The aim of this study was to investigate the long-term effects of a short exposure to natural sediments within the Athabasca oil sand formation to critical stages of embryo-larval development in fathead minnows (Pimephales promelas). Three different sediments were used: Ref sediment from the upper Steepbank River tested at 3 g/L (containing 12.2 ng/g ∑PAHs), and two bitumen-rich sediments tested at 1 and 3 g/L; one from the Ells River (Ells downstream, 6480 ng/g ∑PAHs) and one from the Steepbank River (Stp downstream, 4660 ng/g ∑PAHs). Eggs and larvae were exposed to sediments for 21 days, then transferred to clean water for a 5-month grow-out and recovery period. Larval fish had significantly decreased survival after exposure to 3 g/L sediment from Stp downstream, and decreased growth (length and weight at 16 days post hatch) in Ells and Stp downstream sediments at both 1 and 3 g/L. Decreased tail length was a sensitive endpoint in larval fish exposed to Ells and Stp downstream sediments for 21 days compared to Ref sediment. After the grow-out in clean water, all growth effects from the bitumen-containing sediments recovered, but adult fish from Stp downstream 3 g/L sediment had significant increases in jaw deformities. The study shows the potential for fish to recover from the decreased growth effects caused by sediments containing oil sands-related compounds, but that some effects of the early-life sediment exposure occur later on in adult fish.

Climate change and pharmaceuticals contamination constitute two of the most relevant stressors on the aquatic ecosystems, however, there is a huge lack of information regarding the interactive effects of both stressors. For that, a mesocosm experiment was implemented where adult zebrafish were exposed to combined temperature and the progestin levonorgestrel (LNG) for 21 days. Considering that the liver is one of the organs where there is a greater metabolization and accumulation of toxicants, the main objective of this work was to assess the effects of both stressors on the female zebrafish hepatocytes morphology and functioning, through stereological and immunohistochemical techniques.Our results revealed an increase of coefficient of variation of the number distribution of hepatocytes volume (CVN(υ)) for individuals exposed to LNG, which denotes an increase of the hepatocytes size variability and is suggestive of functional impacts. This was corroborated by the signs of increased glycogen content with the exposure to increased LNG concentrations and temperature, indicating modified hepatocyte glycogen metabolism. Such disturbances can be considered indicators that the fish had to deal with impacts caused by the stress factors.Regarding the immunoreactivity, from the four proteins selected (catalase, CYP1A, HSP90 and Vtg), just in two of them (catalase and Vtg) were observed some responses to both stressors. For catalase there was a hormetic response, in which exposure to lower LNG concentrations caused a significant higher positive immunostaining than under higher LNG concentrations. While, for Vtg, significant effects of temperature and LNG existed, in which a decline in Vtg immunostaining was observed with exposure to higher temperature and lower LNG concentrations. These results should be seen as a warning sign about fine impacts of multiple stressors, such as temperature and progestogens, on the structure and functioning of zebrafish liver and potentially in other aquatic organisms, and on their health implications.

Selenium (Se) is an essential micronutrient for animals with a relatively narrow margin between essentiality and toxicity. To evaluate Se removal efficiency by a constructed wetland treatment system and its potential eco-risk, a floating-leaved macrophyte system was constructed, consisting of three main trophic levels. Over 21-d treatment, water Se concentration was gradually reduced by 40.40%, while 24.03% and 74.41% of the removed Se were found in the plant Nymphoides sp. and sediment, respectively. Among plant tissues, roots accumulated the highest Se level, although the greatest total Se was found in stems, followed by leaves, roots and rhizomes. X-ray absorption spectroscopy revealed that 82.65% of the absorbed selenite by the plants was biotransformed to other forms, as organo-Se species accounted for 45.38% of the Se retained in the sediment, which was primarily responsible for the entry of Se into the detritus food chain. The proportion of organo-Se compounds increased with trophic levels from sediments to fish, indicating, instead of direct uptake of selenite, the food chain transfer and biotransformation of Se may serve as a key exposure route for Se in aquatic organisms. When exposed to organo-Se compounds, i.e., SeCys and SeMet, the plants, shrimp and fish tended to accumulate more Se. However, the greater trophic transfer factor was obtained for selenate, leading to higher Se levels accumulated in fish. Overall, in addition to key mechanisms involved in Se removal, our research also provides a much better understanding of the potential eco-risk that may be posed by the floating-leaved plant system for bioremediation of Se via food chain transfer and biotransformation, paving the way for a low eco-toxic treatment system for Se remediation.

Triclosan (TCS) is a synthetic microbial compound widely used in the formulation of various personal care products. Its frequent detection in marine ecosystems, along with its physical and chemical properties, suggest that TCS can be highly persistent, being easily bioaccumulated by biota and, therefore, eliciting various toxicological responses. Yet, TCS's mechanisms of bioaccumulation and toxicity still deserve further research, particularly focusing on the interactive effects with climate change-related stressors (e.g. warming and acidification), as both TCS chemical behaviour and marine species metabolism/physiology can be strongly influenced by the surrounding abiotic conditions. Hence, the aim of this study was to assess TCS bioaccumulation and ecotoxicological effects (i.e. animal fitness indexes, antioxidant activity, protein chaperoning and degradation, neurotoxicity and endocrine disruption) in three tissues (i.e. brain, liver and muscle) of juvenile Diplodus sargus exposed to the interactive effects of TCS dietary exposure (15.9 μg kg−1 dw), seawater warming (ΔTºC = +5 °C) and acidification (ΔpCO2 ∼ +1000 μatm, equivalent to ΔpH = −0.4 units). Muscle was the primary organ of TCS bioaccumulation, and climate change stressors, particularly warming, significantly reduced TCS bioaccumulation in all fish tissues. Furthermore, the negative ecotoxicological responses elicited by TCS were significantly altered by the co-exposure to acidification and/or warming, through either the enhancement (e.g. vitellogenin content) or counteraction/inhibition (e.g. heat shock proteins HSP70/HSC70 content) of molecular biomarker responses, with the combination of TCS plus acidification resulting in more severe alterations. Thus, the distinct patterns of TCS tissue bioaccumulation and ecotoxicological responses induced by the different scenarios emphasized the need to further understand the interactive effects between pollutants and abiotic conditions, as such knowledge enables a better estimation and mitigation of the toxicological impacts of climate change in marine ecosystems.

Gut microbiota is of critical importance to host health. Aryl hydrocarbon receptor (AhR) is found to be closely involved in the regulation of gut microbial dynamics. However, it is still not clear how AhR signaling shapes the gut microbiota. In the present study, adult zebrafish were acutely exposed to an AhR antagonist (CH223191), an AhR agonist (polychlorinated biphenyl 126; PCB126) or their combination for 7 d. Overall intestinal health and gut microbial community were temporally monitored (1 d, 3 d and 7 d) and inter-compared among different groups. The results showed that single exposure to PCB126 significantly disrupted the overall health of intestines (i.e., neural signaling, inflammation, epithelial barrier integrity, oxidative stress). However, CH223191 failed to inhibit but enhanced the physiological toxicities of PCB126, implying the involvement of extra mechanisms rather than AhR in the regulation of intestinal physiological activities. Dysbiosis of gut microbiota was also caused by PCB126 over time as a function of sex. It is intriguing that CH223191 successfully abolished the holistic effects of dioxin on gut microbiota, which inferred that growth of gut microbes was directly controlled by AhR activation without the involvement of host feedback modulation. When coming to detailed alterations at certain taxon, both antagonistic and synergistic interactions existed between CH223191 and dioxin, depending on fish sex, exposure duration and bacterial species. Correlation analysis found that gut inflammation was positively associated with pathogenic Legionella bacteria, but was negatively associated with epithelial barrier integrity, suggesting that integral intestinal epithelial barrier can prevent the influx of pathogenic bacteria to induce inflammatory response. Overall, this study has deciphered, for the first time, the direct regulative effects of AhR activity on gut microbiota. Future research is warranted to elucidate the specific mechanisms of AhR action on certain bacterial population.

Atrazine is presently one of the most abundantly used herbicides in the United States, and a common contaminant of natural water bodies and drinking waters in high-use areas. Dysregulation of reproductive processes has been demonstrated in atrazine exposed fish, including alteration of key endocrine pathways on hypothalamic-pituitary-gonadal (HPG) axis. However, the potential for atrazine-induced transgenerational inheritance of reproductive effects in fish has not been investigated. The present study examined the effects of early developmental atrazine exposure on transgenerational reproductive dysregulation in Japanese medaka (Oryzias latipes). F0 medaka were exposed to atrazine (ATZ, 5 or 50 μg/L), 17α-ethinylestradiol (EE2, 0.002 or 0.05 μg/L), or solvent control during the first twelve days of development with no subsequent exposure over three generations. This exposure overlapped with the critical developmental window for embryonic germ cell development, gonadogenesis, and sex determination. Exposed males and females of the F0 generation were bred to produce an F1 generation, and this was continued until the F2 generation. Sperm count and motility were not affected in F0 males; however, both parameters were significantly reduced in the males from F2 Low EE2 (0.002 μg/L), Low ATZ (5 μg/L), and High ATZ (50 μg/L) lineages. Fecundity was unaffected by atrazine or EE2 in F0 through F2 generations; however, fertilization rate was decreased in low atrazine and EE2 exposure lineages in the F2 generation. There were significant transgenerational differences in expression of the genes involved in steroidogenesis and DNA methylation. These results suggest that although early life exposure to atrazine did not cause significant phenotypes in the directly exposed F0 generation, subsequent generations of fish were at greater risk of reproductive dysfunction.

Understanding how mercury (Hg) accumulates in the aquatic food web requires information on the factors driving methylmercury (MeHg) contamination. This paper employs data on MeHg in muscle tissue of three black bass species (Largemouth Bass, Spotted Bass, and Smallmouth Bass) sampled from 21 reservoirs in California. During a two-year period, reservoirs were sampled for total Hg in sediment, total Hg and MeHg in water, chlorophyll a, organic carbon, sulfate, dissolved oxygen, pH, conductivity, and temperature. These data, combined with land-use statistics and reservoir morphometry, were used to investigate relationships to size-normalized black bass MeHg concentrations. Significant correlations to black bass MeHg were observed for total Hg in sediment, total Hg and MeHg in surface water, and forested area. A multivariate statistical model predicted Largemouth Bass MeHg as a function of total Hg in sediment, MeHg in surface water, specific conductivity, total Hg in soils, and forested area. Comparison to historical reservoir sediment data suggested there has been no significant decline in sediment total Hg at five northern California reservoirs during the past 20 years. Overall, total Hg in sediment was indicated as the most influential factor associated with black bass MeHg contamination. The results of this study improve understanding of how MeHg varies in California reservoirs and the factors that correlate with fish MeHg contamination.

Hydrocarbons contamination and hypoxia are two stressors that can coexist in coastal ecosystems. At present, few studies evaluated the combined impact of these stressors on fish physiology and behavior. Here, we tested the effect of the combination of hypoxia and petrogenic hydrocarbons on the anti-predator locomotor performance of fish. Specifically, two groups of European sea bass (Dicentrarchus labrax) were exposed to clean water (Ctrl) or oil-contaminated water (Oil). Subsequently, fish of both groups were placed in normoxic (norx) or hypoxic (hyp) experimental tanks (i.e. four groups of fish were formed: Ctrl norx, Ctrl hyp, Oil norx, Oil hyp). In these tanks, escape response was elicited by a mechano-acoustic stimulus and recorded with a high speed camera. Several variables were analyzed: escape response duration, responsiveness (percentage of fish responding to the stimulation), latency (time taken by the fish to initiate a response), directionality (defined as away or toward the stimulus), distance-time variables (such as speed and acceleration), maneuverability variables (such as turning rate), escape trajectory (angle of flight) and distancing of the fish from the stimulus. Results revealed (i) effects of stressors (Ctrl hyp, Oil norx and Oil hyp) on the directionality; (ii) effects of Oil norx and Oil hyp on maneuverability and (iii) effects of Oil hyp on distancing. These results suggest that individual stressors could alter the escape response of fish and that their combination could strengthen these effects. Such an impact could decrease the probability of prey escape success. By investigating the effects of hydrocarbons (and the interaction with hypoxia) on the anti-predator behavior of fish, this work increases our understanding of the biological impact of oil spill. Additionally, the results of this study are of interest for oil spill impact evaluation and also for developing new ecotoxicological tools of ecological significance.

Whereas early life stages are usually considered as particularly sensitive to both organic and inorganic contaminants, field studies assessing contaminant bioaccumulation in these stages are scarce. Selenium (Se) is thought to counteract Hg toxic effects when it is found at Se:Hg molar ratios above 1. However, the variation of this ratio in key fish tissues of different early life stages is mostly unknown. The present study therefore aimed to assess Hg and Se content in gravid female tissues (gonads, muscle, liver, gut, and brain) and different life stages (egg masses, newly hatched larvae (NHL), larvae and juvenile) of Yellow Perch (YP) in a large fluvial lake (Lake Saint-Pierre, Québec, Canada). Se:Hg molar ratios were measured for each compartment in order to fill associated knowledge gaps. Total Hg (THg) and methylmercury (MeHg) concentration varied between tissue according to the following trend: Muscle > Liver > Gut > Brain > Gonads. During YP early life stages, MeHg values increased according to an ontogenetic pattern (mg/kg dw) (mean ± SEM): Egg masses (0.01 ± 0.002) < NHL (0.015 ± 0.001) < Larvae (0.14 ± 0.01) < Juveniles (0.18 ± 0.01). Se concentrations in different YP tissues showed the following trend (mg/kg dw) (mean ± SEM): Gut (3.6 ± 0.1) > Liver (2.5 ± 0.1) > Gonads (1.92 ± 0.06) > Brain (1.26 ± 0.03) > Muscle (1.23 ± 0.06). In YP early life stages, Se concentrations were highest in NHL (3.0 ± 0.2), and then decreased as follows: Egg masses (2.8 ± 0.1) > Larvae (1.37 ± 0.04) > Juveniles (0.93 ± 0.05). Se:Hg molar ratios varied considerably and were systematically above 1. This is the first study to simultaneously report Hg and Se bioaccumulation through fish life cycle.

We analyzed paired serum, urine, and hair samples from 94 Korean children and adults to investigate levels of 11 perfluoroalkyl acids (PFAAs). The effects of demographic factors and dietary habits on PFAA exposure were also assessed based on the paired samples. The total PFAA concentrations were 2.4–31 ng/mL in serum, not detected–9.5 ng/mL in urine, and 0.48–15 ng/g in hair. Levels of perfluoropentanoic acid (PFPeA) and perfluorohexanoic acid (PFHxA), which have short carbon chains, were 1.5–5 fold higher in urine and hair than in serum. The PFAA concentrations in serum exhibited a decreasing trend with age from young childhood to adolescence, followed by an increasing trend after adolescence. For most PFAA species, concentrations in serum were higher in adult males than in adult females (p < 0.01). No sex difference was evident in the urine and hair samples. In addition, there was no age difference in the urine samples, but in the hair samples, we observed higher concentrations of PFAAs in children than in the other age groups (p < 0.01). The consumption rates of fish and water showed significant correlations with serum (positive correlation) and hair (negative) concentrations, respectively. No relationships between serum and hair/urine levels for most PFAAs were observed, except between serum and hair levels for perfluorooctanoic acid (PFOA).