) a similar trend of contamination for each morphotype. The constant and high amount of As implies that stranding management policy and valorization processes of Sargassum must consider As contamination and that this vigilance must be constantly along the year.

Comparison of the accumulation and effects of copper pyrithione and copper sulphate on rainbow trout larvae.

Copper pyrithione (CuPT) is used as a co-biocide in new antifouling paints but its toxicity remains little known. To compare the toxicity of copper-based compounds, rainbow trout (Oncorhynchus mykiss) larvae were exposed for 8-day to CuPT and CuSO4 at equivalent copper concentrations. CuPT exposure led to the greatest accumulation of Cu in larvae. Exposure to 10 µg.L-1 CuPT induced 99% larval mortality but only 4% for CuSO4-exposed larvae. The larval development and growth were affected by CuPT (from 0.5 µg.L-1 Cu) but not by CuSO4. Lipid peroxidation was not induced by either contaminant. The expression of genes involved in oxidative stress defence, detoxification and copper transport was induced in larvae exposed to CuSO4 and CuPT but at higher concentrations for CuPT. This study highlights the marked toxicity of CuPT for early life stages of fish and raises the question of the possible environmental risks of this antifouling compound.

The effects of winter cold acclimation on acute and chronic cadmium bioaccumulation and toxicity in the banded killifish (Fundulus diaphanus).

Temperate freshwater fishes can experience large seasonal temperature fluctuations that could affect their exposure and sensitivity to trace metals. Yet, temperature effects are overlooked in ecotoxicology studies, especially for cold temperatures typical of the winter. In the present study, the effects of long-term cold acclimation on Cd bioaccumulation and toxicity were investigated in a freshwater fish, the banded killifish (Fundulus diaphanus). Killifish were acclimated to 14 °C or gradually cooled (2 °C/week) to 4 °C and cold acclimated for 6 weeks. Then, both acclimation groups were exposed to environmentally realistic waterborne Cd concentrations (0, 0.5 or 5 µg Cd L-1) for a further 28 d at their respective acclimation temperatures. Tissue metal bioaccumulation, fish survival, condition, and markers of oxidative and ionoregulation stress, were measured after 0, 2, 5 and 28 days of Cd exposure. Cadmium tissue accumulation increased over the exposure duration and was typically lower in cold-acclimated fish. In agreement with this lower bioaccumulation, fewer Cd toxic effects were observed in cold-acclimated fish. There was little evidence of a difference in intrinsic Cd sensitivity between 4 °C- and 14 °C-acclimated fish, as Cd toxicity appeared to closely follow Cd bioaccumulation. Our study suggests that current environmental water quality guidelines would be protective in the winter for the abundant and ecologically-important banded killifish.

Influence of ozone microbubble enhanced oxidation on mine effluent mixes and Daphnia magna toxicity.

The mining industry often must mix different kinds of water on the mine site during pre-treatment or post-treatment before the final discharge of the treated water to the environment. Microbubble ozonation has proven to be efficient in the removal of contaminants of concern from mine water, such as metals, metalloids, and nitrogen compounds, which can persist in the environment and entail toxicity issues. This study evaluated the efficiency of ozone microbubbles combined with lime precipitation on contaminant removal and its impact on toxicity for Daphnia magna with five different mine effluent mixes from an active mine site located in Abitibi-Témiscamingue, QC, Canada. For the non-acidic mixes, two scenarios were tested: first, pre-treatment of metals using lime precipitation and a flocculant was conducted prior to ozonation; and second, ozonation was conducted prior to metals post-treatment using the same precipitation and flocculation technique. Results showed that the NH3-N removal efficiency ranged from 90% for the lower initial concentrations (1.1 mg/L) to more than 99% for the higher initial concentrations (58.4 mg/L). Moreover, ozonation without metals pre-treatment improved NH3-N treatment efficiency in terms of kinetics but entailed abnormal toxicity issues. Results of bioassays conducted on water with metals pre-treatment did not show any toxicity events but showed abnormal toxicity patterns on the mixes treated without metals pre-treatment (diluted effluents were toxic, while undiluted were not). At 50% dilution, the water was toxic, probably due to the potential presence of metal oxide nanoparticles. The confirmation of the source of toxicity requires further investigation.

Thermal modulation of mitochondrial function is affected by environmental nickel in rainbow trout (Oncorhynchus mykiss).

In this study, we investigated the combined effects of temperature and nickel (Ni) contamination on liver mitochondria electron transport system (ETS) enzymes, citrate synthase (CS), phospholipid fatty acid composition and lipid peroxidation in rainbow trout (Oncorhynchus mykiss). Juvenile trout were acclimated for two weeks to two different temperatures (5˚C and 15˚C) and exposed to nickel (Ni; 520 µg/L) for three weeks. Using ratios of ETS enzymes and CS activities, our data suggest that Ni and an elevated temperature acted synergistically to induce a higher capacity for reduction status of the ETS. The response of phospholipid fatty acid profiles to thermal variation was also altered under nickel exposure. In control conditions, the proportion of saturated fatty acids (SFA) was higher at 15˚C than at 5˚C, while the opposite was observed for monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA). However, in nickel contaminated fish, the proportion of SFA was higher at 5˚C than at 15˚C, while PUFA and MUFA followed the opposite direction. A higher PUFA ratio is associated with higher vulnerability to lipid peroxidation. Thiobarbituric Acid Reactive Substances (TBARS) content was higher when the PUFA were in higher proportions, except for Ni-exposed, warm-acclimated fish, in which we reported the lowest level of TBARS but the highest proportion of PUFA. We suspect that the interaction of nickel and temperature on lipid peroxidation is due to their synergistic effects on aerobic energy metabolism, as supported by the decrease in the activity of complex IV of the ETS enzyme activity in those fish, or on antioxidant enzymes and pathways. Overall, our study demonstrates that Ni exposure in heat-challenged fish can lead to the remodelling of the mitochondrial phenotype and potentially stimulate alternative antioxidant mechanisms.

Early developmental toxicity of Atlantic salmon exposed to conventional and unconventional oils.

Atlantic salmon is an important species for Canadian culture and economy and its importance extends beyond Canada to Scandinavia and Western Europe. However, it is a vulnerable species facing decline due to habitat contamination and destruction. Existing and new Canadian pipeline projects pose a threat to salmonid habitat. The effects of diluted bitumen (dilbit), the main oil circulating in pipelines, are less studied than those of conventional oils, especially during the critical early embryonic developmental stage occurring in freshwater ecosystems. Therefore, this study aimed to compare the effects of water-accommodated fractions (WAF) of the Clearwater McMurray dilbit and the Lloydminster Heavy conventional oil on Atlantic salmon embryos exposed either from fertilization or from eyed stage. The dilbit contained the highest concentrations of low molecular weight (LMW) compounds (including BTEX and C6-C10), while the conventional oil contained the highest concentrations of PAHs. The Clearwater dilbit caused a higher percentage of mortality and malformations than the conventional oil at similar WAF concentrations. In addition, the embryos exposed from fertilization suffered a higher mortality rate, more developmental delays, and malformations than embryos exposed from the eyed stage, suggesting that early development is the most sensitive developmental stage to oil exposure. Gene expression and enzymatic activity of the detoxification phase I and II enzymes (CYP1A and GST) were measured. Data showed increases in both cyp1a expression and GST activity with increasing WAF concentrations, while gst expression was not affected by the exposures. Also, gene expression of proteins involved in the biotransformation of vitamin A and DNA damage repair were modified by the oil exposures. Overall, this study indicates that Atlantic salmon is mostly affected by oil exposure at the beginning of its development, during which embryos accumulate deformities that may impact their survival at later life stages.

The effects of dissolved petroleum hydrocarbons on benthic organisms: Chironomids and amphipods.

The oil sands industry in Canada, produces heavy unconventional oils, diluted for transport and called diluted bitumen. However, despite advances in our knowledge of the ecotoxicological risk that these products represent, their effects on benthic organisms following a spill are still largely unknown. In order to fill these gaps, this study aims to determine the lethal and sublethal effects of two diluted bitumens (Bluesky and Cold Lake) and one conventional oil (Lloydminster) for two freshwater benthic invertebrates: Chironomus riparius and Hyalella azteca. The objective of this study is to assess the toxicity of dissolved hydrocarbons, resulting from the physical dispersion of oil, immediately after a spill on the benthic invertebrates. To this end, organisms were exposed for 7 days for chironomids and 14 days for amphipods to a fraction containing soluble hydrocarbons (WAF: water accommodated fraction; 10 g/L, 18 h of agitation, followed by 6 h of sedimentation) with natural or artificial sediment. After exposure, the effects of hydrocarbons were determined using size, mortality, and antioxidant capacities. Dissolved hydrocarbons induced mortality for both species, but these hydrocarbons disappeared very quickly from the water column, regardless of the oil type. The amphipods were sensitive to both types of oil while the chironomids were only sensitive to diluted bitumens. The presence of a natural sediment seems to provide a protective role against dissolved hydrocarbons. The antioxidant enzymes measured (CAT, SOD and GPx) do not appear to be relevant biomarkers for the exposure of these organisms to diluted bitumen.

Comparative toxicity of conventional and unconventional oils during rainbow trout (Oncorhynchus mykiss) embryonic development: From molecular to health consequences.

Canadian freshwater ecosystems are vulnerable to oil spills from pipelines, which contain mostly diluted bitumen. This study aimed to compare the toxicity of a dilbit and a conventional oil on developing rainbow trout. A total of five exposure scenarios were performed, from 10 to 43 days, using water-accommodated fraction (WAF) with an initial loading of 1:9 oil to water ratio (w/v) in a range of dilutions from 0.32 to 32% WAF, respectively, with TPAH and VOC concentrations from 2.41 to 17.5 µg/L and 7.94-660.99 µg/L, and with or without a recovery period. Following the five exposures, several endpoints were examined, including survivorship, morphometrics, gene expression, and enzymatic activity. Significant mortality rates were measured for the highest WAF concentration of the dilbit in all five exposures (60-100% mortality at 32% WAF). In comparison, the highest WAF concentration of the conventional oil induced significant mortality in three out of the five exposure (from 35 to 100% mortality at 32% WAF). Hatching delays were noted in embryos exposed to both oils. Developmental delays were observed in dilbit-exposed embryos and are suspected to be an indicator of reduced survivorship after hatching. The induced expression of cyp1a remained a reliable biomarker of exposure and of fish malformations, though it did not always predict mortality. Using CYP1A activity in combination with cyp1a may bring more insights in studies of oil risk assessment. This study demonstrates that dilbits are more toxic to early life stages compared to conventional oils and highlights the need to consider the most sensitive stage of development when performing risk assessment studies on oils.

Trace Metal Residues in Marine Mussels: A Global Survey.

Pressures from anthropogenic activities are causing degradation of estuarine and coastal ecosystems around the world. Trace metals are key pollutants that are released and can partition in a range of environmental compartments, to be ultimately accumulated in exposed biota. The level of pressure varies with locations and the range and intensity of anthropogenic activities. The present study measured residues of trace metals in Mytilus mussel species collected from a range of locations around the world in areas experiencing a gradient of anthropogenic pressures that we classified as low, moderate, or high impact. The data showed no grouping/impact level when sampling sites in all countries were incorporated in the analysis, but there was significant clustering/impact level for most countries. Overall, high-impact areas were characterized by elevated concentrations of zinc, lead, nickel, and arsenic, whereas copper and silver were detected at higher concentrations in medium-impact areas. Finally, whereas most metals were found at lower concentrations in areas classified as low impact, cadmium was typically elevated in these areas. The present study provides a unique snapshot of worldwide levels of coastal metal contamination through the use of Mytilus species, a well-established marine biomonitoring tool. Environ Toxicol Chem 2021;40:3434-3440. © 2021 SETAC.

Comparative developmental toxicity of conventional oils and diluted bitumen on early life stages of the rainbow trout (Oncorhynchus mykiss).

Petroleum hydrocarbons are widely used and transported, increasing the risks of spills to the environment. Although conventional oils are the most commonly produced, the production of unconventional oils (i.e. diluted bitumen or dilbit) is increasing. In this study, we compared the effects of conventional oils (Arabian Light and Lloydminster) and dilbits (Bluesky and Clearwater) on early life stages of a salmonid. To this end, aqueous fractions (WAF: water accommodated fraction) of these oils were extracted using mountain spring water. Rainbow trout (Oncorhynchus mykiss) larvae were exposed to 10 and 50% dilutions of these WAFs from hatching (340 DD; degree days) until yolk sac resorption (541 DD). Exposure to WAFs increased skeletal malformations (both dilbits) and hemorrhage (both conventional oils and Bluesky) and decreased head growth (Arabian Light). In addition, increases in EROD activity and DNA damage were measured for all oils and an increase in cyp1a gene expression was measured for Arabian Light, Bluesky and Clearwater. The PAH and C10C50 concentrations were positively correlated to total larval EROD activity, whereas concentrations of total hydrocarbons, VOCs, PAHs, and C10C50 were positively correlated to cyp1a expression. Total hydrocarbon, VOC, and C10C50 concentrations were also negatively correlated to larval growth. This study supports that petroleum hydrocarbons are toxic to early developmental stages of rainbow trout and show that their degree and spectrum of toxicity depends on their chemical composition.

Time-dependent biological responses of juvenile yellow perch (Perca flavescens) exposed in situ to a major urban effluent.

Municipal wastewater treatment plant (WWTP) effluents are significant sources of organic and inorganic pollutants to aquatic ecosystems. Several studies have shown that the health of aquatic organisms can be adversely impacted following exposure to these complex chemical mixtures. The objective of this study was to examine the effects of in situ exposure in the St. Lawrence River (QC, Canada) of juvenile yellow perch (Perca flavescens) to a major WWTP effluent. Perch were caged at a reference site in the St. Lawrence River and downstream of a WWTP effluent-influenced site for one, three, and six weeks. Fish kept in controlled laboratory setting were also examined at the beginning of the experiment to evaluate the potential effect of caging on fish. Liver metabolites and gill oxidative stress biomarkers as well as body condition of perch were investigated at four time points (zero, one, three, and six weeks). Nitrogen (δ15N) and carbon (δ13C) stable isotopes as well as tissue concentrations of halogenated flame retardants and trace metals were also analyzed. Results indicated that body condition of perch caged in the effluent increased after three and six weeks of exposure compared to that of reference fish. Perch caged at the WWTP effluent-influenced site also had higher muscle δ13C and slightly depleted muscle δ15N after three and six weeks of exposure, suggesting differences in sewage-derived nutrient assimilation between sites. Concentrations of Σ34 polybrominated diphenyl ether (PBDE) were 2-fold greater in perch exposed downstream of the WWTP compared to those caged at the reference site. Metal concentrations in kidney of perch after three weeks of exposure were significantly lower at the effluent-influenced site. Kidney concentrations of Cd, Cu, Se, As, Zn and Fe were, however, higher after six weeks of exposure, supporting that metal accumulation is time- and element-specific. The metabolomes of perch from the effluent-influenced and reference sites were similar, but were distinct from the laboratory control fish, suggesting a caging effect on fish. Seven liver metabolites (glucose, malate, fumarate, glutamate, creatinine, histamine, and oxypurinol) were significantly more abundant in perch from cages than in the laboratory control perch. The combination of metabolomics and physiological variables provides a powerful tool to improve our understanding of the mechanisms of action of complex environmental pollutant mixtures in wild fish.

Lethal and sublethal effects of diluted bitumen and conventional oil on fathead minnow (Pimephales promelas) larvae exposed during their early development.

The increasing extraction of bitumen from the oil sands region in Canada is creating a need for transport. Spills from current and projected pipelines represent a significant environmental risk, especially for freshwater ecosystems. The toxicity of diluted bitumen (dilbit) on freshwater fish is largely unknown. This study assessed the toxicity of two dilbits (Clearwater McMurray and Bluesky) and compared their toxicity to a conventional oil (Lloydminster Heavy) on fathead minnow (Pimephales promelas) larvae. Larvae were exposed to various concentrations of the water-accommodated fraction (WAF) of the oils during 7 days from hatching. In the WAF treatments, the concentrations of volatile organic compounds (VOCs), including benzene, toluene, ethylbenzene, xylene (BTEX), hydrocarbons containing 6 to 10 carbon atoms (C6-10), and polycyclic aromatic hydrocarbons (PAHs) and their alkylated forms were measured. Both dilbits contained higher concentrations of light components, while the conventional oil contained the highest concentrations of PAHs and alkylated PAHs. The Clearwater McMurray dilbit induced a higher mortality, with a maximum of 65.3%, while the other oils induced a similar mortality up to 16.5% and 18.6% for Lloydminster and for Bluesky, respectively. All three oils induced an increase in gene expression of the phase I detoxification enzyme (cyp1a) with increasing total hydrocarbon concentrations. All three exposures induced a similar increase in glutathione S-transferase (GST) activity, but no change in gst gene expression. For the Bluesky and Lloydminster exposures, an increase in malondialdehyde concentration was also observed, suggesting a rate limiting capacity of GST and phase II enzymes to perform the biotransformation of the PAH metabolites. Overall, this study brings new insights on the toxicity of dilbits in comparison to conventional oils on early life stages of North American freshwater fish and demonstrated that dilbits can be more toxic than conventional oils, depending on their composition and diluent proportions.

Fate and Fathead Minnow Embryotoxicity of Weathering Crude Oil in a Pilot-Scale Spill Tank.

For several years now, the Natural Resources Canada research facility at CanmetENERGY Devon (AB, Canada) has been performing experiments in a pilot-scale spill tank using 1200 L of river water to examine the physical and chemical behaviors of various crude oil/water mixtures under varying water temperature regimes. Because oil toxicity can be modulated by weathering of the petroleum products, the present study aimed to assess changes in fish embryotoxicity to mixed sweet blend crude oil as it weathered at air and water temperatures of 14 °C and 15 °C, respectively, for 28 d. The physicochemical behavior of the oil was also monitored. Water samples were taken from the spill tank 5 times during the 28-d experiment on days 1, 6, 14, 21, and 28 and were used to perform toxicity exposures using fathead minnow embryos (Pimephales promelas). For each water sampling day, newly fertilized embryos were exposed to a serial dilution of the spill tank water, noncontaminated river water (used in the spill tank), and a reconstituted water laboratory control. Embryos were raised until hatching. Although mortality was not significantly altered by the oil contamination over the time period, malformation occurrence and severity showed concentration-dependent responses to all contaminated water collected. The results suggest that days 14, 21, and 28 were the most toxic time periods for the fish embryos, which corresponded to increasing concentrations of unidentified oxidized organic compounds detected by a quadropole-time-of-flight system. The present study highlights a novel area for oil research, which could help us to better understand the toxicity associated with oil weathering for aquatic species. Environ Toxicol Chem 2021;40:127-138. © 2020 Her Majesty the Queen in Right of Canada. Reproduced with the permission of the Minister of Natural Resources Canada.

A seasonal comparison of trace metal concentrations in the tissues of Arctic charr (Salvelinus alpinus) in Northern Québec, Canada.

Ecotoxicological research detailing trace metal contamination and seasonal variation in the tissues of northern fishes such as Arctic charr (Salvelinus alpinus) has been poorly represented in the literature beyond examination of mercury. In an effort to address this, anadromous Arctic charr were collected from the Deception River watershed in the late summer and post-winter season, before quantifying seasonal and organotropic variations in dorsal muscle and liver concentrations of arsenic, cadmium, chromium, copper, nickel, lead, and zinc. Potential linkages with biological variables (fork length, age, and somatic condition) and indicators of feeding behavior (δ13C and δ15N) were also assessed. Trace metal organotropism favouring elevation in liver tissue concentrations was exhibited by cadmium, copper, nickel and zinc, while arsenic, chromium and lead exhibited no significant organotropic variation. Seasonal differences in concentrations were metal and tissue dependent, but generally increased in tissues collected from post-winter sampled Arctic charr. Significant correlations with biological and trophic descriptors were also determined to be element and tissue dependent. These parameters, in addition to season, were incorporated into multi-predictor variable models, where variations in trace metal concentration data were often best explained when season, somatic condition, and trophic descriptors were included. These variables were also of greatest relative importance across all considered trace metals and tissue types. These findings suggest that seasonally linked processes have the greatest influence on trace metal concentrations in anadromous Arctic charr. Future metal-related research on Arctic charr and other northern fish species should further consider these variables when evaluating elemental accumulation.

Seasonal variation of total mercury and condition indices of Arctic charr (Salvelinus alpinus) in Northern Québec, Canada.

The winter ecology of anadromous Arctic charr, an important fish species for Indigenous populations, has remained poorly detailed in the literature beyond descriptions of seasonal fasting and resulting declines in condition. However, prolonged periods of reduced feeding can have significant consequences for other variables, such as tissue contaminant levels. To more thoroughly detail seasonal changes, biological information (fork length, total weight, age, sex, somatic condition), stable isotopes (δ13C, % carbon, δ15N, % nitrogen), dorsal muscle % lipid, caloric densities, and total mercury (THg) concentrations were assessed in anadromous Arctic charr collected from Deception Bay, Canada, during the summer and over-wintering periods. Significant reductions in somatic condition, total weight, and % nitrogen, consistent with prolonged periods of fasting, were found for post-winter captured Arctic charr, but % lipid and caloric densities were significantly higher in these fish. THg also varied seasonally and was significantly higher in summer collected tissue. When tested individually via linear regression, significant relationships were seasonally dependent, but limited in number. All previously mentioned parameters were then incorporated into multi-variable models which better explained variations in the data. While there was no clear best model for explaining the % lipid values, caloric densities, and THg, season, condition, and stable isotope values (% carbon and % nitrogen) were the best indicators of % lipid content and caloric densities. THg concentrations were best explained by total weight, somatic condition, and δ13C. Seasonal variation in fish condition measures and THg may be indicative of condition selective mortality that yields apparent improvement through the disproportionate removal of poorer conditioned fish from the population during the over-wintering period. This hypothesis was further supported by mortality estimates and the results of the multi-predictor variable models. Collectively, this research highlights the importance of understanding seasonal dynamics for anadromous Arctic charr populations.

Identification and expression of microRNAs in european eels Anguilla anguilla from two natural sites with different pollution levels.

MicroRNAs (miRNAs) are a class of small non-coding RNA that control multiple biological processes through negative post-transcriptional regulation of gene expression. Recently a role of miRNAs in the response of aquatic organisms to environmental toxicants emerged. Toxicant-induced changes in miRNA expression might then represent novel biomarkers to evaluate the health status of these organisms. In this study, we aimed to identify the miRNA repertoire in the liver of the European eel Anguilla anguilla and to compare their differential expression between a polluted site located in the Gironde Estuary and a pristine site in Arcachon Bay (France). A total of 299 mature miRNAs were identified. In polluted water, 19 miRNAs were up-regulated and 22 were down-regulated. We predicted that these differentially expressed miRNAs could target 490 genes that were involved in ribosome biogenesis, response to hormones, response to chemical and chromatin modification. Moreover, we observed only few examples (29) of negative correlation between the expression levels of miRNAs and their targets suggesting that, in the system studied, miRNAs might not only regulate gene expression directly by degrading mRNA but also by inhibiting protein translation or by regulating other epigenetic processes. This study is the first example of in situ investigation of the role of miRNAs in the response of a fish species to water quality. Our findings provide new insights into the involvement of epigenetic mechanisms in the response of animals chronically exposed to pollution and pave the way for the utilization of miRNAs in aquatic ecotoxicology.

Retrotransposon methylation and activity in wild fish (A. anguilla): A matter of size.

Understanding how organisms cope with global change is a major question in many fields of biology. Mainly, understanding the molecular mechanisms supporting rapid phenotypic changes of organisms in response to stress and linking stress-induced molecular events to adaptive or adverse outcomes at the individual or population levels remain a major challenge in evolutionary biology, ecology or ecotoxicology. In this view, the present study aimed to test (i) whether environmental factors, especially pollutants, can trigger changes in the activity of retrotransposons (RTs) in wild fish and (ii) if changes in RT DNA methylation or transcription levels can be linked to modifications at the individual level. RTs are genetic elements that have the ability to replicate and integrate elsewhere in the genome. Although RTs are mainly quiescent during normal development, they can be experimentally activated under life-threatening conditions, affecting the fitness of their host. Wild eels were collected in four sampling sites presenting differing levels of contamination. The methylation level and the transcriptional activity of two RTs and two genes involved in development and cell differentiation were analyzed in fish liver in addition to the determination of fish contaminants levels and diverse growth and morphometric indices. An up-regulation of RTs associated to lower methylation levels and lower growth indices were observed in highly contaminated fish. Our results suggest that RT activation in fish experiencing stress conditions could have both detrimental and beneficial implications, affecting fish growth but promoting resistance to environmental stressors such as pollutants.

Subcellular partitioning of metals and metalloids (As, Cd, Cu, Se and Zn) in liver and gonads of wild white suckers (Catostomus commersonii) collected downstream from a mining operation.

In the present study, we examined the subcellular distribution of metals and metalloids (As, Cd, Cu, Se and Zn) in the liver and gonads of wild white suckers (Catostomus commersonii) collected downstream from a metal mining operation (exposure area) and in a reference area. Metal partitioning among potentially metal-sensitive fractions (heat-denatured proteins (HDP), mitochondria and microsomes) and potentially biologically detoxified fractions (heat-stable proteins (HSP) and metal-rich granules) within cells was determined after differential centrifugation, NaOH digestion and heat-denaturation steps. Metal-handling strategies between liver and gonads, and between sexes, were examined. Hepatic metal concentrations were significantly higher in exposed compared to reference fish, especially for Se (14x), Cd (5x) and Cu (3x), and did not vary between sexes. In contrast, gonadal Cd, Cu, Se and Zn concentrations were consistently lower in testes than in ovaries; marked differences in Cd and Se concentrations between exposed and reference fish were observed for both sexes. Overall, metal-handling strategies were similar in both liver (male and female pooled) and female gonads, but differed from those in male gonads, likely due to the different functions assigned to ovaries and testes. Subcellular partitioning of As, Cd and Cu showed that the HSP fraction was most responsive to increased metal exposure, presumably reflecting Cu regulation, and possibly Cd and As detoxification. Zinc concentrations were tightly controlled and mainly found in the HDP fraction. Interestingly, changes in Cd-handling strategy in female gonads were particularly evident, with Cd shifting dramatically from the metal-sensitive HDP fraction in reference fish to the metal-detoxified HSP fraction in exposed fish. It seems that Cd detoxification in female gonads was not fully induced in the less contaminated fish, but became more effective above a threshold Cd concentration of 0.05 nmol/g dry weight. Partitioning of Se was different, with the largest contributor to the total liver and gonad Se burdens being the putative metal-sensitive HDP fraction, suggesting that excess Se in this fraction in exposed fish may lead to Se-related stress. The present subcellular partitioning results demonstrate that metal handling strategies vary among metals, between organs and (in some cases) as a function of metal exposure. They also show promise in identifying metals of potential concern in a risk assessment context.

Temporal variations in kidney metal concentrations and their implications for retinoid metabolism and oxidative stress response in wild yellow perch (Perca flavescens).

The objective of this study was to determine if temporal variations in tissue metal concentrations are related to biomarkers of retinoid metabolism and oxidative stress responses in juvenile yellow perch (Perca flavescens). To this end, kidney metal (Cd, Cu and Zn) concentrations were measured in fish sampled in spring and fall 2012 in four lakes representing a wide range of water and sediment metal contamination in the Rouyn-Noranda (Quebec) region. Lakes Opasatica and Hélène were considered as reference lakes while lakes Dufault and Marlon were metal-contaminated. Kidney concentrations of Cd, Cu and Zn varied widely between spring and fall in fish from both clean and metal-contaminated lakes. An inter-lake difference in renal metal concentrations was only observed for Cd, with fish from Lake Marlon consistently displaying higher concentrations. In the spring, the concentrations of liver dehydroretinol, dehydroretinyl palmitate and total vitamin A esters were higher in fish sampled in the most contaminated lake. Strong temporal variations in the concentrations of these metabolites, as well as in the percentage of liver free dehydroretinol and the epidermal retinol dehydrogenase 2 transcription levels, were observed in fish living in the most metal-impacted lake, with generally higher values in the spring. In contrast to liver, in muscle, no clear seasonal variations in the concentrations of dehydroretinol, dehydroretinyl stearate or in the percentage of free dehydroretinol were observed in fish captured in the most contaminated lake. Temporal variations of traditional biomarkers of oxidative stress response were also observed in the most metal-impacted lake. For example, the transcription level of the gene encoding Cu/Zn superoxide dismutase-1 in liver and muscle catalase activity of perch sampled in the most contaminated lake were higher in spring than in fall. Positive relationships were found between kidney Cd concentrations and the transcription level of the gene encoding glucose 6-phosphate dehydrogenase, and all forms of retinoid concentrations in liver in spring, except with the percentage of free dehydroretinol where the correlation was negative. Our results translate to a state of stress caused by Cd and illustrate that temporal variations in tissue metal concentrations affect retinoid metabolism and antioxidant capacities in juvenile wild yellow perch. Overall this study contributes to highlight the importance of considering temporal variations when investigating the consequences of metal contamination on the physiology of wild fish.