Biomethylation of Arsenic in an Arsenic-rich Freshwater Environment

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.

Arsenic speciation and biotransformation pathways in the aquatic ecosystem: The significance of algae

The contamination of aquatic systems with arsenic (As) is considered to be an internationally-important health and environmental issue, affecting over 115 countries globally. Arsenic contamination of aquatic ecosystems is a global threat as it can enter the food chain from As-rich water and cause harmful impacts on the humans and other living organisms. Although different factors (e.g., pH, redox potential, iron/manganese oxides, and microbes) control As biogeochemical cycling and speciation in water systems, the significance of algal species in biotransformation of As is poorly understood. The overarching attribute of this review is to briefly elaborate various As sources and its distribution in water bodies and factors affecting As biogeochemical behavior in aqueous ecosystems. This review elucidates the intriguing role of algae in biotransformation/volatilization of As in water bodies under environmentally-relevant conditions. Also, we critically delineate As sorption, uptake, oxidation and reduction pathways of As by algae and their possible role in bioremediation of As-contaminated water (e.g., drinking water, wastewater). The current review provides the updated and useful framework for government and water treatment agencies to implement algae in As remediation programs globally.

Biotic and Abiotic Factors Influencing Arsenic Biogeochemistry and Toxicity in Fluvial Ecosystems: A Review

This review is focused on the biogeochemistry of arsenic in freshwaters and, especially, on the key role that benthic microalgae and prokaryotic communities from biofilms play together in through speciation, distribution, and cycling. These microorganisms incorporate the dominant iAs (inorganic arsenic) form and may transform it to other arsenic forms through metabolic or detoxifying processes. These transformations have a big impact on the environmental behavior of arsenic because different chemical forms exhibit differences in mobility and toxicity. Moreover, exposure to toxicants may alter the physiology and structure of biofilms, leading to changes in ecosystem function and trophic relations. In this review we also explain how microorganisms (i.e., biofilms) can influence the effects of arsenic exposure on other key constituents of aquatic ecosystems such as fish. At the end, we present two real cases of fluvial systems with different origins of arsenic exposure (natural vs. anthropogenic) that have improved our comprehension of arsenic biogeochemistry and toxicity in freshwaters, the Pampean streams (Argentina) and the Anllóns River (Galicia, Spain). We finish with a briefly discussion of what we consider as future research needs on this topic. This work especially contributes to the general understanding of biofilms influencing arsenic biogeochemistry and highlights the strong impact of nutrient availability on arsenic toxicity for freshwater (micro) organisms.

Influence of titanium dioxide nanoparticles on the toxicity of arsenate in Nannochloropsis maritima

Interest is growing in the role that nanoparticles play in modifying the biological effects of contaminants. This study aimed to determine whether nano-TiO₂ exhibited pronounced influence on arsenate (As(V)) toxicity levels to the marine microalgae Nannochloropsis maritima. We compared individual and combined toxicity levels of As(V) and nano-TiO₂ by assessing the inhibition percentages of algal growth. Compared to groups treated with As(V) alone, an EC₅₀ of 53.0 mg/L decreased by 28.8% after the addition of nanoparticles. This enhanced toxicity was attributed to the inhibition of As methylation and the promotion of lipid peroxidation in the presence of nano-TiO₂. Additionally, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) also showed that algal cells exhibited different degrees of shrinkage, that cell wall were destroyed in the process, and that the photosynthetic apparatus was virtually indiscernible after the addition of nano-TiO₂. In addition, for low As(V) concentration exposure groups, nano-TiO₂ could alleviate As(V) toxicity to some extent by reducing As sorption onto algal cells and subcellular distribution in organelles, but this alleviation effect could not protect against the combined toxicity (both As(V) and nano-TiO₂) effect on N. maritima, which was verified by the higher inhibition percentage of the algal growth rate in the combined exposure group treatment compared to the As(V) exposure treatment alone. Our results suggest that more attention must be paid to the potential impact of nanoparticles on the bioavailability and biotransformation of contaminants in phytoplankton.

Increased exposure of plankton to arsenic in contaminated weakly-stratified lakes

Arsenic, a priority Superfund contaminant and carcinogen, is a legacy pollutant impacting aquatic ecosystems in urban lakes downwind of the former ASARCO copper smelter in Ruston, WA, now a Superfund site. We examined the mobility of arsenic from contaminated sediments and arsenic bioaccumulation in phytoplankton and zooplankton in lakes with varying mixing regimes. In lakes with strong seasonal thermal stratification, high aqueous arsenic concentrations were limited to anoxic bottom waters that formed during summer stratification, and arsenic concentrations were low in oxic surface waters. However, in weakly-stratified lakes, the entire water column, including the fully oxic surface waters, had elevated concentrations of arsenic (up to 30μgL-1) during the summer. We found enhanced trophic transfer of arsenic through the base of the aquatic food web in weakly-stratified lakes; plankton in these lakes accumulated up to an order of magnitude more arsenic on multiple sampling days than plankton in stratified lakes with similar levels of contamination. We posit that greater bioaccumulation in weakly-stratified lakes was due to elevated arsenic in oxic waters. Aquatic life primarily inhabits oxic waters and in the oxic water column of weakly-stratified lakes arsenic was speciated as arsenate, which is readily taken up by phytoplankton because of its structural similarities to phosphate. Our study indicates that mobilization of arsenic from lake sediments into overlying oxic water columns in weakly-stratified lakes leads to increased arsenic exposure and uptake at the base of the aquatic food web.

Arsenic Speciation in Organisms from two Large Shallow Freshwater Lakes in China

This study measured the elemental and species concentrations of arsenic (As) in the water, sediments and food webs of two shallow Chinese freshwater lakes. Organic As species were widely detected in various organisms from the two lakes (60%-100% of the total). Among these organisms, dimethylarsinic acid (DMA) was predominant in most of the samples. The average concentrations and corresponding proportions were 0.59 mg/kg, 81% in fish; 3.24 mg/kg, 70.63% in zoobenthos; and 1.34 mg/kg, 79% in plants. The average concentrations and corresponding proportions of monomethylarsonic acid (MMA) and inorganic As were much lower, ranging from n.d. (not detected) to 1.94 mg/kg and from n.d. to 1.54 mg/kg, with an average proportion of 14 and 7.4%, respectively. In Lake Taihu, the mean As concentrations in different fish tissues were generally low and in the following order: eggs (0.47) < skin (0.62) < muscles (0.91) < gills (1.65) < livers (5.47) mg/kg. DMA occupied 75%-100% of the total As species, while MMA and inorganic As were much less prevalent.

Induction of Aneuploidy, Centrosome Abnormality, Multipolar Spindle, and Multipolar Division in Cultured Mammalian Cells Exposed to an Arsenic Metabolite, Dimethylarsinate

Toxicological studies of arsenic compounds were conducted in cultured mammalian cells to investigate the effects of glutathione (GSH) depletion. Dimethylarsinate DMA(V) was not cytotoxic in cells depleted of GSH, but was found to be cytotoxic when GSH was present outside the cells. The results suggested that a reactive form of DMA(V) was generated through interaction with GSH. Dimethylarsine iodide DMI(III) was used as a model compound of DMA(III), and the biological effects were investigated. DMI(III) was about 10000 times more toxic to the cells than DMA(V). Chromosome structural aberrations and numerical changes, such as aneuploidy, were induced by DMI(III). DMA(V) induced multiple foci of the centrosome protein, γ-tubulin, which were colocalized with multipolar spindles in mitotic cells. The multiple foci coalesced into a single dot on disruption of the microtubules (MT). However, reorganization of the MT caused multiple foci of γ-tubulin, suggesting that the induction of centrosome abnormalities by DMA(V) required intact MT. Inhibition of the MT-dependent motor, kinesin, prevented formation of multiple foci of γ-tubulin, which pointed to the involvement of the MT-dependent mitotic motor, kinesin, in the maintenance of centrosome abnormalities. DMI(III) caused abnormal cytokinesis (multipolar division). In addition, DMI(III) caused morphological transformation in Syrian hamster embryo cells. Consideration of the overall process following the centrosome abnormalities caused by DMA(V) suggested a mode of cytotoxicity in which the mitotic centrosome is a critical target.

Environmental concerns of roxarsone in broiler poultry feed and litter in Maryland, USA

Roxarsone has been used extensively in the broiler chicken industry. We reviewed the environmental concerns of this usage. To summarize, arsenic added to poultry feed as roxarsone ends up in poultry litter. Fresh litter contains predominately roxarsone, whereas aged litter contains predominately inorganic arsenic. Soil arsenic concentrations from long-term poultry litter applications can exceed Maryland arsenic soil background remediation standards. Due to continued soil accumulation, arsenic-amended litter use as fertilizer is thought to be unsustainable. Surface-applied roxarsone-amended litter does not influence deep aquifer arsenic concentrations but is transported as inorganic arsenic to receiving waters and very shallow groundwater after precipitation. Arsenic in some receiving waters and sediments from agriculturally dominated watersheds have levels above established criteria. Arsenic in fish and shellfish is mostly organic. Phosphorus-based nutrient management will tend to limit PL application rates in areas that have over-applied phosphorus relative to crop needs, resulting in decreased rates of arsenic application and accumulation. Despite most arsenic in surface soils being tightly bound, as surface soils become more enriched in arsenic, the potential for downward movement increases but is limited in most soils due to the high capacity for binding of arsenic to clay minerals and oxides of iron and aluminum in subsoil horizons. In 2012, Maryland passed a law banning the use of arsenic additives except nitarsone in poultry feed. In 2013, the USFDA withdrew approval of roxarsone, carbarsone, and arsanilic but is reviewing nitarsone.

Arsenic efflux from Microcystis aeruginosa under different phosphate regimes

Phytoplankton plays an important role in arsenic speciation, distribution, and cycling in freshwater environments. Little information, however, is available on arsenic efflux from the cyanobacteria Microcystis aeruginosa under different phosphate regimes. This study investigated M. aeruginosa arsenic efflux and speciation by pre-exposing it to 10 µM arsenate or arsenite for 24 h during limited (12 h) and extended (13 d) depuration periods under phosphate enriched (+P) and phosphate depleted (−P) treatments. Arsenate was the predominant species detected in algal cells throughout the depuration period while arsenite only accounted for no greater than 45% of intracellular arsenic. During the limited depuration period, arsenic efflux occurred rapidly and only arsenate was detected in solutions. During the extended depuration period, however, arsenate and dimethylarsinic acid (DMA) were found to be the two predominant arsenic species detected in solutions under −P treatments, but arsenate was the only species detected under +P treatments. Experimental results also suggest that phosphorus has a significant effect in accelerating arsenic efflux and promoting arsenite bio-oxidation in M. aeruginosa. Furthermore, phosphorus depletion can reduce arsenic efflux from algal cells as well as accelerate arsenic reduction and methylation. These findings can contribute to our understanding of arsenic biogeochemistry in aquatic environments and its potential environmental risks under different phosphorus levels.

Is arsenic biotransformation a detoxification mechanism for microorganisms?

Arsenic (As) is extremely toxic to living organisms at high concentration. In aquatic systems, As exists in different chemical forms. The two major inorganic As (iAs) species are As(V), which is thermodynamically stable in oxic waters, and As(III), which is predominant in anoxic conditions. Photosynthetic microorganisms (e.g., phytoplankton and cyanobacteria) take up As(V), biotransform it to As(III), then biomethylate it to methylarsenic (MetAs) forms. Although As(III) is more toxic than As(V), As(III) is much more easily excreted from the cells than As(V). Therefore, majority of researchers consider the reduction of As(V) to As(III) as a detoxification process. The biomethylation process results in the conversion of toxic iAs to the less toxic pentavalent MetAs forms (monomethylarsonate; MMA(V), dimethylarsonate; DMA(V), and trimethylarsenic oxide; TMAO(V)) and trimethylarsine (TMAO(III)). However, biomethylation by microorganisms also produces monomethylarsenite (MMA(III)) and dimethylarsenite (DMA(III)), which are more toxic than iAs, as a result of biomethylation by the microorganisms, demonstrates the need to reconsider to what extent As biomethylation contributes to a detoxification process. In this review, we focused on the discussion of whether the biotransformation of As species in microorganisms is really a detoxification process with recent data.

Bioaccumulation, biotransformation and trophic transfer of arsenic in the aquatic food chain

The occurrence, distribution, speciation, and biotransformation of arsenic in aquatic environment (marine and freshwater) have been studied extensively by several research groups during last couple of decades. However, most of those studies have been conducted in marine waters, and the results are available in a number of reviews. Speciation, bioaccumulation, and biotransformation of arsenic in freshwaters have been studied in recent years. Although inorganic arsenic (iAs) species dominates in both marine and freshwaters, it is biotransformed to methyl and organoarsenic species by aquatic organisms. Phytoplankton is considered as a major food source for the organisms of higher trophic levels in the aquatic food chain, and this autotrophic organism plays important role in biotransformation and distribution of arsenic species in the aquatic environment. Bioaccumulation and biotransformation of arsenic by phytoplankton, and trophic transfer of arsenic in marine and freshwater food chains have been important concerns because of possible human health effects of the toxic metalloid from dietary intake. To-date, most of the studies on arsenic biotransformation, speciation, and trophic transfer have focused on marine environments; little is known about these processes in freshwater systems. This article has been reviewed the bioaccumulation, biotransformation, and trophic transfer of arsenic in marine and freshwater food chain.

Arsenic speciation in plankton organisms from contaminated lakes: transformations at the base of the freshwater food chain

The two complementary techniques high performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) and X-ray absorption near edge structure (XANES) analysis were used to assess arsenic speciation in freshwater phytoplankton and zooplankton collected from arsenic-contaminated lakes in Yellowknife (Northwest Territories, Canada). Arsenic concentrations in lake water ranged from 7 μg L(-1) in a noncontaminated lake to 250 μg L(-1) in mine-contaminated lakes, which resulted in arsenic concentrations ranging from 7 to 340 mg kg(-1) d.w. in zooplankton organisms (Cyclops sp.) and from 154 to 894 mg kg(-1) d.w. in phytoplankton. The main arsenic compounds identified by HPLC-ICP-MS in all plankton were inorganic arsenic (from 38% to 98% of total arsenic). No other arsenic compounds were found in phytoplankton, but zooplankton organisms showed the presence of organoarsenic compounds, the most common being the sulfate arsenosugar, up to 47% of total arsenic, with traces of phosphate sugar, glycerol sugar, methylarsonate (MMA), and dimethylarsinate (DMA). In the uncontaminated Grace Lake, zooplankton also contained arsenobetaine (AB). XANES characterization of arsenic in the whole plankton samples showed As(V)-O as the only arsenic compound in phytoplankton, and As(III)-S and As(V)-O compounds as the two major inorganic arsenic species in zooplankton. The proportion of organoarsenicals and inorganic arsenic in zooplankton depends upon the arsenic concentration in lakes and shows the impact of arsenic contamination: zooplankton from uncontaminated lake has higher proportions of organoarsenic compounds and contains arsenobetaine, while zooplankton from contaminated area contains mostly inorganic arsenic.

On the potential of biological treatment for arsenic contaminated soils and groundwater

Bioremediation of arsenic contaminated soils and groundwater shows a great potential for future development due to its environmental compatibility and possible cost-effectiveness. It relies on microbial activity to remove, mobilize, and contain arsenic through sorption, biomethylation-demethylation, complexation, coprecipitation, and oxidation-reduction processes. This paper gives an evaluation on the feasibility of using biological methods for the remediation of arsenic contaminated soils and groundwater. Ex-situ bioleaching can effectively remove bulk arsenic from contaminated soils. Biostimulation such as addition of carbon sources and mineral nutrients can be applied to promote the leaching rate. Biosorption can be used either ex-situ or in-situ to remove arsenic from groundwater by sorption to biomass and/or coprecipitation with biogenic solids or sulfides. Introduction of proper biosorbents or microorganisms to produce active biosorbents in-situ is the key to the success of this method. Phytoremediation depends on arsenic-hyperaccumulating plants to remove arsenic from soils and shallow groundwater by translocating it into plant tissues. Engineering genetic strategies can be employed to increase the arsenic-hyperaccumulating capacity of the plants. Biovolatilization may be developed potentially as an ex-situ treatment technology. Further efforts are needed to focus on increasing the volatilization rate and the post-treatment of volatilization products.

Rapid determination of arsenic species in freshwater organisms from the arsenic-rich Hayakawa River in Japan using HPLC-ICP-MS

Speciation analyses of water-soluble arsenicals from freshwater and biological samples collected from the Hayakawa River (Kanagawa, Japan), which contains a high concentration of arsenic, were performed using high performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC-ICP-MS). River water contained only arsenate, which is a pentavalent inorganic arsenical. The water bug Stenopsyche marmorata contained inorganic arsenicals accounting for 77% of the water-soluble arsenicals, followed by oxo-arsenosugar-glycerol, which is a type of dimethylarsinoylriboside (arsenosugar). The freshwater green macroalga Cladophora glomerata contained oxo-arsenosugar-glycerol and oxo-arsenosugar-phosphate as 64% of the water-soluble arsenicals. Production of the same types of arsenosugars was confirmed in the freshwater green microalga Chlamydomonas reinhardtii CC125 experimentally exposed to arsenate. The muscle tissues of all freshwater fish and crustaceans analyzed contained arsenobetaine, oxo-arsenosugar-glycerol, and/or oxo-arsenosugar-phosphate in various concentrations. Seven freshwater fish (Cobitis biwae, Leuciscus hakonensis, Phoxinus lagowski steindachneri, Plecoglossus altivelis, Rhinogobius sp. CB, Rhinogobius sp. CO, Sicyopterus japonicus) and the crustacean Macrobracbium nipponenese contained arsenobetaine in their muscle tissues as the predominant form, contributing up to 80% of the water-soluble arsenicals, while the freshwater fish Anguilla japonica muscle tissues primarily contained dimethylarsinic acid as 77% of the water-soluble arsenicals, followed by arsenobetaine. The freshwater fish Zacco platypus muscle tissues predominantly contained oxo-arsenosugar-phosphate, accounting for 51% of the water-soluble arsenicals, followed by dimethylarsinic acid and arsenobetaine. These biological samples possessed non-extractable arsenical(s) accounting for more than 50% of the total arsenic concentration.

Arsenic concentration and speciation in five freshwater fish species from Back Bay near Yellowknife, NT, CANADA

The concentration of total arsenic and five different arsenic species [As(III), As(V), monomethylarsonic acid (MMA), dimethylarsenic acid (DMA), and arsenobetaine (AsB)], were measured in the muscle, liver and gastrointestinal tract (GIT) of five different fish species [lake whitefish (Coregonus clupeaformis), walleye (Stizostedion vitreum), northern pike (Esox lucius), white sucker (Catostomus commersoni) and longnose sucker (Catostomus catostomus)] from Back Bay, Great Slave Lake, near the city of Yellowknife, NT, Canada. The total concentration (dry weight) of arsenic in muscle ranged from 0.57 to 1.15 mg/kg, in the liver from 0.42 to 2.52 mg/kg and in the GIT from 1.48 to 8.92 mg/kg. Among fish species, C. commersoni had significantly higher total arsenic concentrations in the GIT than S. vitreum, E. lucius and C. clupeaformis, and higher total arsenic concentrations in the liver than C. clupeaformis. The mean concentration of As(III) and As(V) in the muscle of all fish ranged from < or =0.01 to 0.05 mg/kg and < or =0.01 to 0.02 mg/kg, respectively, and together comprised < or =7.5% of the total arsenic measured in muscle. The concentrations of MMA were below detection in the muscle of all five fish species. However, AsB and DMA were measured in all fish species and nearly all fish tissues. The concentrations of AsB ranged from 0.01 to 0.13 mg/kg and the concentrations of DMA ranged from <0.02 to 0.45 mg/kg. The majority (>50%) of organic arsenic in almost all of the tissues from fish caught in Back Bay was not directly identified. Evidence from the literature suggests that most of these other organic arsenic species were likely trimethylated arsenic compounds, however, further analytical work would need to be performed to verify this hypothesis.

Volatile arsenic species released from Escherichia coli expressing the AsIII S-adenosylmethionine methyltransferase gene

Biological systems, ranging from bacteria and fungi to humans, can methylate arsenic. Recent studies have suggested that the AsIII S-adenosylmethionine methyltransferase (arsM) gene in bacteria was responsible for the removal of arsenic as the volatile arsines from the bacteria. However, there has been no direct measure of the arsines released from bacteria cultures. We describe here an integrated system incorporating the bacterial incubation and volatile arsenic species analysis, and we demonstrate its application to the identification of the volatile arsines produced in bacterial cultures. The headspace of the bacterial cultures was purged with helium, and the volatile arsenic species were trapped in a chromatographic column immersed in liquid nitrogen. The cryogenically trapped arsines [AsH3, (CH3)AsH2, (CH3)2AsH, and (CH3)3As] were separated by gas chromatography and were detected by inductively coupled plasma mass spectrometry. A hydride generation system was coupled to the bacterial culture system, allowing for spiking standards and for generating calibration arsines necessary for quantitative analysis. Both bacteria containing the arsM gene or its variant arsMC2 gene were able to produce 400-500 ng of trimethylarsine. No trimethylarsine was detectable in bacteria lacking the arsM gene (containing the vector plasmid as negative control). These results confirm that arsM is responsible for releasing arsenic as volatile species from the arsenic-resistant bacteria. Our results also show traces of AsH3, CH3AsH2, and (CH3)2AsH in cultures of bacteria expressing arsM. The method detection limits for AsH3, CH3AsH2, (CH3)2AsH, and (CH3)3As were 0.5, 0.5, 0.7, and 0.6 pg, respectively. The ability to quantify trace levels of these volatile arsenic species makes it possible to study the biotransformation and biochemical roles of the evolution of these volatile arsenic species by biological systems.

Biologically active compounds of semi-metals

Semi-metals (boron, silicon, arsenic and selenium) form organo-metal compounds, some of which are found in nature and affect the physiology of living organisms. They include, e.g., the boron-containing antibiotics aplasmomycin, borophycin, boromycin, and tartrolon or the silicon compounds present in "silicate" bacteria, relatives of the genus Bacillus, which release silicon from aluminosilicates through the secretion of organic acids. Arsenic is incorporated into arsenosugars and arsenobetaines by marine algae and invertebrates, and fungi and bacteria can produce volatile methylated arsenic compounds. Some prokaryotes can use arsenate as a terminal electron acceptor while others can utilize arsenite as an electron donor to generate energy. Selenium is incorporated into selenocysteine that is found in some proteins. Biomethylation of selenide produces methylselenide and dimethylselenide. Selenium analogues of amino acids, antitumor, antibacterial, antifungal, antiviral, anti-infective drugs are often used as analogues of important pharmacological sulfur compounds. Other metalloids, i.e. the rare and toxic tellurium and the radioactive short-lived astatine, have no biological significance.

Speciation of five arsenic species (arsenite, arsenate, MMAAV, DMAAV and AsBet) in different kind of water by HPLC-ICP-MS

A method using Ion Chromatography hyphenated to an Inductively Coupled Plasma-Mass Spectrometer has been developed to accurately determine arsenite (As(III)), arsenate (As(V)), mono-methylarsonic acid (MMAA(V)), dimethylarsinic acid (DMAA(V)) and arsenobetaine (AsBet) in different water matrices. The developed method showed a high sensitivity with detection limits for each arsenic species close to 0.4pg injected. Arsenite and arsenate were the major species found in surface and well waters, but AsBet and DMAA(V) were found in some surface waters, which has never been reported before, while in some natural mineral waters located in volcanic region, the arsenic content exceeded the maximal admissible arsenic content by European legislation standards and the predominant form was As(V).

Physiological changes and differential gene expression in mummichogs (Fundulus heteroclitus) exposed to arsenic

Arsenic has been detected as a contaminant in water bodies around the world. Although a number of studies have shown toxicity to adult fish, little is known about its effects on the offspring. However, human epidemiological studies have shown that arsenic increases the number of stillbirths and prematurely born infants. We examined changes in the morphology and gene expression in juvenile mummichogs (Fundulus heteroclitus) whose parents were exposed to 230 ppb arsenic for 10 days immediately prior to spawning. The hatchlings of exposed fish had a 2.8-fold increased incidence of curved or stunted tails. Total RNA from 6-week-old hatchlings, reared in clean water, was used to construct a cDNA subtractive hybridization library. Using this library, we found 13 genes whose expression was altered in the hatchlings as a result of arsenic exposure. We confirmed differential expression by real-time PCR and found significant up-regulation of myosin light chain 2 (4.2-fold), type II keratin (1.5-fold), tropomyosin (3.1-fold) and parvalbumin (3.5-fold) in the hatchlings whose parents were exposed to arsenic. These genes are important during embryogenesis and their differential expression may be linked to the morphological changes observed in the hatchlings.

Arsenic speciation in farmed Hungarian freshwater fish

Arsenic speciation analysis was carried out on freshwater farmed fish collected from an area with elevated groundwater arsenic concentrations in Hungary as well as from outside of the area (control samples). The arsenic species were determined by high-performance liquid chromatography-inductively coupled plasma mass spectrometry on methanol extracts of the muscle tissue from the fish. Catfish (Claries gariepinus) were raised in geothermal water where the average total arsenic concentrations were 167 (contaminated sites) and 15.1 ng As mL(-1) (control); they were all fed an artificial diet containing 2880 microg As kg(-1) total arsenic, mostly present as arsenobetaine. In the catfish, the accumulated total arsenic (2510-4720 microg As kg(-1)) was found mostly in the form of arsenobetaine suggesting that uptake of arsenic was dominated by their diet. Carp (Cyprinus carpio) were cultured in surface lakes with no significant arsenic pollution and had total arsenic concentrations ranging from 62 to 363 microg As kg(-1). The arsenic species found in the carp extracts differed markedly from those in the catfish in that no arsenobetaine was detected. Most samples of carp from the investigated sites contained low concentrations of As(III) (arsenite), As(V) (arsenate), MA (methylarsonate), and DMA (dimethylarsinate), and no other compounds were detected. The four individuals from the control site, however, all contained appreciable levels of oxo-arsenosugar-glycerol and oxo-arsenosugar-phosphate. Indeed, the oxo-arsenosugar-phosphate dominated the speciation pattern for these carp contributing about 75% of the sum of species. The contrast between these two freshwater aquaculture species regarding total arsenic and arsenic species has relevant toxicological aspects in terms of food safety.

Arsenolipids

Natural arsenolipids are analogues of neutral lipids, like monoglycerides, glycolipids, phospho- and also phosphonolipids. They have been found in microorganisms, fungi, plants, lichens, in marine mollusks, sponges, other invertebrates, and in fish tissues. This review presented structures of natural arsenolipids (and derivatives), their distribution, biogenesis in algae and invertebrates, synthesis, and also biological activity. Arsenolipids are thought to be end products of arsenate detoxification processes, involving reduction and oxidative methylation and adenosylation. The proposed biogenesis of arsenolipids is based on the natural occurrence of arsenic metabolites, and all the intermediates in the proposed pathway have been identified as natural products of algal origin. Different arseno species are shown to be inhibitors of glycerol kinase, bovine carbonic anhydrase, and also is an effective therapy for acute promyelocytic leukemia, and there has been promising activity noted in other hematologic and solid tumors. Arsonoliposomes demonstrated high anti-trypanosomal activity against Trypanosoma brucei and inhibit growth of some types of cancer cells (HL-60,C6 and GH3).

Arsenic accumulation in the liver tissue of marine mammals

Arsenic concentrations were determined in livers of 226 individuals representing 16 different marine mammal species to elucidate its accumulation with age, sex, and feeding habits. Arsenic concentrations varied widely among species and individuals, and ranged from < 0.10 to 7.68 micrograms g-1 dry weight. Marine mammals feeding on cephalopods and crustaceans contained higher arsenic concentrations than those feeding on fishes. No significant gender difference in arsenic concentration was found for almost all the species. Also, no apparent trend with age (or body length) in arsenic accumulation was found for most of the species. It was noted that two seal species, Baikal seal and Caspian seal, from landlocked water environments, contained lower arsenic concentrations than the marine species. To our knowledge, this is the first comprehensive study of arsenic accumulation in a wide range of marine mammal species.

Arsenic in the Meager Creek hot springs environment, British Columbia, Canada

Levels of arsenic in water from Meager Creek hot springs, British Columbia, Canada, were found to be naturally elevated. Biota including microbial mats, green algae, sedge, cedar, fleabane, monkey flower, moss, mushrooms and lichens, that were expected to be impacted by the water, were analyzed for total levels of arsenic and for arsenic species. The major arsenic species extracted from all samples were arsenate and arsenite, which are toxic forms of arsenic. Additionally, small amounts of arsenosugars X and XI were detected in microbial mats and green algae, implying that cyanobacteria/bacteria, and possibly green algae are capable of synthesizing arsenosugars from arsenate. Low to trace amounts of arsenosugars X and XI were detected in lichens and the fungus Tarzetta cupularis. A large fraction (on average, greater than 50%) of arsenic was not extracted by using methanol/water (1:1) and the chemical and toxicological significance of this arsenic remains unknown.