The herbicide linuron inhibits cholesterol biosynthesis and induces cellular stress responses in brown trout

Residual levels of dietary deltamethrin interfere with growth and intestinal health in Litopenaeus vannamei

To date, few study explored the damage of chronic dietary exposure to the lipophilic pesticide deltamethrin (DM) in aquatic animals, and it remains unclear whether its toxicity and residue levels would be affected by dietary lipid levels. Therefore, the present study aimed to elucidate the interactions between dietary lipid levels and DM levels in the Pacific white shrimp, focusing on growth performance, antioxidant capacity, and intestinal microbiota. DM has excellent insecticidal activity and has been used worldwide. Previous research has shown that environmental DM poses toxicity risks to aquatic animals. Six different diets were formulated to feed shrimp for 6 weeks with two lipid levels (6.96 %, 10.88 %) and three DM levels (0.2 mg·kg-1, 1 mg·kg-1, 5 mg·kg-1), namely LF0.2, LF1, LF5, HF0.2, HF1, HF5, respectively. Each diet was assigned to three net cages with a total of 18 cages (40 shrimp per tank, average weight (0.382±0.001 g), of which 0.2 mg·kg-1, are grouped in environmental DM control groups. The growth of shrimp was reduced as the dietary DM levels increased. When shrimp were fed a diet containing a high dose of DM, a reduction in their antioxidant capacity was also observed. Enzyme activity and gene expression related to lipid metabolism in hepatopancreas and hemolymph indicated a significant interaction between dietary lipid levels and DM in the lipid metabolism of shrimp. The terms of detoxification-related genes (gst, sult, cyp1a1) were upregulated in shrimp fed the high-dose DM. Additionally, the presence of DM in the diet severely harmed the hepatopancreas and intestinal histological morphology. DM in the diet increased the susceptibility of shrimp to pathogens and induced intestine microbiota dysbiosis, disrupting the balance of inter-species interactions. DM was not detected in the muscle and hepatopancreas of the shrimp after six weeks of exposure. In conclusion, the presence of DM in feed reduced the growth performance and antioxidant capacity of shrimp, damaging intestinal health. DM was rapidly metabolized by shrimp.

Toxicity of representative organophosphate, organochlorine, phenylurea, dinitroaniline, carbamate, and viologen pesticides to the growth and survival of H. vulgaris, L. minor, and C. elegans

Pesticides are commonly found in the environment and pose a risk to target and non-target species; therefore, employing a set of bioassays to rapidly assess the toxicity of these chemicals to diverse species is crucial. The toxicity of nine individual pesticides from organophosphate, organochlorine, phenylurea, dinitroaniline, carbamate, and viologen chemical classes and a mixture of all the compounds were tested in three bioassays (Hydra vulgaris, Lemna minor, and Caenorhabditis elegans) that represent plant, aquatic, and soil-dwelling species, respectively. Multiple endpoints related to growth and survival were measured for each model, and EC10 and EC50 values were derived for each endpoint to identify sensitivity patterns according to chemical classes and target organisms. L. minor had the lowest EC10 and EC50 values for seven and five of the individual pesticides, respectively. L. minor was also one to two orders of magnitude more sensitive to the mixture compared to H. vulgaris and C. elegans, where EC50 values were calculated to be 0.00042, 0.0014, and 0.038 mM, respectively. H. vulgaris was the most sensitive species to the remaining individual pesticides, and C. elegans consistently ranked the least sensitive to all tested compounds. When comparing the EC50 values across all pesticides, the endpoints of L. minor were correlated with each other while the endpoints measured in H. vulgaris and C. elegans were clustered together. While there was no apparent relationship between the chemical class of pesticide and toxicity, the compounds were more closely clustered based on target organisms (herbicide vs insecticide). The results of this study demonstrate that the combination of these plant, soil, and aquatic specie can serve as representative indicators of pesticide pollution in environmental samples.

Tissue-specific toxic effects of nano-copper on zebrafish

Understanding the behavior and potential toxicity of copper nanoparticles (nano-Cu) in the aquatic environment is a primary way to assess their environmental risks. In this study, RNA-seq was performed on three different tissues (gills, intestines, and muscles) of zebrafish exposed to nano-Cu, to explore the potential toxic mechanism of nano-Cu on zebrafish. The results indicated that the toxic mechanism of nano-Cu on zebrafish was tissue-specific. Nano-Cu enables the CB1 receptor of the presynaptic membrane of gill cells to affect short-term synaptic plasticity or long-term synaptic changes (ECB-LTD) through DSI and DSE, causing dysfunction of intercellular signal transmission. Imbalance of de novo synthesis of UMP in intestinal cells and its transformation to UDP, UTP, uridine, and uracil, resulted in many functions involved in the pyrimidine metabolic pathway being blocked. Meanwhile, the toxicity of nano-Cu caused abnormal expression of RAD51 gene in muscle cells, which affects the repair of damaged DNA through Fanconi anemia and homologous recombination pathway, thus causing cell cycle disorder. These results provide insights for us to better understand the differences in toxicity of nano-Cu on zebrafish tissues and are helpful for a comprehensive assessment of nano-Cu's effects on aquatic organisms.

Non-covalent interaction, adsorption characteristics and solvent effect of procainamide anti-arrhythmias drug on silver and gold loaded silica surfaces: SERS spectroscopy, density functional theory and molecular docking investigations†

First-principle calculations were systematically carried out to explore the structural and electronic properties of the non-covalent interaction of procainamide (PA) anti-arrhythmias drug molecules on silver-loaded and gold-loaded silica nanostructures. Computed adsorption energies presented a higher affinity of PA towards the Ag–SiO₂ as compared with Au–SiO₂ surfaces. The non-covalent interaction analysis revealed a weak van der Waals type of forces and hydrogen bonding, associated with a noticeable repulsive steric interaction. It was conceived that silver and gold decorated silica can be used for drug administration in biological systems due to the fact that their frontier molecular orbital energy levels were considerably altered upon absorption, decreasing the pertinent energy gaps. Moreover, the electronic spectra of PA⋯Ag–SiO₂ and PA⋯Au–SiO₂ structures investigated in different solvents display a notable blue shift, suggesting that noble metal-loaded silica can be effective in the context of drug delivery systems. Therefore, silver- and gold-decorated silica of three possible drug adsorption scenarios was fully analyzed to realize the associated bioactivity and drug likeness. Theoretical findings suggest that Ag- and Au–SiO₂ nanocomposites can be considered potential drug delivery platforms for procainamide in medication protocols.

The structural and electronic properties of the non-covalent interaction of procainamide (PA) anti-arrhythmias drug molecules on silver-loaded and gold-loaded silica nanostructures were explored using first-principle calculations.

Exposure to the pesticides linuron, dimethomorph and imazalil alters steroid hormone profiles and gene expression in developing rat ovaries

Inhibition of androgen signaling during critical stages of ovary development can disrupt folliculogenesis with potential consequences for reproductive function later in life. Many environmental chemicals can inhibit the androgen signaling pathway, which raises the question if developmental exposure to anti-androgenic chemicals can negatively impact female fertility. Here, we report on altered reproductive hormone profiles in prepubertal female rats following developmental exposure to three pesticides with anti-androgenic potential: linuron (25 and 50 mg/kg bw/d), dimethomorph (60 and 180 mg/kg bw/d) and imazalil (8 and 24 mg/kg bw/d). Dams were orally exposed from gestational day 7 (dimethomorph and imazalil) or 13 (linuron) until birth, then until end of dosing at early postnatal life. Linuron and dimethomorph induced dose-related reductions to plasma corticosterone levels, whereas imazalil mainly suppressed gonadotropin levels. In the ovaries, expression levels of target genes were affected by linuron and dimethomorph, suggesting impaired follicle growth. Based on our results, we propose that anti-androgenic chemicals can negatively impact female reproductive development. This highlights a need to integrate data from all levels of the hypothalamic-pituitary-gonadal axis, as well as the hypothalamic-pituitary-adrenal axis, when investigating the potential impact of endocrine disruptors on female reproductive development and function.

Conformational analysis and concentration detection of linuron: Spectroscopic NMR and SERS study

Linuron is a commonly used organic herbicide which is used in plant growth control. Due to its potential health concerns, the characterization and monitoring of linuron have been a subject of several studies. In this work, we employed nuclear magnetic resonance (NMR) and Raman spectroscopic techniques supported with the density functional theory (DFT) to investigate the conformational behavior and electronic aspects of linuron. The selective nuclear Overhauser effect (SelNOE) spectra confirmed that linuron exists predominantly in the anti configuration and is facilitated with a weak intramolecular hydrogen bonding between the acidic amide proton and oxygen of methoxy moiety. Quantum chemical results showed that the corresponding syn form of the molecule is 8.5 kcal/mol less stable. Further, the surface enhanced Raman scattering (SERS) technique using gold nanoparticles (AuNPs) was implemented as a potential spectroscopic protocol for the concentration monitoring of trace linuron. The Raman responses of four vibrational modes, namely CC stretching, CN stretching, N-H rocking and ring deformation, were successfully enhanced with an excellent linear concentration-intensity dependency. The aromatic CC stretching vibration at 1595 cm^-1 in the Raman spectra has demonstrated the highest enhancement factor (6.5 × 10⁴) and the lowest limit of detection (10^-7 M). The interaction of linuron with the gold nanocluster was simulated by establishing a simple DFT model which predicted that the most pronounced binding with the gold atom takes place at the benzene ring.

The Impact of Cultivation Management and Weed Control Systems of Very Early Potato on Weed Infestation, Biodiversity, and Health Safety of Tubers

The aim of the research was to determine the impact of potato cultivation management and weeding systems on weed infestation and to evaluate the possibility of using biomarkers to assess consumer exposure to herbicide residues in potato tubers. The experiment was carried out in 2016–2018 in Central-Eastern Poland. The subject of research was the very early variety Lord. The experiment was established using the randomized block method in a split-plot design. The first order factor was cultivation management: (A) traditional and (B) under polyethylene sheeting (PE-sheeting) put “on flat”. The second-order factors were weed control systems: (a) mechanical (b) to (d)-chemical. The study determined the degree of damage to crops and weeds, fresh and dry weight of weeds, their number and floristic composition, and herbicide residues in tubers and in the soil. The fresh and dry mass of weeds was most effectively limited by mechanical and chemical treatment with the use of a preparation containing linuron. Managing potato cultivation with PE-sheeting and soil herbicides has proven to be safe for very early potato production. Used for pre-emergence care, the preparation containing linuron did not leave even trace amounts of this active substance in the tubers. The determined amount of the active substance fluorochloridon and clomazone was lower than the Maximum Residue Level (MRL) norm in the EU (European Union). As a result, the adopted, innovative management and weeding control systems in the cultivation of early potato varieties can be considered safe for the consumer.

An Experimental Approach to Study the Effects of Realistic Environmental Mixture of Linuron and Propamocarb on Zebrafish Synaptogenesis

The reasons behind the extensive use of pesticides include the need to destroy vector organisms and promote agricultural production in order to sustain population growth. Exposure to pesticides is principally occupational, even if their persistence in soil, surface water and food brings the risk closer to the general population, hence the demand for risk assessment, since these compounds exist not only as individual chemicals but also in form of mixtures. In light of this, zebrafish represents a suitable model for the evaluation of toxicological effects. Here, zebrafish embryos were exposed for 96 h post fertilization (hpf) to sublethal concentrations (350 µg/L) of linuron and propamocarb, used separately and then combined in a single solution. We investigated the effects on morphological traits and the expression of genes known to be implicated in synaptogenesis (neurexin1a and neuroligin3b). We observed alterations in some phenotypic parameters, such as head width and interocular distance, that showed a significant reduction (p < 0.05) for the mixture treatment. After individual exposure, the analysis of gene expression showed an imbalance at the synaptic level, which was partially recovered by the simultaneous administration of linuron and propamocarb. This preliminary study demonstrates that the combined substances were responsible for some unpredictable effects, diverging from the effect observed after single exposure. Thus, it is clear that risk assessment should be performed not only on single pesticides but also on their mixtures, the toxicological dynamics of which can be totally unpredictable.

In silico and in vitro assessment of androgen receptor antagonists

There is a growing concern for male reproductive health as studies suggest that there is a sharp increase in prostate cancer and other fertility related problems. Apart from lifestyle, pollutants are also known to negatively affect the reproductive system. In addition to many other compounds that have been shown to alter androgen signaling, several environmental pollutants are known to disrupt androgen signaling via binding to androgen receptor (AR) or indirectly affecting the androgen synthesis. We analyzed here the molecular mechanism of the interaction between the human AR Ligand Binding Domain (hAR-LBD) and two environmental pollutants, linuron (a herbicide) and procymidone (a pesticide), and compared with the steroid agonist dihydrotestosterone (DHT) and well-known hAR antagonists bicalutamide and enzalutamide. Using molecular docking and dynamics simulations, we showed that the co-activator interaction site of the hAR-LBD is disrupted in different ways by different ligands. Binding free energies of the ligands were also ordered in increasing order as follows: linuron, procymidone, DHT, bicalutamide, and enzalutamide. These data were confirmed by in vitro assays. Reporter assay with MDA-kb2 cells showed that linuron, procymidone, bicalutamide and enzalutamide can inhibit androgen mediated activation of luciferase activity. Gene expression analysis further showed that these compounds can inhibit the expression of prostate specific antigen (PSA) and microseminoprotein beta (MSMB) in prostate cell line LNCaP. Comparative analysis showed that procymidone is more potent than linuron in inhibiting AR activity. Furthermore, procymidone at 10 μM dose showed equivalent and higher activity to AR inhibitor enzalutamide and bicalutamide respectively.

Environmental Risk of Pesticides for Fish in Small- and Medium-Sized Streams of Switzerland

This study assessed the acute and chronic risk of pesticides, singly and as mixtures, for fish using comprehensive chemical data of four monitoring studies conducted in small- and medium-sized streams of Switzerland between 2012 and 2018. Pesticides were ranked based on single substance risk quotients and relative contribution to mixture risk. Concentrations of the pyrethroid insecticides, λ-cyhalothrin, cypermethrin and deltamethrin, and the fungicides, carbendazim and fenpropimorph, posed acute or chronic single substance risks. Risk quotients of eighteen additional pesticides were equal or greater than 0.1, and thirteen of those contributed ≥30% to mixture risk. Relatively few substances dominated the mixture risk in most water samples, with chronic and acute maximum cumulative ratios never exceeding 5 and 7, respectively. A literature review of toxicity data showed that concentrations of several pesticides detected in Swiss streams were sufficient to cause direct sublethal effects on fish in laboratory studies. Based on the results of our study, we conclude that pesticides detected in Swiss streams, especially pyrethroid insecticides, fungicides and pesticide mixtures, pose a risk to fish health and can cause direct sublethal effects at environmental concentrations. Sensitive life stages of species with highly specialized life history traits may be particularly vulnerable; however, the lack of toxicity data for non-model species currently prevents a conclusive assessment across species.

Assessment of oxidative DNA damage, oxidative stress responses and histopathological alterations in gill and liver tissues of Oncorhynchus mykiss treated with linuron

We investigated changes in 8-hydroxy-2-deoxyguanosine (8-OHdG) activity which is a product of oxidative DNA damage, histopathological changes and antioxidant responses in liver and gill tissues of rainbow trout, following a 21-day exposure to three different concentrations of linuron (30 µg/L, 120 µg/L and 240 µg/L). Our results indicated that linuron concentrations caused an increase in LPO levels of liver and gill tissues (p < 0.05). While linuron induced both increases and decreases in GSH levels and SOD activity, CAT activity was decreased by all concentrations of linuron (p < 0.05). The immunopositivity of 8-OHdG was detected in the hepatocytes of liver and in the epithelial and chloride cells of the secondary lamellae of the gill tissues. Our results suggested that linuron could cause oxidative DNA damage by causing an increase in 8-OHdG activity in tissues, and it induces histopathological damage and alterations in the antioxidant parameters of the tissues.

α-lipoic acid protects testis and epididymis against linuron-induced oxidative toxicity in adult rats

Linuron is well known for its antiandrogenic property. However, the effects of linuron on testicular and epididymal pro- and antioxidant status are not well defined. On the other hand, α-lipoic acid is well known as universal antioxidant. Therefore, the purpose of this study was twofold: firstly to investigate whether linuron exposure alters antioxidant status in the testis and epididymis of rats and if so, whether the supplementation of α-lipoic acid mitigates linuron-induced oxidative toxicity in rats. To address this question, α-lipoic acid at a dose of 70 mg/Kg body weight (three times a week) was administered to linuron exposed rats (10 or 50 mg/Kg body weight, every alternate day over a period of 60 days), and the selected reproductive endpoints were analyzed after 60 days. Respective controls were maintained in parallel. Linuron at selected doses reduced testicular daily sperm count, and epididymal sperm count, sperm motility, sperm viability, and number of tail coiled sperm, reduced activity levels of 3β- and 17β-hydroxysteroid dehydrogenases, decreased expression levels of StAR mRNA, inhibition of testosterone levels, and elevated levels of testicular cholesterol in rats over controls. Linuron intoxication deteriorated the structural integrity of testis and epididymis associated with reduced the reproductive performance over controls. Conversely, α-lipoic acid supplementation enhanced sperm quality and improved the testosterone synthesis pathway in linuron exposed rats over its respective control. Administration of α-lipoic acid restored inhibition of testicular and epididymal enzymatic (superoxide dismutase, catalase, glutathione reductase, glutathione peroxidise) and non-enzymatic (glutathione content), increased lipid peroxidation and protein carbonyl content produced by linuron in rats. α-lipoic acid supplementation inhibited the expression levels of testicular caspase-3 mRNA levels and also its activity in linuron treated rats. To summate, α-lipoic acid-induced protection of reproductive health in linuron treated rats could be attributed to its antioxidant, and steroidogenic properties.

Hypoxia modifies the response to flutamide and linuron in male three-spined stickleback (Gasterosteus aculeatus)

Hypoxia is a major stressor in aquatic environments and it is frequently linked with excess nutrients resulting from sewage effluent discharges and agricultural runoff, which often also contain complex mixtures of chemicals. Despite this, interactions between hypoxia and chemical toxicity are poorly understood. We exposed male three-spined stickleback during the onset of sexual maturation to a model anti-androgen (flutamide; 250 μg/L) and a pesticide with anti-androgenic activity (linuron; 250 μg/L), under either 97% or 56% air saturation (AS). We assessed the effects of each chemical, alone and in combination with reduced oxygen concentration, by measuring the transcription of spiggin in the kidney, as a marker of androgen signalling, and 11 genes in the liver involved in some of the molecular pathways hypothesised to be affected by the exposures. Spiggin transcription was strongly inhibited by flutamide under both AS conditions. In contrast, for linuron, a strong inhibition of spiggin was observed under 97% AS, but this effect was supressed under reduced air saturation, likely due to interactions between the hypoxia inducible factor and the aryl hydrocarbon receptor (AhR) pathways. In the liver, hypoxia inducible factor 1α was induced following exposure to both flutamide and linuron, however this was independent of the level of air saturation. This work illustrates the potential for interactions between hypoxia and pollutants with endocrine or AhR agonist activity to occur, with implications for risk assessment and management.

Sub-lethal toxicity assessment of the phenylurea herbicide linuron in developing zebrafish (Danio rerio) embryo/larvae

Due to run-off and rain events, agrochemicals can enter water catchments, exerting endocrine disruption effects and toxicity to aquatic organisms. Linuron is a phenylurea herbicide used to control a wide variety of vegetative weeds in agriculture in addition to residential applications. However, there are few studies that quantify its toxicity to early developmental stages of fish. The objectives of this study were to assess the acute toxicity of linuron to zebrafish embryos/larvae by measuring mortality, morphological deformities, oxidative respiration, gene expression, and locomotor activity via the Visual Motor Response test. Zebrafish embryos at ~6-h post-fertilization (hpf) were exposed to either embryo rearing medium (ERM), or one dose of 0.625, 1.25, 2.5, 5, and 10 μM linuron for up to 7 days post-fertilization (dpf) depending on the assay. Zebrafish larvae exposed to linuron displayed pericardial edema, yolk sac edema, and spinal curvature. Oxidative respiration assessments in embryos using the Agilent XF^e24 Flux Analyzer revealed that linuron decreased mean basal respiration and oligomycin-induced ATP-linked respiration in 30 hpf embryos at 20 μM after a 24-hour exposure. In 7 dpf larvae, transcript abundance was determined for 6 transcripts that have a role in oxidative respiration (atp06, cox1, cox4-1, cox5a1, cytb, and nd1); the relative abundance of these transcripts was not altered with linuron treatment. A Visual Motor Response test was conducted on 7 dpf larvae to determine whether linuron (0.625 to 5 μM) impaired locomotor activity. Larval activity in the dark period decreased in a dose dependent manner and there were indications of hypoactivity as low as 1.25 μM. Transcript abundance was thus determined for tyrosine hydroxylase (th1) and glutamic acid decarboxylase 67 (gad1b), two rate limiting enzymes that control the production of dopamine and gamma-aminobutyric acid respectively. The mRNA levels of gad1b (p = 0.019) were reduced with increasing concentrations of linuron while th1 (p = 0.056) showed a similar decreasing trend, suggesting that neurotransmitter biosynthesis may be altered with exposure to linuron. This study improves knowledge related to the toxicity mechanisms for linuron and is the first to demonstrate that this anti-androgenic chemical impairs oxidative respiration and exerts neurotoxic effects associated with neurotransmitter biosynthesis during early development. These data are significant for environmental risk assessment of agrochemicals.

Assessing the impact of wastewater treatment plant effluent on downstream drinking water-source quality using a zebrafish (Danio Rerio) liver cell-based metabolomics approach

Cell-based metabolomics was used in a proof-of-concept fashion to investigate the biological effects of contaminants as they traveled from a wastewater treatment plant (WWTP) discharge to a drinking water treatment plant (DWTP) intake in a surface-water usage cycle. Zebrafish liver (ZFL) cells were exposed to water samples collected along a surface-water flowpath, where a WWTP was located ∼14.5 km upstream of a DWTP. The sampling sites included: 1) upstream of the WWTP, 2) the WWTP effluent discharging point, 3) a proximal location downstream of the WWTP outfall, 4) a distal location downstream of the WWTP outfall, 5) the drinking water intake, and 6) the treated drinking water collected prior to discharge to the distribution system. After a 48-h laboratory exposure, the hydrophilic and lipophilic metabolites in ZFL cell extracts were analyzed by proton nuclear magnetic resonance (¹H NMR) spectroscopy and gas chromatography-mass spectrometry (GC-MS), respectively. Multivariate statistical analysis revealed distinct changes in metabolite profiles in response to WWTP effluent exposure. These effects on the hydrophilic metabolome gradually diminished downstream of the WWTP, becoming non-significant at the drinking water intake (comparable to upstream of the WWTP, p = 0.98). However, effects on the lipophilic metabolome increased significantly as the river flowed from the distal location downstream of the WWTP to the drinking water intake (p < 0.001), suggesting a source of bioactive compounds in this watershed other than the WWTP. ZFL cells exposed to treated drinking water did not exhibit significant changes in either the hydrophilic (p = 0.15) or lipophilic metabolome (p = 0.83) compared to the upstream site, suggesting that constituents in the WWTP effluent were efficiently removed by the drinking water treatment process. Impacts on ZFL cells from the WWTP effluent included disrupted energy metabolism, a global decrease in amino acids, and altered lipid metabolism pathways. Overall, this study demonstrated the utility of cell-based metabolomics as an effective tool for assessing the biological effects of complex pollutant mixtures, particularly when used as a complement to conventional chemical monitoring.

Metabolite profiles of striped marsh frog (Limnodynastes peronii) larvae exposed to the anti-androgenic fungicides vinclozolin and propiconazole are consistent with altered steroidogenesis and oxidative stress

Amphibians use wetlands in urban and agricultural landscapes for breeding, growth and development. Fungicides and other pesticides used in these areas have therefore been identified as potential threats that could contribute towards amphibian population declines. However, relatively little is known about how such chemicals influence sensitive early life-stages or how short episodic exposures influence sub-lethal physiological and metabolic pathways. The present study applied untargeted metabolomics to evaluate effects in early post-hatch amphibian larvae exposed to the anti-androgenic fungicides vinclozolin and propiconazole. Recently hatched (Gosner developmental stage 25) striped marsh frog (Limnodynastes peronii) larvae were exposed for 96 h to vinclozolin at 17.5, 174.8 and 1748.6 nM and propiconazole at 5.8, 58.4 and 584.4 nM. Nuclear Magnetic Resonance (NMR) spectroscopy was performed on polar metabolites obtained from whole-body extracts. Both fungicides altered metabolite profiles compared to control animals at all concentrations tested, and there were notable differences between the two chemicals. Overall responses were consistent with altered steroidogenesis and/or cholesterol metabolism, with inconsistent responses between the two fungicides likely reflecting minor differences in the mechanisms of action of these chemicals. Broad down-regulation of the tricarboxylic acid (TCA) cycle was also observed and is indicative of oxidative stress. Interestingly, formic acid was significantly increased in larvae exposed to vinclozolin but not propiconazole, suggesting this metabolite may serve as a useful biomarker of exposure to androgen-receptor binding anti-androgenic contaminants. This study demonstrates the power of untargeted metabolomics for distinguishing between similarly acting, but distinct, pollutants and for unraveling non-endocrine responses resulting from exposure to known endocrine active contaminants.

QSAR prediction of additive and non-additive mixture toxicities of antibiotics and pesticide

Antibiotics and pesticides may exist as a mixture in real environment. The combined effect of mixture can either be additive or non-additive (synergism and antagonism). However, no effective predictive approach exists on predicting the synergistic and antagonistic toxicities of mixtures. In this study, we developed a quantitative structure-activity relationship (QSAR) model for the toxicities (half effect concentration, EC₅₀) of 45 binary and multi-component mixtures composed of two antibiotics and four pesticides. The acute toxicities of single compound and mixtures toward Aliivibrio fischeri were tested. A genetic algorithm was used to obtain the optimized model with three theoretical descriptors. Various internal and external validation techniques indicated that the coefficient of determination of 0.9366 and root mean square error of 0.1345 for the QSAR model predicted that 45 mixture toxicities presented additive, synergistic, and antagonistic effects. Compared with the traditional concentration additive and independent action models, the QSAR model exhibited an advantage in predicting mixture toxicity. Thus, the presented approach may be able to fill the gaps in predicting non-additive toxicities of binary and multi-component mixtures.

Effects of the herbicides linuron and S-metolachlor on Perez's frog embryos

Presence of pesticides in the environment and their possible effects on aquatic organisms are of great concern worldwide. The extensive use of herbicides in agricultural areas are one of the factors contributing to the known decline of amphibian populations. Thus, as non-target species, amphibians can be exposed in early life stages to herbicides in aquatic systems. In this context, this study aims to evaluate effects of increasing concentrations of two maize herbicides, linuron and S-metolachlor on embryos of the Perez' frog (Pelophylax perezi) during 192 h. Apical endpoints were determined for each herbicide: mortality, hatching rate, malformations and length. Frog embryos presented a LC₅₀ of 21 mg/l linuron and 37.5 mg/l S-metolachlor. Furthermore, sub-lethal concentrations of both herbicides affected normal embryonic development, delaying hatching, decreasing larvae length and causing several malformations. Length of larvae decreased with increasing concentrations of each herbicide, even at the lower concentrations tested. Malformations observed in larvae exposed to both herbicides were oedemas, spinal curvature and deformation, blistering and microphtalmia. Overall, these results highlight the need to assess adverse effects of xenobiotics to early life stages of amphibians regarding beside mortality the embryonic development, which could result in impairments at later stages. However, to unravel mechanisms involved in toxicity of these herbicides further studies regarding lower levels of biological organisation such as biochemical and genomic level should be performed.

Multiresidue determination and potential risks of emerging pesticides in aquatic products from Northeast China by LC-MS/MS

A simple method for determining 33 pesticides with a wide polarity range (logK_ow 0.6-4.5) in aquatic products was developed based on LC-MS/MS. The target analytes included three types of widely used pesticides: insecticides, fungicides and herbicides. Based on the optimization of ultrasonic assisted extraction and GPC clean-up procedures, the matrix effect, extraction recoveries and LOD were improved distinctively. LOQ of this method was below 0.5ng/g for all pesticides, which is superior to values in the literature, and the matrix effect was reduced effectively (-14.7% to 7.5%). The method was successfully applied to investigate the pesticide residue levels of twenty-five samples including seven common kinds of fishes from Northeast China. The results showed that all targeted pesticides were present in the fish samples; however, their levels were low, except for atrazine, linuron, ethoprophos, tetrachlorvinphos, acetochlor and fenthion. Atrazine and linuron caught our attention because the concentrations of atrazine in fish samples from Liaoning province were in the range of 0.5-8ng/g (w/w) with mean concentration of 2.3ng/g, which were far above those of other pesticides. The levels of linuron were in the range of 0.6-6ng/g (mean concentration 2.8ng/g), which were the highest among all targeted pesticides in the Inner Mongolia. This is the first systematic investigation on the characteristics and levels of these pesticides in aquatic products from northeast China. Considering their toxicity and bioaccumulation, the potential risk of atrazine and linuron from consuming aquatic products should be paid more attention.

Endocrine and physiological effects of linuron and S-metolachlor in zebrafish developing embryos

Evaluation of the effects of linuron and S-metolachlor on apical, biochemical and transcriptional endpoints in zebrafish (Danio rerio) early life stages was the main purpose of this work. Embryos were exposed for 96h to a range of concentrations of each herbicide to determine lethal and sub-lethal effects on apical (e.g. malformations, hatching) and biochemical parameters (cholinesterase, ChE; catalase, CAT; glutathione S-transferase, GST; lipid peroxidation, LPO and lactate dehydrogenase, LDH). To evaluate endocrine disruption effects, embryos were exposed during 96h to 0.88mg/L linuron and 9.66mg/L S-metolachlor, isolated or in binary mixture. Expression of a suite of genes involved in HPT, HPG and HPA-axis was then assessed. Highest concentration of linuron (5.0mg/L) decreased hatching rate to 5% and 70.0mg/L S-metolachlor completely inhibited hatching, about 100%. Both herbicides impaired development by inducing several malformations (100% in 5.0mg/L linuron and 70.0mg/L S-metolachlor). Linuron only affected GST and CAT at concentrations of 0.25 and 0.0025mg/L, respectively. S-metolachlor induced GST (to 256%), inhibited ChE (to 61%) and LDH (to 60%) and reduced LPO levels (to 63%). Linuron isolated treatment seems to have an estrogenic mode of action due to the observed induction of vtg1. Exposure to S-metolachlor seems to interfere with steroidogenesis and with HPT and HPA-axis, since it has inhibited cyp19a2, TSHβ and CRH gene expression. In addition to vtg1 induction and CRH inhibition, herbicide combination also induced sox9b that has a role in regulation of sexual development in zebrafish. This study pointed out adverse effects of linuron and S-metolachlor, namely impairment of neurotransmission and energy production, induction of steroidogenesis, and interference with HPT and HPA-axis. These results contributed to elucidate modes of action of linuron and S-metolachlor in zebrafish embryo model. Furthermore, gene expression patterns obtained are indicative of endocrine disruption action of these herbicides.

Biological responses to phenylurea herbicides in fish and amphibians: New directions for characterizing mechanisms of toxicity

Urea-based herbicides are applied in agriculture to control broadleaf and grassy weeds, acting to either inhibit photosynthesis at photosystem II (phenylureas) or to inhibit acetolactate synthase acetohydroxyacid synthase (sulfonylureas). While there are different chemical formulas for urea-based herbicides, the phenylureas are a widely used class in North America and have been detected in aquatic environments due to agricultural run-off. Here, we summarize the current state of the literature, synthesizing data on phenylureas and their biological effects in two non-target animals, fish and amphibians, with a primary focus on diuron and linuron. In fish, although the acutely lethal effects of diuron in early life stages appear to be >1mg/L, recent studies measuring sub-lethal behavioural and developmental endpoints suggest that diuron causes adverse effects at lower concentrations (i.e. <0.1mg/L). Considerably less toxicity data exist for amphibians, and this is a knowledge gap in the literature. In terms of sub-lethal effects and mode of action (MOA), linuron is well documented to have anti-androgenic effects in vertebrates, including fish. However, there are other MOAs that are not adequately assessed in toxicology studies. In order to identify additional potential MOAs, we conducted in silico analyses for linuron and diuron that were based upon transcriptome studies and chemical structure-function relationships (i.e. ToxCast™, Prediction of Activity Spectra of Substances). Based upon these analyses, we suggest that steroid biosynthesis, cholesterol metabolism and pregnane X receptor activation are common targets, and offer some new endpoints for future investigations of phenylurea herbicides in non-target animals.

A glyphosate-based herbicide induces histomorphological and protein expression changes in the liver of the female guppy Poecilia reticulata

Glyphosate-based herbicides (GBH) are among the most common herbicides found in aquatic systems, but limited data are available about their mode of action and hepatotoxicity in fish. This study investigated the hepatotoxicity induced by GBH in the guppy Poecilia reticulata using a histopathological assessment associated with a proteomic approach. Guppies were exposed to GBH for 24 h at 1.8 mg of glyphosate L-1, corresponding to 50% of the LC50, 96 h. The results indicate that the GBH at 1.8 mg of glyphosate L-1 induce the development of hepatic damage in P. reticulata, which is exposure-time dependent. The histopathological indexes demonstrate that GBH cause inflammatory, regressive, vascular and progressive disorders in the liver of guppies. Using 2D gel electrophoresis associated with mass spectrometry, 18 proteins that changed by GBH were identified and were related to the cellular structure, motility and transport, energy metabolism and apoptosis. The results show that the acute exposure to GBH causes hepatic histopathological damage related to protein expression profile changes in P. reticulata, indicating that a histopathological assessment associated with a proteomic analysis provides a valuable approach to assess the toxic effects of GBH in sentinel fish species.

Evaluation of 8-hydroxy-2-deoxyguanosine and NFkB activation, oxidative stress response, acetylcholinesterase activity, and histopathological changes in rainbow trout brain exposed to linuron

Linuron is a widely used herbicide to control grasses and annual broad leaf weeds. It is known that linuron has toxic effects on different organisms. However, the toxic effects of linuron on aquatic organisms, especially fish, is completely unknown. Thus, we aimed to investigate changes in 8-hydroxy-2-deoxyguanosine (8-OHdG) and nuclear factor kappa B (NFkB) activity, histopathological changes, antioxidant responses and acetylcholinesterase (AChE) activity in rainbow trout brain after exposure to linuron. Fish were exposed to 30μg/L, 120μg/L and 240μg/L concentrations of linuron for twenty-one days. Brain tissues were taken from fish for 8-OHdG and NFkB activity, histopathological examination and determination of superoxide dismutase (SOD), catalase (CAT) enzyme activity, lipid peroxidation (LPO), and reduced glutathione (GSH) levels. Our data indicated that high linuron concentrations caused a decrease in GSH levels, SOD and CAT activities in brain tissues (p<0.05). LPO levels were significantly increased by 240μg/L linuron. All concentrations caused a significant inhibition in brain AChE enzyme activity (p<0.05). Immunopositivity was detected for 8-OHdG and NFkB, and linuron exposure caused histopathological damage to the brain tissues. The results of this study can provide useful information for understanding of linuron-induced toxicity.

Prometryn and humic acid induce Cytochrome P450 1A expression in Danio rerio (zebrafish)

Humic acid (HA) is a major component of dissolved organic matter, is ubiquitous in the aquatic environment and influences the biological toxicity of organic pollutants. In this study, we investigated the cytochrome P450 1A (CYP 1A) mRNA expression and ethoxyresorufin-O-deethylase (EROD) activity in the gills and liver of zebrafish following exposure to the s-triazine herbicide prometryn with or without HA present. Prometryn induced both CYP 1A mRNA expression and EROD activity. The CYP 1A mRNA expression of zebrafish that were exposed to a combination of prometryn and HA was increased compared to those exposed to prometryn alone. A likely cause for CYP 1A induction is the impact of special components of HA, functioning as aryl hydrocarbon receptor (AHR) agonists. In combination with HA, these increase prometryn levels in tissues. Similar results for EROD activity were evident. In our time course study, CYP 1A mRNA expression reached maximum values during 24h. This revealed CYP 1A mRNA transcription as a comparatively sensitive toxicity index. In a recovery experiment, we found a faster decrease of CYP 1A mRNA expression to control levels (CK) in gills compared to liver tissue. Following exposure to HA, CYP 1A mRNA expression in liver tissue displayed a faster decrease to CK levels. HA induced enhanced metabolic rates for prometryn. In contrast, recovery regularity of CYP 1A expression in gills was independent of the presence of HA. This result indicates different detoxification mechanisms for HA in liver and gills.

Screening for potential endocrine disruptors in fish: evidence from structural alerts and in vitro and in vivo toxicological assays

BACKGROUND

The European chemicals' legislation REACH aims to protect man and the environment from substances of very high concern (SVHC). Chemicals like endocrine disruptors (EDs) may be subject to authorization. Identification of (potential) EDs with regard to the environment is limited because specific experimental assessments are not standard requirements under REACH. Evidence is based on a combination of in vitro and in vivo experiments (if available), expert judgement, and structural analogy with known EDs.

OBJECTIVES

The objectives of this study are to review and refine structural alerts for the indication of potential estrogenic and androgenic endocrine activities based on in vitro studies; to analyze in vivo mammalian long-term reproduction studies with regard to estrogen- and androgen-sensitive endpoints in order to identify potential indicators for endocrine activity with regard to the environment; to assess the consistency of potential estrogenic and androgenic endocrine activities based on in vitro assays and in vivo mammalian long-term reproduction studies and fish life-cycle tests; and to evaluate structural alerts, in vitro assays, and in vivo mammalian long-term reproduction studies for the indication of potential estrogenic and androgenic endocrine disruptors in fish.

RESULTS

Screening for potential endocrine activities in fish via estrogenic and androgenic modes of action based on structural alerts provides similar information as in vitro receptor-mediated assays. Additional evidence can be obtained from in vivo mammalian long-term reproduction studies. Conclusive confirmation is possible with fish life-cycle tests. Application of structural alerts to the more than 33,000 discrete organic compounds of the EINECS inventory indicated 3585 chemicals (approx. 11%) as potential candidates for estrogenic and androgenic effects that should be further investigated. Endocrine activities of the remaining substances cannot be excluded; however, because the structural alerts perform much better for substances with (very) high estrogenic and androgenic activities, there is reasonable probability that the most hazardous candidates have been identified.

CONCLUSIONS

The combination of structural alerts, in vitro receptor-based assays, and in vivo mammalian studies may support the priority setting for further assessments of chemicals with potential environmental hazards due to estrogenic and androgenic activities.

Identification of conserved hepatic transcriptomic responses to 17β-estradiol using high-throughput sequencing in brown trout

Estrogenic chemicals are major contaminants of surface waters and can threaten the sustainability of natural fish populations. Characterization of the global molecular mechanisms of toxicity of environmental contaminants has been conducted primarily in model species rather than species with limited existing transcriptomic or genomic sequence information. We aimed to investigate the global mechanisms of toxicity of an endocrine disrupting chemical of environmental concern [17β-estradiol (E2)] using high-throughput RNA sequencing (RNA-Seq) in an environmentally relevant species, brown trout (Salmo trutta). We exposed mature males to measured concentrations of 1.94, 18.06, and 34.38 ng E2/l for 4 days and sequenced three individual liver samples per treatment using an Illumina HiSeq 2500 platform. Exposure to 34.4 ng E2/L resulted in 2,113 differentially regulated transcripts (FDR < 0.05). Functional analysis revealed upregulation of processes associated with vitellogenesis, including lipid metabolism, cellular proliferation, and ribosome biogenesis, together with a downregulation of carbohydrate metabolism. Using real-time quantitative PCR, we validated the expression of eight target genes and identified significant differences in the regulation of several known estrogen-responsive transcripts in fish exposed to the lower treatment concentrations (including esr1 and zp2.5). We successfully used RNA-Seq to identify highly conserved responses to estrogen and also identified some estrogen-responsive transcripts that have been less well characterized, including nots and tgm2l. These results demonstrate the potential application of RNA-Seq as a valuable tool for assessing mechanistic effects of pollutants in ecologically relevant species for which little genomic information is available.