Impact of chronic exposure of rainbow trout, Oncorhynchus mykiss, to low doses of glyphosate or glyphosate-based herbicides

Glyphosate and aminomethylphosphonic acid impact on redox status and biotransformation in fish and the mitigating effects of diet supplementation

Fish reared under seminatural conditions can be challenged by exposure to herbicides. Farming facilities relying on the surrounding area's water quality can be affected by glyphosate and aminomethylphosphonic acid (AMPA) contamination. This review summarizes findings on how glyphosate and AMPA in the amounts registered in surface waterbodies affect redox status and biotransformation in fish and covers the aspect of diet supplementation for oxidative stress relief. Environmentally relevant concentrations of glyphosate and AMPA can alter the transcription and catalytic activities of antioxidant enzymes, decrease the content of reduced glutathione, and increase the accumulation of lipid peroxidation products, all of which are signs of a redox imbalance. Glyphosate has been shown to affect complex I in the mitochondrial respiratory chain and dysregulate iron transport-related genes, causing redox disturbance. Relatively high but environmentally realistic glyphosate concentrations can initiate the induction of cytochrome P450 biotransformation enzymes, alter the regulation of ABC exporters, and cause the inhibition of the redox-sensitive Nrf2 signaling pathway. Studies on reducing herbicide toxicity through dietary supplementation are a promising area of research. Natural functional supplements have been proven to have great potential for mitigating glyphosate-induced oxidative stress and thereby improving fish health, which in turn means maintaining productivity in fish farms that use natural water. However, data on the effects of AMPA on fish are scarce, and studies on the alleviation of its toxicity in fish are lacking. Considering the variety of AMPA contamination routes, one cannot underestimate the need for further research.

Alterations of Plasma Biochemical and Immunological Parameters and Spatiotemporal Expression of TLR2 and TLR9 in Gibel Carp (Carassius auratus gibelio) after CyHV-2 Infection

Cyprinid herpesvirus II (CyHV-2), a highly contagious pathogen of gibel carp (Carassius auratus gibelio), causes herpesviral hematopoietic necrosis disease (HVHND) and enormous financial losses. However, there is limited information available regarding the changes in plasma biochemical and immunological parameters and the response characteristics of Toll-like receptor 2 (TLR2) and Toll-like receptor 9 (TLR9) in gibel carp after CyHV-2 infection. To address this knowledge gap, a sub-lethal CyHV-2 infection was conducted in gibel carp, and the sample was collected daily from 1 to 7 days post infection. The plasma biochemical analyses showed significant decreases in the content of glucose, total cholesterol (TCHO), and total protein (TP), along with marked increases in the level of uric acid, urea, creatinine (CREA), Complement 3 (C3), immunoglobulin D (IgD), and immunoglobulin M (IgM) as well as in the activity of alanine aminotransferase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH) in the infected group. Compared with the control group, the concentration of cortisol, triglyceride (TG), and Complement 4 (C4) had no noticeable alterations in the infected group. Real-time quantitative PCR analysis showed significant upregulation of TLR2 and TLR9 mRNA expression in the spleen, kidney, brain, liver, intestine, and gill post CyHV-2 infection. Interestingly, a time- and tissue-dependent expression profile has been comparatively observed for TLR2 and TLR9 in the above tissues of gibel carp after CyHV-2 infection, suggesting distinct roles between TLR2 and TLR9 in antiviral response to CyHV-2 infection. Overall, our results demonstrated that CyHV-2 infection led to the disruption of the physiological metabolic process and damage to the liver and kidney, and induced different spatiotemporal expression patterns of TLR2 and TLR9, ultimately stimulating antiviral response via innate and adaptive immune system. These findings may provide a deeper understanding of the host immunity response to CyHV-2 infection and offer novel perspectives for the prevention and treatment and therapeutic drug development against CyHV-2.

Analysis of environmental pollutants using ion chromatography coupled with mass spectrometry: A review

The rise of emerging pollutants in the current environment and requirements of trace analysis in complex substrates pose challenges to modern analytical techniques. Ion chromatography coupled with mass spectrometry (IC-MS) is the preferred tool for analyzing emerging pollutants due to its excellent separation ability for polar and ionic compounds with small molecular weight and high detection sensitivity and selectivity. This paper reviews the progress of sample preparation and ion-exchange IC-MS methods in the analysis of several major categories of environmental polar and ionic pollutants including perchlorate, inorganic and organic phosphorus compounds, metalloids and heavy metals, polar pesticides, and disinfection by-products in past two decades. The comparison of various methods to reduce the influence of matrix effect and improve the accuracy and sensitivity of analysis are emphasized throughout the process from sample preparation to instrumental analysis. Furthermore, the human health risks of these pollutants in the environment with natural concentration levels in different environmental medias are also briefly discussed to raise public attention. Finally, the future challenges of IC-MS for analysis of environmental pollutants are briefly discussed.

Effect of zinc supplementation on immunotoxicity induced by subchronic oral exposure to glyphosate-based herbicide (GOBARA®) in Wistar rats

OBJECTIVES

To evaluate the effect of zinc supplementation on immunotoxicity induced by subchronic oral exposure to glyphosate-based herbicide (GBH).

METHODS

Sixty adult male Wistar rats randomly divided equally into six groups were exposed to GBH by gavage daily for 16 weeks with or without zinc pretreatment. Group DW rats received distilled water (2 mL/kg), group Z rats received zinc (50 mg/kg), and group G1 and G2 rats received 187.5 and 375 mg/kg GBH, respectively. Group ZG1 and ZG2 rats were pretreated with 50 mg/kg zinc before exposure to 187.5 and 375 mg/kg GBH, respectively. Tumor necrosis factor alpha (TNF-α) and immunoglobulin (IgG, IgM, IgE) levels were measured by enzyme-linked immunosorbent assay. Spleen, submandibular lymph node, and thymus samples were processed for histopathology.

RESULTS

Exposure to GBH (G1 and G2) significantly increased serum TNF-α concentrations and significantly decreased serum IgG and IgM concentrations compared with the control levels. Moderate-to-severe lymphocyte depletion occurred in the spleen, lymph nodes, and thymus in the GBH-exposed groups. Zinc supplementation mitigated the immunotoxic effects of GBH exposure.

CONCLUSIONS

GBH exposure increased pro-inflammatory cytokine responses, decreased immunoglobulin production, and depleted lymphocytes in lymphoid organs in rats, but zinc supplementation mitigated this immunotoxicity.

Persistent and transgenerational effects of pesticide residues in zebrafish

Highly toxic chemical compounds are present in rivers and lakes, endangering the survival of non-target species. To evaluate the effects of environmental contamination on non-target species, we used the zebrafish as an animal model. Environmental concentrations of the widely used pesticides, glyphosate (GBH) at 4.8 μg·L^-1 and 2,4-dichlorophenoxyacetic acid (DBH) at 3.4 μg·L^-1, were used. The animals were exposed during the entire period of organogenesis and evaluated in our previous study regarding initial developmental parameters. In the present study, we evaluate these fish when achieve the adult phase, using the novel tank test (NTT) and the aversivity test. In the second step, the animals were allowed to reproduce, and the initial parameters of development, behavioral parameters in the open field test (OFT) and in the aversivity test (AST), and biochemical biomarkers as acetylcholinesterase (AChE), catalase (CAT), and superoxide dismutase (SOD) in the F1 generation were studied. Fish exposed to GBH showed hypermobility, and their anti-predatory reaction was impaired during adulthood, indicating a persistent effect. We also showed that fish had impaired behavioral and survival changes in the F1 generation as well as effects on AChE activity and antioxidant enzymes, characterizing a transgenerational effect. The fish did not show persistent effects in adulthood due to DBH exposure; however, they were unable to reproduce. Our findings demonstrate the serious impact of pesticides on fish, where the effects of contamination can affect future generations and compromise the species' survival.

Heat waves rather than continuous warming exacerbate impacts of nutrient loading and herbicides on aquatic ecosystems

Submerged macrophytes are vital components in shallow aquatic ecosystems, but their abundances have declined globally. Shading by periphyton and phytoplankton/turbidity plays a major role in this decline, and the competing aquatic primary producers are subject to the complex influence of multiple stressors such as increasing temperatures, nutrient loading and herbicides. Their joint impact has rarely been tested and is difficult to predict due to potentially opposing effects on the different primary producers, their interactions and their grazers. Here, we used 48 mesocosms (2500 L) to simulate shallow lakes dominated by two typical submerged macrophytes, bottom-dwelling Vallisneria denseserrulata and canopy-forming Hydrilla verticillata, and associated food web components. We applied a combination of nutrient loading, continuous warming, heat waves and glyphosate-based herbicides to test how these stressors interactively impact the growth of submerged macrophytes, phytoplankton and periphyton as competing primary producers. Warming or heat waves alone did not affect phytoplankton and periphyton abundance, but negatively influenced the biomass of V. denseserrulata. Nutrient loading alone increased phytoplankton biomass and water turbidity and thus negatively affected submerged macrophyte biomass, particularly for V. denseserrulata, by shading. Glyphosate alone did not affect biomass of each primary producer under ambient temperatures. However, heat waves facilitated phytoplankton growth under combined nutrient loading and glyphosate treatments more than continuous warming. As a consequence, H. verticillata biomass was lowest under these conditions indicating the potential of multiple stressors for macrophyte decline. Our study demonstrated that multiple stressors interactively alter the biomass of primary producers and their interactions and can eventually lead to a loss of macrophyte communities and shift to phytoplankton dominance. These results show the risks in shallow lakes and ponds in agricultural landscapes and underline the need for multiple stressor studies as a base for their future management.

Glyphosate-based herbicide exposure: effects on gill microbiota of rainbow trout (Oncorhynchus mykiss) and the aquatic bacterial ecosystem

The herbicide glyphosate has been widely used in the past 40 years, under the assumption that side effects were minimal. In recent years, its impact on microbial compositions and potential indirect effects on plant, animal and human health have been strongly suspected. Glyphosate and co-formulates have been detected in various water sources, but our understanding of their potential effects on aquatic animals is still in its infancy compared with mammals. In this study, we investigated the effect of chronic exposure to an environmentally relevant concentration of glyphosate on bacterial communities of rainbow trout (Oncorhynchus mykiss). Gills, gut contents and gut epithelia were then analyzed by metabarcoding targeting the 16S rRNA gene. Our results revealed that rainbow trout has its own bacterial communities that differ from their surrounding habitats and possess microbiomes specific to these three compartments. The glyphosate-based herbicide treatment significantly affected the gill microbiome, with a decrease in diversity. Glyphosate treatments disrupted microbial taxonomic composition and some bacteria seem to be sensitive to this environmental pollutant. Lastly, co-occurrence networks showed that microbial interactions in gills tended to decrease with chemical exposure. These results demonstrate that glyphosate could affect microbiota associated with aquaculture fish.

Risk assessment of glyphosate and malathion pollution and their potential impact on Oreochromis niloticus: role of organic selenium supplementation

A field survey was conducted on five fish farms to trace glyphosate and malathion pollution with some physicochemical parameters. A precise half-life time, LC50-96h, of these agrochemicals on Oreochromis niloticus, as well as chronic exposure with organic selenium (OS) supplementation, were experimentally investigated. Oreochromis niloticus was subjected to the following: (negative control); (2 mg L-1 glyphosate); (0.5 mg L-1 malathion); (glyphosate 1.6 mg L-1 and 0.3 mg L-1 malathion); (glyphosate 2 mg L-1 and OS 0.8 g kg-1 diet); (malathion 0.5 mg L-1 and OS 0.8 g kg-1 diet) and (glyphosate 1.6 mg L-1; malathion 0.3 mg L-1 and OS 0.8 g kg-1 diet). Furthermore, data from the analyzed pond revealed a medium risk quotient (RQ) for both agrochemicals. The detected agrochemicals were related to their application, and vegetation type surrounding the farms, also their biodegradation was correlated to water pH, temperature, and salinity. Glyphosate and malathion had half-lives of 2.8 and 2.3 days and LC50-96h of 2.331 and 0.738 mg L-1, respectively. The severest nervous symptoms; increased oxidative stress markers, as well as high bacterial count in the livers and kidneys of fish challenged with Aeromonas hydrophila, were observed in the combined exposure, followed by a single exposure to malathion and then glyphosate. Organic selenium mitigated these impacts.

Automated Counting of Daphnid Neonates, Artemia Nauplii, and Zebrafish Eggs: A Proof of Concept

In aquatic invertebrate (e.g., daphnids and Artemia sp.) and zebrafish cultures, in ecotoxicological bioassays, or when addressing complex population-level experimental designs, the counting of an organism's progeny is often required. This counting process is laborious, repetitive, and time-consuming, potentially posing health hazards to the operators, and necessarily entailing a higher likelihood of human error. We present an experimental evaluation of a computer-based device for counting neonates (Daphnia magna, Daphnia longispina, and Ceriodaphnia sp.), nauplii (Artemia salina and Artemia franciscana), and zebrafish (Danio rerio) eggs. Manual counts by an experienced technician were compared with the corresponding automated counts achieved by the computer-based counting device. A minimum of 55 counts/species was performed, with the number of counted organisms being up to a maximum of 150 neonates of Ceriodaphnia dubia, 200 neonates of D. magna and D. longispina, 200 nauplii of A. franciscana and A. salina, and 500 zebrafish eggs. Manual and automated counts were both performed in culture medium solutions of 50 ml of volume. Automated counts showed a mean relative acccuracy of 98.9% (97.9%-99.4%) and a relative standard deviation of 1.72%. The results demonstrate that the computer-based device can be used for accurately counting these aquatic organisms. This computer-based counting might be extended to other organisms of similar size, thus facilitating reproduction and life-cycle ecotoxicity tests. Environ Toxicol Chem 2022;41:1451-1458. © 2022 SETAC.

Changes in defense capacity to infectious hematopoietic necrosis virus (IHNv) in rainbow trout intergenerationally exposed to glyphosate

Glyphosate, the most widely used herbicide active substance worldwide, has raised many scientific, political and public debates in the context of its recent re-registration in the European Union, highlighting in particular a lack of data concerning its potential generational effects. In this study, we investigated the intergenerational toxicity of this active substance used alone or coformulated in glyphosate-based herbicides (GBHs) on the ability of rainbow trout (Oncorhynchus mykiss) to face a viral challenge. Juvenile trout from parents exposed for eight months to four different chemical exposure conditions (non-exposed control, pure glyphosate, Roundup Innovert®, and Viaglif Jardin® were experimentally infected with the infectious hematopoietic necrosis virus (IHNv). Various enzymatic and hemato-immunological markers were assessed before and after the viral challenge. Chemical contamination with GBHs strongly modulated viral trout susceptibility. Pure glyphosate induced a cumulative mortality of 35.8%, comparable to the control (37.0%), which was significantly reduced with Roundup Innovert® (-9.9%) and increased (+14.8%) with Viaglif Jardin®. No modification was observed for the biomarkers analysed for any conditions. These results demonstrate that the nature of the co-formulants associated to glyphosate in GHBs can modulate the susceptibility of fish to pathogens.

Assessing glyphosate in water, marine particulate matter, and sediments in the Lagoon of Venice

Lagoon water, suspended particulate matter, and sediment samples from seven sites at Lagoon of Venice were collected from 2019 to 2021 in order to study the presence of the herbicide glyphosate (N-(phosphonomethyl)glycine), among the most widely used agricultural chemicals worldwide, but its occurrence in lagoon water environment has not been deeply investigated. The sites were selected considering a supposed diversity of inputs and of pollution levels. An analytical method based on ion chromatography coupled with tandem mass spectrometry was optimized and validated for lagoon water, marine particulate matter, and sediment samples. Maximum concentrations of glyphosate were 260 and 7 ng L-1 for lagoon water and suspended particulate matter, respectively, and 15 ng g-1 for sediment, with some spatial and temporal fluctuations. Our results demonstrate that glyphosate content in the Venice Lagoon mainly depends on external forcing from river inlets and agricultural lagoon activities.

Metabolomic and Transcript Analysis Revealed a Sex-Specific Effect of Glyphosate in Zebrafish Liver

Glyphosate is a component of commonly used herbicides for controlling weeds in crops, gardens and municipal parks. There is increasing awareness that glyphosate-based herbicides, in addition to acting on plants, may also exert toxicity in wildlife and humans. In this study, male and female adult zebrafish were exposed to 700 µg/L of glyphosate (GLY), for 28 days. We used the metabolomic approach and UHPLC-ESI-MS to analyze liver samples to investigate the adverse effects of glyphosate on hepatic metabolism. The impact of GLY was found to be sex-specific. In female, GLY exposure affected purine metabolism by decreasing the levels of AMP, GMP and inosinic acid, consequently increasing uric acid levels with respect to the control (CTRL). Exposure to GLY also caused a decrease of UMP levels in the pyrimidine metabolism pathway. In male, GLY exposure decreased the aminoadipic acid within the lysine degradation pathway. Transcript analysis of genes involved in stress response, oxidative stress and the immune system were also performed. Results demonstrated an increased stress response in both sexes, as suggested by higher nr3c1 expression. However, the hsp70.2 transcript level was increased in female but decreased in male. The results demonstrated reduced sod1, sod2, and gpx1a in male following exposure to GLY, indicating an impaired oxidative stress response. At the same time, an increase in the cat transcript level in female was observed. mRNA levels of the pro-inflammatory interleukins litaf and cxcl8b.1 were increased in female. Taken together, the results provide evidence of disrupted nucleotide hepatic metabolism, increased stress inflammatory response in female and disruption of oxidative stress response in male.

Toxicity and biochemical responses induced by phosmet in rainbow trout (Oncorhynchus mykiss)

Phosmet is a non-systemic organophosphorus insecticide exerting its toxicity by inhibiting acetylcholinesterase upon entering the body via contact, ingestion and inhalation. Data regarding its sublethal effects on fish are limited, and therefore, with this study it was aimed to investigate the effects of phosmet on liver and brain tissues of juvenile Oncorhynchus mykiss following 24, 48, 72 and 96 h of exposure to 5, 25 and 50 μg/l concentrations. Pesticide treatment caused notable decrease in the levels of serum glucose, protein and cholesterol, whereas there was prominent elevation in the activities of alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase. Anticholinesterase activity of phosmet was observed in brain tissue reaching maximum of 46%. In both tissues, increase in the activities of superoxide dismutase, catalase and glutathione peroxidase and level of glutathione was accompanied by elevated thiobarbituric acid reactive substances level. Our results clearly indicate the modulatory effect of phosmet on acetylcholinesterase activity and its potency to provoke oxidative stress condition. The determined alteration in alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase activities indicates hepatotoxic potential of pesticide; meanwhile, obtained hypoglycaemia and hypoproteinaemia are evaluated as adaptive responses to handle the stress to survive.

Global transcriptome profiling reveals antagonizing response of head kidney of juvenile common carp exposed to glyphosate

Glyphosate (GLY) frequently detected in various water bodies has imposed a serious risk on fish. Head kidney of fish is an important defense organ, playing a vital part in antagonizing exogenous hazardous matter. The objective of this study was to characterize toxic mechanisms of GLY in head kidney of common carp based on transcriptome profiling. After 45-days exposure of GLY at environmentally relevant concentrations, juvenile common carp were used as experimental subjects to analyze how the head kidney responded to GLY. The transcriptome profiling identified 1381 different expressed genes (DEGs) between the control and exposure groups (5 and 50 mg/L). Functional analysis of DEGs substantiated over-representative pathways mainly involving cellular stress responses, cell proliferation and turnover, apoptosis, lipid metabolism, and innate immune processes in both treated groups compared with the control group. Predicted network of gene regulation indicated that GLY-induced tp53 played a vital role in linking a battery of signals. Furthermore, the expression of 10 candidate genes by qRT-PCR aligned with transcriptional profiling. In addition, western blotting analysis confirmed that GLY-induced apoptosis and cellular proliferation were closely involved in activating MAKP signaling pathway and lipid metabolism pathway in both treated groups. Collectively, these data demonstrate that head kidney of juvenile common carp mainly leverages upregulation of genes related to cell proliferation and turnover, apoptosis, and lipid metabolism to combat sub-chronic exposure of GLY. This study casts new understanding into the risk of GLY in aquatic animals.

Glyphosate disrupts sperm quality and induced DNA damage of rainbow trout (Oncorhynchus mykiss) sperm

As a widespread pollutant, glyphosate (GLY) adversely affects the aquatic environment and can impair the reproductive ability and functions of fish. The purpose of the current study was to assess in vitro effect of GLY on rainbow trout (Oncorhynchus mykiss) sperm cells. The sperm cells were exposed to different GLY concentrations (2.5, 5, 10 mg/L). Sperm motility parameters were analyzed with computer assisted sperm analysis. DNA fragmentation (%) was measured by the comet assay using fluorescence microscopy. With increased GLY concentration, sperm motility and duration decreased after exposure. DNA fragmentation (% DNA in tail) in sperm cells was higher in treatments containing GLY than control (p < 0.05). Consequently, sperm cells are sensitive to low doses of GLY, and this can negatively affect natural populations.

Developmental effect of parental or direct chronic exposure to environmental concentration of glyphosate on the larvae of rainbow trout, Oncorhynchus mykiss

The environmental safety profile of glyphosate, the most commonly used herbicide worldwide, is still a subject of debate and little is known about the generational toxicity of this active substance (AS) and the associated commercial formulations called "glyphosate-based herbicides" (GBHs). This study investigated the impact of parental and direct exposure to 1μgL-1 of glyphosate using the AS alone or one of two GBH formulations (i.e. Roundup Innovert® and Viaglif Jardin®) in the early developmental stages of rainbow trout. Three different modes of exposure on the F1 generation were studied: (1) intergenerational (i.e. fish only exposed through their parents); (2) direct (i.e. fish exposed only directly) and (3) multigenerational (i.e. fish both exposed intergenerationally and directly). The impact of chemical treatments on embryo-larval development (survival, biometry and malformations), swimming behaviour, biochemical markers of oxidative stress equilibrium (TBARS and catalase), acetylcholine esterase (AChE) and energy metabolism (citrate synthase, CS; cytochrome-c oxidase, CCO; lactate dehydrogenase, LDH; glucose-6-phosphate dehydrogenase, G6PDH) was explored. Chemical exposure did not affect the survival of F1 embryos or malformation rates. Direct exposure to the AS induced some biometric changes, such as reduction in head size (with a 10% decrease in head length), independently of co-formulants. Intergenerational exposure to the AS or the Roundup GBH increased swimming activity of the larvae, with increase of between 78 and 102% in travel speeds. Viaglif co-formulants appear to have counteracted this behavioural change. The minor changes detected in the assayed biochemical markers suggested that observed effects were not due to oxidative damage, AChE inhibition or alterations to energy metabolism. Nonetheless, multi- and intergenerational exposure to Roundup increased CS:CCO and LDH:CS ratios by 46% and 9%, respectively, with a potential modification of the aerobic-to-anaerobic energy production balance. These biochemical effects were not correlated with those observed on individual level of biological organization. Therefore, further studies on generational toxicity of glyphosate and its co-formulants are needed to identify the other mechanisms of glyphosate toxicity at the cellular level.