Kinetic study of transformations of arsenic species during heat treatment

The combination of temperatures and pH levels applied in domestic or industrial cooking and in the sterilization of seafood might cause the transformation of certain species of arsenic into other more toxic species, which could pose a risk to the consumer. To clarify the effect of the temperatures traditionally used in cooking or sterilization on the stability of the various species of arsenic, a kinetic study was carried out, using standards of arsenobetaine (AB), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), trimethylarsine oxide (TMAO), tetramethylarsonium ion (TMA(+)), and arsenocholine (AC) heated at different temperatures (85--190 degrees C) and for different treatment times. Various pH levels (4.5, 5.5, 6.5, and 8.0) were applied during the heating process. The results obtained indicated that there were no transformations of arsenic species after temperature treatments up to 120 degrees C. However, when temperatures between 150 and 190 degrees C were used, a partial decomposition of AB was achieved, producing TMAO at 150 degrees C and TMAO and TMA(+) at temperatures of 160 degrees C or above, in proportions that varied according to the temperature and duration of the heat treatment.     

Quantitation of toxic arsenic species and arsenobetaine in Pacific oysters using an off-line process with hydride generation-atomic absorption spectroscopy

An off-line process-based speciation technique was devised here to quantitatively determine toxic inorganic arsenic (iAs), methylarsonic acid (MA), dimethylarsinic acid (DMA), and the dominant, albeit virtually nontoxic, arsenobetaine (AB) in Pacific oysters (Crassostrea gigas). Oysters were extracted with fresh methanol-water (8+2), and this was replicated three times. They were then evaporated to near dryness and subsequently redissolved in pure water; defatting was then performed with a C18 cartridge. The trace hydride active arsenic species, that is, iAs, MA, and DMA, in the defatted solutions were determined with a sensitive hydride generation-packed coldfinger trap-atomic absorption spectrometric (HG-PCFT-AAS) coupled system. The arsenicals that were desorbed from the cation-exchange resin (Dowex 50W-X8) in the washings of 4 M NH3 were categorized on the basis of AB + DMA. The total quantity of arsenic in the recovered AB + DMA was determined with a commercial hydride generation-atomic absorption spectrometric (HG-AAS) system, and finally, AB was calculated from (AB + DMA) - DMA. The average concentrations of iAs, MA, DMA, AB, and total arsenic (TAs) in the oysters collected from six aquacultural sites along the west coast of Taiwan were, respectively, 0.15, 0.06, 0.64, 6.93, and 13.74 mg kg(-1) of dry weight. AB was the major species, whereas iAs (arsenite + arsenate) were the most toxic species, although the iAs made up only approximately 1% of the TAs in the oysters. The lifetime target cancer risk, as determined by the concentration of iAs on a fresh weight basis in the oysters, was well below the ordinary health protection criteria (10(-6)).     

Bioaccessibility and transport by Caco-2 cells of organoarsenical species present in seafood

Organoarsenical standards and raw and cooked seafood (DORM-2, sole, and Greenland halibut) were subjected to in vitro gastrointestinal digestion to estimate arsenic bioaccessibility (maximum soluble concentration in gastrointestinal medium). The in vitro digestion did not modify the chemical form of the organoarsenic species standards. In seafood, bioaccessibility was 67.5-100% for arsenobetaine (AB), 30% for dimethylarsinic acid (DMA), 45% for tetramethylarsonium ion (TETRA), and >50% for trimethylarsine oxide (TMAO). Cooking induced no changes in bioaccessible contents. In addition, transport by Caco-2 cells, an intestinal epithelia model, was evaluated from organoarsenical standards and DORM-2. For standards, transport ranged from 1.7% for AB to 15.5% for TETRA. In DORM-2, transport was observed for only AB (12%), with far higher efficiency than in the case of the standard solution, thus illustrating the interest of using whole foods for studying bioavailability.     

Organoarsenical species contents in cooked seafood

The organoarsenical species arsenobetaine (AB), arsenocholine (AC), tetramethylarsonium ion (TMA+), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA) were determined in 64 cooked seafood products (fish, bivalves, squid, crustaceans) included in a Total Diet Study carried out in the Basque Country (Spain). For cooking, various treatments were employed (grilling, roasting, baking, stewing, boiling, steaming, microwaving). The results obtained show that in cooked seafood AB is the major species, followed by DMA and TMA+. AC and MMA are minor species. The results in cooked seafood were compared with the arsenic species contents obtained for the same product raw. After cooking there was an increase in DMA for sardines and bivalves and an increase or appearance of TMA+ for meagrim, anchovy, Atlantic horse mackerel, and sardine. The data provided add to the very scant information available about organoarsenical species contents in cooked seafood.     

Organoarsenical species contents in fresh and processed seafood products

A study was carried out to determine organic species of arsenic in the main varieties of seafood consumed in the Basque country (Spain). The concentrations of arsenobetaine (AB), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), arsenocholine (AC), and tetramethylarsonium ion (TMA(+)) in 64 samples corresponding to different food items are presented. The study provides information about a possible distribution pattern of organoarsenical species in seafood products. AB was detected in all of the samples [0.3-104.1 microg g(-1) dry weight (dw)]. DMA was detected in all of the samples except squid and salted cod (0.027-1.757 microg g(-1) dw). MMA was detected only in certain fatty fish (0.004-0.028 microg g(-1) dw) and bivalves (0.031-0.047 microg g(-1) dw). AC was only present in some samples of lean fish (0.014-0.089 microg g(-1) dw), and TMA(+) was detected only in anchovy (0.039-0.169 microg g(-1) dw) and crustaceans (0.044-0.966 microg g(-1) dw).     

Determination of water-soluble arsenic compounds in commercial edible seaweed by LC-ICPMS

This paper reports arsenic speciation in edible seaweed (from the Galician coast, northwestern Spain) produced for human consumption. Chondrus crispus , Porphyra purpurea , Ulva rigida , Laminaria ochroleuca , Laminaria saccharina , and Undaria pinnatifida were analyzed. The study focused on arsenosugars, the most frequently occurring arsenic species in algae. As(III) and As(V) were also determined in aqueous extracts. Total arsenic in the samples was determined by microwave digestion and inductively coupled plasma mass spectrometry (ICPMS). For arsenic speciation, a water extraction especially suitable for arsenosugars was used, and the arsenic species were analyzed by liquid chromatography with both anionic and cationic exchange and ICPMS detection (LC-ICPMS). The total arsenic content of the alga samples ranged from 5.8 to 56.8 mg As kg(-1). The mass budgets obtained in the extracts (column recovery × extraction efficiency) ranged from 38 to 92% except for U. pinnatifida (4%). The following compounds were detected in the extracts: arsenite (As(III)), arsenate (As(V)), methylarsonate (MA), dimethylarsinate (DMA), sulfonate sugar (SO(3)-sug), phosphate sugar (PO(4)-sug), arsenobetaine (AB), and glycerol sugar (Gly-sug). The highest concentrations corresponded to the arsenosugars.     

Effect of cooking temperatures on chemical changes in species of organic arsenic in seafood

The concentrations of arsenobetaine (AB), tetramethylarsonium ion (TMA(+)), and trimethylarsine oxide (TMAO) were determined in samples of sole, dory, hake, and sardine, raw and after being subjected to cooking processes--baking, frying, and grilling--at various temperatures. In all cases, the temperature attained inside the product during the cooking process was measured. The arsenic species extracted from the samples with methanol/water were separated by means of a column switching technique between a PRP-X100 column and a PRP-X200 column. AB was detected by hydride generation atomic absorption spectrometry, whereas TMA(+) and TMAO were detected by hydride generation atomic fluorescence spectrometry. The results obtained showed that, in all of the types of seafood studied, TMA(+) appeared after cooking, possibly because heating facilitates decarboxylation of AB to TMA(+).     

Safety evaluation of organoarsenical species in edible Porphyra from the China Sea

A study was carried out to determine arsenic species in Porphyra seaweed originating from the China Sea. Information about arsenic species in Porphyra was provided by HPLC-ICP-MS and ES-MS-MS. The total arsenic concentrations of Porphyra samples from five different producing areas ranged from 2.1 to 21.6 mg/kg. The analysis report also showed that arsenosugars were the only arsenic species that could be detected in all of the extracts of samples. Arsenosugar PO(4) was the major compound in most samples (0.3-13.9 mg/kg of dry weight), followed by arsenosugar OH (0.7-6.2 mg/kg of dry weight). A further experiment was done to investigate the stability of arsenosugars in the process of being heated. It was observed that the arsenosugars were stable during a short-term heating at 100 degrees C. Their stability in human ingestion was also studied. A substantial increase of dimethylarsinic acid (DMA) was detected in urine samples collected from six volunteers after the consumption of this seaweed. The results obtained indicated that arsenosugars had been metabolized to DMA, which is more toxic than arsenosugars. From this point of view, consumers should consider the possible adverse effects of edible Porphyra on human health and choose those Porphyra having lower arsenic concentrations.     

Arsenic species: effects on and accumulation by tomato plants.

The uptake of arsenic (As) species by Lycopersicum esculentum, growing under soilless culture conditions, was studied. A 4 x 3 x 2 factorial experiment was conducted with four As species (arsenite, arsenate, methylarsonate, and dimethylarsinate), three As concentrations (1, 2, and 5 mg L(-)(1)) and two tomato cultivars (Marmande and Muchamiel). The phytoavailability and phytotoxicity were primarily determined by the As species. The concentrations of As in plant increased significantly with increasing As concentration in solution. Both MA and DMA showed a higher upward translocation than arsenite and arsenate, and treatments with MA and DMA clearly reduced plant growth and fruit yield. The As concentration in tomatoes treated with arsenite or arsenate were within the range considered normal in food crops; however, the As concentration in tomatoes treated with MA and DMA were close to or even above the maximum limit. When tomato plants are exposed to high concentrations of As in nutrient solutions, they may uptake As to concentrations unacceptable for human food.     

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.     

Arsenic transport and transformation associated with MSMA application on a golf course green

The impact of extensively used arsenic-containing herbicides on groundwater beneath golf courses has become a topic of interest. Although currently used organoarsenicals are less toxic, their application into the environment may produce the more toxic inorganic arsenicals. The objective of this work was to understand the behavior of arsenic species in percolate water from monosodium methanearsonate (MSMA) applied golf course greens, as well as to determine the influences of root-zone media for United State Golf Association (USGA) putting green construction on arsenic retention and species conversion. The field test was established at the Fort Lauderdale Research and Education Center (FLREC), University of Florida. Percolate water was collected after MSMA application for speciation and total arsenic analyses. The results showed that the substrate composition significantly influenced arsenic mobility and arsenic species transformation in the percolate water. In comparison to uncoated sands (S) and uncoated sands and peat (S + P), naturally coated sands and peat (NS + P) showed a higher capacity of preventing arsenic from leaching into percolate water, implying that the coatings of sands with clay reduce arsenic leaching. Arsenic species transformation occurred in soil, resulting in co-occurrence of four arsenic species, arsenite (As(III)), arsenate (As(V)), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) in percolate water. The results indicated that substrate composition can significantly affect both arsenic retention in soil and arsenic speciation in percolate water. The clay coatings on the soil particles and the addition of peat in the soil changed the arsenic bioavailability, which in turn controlled the microorganism-mediated arsenic transformation. To better explain and understand arsenic transformation and transport after applying MSMA in golf green, a conceptual model was proposed.     

Gas chromatographic method for determination of dimethylamine, trimethylamine, and trimethylamine oxide in fish-meat frankfurters

A method is described for analysis of minced fish-meat and surimi-meat frankfurters for dimethylamine (DMA), trimethylamine (TMA), and trimethylamine oxide (TMAO) using a headspace-gas chromatographic technique. After simple acid extraction and addition of NaOH, the headspace was directly injected into a gas chromatograph by a gas-tight syringe. DMA and TMA were separated on a Chromosorb 103 column and detected by a flame ionization detector. TMAO was measured as TMA after Zn reduction. Repeatability of the method for DMA, TMA, and TMAO was 6.6, 1.0, and 18.8 ppm, respectively. The method was applicable to Alaska pollock-meat and Atlantic menhaden-meat frankfurters, unwashed, and washed mince and surimi.     

Assessment of Arsenic Toxicity and Tolerance Characteristics of Bean Plants (Phaseolus Vulgaris) Exposed to Different Species of Arsenic

Experiments were conducted to evaluate the arsenic toxicity, its accumulation and phytoremediation potential of bean plants (Phaseolus vulgaris) grown in soils contaminated with different species of arsenic such as arsenite (As(III)), arsenate (As(V)) and dimethylarsinic acid (DMA). Bean plants were grown in soils amended by aqueous solutions of 20 and 50 mg kg^?1 of As (III), As(V) or DMA. Arsenic species negatively affected the yield and growth of the plant. The study demonstrated arsenic accumulation in the plant parts. The concentration of arsenic compounds in the shoots decreased in the order arsenate > arsenite > dimethylarsinic acid while in the roots as arsenite > arsenate > dimethylarsinic acid. Most arsenic is accumulated in the roots with limited transfer to shoots. Thus, bean plants can be considered as an arsenic excluder and has the potential for phytostabilization of arsenic contaminated sites. The study also reveals that removal of arsenic by boiling the vegetables with excess of water is not possible.     

Application of HPLC-ICP-MS and HPLC-ESI-MS procedures for arsenic speciation in seaweeds

Speciation of arsenic in seaweeds was carried out using ion chromatography (IC) for separation and inductively coupled mass spectrometry (ICP-MS) for detection. The arsenic species studied were arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB), and arsenocholine (AsC). Chromatographic separation of all the species was achieved in <9 min in gradient elution mode using (NH(4))(2)CO(3) and methanol at pH 8.5. The outlet of the IC column was directly connected to the nebulizer of ICP-MS for the determination of arsenic. The speciation of arsenic has been carried out in several seaweed samples. A microwave-assisted extraction method was used for the extraction of arsenic species from seaweed samples. With a mixture of mobile phase A and methanol as extractant, the extraction efficiency was >84%, and the recoveries from spiked samples were in the range of 90-106%. The unknown compounds detected in different seaweeds were identified by coupling IC directly with electrospray ionization-mass spectrometry (ESI-MS). Two arsenosugars and tetramethylarsonium ion (TETRA) were identified in different seaweeds. A fat-soluble arsenolipid compound was identified in the extract of certified reference material BCR-279 Ulva lactuca when 1% HNO(3) was used as the extractant. The precision between sample replicates was >9% for all determinations. The limits of detection were in the range of 0.006-0.015 μg L(-1) for various arsenic species based on peak height.     

Demethylation of Dimethylarsinic Acid and Arsenobetaine in Different Organic Soils

Methylation and demethylation of arsenic may change substantially the toxicity and mobility of arsenic in soils. Little is known about demethylation of organic arsenic species in organic soils. We incubated dimethylarsinic acid (DMA) and arsenobetaine (AsB) in soils and aqueous soil extracts from a forest floor and fen, in order to investigate demethylation processes. Incubations were conducted at 5°C in the dark under oxic or anoxic conditions. Arsenobetaine demethylated rapidly in all soil extracts with half-lives of 3.6–12 days, estimated from first order kinetic. Demethylation of DMA was relatively slow with half-lives of 187 and 46 days in the forest floor extracts and oxic fen extracts, respectively. In comparison, DMA was stable for 100 days in anoxic fen extracts. The apparent half-lives were much shorter in soils for DMA (1.3–12.6 days) and AsB (0.5–1.9 days) than in soil extracts, suggesting also irreversible AsB and DMA adsorption to soils beside demethylation. An unknown arsenic species and DMA were detected as metabolites of AsB demethylation. The results indicate rapid demethylation of AsB probably via the pathway AsB → Dimethylarsenoylacetate → DMA, followed up by slow demethylation of DMA → monomethylarsonic acid → inorganic As species.     

添加外源耐砷菌与零价铁对土壤砷有效性和形态的影响

采用室内土壤培养试验,探讨了外源添加耐砷真菌棘孢木霉（TrichodermaasperellumL．）和零价铁对土壤砷的有效性和形态转化的影响。结果表明：向污染土壤中添加耐砷真菌棘孢木霉后,随着培养时间的延长,土壤中水溶态砷和NaHCO,提取态砷含量均呈稳定增加趋势,耐砷真菌促进了土壤中砷的溶出和释放;培养30d时,耐砷菌处理土壤有效砷含量比同期对照增幅达3．9％-10．7％,水溶态砷以As（V）为主,未检测到As（Ⅲ）、一甲基胂（MMA）、二甲基胂（DMA）等其他形态的砷;随着外源零价铁的加入,土壤中砷的活性大大降低,其有效砷含量降幅为76．5％-90．4％;在耐砷菌与零价铁联合作用下,相比于单纯的零价铁处理,土壤有效砷含量显著增加（p〈0．05）,因耐砷真菌棘孢木霉的加入导致零价铁对土壤砷的固定效率下降7．0％-11．1％。耐砷菌导致土壤砷活化可能主要与残渣态向非专性吸附态砷的转化等过程有关,外源零价铁对土壤砷的固定作用可能与非专性吸附态向无定形及弱晶质氧化物结合态、残渣态砷等转化过程相关;耐砷菌的加入抵消了零价铁对土壤砷的部分固定效果,但短期内（〈30d）不会构成大的影响。     

Arsenic resistant microorganisms isolated from agricultural drainage water and evaporation pond sediments

Elevated levels of As in contaminated water and soil could pose a major threat to the environment. Relatively high levels of As have been reported in agricultural drainage water and in evaporation pond sediments in Kern County, California. The objective of this study was to enumerate and isolate As-resistant microorganisms from agricultural drainage water and evaporation pond sediments and to assess their tolerance to metals, metalloids and antibiotics. The culture medium was amended with arsenite (III), arsenate (V), methylarsonic acid (MAA), and dimethylarsinic acid (DMA). Among the water samples, As(V), MAA, and DMA added to the medium at concentrations from 0.1 to 1000 mg L^?1 showed no effect on the colony forming units (CFUs) compared with no As supplementation, while arsenite (III) (> 1.0 mg L^?1) inhibited the population. The sediments showed three trends: (i) no effect on CFUs in the presence of As(V) up to 1000 mg kg^?1, (ii) a decline in CFUs in the presence of > 100 mg kg^?1, As(III), and (iii) an increase in CFUs upon the addition of MAA or DMA at > 25 mg kg^?1, Arsenite (III) was much more toxic to the indigenous microflora than any other As species. Arsenite (III) inactivates many enzymes by having a high affinity for thiol groups of proteins. A plate diffusion method was used to assess the tolerance of the As-resistant bacteria to heavy metals, metalloids and antibiotics. Of 14 isolates tested, all were resistant to Co, Cu, Pb, Ni, Mo, Cr, Se(IV), Se(VI), As(III), As(V), Sb, Sn, and Ag (50 µg mL^?1). The most toxic trace elements were Cd followed by Hg>Te>Zn. Multiple antibiotic tolerance (resistance to 2 or more antibiotics) was found among 43% of the isolates. The As-resistant bacteria showed a high tolerance to metals and antibiotics.     

Arsenosugars in raw and cooked edible seaweed: characterization and bioaccessibility

The aim of this study was to examine arsenic species contents in raw and cooked edible seaweed and the bioaccessibility (maximum soluble concentration in gastrointestinal medium) of arsenosugars (glycerol ribose, phosphate ribose, sulfonate ribose, and sulfate ribose). For the analysis, a new chromatographic separation was developed in anion exchange, coupled with thermooxidation-hydride generation-atomic fluorescence spectrometry. An in vitro digestion (pepsin, pH 2; pancreatin-bile extract, pH 7) was applied to estimate arsenosugar bioaccessibility. Cooking of Undaria pinnatifida and Porphyra sp. did not alter the arsenic species present in the methanol-water extract, but it produced a substantial increase (2 and 5 times) in the As(V) extracted from Hizikia fusiforme. In all of the seaweeds analyzed, arsenosugar bioaccessibility was high (>80%) and did not vary as a result of cooking. Arsenosugar degradation as a result of in vitro digestion was not observed.     

Transformation of bioactive compounds by Fusarium sacchari fungus isolated from the soil-cultivated ginseng

Ginsenoside bioactive compounds, namely, compound K (C-K), compound Mx (C-Mx), and ginsenoside Mc (G-Mc), were the metabolites of ginsenosides Rb 1, Rb 2, Rb 3, and Rc by intestinal microflora of humans or rats, microorganisms, and enzymes, and C-K showed beneficial effects in vitro and in vivo as an antitumoral agent. The objective of this work was to explore an efficient procedure for biotransformation of these bioactive compounds. Thus, a filamentous fungus, Fusarium sacchari, was first obtained from the soil-cultivated ginseng, which was verified to possess a potent capacity of transformation of C-K, C-Mx, and G-Mc. The optimal biotransformation conditions of F. sacchari with C-K, C-Mx, and G-Mc were obtained as follows: transforming temperature, 30 degrees C; transforming time, 6 days; rotary speed, 160 rpm; pH of the medium, 5.5. HPLC analysis indicated that these three bioactive compounds were key metabolites and their structures were confirmed by (1)H and (13)C NMR analysis. Moreover, the in vitro antitumor activities of C-K, C-Mx, and G-Mc and the in vivo antitumor activities of the transformed product mainly containing these compounds were also evaluated. Among C-K, C-Mx, and G-Mc, C-K exhibited the most potent antitumor activities. The in vivo study showed that the transformed products by F. sacchari had much more antitumor activity than those of commonly used ginsenoside Rg3 and Paclitaxel.