Toxicity mechanisms of arsenic compounds in aquatic organisms

Effects of arsenic on gut microbiota and its bioaccumulation and biotransformation in freshwater invertebrate

This study aimed to investigate the impact of arsenic stress on the gut microbiota of a freshwater invertebrate, specifically the apple snail (Pomacea canaliculata), and elucidate its potential role in arsenic bioaccumulation and biotransformation. Waterborne arsenic exposure experiments were conducted to characterize the snail's gut microbiomes. The results indicate that low concentration of arsenic increased the abundance of gut bacteria, while high concentration decreased it. The dominant bacterial phyla in the snail were Proteobacteria, Firmicutes, Bacteroidota, and Actinobacteriota. In vitro analyses confirmed the critical involvement of the gut microbiota in arsenic bioaccumulation and biotransformation. To further validate the functionality of the gut microbiota in vivo, antibiotic treatment was administered to eliminate the gut microbiota in the snails, followed by exposure to waterborne arsenic. The results demonstrated that antibiotic treatment reduced the total arsenic content and the proportion of arsenobetaine in the snail's body. Moreover, the utilization of physiologically based pharmacokinetic modeling provided a deeper understanding of the processes of bioaccumulation, metabolism, and distribution. In conclusion, our research highlights the adaptive response of gut microbiota to arsenic stress and provides valuable insights into their potential role in the bioaccumulation and biotransformation of arsenic in host organisms. ENVIRONMENTAL IMPLICATION: Arsenic, a widely distributed and carcinogenic metalloid, with significant implications for its toxicity to both humans and aquatic organisms. The present study aimed to investigate the effects of As on gut microbiota and its bioaccumulation and biotransformation in freshwater invertebrates. These results help us to understand the mechanism of gut microbiota in aquatic invertebrates responding to As stress and the role of gut microbiota in As bioaccumulation and biotransformation.

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.

Arsenic pollution concerning surface water and sediment of Jie River: A pilot area where gold smelting enterprises are concentrated

A comprehensive monitoring and risk assessment of arsenic (As) pollution concerning surface water and sediment is performed in the Jie River basin, where gold smelting enterprises are concentrated. The study area is divide into six regions, labeled as A, B, C, D, E, and F, from sewage outlets to downstream. Results shows that with far away from the sewage outlets, the total As concentrations in water and sediment gradually decrease from regions A to F. However, in region F, the concentration of bioavailable As significantly increases in the sediment due to the higher pH, leading to the transformation of As(V) into more mobile As(III). In sediment, Paracladius sp. exhibits strong resistance to As pollution in sediment, which can potentially elevate the risk of disease transmission. In water bodies, diatoms and euglena are the main phytoplankton in the Jie River while toxic cyanobacteria exhibits lower resistance to As pollution. Overall, measures should be taken to ecologically remediate the sediment in downstream while implementing appropriate isolation methods to prevent the spread of highly contaminated sediments from regions near sewage outlets.

Arsenic and chromium induced hepatotoxicity in zebrafish (Danio rerio) at environmentally relevant concentrations: Mixture effects and involvement of Nrf2-Keap1-ARE pathway

Arsenic (As) and chromium (Cr), two well-known cytotoxic and carcinogenic metals are reported to coexist in industrial effluents and groundwater. Their individual toxicities have been thoroughly studied but the combined effects, especially the mechanism of toxicity and cellular stress response remain unclear. Considering co-exposure as a more realistic scenario, current study compared the individual and mixture effects of As and Cr in the liver of zebrafish (Danio rerio). Fish were exposed to environmentally relevant concentrations of As and Cr for 15, 30 and 60 days. ROS generation, biochemical stress parameters like lipid peroxidation, reduced glutathione content, catalase activity and histological alterations were studied. Results showed increase in ROS production, MDA content and GSH level; and vicissitude in catalase activity as well as altered histoarchitecture, indicating oxidative stress conditions after individual and combined exposure of As and Cr which were additive in nature. This study also included the expression of Nrf2, the key regulator of antioxidant stress responses and its nuclear translocation. Related antioxidant and xenobiotic metabolizing enzyme genes like keap1, nqo1, ho1, mnsod and cyp1a were also studied. Overall results indicated increased nrf2, nqo1, ho1, mnsod expression at all time points and increased cyp1a expression after 60 days exposure. Emphasizing on the Nrf2-Keap1 pathway, this study exhibited additive or sometimes synergistic effects of As and Cr in zebrafish liver.

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.

Induction of Oxidative Stress by Waterborne Copper and Arsenic in Larvae of European Seabass (Dicentrarchus labrax L.): A Comparison with Their Effects as Nanoparticles

The aim of this work was to compare the potential induction of oxidative stress and the antioxidant enzymatic response after a short-term waterborne exposure to copper (Cu) and arsenic (As) with that of the nanoparticles (NPs) of these elements (Cu-NPs and As-NPs) in fish larvae of the species Dicentrarchus labrax. Larvae were grouped in several tanks and exposed to different concentrations of contaminants (0 to 10 mg/L) for 24 or 96 h under laboratory conditions. Copper and arsenic concentrations were analysed in larval tissues using ICP-MS. A set of oxidative stress biomarkers, including the levels of hydroperoxides (HPs), and superoxide dismutase (SOD) and catalase (CAT) activities were assessed. The trace element concentrations (mg/kg d.w.) in larvae ranged as follows: 3.28-6.67 (Cu at 24 h) and 2.76-3.42 (Cu at 96 h); 3.03-8.31 (Cu-NPs at 24 h) and 2.50-4.86 (Cu-NPs at 96 h); 1.92-3.45 (As at 24 h) and 2.22-4.71 (As at 96 h); and 2.19-8.56 (As-NPs at 24 h) and 1.75-9.90 (As-NPs at 96 h). In Cu tests, the oxidative damage (ROOH levels) was induced from 0.1 mg/L at both exposure times, while for Cu-NPs, this damage was not observed until 1 mg/L, which was paralleled by concomitant increases in SOD activity. The CAT activity was also increased but at lower metal concentrations (0.01 mg/L and 0.1 mg/L for both chemical forms). No oxidative damage was observed for As or As-NPs after 24 h, but it was observed for As after 96 h of treatment with 0.01 mg/L. A decrease in SOD activity was observed for As after 24 h, but it turned out to be increased after 96 h. However, As-NPs did not alter SOD activity. The CAT activity was stimulated only at 96 h by As and at 24 h by As-NPs. Therefore, the two chemical forms of Cu exhibited a higher bioaccumulation and toxicity potential as compared to those of As. Importantly, the association of both Cu and As in NPs reduced the respective trace metal bioaccumulation, resulting also in a reduction in the toxic effects (mortality and biochemical). Furthermore, the assessment of oxidative stress-related biomarkers in seabass larvae appears to be a useful tool for biomonitoring environmental-occurring trace elements.

Effects of Intestinal Microbiota on the Biological Transformation of Arsenic in Zebrafish: Contribution and Mechanism

Both the gut microbiome and their host participate in arsenic (As) biotransformation, while their exact roles and mechanisms in vivo remain unclear and unquantified. In this study, as3mt-/- zebrafish were treated with tetracycline (TET, 100 mg/L) and arsenite (iAsIII) exposure for 30 days and treated with probiotic Lactobacillus rhamnosus GG (LGG, 1 × 108 cfu/g) and iAsIII exposure for 15 days, respectively. Structural equation modeling analysis revealed that the contribution rates of the intestinal microbiome to the total arsenic (tAs) and inorganic As (iAs) metabolism approached 44.0 and 18.4%, respectively. Compared with wild-type, in as3mt-/- zebrafish, microbial richness and structure were more significantly correlated with tAs and iAs, and more differential microbes and microbial metabolic pathways significantly correlated with arsenic metabolites (P < 0.05). LGG supplement influenced the microbial communities, significantly up-regulated the expressions of genes related to As biotransformation (gss and gst) in the liver, down-regulated the expressions of oxidative stress genes (sod1, sod2, and cat) in the intestine, and increased arsenobetaine concentration (P < 0.05). Therefore, gut microbiome promotes As transformation and relieves As accumulation, playing more active roles under iAs stress when the host lacks key arsenic detoxification enzymes. LGG can promote As biotransformation and relieve oxidative stress under As exposure.

Transcriptomic and metabolomic analysis of the mechanisms underlying stress responses of the freshwater snail, Pomacea canaliculata, exposed to different levels of arsenic

Arsenic (As) pollution poses an important problem, but limited information is available about the physiological effects of As on freshwater invertebrates. Here, we investigated the physiological effects of chronic As exposure on Pomacea canaliculata, a freshwater invertebrate. High level of As (Ⅲ, 5 mg/L) inhibited the growth of P. canaliculata, whereas low level of As (Ⅲ, 2 mg/L) promoted growth. Pathological changes in shell and cellular ultrastructure due to As accumulation likely explain the growth inhibition at high As level. Low level of As simulated the expression of genes related to DNA replication and chitosan biosynthesis, potentially accounting for the growth promotion observed. High level of As enrichment pathways primarily involved cytochrome P450, glutathione, and arachidonic acid-mediated metabolism of xenobiotics. ATP-binding cassette (ABC) transporters, specifically the ABCB and ABCC subfamilies, were involved in As transport. Differential metabolites were mainly associated with the metabolism and biosynthesis of amino acids. These findings elucidate the dose-dependent effects of As stress on P. canaliculata growth, with low levels promoting and high levels inhibiting. Additionally, our findings also provide insights into As metabolism and transport in P. canaliculata.

Promoted micropollutant degradation and structural evolution of natural organic matter by a novel S(IV)-based water treatment strategy

The ubiquity of various organic micropollutants in global water and wastewater has raised considerable concern about their cost-efficient elimination. This study reported that the novel UV365/FeTiOX/S(IV) system could accomplish superior abatement of different micropollutants (e.g., carbamazepine, CMZ) in 30-45 min with excellent reusability and stability of FeTiOX. In addition, this system functioned effectively to remove roxarsone and As(III)/As(V) by catalytic oxidation and adsorption, respectively. Mechanistic investigations suggested the dual roles of S(IV) in enhancing pollutant oxidation, i.e., promoted Fe(II)/Fe(III) cycle and photocatalysis. These processes facilitated the continuous generation of multiple oxidizing intermediates (e.g., hydroxyl radicals, sulfate radicals, and singlet oxygen), in which the last one was first proposed as the main contributor in iron-mediated S(IV)-based oxidation processes. Based on the product identification, the transformation pathways of four different micropollutants were tentatively unraveled. The in silico prediction suggested the lower environmental risks of the final reaction products than the precursors. Particularly, the structural alteration of humic acid was analyzed, indicating an increased O/C ratio after oxidative treatment. Overall, this study has implications for developing an efficient oxidation technique for removing multiple micropollutants in water and facilitating the mechanistic reactivity modulation of the S(IV)-based oxidation strategies in water treatment.

Toxicity of antimony to Daphnia magna: Influence of environmental factors, development of biotic ligand approach and biochemical response at environmental relevant concentrations

Acute toxicity of antimony pentavalent to neonatal Daphnia magna and the influence of water quality parameters were investigated, and enzymatic activities of organisms at environmentally relevant levels of antimony were determined. EC50 values of antimony to neonatal D. magna were 90.3 and 63.8 mg/L at 24 and 48 h of exposure, respectively. Dissolved organic matter (FA and HA) and cation (Ca2+, Mg2+ or Na+) had significant protective effects on D. magna against antimony toxicity. With increasing pH in the range from 7.4 to 8.5, increase of EC50 were observed due to the competition of OH- on biotic ligands. Based on the biotic ligand model (BLM) concept, stability constants for the binding of Sb(OH)6- and OH- to the biotic ligand were estimated, and the Log [Formula: see text] - and LogKXOH- were 3.137 and 2.859, respectively. Moreover, antimony exposure in low concentrations significantly increased MDA levels and maybe exert oxidative stress to the organisms. Antimony can also induce toxicity in D. magna by affecting oxidative stress and neurotransmitter systems. The relatively comprehensive toxicological data can contribute to the toxicity prediction and ecological risk assessments of antimony.

Trophic transfer and biomagnification potential of environmental contaminants (heavy metals) in aquatic ecosystems

Physical, chemical weathering and volcanic eruptions release heavy metals into soils and surface waters naturally. Contaminants from anthropogenic sources originated from industrial and municipality waste substantially modify and increase their contributions. They are then absorbed by fish gills, amphipod cuticles, and other sensitive organs of aquatic creatures. This article discusses the essences on the determination, potential and plausible factors of trophic transfer and biomagnification of environmental contaminants particularly heavy metals across aquatic ecosystem. In general, arsenic is found to be bio-diminished across food webs in freshwater ecosystem while it biomagnified in marine ecosystem of higher trophic level (tertiary consumer of predatory fish) and dilute its concentration from lower trophic level (from producer to bottom level of consumer, secondary and lastly to tertiary consumer (forage fish)). Early study for Cadmium shown that it has no potential for biomagnification while later studies prove that cadmium does magnify for gastropod and epiphyte-based food webs. Mercury shown obvious biomagnification potential where it can bio-magnify from trophic level as low as particulate organic matter (POM) to higher trophic of fish. These findings proved that aquatic ecosystems must be preserved from contamination not just for human benefit, but also to prevent environmental degradation and biodiversity loss.

Biodilution of Organic Species of Arsenic in Freshwater Food Webs

Arsenic can accumulate in freshwater biota, sometimes reaching potentially harmful levels. However, the toxicity of arsenic strongly depends on which arsenic species are present. Although organic species are considered less harmful than inorganic ones, they have not been extensively studied in freshwater environments, and drivers of variation in arsenic speciation among sites and taxa remain unclear. We assessed concentrations of two organic arsenic species, arsenobetaine (AsB) and dimethylarsinic acid (DMA), in fish and invertebrates from three lakes near Sudbury, Ontario, Canada-a region with widespread mining impacts. Both AsB and DMA were detected in most samples (n = 212), varying across a wide range of concentrations (<0.001-30.144 and <0.006-5.262 mg/kg dry wt, respectively). The lake with the most severe mining impacts typically had the highest concentrations (designated by square brackets []) of AsB and DMA. In contrast, the percentage of total arsenic made up by AsB (%AsB) and DMA (%DMA) did not vary significantly between lakes. Arsenic speciation in fish muscle varied with fish size, selenium concentrations, and trophic elevation (inferred from nitrogen stable isotope ratios δ15 N), but relationships with dietary carbon source (inferred from carbon stable isotope ratios δ13 C) were more varied. Within all three lake food webs, [AsB] and [DMA] typically underwent biodilution, decreasing with trophic elevation (i.e., δ15 N). Although the aforementioned factors explained some variation in arsenic speciation, there remains considerable unexplained variation. Further studies on arsenic speciation in freshwater biota should target a wider diversity of taxa to better understand drivers of variation in arsenic speciation. In addition, research emphasizing the percentage of inorganic arsenic and other organic arsenic species is needed to improve environmental and human health risk assessments. Environ Toxicol Chem 2024;00:1-14. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Synergistic photocatalytic oxidation and adsorption boost arsenic removal by in-situ carbon-doped TiO2 and nitrogen deficiency C3N4 heterojunction

The efficient removal of arsenic from wastewater is still a challenge. In this paper, a heterojunction consisting of in-situ carbon-doped TiO2 and nitrogen deficiency g-C3N4 (C/TiO2@ND-C3N4) has been constructed, which can completely oxidize As(III) (10,000 μg/L, 40 mL) to As(V) within 12 min under visible light and simultaneously adsorb total As (95.0%) with the pseudo-secondary kinetic equation, superior than in-situ carbon-doped TiO2 (75.0%) and nitrogen deficiency g-C3N4 (50.5%). The good photocatalytic oxidation and adsorption performances of C/TiO2@ND-C3N4 on As(III) removal can be attributed to the successful synthesis of heterojunction. On one hand, the building of C-O-Ti interfacial chemical bonds enable rapid electron transfer and improve the efficiency of photocatalytic oxidation. On the other hand, the decreased As(V) adsorption energy resulted from the synthesized heterojunction boost the adsorption capability of As(V), which was completed by the generation of O-As bonds with oxygen-containing functional groups on the surface of TiO2 and hydrogen bonds with high content pyrrole nitrogen derived from ND-C3N4, respectively. The results manifest that the preparation of bifunctional materials with both photocatalytic oxidation and adsorption properties provides a new strategy to achieve the removal of As.

Mitigation of arsenic accumulation in rice (Oryza sativa L.) seedlings by oxygen nanobubbles in hydroponic cultures

Arsenic (As) is a toxic non-essential metal. Its accumulation in rice has not only seriously affected the growth of rice, but also poses a significant threat to human health. Many reports have been published to decrease the arsenic accumulation in the rice plant by various additives such as chemicals, fertilizers, adsorbents, microorganisms and analyzing the mechanism. Nanobubble is a new technology widely used in agriculture because of its long existence time and high mass transfer efficiency. However, a few studies have investigated the effect of nanobubbles on arsenic uptake in rice. This study investigated the effect of oxygen nanobubbles on the growth and uptake of As in rice. The oxygen nanobubbles could rupture the salinity of nutrients and produce the hydroxyl radical. The hydroxyl radical caused the oxidation of arsenic As(III) to As (V) and the oxidation of ferrous ions. At the same time, the oxidized iron adsorbing As (V) created the iron plaque on the rice roots to stop arsenic introduction into the rice plant. The results indicated that the treatment of oxygen nanobubbles increased rice biomass under As stress, while they increased the chlorophyll content and promoted plant photosynthesis. Oxygen nanobubbles reduced the As content in rice roots to 12.5% and shoots to 46.4%. In other words, it significantly decreased As accumulation in rice. Overall, oxygen nanobubbles mitigated the toxic effects of arsenic on rice and had the potential to reduce the accumulation of arsenic in rice.

Comprehensive evaluation of the risk system for heavy metals in the rehabilitated saline-alkali land

A comprehensive assessment of the heavy metal system in the rehabilitated saline-alkali land holds significant importance, as the in-situ remediation process utilizing amendments substantially alters the initial physicochemical properties of the soil, which could lead to the migration or reactivation of previously stabilized heavy metals. In this context, the present study aims to evaluate the heavy metal content and health risk within the improved saline-alkali soil-plant system. Moreover, a comprehensive evaluation based on the TOPSIS-RSR method is carried out to accurately gauge the soil health status. The findings indicate that the modification process has an impact on the concentrations of heavy metals in the soil and crops, causing either an increase or decrease. However, the level of heavy metal pollution in the improved saline-alkali soil and rape remains within safe limits. The results of the migration of heavy metals after amendment application indicated that the migration of heavy metals in the soil was influenced by the properties of the heavy metals, the composition of the amendment, and leaching. Furthermore, the total non-carcinogenic hazard quotients in the soil and rape were within the safe threshold for all populations. The findings provided novel insights into the status and risk assessment of the pollution of improved saline-alkali soil.

Polystyrene microplastic alters the redox state and arsenic metabolization in the freshwater bivalve Limnoperna fortunei

Most organisms possess the capacity to metabolize arsenic (As) accumulating compounds to less toxic forms, thus minimizing the adverse effect induced by this metalloid. However, other contaminants may to interfere with As metabolism, contributing to the accumulation of more toxic compounds. Microplastics (MPs) are omnipresent in aquatic environment and may induce toxicological effects (alone or in combination with other contaminants) on living organisms. Therefore, the objective of the present study was to evaluate the effect of the exposure of the freshwater clam Limnoperna fortunei to a combination of MP (4 and 40 μg/L of polystyrene microbeads, 1.05 μm) and As (50 μg/L) for 48 h, evaluating the accumulation and metabolization of As and oxidative stress parameters, such as catalase (CAT), glutathione-S-transferase activities, total antioxidant competence, reduced glutathione (GSH), and lipid damage in the gills and digestive glands. Results revealed that low MP concentration disrupts the redox state of the digestive gland by a decrease in the antioxidant activity (CAT and total antioxidant capacity). GSH levels in the gills of animals exposed to MP (4 μg/L) alone and the combination of MP + As increased, concomitant with an increase in the percentage of toxic compounds, indicating the effect of MP on As metabolism. Although, few studies evaluated the effect of coexposure to MP + As by considering metabolization of metalloid in freshwater bivalve, our results revealed that exposure to MP reduced the metabolization capacity of As, favoring the accumulation of more toxic compounds besides the MP alone, which showed a pro-oxidant effect in L. fortunei.

Recent Review on Selected Xenobiotics and Their Impacts on Gut Microbiome and Metabolome

As it is well known, the gut is one of the primary sites in any host for xenobiotics, and the many microbial metabolites responsible for the interactions between the gut microbiome and the host. However, there is a growing concern about the negative impacts on human health induced by toxic xenobiotics. Metabolomics, broadly including lipidomics, is an emerging approach to studying thousands of metabolites in parallel. In this review, we summarized recent advancements in mass spectrometry (MS) technologies in metabolomics. In addition, we reviewed recent applications of MS-based metabolomics for the investigation of toxic effects of xenobiotics on microbial and host metabolism. It was demonstrated that metabolomics, gut microbiome profiling, and their combination have a high potential to identify metabolic and microbial markers of xenobiotic exposure and determine its mechanism. Further, there is increasing evidence supporting that reprogramming the gut microbiome could be a promising approach to the intervention of xenobiotic toxicity.

Assessment of Joint Toxicity of Arsenate and Lead by Multiple Endpoints in Chlamydomonas reinhardtii

In aquatic ecosystems, arsenate (As(V)) and lead (Pb(II)) frequently coexist but their joint toxicity on microalgae remains unknown. In this study, Chlamydomonas reinhardtii was exposed to various levels of combined As(V) and Pb(II) treatments. The cell growth, respiration, pigment synthesis, polysaccharides and protein secretion as well as As speciation of C. reinhardtii were analyzed. The low-level coexistence of As(V) and Pb(II) had a stimulatory effect, as indicated by enhanced cell proliferation. In the middle-level coexistence, the cells resisted the toxicity by significant increasing protein secretion. Under high-level coexistence, the presence of Pb(II) inhibited the efflux of As and caused the decline of cell numbers and occurrence of cell lysis, indicating that the interaction mode between As(V) and Pb(II) switched to synergistic. Taken together, the above findings may deepen the understanding of detoxification mechanisms of algae upon exposure to combined metal(loid)s in aqueous environments.

Natural Microbial Reactor-Based Sensing Platform for Highly Sensitive Detection of Inorganic Arsenic in Rice Grains

Rice is a major dietary source of inorganic arsenic (iAs), a highly toxic arsenical that accumulates in rice and poses health risks to rice-based populations. However, the availability of detection methods for iAs in rice grains is limited. In this study, we developed a novel approach utilizing a natural bacterial biosensor, Escherichia coli AW3110 (pBB-ArarsR-mCherry), in conjunction with amylase hydrolysis for efficient extraction, enabling high-throughput and quantitative detection of iAs in rice grains. The biosensor exhibits high specificity for arsenic and distinguishes between arsenite [As(III)] and arsenate [As(V)] by modulating the concentration of PO43- in the detection system. We determined the iAs concentrations in 19 rice grain samples with varying total As concentrations and compared our method with the standard technique of microwave digestion coupled with HPLC-ICP-MS. Both methods exhibited comparable results, without no significant bias in the concentrations of As(III) and As(V). The whole-cell biosensor demonstrated excellent reproducibility and a high signal-to-noise ratio, achieving a limit of detection of 16 μg kg-1 [As(III)] and 29 μg kg-1 [As(V)]. These values are considerably lower than the maximum allowable level (100 μg kg-1) for infant rice supplements established by the European Union. Our straightforward sensing strategy presents a promising tool for detecting iAs in other food samples.

Toxicity of Heavy Metals and Recent Advances in Their Removal: A Review

Natural and anthropogenic sources of metals in the ecosystem are perpetually increasing; consequently, heavy metal (HM) accumulation has become a major environmental concern. Human exposure to HMs has increased dramatically due to the industrial activities of the 20th century. Mercury, arsenic lead, chrome, and cadmium have been the most prevalent HMs that have caused human toxicity. Poisonings can be acute or chronic following exposure via water, air, or food. The bioaccumulation of these HMs results in a variety of toxic effects on various tissues and organs. Comparing the mechanisms of action reveals that these metals induce toxicity via similar pathways, including the production of reactive oxygen species, the inactivation of enzymes, and oxidative stress. The conventional techniques employed for the elimination of HMs are deemed inadequate when the HM concentration is less than 100 mg/L. In addition, these methods exhibit certain limitations, including the production of secondary pollutants, a high demand for energy and chemicals, and reduced cost-effectiveness. As a result, the employment of microbial bioremediation for the purpose of HM detoxification has emerged as a viable solution, given that microorganisms, including fungi and bacteria, exhibit superior biosorption and bio-accumulation capabilities. This review deals with HM uptake and toxicity mechanisms associated with HMs, and will increase our knowledge on their toxic effects on the body organs, leading to better management of metal poisoning. This review aims to enhance comprehension and offer sources for the judicious selection of microbial remediation technology for the detoxification of HMs. Microbial-based solutions that are sustainable could potentially offer crucial and cost-effective methods for reducing the toxicity of HMs.

Effect of heavy metals on the energy metabolism in the brackish water flea Diaphanosoma celebensis

Heavy metals such as lead (Pb), cadmium (Cd), and arsenic (As) are of great concern in aquatic ecosystems because of their global distribution, persistence, and biomagnification via the food web. They can induce the expression of cellular protective systems (e.g., detoxification enzymes and antioxidant enzymes) to protect organisms from oxidative stress, which is a high-energy-consuming process. Thus, energy reserves (e.g., glycogen, lipids, and proteins) are utilized to maintain metabolic homeostasis. Although a few studies have suggested that heavy metal stress can modulate the metabolic cycle in crustaceans, information on changes in energy metabolism under metal pollution remains lacking in planktonic crustaceans. In the present study, the activity of digestive enzymes (amylase, trypsin, and lipase) and the contents of energy storage molecules (glycogen, lipid, and protein) were examined in the brackish water flea Diaphanosoma celebensis exposed to Cd, Pb, and As for 48 h. Transcriptional modulation of the three AMP-activated protein kinase (AMPK) and metabolic pathway-related genes was further investigated. Amylase activity was highly increased in all heavy metal-exposed groups, whereas trypsin activity was reduced in Cd- and As-exposed groups. While glycogen content was increased in all exposed groups in a concentration-dependent manner, lipid content was reduced at higher concentrations of heavy metals. The expression of AMPKs and metabolic pathway-related genes was distinct among heavy metals. In particular, Cd activated the transcription of AMPK-, glucose/lipid metabolism-, and protein synthesis-related genes. Our findings indicate that Cd can disrupt energy metabolism, and may be a potent metabolic toxicant in D. celebensis. This study provides insights into the molecular mode of action of heavy metal pollution on the energy metabolism in planktonic crustaceans.

Integrated metabolomics and network pharmacology revealing the mechanism of arsenic-induced hepatotoxicity in mice

Endemic arsenic (As) poisoning is a severe biogeochemical disease that endangers human health. Epidemiological investigations and animal experiments have confirmed the damaging effects of As on the liver, but there is an urgent need to investigate the underlying mechanisms. This study adopted a metabolomic approach using UHPLC-QE/MS to identify the different metabolites and metabolic mechanisms associated with As-induced hepatotoxicity in mice. A network pharmacology approach was applied to predict the potential target of As-induced hepatotoxicity. The predicted targets of differential metabolites were subjected to a deep matching for elucidating the integration mechanisms. The results demonstrate that the levels of ALT and AST in plasma significantly increased in mice after As exposure. In addition, the liver tissue showed disorganized liver lobules, lax cytoplasm and inflammatory cell infiltration. Metabolomic analysis revealed that As exposure caused disturbance to 40 and 75 potential differential metabolites in plasma and liver, respectively. Further investigation led to discovering five vital metabolic pathways, including phenylalanine, tyrosine, and tryptophan biosynthesis and nicotinate and nicotinamide metabolism pathways. These pathways may responded to As-induced hepatotoxicity primarily through lipid metabolism, apoptosis, and deoxyribonucleic acid damage. The network pharmacology suggested that As could induce hepatotoxicity in mice by acting on targets including Hsp90aa1, Akt2, Egfr, and Tnf, which regulate PI3K Akt, HIF-1, MAPK, and TNF signaling pathways. Finally, the integrated metabolomics and network pharmacology revealed eight key targets associated with As-induced hepatoxicity, namely DNMT1, MAOB, PARP1, MAOA, EPHX2, ANPEP, XDH, and ADA. The results also suggest that nicotinic acid and nicotinamide metabolisms may be involved in As-induced hepatotoxicity. This research identified the metabolites, targets, and mechanisms of As-induced hepatotoxicity, offering meaningful insights and establishing the groundwork for developing antidotes for widespread As poisoning.

Study effect and mechanism of levofloxacin on the neurotoxicity of Rana nigromaculata tadpoles exposed to imidacloprid based on the microbe-gut-brain axis

Aquatic organisms may be simultaneously exposed to antibiotics and pesticides. After levofloxacin (LVFX), imidacloprid (IMI) exposure and co-exposure at environmental levels, we found LVFX and IMI had antagonistic effect on the neurotoxicity of tadpoles. IMI-induced neurotoxicity on tadpoles can be explained by oxidative stress and hormone levels in some degree. By regulating ornithine, l-asparagine, putrescine and tryptamine in the intestine, LVFX affected glutathione metabolism, arginine and proline metabolism, alanine, aspartate and glutamate metabolism, tyrosine metabolism and aminoacyl tRNA biosynthesis, so then eased the neurotoxicity caused by IMI. More interestingly, Fusobacteriota and Cetobacterium might play an important role on easing the neurotoxicity caused by IMI. In addition, LVFX might have a laxation effect on the increased relative abundance of Bacteroidota caused by IMI. In conclusion, IMI not only affected oxidative stress and hormone levels in the brain, but also affected the synthesis of neurotransmitters in the intestine by regulating intestinal microbiota. In LVFX and IMI co-exposed groups, LVFX alleviated the neurotoxicity caused by IMI through regulating the intestinal microbiota, showing as an antagonistic effect. Our results provided a new perspective for aquatic ecological risk assessment under co-exposure of antibiotics and pesticides.

Heavy metals and metalloid in aquatic invertebrates: A review of single/mixed forms, combination with other pollutants, and environmental factors

Heavy metals (HMs) and metalloid occur naturally and are found throughout the Earth's crust but they are discharged into aquatic environments at high concentrations by human activities, increasing heavy metal pollution. HMs can bioaccumulate in higher organisms through the food web and consequently affect humans. In an aquatic environment, various HMs mixtures can be present. Furthermore, HMs adsorb on other environmental pollutants, such as microplastics and persistent organic pollutants, causing a synergistic or antagonistic effect on aquatic organisms. Therefore, to understand the biological and physiological effects of HMs on aquatic organisms, it is important to evaluate the effects of exposure to combinations of complex HM mixtures and/or pollutants and other environmental factors. Aquatic invertebrates occupy an important niche in the aquatic food chain as the main energy link between higher and lower organisms. The distribution of heavy metals and the resulting toxic effects in aquatic invertebrates have been extensively studied, but few reports have dealt with the relationship between HMs, pollutants, and environmental factors in biological systems with regard to biological availability and toxicity. This review describes the overall properties of individual HM and their effects on aquatic invertebrates and comprehensively reviews physiological and biochemical endpoints in aquatic invertebrates depending on interactions among HMs, other pollutants, and environmental factors.

Proteomic Analysis of Arsenic Resistance during Cyanide Assimilation by Pseudomonas pseudoalcaligenes CECT 5344

Wastewater from mining and other industries usually contains arsenic and cyanide, two highly toxic pollutants, thereby creating the need to develop bioremediation strategies. Here, molecular mechanisms triggered by the simultaneous presence of cyanide and arsenite were analyzed by quantitative proteomics, complemented with qRT-PCR analysis and determination of analytes in the cyanide-assimilating bacterium Pseudomonas pseudoalcaligenes CECT 5344. Several proteins encoded by two ars gene clusters and other Ars-related proteins were up-regulated by arsenite, even during cyanide assimilation. Although some proteins encoded by the cio gene cluster responsible for cyanide-insensitive respiration decreased in the presence of arsenite, the nitrilase NitC required for cyanide assimilation was unaffected, thus allowing bacterial growth with cyanide and arsenic. Two complementary As-resistance mechanisms were developed in this bacterium, the extrusion of As(III) and its extracellular sequestration in biofilm, whose synthesis increased in the presence of arsenite, and the formation of organoarsenicals such as arseno-phosphoglycerate and methyl-As. Tetrahydrofolate metabolism was also stimulated by arsenite. In addition, the ArsH2 protein increased in the presence of arsenite or cyanide, suggesting its role in the protection from oxidative stress caused by both toxics. These results could be useful for the development of bioremediation strategies for industrial wastes co-contaminated with cyanide and arsenic.

Chronic environmental inorganic arsenic exposure causes social behavioral changes in juvenile zebrafish (Danio rerio)

Arsenic (As) is a metalloid commonly found worldwide. Environmental As exposure may cause potential health hazards and behavioral changes in humans and animals. However, the effects of environmental As concentrations on social behavior, especially during the juvenile stage, are unclear. In this study, we observed behavioral changes in juvenile zebrafish after 28 days of exposure to inorganic As (NaAsO₂ 100 and 500 ppb) in water, especially anxiety and social deficits. Additionally, the level of oxidative stress in the zebrafish brain after As treatment increased, the content of dopamine (DA) decreased, and the transcription level of genes involved in DA metabolism with the activity of monoamine oxidase (MAO) increased. Oxidative stress is a recognized mechanism of nerve damage induced by As exposure. The zebrafish were exposed to N-acetylcysteine (NAC) to reduce As exposure-induced oxidative stress. The results showed improvements in social behavior, DA content, MAO activity, and gene transcription in zebrafish. In conclusion, environmental As exposure can induce behavioral abnormalities, such as anxiety and social deficits in zebrafish, which may be caused by As-induced oxidative stress altering gene transcription levels, causing an increase in MAO activity and a decrease in DA.

Microbial remediation and plant-microbe interaction under arsenic pollution

Arsenic contamination in aquatic and terrestrial ecosystem is a serious environmental issue. Both natural and anthropogenic processes can introduce it into the environment. The speciation of the As determine the level of its toxicity. Among the four oxidation states of As (-3, 0, +3, and + 5), As(III) and As(V) are the common species found in the environment, As(III) being the more toxic with adverse impact on the plants and animals including human health. Therefore, it is very necessary to remediate arsenic from the polluted water and soil. Different physicochemical as well as biological strategies can be used for the amelioration of arsenic polluted soil. Among the microbial approaches, oxidation of arsenite, methylation of arsenic, biosorption, bioprecipitation and bioaccumulation are the promising transformation activities in arsenic remediation. The purpose of this review is to discuss the significance of the microorganisms in As toxicity amelioration in soil, factors affecting the microbial remediation, interaction of the plants with As resistant bacteria, and the effect of microorganisms on plant arsenic tolerance mechanism. In addition, the exploration of genetic engineering of the bacteria has a huge importance in bioremediation strategies, as the engineered microbes are more potent in terms of remediation activity along with quick adaptively in As polluted sites.

Effects of phosphate on the toxicity and bioaccumulation of arsenate in marine diatom Skeletonema costatum

The effects of nutrient phosphate (P) at environmentally relevant levels on the toxicity of arsenic (As) in marine microalgae have been rarely known. In the present study, we explored the toxicity and bioaccumulation of As in a globally distributed diatom species Skeletonema costatum at different ambient P concentrations. The results showed that As toxicity was suppressed at elevated P concentrations. Intracellular As content ([As]_intra) and the molar ratio of intracellular As to P ([As:P]) were negatively correlated with the ambient P concentrations. The trends of As bioaccumulation were substantially different between the relatively low (0, 0.5 and 1.5 μM) and high P concentrations (7.5 and 37.5 μM). Both [As]_intra and [As:P] suggested that As bioaccumulation was a better factor to explain the As toxicity comparing to the ambient As concentration. The 4 h As uptake kinetics at different P concentrations followed Michaelis-Menten kinetic pattern. The maximum uptake rates (V_max) decreased with the increase in P concentrations, and the half-saturation constants (K_d) remained constant except for that at extremely high P concentration (37.5 μM-P), suggesting the depression of P on As uptake was mainly due to the non-competitive effect. Overall, these results demonstrate that the P concentration in seawater is an important factor affecting As toxicity and bioaccumulation in the marine diatom. This study therefore helps us better understand the effects of eutrophication on the toxicity and biogeochemistry of As in the marine environment.

Analyzing toxicological effects of AsIII and AsV to Chlamys farreri by integrating transcriptomic and metabolomic approaches

Inorganic arsenic (iAs) is a widespread contaminant in marine environments, which is present in two different oxidation states (arsenate (AsV) and arsenite (AsIII)) that have complex toxic effects on marine organisms. The scallop Chlamys farreri (C. farreri) accumulates high levels of As and is a suitable bioindicator of As. In this report, we integrated transcriptomics and metabolomics to investigate genetic and metabolite changes and functional physiological disturbances in C. farreri exposured to inorganic arsenic. Physiological indicators antioxidant factors and cell apoptosis analysis macroscopically corroborated the toxic effects of inorganic arsenic revealed by omics results. Toxic effects of inorganic arsenic on C. farreri were signaling-mediated, causing interference with a variety of cell growth and small molecule metabolism. The results provide evidence that inorganic arsenic disrupts the physiological functions of bivalves, highlighting the correlations between different metabolic pathways and providing new insights into the toxic effects of environmental pollutants on marine organisms.

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.

Environmental impact of Sargassum spp. landings: an evaluation of leachate released from natural decomposition at Mexican Caribbean coast

Large volumes of pelagic Sargassum spp. have stranded periodically on the Mexican Caribbean shoreline. The aim of this research was to study the mobility of metals through the leachates released into the environment during the natural decomposition process of Sargassum spp. Fresh Sargassum samples were placed in cone-bed reactors: under laboratory and local environmental conditions. The leachate generated naturally by decomposition in both conditions was recovered periodically and analyses of pH, volume, and metal content were carried out. Sargassum biomass was monitored by electron microscopy, FT-IR, and CHNS analysis. The Sargassum biomass studied presented a C: N ratio of 24.39, making it a potential raw feedstock for biofuels and other value-added products. Calculations performed on leachate production allowed inferring that each ton of fresh Sargassum that decomposes at a controlled temperature of 27 °C can produce 316 L of leachate. This leachate can contain 5.67 g of As and other potentially toxic metals (e.g., B, Al, Cu). At the end of both experiments, the biomass that was incubated for 30 days presented a C: N ratio of 28.86, so it can still be used as raw material for biofuels; however, the Sargassum biomass that remained 180 days in incubation decreased its C:N ratio at 8.45 at this point, it can be considered a waste. The leachate generated during the natural decomposition process of Sargassum on beaches or disposal sites represents a high risk of contamination of the Yucatan Peninsula water system due to the high content of arsenic and the presence of potentially toxic metals.

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.

Oxidative stress in Physella acuta: An integrative response of exposure to water from two rivers of Atlantic Mexican slope

Freshwater pollution is a complex mixture of xenobiotics due to the wastewater and the various chemicals routinely applied to agricultural lands that are discharged into water bodies. Xenobiotics can exert damage to the aquatic biota threatening the biodiversity of aquatic ecosystems. The oxidative damage and antioxidant responses have been widely investigated in freshwater organisms, mainly in fish and some invertebrates but in freshwater snails are scarce. This study aimed to assess the oxidative stress exerted by potential toxicity of water from two rivers of the Mexican Atlantic Slope (Tecolutla and Tuxpan rivers) in a freshwater mollusk Physella acuta. Lipid peroxidation level and a battery of antioxidant enzymes (Superoxide dismutase, Catalase and Glutathione peroxidase) were measured in P. acuta. The results are contextualized from an ecological point of view, associating the bioassay results with water quality characteristics. Water samples were obtained from three study sites for each river (in two seasons: Northern wind and dry). Twelve water quality variables were analyzed, and an additional water sample was used to perform a static bioassay for 96 h with snails grown in laboratory. After the exposure, we assessed lipid peroxidation level and the antioxidant responses of P. acuta exposed to water of rivers, and the Integrated Biomarker Response was computed. The highest lipid peroxidation level occurred in organisms exposed to water during the Northern wind season in both rivers. During this season, in the Tecolutla river, the superoxide dismutase activity was able to counteract the lipid peroxidation process, representing an adaptive response. In contrast, in the Tuxpan river, the superoxide dismutase was unable to counteract that process, stimulating CAT and GPx activities. The Integrated Biomarker Response showed that the Tecolutla river had higher values in the upper reaches than the Tuxpan river, showing a decreasing downstream gradient in both seasons. In the Tuxpan river, during the Dry season, the IBR score showed an increasing downstream gradient. During the Northern wind season, the IBR was higher in the upper reaches of both rivers, possibly due to the increased materials transported by runoff from the catchment, which includes a complex mixture of xenobiotics that affects the health of the sentinel species and aquatic biota in general. Based on our results, Physella acuta is proposed as sentinel species.

Influence of humic acid and fluvic acid on the altered toxicities of arsenite and arsenate toward two freshwater algae

Arsenic pollution in freshwater poses a serious threat to aquatic organisms. However, dissolved organic matter (DOM) in water can modulate arsenic environmental toxicity by either suppressing or promoting its bioaccumulation. In this study, we investigated the toxicity, bioaccumulation, and biotransformation of inorganic arsenic (arsenite As^III and arsenate As^V) combined with two types of DOM, i.e., humic acid (HA) and fulvic acid (FA), in the algae Chlamydomonas reinhardtii and Ochromonas danica. C. reinhardtii has a cell wall and cannot bioaccumulate arsenic complexation, whereas O. danica has no cell wall. Without DOM, As^V was more toxic than As^III for C. reinhardtii, and As^V was less toxic than As^III for O. danica. HA and FA addition reduced As^V and As^III toxicities; the larger molecular weight (M_w) of HA contributed to the reduction in toxicity to an even greater extent, and reduced arsenic accumulation while promoting the biotransformation ability of C. reinhardtii, which has a cell wall. However, HA and FA addition increased As^V and As^III toxicities and arsenic accumulation while relatively enhancing the biotransformation ability of O. danica, which has no cell wall. Coupling toxicity, bioaccumulation, and biotransformation, DOM (HA and FA) contributed to the altered toxicity of freshwater algae to As^V and As^III through reduced/increased arsenic accumulation and enhanced biotransformation. Overall, our study considered the combined toxicity of inorganic arsenic and DOM in phytoplankton, helping estimate the potential environmental risk of arsenic in aqueous environments.

The Potential Key Role of the NRF2/NQO1 Pathway in the Health Effects of Arsenic Pollution on SCC

Arsenic is widely present in nature and is a common environmental poison that seriously damages human health. Chronic exposure to arsenic is a major environmental poisoning factor that promotes cell proliferation and leads to malignant transformation. However, its molecular mechanism remains unclear. In this study, we found that arsenite can promote the transformation of immortalized human keratinocyte cells (HaCaT) from the G0/G1 phase to S phase and demonstrated malignant phenotypes. This phenomenon is accompanied by obviously elevated levels of NRF2, NQO1, Cyclin E, and Cyclin-dependent kinase 2 (CDK2). Silencing the NRF2 expression with small interfering RNA (siRNA) in arsenite-transformed (T-HaCaT) cells was shown to reverse the malignant phenotype. Furthermore, the siRNA silencing of NQO1 significantly decreased the levels of the cyclin E-CDK2 complex, inhibiting the G0/G1 to S phase cell cycle progression and transformation to the T-HaCaT phenotypes. Thus, we hypothesized that the NRF2/NQO1 pathway played a key role in the arsenite-induced malignancy of HaCaT cells. By increasing the expression of Cyclin E-CDK2, the NRF2/NQO1 pathway can affect cell cycle progression and cell proliferation. A new common health effect mechanism of arsenic carcinogenesis has been identified; thus, it would contribute to the development of novel treatments to prevent and treat skin cancer caused by arsenic.

Arsenic speciation in shellfish from South China Sea: Levels, estimated daily intake and health risk assessment

The purposes of this study were to measure the concentrations of arsenic speciation in shellfish from South China Sea and evaluate the health risk by local residents through shellfish consumption. The median concentrations (in wet weight) of arsenic speciation in shellfish samples were in the following order: AsB (16.0 mg·kg^-1) > DMA (1.30 mg·kg^-1) > AsV (0.23 mg·kg^-1) > AsC (0.08 mg·kg^-1) > AsIII (0.05 mg·kg^-1) > MMA (0.01 mg·kg^-1). Among shellfish species, Mactra mera and Babylonia areolata were found to accumulate iAs and AsB, respectively. The target hazard quotient values of iAs (THQ_iAs) in all shellfish samples were lower than 1. However, the carcinogenic risk values of iAs (CR_iAs) in the Mactra mera, Mytilus galloprovincialis and Pinctada margaritifera were beyond the acceptable range, implying that continuous exposure to iAs pollution via the consumption of these shellfish would pose a potential cancer risk to local consumers.

The ZrO2 NPs enhanced the risk of arsenate by promoting its accumulation and reducing its detoxification during food chain transfer from Daphnia magna to zebrafish

Arsenic (As) can co-occur with zirconium dioxide nanoparticles (ZrO₂ NPs) in aquatic environments, but their combined influence along the aquatic food chain is barely explored. This study constructed water flea Daphnia magna - zebrafish Danio rerio to evaluate the impact of ZrO₂ NPs on the accumulation, trophic transfer, transformation, and detoxification of arsenate (As(V)). The zebrafish were fed D. magna exposed to As(V), ZrO₂ NPs, or As(V) + ZrO₂ NPs for 20 d. Results demonstrated that ZrO₂ NPs significantly facilitated total As and As(V) sorption in D. magna and in tissues of zebrafish. ZrO₂ NPs enhanced the transformation of inorganic arsenic (iAs) to monomethylated acid (MMA), while decreased synthesis of arsenobetaine (AsB) in tissues, leading to iAs increased. Co-exposed As(V) and ZrO₂ NPs facilitated upregulation of absorption-related genes (aqp7) and As biotransformation-related genes (gst, gss), and detoxification and oxidative stress-related genes (mt2, cat, sod1 and sod2). Therefore, genetic expression coupling with biotransformation for the first time demonstrated that As(V) combined with ZrO₂ NPs led to increased harm to D. magna and zebrafish and amplified the ecological risks of As(V) along the aquatic food chain. Attention should be paid to the combined toxicity of As(V) and ZrO₂ NPs in aquatic environment.

Effects of acute arsenic exposure in two different populations of Hyalella curvispina amphipods from North Patagonia Argentina

Arsenic (As) is a toxic metalloid present in high levels in diverse regions of Argentina. The aim of this study was to determine acute As-mediated toxicity in two different populations of autochthonous Hyalella curvispina amphipods from a reference site (LB) and an agricultural one (FO) within North Patagonia Argentina. Previously, both populations exhibited significant differences in pesticide susceptibility. Lab assays were performed to determine acute lethal concentrations, as well as some biochemical parameters. Lethal concentration (LC₅₀) values obtained after 48 and 96 hr As exposure were not significantly different between these populations, although FO amphipods appeared slightly less susceptible. LC₅₀-48 hr values were 3.33 and 3.92 mg/L As, while LC₅₀-96 hr values were 1.76 and 2.14 mg/L As for LB and FO amphipods. The no observed effect concentration (NOEC) values were 0.5 mg/L As. Cholinesterase (ChE) activity was significantly diminished by As acute exposure (0.5-1.5 mg/L As), indicative of a significant neurotoxic action for this metalloid in both amphipod populations. Activities of catalase (CAT) and glutathione S-transferase (GST) and levels of reduced glutathione (GSH) were differentially altered following As exposure. CAT activity was increased after 96 hr As exposure. GST activity and GSH levels were significantly elevated followed by either a decrease or a return to control values after 96 hr treatment. However, additional studies are necessary to understand the mechanisms underlying the As-mediated oxidative effects in H. curvispina. Our findings suggest that measurement of ChE activity in H. curvispina amphipods might serve as a useful biomarker of As exposure and effect.

OUP accepted manuscript

Although arsenic (As) is a persistent contaminant in the environment, few studies have assessed its effects over generations, as it requires an animal model with a short lifespan and rapid development, such as the nematode Caenorhabditis elegans. Furthermore, few studies have evaluated the effects of As metabolites such as dimethylarsinic acid (DMA^V), and several authors have considered DMA as a moderately toxic intermediate of As, although recent studies have shown that this chemical form can be more toxic than inorganic arsenic (iAs) even at low concentrations. In the present study, we compared the toxic effects of arsenate (As^V) and DMA^V in C. elegans over 5 subsequent generations. We evaluated biochemical parameters such as reactive oxygen species (ROS) concentration, the activity of antioxidant defense system (ADS) enzymes such as catalase (CAT) and glutathione-S-transferase (GST), and nonenzymatic components of ADS such as reduced glutathione (GSH) and protein-sulfhydryl groups (P-SH). Exposure to 50 μg L^-1 of As^V led to an increase in ROS generation and GSH levels together with a decrease in GST activity, while exposure to DMA^V led to an increase in ROS levels, with an increase in lipid peroxidation, CAT activity, and a decrease in GSH levels. In addition, both treatments reduced animal growth from the third generation onward and caused disturbances in their reproduction throughout all 5 generations. This study shows that the accumulated effects of DMA need to be considered; it highlights the importance of this type of multigenerational approach for evaluating the effects of organic contaminants considered low or nontoxic.

The freshwater water flea Daphnia magna NIES strain genome as a resource for CRISPR/Cas9 gene targeting: The glutathione S-transferase omega 2 gene

The water flea Daphnia magna is a small freshwater planktonic animal in the Cladocera. In this study, we assembled the genome of the D. magna NIES strain, which is widely used for gene targeting but has no reported genome. We used the long-read sequenced data of the Oxford nanopore sequencing tool for assembly. Using 3,231 genetic markers, the draft genome of the D. magna NIES strain was built into ten linkage groups (LGs) with 483 unanchored contigs, comprising a genome size of 173.47 Mb. The N50 value of the genome was 12.54 Mb and the benchmarking universal single-copy ortholog value was 98.8%. Repeat elements in the D. magna NIES genome were 40.8%, which was larger than other Daphnia spp. In the D. magna NIES genome, 15,684 genes were functionally annotated. To assess the genome of the D. magna NIES strain for CRISPR/Cas9 gene targeting, we selected glutathione S-transferase omega 2 (GST-O2), which is an important gene for the biotransformation of arsenic in aquatic organisms, and targeted it with an efficient make-up (25.0%) of mutant lines. In addition, we measured reactive oxygen species and antioxidant enzymatic activity between wild type and a mutant of the GST-O2 targeted D. magna NIES strain in response to arsenic. In this study, we present the genome of the D. magna NIES strain using GST-O2 as an example of gene targeting, which will contribute to the construction of deletion mutants by CRISPR/Cas9 technology.

Interactions with Arsenic: Mechanisms of Toxicity and Cellular Resistance in Eukaryotic Microorganisms

Arsenic (As) is quite an abundant metalloid, with ancient origin and ubiquitous distribution, which represents a severe environmental risk and a global problem for public health. Microbial exposure to As compounds in the environment has happened since the beginning of time. Selective pressure has induced the evolution of various genetic systems conferring useful capacities in many microorganisms to detoxify and even use arsenic, as an energy source. This review summarizes the microbial impact of the As biogeochemical cycle. Moreover, the poorly known adverse effects of this element on eukaryotic microbes, as well as the As uptake and detoxification mechanisms developed by yeast and protists, are discussed. Finally, an outlook of As microbial remediation makes evident the knowledge gaps and the necessity of new approaches to mitigate this environmental challenge.

Comparison of the Proximate Composition and Nutritional Profile of Byproducts and Edible Parts of Five Species of Shrimp

The nutritional components of different parts (meat, head, shell and tail) of Litopenaeus vannamei (L.v), Macrobrachium rosenbergii (M.r), Penaeus monodon (P.m), Fenneropenaeus chinensis (F.c), and Penaeus japonicus (P.j) were analyzed and their nutritional values were evaluated. For the five species of shrimp, the meat yield was 37.47–55.94%, and the byproduct yield was 44.06–62.53%. The meat yields of L.v and F.c were the highest (55.94 and 55.92%, respectively), and the meat yield of M.r was the lowest (37.47%). The shrimp contain high amounts of crude protein, and the values of the amino acid score (AAS), chemical score (CS), and essential amino index (EAAI) were greater than or close to 1.00, indicating that shrimp protein had higher nutritional value. The shrimp head was rich in polyunsaturated fatty acids and the ratio of n-6 to n-3 PUFAs was from 0.37 to 1.68, indicating that the shrimp head is rich in n-3 PUFAs and is a good source of n-3 PUFAs. The five species of shrimp were rich in macro- and micro-minerals, especially in shrimp byproducts. The shrimp byproducts were also rich in other bioactive ingredients (astaxanthin), which are also very valuable for developing biological resources. Therefore, shrimp have many nutritional benefits, and their byproducts can also be used to develop natural nutraceuticals, which are considered to be one of the healthiest foods.

Enhanced Bioaccumulation and Toxicity of Arsenic in Marine Mussel Perna viridis in the Presence of CuO/Fe3O4 Nanoparticles

Leakage of metal oxide nanoparticles (MNPs) into marine environments is inevitable with the increasing use of MNPs. However, little is known about the effects of these lately emerged MNPs on the bioaccumulation and toxicity of pre-existing contaminants in marine biota. The current study therefore investigated the effects of two common MNPs, CuO nanoparticles (nCuO) and Fe₃O₄ nanoparticles (nFe₃O₄), on bioaccumulation and toxicity of arsenic (As) in green mussel Perna viridis. Newly introduced MNPs remarkably promoted the accumulation of As and disrupted the As distribution in mussels because of the strong adsorption of As onto MNPs. Moreover, MNPs enhanced the toxicity of As by disturbing osmoregulation in mussels, which could be supported by decreased activity of Na⁺-K⁺-ATPase and average weight loss of mussels after MNPs exposure. In addition, the enhanced toxicity of As in mussels might be due to that MNPs reduced the biotransformation efficiency of more toxic inorganic As to less toxic organic As, showing an inhibitory effect on As detoxifying process of mussels. This could be further demonstrated by the overproduction of reactive oxygen species (ROS), as implied by the rise in quantities of superoxide dismutase (SOD) and lipid peroxidation (LPO), and subsequently restraining the glutathione-S-transferases (GST) activity and glutathione (GSH) content in mussels. Taken together, this study elucidated that MNPs may elevate As bioaccumulation and limit As biotransformation in mussels, which would result in an enhanced ecotoxicity of As towards marine organisms.