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.

High water level fluctuations (WLFs) lead to periodic drying and re-inundation of sediments in the littoral area of eutrophic lakes. In this study, a series of littoral sediment cores were dried for different periods (5–30 d) and rewetted for 48 h. The sediment cores that dried for 30 d were then re-inundated for 90 d. The exchanges of nitrogen (N) and phosphorus (P) across the sediment–water interface (SWI) and the mechanisms were studied. The results showed that ammonium nitrogen (NH4+–N) fluxes increased after 5–25 d of drying, which was followed by an obvious decrease after 30 d of drying. The decreased NH4+–N fluxes remained at low levels during the 90 d re-inundation period. The soluble reactive P (SRP) fluxes decreased significantly after 15 d of drying. However, further re-inundation increased the SRP fluxes to their initial levels. The decreased water content and porosity, the oxidation of the sediment during drying, and the associated transformations of the N and P fractions in the sediment from drying to re-inundation influenced the exchanges of NH4+–N and SRP across the SWI. The decrease of labile NH4+–N in the sediment during drying was non-reversible, while the transformations between redox sensitive P (Fe-P) and aluminum-bound P were more likely to be reversible from drying to re-inundation. The increase of Fe-P during drying and dissolution of Fe-P during the re-inundation were responsible for the development of SRP fluxes from drying to re-inundation. Therefore, the periodic drying and re-inundation of the littoral eutrophic sediments reduced the release of NH4+–N but accelerated the release of SRP from the sediment. This should be given more consideration for the remediation and management of eutrophication in the lake and other similar lakes with high WLFs.

Natural environments are receiving an increasing number of contaminants. Therefore, the evaluation and identification of early responses to pollution in these complex habitats is an urgent and challenging task. Doñana National Park (DNP, SW Spain) has been widely used as a model area for environmental studies because, despite its strictly protected core, it is surrounded by numerous threat sources from agricultural, mining and industrial activities. Since many pollutants often induce oxidative stress, redox proteomics was used to detect redox-based variations within the proteome of Mus spretus mice captured in DNP and the surrounding areas. Functional analysis showed that most differentially oxidized proteins are involved in the maintenance of homeostasis, by eliciting mechanisms to respond to toxic substances and oxidative stress, such as antioxidant and biotransformation processes, immune and inflammatory responses, and blood coagulation. Furthermore, changes in the overall protein abundance were also analysed by label-free quantitative proteomics. The upregulation of phase I and II biotransformation enzymes in mice from Lucio del Palacio may be an alert for organic pollution in the area located at the heart of DNP. Metabolic processes involved in protein turnover (proteolysis, amino acid catabolism, new protein biosynthesis and folding) were activated in response to oxidative damage to these biomolecules. Consequently, aerobic respiratory metabolism increased to address the greater ATP demands. Alterations of cholesterol metabolism that could cause hepatic steatosis were also detected. The proteomic detection of globally altered metabolic and physiological processes offers a complete view of the main biological changes caused by environmental pollution in complex habitats.

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.

PM2.5 is becoming a worldwide environmental problem, which profoundly endangers public health, thus progressively capturing public attention this decade. As a fragile target of PM2.5, the underlying mechanisms of endothelial cell damage are still obscure. According to the previous microarray data and signaling pathway analysis, a new form of cell death termed ferroptosis in the current study is proposed following PM2.5 exposure. In order to verify the vital role of ferroptosis in PM2.5-induced endothelial lesion and further understand the potential mechanism involved, intracellular iron content, ROS release and lipid peroxidation, as well as biomarkers of ferroptosis were detected, respectively. As a result, uptake of particles increases cellular iron content and ROS production. Meanwhile, GSH depletion, and the decrease of GSH-Px and NADPH play significant roles in PM2.5-induced endothelial cell ferroptosis. Moreover, significantly changed expression of TFRC, FTL and FTH1 hinted that dysfunction of iron uptake and storage is a major inducer of ferroptosis. Importantly, index monitored above can be partially rescued by lipid peroxidation inhibitor ferrostatin-1 and iron chelator deferoxamine mesylate, which mediated antiferroptosis activity mainly depends on the restoration of antioxidant activity and iron metabolism. In conclusion, our data basically show that PM2.5 enhances ferroptosis sensitivity with increased ferroptotic events in endothelial cells, in which iron overload, lipid peroxidation and redox imbalance act pivotal roles.

Despite their ecological and socioeconomic importance, mangroves are among the most threatened tropical environments in the world. In the past two decades, the world's mangrove degradation and loss were estimated to lie between an 35% and >80%. However, appropriate bioindicators for assessing the impact of external factors, and for differentiating polluted from unpolluted areas are still scarce. Here, we determine the physicochemical profiles of the soils of two mangroves, one exposed to and one not exposed to anthropogenic factors. By metagenomic analysis based on 16S rRNA, we generated the bacterial diversity profiles of the soils and estimated their functional profiles. Our results showed that the two examined mangrove forests differed significantly in the physicochemical properties of the soils, especially regarding organic carbon, phosphorus and metal content, as well as in their microbial communities, which was likely caused by anthropogenic pollution. The physicochemical differences between the soils explained 76% of the differential bacterial composition, and 64% depended solely on gradients of phosphorus, metal ions and potassium. We found two genera JL-ETNP-Z39 and TA06 exclusively in polluted and non-polluted mangroves, respectively. Additionally, the polluted mangrove was enriched in Gemmatimonadetes, Cyanobacteria, Chloroflexi, Firmicutes, Acidobacteria, and Nitrospirae. A total of 77 genera were affected by anthropic contamination, of which we propose 33 as bioindicators; 26 enriched, and 7 depleted upon pollution.

Per- and polyfluoroalkyl substances (PFASs) are a large group of chemicals and can be detected in environmental and human samples all over the world. Toxicity of existing and emerging PFASs will be a long-term source of concern. This study aimed to investigate structure-dependent inhibitory effects of 14 PFASs towards the activity of 11 UDP-glucuronosyltransferase (UGT) isoforms. In vitro UGTs-catalyzed glucuronidation of 4-methylumbelliferone (4-MU) was employed to determine the inhibition of PFASs towards different UGT isoforms. All the PFASs showed <75% of inhibition or stimulation effects on UGT1A3, UGT1A7, UGT1A9, UGT2B4, UGT2B7 and UGT2B17. However, PFASs showed broad inhibition on the activity of UGT1A1 and UGT1A8. The activity of UGT1A1 was inhibited by 98.8%, 98%, 79.9%, 77.1%, and 76.9% at 100 μmoL/L of perfluorodecanoic acid (PFDA), perfluorooctanesulfonic acid potassium salt (PFOS), perfluorotetradecanoic acid (PFTA), perfluorooctanoic acid (PFOA) and perfluorododecanoic acid (PFDoA), respectively. UGT1A8 was inhibited by 97.6%, 94.8%, 86.3%, 83.4% and 77.1% by PFDA, PFTA, perfluorooctadecanoic acid (PFOcDA), PFDoA and PFOS, respectively. Additionally, PFDA significantly inhibited UGT1A6 and UGT1A10 by 96.8% and 91.6%, respectively. PFDoA inhibited the activity of UGT2B15 by 88.2%. PFDA and PFOS exhibited competitive inhibition towards UGT1A1, and PFDA and PFTA showed competitive inhibition towards UGT1A8. The inhibition kinetic parameter (Kᵢ) were 3.15, 1.73, 13.15 and 20.21 μmoL/L for PFDA-1A1, PFOS-1A1, PFDA-1A8 and PFTA-1A8, respectively. The values were calculated to be 0.3 μmoL/L and 1.3 μmoL/L for the in vivo inhibition of PFDA towards UGT1A1-and UGT1A8-catalyzed metabolism of substances, and 0.2 μmoL/L and 2.0 μmoL/L for the inhibition of PFOS towards UGT1A1 and the inhibition of PFTA towards UGT1A8, respectively. Molecular docking indicated that hydrogen bonds and hydrophobic interactions contributed to the interaction between PFASs and UGT isoforms. In conclusion, exposure to PFASs might inhibit the activity of UGTs to disturb metabolism of endogenous compounds and xenobiotics. The structure-related effects of PFASs on UGTs would be very important for risk assessment of PFASs.

Propylea japonica is a very important predator in agricultural ecosystems, which could be exposed to Bt protein. In this study, the bacterial community of P. japonica fed with normal food and food containing Cry2Ab protein was characterized for the first time using qPCR and high-throughput sequencing approaches. Results showed no effect of Cry2Ab on P. japonica development and reproduction. The most abundant bacterial phylum was Firmicutes, and the most abundant genus was Staphylococcus. The total bacteria copy number was not significantly different across four larval stages. Bacteria species composition was gathered more closely in feed on sucrose solution (sucrose-fed) than in larvae only fed on pea aphid (aphid-fed), the diversity indices of some operational taxonomic unit (OTU) were significantly different between sucrose-fed and aphid-fed samples. Different instar larval stages of P. japonica fed with sucrose solution containing Cry2Ab Bt protein and found no effect on microbial community composition and total bacteria copy numbers. However, effects on relative abundance of microbes, copy numbers of Corynebacterium 1 and Glutamicibacter arilaitensis were observed significantly lower in Bt-fed first and fourth larval stages. Low and high concentrations of Cry2Ab protein altered the microbial abundance relative to sucrose-fed P. japonica and copy numbers of G. arilaitensis and Staphylococcus xylosus were significantly lower in Bt-fed samples than control sucrose-fed. Our results are the first report showing that feeding on Cry2Ab protein does not alter microbial species composition in P. japonica, but effects gene copy number of some dominant bacteria. Further investigations are needed to assess the effect of copy number change on P. japonica.

Preoxidation of As(III) to As(V) is required for the efficient removal of total arsenic in the treatment of wastewater. In this work, the electro-Fenton oxidation of As(III) with a high efficiency was successfully achieved by using the system of the stainless steel net (SSN) coating with reduced graphene oxide (RGO@SSN) as the cathode and stainless steel net (SSN) as the sacrificial anode. The RGO@SSN was synthesized by electrophoretic deposition-annealing method. The carbon disorder and defects of RGO resulted from the remained oxygen-containing functional groups facilitated the electrocatalytically active sites for two-electron oxygen reduction reaction (ORR). A high concentration (up to 1000 μmol/L) of H₂O₂ was in-situ produced through two-electron oxygen reduction reaction of electro-catalysis, and then served as the electro-Fenton reagent for the oxidation of As(III). HO generated by H₂O₂ participating the electro-Fenton reaction or decomposed at the surface of RGO@SSN cathode at acid condition endowed the strong oxidizing ability for As(III). The electro-Fenton equipped with RGO@SSN cathode has a promising application in the oxidation and removal of organic or inorganic pollutants in wastewater.