Uptake and biotransformation of arsenate in the lichen Hypogymnia physodes (L.) Nyl

Biotransformation and detoxification mechanism of inorganic arsenic in a freshwater benthic fish Tachysurus fulvidraco with dietborne exposure

Inorganic arsenic (iAs) is a pervasive environmental toxin, its metabolism and detoxification mechanism in freshwater benthic fish under dietary exposure remain unknown. In this study, dietborne exposure of two iAs (arsenate (AsV) and arsenite (AsIII)) was conducted for yellow catfish (Tachysurus fulvidraco) to investigate the bioaccumulation, biotransformation, and detoxification of iAs in the fish liver. The results showed that As significantly accumulated in both the AsIII and AsV treatments compared to the control, and the final As concentration was comparable for both treatments. The detoxification of iAs in freshwater fish depends on the degree of arsenic methylation and the level of antioxidants. Both reduction processes of AsV to AsIII and oxidation processes of AsIII to AsV were found in AsV and AsIII treatments. The major-low toxicity intermediates, which also are detoxification products in the AsIII treatment, were pentavalent dimethylarsinic acid and arsenobetaine (AsB), and AsB was major-low toxicity intermediate in the AsV treatment. Both antioxidants glutathione and glutathione S-transferase contribute to the detoxification of iAs by scavenging excessive reactive oxygen species and promoting iAs methylation in yellow catfish under iAs exposure.

Towards understanding the effect of heavy metals on mycobiont physiological condition in a widespread metal-tolerant lichen Cladonia rei

Heavy metals present in the environment can cause a variety of injury symptoms in various organisms including lichens. Most studies examined metal-induced stress under controlled laboratory conditions, and little is known about actual response of lichens in their natural habitat. This study aims to recognize the effect of heavy metal accumulation (total and intracellular) on lichen physiological and biochemical parameters specifically related to the functioning of fungal component. Cladonia rei was used as a model species due to its common occurrence both in unpolluted and extremely polluted sites. We observed a decline in the fungal metabolism which was expressed by a decrease in ergosterol content and an increase in cell membrane damage as a result of increased Zn, Cd, Cu and Ni accumulation. Additionally, the results indicated that increased accumulation of xenobiotics (Pb and As) caused reduction of glutathione (GSH) concentrations and increased membrane lipid peroxidation. Therefore, we conclude that GSH does not provide high oxidative stress protection in C. rei which is somewhat against its insensitivity to pollution. The reduced pool of GSH could be explained by its oxidation to glutathione disulphide induced by heavy metal stress or its use for phytochelatin (PC) synthesis. The content of secondary metabolites was not related to heavy metal accumulation and remained at a relatively stable level. This indicates that the decline in the physiological condition did not weaken the mycobiont of C. rei enough to inhibit the synthesis of secondary metabolites and their precursors were supplied at a sufficient level. Thus, the potential function of main secondary metabolites as extracellular metal immobilizers and antioxidants is still possible even in individuals growing at extremely polluted sites. Despite the evident heavy metal stress, C. rei copes well and spreads easily through extremely polluted environments, which underlines its unique pioneering abilities in highly disturbed sites.

Bioaccumulation and biotransformation of inorganic arsenic in zhikong scallop (Chlamys farreri) after waterborne exposure

Arsenic (As) and As speciation in marine bivalves have been widely investigated. However, little is known about the bioaccumulation and biotransformation of inorganic As in different tissues of scallops. Therefore, the tissue-specific accumulation, biotransformation and subcellular partitioning of As were investigated in Chlamys farreri following 12 d inorganic As [arsenite (AsⅢ) and arsenate (AsⅤ)] exposure and 30 d depuration. Total As levels were highest in the kidneys and lowest in the adductor muscle after 12 d exposure for both As (Ⅲ) and As (Ⅴ) treatment groups, and the bioavailability of As (Ⅲ) was significantly higher than that of As (Ⅴ) for C. farreri. After 30 d elimination, total As levels were significantly decreased to the control levels. The subcellular fate of As in five different tissues was similar for different inorganic As treatment groups. The greatest proportion of As was found in the metallothionein-like protein fraction (MTLP) and the second was the cellular debris (CD). A little part of As (Ⅲ) could be oxidized to As (Ⅴ) in the gill and digestive gland for As (Ⅲ) treatment groups, and the reduction of As (Ⅴ) to As (Ⅲ) happened in the gill and kidney under As (Ⅴ) exposure. Although a high methylation activity was found in C. farreri, it varied in different tissues with different inorganic As species exposure. The present results indicated that exposure to As (Ⅲ) and As (Ⅴ) could induce different responses in bioaccumulation and biotransformation in five tissues of C. farreri.

Histopathological examination and transcriptome analyses to assess the acute toxic effects of arsenite exposure on rare minnows (Gobiocypris rarus)

Arsenic is ubiquitously present in the aquatic environment. We investigated the acute toxic effects of arsenite [As(III)] exposure on rare minnows (Gobiocypris rarus) in vivo. The 96-h LC₅₀ value for exposure to As(III) was 13.73 mg/L. As(III) bioaccumulation in different tissues was measured using inductively-coupled plasma mass spectrometry, and the extent of As(III) accumulation was, from greatest to least, liver > intestine > gills > muscle > kidney > testis > brain. Histological examination revealed that in As(III)-treated fish, numerous cellular and tissue alterations were present in the gill, liver, and intestine tissues. Moreover, transmission electron microscopy showed ultrastructural alterations in hepatocytes. We also performed transcriptome analyses to investigate As(III)-induced toxicity response in the liver of As(III)-treated fish; various oxidative-related genes were differentially expressed, and their expression levels were further validated using qPCR. This study is one of the many steps we aim to take on the way to promote the rare minnow to an international standard laboratory animal.

Biotransformation of dietary inorganic arsenic in a freshwater fish Carassius auratus and the unique association between arsenic dimethylation and oxidative damage

The metabolic process and toxicity mechanism of dietary inorganic arsenic (iAs) in freshwater fish remain unclear to date. The present study conducted two iAs [arsenate (As(V)) and arsenite (As(III))] dietary exposures in freshwater fish crucian carp (Carassius auratus). The fish were fed on As supplemented artificial diets at nominal concentrations of 50 and 100 μg As(III) or As(V) g^-1 (dry weight) for 10 d and 20 d. We found that the liver, kidney, spleen, and intestine of fish accumulated more As in As(V) feeding group than that in As(III), while the total As levels in muscle were similar between As(V) and As(III) group at the end of exposure. Reduction of As(V) to As(III) and oxidation of As(III) to As(V) occurred in fish fed with As(V) and As(III), respectively, indicating that toxicity of iAs was likely elevated or reduced when iAs was absorbed by fish before entering into human body through diet. Biomethylation to monomethylarsonic acid and dimethylarsinic acid and transformation to arsenocholine and arsenobetaine were also found in the fish. The linear regression analysis showed a positive correlation between secondary methylation index and the malondialdehyde content in tissues, highlighting the vital role of arsenic dimethylation in the oxidative damages in fish.

Optimized extraction of inorganic arsenic species from a foliose lichen biomonitor

To assess the two most toxicologically relevant species of As, namely arsenite (As(III)) and arsenate (As(V)), chromatographic separations often require two separate chromatographic columns to address the co-elution of arsenobetaine (AsB) with As(III). This issue is typically observed using conventional isocratic methods on anion exchange columns, increasing cost and analysis time. Here, we optimize the extraction of inorganic As from a lichen air biomonitor and develop an isocratic method for the chromatographic separation of five common As species on a PRP X-100 anion exchange column, resulting in the complete baseline separation of all species under study. This method was then applied to lichen biomonitors from an urban and rural site to demonstrate its use. In order of abundance, the various arsenic species in lichens from the urban site in South Africa were As(V) > As(III) > AsB > dimethylarsinic acid (DMA) > monomethylarsonic acid (MMA), and As(V) > AsB > As(III) > DMA > MMA for the rural site, where MMA was present in extremely low, non-quantifiable concentrations in lichens from both sites. Total concentrations of As were higher in samples from the urban site (6.43 ± 0.25 μg/g) than in those from the rural site (1.87 ± 0.05 μg/g), with an overall extraction efficiency of 19% and 40%, respectively. The optimized method utilized relatively inexpensive solvents and is therefore low-cost and eco-friendly in comparison with conventional chromatographic techniques. This is the first study which addresses the optimized extraction and characterization of As species in a South African lichen biomonitor of air pollution. Graphical abstract .

Adaptions of Lichen Microbiota Functioning Under Persistent Exposure to Arsenic Contamination

Host-associated microbiota play an important role in the health and persistence of more complex organisms. In this study, metagenomic analyses were used to reveal microbial community adaptations in three lichen samples as a response to different arsenic concentrations at the sampling sites. Elevated arsenic concentrations at a former mining site expanded the spectrum and number of relevant functions in the lichen-associated microorganisms. Apparent changes affected the abundance of numerous detoxification-related genes, they were substantially enhanced in arsenic-polluted samples. Complementary quantifications of the arsenite S-adenosylmethionine methyltransferase (arsM) gene showed that its abundance is not strictly responding to the environmental arsenic concentrations. The analyzed samples contained rather low numbers of the arsM gene with a maximum of 202 gene copies μl^-1 in total community DNA extracts. In addition, bacterial isolates were screened for the presence of arsM. Positive isolates were exposed to different As(III) and As(V) concentrations and tolerated up to 30 mM inorganic arsenic in fluid media, while no substantial biotransformations were observed. Obtained data deepens our understanding related to adaptions of whole microbial communities to adverse environmental conditions. Moreover, this study provides the first evidence that the integrity of bacteria in the lichen holobiont is maintained by acquisition of specific resistances.

Arsenic biokinetics and bioavailability in deposit-feeding clams and polychaetes

In the present study, the arsenic (As) biokinetics and bioavailability in two deposit-feeding invertebrates (clams Gafrarium tumidum and polychaetes Nereis succinea) were quantified. Radiotracer techniques were applied to measure the dissolved uptake rate, dietary assimilation efficiency and efflux of As by the clams and polychaetes. Simultaneously, arsenic species analysis was conducted to examine the As biotransformation following dietary uptake. The radiotracer results showed that the uptake rate constant and efflux rate constant were 0.068L/g/d and 0.07d^-1, and 0.173L/g/d and 0.09d^-1, in the clams and polychaetes, respectively. Sediments labeled for different times (1.5-60 d) with different inorganic/organic As percentages led to diverse assimilation efficiencies of As (35.1-56.1% in the clams, and 51.6-72.6% in the polychaetes). Modeling calculations showed that sediment was a significant source for As bioaccumulation in the two deposit-feeders. After feeding on the spiked sediments, inorganic As (75.6%) was initially the predominant form, but arsenobetaine (AsB) became the predominant compound (>90%) in the clams and polychaetes during depuration, suggesting biotransformation of inorganic As. Combined with the biokinetics and biotransformation measurements, we showed that AsB was more efficiently assimilated and tended to be accumulated, whereas As(III) was less efficiently assimilated and more rapidly eliminated by the two invertebrates. This study demonstrated that As speciation in the sediments as a significant source for As bioaccumulation caused different bioavailability in deposit-feeding clams and polychaetes.

Biotransformation of inorganic arsenic in a marine herbivorous fish Siganus fuscescens after dietborne exposure

Arsenic (As) is well known to be biodiminished along marine food chains. The marine herbivorous fish at a lower trophic level are expected to accumulate more As. However, little is known about how marine herbivorous fish biotransform the potential high As bioaccumulation. Therefore, the present study quantified the biotransformation of two inorganic As species (As(III) and As(V)) in a marine herbivorous fish Siganus fuscescens following dietborne exposure. The fish were fed on As contaminated artificial diets at nominal concentrations of 400 and 1500 μg As(III) or As(V) g(-1) (dry weight) for 21 d and 42 d. After exposure, As concentrations in intestine, liver, and muscle tissues of rabbitfish increased significantly and were proportional to the inorganic As exposure concentrations. The present study demonstrated that both inorganic As(III) and As(V) in the dietborne phases were able to be biotransformed to the less toxic arsenobetaine (AsB) (63.3-91.3% in liver; 79.0%-95.2% in muscle). The processes of As biotransformation in rabbitfish could include oxidation of As(III) to As(V), reduction of As(V) to As(III), methylation to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), and subsequent conversion to AsB. These results also demonstrated that AsB synthesis processes were diverse facing different inorganic As species in different tissues. In summary, the present study elucidated that marine herbivorous fish had high ability to biotransform inorganic As to the organic forms (mainly AsB), resulting in high As bioaccumulation. Therefore, marine herbivorous fish could detoxify inorganic As in the natural environment.

Biotransformation and detoxification of inorganic arsenic in Bombay oyster Saccostrea cucullata

Arsenic (As) exists as the toxic inorganic forms in marine water and sediment, while marine oysters usually accumulate high As contents mostly as the less toxic organic forms. It has not yet been clear that how As is biotransformed in marine oysters. This study therefore investigated the biotransformation and detoxification of two inorganic As forms (As(III) and As(V)) in Bombay oyster Saccostrea cucullata after waterborne exposures for 30 days. Seven treatments of dissolved As exposure (clean seawater, 1, 5, 20 mg/L As(III), and 1, 5, 20 mg/L As(V)) were performed. Body As concentration increased significantly after all As exposure treatments except 1mg/L As(V). Total As, As(III), and As(V) concentration were positive correlated with glutathione-S-transferases (GST) activities, suggesting GST might play an important role in the As biotransformation and detoxification process. Organic As species were predominant in control and the low As exposed oysters, whereas a large fraction of As was remained as the inorganic forms in the high As exposed oysters, suggesting As could be biotransformed efficiently in the oysters in clean or light contaminated environment. The results of As speciation demonstrated the As biotransformation in the oysters included As(V) reduction, methylation to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), and subsequent conversion to arsenobetaine (AsB). More As was distributed in the subcellular metallothionein-like proteins fraction (MTLP) functioning sequestration and detoxification in the inorganic As exposed oysters, suggesting it was also a strategy for oysters against As stress. In summary, this study elucidated that marine oysters had high ability to accumulate, biotransform, and detoxify inorganic As.

Biovolatilisation: a poorly studied pathway of the arsenic biogeochemical cycle

It has been known for over a hundred years that microorganisms can produce volatile arsenic (As) species, termed "arsines". However, this topic has received relatively little attention compared to As behaviour in soils and biotransformation through the trophic level in the marine and terrestrial environment. We believe this is due to long-standing misconceptions regarding volatile As stability and transport as well as an absence, until recently, of appropriate sampling methods. First and foremost, an attempt is made to unify arsines' designations, notations and formulas, taking into account all the different terms used in the literature. Then, the stability of As volatile species is discussed and new analytical developments are explored. Further, the special cases of diffuse low-level emissions (e.g. soil and sediment biovolatilisation), and point sources with high-level emissions (geothermal environments, landfills, and natural gas) are comprehensively reviewed. In each case, future possible areas of research and unknown mechanisms are identified and their importance towards the global As biogeochemical cycle is explored. This review gathers new information regarding mechanisms, stability, transport and sampling of the very elusive arsines and shows that more research should be conducted on this important process.

Biotransformation and detoxification of inorganic arsenic in a marine juvenile fish Terapon jarbua after waterborne and dietborne exposure

Arsenic (As) is a major hazardous metalloid in many aquatic environments. This study quantified the biotransformation of two inorganic As species [As(III) and As(V)] in a marine juvenile grunt Terapon jarbua following waterborne and dietborne exposures for 10d. The fish were fed As contaminated artificial diets at nominal concentrations of 50, 150, and 500μg As(III) and As(V)/g (dry weight), and their transformation and growth responses were compared to those exposed to 100μg/L waterborne As(III) and As(V). Within the 10d exposure period, waterborne and dietborne inorganic As exposure had no significant effect on the fish growth performance. The bioaccumulation of As was very low and not proportional to the inorganic As exposure concentration. We demonstrated that both inorganic As(III) and As(V) in the dietborne and waterborne phases were rapidly biotransformed to the less toxic arsenobetaine (AsB, 89-97%). After exposure to inorganic As, T. jarbua developed correspondingly detoxified strategies, such as the reduction of As(V) to As(III) followed by methylation to less toxic organic forms, as well as the synthesis of metal-binding proteins such as metallothionein-like proteins. This study elucidated that As(III) and As(V) had little potential toxicity on marine fish.

Physiological effects of arsenate on transplant thalli of the lichen Pyxine cocoes (Sw.) Nyl

INTRODUCTION

The changes in photosynthetic pigments, chlorophyll fluorescence, protein content, and antioxidant enzymes were investigated in a foliose lichen Pyxine cocoes, which was subjected to increasing concentrations of arsenate.

METHODS

The arsenate concentrations of 10, 25, 50, 75, 100, and 200 μM were sprayed every alternate day on the lichen thallus. The thalli were then harvested on 10, 20, 30, and 45 days.

RESULTS

The quantity of photosynthetic pigments exhibited a decreasing trend till 20 days but increased from 30 days onwards. Concomitantly, chlorophyll fluorescence also showed a decreasing trend with increasing arsenic treatment duration as well as concentration. The higher concentration of arsenate was found to be deleterious to the photosynthesis of lichen as the chlorophyll fluorescence and the amount of pigments decreased significantly. The protein content of lichen increased uninterruptedly as the concentration of arsenate as well as duration of treatment increased. The activities of superoxide dismutase and ascorbate peroxide increased initially at lower concentration of arsenate but declined at higher concentrations and longer duration of treatment.

CONCLUSIONS

The catalase activity was found to be most susceptible to arsenate stress as its activity started declining from very beginning of the experiment. P. cocoes also proved to be an excellent accumulator of arsenate whose concentration increased in the thallus corresponding to its increase in the treatment and duration. Thus, it can be utilized for active biomonitoring of arsenic pollution.

Accumulation, biotransformation, and biochemical responses after exposure to arsenite and arsenate in the estuarine polychaete Laeonereis acuta (Nereididae)

INTRODUCTION

This study aimed to analyze antioxidant responses and oxidative damage induced by two inorganic forms of arsenic (As; As(III) and As(V)) in an estuarine polychaete species, Laeonereis acuta (Nereididae). The capacity of arsenic biotransformation was also evaluated through the methylation process considering the activity of a key enzyme involved in the metabolization process.

MATERIALS AND METHODS

Worms were exposed to 50 μg (As(III) or As(V))/l during 2 or 7 days, plus a control group. Endpoints analyzed included concentration of reactive oxygen species (ROS), activities of antioxidant enzymes such as glutathione reductase (GR), total glutathione-S-transferase (GST), and omega isoform (GST Ω), glucose-6-phosphate deshydrogenase (G6PDH), levels of the antioxidant glutathione (GSH), and lipid peroxides concentration (TBARS).

RESULTS AND DISCUSSION

Results showed: (1) GR inhibition after 2-day exposure to both As forms (p < 0.05); (2) GST Ω inhibition after 7-day exposure to As(III) paralleled by an increase in total GST activity (p < 0.05); (3) augmented G6PDH activity after 7-day exposure to both As forms (p < 0.05); (4) no differences in terms of ROS and TBARS; and (5) inhibition of GST Ω activity in As(III) exposed worms, which was concomitant with a lowering of mono- and dymethylated arsenic species.

CONCLUSION

These results confirm the reactivity of some biochemical variables of L. acuta to As and indicates its importance as a sentinel species in estuarine regions with presence of arsenic.

Arsenic toxicity in mammals and aquatic animals: a comparative biochemical approach

Arsenic (As) is a widespread pollutant in the world and its toxicity is related to its chemical form, with inorganic forms being considered more toxic than the organic form, and huge differences in effects and processes of metabolism. This paper reviews the potential biochemical mechanisms of uptake of arsenic by aquaporins, capacity for metabolism and cellular efflux of As. It is known that As can affect signaling pathways since it can activate proteins such as ERK2, p38 and JNK, as shown in mammals. A comparison between phosphorylation sites of these proteins is presented in order to determine whether the same effect triggered by As in mammals might be observed in aquatic animals. The toxicity resulting from As exposure is considered to be linked to an imbalance between pro-oxidant and antioxidant homeostasis that results in oxidative stress. So, present review analyzes examples of oxidative stress generation by arsenic. Biotransformation of As is a process where firstly the arsenate is converted into arsenite and then transformed into mono-, di-, and trimethylated products. In the methylation process, the role of the omega isoform of glutathione-S-transferase (GST) is discussed. In addition, a phylogenetic tree was constructed for aquaporin proteins of different species, including aquatic animals, taking into account their importance in trivalent arsenic uptake.

Physiological effects of arsenic in the lichen Xanthoria parietina (L.) Th. Fr

The aim of this study was to test in a short term laboratory experiment the accumulation and physiological effects of As in the epiphytic lichen Xanthoria parietina. Arsenic content in treated samples increased progressively with increasing concentration in treatment solutions. Treatment of X. parietina thalli with 0.1, 1, 10 ppm As solutions caused significant decrease of viability, measured as intensity of respiratory activity, and damages to cell membranes, assessed by increase of electric conductivity of rinsing water and lipid peroxidation products. Soluble proteins content decreased and H₂O₂ content increased already at the lowest As concentration tested (0.01 ppm). Photosynthetic efficiency, measured in terms of F(V)/F(M) ratio, decreased significantly only at the highest As concentration (10 ppm). It was concluded that As exposure causes physiological stress both on the mycobiont and the photobiont and that cell membrane damage, expressed in terms of electric conductivity of rinsing water, is the parameter most affected by As treatment.

Biological responses of duckweed (Lemna minor L.) exposed to the inorganic arsenic species As(III) and As(V): effects of concentration and duration of exposure

The accumulation of arsenic (As) and physiological responses of Lemna minor L. under different concentration (0, 1, 4, 16 and 64 microM) and duration (1, 2, 4 and 6 days) of two species As, NaAsO(2) and Na(2)HAsO(4).7H(2)O, were studied in hydroponics. The accumulation of both As species depended on As concentration and exposure duration. The highest accumulation of As was found as 17408 and 8674 microg g(-1), for plants exposed to 64 microM of As(III) and As(V), respectively, after 6 days. Two-way ANOVA analyses indicated that, for plants exposed to arsenite (As(III)), exposure duration had a greater effect than concentration on As accumulation. Conversely, exposure concentration had a greater effect on As accumulation in plants exposed to arsenate (As(V)). Arsenic exposure levels, approaching 16 microM for As(III) and 64 microM for As(V), did not significantly affect EC values. Beyond these exposure concentrations, EC values increased in a manner that depended on duration. Significant effect of As(III) on lipid peroxidation was observed at 1 microM application whereas, this effect started to be significant after an exposure to 16 microM As(V). For both As(III) and As(V), photosynthetic pigment levels slightly increased for the first day with respect to the control, followed by a gradual decline at higher concentrations and durations. An increase in protein content and enzyme activity was observed at moderate exposure conditions, followed by a decrease. Significant positive correlations were determined between accumulated As and ion leakage and lipid peroxidation. Negative correlations were found between accumulated As and total chlorophyll and protein content. Our results suggested that exposure duration and concentration had a strong synergetic effect on antioxidant enzyme activity. The findings of the present study may be useful when this plant is used as a phytoremediator in arsenic-polluted water.