Multi-tissue proteogenomic analysis for mechanistic toxicology studies in non-model species

New approach methodologies (NAM), including omics and in vitro approaches, are contributing to the implementation of 3R (reduction, refinement and replacement) strategies in regulatory science and risk assessment. In this study, we present an integrative transcriptomics and proteomics analysis workflow for the validation and revision of complex fish genomes and demonstrate how proteogenomics expression matrices can be used to support multi-level omics data integration in non-model species in vivo and in vitro. Using Atlantic salmon as an example, we constructed proteogenomic databases from publicly available transcriptomic data and in-house generated RNA-Seq and LC-MS/MS data. Our analysis identified ∼80,000 peptides, providing direct evidence of translation for over 40,000 RefSeq structures. The data also highlighted 183 co-located peptide groups that supported a single transcript each, and in each case, either corrected a previous annotation, supported Ensembl annotations not present in RefSeq, or identified novel previously unannotated genes. Proteogenomics data-derived expression matrices revealed distinct profiles for the different tissue types analyzed. Focusing on proteins involved in defense against xenobiotics, we detected distinct expression patterns across different salmon tissues and observed homology in the expression of chemical defense proteins between in vivo and in vitro liver systems. Our study demonstrates the potential of proteogenomic analyses in extending our understanding of complex fish genomes and provides an advanced bioinformatic toolkit to support the further development of NAMs and their application in regulatory science and (eco)toxicological studies of non-model species.

Dietary beauvericin and enniatin B exposure cause different adverse health effects in farmed Atlantic salmon

The extensive use of plant ingredients in novel aquafeeds have introduced mycotoxins to the farming of seafood. The emerging enniatin B (ENNB) and beauvericin (BEA) mycotoxins have been found in the novel aquafeeds and farmed fish. Little is known about the potential toxicity of ENNs and BEA in farmed fish and their feed-to-organ transfer. Atlantic salmon (Salmo salar) pre-smolt (75.3 ± 8.10 g) were fed four graded levels of spiked chemical pure ENNB or BEA feeds for three months, in triplicate tanks. Organismal adverse health end-point assessment included intestinal function (protein digestibility), disturbed hematology (red blood cell formation), bone formation (spinal deformity), overall energy use (feed utilization), and lipid oxidative status (vitamin E). Both dietary BEA and ENNB had a low (<∼0.01%) transfer to organs (kidney > liver > brain > muscle), with a higher transfer for ENNB compared to BEA. BEA caused a growth reduction combined with a decreased protein digestion and feed conversion rate- ENNB caused a stunted growth, unrelated to feed utilization capacity. In addition, ENNB caused anemia while BEA gave an oxidative stress response. Lower bench-mark dose regression assessment showed that high background levels of ENNB in commercial salmon feed could pose a risk for animal health, but not in the case of BEA.

Arsenic species in mesopelagic organisms and their fate during aquafeed processing

A responsible harvest of mesopelagic species as aquafeed ingredients has the potential to address the United Nations Sustainable Development Goal 14, which calls for sustainable use of marine resources. Prior to utilization, the levels of undesirable substances need to be examined, and earlier studies on mesopelagic species have reported on total arsenic (As) content. However, the total As content does not give a complete basis for risk assessment since As can occur in different chemical species with varying toxicity. In this work, As speciation was conducted in single-species samples of the five most abundant mesopelagic organisms in Norwegian fjords. In addition, As species were studied in mesopelagic mixed biomass and in the resulting oil and meal feed ingredients after lab-scale feed processing. Water-soluble As species were determined based on ion-exchange high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). This was supplemented by extracting arsenolipids (AsLipids) and determining total As in this fraction. The non-toxic arsenobetaine (AB) was the dominant form in mesopelagic crustaceans and fish species, accounting for approximately 70% and 50% of total As, respectively. Other water-soluble species were present in minor fractions, including carcinogenic inorganic As, which, in most samples, was below limit of quantification. The fish species had a higher proportion of AsLipids, approximately 35% of total As, compared to crustaceans which contained 20% on average. The feed processing simulation revealed generally low levels of water-soluble As species besides AB, but considerable fractions of potentially toxic AsLipids were found in the biomass, and transferred to the mesopelagic meal and oil. This study is the first to report occurrence data of at least 12 As species in mesopelagic organisms, thereby providing valuable information for future risk assessments on the feasibility of harnessing mesopelagic biomass as feed ingredients.

Use of (Q)SAR genotoxicity predictions and fuzzy multicriteria decision-making for priority ranking of ethoxyquin transformation products

Ethoxyquin (EQ; 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline) has been used as an antioxidant in feed for pets and food-producing animals, including farmed fish such as Atlantic salmon. In Europe, the authorization for use of EQ as a feed additive was suspended, due to knowledge gaps concerning the presence and toxicity of EQ transformation products (TPs). Recent analytical studies focusing on the detection of EQ TPs in farmed Atlantic salmon feed and fillets reported the detection of a total of 27 EQ TPs, comprising both known and previously not described EQ TPs. We devised and applied an in silico workflow to rank these EQ TPs according to their genotoxic potential and their occurrence data in Atlantic salmon feed and fillet. Ames genotoxicity predictions were obtained applying a suite of five (quantitative) structure-activity relationship ((Q)SAR) tools, namely VEGA, TEST, LAZAR, Derek Nexus and Sarah Nexus. (Q)SAR Ames genotoxicity predictions were aggregated using fuzzy analytic hierarchy process (fAHP) multicriteria decision-making (MCDM). A priority ranking of EQ TPs was performed based on combining both fAHP ranked (Q)SAR predictions and analytical occurrence data. The applied workflow prioritized four newly identified EQ TPs for further investigation of genotoxicity. The fAHP-based prioritization strategy described here, can easily be applied to other toxicity endpoints and groups of chemicals for priority ranking of compounds of most concern for subsequent experimental and mechanistic toxicology analyses.

Do background levels of the pesticide pirimiphosmethyl in plant-based aquafeeds affect food safety of farmed Atlantic salmon?

The substitution of fish oil and fishmeal with plant-based ingredients in commercial aquafeeds for Atlantic salmon, may introduce novel contaminants that have not previously been associated with farmed fish. The organophosphate pesticide pirimiphos-methyl (PM) is one of the novel contaminants that is most prevalent in commercial salmon feed. In this study, the feed-to-fillet transfer of dietary PM and its main metabolites was investigated in Atlantic salmon fillet. Based on the experimental determined PM and metabolite uptake, metabolisation, and elimination kinetics, a physiologically based toxicokinetic (PBTK) compartmental model was developed. Fish fed PM had a relatively low (~4%) PM retention and two main metabolites (2-DAMP and Desethyl-PM) were identified in liver, muscle, kidney and bile. The absence of more metabolised forms of 2-DAMP and Desethyl-PM in Atlantic salmon indicates different metabolism in cold-water fish compared to previous studies on ruminants. The model was used to simulate the long term (>1.5 years) feed-to-fillet transfer of PM + metabolite in Atlantic salmon under realistic farming conditions including seasonal fluctuations in feed intake, growth, and fat deposition in muscle tissue. The model predictions show that with the constant presence of the highest observed PM concentration in commercial salmon feed, fillet PM+ metabolite levels were approximately 5 nmol kg^-1, with highest levels for the metabolite 2-DAMP. No EU maximum residue levels (MRL) for PM and its main metabolites exist in seafood to date, but the predicted levels were lower than the MRL for PM in swine of 32.7 nmol kg^-1.

Undesirables in Mesopelagic Species and Implications for Food and Feed Safety-Insights from Norwegian Fjords

The increase in the global population demands more biomass from the ocean as future food and feed, and the mesopelagic species might contribute significantly. In the present study, we evaluated the food and feed safety of six of the most abundant mesopelagic species in Norwegian fjords. Trace elements (i.e., arsenic, cadmium, mercury, and lead), organic pollutants (i.e., dioxins, furans, dioxin-like polychlorinated biphenyls, and polybrominated flame-retardants), and potentially problematic lipid compounds (i.e., wax esters and erucic acid) were analyzed and compared to existing food and feed maximum levels and intake recommendations. Furthermore, contaminant loads in processed mesopelagic biomass (protein, oil, and fish meal) was estimated using worst-case scenarios to identify possible food and feed safety issues. While most undesirables were low considering European food legislation, we identified a few potential food safety issues regarding high levels of fluoride in Northern krill, wax esters in glacier lanternfish, and long-chain monounsaturated fatty acids in silvery lightfish. Our estimates in processed biomass indicated high levels of undesirable trace elements in the protein fraction, frequently exceeding the maximum levels for feed ingredients. However, in fish meal, almost no exceedances were seen. In the oil fraction, dioxins and furans were above the maximum levels, given for food and feed ingredients. The present study is crucial to enable an evaluation of the value of these species; however, more data is needed before proceeding with large-scale harvesting of mesopelagic biomass.

No transfer of the non-regulated mycotoxins, beauvericin and enniatins, from feeds to farmed fish reared on plant-based diets

Concern about the risk of exposure to emerging plant-derived mycotoxins such as beauvericin and enniatins has been addressed by the European Commission who requested the European Food Safety Authority for a scientific opinion on their risk to human and animal health. The studied mycotoxins were found in feeds with enniatin B and beauvericin at average concentrations of 19.9 μg/kg and 30 μg/kg, respectively. In all cases, concentrations of all the mycotoxins analyzed were below quantification limits (<0.1 μg/kg) in fish samples (n = 82). The present work provides comprehensive and traceable data of emerging mycotoxins in plant-based aquafeeds and fish reared on the feeds, responding to increasing concerns about safety of farmed fish fed on sustainable feeds. On the basis of data reported, there was no transfer of the emerging mycotoxins, beauvericin and enniatins, from feeds to fish and so, no risk for human consumption.

LC-MS/MS method for the determination of organophosphorus pesticides and their metabolites in salmon and zebrafish fed with plant-based feed ingredients

The composition of Atlantic salmon feed has changed considerably over the last two decades from being marine-based (fishmeal and fish oil) to mainly containing plant ingredients. Consequently, concern related to traditional persistent contaminants typically associated with fish-based feed has been replaced by other potential contaminants not previously associated with salmon farming. This is the case for many pesticides, which are used worldwide to increase food production, and may be present in plant ingredients. Earlier studies have identified two organophosphorus pesticides, chlorpyrifos-methyl and pirimiphos-methyl, in plant ingredients used for aquafeed production. In the present study, we developed a reliable and sensitive analytical method, based on liquid chromatography coupled to tandem mass spectrometry, for the determination of these pesticides and their main metabolites in warm water (zebrafish) and cold water (Atlantic salmon) species, where possible differences in metabolites could be expected. The method was tested in whole zebrafish and in different salmon tissues, such as muscle, bile, kidney, fat, and liver. The final objective of this work was to assess kinetics of chlorpyrifos-methyl and pirimiphos-methyl and their main metabolites in fish tissue, in order to fill the knowledge gaps on these metabolites in fish tissues when fed over prolonged time.

Effects of Agricultural Pesticides in Aquafeeds on Wild Fish Feeding on Leftover Pellets Near Fish Farms

Screening has revealed that modern-day feeds used in Atlantic salmon aquaculture might contain trace amounts of agricultural pesticides. To reach slaughter size, salmon are produced in open net pens in the sea. Uneaten feed pellets and undigested feces deposited beneath the net pens represent a source of contamination for marine organisms. To examine the impacts of long-term and continuous dietary exposure to an organophosphorus pesticide found in Atlantic salmon feed, we fed juvenile Atlantic cod (Gadus morhua), an abundant species around North Atlantic fish farms, three concentrations (0.5, 4.2, and 23.2 mg/kg) of chlorpyrifos-methyl (CPM) for 30 days. Endpoints included liver and bile bioaccumulation, liver transcriptomics and metabolomics, as well as plasma cholinesterase activity, cortisol, liver 7-ethoxyresor-ufin-O-deethylase activity, and hypoxia tolerance. The results show that Atlantic cod can accumulate relatively high levels of CPM in liver after continuous exposure, which is then metabolized and excreted via the bile. All three exposure concentrations lead to significant inhibition of plasma cholinesterase activity, the primary target of CPM. Transcriptomics profiling pointed to effects on cholesterol and steroid biosynthesis. Metabolite profiling revealed that CPM induced responses reflecting detoxification by glutathione-S-transferase, inhibition of monoacylglycerol lipase, potential inhibition of carboxylesterase, and increased demand for ATP, followed by secondary inflammatory responses. A gradual hypoxia challenge test showed that all groups of exposed fish were less tolerant to low oxygen saturation than the controls. In conclusion, this study suggests that wild fish continuously feeding on leftover pellets near fish farms over time may be vulnerable to organophosphorus pesticides.

Feed-to-Fillet Transfer of Selenite and Selenomethionine Additives to Plant-Based Feeds to Farmed Atlantic Salmon Fillet

This study investigated the transfer kinetics of dietary selenite and selenomethionine (SeMet) to the fillet of farmed Atlantic salmon (Salmo salar). The uptake and elimination rate constants of the two selenium (Se) forms were determined in Atlantic salmon fed either selenite- or SeMet-supplemented diets followed by a depuration period. The fillet half-life of selenite and SeMet was 779 ± 188 and 339 ± 103 days, respectively. The elimination and uptake rates were used in a simple one-compartmental kinetic model to predict levels in fillet based on long-term (whole production cycle) feeding with given dietary Se levels. Model predictions for Atlantic salmon fed plant-based feeds low in natural Se and supplemented with either 0.2 mg of selenite or SeMet kg^-1 gave a predicted fillet level of 0.042 and 0.058 mg Se kg^-1 wet weight, respectively. Based on these predictions and the European Food Safety Authority risk assessment of Se feed supplementation for food-producing terrestrial farm animals, the supplementation with 0.2 mg of selenite kg^-1 would likely be safe for the most sensitive group of consumers (toddlers). However, supplementing feed to farm animals, including salmon, with 0.2 mg of SeMet kg^-1 would give a higher (114%) Se intake than the safe upper intake limit for toddlers.

Modelling of the feed-to-fillet transfer of ethoxyquin and one of its main metabolites, ethoxyquin dimer, to the fillet of farmed Atlantic salmon (Salmon salar L.)

Ethoxyquin (EQ) is an antioxidant supplemented to feed ingredients, mainly fish meal, which is currently under re-evaluation for use in the food production chain. EQ is partly metabolized into several metabolites of which the ethoxyquin dimer (EQDM) accumulates most in the farmed fish fillet. In this study, the feed-to-fillet transfer of dietary EQ and EQDM in Atlantic salmon fillet was investigated, and a physiologically based pharmacokinetic (PBPK-) two-compartmental model was developed, based on experimental determined EQ and EQDM uptake, metabolism, and elimination kinetics. The model was verified with an external data-set and used to simulate the long term (>1.5 years) EQ and EQDM feed-to fillet transfer in Atlantic salmon under realistic farming conditions such as the seasonal fluctuations in feed intake, growth, and fillet fat deposition. The model predictions showed that initial EQDM levels in juvenile fish are the driving factor in final levels found in food-producing animals, while for EQ the levels in feed, and seasonal variations were the driving factor for food EQ levels.

Species-Specific Discrimination of Insect Meals for Aquafeeds by Direct Comparison of Tandem Mass Spectra

Insect protein has the potential to become a sustainable feed ingredient for the rapidly growing aquaculture industry. In the European Union, insect derived protein is placed under the same legislation as processed animal proteins (PAP). It is therefore of interest to develop methods for regulatory use, which unambiguously identify the species origin of insect-based ingredients. We performed (i) total protein quantification of insect samples using the traditional nitrogen-to-protein conversion factor of 6.25 and the sum of anhydrous amino acids, (ii) quantitative amino acid profiling and (iii) high-throughput tandem mass spectrometry to describe and differentiate 18 different commercial-grade insect meal samples derived from Hermetia illucens (8), Tenebrio molitor (5), Alphitobius diaperinus (3) and Acheta domesticus (2). In addition, we investigated and compared different protein extraction and digestion protocols for proteomic analysis. We found that irrespective of sample preparation, shotgun proteomics in combination with direct spectral comparison were able to differentiate insect meal according to their taxonomic classification. The insect specific spectral libraries created in the present work can in future be used to develop more sensitive targeted methods of insect PAP identification and quantification in commercial feed mixtures.

Tolerance and dose-response assessment of subchronic dietary ethoxyquin exposure in Atlantic salmon (Salmo salar L.)

Ethoxyquin (EQ; 6-Ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline) has been used as an antioxidant in feed components for pets, livestock and aquaculture. However, possible risks of EQ used in aquafeed for fish health have not yet been characterized. The present study investigated the toxicity and dose-response of subchronic dietary EQ exposure at doses ranging from 41 to 9666 mg EQ/kg feed in Atlantic salmon (Salmo salar L.). Feed at concentrations higher than 1173 mg EQ/kg were rejected by the fish, resulting in reduced feed intake and growth performance. No mortality was observed in fish exposed to any of the doses. A multi-omic screening of metabolome and proteome in salmon liver indicated an effect of dietary EQ on bioenergetics pathways and hepatic redox homeostasis in fish fed concentrations above 119 mg EQ/kg feed. Increased energy expenditure associated with an upregulation of hepatic fatty acid β-oxidation and induction and carbohydrate catabolic pathways resulted in a dose-dependent depletion of intracytoplasmic lipid vacuoles in liver histological sections, decreasing whole body lipid levels and altered purine/pyrimidine metabolism. Increased GSH and TBARS in the liver indicated a state of oxidative stress, which was associated with activation of the NRF2-mediated oxidative stress response and glutathione-mediated detoxification processes. However, no oxidative DNA damage was observed. As manifestation of altered energy metabolism, the depletion of liver intracytoplasmic lipid vacuoles was considered the critical endpoint for benchmark dose assessment, and a BMDL10 of 243 mg EQ/kg feed was derived as a safe upper limit of EQ exposure in Atlantic salmon.

Factors influencing risk assessments of brominated flame-retardants; evidence based on seafood from the North East Atlantic Ocean

Brominated flame-retardants (BFRs) such as polybrominated diphenyl ethers (PBDE) and hexabromocyclododecane (HBCD) are considered hazardous to human health. Due to their persistence, they are still present in the environment and in biota and seafood is major contributor of BFRs to human exposure. Here, we used data from >9700 samples of wild and farmed fish, fish feed and fish feed ingredients collected from the North Atlantic between 2006 and 2016 aiming to investigate factors influencing the risk assessments of BFRs. Due to most representative number of analyses, PBDEs were the main focus of investigation. Mean ∑PBDE in fillet samples ranged from below quantification in Atlantic cod fillet to 2.0 μg kg^-1 in Atlantic halibut. The main congener contributing to the ∑PBDE in all species was BDE 47. Factors affecting the level of BFR in seafood were multifaceted, and the levels were within species mainly determined by fish age, geographical origin and time of sampling. BDE 47, 99, 153 and HBCD were selected for margin of exposure (MOE) evaluation. When other sources of BFR than seafood were excluded, our risk assessment showed low risk at the current dietary intake of seafood. However, the dietary intake of BDE 99 may be of concern for toddlers when all sources are considered. The choice of fish species, dietary studies, choice of statistics, as well as exposure from other sources than seafood, were all factors that influenced the final MOE of BFRs. We propose the use of regression on order statistics as a tool for risk assessment, to illustrate means and spreads in large surveillance datasets to avoid the issue of measurements below the limit of quantification. A harmonized, updated evaluation of the risk associated with exposure to BFRs from diet, air and dust is warranted, where the fish species most commonly consumed also is taken into consideration.

Selenium and selenium species in feeds and muscle tissue of Atlantic salmon

Selenium (Se) is an essential element for animals, including fish. Due to changes in feed composition for Atlantic salmon (Salmo salar), it may be necessary to supplement feeds with Se. In the present work, the transfer of Se and Se species from feed to muscle of Atlantic salmon fed Se supplemented diets was studied. Salmon were fed basal fish feed (0.35 mg Se/kg and 0.89 mg Se/kg feed), or feed supplemented either with selenised yeast or sodium selenite, at low (1-2 mg Se/kg feed) and high (15 mg Se/kg feed) levels, for 12 weeks. For the extraction of Se species from fish muscle, enzymatic cleavage with protease type XIV was applied. The extraction methods for Se species from fish feed were optimised, and two separate extraction procedures were applied, 1) enzymatic cleavage for organic Se supplemented feeds and 2) weak alkaline solvent for inorganic Se supplemented feeds, respectively. For selenium speciation analysis in feed and muscle tissue anion-exchange HPLC-ICP-MS for analysis of inorganic Se species and cation-exchange HPLC-ICP-MS for analysis of organic Se species, were applied. In addition, reversed phase HPLC-ICP-MS was applied for analysis of selenocysteine (SeCys) in selected muscle samples. The results demonstrated that supplemented Se (organic and inorganic) accumulated in muscle of Atlantic salmon, and a higher retention of Se was seen in the muscle of salmon fed organic Se diets. Selenomethionine (SeMet) was the major Se species in salmon fed basal diets and diets supplemented with organic Se, accounting for 91-118% of the total Se. In contrast, for muscle of salmon fed high inorganic Se diet, SeMet accounted for 30% of the total Se peaks detected. Several unidentified Se peaks were detected, in the fish fed high inorganic diet, and analysis showed indicated SeCys is a minor Se species present in this fish muscle tissue.

Transepithelial transfer of phenanthrene, but not of benzo[a]pyrene, is inhibited by fatty acids in the proximal intestine of rainbow trout (Oncorhynchus mykiss)

The inclusion of vegetable oils in aquafeeds introduces contaminating polycyclic aromatic hydrocarbons (PAHs) in salmonids. Since lipophilic PAHs solubilize in micelles composed of lipids, bile salts and fatty acids, dietary lipid composition can alter intestinal transepithelial PAH transfer. We studied the uptake of two PAHs, viz. benzo[a]pyrene (BaP) and phenanthrene (PHE), in rainbow trout (Oncorhynchus mykiss) intestine. We also investigated the effects of two fatty acids, viz. fish oil-derived eicosapentaenoic acid (EPA, 20:5n-3) and vegetable oil-derived oleic acid (18:1n-9) on intestinal uptake. Radiolabeled PAHs were solubilized in micelles composed of tritiated EPA and oleic acid, respectively, and administrated to intestinal segments mounted in Ussing chambers. In the absence of micelles, PHE accumulation was two times higher than BaP in the mucosal and serosal layers of proximal and distal intestine. Administration of PHE in micelles composed of oleic acid resulted in a 50% lower accumulation of PHE in the mucosal layers of the proximal intestine compared to EPA-composed micelles. Accumulation of EPA and oleic acid in the proximal intestinal mucosa correlated negatively with the transepithelial transfer of these fatty acids across the proximal intestinal epithelium. Transepithelial PHE transfer across the proximal intestine was reduced by 30% in co-exposure with EPA-composed micelles compared to 80% with oleic acid micelles. BaP was not transferred across the intestine. We conclude that the lipid composition of an aquafeed is an important determinant of PAH bioavailability. Therefore, lipid composition should be an important consideration in choosing vegetable oils as alternatives for fish oil in aquafeeds.

Sensitivity and toxic mode of action of dietary organic and inorganic selenium in Atlantic salmon (Salmo salar)

Depending on its chemical form, selenium (Se) is a trace element with a narrow range between requirement and toxicity for most vertebrates. Traditional endpoints of Se toxicity include reduced growth, feed intake, and oxidative stress, while more recent finding describe disturbance in fatty acid synthesis as underlying toxic mechanism. To investigate overall metabolic mode of toxic action, with emphasis on lipid metabolism, a wide scope metabolomics pathway profiling was performed on Atlantic salmon (Salmo salar) (572±7g) that were fed organic and inorganic Se fortified diets. Atlantic salmon were fed a low natural background organic Se diet (0.35mg Se kg^-1, wet weight (WW)) fortified with inorganic sodium selenite or organic selenomethionine-yeast (SeMet-yeast) at two levels (∼1-2 or 15mgkg^-1, WW), in triplicate for 3 months. Apparent adverse effects were assessed by growth, feed intake, oxidative stress as production of thiobarbituric acid-reactive substances (TBARS) and levels of tocopherols, as well as an overall metabolomic pathway assessment. Fish fed 15mgkg^-1 selenite, but not 15mgkg^-1 SeMet-yeast, showed reduced feed intake, reduced growth, increased liver TBARS and reduced liver tocopherol. Main metabolic pathways significantly affected by 15mgkg^-1 selenite, and to a lesser extent 15mgkg^-1 SeMet-yeast, were lipid catabolism, endocannabinoids synthesis, and oxidant/glutathione metabolism. Disturbance in lipid metabolism was reflected by depressed levels of free fatty acids, monoacylglycerols and diacylglycerols as well as endocannabinoids. Specific for selenite was the significant reduction of metabolites in the S-Adenosylmethionine (SAM) pathway, indicating a use of methyl donors that could be allied with excess Se excretion. Dietary Se levels to respectively 1.1 and 2.1mgkg^-1 selenite and SeMet-yeast did not affect any of the above mentioned parameters. Apparent toxic mechanisms at higher Se levels (15mgkg^-1) included oxidative stress and altered lipid metabolism for both inorganic and organic Se, with higher toxicity for inorganic Se.

The polycyclic aromatic hydrocarbons benzo[a]pyrene and phenanthrene inhibit intestinal lipase activity in rainbow trout (Oncorhynchus mykiss)

Elevated levels of polycyclic aromatic hydrocarbons (PAHs) are detected in aquafeeds where fish oils are (partially) replaced by vegetable oils. The highly lipophilic PAHs solubilize readily in oil droplets and micelles in the intestinal lumen that can affect enzymatic lipid digestion by altering lipase activity. We therefore investigated the effect of two PAHs, benzo[a]pyrene (BaP) and phenanthrene (PHE), on bile salt-activated lipase (BAL) activity in desalted luminal extracts of the proximal intestine of rainbow trout (Oncorhynchus mykiss) using the triacylglycerides rapeseed oil and fish oil as substrates. The hydrolysis of rapeseed oil and fish oil measured at a calculated substrate concentration of 2.2mM, increased linearly up to 30min at 15°C. Substrate dependency under initial velocity conditions was described by simple Michaelis-Menten kinetics with a K_m value of 1.2mM for rapeseed and fish oil. Rapeseed oil hydrolysis was inhibited by 1nM BaP and 10nM PHE. The hydrolysis of fish oil was only inhibited by 10μM BaP. The in vitro lipase activity data were corroborated by TLC/HPLC analysis of the reaction products, showing that in the presence of BaP and PHE, 46-80% less free fatty acids (FFA) were hydrolysed from rapeseed and fish oil triacylglycerides. The presence of low concentrations of BaP and PHE decreased rapeseed oil hydrolysis by BAL whereas fish oil hydrolysis was not affected. The replacement of fish oil by rapeseed oil in aquafeeds introduces PAHs that could affect lipid digestion.

Comprehensive strategy for pesticide residue analysis through the production cycle of gilthead sea bream and Atlantic salmon

Plant ingredients and processed animal proteins are alternative feedstuffs for fish feeds in aquaculture. However, their use can introduce contaminants like pesticides that are not previously associated with marine Atlantic salmon and gilthead sea bream farming. This study covers the screening of around 800 pesticides by gas chromatography (GC) and liquid chromatography (LC) coupled to high resolution time-of-flight mass spectrometry in matrices throughout the entire marine food production chain. Prior to analysis of real-world samples, the screening methodology was validated for 252 pesticides to establish the screening detection limit. This was 0.01 mg kg^-1 for 113 pesticides (45%), 0.05 mg kg^-1 for 73 pesticides (29%) and >0.05 mg kg^-1 for 66 pesticides (26%). After that, a quantitative methodology based on GC coupled to tandem mass spectrometry with atmospheric pressure chemical ionization source (GC-APCI-MS/MS) was optimized for the pesticides found in the screening. Although several polar pesticides, of which pirimiphos methyl and chlorpyriphos-methyl were most dominant, were found in plant material and feeds based on these ingredients, none of them were observed in fillets of Atlantic salmon and gilthead sea bream fed on these feeds.

Uptake of benzo[a]pyrene, but not of phenanthrene, is inhibited by fatty acids in intestinal brush border membrane vesicles of rainbow trout (Oncorhynchus mykiss)

Partial replacement of fish ingredients with vegetable ingredients has elevated levels of polycyclic aromatic hydrocarbons (PAHs) in Atlantic salmon reared on these feeds. PAH uptake in the intestinal tract is postulated to occur in association with lipid absorption and could well be affected by fatty acid composition. We therefore investigated the effects of a fish oil and vegetable oil fatty acid, eicosapentaenoic acid (EPA; 20:5n-3) and oleic acid (18:1n-9) respectively, on the uptake of benzo[a]pyrene (BaP) and phenanthrene (PHE) across the intestinal brush border membrane in the salmonid species rainbow trout (Oncorhynchus mykiss). BaP and PHE were solubilized in mixed micelles composed of either EPA or oleic acid and administrated to isolated brush border membrane vesicles (BBMV) derived from the pyloric caeca, proximal intestine and distal intestine. In the absence of free fatty acids (FFA) trans-membrane uptake of BaP and PHE was 2-7 times lower than the fraction associated to or in the membrane. In the presence of FFA, trans-membrane BaP uptake had decreased by 80 and 40% at the highest EPA and oleic acid concentration, respectively, whereas PHE uptake was virtually unaffected. In the presence of BaP, but not PHE, trans-membrane EPA uptake in BBMV had decreased. This study obtained evidence for PAH-dependent interactions with FFA uptake. We conclude that intestinal BaP uptake is reduced by luminal FFA contents whereas PHE uptake is not. A large fraction of the administrated BaP and PHE remains associated with the cellular membrane of enterocytes and may interfere with uptake of nutrients.

Comprehensive characterization of ethoxyquin transformation products in fish feed by traveling-wave ion mobility spectrometry coupled to quadrupole time-of-flight mass spectrometry

Feed additives are typically used in intensive farming production over long periods, and hence, they can accumulate in farmed animal tissues. Concerns regarding the use of ethoxyquin as an antioxidant feed additive, have recently arisen due to its potential conversion into a series of transformation products (TPs). The aim of this work was to characterize the TPs of ethoxyquin in fish feed by a novel approach based on the use of traveling-wave ion mobility spectrometry (TWIMS) coupled to high-resolution quadrupole time-of-flight mass spectrometry (QTOFMS). First, ethoxyquin was oxidized under controlled conditions and the generated TPs were added to a comprehensive database. Atlantic salmon feeds were then screened for ethoxyquin TPs using both targeted and untargeted approaches. Twenty-seven TPs were tentatively identified during the oxidation experiments, fifteen of them also being present in the feed samples. In addition, ten other potential TPs were detected in fish feed following the untargeted approach. Thirty-one of these TPs have been reported for the first time in this work through the oxidation experiments and the feed samples. Therefore, this study provides valuable information on the oxidative fate of ethoxyquin in feed, which can be used for future evaluations of potential risk related to this additive.

Ion-Mobility-Derived Collision Cross Section as an Additional Identification Point for Multiresidue Screening of Pesticides in Fish Feed

Ion mobility spectrometry allows for the measurement of the collision cross section (CCS), which provides information about the shape of an ionic molecule in the gas phase. Although the hyphenation of traveling-wave ion mobility spectrometry (TWIMS) with high-resolution quadrupole time-of-flight mass spectrometry (QTOFMS) has been mainly used for structural elucidation purposes, its potential for fast screening of small molecules in complex samples has not yet been thoroughly evaluated. The current work explores the capabilities of ultrahigh-performance liquid chromatography (UHPLC) coupled to a new design TWIMS-QTOFMS for the screening and identification of a large set of pesticides in complex salmon feed matrices. A database containing TWIMS-derived CCS values for more than 200 pesticides is hereby presented. CCS measurements showed high intra- and interday repeatability (RSD < 1%), and they were not affected by the complexity of the investigated matrices (ΔCCS ≤ 1.8%). The use of TWIMS in combination with QTOFMS was demonstrated to provide an extra-dimension, which resulted in increased peak capacity and selectivity in real samples. Thus, many false-positive detections could be straightforwardly discarded just by applying a maximum ΔCCS tolerance of ±2%. CCS was proposed as a valuable additional identification point in the pesticides screening workflow. Several commercial fish feed samples were finally analyzed to demonstrate the applicability of the proposed approach. Ethoxyquin and pirimiphos-methyl were identified in most of the analyzed samples, whereas tebuconazole and piperonil butoxide were identified for the first time in fish feed samples.

Modelling scenarios on feed-to-fillet transfer of dioxins and dioxin-like PCBs in future feeds to farmed Atlantic salmon (Salmo salar)

The salmon feed composition has changed the last decade with a replacement of traditionally use of fish oil and fishmeal diets with vegetable ingredients and the use decontaminated fish oils, causing reduced concentrations of dioxins and dioxin-like PCBs in farmed Norwegian Atlantic salmon. The development of novel salmon feeds has prompted the need for prediction on dioxins and dl-PCB concentrations in future farmed salmon. Prediction on fillet dioxins and dl-PCB concentrations from different feed composition scenarios are made using a simple one-compartmental transfer model based on earlier established dioxin and dl-PCB congener specific uptake and elimination kinetics rates. The model is validated with two independent feeding trials, with a significant linear correlation (r(2) = 0.96, y = 1.0x, p < 0.0001, n = 116) between observed and predicted values. Model fillet predictions are made for the following four scenarios; (1) general feed composition of 1999, (2) feed composition of 2013, (3) future feed composition with high fish oil and meal replacement, (4) future feed composition with high fish oil and meal replacement and decontaminated fish oil. Model predictions of fillet dioxin and dl-PCB concentrations from 1999 (1.05 ng WHO2005-TEQs kg(-1)ww) and 2013 (0.57 ng WHO2005-TEQs kg(-1)ww) are in line with the data observed in national surveillance programs of those years (1.1 and 0.52 ng WHO2005-TEQs kg(-1)ww, respectively). Future use of high replacement and decontaminated oils feeds gave predicted fillet concentrations of 0.27 ng WHO2005-TEQs kg(-1)ww, which is near the limit of quantification.

Investigation of pharmaceuticals in processed animal by-products by liquid chromatography coupled to high-resolution mass spectrometry

There is an on-going trend for developing more sustainable salmon feed in which traditionally applied marine feed ingredients are replaced with alternatives. Processed animal products (PAPs) have been re-authorized as novel high quality protein ingredients in 2013. These PAPs may harbor undesirable substances such as pharmaceuticals and metabolites which are not previously associated with salmon farming, but might cause a potential risk for feed and food safety. To control these contaminants, an analytical strategy based on a generic extraction followed by ultra-high performance liquid chromatography coupled to high resolution mass spectrometry (UHPLC-HRMS) using quadrupole time-of-flight mass analyzer (QTOF MS) was applied for wide scope screening. Quality control samples, consisting of PAP commodities spiked at 0.02, 0.1 and 0.2 mg/kg with 150 analytes, were injected in every sample batch to verify the overall method performance. The methodology was applied to 19 commercially available PAP samples from six different types of matrices from the EU animal rendering industry. This strategy allows assessing possible emergent risk exposition of the salmon farming industry to 1005 undesirables, including pharmaceuticals, several dyes and relevant metabolites.

The effect of dietary lipid composition on the intestinal uptake and tissue distribution of benzo[a]pyrene and phenanthrene in Atlantic salmon (Salmo salar)

Uptake of polycyclic aromatic hydrocarbons (PAHs) across the intestine is suggested to occur in association with dietary lipids. Partial replacement of fish ingredients by vegetable ingredients in aquafeeds has led to increased levels of PAHs in marine farmed fish. We therefore investigated, intestinal uptake, tissue distribution and PAH metabolism after a single dose of (14)C-benzo[a]pyrene (BaP) or (14)C-phenanthrene (PHE) given to Atlantic salmon (Salmo salar) acclimatized to a fish oil or vegetable oil based diet. Both BaP and PHE were absorbed along the intestine. Fish oil based feed increased BaP concentration in the pyloric caeca and that of PHE in the proximal intestine. In contrast, vegetable oil increased BaP concentrations in the distal intestine. Extraction of whole body autoradiograms removed PHE-associated radiolabeling almost completely from the intestinal mucosa, but not BaP-associated radiolabeling, indicating the presence of BaP metabolites bound to cellular macromolecules. This observation correlates with the increased cyp1a expression in the proximal intestine, distal intestine and liver in the BaP exposed group. Furthermore, BaP-induced cyp1a expression was higher in the distal intestine of salmon fed fish oil compared to the vegetable oil fed group. PHE had no significant effect on cyp1a expression in any of these tissues. We conclude that dietary lipid composition affects intestinal PAH uptake. Fish oil based feed increased intestinal PAH concentrations probably due to an enhanced solubility in micelles composed of fish oil fatty acids. Increased BaP accumulation in the distal intestine of vegetable oil fed fish seems to be associated with a reduced Cyp1a-mediated BaP metabolism.

Species and tissues specific differentiation of processed animal proteins in aquafeeds using proteomics tools

The rapidly growing aquaculture industry drives the search for sustainable protein sources in fish feed. In the European Union (EU) since 2013 non-ruminant processed animal proteins (PAP) are again permitted to be used in aquafeeds. To ensure that commercial fish feeds do not contain PAP from prohibited species, EU reference methods were established. However, due to the heterogeneous and complex nature of PAP complementary methods are required to guarantee the safe use of this fish feed ingredient. In addition, there is a need for tissue specific PAP detection to identify the sources (i.e. bovine carcass, blood, or meat) of illegal PAP use. In the present study, we investigated and compared different protein extraction, solubilisation and digestion protocols on different proteomics platforms for the detection and differentiation of prohibited PAP. In addition, we assessed if tissue specific PAP detection was feasible using proteomics tools. All work was performed independently in two different laboratories. We found that irrespective of sample preparation gel-based proteomics tools were inappropriate when working with PAP. Gel-free shotgun proteomics approaches in combination with direct spectral comparison were able to provide quality species and tissue specific data to complement and refine current methods of PAP detection and identification.

SIGNIFICANCE

To guarantee the safe use of processed animal protein (PAP) in aquafeeds efficient PAP detection and monitoring tools are required. The present study investigated and compared various proteomics workflows and shows that the application of shotgun proteomics in combination with direct comparison of spectral libraries provides for the desired species and tissue specific classification of this heat sterilized and pressure treated (≥133°C, at 3bar for 20min) protein feed ingredient.

Dietary vitamin A supplementation ameliorates the effects of poly-aromatic hydrocarbons in Atlantic salmon (Salmo salar)

Several studies have reported on the interaction between vitamin A (VA) and aryl hydrocarbon receptor (AhR)-binding toxicants, including poly-aromatic hydrocarbons (PAHs). In aquaculture, the use of plant oils in novel aquafeeds can increase PAH levels while simultaneously lowering natural VA background levels, causing the need to supplement plant oil-based feeds with synthetic VA. To study dietary VA-PAH interactions, Atlantic salmon (initial weight 195±0.15g) were fed four identical plant-based diets that were supplemented with PAHs (100 and 10mgkg(-1) benzo[a]pyrene (BaP) and phenanthrene (Phe), respectively) or VA (retinyl acetate 8721IUkg(-1)) separately or combined for 2.5 months in a 2×2 factorial design, with triplicate net-pens per diet. Dietary PAH significantly reduced hepatic VA storage, and VA-enriched diets restored hepatic VA. There was a significant PAH-VA interaction effect on hepatic BaP, but not Phe, accumulation, with reduced hepatic BaP concentrations in fish fed VA+PAH compared to fish fed PAH alone. Concurrently, PAH and VA significantly interacted in their effects on CYP1A phase I biotransformation as observed from increased ethoxyresorufin-O-deethylase (EROD) activity, increased CYP1A protein concentration, and elevated transcription (cyp1a1 gene expression) in fish fed PAH+VA compared to PAH alone. Dietary VA supplementation alone had no significant effect on CYP1A phase I biotransformation. Metabolomic assessment showed that dietary VA caused a restoration of metabolic intermediates involved in energy metabolism that were affected by dietary PAH. Moreover, a PAH-induced growth inhibition was partially ameliorated by dietary VA supplementation. In conclusion, dietary VA interacted with PAH toxicity on the level of CYP1A-mediated detoxification, hepatic PAH accumulation, energy allocation, and growth.

The mining chemical Polydadmac is cytotoxic but does not interfere with Cu-induced toxicity in Atlantic salmon hepatocytes

To speed up sedimentation of suspended solids the mining industry often uses flocculent chemicals. In this work we evaluated the cytotoxic and mechanistic effects of Polydadmac, and its basic component Dadmac, on fish cells. Dose-response effects, temperature-dependent effects and impact of Dadmac and Polydadmac on Cu toxicity were studied in Atlantic salmon hepatocytes. We used the xCELLigence system and the MTT test for cytotoxicity assessments, and real-time RT-qPCR to evaluate molecular effects. The results showed a cytotoxic response for Polydadmac but not for Dadmac. Elevated levels of Cu were cytotoxic. Moderately cytotoxic concentrations of Cu (100-1000 μM) induced significant responses on the transcription of a number of genes in the cells, i.e. cuznsod (sod1), cat, mnsod (sod2), nfe2l2, hmox1, mta, casp3b, casp6, bclx, cyp1a, ccs, atp7a, app, mmp13, esr1, ppara, fads2 and ptgs2. A factorial PLS regression model for mnsod transcription showed a synergistic effect between Dadmac and Cu exposure in the cells, indicating an interaction effect between Dadmac and Cu on mitochondrial ROS scavenging. No interaction effects were seen for Polydadmac on Cu toxicity. In conclusion, Polydadmac is cytotoxic at elevated concentrations but appears to have low ability to interfere with Cu toxicity in Atlantic salmon liver cells.

Occurrence and potential transfer of mycotoxins in gilthead sea bream and Atlantic salmon by use of novel alternative feed ingredients

Plant ingredients and processed animal proteins (PAP) are suitable alternative feedstuffs for fish feeds in aquaculture practice, although their use can introduce contaminants that are not previously associated with marine salmon and gilthead sea bream farming. Mycotoxins are well known natural contaminants in plant feed material, although they also could be present on PAPs after fungi growth during storage. The present study surveyed commercially available plant ingredients (19) and PAP (19) for a wide range of mycotoxins (18) according to the EU regulations. PAP showed only minor levels of ochratoxin A and fumonisin B1 and the mycotoxin carry-over from feeds to fillets of farmed Atlantic salmon and gilthead sea bream (two main species of European aquaculture) was performed with plant ingredient based diets. Deoxynivalenol was the most prevalent mycotoxin in wheat, wheat gluten and corn gluten cereals with levels ranging from 17 to 814 and μg kg(-1), followed by fumonisins in corn products (range 11.1-4901 μg kg(-1) for fumonisin B1+B2+B3). Overall mycotoxin levels in fish feeds reflected the feed ingredient composition and the level of contaminant in each feed ingredient. In all cases the studied ingredients and feeds showed levels of mycotoxins below maximum residue limits established by the Commission Recommendation 2006/576/EC. Following these guidelines no mycotoxin carry-over was found from feeds to edible fillets of salmonids and a typically marine fish, such as gilthead sea bream. As far we know, this is the first report of mycotoxin surveillance in farmed fish species.

Modifying effects of vitamin E on chlorpyrifos toxicity in atlantic salmon

The aim of this study was to elucidate how vitamin E (alpha tocopherol) may ameliorate the toxicity of the pesticide chlorpyrifos in Atlantic salmon. Freshly isolated hepatocytes were exposed to vitamin E, chlorpyrifos or a combination of vitamin E and chlorpyrifos (all 100 μM). Transcriptomics (RNA-seq) and metabolomics were used to screen for effects of vitamin E and chlorpyrifos. By introducing vitamin E, the number of upregulated transcripts induced by chlorpyrifos exposure was reduced from 941 to 626, while the number of downregulated transcripts was reduced from 901 to 742 compared to the control. Adding only vitamin E had no effect on the transcriptome. Jak-STAT signaling was the most significantly affected pathway by chlorpyrifos treatment according to the transcriptomics data. The metabolomics data showed that accumulation of multiple long chain fatty acids and dipeptides and amino acids in chlorpyrifos treated cells was partially alleviated by vitamin E treatment. Significant interaction effects between chlorpyrifos and vitamin E were seen for 15 metabolites, including 12 dipeptides. The antioxidant had relatively modest effects on chlorpyrifos-induced oxidative stress. By combining the two data sets, the study suggests that vitamin E supplementation prevents uptake and accumulation of fatty acids, and counteracts inhibited carbohydrate metabolism. Overall, this study shows that vitamin E only to a moderate degree modifies chlorpyrifos toxicity in Atlantic salmon liver cells.

Contaminant levels in Norwegian farmed Atlantic salmon (Salmo salar) in the 13-year period from 1999 to 2011

BACKGROUND

Environmental pollutants such as dioxins and PCBs, heavy metals, and organochlorine pesticides are a global threat to food safety. In particular, the aquatic biota can bioaccumulate many of these contaminants potentially making seafood of concern for chronic exposure to humans.

OBJECTIVES

The main objective was to evaluate trends of contaminant levels in Norwegian farmed Atlantic salmon in light of the derived tolerable intakes.

METHODS

Through an EU-instigated surveillance programme, the Norwegian Food Safety Authority (NFSA) has between 1999 and 2011 collected more than 2300 samples of Norwegian farmed Atlantic salmon (Salmo salar) for contaminant analyses. The fillets of these fish were homogenised and analysed for dioxins, PCBs, heavy metals and organochlorine pesticides.

RESULTS

The levels of the contaminants mercury, arsenic, dioxins, dioxin-like PCBs and DDT in Norwegian farmed salmon fillet have decreased during our period of analyses. The levels of cadmium, lead and several organochlorine pesticides were too close to the limit of quantification to calculate time trends. For PCB6 and quantifiable amounts of pesticides, except DDT, stable levels were observed.

CONCLUSION

The contaminant levels in Norwegian farmed salmon have generally decreased between 1999 and 2011. Excluding other dietary sources, the levels of dioxins and dioxin-like PCBs in 2011 allowed consumption of up to 1.3kg salmon per week to reach the tolerable weekly intake. The group of contaminants which was the limiting factor for safe consumption of Norwegian farmed salmon, based on currently established TWI values, is the sum of dioxins and dioxin-like PCBs.

Toxicological effect of single contaminants and contaminant mixtures associated with plant ingredients in novel salmon feeds

Increasing use of plant feed ingredients may introduce contaminants not previously associated with farming of salmonids, such as pesticides and PAHs from environmental sources or from thermal processing of oil seeds. To screen for interaction effects of contaminants newly introduced in salmon feeds, Atlantic salmon primary hepatocytes were used. The xCELLigence cytotoxicity system was used to select optimal dosages of the PAHs benzo(a)pyrene and phenanthrene, the pesticides chlorpyrifos and endosulfan, and combinations of these. NMR and MS metabolic profiling and microarray transcriptomic profiling was used to identify novel biomarkers. Lipidomic and transcriptomic profiling suggested perturbation of lipid metabolism, as well as endocrine disruption. The pesticides gave the strongest responses, despite having less effect on cell viability than the PAHs. Only weak molecular responses were detected in PAH-exposed hepatocytes. Chlorpyrifos suppressed the synthesis of unsaturated fatty acids. Endosulfan affected steroid hormone synthesis, while benzo(a)pyrene disturbed vitamin D3 metabolism. The primary mixture effect was additive, although at high concentrations the pesticides acted in a synergistic fashion to decrease cell viability and down-regulate CYP3A and FABP4 transcription. This work highlights the usefulness of 'omics techniques and multivariate data analysis to investigate interactions within mixtures of contaminants with different modes of action.

Polyaromatic hydrocarbons do not disturb liquid-liquid phase coexistence, but increase the fluidity of model membranes

Polyaromatic hydrocarbons (PAHs) is a group of compounds, many of which are toxic, formed by incomplete combustion or thermal processing of organic material. They are highly lipophilic and thus present in some seed oils used for human consumption as well as being increasingly common in aquaculture diets due to inclusion of vegetable oils. Cytotoxic effects of PAHs have been thought to be partly due to a membrane perturbing effect of these compounds. A series of studies were here performed to examine the effects of three different PAHs (naphthalene, phenanthrene and benzo[a]pyrene) with different molecular sizes (two, three and five rings, respectively) and fat solubility (Kow 3.29, 4.53 and 6.04, respectively) on membrane models. The effects of PAHs on liquid-liquid phase coexistence in solid-supported lipid bilayers (dioleoylphosphocholine:dipalmitoylphosphatidylcholine:cholesterol) were assessed using fluorescence microscopy. Benzo[a]pyrene had a slight affinity for the liquid-ordered phase, but there were no effects of adding any of the other PAHs on the number or size of the liquid domains (liquid-ordered and liquid-disordered). Benzo[a]pyrene and phenanthrene, but not naphthalene, lowered the transition temperature (Tm) and the enthalpy (ΔH) characterising the transition from the solid to the liquid-crystalline phase in DPPC vesicles. The membrane effects of the PAH molecules are likely related to size, with bigger and more fat-soluble molecules having a fluidising effect when embedded in the membrane, possibly causing some of the observed toxic effects in fish exposed to these contaminants.

Screening of pesticides and polycyclic aromatic hydrocarbons in feeds and fish tissues by gas chromatography coupled to high-resolution mass spectrometry using atmospheric pressure chemical ionization

This paper reports a wide-scope screening for detection and identification of pesticides and polycyclic aromatic hydrocarbons (PAHs) in feeds and fish tissues. QuEChERS sample treatment was applied, using freezing as an additional cleanup. Analysis was carried out by gas chromatography coupled to hybrid quadrupole time-of-flight mass spectrometry with atmospheric pressure chemical ionization (GC-(APCI) QTOF MS). The qualitative validation was performed for over 133 representative pesticides and 24 PAHs at 0.01 and 0.05 mg/kg. Subsequent application of the screening method to aquaculture samples made it possible to detect several compounds from the target list, such as chlorpyrifos-methyl, pirimiphos-methyl, and ethoxyquin, among others. Light PAHs (≤4 rings) were found in both animal and vegetable samples. The reliable identification of the compounds was supported by accurate mass measurements and the presence of at least two representative m/z ions in the spectrum together with the retention time of the peak, in agreement with the reference standard. Additionally, the search was widened to include other pesticides for which standards were not available, thanks to the expected presence of the protonated molecule and/or molecular ion in the APCI spectra. This could allow the detection and tentative identification of other pesticides different from those included in the validated target list.

Low impact of exposure to environmentally relevant doses of 226Ra in Atlantic cod (Gadus morhua) embryonic cells

The aim of this study was to investigate whether (226)Ra, a radionuclide present in produced water from oil platforms in the North Sea and other offshore drilling areas, could affect vulnerable early life stages of Atlantic cod (Gadus morhua). Blastula-stage embryonic cells (EC) from fertilized eggs of Atlantic cod were isolated and exposed to environmental relevant concentrations of (226)Ra and transcription of selected genes quantified. The results showed a weak, but significant up-regulation of GPx3 and HSP70 transcripts after 48 h of exposure to 2.11 Bq/L. In EC exposed to three (226)Ra concentrations (2.11, 23 and 117 Bq/L) for 12 h, metallothionein, HSP90AA, thioredoxin and caspase 8 were significantly up-regulated in cells exposed to 117 Bq/L, whereas thioredoxin was also significantly up-regulated in EC exposed to 23 Bq/L. When EC were exposed to the same (226)Ra concentrations for 48 h, only heme oxygenase was significantly up-regulated in the 23 Bq/L exposure group. The results suggest that environmentally relevant activities of (226)Ra may induce oxidative stress and apoptosis in fish ECs. Exposure of Atlantic cod EC to Cd, selected as a model toxicant, supported the ability of EC around blastula stage to respond to toxicants by altered transcription. Due to dilution, environmentally relevant concentrations of radionuclides present in produced water would be expected to pose a minor threat to early life stages of fish.

Dechlorination of the dietary nona-chlorinated toxaphene congeners 62 and 50 into the octa-chlorinated toxaphene congeners 44 and 40 in zebrafish (Danio rerio) and Atlantic salmon (Salmo salar)

The relative feed-to-fish accumulation and possible biotransformation of the nona-chlorinated toxaphene congeners currently included in EU-legislation (CHB-50 and -62) and the octa-chlorinated congeners recommended by the European Food Safety Authority to be included in future surveillance of fish samples (CHB-40, 41, and 44) were investigated in the present study. Model fish Danio rerio were fed either (a) diets spiked with a combination as well as the pure individual toxaphene congeners CHB-50 or 62 or (b) diets spiked with the combination of CHB ∑50+62 and/or CHB ∑40+41+44. In addition, seawater adapted Atlantic salmon smolts were fed technical toxaphene enriched feeds for 62 days. Zebrafish fed a diet containing CHB-50 and CHB-62 accumulated newly formed CHB-40&41 and CHB-44, respectively. The biomagnifications factors (BMF) of the toxaphene congeners in Atlantic salmon muscle from the feeds spiked with technical toxaphene were significantly correlated with their relative lipophilicity (expressed as logK(ow)). An exception was CHB-44 which had a higher BMF than could be expected from its specific logK(ow), reflecting that CHB-44 is a metabolite formed under dietary exposure to CHB-62. This paper reports the in vivo dechlorination of nona-chlorinated toxaphene congeners into octa-chlorinated congeners in feeding trials with a model fish (zebrafish) and an oily food fish (Atlantic salmon).

Atlantic salmon (Salmo salar L.) as a net producer of long-chain marine ω-3 fatty acids

The objective of the present study was to investigate the effects of replacing high levels of marine ingredients with vegetable raw materials and with emphasis on lipid metabolism and net production of long-chain polyunsaturated ω-3 fatty acids (EPA + DHA). Atlantic salmon were fed three different replacement vegetable diets and one control marine diet before sensory attributes, β-oxidation capacity, and fatty acid productive value (FAPV) of ingested fatty acids (FAs) were evaluated. Fish fed the high replacement diet had a net production of 0.8 g of DHA and a FAPV of 142%. Fish fed the marine diet had a net loss of DHA. The present work shows that Atlantic salmon can be a net producer of marine DHA when dietary fish oil is replaced by vegetable oil with minor effects on sensory attributes and lipid metabolism.

Biomarkers in natural fish populations indicate adverse biological effects of offshore oil production

Background

Despite the growing awareness of the necessity of a sustainable development, the global economy continues to depend largely on the consumption of non-renewable energy resources. One such energy resource is fossil oil extracted from the seabed at offshore oil platforms. This type of oil production causes continuous environmental pollution from drilling waste, discharge of large amounts of produced water, and accidental spills.

Methods and principal findings

Samples from natural populations of haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua) in two North Sea areas with extensive oil production were investigated. Exposure to and uptake of polycyclic aromatic hydrocarbons (PAHs) were demonstrated, and biomarker analyses revealed adverse biological effects, including induction of biotransformation enzymes, oxidative stress, altered fatty acid composition, and genotoxicity. Genotoxicity was reflected by a hepatic DNA adduct pattern typical for exposure to a mixture of PAHs. Control material was collected from a North Sea area without oil production and from remote Icelandic waters. The difference between the two control areas indicates significant background pollution in the North Sea.

Conclusion

It is most remarkable to obtain biomarker responses in natural fish populations in the open sea that are similar to the biomarker responses in fish from highly polluted areas close to a point source. Risk assessment of various threats to the marine fish populations in the North Sea, such as overfishing, global warming, and eutrophication, should also take into account the ecologically relevant impact of offshore oil production.

Carry-over of dietary organochlorine pesticides, PCDD/Fs, PCBs, and brominated flame retardants to Atlantic salmon (Salmo salar L.) fillets

Information on carry-over of contaminants from feed to animal food products is essential for appropriate human risk assessment of feed contaminants. The carry-over of potentially hazardous persistent organic pollutants (POPs) from feed to fillet was assessed in consumption sized Atlantic salmon (Salmo salar). Relative carry-over (defined as the fraction of a certain dietary POP retained in the fillet) was assessed in a controlled feeding trial, which provided fillet retention of dietary organochlorine pesticides (OCPs), dioxins (PCDD/Fs), polychlorinated biphenyls (PCBs), and brominated flame retardants (BFRs). Highest retention was found for OCPs, BFRs and PCBs (31-58%), and the lowest retentions were observed for PCDD/Fs congeners (10-34%). National monitoring data on commercial fish feed and farmed Atlantic salmon on the Norwegian market were used to provide commercially relevant feed-to-fillet transfer factors (calculated as fillet POP level divided by feed POP level), which ranged from 0.4 to 0.5, which is a factor 5-10 times higher than reported for terrestrial meat products. For the OCP with one of the highest relative carry-over, toxaphene, uptake and elimination kinetics were established. Model simulations that are based on the uptake and elimination kinetics gave predicted levels that were in agreement with the measured values. Application of the model to the current EU upper limit for toxaphene in feed (50 μg kg(-1)) gave maximum fillet levels of 22 μg kg(-1), which exceeds the estimated permissible level (21 μg kg(-1)) for toxaphene in fish food samples in Norway.

Effects of refining and removal of persistent organic pollutants by short-path distillation on nutritional quality and oxidative stability of fish oil

Food and feed legislations are implemented to control the level of unwanted persistent organic pollutants (POPs) below health risk concerns. Short-path distillation is established as the most effective industrial process to remove POPs in fish oil. However, the technology involves heating of the oil to high temperature levels (>200 °C) that possibly give unwanted heat-induced side reactions and coevaporation of minor compounds of importance for the nutritional quality of the oil. The effects on retention of vitamins, cholesterol, and unsaponifiable compounds, geometrical isomerization, loss of polyunsaturated fatty acids (PUFA), oxidation level, and oxidative stability have been studied on the basis of experiments designed to optimize and model the effect of process conditions (i.e., evaporator temperature, feed rate, and addition of working fluid) on the reduction of POPs. Loss of volatile nutrients was observed, but the extent will depend on the process conditions needed to obtain target decontamination level, as well as the concentration ratio and difference in vapor pressure between free and esterified forms of the studied compounds. Some reduction in oxidation level was documented with preservation of PUFA level and quality. Oxidative stability was influenced both positively and negatively depending on the applied process conditions. Generally, no adverse negative effects on the nutritional quality of the fish oil could be documented. Optimal process conditions were modeled that ensure removal of POPs to within legislation levels while retaining most of the vitamin levels in fish oil. A 76% reduction of the WHO-PCDD/F-PCB-TEQ level in the used feedstock was needed to be in accordance with the voluntary industrial monograph of GOED. This could be achieved on the basis of operation conditions giving <20% loss of vitamins. A 90% decontamination rate gave vitamin retentions in the 60-90% range.

Reducing persistent organic pollutants while maintaining long chain omega-3 fatty acid in farmed Atlantic salmon using decontaminated fish oils for an entire production cycle

Oily fish are an important source of health promoting nutrients such as the very long chain marine omega-3 (VLC-n3) fatty acids and simultaneously a source of potentially hazardous contaminants. Fish oils that are used in fish feed are the main source for both contaminants and VLC-n3. Decontamination techniques have recently been developed to effectively remove persistent organic contaminants from fish oils. The aim of the present study was to assess the level of potentially hazardous contaminants and the health beneficial fatty acids in Atlantic salmon reared on novel decontaminated feeds. Atlantic salmon were fed for 18 months (an entire seawater production cycle) on diets based on decontaminated or non-treated (control) fish oils until market size (approximately 5 kg). The level of known notorious persistent organic pollutants (POPs, i.e. dioxins, dioxin-like polychlorinated biphenyls (DL-PCBs), non dioxin-like PCBs, poly brominated diphenyl ethers (PBDE), and organochlorine pesticides), as well as fatty acid composition were analysed in fish oils, the two diets, and Atlantic salmon fillet. The oil decontamination process was a two-step procedure using active carbon and short path distillation. The fillet levels of POPs in market size fish were reduced by 68-85% while the concentration of very long chain omega-3 fatty acids was reduced by 4-7%. No differences in biomarkers of dioxin-like component exposures, such as hepatic gene expression of CYP1A or AhR2B, CYP1A protein expression and 7-ethoxyresorufin O-deethylase (EROD) activity, were observed between salmon raised on normal or decontaminated feeds, thus indicating that the difference in POPs levels were of no biological significance to the fish. Atlantic salmon reared on decontaminated feeds had sum polychlorinated dibenzodioxins/furans (PCDD/Fs) and DL-PCB concentrations that were comparable with terrestrial food products such as beef, while the level of marine omega-3 fatty acids remained as high as for commercially farmed Atlantic salmon.

Modeling of a short-path distillation process to remove persistent organic pollutants in fish oil based on process parameters and quantitative structure properties relationships

A factorial experimental design based on temperature, feed rate and addition of "working fluid" (WF; fatty acid ethyl esters) was used to model a short-path distillation process applied for removal of persistent organic pollutants (POPs) in fish oil. Decontamination effect was assessed by measuring the level of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (DL-PCBs) and polybrominated diphenylethers (PBDEs). The average reduction in chemical concentration of the individual PCDD, PCDF, DL-PCB and PBDE congeners was linearly dependent on the number of chlorine or bromine substitutions within each homologue group. DL-PCB and PBDE congeners could also be separated based on ortho-substitution. The quantitative structure properties relationships (QSPR) were combined with process parameters to establish response surface models for each homologue congener group based on partial least squares regression (PLSR). Cross validated predictive ability of the models was in the 4-9% range. Generally high temperature, low feed rate and WF addition improved the decontamination efficiency. The WHO-PCDD/F-PCB-TEQ level could be reduced by up to 98% based on the best experimental settings with residual concentration considerably below present maximum permitted levels in European food and feed legislations.

Oxidative stress responses in rainbow trout (Oncorhynchus mykiss) hepatocytes exposed to pro-oxidants and a complex environmental sample

A wide range of pollutants in the aquatic environment have the capacity to induce toxic effects expressed as cellular oxidative stress. In the current study, the potential of an in vitro toxicity testing system was therefore investigated using rainbow trout (Oncorhynchus mykiss) hepatocytes to assess different endpoints of oxidative stress. The pro-oxidants CuSO(4) and paraquat were used as models for comparison to a complex environmental sample. Results following 6, 24, 48 and 96h exposure to different concentrations of these substances show cellular effects on intracellular ROS formation, glutathione levels and redox status, expression of the antioxidant enzymes superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, gamma-glutamyl-cysteine synthetase (GCS) and thioredoxin, as well as cytotoxicity parameters. The most consistent effects (maximum values within brackets), observed in dose and time parameters for both model compounds and environmental sample, were the depletion of total glutathione (9.4% of control), induced levels of oxidized glutathione (695% of control), and gene expression regulation depicted relative to the control gene beta-actin of GCS mRNA (239% of control) and catalase (29% of control). In conclusion, the responses on several antioxidant defence system parameters demonstrated the validity of the in vitro toxicity testing system. Not only could multiple effects be detected at sub-lethal exposure concentrations, but these effects also gave valuable insight to the toxic mechanisms at the molecular level.

Chemical contaminants in aquafeeds and Atlantic salmon (Salmo salar) following the use of traditional- versus alternative feed ingredients

Marine feed ingredients, traditionally used in commercial fish feeds, are the source of these pollutants in farmed fish. The aim of the study was to assess the chemical contaminant load in Atlantic salmon (Salmo salar L.) raised on novel sustainable feeds based on a combination of alternative ingredients. Atlantic salmon were reared on feeds based on either traditional or alternative feed ingredients for an entire seawater production cycle up to approximately 4kg, which is a typical market-size for this species. The levels of several notorious contaminants were analysed in feed ingredients, feed, and skin-off fillets. These included persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs), dioxins and furans (PCDD/Fs), organochlorine pesticides (OCPs), and polybrominated diphenyl ethers (PBDEs), as well as elements such as arsenic, mercury, cadmium, lead, copper, zinc and fluorine. In addition, poly-aromatic hydrocarbons (PAHs) were analysed. The use of alternative feed ingredients reduced the fillet load of POPs by 51-82% and the level of arsenic and mercury by 80-96%. In contrast, the PAH levels in fish reared on the novel feeds were significantly (p<0.05) higher than the PAH concentrations in traditionally-raised fish. The present study shows that developments in feed formulation will reduce the load of most persistent organic pollutants in farmed salmon, but may increase concentrations of other contaminants such as PAHs, which are normally not associated with Atlantic salmon. The paper also compares the levels of contaminants in farmed Atlantic salmon expected in the future with those levels reported in the literature and currently on the market.

A study of metal concentrations and metallothionein binding capacity in liver, kidney and brain tissues of three Arctic seal species

Arctic seals are known to accumulate relatively high concentrations of potential toxic heavy metals in their vital organs, such as livers and kidneys, as well as in their central nervous system. We therefore decided to determine whether mercury, copper, cadmium and zinc levels in liver, kidney and brain tissues of three Arctic seal species were associated with the intracellular metal-binding protein metallothionein (MT) as a sign of toxic exposure. Samples from four ringed (Phoca hispida), five harp (P.groenlandica) and five hooded (Cystophora cristata) seals taken during field trips to Central West Greenland (Godhavn) and the Barents Sea in the spring of 1999 were used for the present study. In all three seal species concentrations of mercury, zinc and copper were highest in the liver, except for cadmium which was highest in the kidneys. Metal concentrations increased significantly in the order: ringed seal<harp seal<hooded seal for both kidney and liver tissues. MT concentrations were highest in the kidneys and the concentrations increased in the order: ringed seal<hooded seal<harp seal. MT metal-binding capacity was highest in the kidneys for all three species and increased in the same order: ringed seals (2-10%)<hooded seals (8-15%)<harp seals (27-63%). We therefore suggest that there are species-specific differences in the sub-cellular handling of heavy metals which indicate differences in sensitivity and health implications. However, a larger sample size is needed in order to test the relationship between metal concentrations and MT up-regulation in order to decide which metals are the most important and to elucidate whether the MT binding capacity is sufficient to protect tissues (i.e. kidney) from metal toxicosis. MT with its binding capacity could be a useful marker for environmental exposure to metals and their potential toxicity in the Arctic.

Accumulation and elimination kinetics of dietary endosulfan in Atlantic salmon (Salmo salar)

The carry-over of dietary endosulfan to the fillet of farmed Atlantic salmon was studied. The uptake and elimination rate constants of the alpha and beta isoform of endosulfan were determined in seawater adapted Atlantic salmon (initial weigh 173+/-25 g) fed on endosulfan enriched diets (724 and 315 microg kg(-1) for alpha- and beta-endosulfan, respectively) for 92 days, followed by a 56 days depuration period with feeding on control diets (<0.3 microg kg(-1) endosulfan). The accumulation of the toxic metabolite endosulfan sulphate, which was not detected (<0.5 microg kg(-1)) in the experimental feeds, was also determined. Dietary beta-endosulfan was more persistent than alpha-endosulfan as demonstrated by a higher uptake (41+/-8% vs. 21+/-2%) and lower elimination (26+/-2 x 10(-3) day(-1) vs. 40+/-1 x 10(-3) day(-1)) rate constants, and a higher biomagnification factor (0.10+/-0.026 vs. 0.05+/-0.003, p<0.05). Based on the decrease in diastereometric factor over time, biotransformation was estimated to account for at least 50% of the endosulfan elimination. The formation of the metabolite endosulfan sulphate comprised a maximum 1.2% of the total accumulation of endosulfan. Using a simple one-compartmental model and the experimentally-determined rate constants, it was predicted that only dietary concentration higher than 7.5 mg kg(-1) would cause the estimated maximum residue level (MRL) in fillet of 0.47 mg kg(-1) to be exceeded. Model estimations also predict that current EU maximum permitted levels in fish feeds (0.005 mg kg(-1)) would give fillet concentrations that are under the detection limit (0.3 microg kg(-1)), which is in agreement with the general absence of endosulfan in monitored farmed Atlantic salmon.