Physiologically Based Pharmacokinetic Model for the Biotransportation of Arsenic in Marine Medaka (Oryzias melastigma)

Arsenite-induced liver apoptosis via oxidative stress and the MAPK signaling pathway in marine medaka

Arsenic (As) is widely recognized for its hazards to aquatic organisms; however, its toxicological impacts on apoptosis in marine fish remain inadequately explored. This study investigated the effects of in vivo dietary exposure to 50 or 500 mg/kg AsIII (as NaAsO2) over 28 days in marine medaka, alongside in vitro exposure to 50-750 μg/L AsIII for 48 h in a hepatic cell line derived from marine medaka, to elucidate the toxicity and underlying molecular mechanisms. In vivo, As significantly accumulated in liver tissue (1.79-fold compared to the control), causing hepatic lesions and increased apoptosis (4.85 ± 0.56 % and 9.29 ± 1.82 %, respectively). Gene expression analysis showed downregulation of bcl2l1 and upregulation of bax, caspase-3 and caspase-9, indicating mitochondrial pathway-mediated apoptosis. In vitro, As exposure induced hepatocyte morphological changes, reactive oxygen species (ROS) production, and apoptosis. Additionally, mapk1 and mapk3 (ERK pathway) were downregulated both in vivo and in vitro, while mapk14a (P38 pathway), mapk8b and mapk9 (JNK pathway) were upregulated exclusively in hepatocytes. Furthermore, n-acetyl cysteine (NAC) attenuated As-induced apoptosis and modulated the expression of MAPK signaling pathway genes, including mapk3 and mapk8b, suggesting that As-induced oxidative stress regulates apoptosis via the MAPK signaling pathway. In contrast, phenylbutyric acid (PBA) was ineffective in preventing apoptosis. Overall, these results demonstrate that As induces endogenous apoptosis through oxidative stress and the MAPK signaling pathway in marine medaka.

Arsenic accumulation and reproductive toxicity in freshwater snail (Pomacea canaliculata)

This study aimed to investigate the tissue-specific accumulation patterns of arsenic (As) and the potential toxicological effects of As on the oviposition of a globally distributed aquatic invertebrate, the apple snail (Pomacea canaliculata). An eight-compartment physiologically based pharmacokinetic (PBPK) model was utilized to simulate the distribution and depuration kinetics of arsenite and arsenate in the snails. Modeling and biotransformation suggested that intestine-stomach was the main uptake site for As and plays an important role in maintaining the balance of As species. Liver and kidney were the accumulation and biotransformation sites, while shell was the main storage site. Moreover, compared with arsenite, arsenate was more prone to accumulate in the organs (intestine-stomach, head-foot, kidney, gonad, shell, heart, and hemolymph). Excretion through excrement is likely the primary mechanism contributing to the low accumulation of As and the subsequent rapid decline in As concentrations observed in various organs during the depuration period. Furthermore, our findings revealed a stimulating effect of As on the oviposition of P. canaliculata. Specifically, a concentration of 500 μg L-1 of arsenite in water significantly increased the oviposition rate by 36.88 %. These findings suggest a behavioral response and changes in reproductive patterns under As exposure. The increased egg production observed in response to As exposure provides insights into the adaptive mechanisms of this species in contaminated habitats.

Significance of zinc re-absorption in Zn dynamic regulation in marine fish revealed by pharmacokinetic model

Zinc (Zn) is an essential but toxic trace element and is widely available in the natural environment. In the present study, we developed a re-absorption physiologically based pharmacokinetic (PBPK) model based on long-term dietary exposure to gain insights into the physiological mechanisms of uptake, tissue distribution, storage, and excretion of Zn in marine juvenile gilt-head breams Sparus aurata (with stomach). The PBPK model incorporated the kinetic processes of Zn transfer from fish liver to gastrointestinal system and used the Markov Monte Carlo algorithm to estimate the distribution of model parameters. The model fit indicated that the stomach and intestine of fish were key organs in regulating the concentration of Zn entering the internal environment, with excess exogenous Zn (120 mg/kg) being excreted in feces (rate constant of 5.23 d-1). Modeling results also indicated that liver (3.00 d-1), spleen (1.41 d-1) and kidney (0.51 d-1) were the main tissues responding to blood Zn flux by accumulation and detoxification. Fish kidneys exposed to 60 mg/kg and 120 mg/kg Zn had different regenerative capacities, resulting in different detoxification functions. A higher dietary Zn (120 mg/kg) disrupted the intestinal reabsorption process in marine fish. This study showed that exogenous Zn was directly accumulated in organs through the gastrointestinal-hepatic system, which is an important pathways for regulating metal homeostasis in marine fish. The results provided important understanding of the mechanisms of metal regulation and transport in marine fish.

Bioaccumulation and toxicological effects of dietborne arsenic exposure on the apple snail (Pomacea canaliculata)

An eight-compartment physiologically based pharmacokinetic (PBPK) model was used to simulate the bioaccumulation and distribution of arsenic (As) within the apple snail (Pomacea canaliculata) following the ingestion of As-contaminated lettuce. The bioaccumulation results revealed that the shell contained the majority (67.21 %) of the total As content, with the liver and the head-foot containing approximately 11.14 % and 10.45 % of the total As content in the snail, respectively. Modeling quantified the process of intestine-stomach absorption of dietborne As and revealed its crucial role in the subsequent distribution of As within the body. The liver is the primary metabolic site, whereas the shell is the primary storage site. Exposure to dietborne As leads to pronounced physiological and biochemical alterations in apple snails. Total protein levels decreased by 24.06 %, superoxide dismutase (SOD) activity decreased by 24.43 %, malondialdehyde (MDA) content increased by 47.51 %, glutathione (GSH) content decreased by 46.99 %, and glutathione S-transferase (GST) activity decreased by 42.22 %. Furthermore, the subcellular-level results indicated that dietborne As exposure altered subcellular distribution in the liver. Additionally, dietborne As exposure significantly reduced the abundance of gut microbiota in apple snails.

Metabolome analysis revealed the critical role of betaine for arsenobetaine biosynthesis in the marine medaka (Oryzias melastigma)

Arsenobetaine (AsB), a non-toxic arsenic (As) compound found in marine fish, structurally resembles betaine (GB), a common methyl donor in organisms. This study investigates the potential role of GB in AsB synthesis in marine medaka (Oryzias melastigma) using metabolomic analysis. Dietary exposure to arsenate (As(V)) and varying GB concentrations (0.05% and 0.1% in diets) increased total As and AsB bioaccumulation, particularly in marine medaka muscle. Metabolomic analysis revealed that GB played a crucial role in promoting up-regulation in methylthioadenosine (MTA) by modulating the methionine cycle and down-regulation in glutathione (GSH) by modulating the glutathione cycle. Methionine metabolism and GSH, potentially binding again to exogenous GB, could synchronously produce more non-toxic AsB. Combining verification experiments of differential metabolites of Escherichia coli in vitro, GB, GSH, S-adenosylmethionine (SAM), and arsenocholine (AsC) entered methionine and glutathione metabolism pathways to generate more AsB. These findings underscore the GB's crucial regulatory role in modulating the synthesis of AsB. This study provides vital insights into the interplay between the structural analogs GB and AsB, offering specific strategies to enhance the detoxification mechanisms of marine fish in As-contaminated environments.

Integrating Transcriptome and Metabolome Analyses Revealed Salinity Induces Arsenobetaine Biosynthesis in Marine Medaka (Oryzias melastigma)

Marine fish exhibit elevated levels of arsenobetaine (AsB), while the impact and underlying mechanism of salinity on AsB biosynthesis remain inadequately explored. In this study, marine medaka (Oryzias melastigma), typically inhabiting 30‰ high salinity, were gradually acclimated to low salinities of 20, 10, and 0‰. Following acclimation, the fish were exposed to arsenate (As(V)) in their diet for 30 days. Results showed a significant accumulation of total arsenic (As) and AsB concentrations in the muscle and head tissues of the exposed fish, with these accumulations exhibiting a positive correlation with water salinity. Transcriptome analyses revealed that exposure to As(V) at low salinity may disrupt membrane components and induce cytoskeletal injuries, while at high salinity, it triggered oxidoreductase activity and transmembrane transport. Metabolome analyses indicated that low salinity induced osmotic stress, resulting in an increased requirement for amino acids to upload intracellular osmotic equilibrium in O. melastigma. Furthermore, the key organic osmolytes and amino acids, including taurine, l-methionine, guanidinoethyl sulfonate, and N-acetyl-l-aspartic acid, exhibited a negative correlation with the AsB concentration. These findings indicated that salinity can regulate osmotic balance by influencing amino acid synthesis under low salinity and stimulating AsB synthesis under high salinity conditions in O. melastigma. This study provides insights into the impact of high salinity on AsB biosynthesis, the underlying regulatory mechanisms, and implications for managing As(V) risk.

Poison in the water: Arsenic's silent assault on fish health

Arsenic occurs across the world in freshwater and marine environments, menacing the survival of aquatic organisms. Organic and inorganic forms of this substance can be found, in which the inorganic form is more hazardous than the organic form. Most aquatic bodies contain inorganic arsenic species, but organic species are believed to be the dominant form of arsenic in the majority of fish. Natural and anthropogenic both are the sources of water contamination with arsenic. Its bioaccumulation and transfer from one trophic level to another in the aquatic food chain make arsenic a vital environmental issue. Continuous exposure to low concentrations of arsenic in aquatic organisms including fish leads to its bioaccumulation, which may affect organisms of higher trophic levels including large fishes or humans. Humans can be exposed to arsenic through the consumption of fish contaminated with arsenic. Hence, the present review facilitates our understanding about sources of arsenic, its bioaccumulation, food chain transfer, and its effect on the fish health. Also, "Poison in the Water: Arsenic's Silent Assault on Fish Health" serves as a wake-up call to recognize the pressing need to address arsenic contamination in water bodies. By understanding its devastating impact on fish health, we can strive to implement sustainable practices and policies that safeguard our precious aquatic environments and ensure the well-being of both wildlife and human communities that depend on them.

Arsenic bioaccumulation and biotransformation in the marine copepod Tigriopus japonicus under chronic dietborne and waterborne exposure

Arsenic (As) can be transferred along the food chain, while little is known about the toxic effects of dietborne As on marine copepods. In this study, we investigated the short-term and long-term effects of waterborne and dietborne As exposure on the bioaccumulation and biotransformation, as well as developmental toxicity of Tigriopus japonicus. Under acute As exposure, As bioaccumulation increased and reached a plateau with increasing exposure concentration. Moreover, As accumulation at dietborne exposure was 4.3 and 5.7 times greater than that at control group for AsIII and AsV, respectively. At chronic As exposure, As accumulation increased continuously with exposure time, with a 2.8-day extension of development time and a 45% reduction in 10-d fecundity under dietborne exposure compared to control, whereas 2.3-day extension of development time and a 20% reduction in 10-d fecundity were observed under waterborne exposure. Among As species, inorganic As had the highest concentrations, but the proportion of inorganic As decreased from 89% to 63% during 4 to 21 d of exposure, suggesting the conversion of inorganic As to organic As. The organic As was dominated by arsenobetaine (AsB, 13-25%), followed by monomethylarsenic (MMA, 8-25%). These results suggest that dietborne exposure has more pronounced toxic effects on T. japonicus, but the toxicity of As could be reduced through biotransformation under chronic exposure. Therefore, the arsenic species should be considered when assessing As toxicity.

The response of gut microbiota to arsenic metabolism is involved in arsenic-induced liver injury, which is influenced by the interaction between arsenic and methionine synthase

The drivers of changes in gut microbiota under arsenic exposure and the mechanism by which microbiota affect arsenic metabolism are still unclear. Here, C57BL/6 mice were exposed to 0, 5, or 10 ppm NaAsO2 in drinking water for 6 months. The results showed that arsenic exposure induced liver injury and increased the abundance of folic acid (FA)/vitamin B12 (VB12)- and butyrate-synthesizing microbiota. Statistical analysis and in vitro cultures showed that microbiota were altered to meet the demand for FA/VB12 by arsenic metabolism and to resist the toxicity of unmetabolized arsenic. However, at higher arsenic levels, changes of these microbiota were inconsistent. A 3D molecular simulation showed that arsenic bound to methionine synthase (MTR), which was confirmed by SEC-UV-DAD (1 μM recombinant human MTR was purified with 0 or 2 μM NaAsO2 at room temperature for 1 h) and fluorescence-labeled arsenic co-localization (primary hepatocytes were exposed to 0, 0.5, or 1 μM ReAsH-EDT2 for 24 h) in non-cellular and cellular systems. Mechanistically, the arsenic-MTR interaction in the liver interferes with the utilization of FA/VB12, which increases arsenic retention and thus results in a substantial increase in the abundance of butyrate-synthesizing microbiota compared to FA/VB12-synthesizing microbiota. By exposing C57BL/6J mice to 0 or 10 ppm NaAsO2 with or without FA (6 mg/L) and VB12 (50 μg/L) supplementation in their drinking water for 6 months, we constructed an FA/VB12 intervention mouse model and found that FA/VB12 supplementation blocked the disturbance of gut microbiota, restored MTR levels, promoted arsenic metabolism, and alleviated liver injury. We demonstrate that the change of gut microbiota is a response to arsenic metabolism, a process influenced by the arsenic-MTR interaction. This study provides new insights for understanding the relationship between gut microbiota and arsenic metabolism and present therapeutic targets for arseniasis.

Toxicity and speciation of inorganic arsenics and their adverse effects on in vivo endpoints and oxidative stress in the marine medaka Oryzias melastigma

Here, we investigate the effects of acute and chronic exposure to arsenate (AsV) and arsenite (AsIII) in the marine medaka Oryzias melastigma. In vivo effects, biotransformation, and oxidative stress were studied in marine medaka exposed to the two inorganic arsenics for 4 or 28 days. An investigation of embryonic development revealed no effect on in vivo parameters, but the hatching rate increased in the group exposed to AsIII. Exposure to AsIII also caused the greatest accumulation of arsenic in medaka. For acute exposure, the ratio of AsV to AsIII was higher than that of chronic exposure, indicating that bioaccumulation of inorganic arsenic can induce oxidative stress. The largest increase in oxidative stress was observed following acute exposure to AsIII, but no significant degree of oxidative stress was induced by chronic exposure. During acute exposure to AsV, the increase in the enzymatic activity of glutathione-S-transferase (GST) was twice as high compared with exposure to AsIII, suggesting that GST plays an important role in the initial detoxification process. In addition, an RNA-seq-based ingenuity pathway analysis revealed that acute exposure to AsIII may be related to cell-cycle progression. A network analysis using differentially expressed genes also revealed a potential link between the generation of inflammatory cytokines and oxidative stress due to arsenic exposure.

Alleviative effects of C60 fullerene nanoparticles on arsenate transformation and toxicity to Danio rerio

Widely-used C60 fullerene nanoparticles (C60) result in their release into the aquatic environment, which may affect the distribution and toxicity of pollutants such as arsenic (As), to aquatic organism. In this study, arsenate (As(V)) accumulation, speciation and subcellular distribution was determined in Danio rerio (zebrafish) intestine, head and muscle tissues in the presence of C60. Meanwhile we compared how single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), graphene oxide (GO) and graphene (GN) nanoparticles alter the behaviors of As(V). Results showed that C60 significantly inhibited As accumulation and toxicity in D. rerio, due to a decrease in total As and monomethylarsonic acid (MMA) and As(V) species concentrations, a lower relative distribution in the metal-sensitive fraction (MSF). It was attributed that C60 may coat As(V) ion channels and consequently, affect the secretion of digestive enzymes in the gut, favoring As excretion and inhibiting As methylation. Similarly, MWCNTs reduced the species concentration of MMA and As(V) in the intestines, low GSH (glutathione) contents in the intestine. Due to the disparity of other carbon-based nanomaterial morphologies, SWCNTs, GO and GN exhibited the various effects on the toxicity of As(V). In addition, the possible pathway of arsenobetaine (AsB) biosynthesis included migration from the intestine to muscle in D. rerio, with the precursor of AsB likely to be 2-dimethylarsinylacetic acid (DMAA). The results of this study suggest that C60 is beneficial for controlling As(V) pollution and reducing the impact of As(V) biogeochemical cycles throughout the ecosystem.

Arsenic bioaccumulation and biotransformation in different tissues of Nile tilapia (Oreochromis niloticus): A comparative study between As(III) and As(V) exposure and evaluation of antagonistic effects of selenium

The speciation of arsenic in fish has been widely investigated, but bioaccumulation and biotransformation of inorganic As in different tissues of Nile tilapia (Oreochromis niloticus) are not fully understood. The present study aimed to investigate the bioaccumulation of As in Nile tilapia, as well as to evaluate the distribution of the main arsenic species (As(III), As(V), MMA, DMA, and AsB) in liver, stomach, gill, and muscle, after controlled exposures to As(III) and As(V) at concentrations of 5.0 and 10.0 mg L-1 during periods of 1 and 7 days. Total As was determined by inductively coupled plasma mass spectroscopy (ICP-MS). For both exposures (As(III) and As(V)), the total As levels after 7-day exposure were highest in the liver and lowest in the muscle. Overall, the Nile tilapia exposed to As(III) showed higher tissue levels of As after the treatments, compared to As(V) exposure. Speciation of arsenic present in the tissues employed liquid chromatography coupled to ICP-MS (LC-ICP-MS), revealing that the biotransformation of As included As(V) reduction to As(III), methylation to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), and subsequent conversion to nontoxic arsenobetaine (AsB), which was the predominant arsenic form. Finally, the interactions and antagonistic effects of selenium in the bioaccumulation processes were tested by the combined exposure to As(III), the most toxic species of As, together with tetravalent selenium (Se(IV)). The results indicated a 4-6 times reduction of arsenic toxicity in the tilapia.

Recent Progress on Physiologically Based Pharmacokinetic (PBPK) Model: A Review Based on Bibliometrics

Physiologically based pharmacokinetic/toxicokinetic (PBPK/PBTK) models are designed to elucidate the mechanism of chemical compound action in organisms based on the physiological, biochemical, anatomical, and thermodynamic properties of organisms. After nearly a century of research and practice, good results have been achieved in the fields of medicine, environmental science, and ecology. However, there is currently a lack of a more systematic review of progress in the main research directions of PBPK models, especially a more comprehensive understanding of the application in aquatic environmental research. In this review, a total of 3974 articles related to PBPK models from 1996 to 24 March 2024 were collected. Then, the main research areas of the PBPK model were categorized based on the keyword co-occurrence maps and cluster maps obtained by CiteSpace. The results showed that research related to medicine is the main application area of PBPK. Four major research directions included in the medical field were "drug assessment", "cross-species prediction", "drug-drug interactions", and "pediatrics and pregnancy drug development", in which "drug assessment" accounted for 55% of the total publication volume. In addition, bibliometric analyses indicated a rapid growth trend in the application in the field of environmental research, especially in predicting the residual levels in organisms and revealing the relationship between internal and external exposure. Despite facing the limitation of insufficient species-specific parameters, the PBPK model is still an effective tool for improving the understanding of chemical-biological effectiveness and will provide a theoretical basis for accurately assessing potential risks to ecosystems and human health. The combination with the quantitative structure-activity relationship model, Bayesian method, and machine learning technology are potential solutions to the previous research gaps.

Survival strategies in arsenic-contaminated environments: Comparative insights from native and exotic aquatic species

The aim of this work was to study the sublethal effects, biokinetics, subcellular partitioning and detoxification of arsenic in two native Chinses species, Bellamya quadrata and Cipangopaludina cathayensis, as well as an exotic South American species, Pomacea canaliculata. The exotic species exhibited higher tolerance than native species. Physiologically based pharmacokinetic model results showed that the exotic species P. canaliculata exhibited a lower bioaccumulation rate and a greater metabolism capacity of As. Subcellular partitioning of As revealed that P. canaliculata exhibits superior As tolerance compared to the native species B. quadrata and C. cathayensis. This is attributed to P. canaliculata effective management of the metal sensitive fraction and enhanced accumulation of As in the biologically detoxified metal fraction. Under As stress, the biochemical parameters (superoxide dismutase, malondialdehyde, glutathione and glutathione S-transferase) of the exotic species P. canaliculata changed less in the native species, and they returned to normal levels at the end of depuration period. Our study provides evidence of the superior survival capability of the exotic species P. canaliculata compared to the native species B. quadrata and C. cathayensis under environmentally relevant levels of As contamination.

Arsenic speciation and arsenic feed-to-fish transfer in Atlantic salmon fed marine low trophic feeds based blue mussel and kelp

BACKGROUND

Aquaculture aims to reduce the environmental and climate footprints of feed production. Consequently, low trophic marine (LTM) resources such as blue mussels and kelp are potential candidates to be used as ingredients in salmon feed. It is relevant to study potential undesirables associated with their use, as well as assessing food safety by investigating their transfer from feed-to-fish. The marine biota is well known to contain relatively high levels of arsenic (As), which may be present in different organic forms depending on marine biota type and trophic position. Thus, it is important to not only obtain data on the concentrations of As, but also on the As species present in the raw materials, feed and farmed salmon when being fed novel LTM feed resources.

METHODS

Atlantic salmon were fed experimental diets for 70 days. A total of nine diets were prepared: four diets containing up to 4 % fermented kelp, three diets containing up to 11 % blue mussel silage, and one diet containing 12 % blue mussel meal, in addition to a standard reference diet containing 25 % fish meal. Concentrations of As and As species in feeds, faeces, liver and fillet of Atlantic salmon were determined by inductively coupled plasma mass spectrometry (ICP-MS) and high-performance liquid chromatography coupled to ICP-MS (HPLC-ICP-MS), respectively.

RESULTS

The use of kelp or blue mussel-based feed ingredients increased the concentration of total As, but maximum level as defined in Directive 2002/32 EC and amendments was not exceeded. The concentrations found in the experimental feeds ranged from 3.4 mg kg-1 to 4.6 mg kg-1 ww. Arsenic speciation in the feed varied based on the ingredient, with arsenobetaine dominating in all feed samples (36-60 % of the total As), while arsenosugars (5.2-8.9 % of the total As) were abundant in kelp-included feed. The intestinal uptake of total As ranged from 67 % to 83 %, but retention in fillet only ranged from 2 % to 22 % and in liver from 0.3 % to 0.6 %, depending on the marine source used. Fish fed feeds containing blue mussel showed higher intestinal uptake of total As when compared with fish fed feeds containing fermented kelp. Fish fed fermented kelp-based feeds had higher retained concentrations of total As when comparing with fish fed feeds containing blue mussel. Despite relatively high intestinal uptake of total As, inorganic and organic As, the retained concentrations of As did not reflect the same trend.

CONCLUSION

Although the use of LTM feed ingredients increased the level of total As in this feeds, salmon reared on these diets did not show increased total As levels. The well-known toxic inorganic As forms were not detected in salmon muscle reared on LTM diets, and the non-toxic organic AsB was the dominant As species that was retained in salmon muscle, while the organic AsSug forms were not. This study shows that speciation analysis of the LTM resources provides valuable information of the feed-to-fish transfer of As, needed to assess the food safety of farmed Atlantic salmon reared on novel low trophic feeds.

Key genes for arsenobetaine synthesis in marine medaka (Oryzias melastigma) by transcriptomics

Marine fish undergo detoxification to overcome As stress, forming non-toxic metabolites arsenobetaine (AsB). Genes associated with AsB synthesis remain unknown. Therefore, in this study, we explored the key genes involved in the synthesis of AsB by transcriptomic analysis in marine medaka (Oryzias melastigma), and then screened candidate genes related to AsB synthesis. In the liver, 40 genes were up-regulated and 23 genes were down-regulated, whereas in muscle, 83 genes were up-regulated and 331 genes were down-regulated. We revealed that bhmt, mat2aa, and gstt1a can play a significant role in the glutathione and methionine metabolic pathway. These three genes can affect the conversion of arsenocholine (AsC) to AsB by the vitro gene transformation experiments of E. coli BL21(DE3). E. coli BL21-bhmt overexpressing bhmt resulted in more oxidation of precursor AsC to AsB. Furthermore, the AsB concentration was decreased after E. coli BL21 overexpressing mat2aa and gstt1a, which were down-regulated in marine medaka. Therefore, we concluded that bhmt, mat2aa, and gstt1a are involved in AsB synthesis. Overall, this is the first report on transcriptome screening and identification of key genes for AsB synthesis in marine medaka. We provided important insights to reveal the mystery of AsB synthesis in marine fish.

Recent advancements in toxicology, modern technology for detection, and remedial measures for arsenic exposure: review

Arsenic toxicity has become a major global health concern for humans and animals due to extensive environmental and occupational exposure to arsenic-contaminated water, air, soil, and plant and animal origin food. It has a wide range of detrimental effects on animals, humans, and the environment. As a result, various experimental and clinical studies were undertaken and are undergoing to understand its source of exposures, pathogenesis, identify key biomarkers, the medical and economic impact on affected populations and ecosystems, and their timely detection and control measures. Despite these extensive studies, no conclusive information for the prevention and control of arsenic toxicity is available, owing to complex epidemiology and pathogenesis, including an imprecise approach and repetitive work. As a result, there is a need for literature that focuses on recent studies on the epidemiology, pathogenesis, detection, and ameliorative measures of arsenic toxicity to assist researchers and policymakers in the practical future planning of research and community control programs. According to the preceding viewpoint, this review article provides an extensive analysis of the recent progress on arsenic exposure to humans through the environment, livestock, and fish, arsenic toxicopathology, nano-biotechnology-based detection, and current remedial measures for the benefit of researchers, academicians, and policymakers in controlling arsenic eco-toxicology and directing future research. Arsenic epidemiology should therefore place the greatest emphasis on the prevalence of different direct and indirect sources in the afflicted areas, followed by control strategies.

Gut microbiota promote biotransformation and bioaccumulation of arsenic in tilapia

Aquatic organisms such as fish can accumulate high levels of arsenic (As) and transform toxic inorganic As (iAs) to non-toxic arsenobetaine (AsB). Whether the gut microbiota are involved in the process of As accumulation and transformation in fish is unclear. Herein, we subjected tilapia (Oreochromis mossambicus) to antibiotic treatment for 19 d to remove the gut microbiota, followed by the dietary exposure to arsenate (As(V)) for 16 d. The antibiotic-treated fish accumulated significantly less total As and AsB levels in the intestine and muscle than the fish in the control group. The gut contents (mixture of microbiota, digestive fluid, and diet debris) in the control fish metabolized As(V) to arsenite (As(III)) and organoarsenicals in vitro, while those in the antibiotic-treated fish lost this ability. As(V) exposure significantly changed the fish gut microbiota community. Stenotrophomonas maltophilia was found to be the dominant species (>60% of total operational taxonomic unit (OTU) number) in the gut microbiota of As-treated fish. The isolated As-resistant strain S. maltophilia SCSIOOM owned a high capability to metabolize As(V) to As(III) and organoarsenicals. Overall, these results demonstrated that the gut microbiota, at least the As-resistant bacteria, were involved in As biotransformation pathways in fish.

Intestinal uptake and low transformation increase the bioaccumulation of inorganic arsenic in freshwater zebrafish

Arsenate [As(V)] is the main form of arsenic (As) present in freshwater taken up by freshwater fish. Data on the main uptake tissue, biotransformation, and bioaccumulation in freshwater fish exposed to As(V) were limited, and the reasons for its bioaccumulation in the muscle tissue of freshwater fish remain undetermined. Accordingly, we simulated bioaccumulation and depuration in zebrafish (Danio rerio) exposed to waterborne As(V) by employing a six-compartment physiologically based pharmacokinetic model and As speciation analysis. Modeling and biotransformation suggested that intestines were the main uptake site for waterborne As(V), instead of the gills. This novel finding was evidenced by the higher As transfer constant from water to intestines (k₀₃ = 1.52 × 10^-4 L d^-1) compared to gills (k₀₂ = 5.28 × 10^-5 L d^-1). The low concentration and percentage of arsenobetaine (AsB) in the intestines suggested a weak ability to synthesize AsB. Our results showed a substantial proportion of inorganic As in intestines and a relatively substantial percentage in muscle tissue. Therefore, high As(V) uptake in the intestines and lack of biotransformation contributed to high bioaccumulation of inorganic As in freshwater fish. Inorganic As posed concerns due to the human health risks associated with consuming As(V)-contaminated fish and should be addressed.

Arsenic bioaccumulation and biotransformation in aquatic organisms

Arsenic exists universally in freshwater and marine environments, threatening the survival of aquatic organisms and human health. To elucidate arsenic bioaccumulation and biotransformation processes in aquatic organisms, this review evaluates the dissolved uptake, dietary assimilation, biotransformation, and elimination of arsenic in aquatic organisms and discusses the major factors influencing these processes. Environmental factors such as phosphorus concentration, pH, salinity, and dissolved organic matter influence arsenic absorption from aquatic systems, whereas ingestion rate, gut passage time, and gut environment affect the assimilation of arsenic from foodstuffs. Arsenic bioaccumulation and biotransformation mechanisms differ depending on specific arsenic species and the involved aquatic organism. Although some enzymes engaged in arsenic biotransformation are known, deciphering the complicated synthesis and degradation pathway of arsenobetaine remains a challenge. The elimination of arsenic involves many processes, such as fecal excretion, renal elimination, molting, and reproductive processes. This review facilitates our understanding of the environmental behavior and biological fate of arsenic and contributes to regulation of the environmental risk posed by arsenic pollution.

Wild shrimp have an order of magnitude higher arsenic concentrations than farmed shrimp from Brazil illustrating the need for a regulation based on inorganic arsenic

BACKGROUND

Shrimp is a worldwide food commodity, it is a source of several nutrients and vitamins; however, this food is one of the major sources of arsenic for humans. Legislation around the world set limits for the concentration of this element in crustaceans but is mainly concerned with total analysis. Although, arsenic species have different toxicities and total analysis could be ineffective for making decisions about food security.

METHODS

Samples of wild (Farfantepenaeus brasiliensis) and farmed shrimps (Litopenaeus vannamei) from NE Brazil were fractionated in subsamples of carapace, muscle tissue and viscera. The whole shrimp as well as the animal tissue fractions were decomposed using microwave digestion and total arsenic was analyzed by mass spectrometry inductively coupled plasm (ICP-MS). The water-soluble arsenic species were extracted, and the extract was carried for speciation analysis using HPLC-ICP-MS with an anionic and cationic column.

RESULTS

Total As in wild shrimp samples exceeded Brazilian and USA food legislation by one order of magnitude, with concentrations of 11.5 ± 0.5 mg kg-1, while farmed shrimp had significantly lower total arsenic levels (0.53 ± 0.09 mg kg-1). More than 60% of the As was in the edible fraction in the wild shrimp, while in farmed shrimp this was less than 50%. The speciation analysis showed that arsenobetaine (AsB) was the predominant As form and iAs was below the Chinese legislation levels (iAs <0.50 mg kg-1) for shrimp in both species.

CONCLUSION

The arsenic uptake in wild and farmed shrimp was discussed and some differences were found related to feed and salinity. About legislation, it has been concluded that most food legislations that consider only tAs are not appropriate to assess the toxicity of As in seafood. It is necessary to update the legislation of food control agencies to insert As speciation analysis in their protocols.

Environmental level of bisphenol F induced reproductive toxicity toward zebrafish

Bisphenol F (BPF), as an important bisphenol A substitute, is being increasingly used for industrial production. Here we performed large scale fecundity test for zebrafish that are continuous exposed to environmental levels of BPF (0.5, 5 and 50 μg/L) from embryonic stage, and identified suppressed spawning capacity of females and reduced fertility rate of males in adulthood. Although pathological change is only observed in female gonads, the transcriptional change in the hypothalamic-pituitary-gonad axis genes occurred in the gonads of both female and male fish at 150 days post-exposure. F1 generation embryos showed abnormal developmental outcomes including decreased heart rate, reduced body length, and inhibition of spontaneous movement after parental exposure to BPF. RNA-sequencing showed that the genes involved in skeletal/cardiac muscle development were significantly altered in F1 embryos spawned by BPF-treated zebrafish. The advanced pathway analysis showed that cancer and tumour formation were the most enriched pathways in the offspring of 0.5 and 5.0 μg/L groups; organismal development and cardiovascular system development were mainly affected after parental exposure to 50 μg/L of BPF; these changes were mediated by several involved regulators such as GATA4, MYF6, and MEF2C. These findings confirmed that long-term exposure to BPF at environment relevant concentration would result in reproductive toxicity among zebrafish indicating the urgent demand for the control of BPA substitutes.

Physiologically based pharmacokinetic model revealed the distinct bio-transportation and turnover of arsenobetaine and arsenate in marine fish

Arsenobetaine (AsB) is the major form of arsenic in marine fish; however, its biodynamics within the fish tissues is not well understood. This study simulated the biodynamics and biotransportation (absorption, distribution, and elimination) of dietary AsB and arsenate [As(V)] in the marine grouper Epinephelus fuscoguttatus, by constructing a physiologically based pharmacokinetic (PBPK) model. The transfer rates between different compartments (gill, intestine, liver, heart, kidney, and muscle) and blood were modeled during exposure (14 d) and depuration (20 d). The model showed that AsB had a weak ability to cross the intestinal membranes and circulated slowly in the blood. The newly AsB absorbed from the blood did not enter the hepatointestinal circulation for elimination, but was effectively distributed in liver. Thereafter, it was slowly absorbed and finally stored in the muscle, the most important organ for AsB deposition, at a constant rate of 63.5 d^-1. In contrast, As(V) displayed a dynamic behavior, including rapid crossing through the intestinal membranes, quick circulation in the blood and transportation to other tissues, and elimination. Biodynamics coupled with biotransformation illustrated, for the first time, the unique strategies of dietary AsB that passed slowly through the fish intestine with the highest deposition rate in the muscle, thereby contributing to the high AsB bioaccumulation in the muscle tissue of marine fish. CAPSULE: AsB displayed a weaker ability to cross the intestine membranes, slowly absorbed and finally stored in muscle, whereas As(V) displayed rapid crossing the intestine membranes, quick transportation, and elimination.

Accumulation, transformation and subcellular distribution of arsenite associated with five carbon nanomaterials in freshwater zebrafish specific-tissues

Although carbon nanomaterials (CNMs) commonly exist throughout the aquatic environment, their effect on arsenic (As) distribution and toxicity is unclear. In this study, arsenite accumulation, transformation, subcellular distribution, and enzyme activity were assessed in adult zebrafish (Danio rerio) intestines, heads and muscles, following co-exposure to arsenite and CNMs with different structures (single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), fullerene (C₆₀), graphene oxide (GO), and graphene (GN)). Results show that GN and GO promoted As toxicity in D. rerio, as carriers increasing total As accumulation in the intestine, resulting in arsenite adsorbed by GO and GN being released and transformed mainly into moderately-toxic monomethylarsonic acid (MMA), which was mostly distributed in organelles and metallothionein-like proteins (MTLPs). Moreover, GO and GN influenced As species distribution in D. rerio due to the excellent electron transfer ability. However, the effect was marginal for SWCNT, MWCNT and C₆₀, because of the different structure and suspension stability in fish-culture water. In addition, in the muscle and head tissues, As was mainly distributed in cellular debris in the forms of dimethylarsinic acid (DMA) and arsenobetaine (AsB). These findings help better understand the influence of CNMs on the mechanism of As toxicity in natural aquatic environments.