Arsenic speciation in the earthworms Lumbricus rubellus and Dendrodrilus rubidus

Two species of earthworm, Lumbricus rubellus Hoffmeister and Dendrodrilus rubidus (Savigny) collected from an arsenic-contaminated mine spoil site and an uncontaminated site were investigated for total tissue arsenic concentrations and for arsenic compounds by liquid chromatography-mass spectrometry (LC-MS) and liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS). For L. rubellus, whole-body total tissue arsenic concentrations were 7.0 to 17.0 mg arsenic/ kg dry weight in uncontaminated soil and 162 to 566 mg arsenic/kg dry weight in contaminated soil. For D. rubidus, whole-body tissue concentrations were 2.0 to 5.0 mg arsenic/kg dry weight and 97 to 321 mg arsenic/kg dry weight, respectively. Arsenobetaine was the only organic arsenic species detected in both species of earthworms, with the remainder of the extractable arsenic being arsenate and arsenite. There was an increase in the proportion of arsenic present as arsenobetaine in the total arsenic burden. Lumbricus rubellus and D. rubidus have similar life styles, both being surface living and litter feeding. Arsenic speciation was found to be similar in both species for both uncontaminated and contaminated sites, with dose-dependent formation of arsenobetaine. When L. rubellus and D. rabidus from contaminated sites were incubated in arsenic-free soils, the total tissue burden of arsenic diminished. Initially, L. rubellus from the tolerant populations (from the contaminated site) eliminated arsenic in the first 7 d of exposure before accumulating arsenic in tissues, whereas nontolerant populations (from the uncontaminated site) accumulated arsenic linearly. The tolerant and nontolerant L. rubellus eliminated tissue arsenic linearly over 21 d when incubated in uncontaminated soil.     

Effects of arsenic speciation and low dissolved oxygen condition on the toxicity of arsenic to a lotic mayfly

The influence of site-specific conditions on contaminant bioavailability and toxicity to benthic invertebrates is a key consideration in the environmental risk assessment process. This is particularly relevant for contaminants with complex speciation chemistries, such as arsenic. The present study addressed uncertainties regarding arsenic toxicity to a mayfly (Baetis tricaudatus) under low dissolved oxygen (DO) conditions characteristic of many contaminated sites. Arsenic toxicity (arsenite, As(III); arsenate, As(V)) to mayfly nymphs was assessed under two DO scenarios (68 and 84% saturation). Arsenic speciation ratios were determined during testing to confirm the nature of arsenic exposure. The present study found that As(III) was more lethal and bioaccumulated to a greater degree in B. tricaudatus compared to As(V), but the sublethal toxicities of the two arsenic species were similar. Nymph growth and development were significantly inhibited after 12 d of exposure to both 1 mg/L of As(III) and As(V). Exposure to arsenic under low DO conditions (6.5 mg/L, 68% saturation) did not significantly affect As(III) or As(V) toxicity and bioaccumulation over 12 d. The DO level of 6.5 mg/L, however, appeared to be marginally lethal to B. tricaudatus. Results indicate that the Canadian arsenic criterion for the protection of aquatic life (5 microg/L) is protective of B. tricaudatus and is low enough to accommodate differences in arsenic toxicity because of the interconversions between As(III) and As(V). These findings provide insight regarding the toxicity and speciation of arsenic under DO conditions considered to be low for this lotic mayfly species and representative of existing conditions at mine sites in northern Canada.     

Arsenic accumulation in rice (Oryza sativa L.): human exposure through food chain

Although human exposure to arsenic is thought to be caused mainly through arsenic-contaminated underground drinking water, the use of this water for irrigation enhances the possibility of arsenic uptake into crop plants. Rice is the staple food grain in Bangladesh. Arsenic content in straw, grain and husk of rice is especially important since paddy fields are extensively irrigated with underground water having high level of arsenic concentration. However, straw and husk are widely used as cattle feed. Arsenic concentration in rice grain was 0.5+/-0.02 mg kg(-1) with the highest concentrations being in grains grown on soil treated with 40 mg As kg(-1) soil. With the average rice consumption between 400 and 650 g/day by typical adults in the arsenic-affected areas of Bangladesh, the intake of arsenic through rice stood at 0.20-0.35 mg/day. With a daily consumption of 4 L drinking water, arsenic intake through drinking water stands at 0.2mg/day. Moreover, when the rice plant was grown in 60 mg of As kg(-1) soil, arsenic concentrations in rice straw were 20.6+/-0.52 at panicle initiation stage and 23.7+/-0.44 at maturity stage, whereas it was 1.6+/-0.20 mg kg(-1) in husk. Cattle drink a considerable amount of water. So alike human beings, arsenic gets deposited into cattle body through rice straw and husk as well as from drinking water which in turn finds a route into the human body. Arsenic intake in human body from rice and cattle could be potentially important and it exists in addition to that from drinking water. Therefore, a hypothesis has been put forward elucidating the possible food chain pathways through which arsenic may enter into human body.     

Assessing and managing exposure from arsenic in CCA-treated wood play structures

BACKGROUND: Chromated copper arsenate (CCA)-treated wood has been widely used for outdoor play structures. There is a growing scientific concern about children's exposure to the arsenic that leaches from these structures. The purpose of this study was to measure arsenic from CCA-treated wood play structures owned by the City of Toronto to guide an appropriate exposure reduction strategy. METHODS: In the fall of 2002, 4 soil and 2 wood surface samples (dislodgeable arsenic) were collected from 217 play structures and analyzed for total arsenic content. Soil arsenic concentrations were compared to the federal soil guideline of 12 microg/g. Dislodgeable arsenic concentrations were compared to a Toronto Public Health-derived interim action level of 100 microg/100 cm2. RESULTS: Soil arsenic levels in samples taken from within one metre of CCA-treated wood were low (mean 2.1; range 0.5-10 microg/g). However, the means of the arsenic level in the composite soil samples taken from beneath an elevated platform were significantly greater (p<0.01) than the background soil sample and soil from within one metre of the CCA-treated wood (mean 20.3; range 12.4-47.5 microg/g). Composite soil samples exceeded the federal soil guideline of 12 microg/g at 32 play structures. Dislodgeable arsenic values varied widely (mean 41.9 microg/100 cm2; non-detectable to 521.5 microg/100 cm2). 32 play structures had dislodgeable arsenic levels that exceeded the interim action level. Mean arsenic concentrations on vertical surfaces were significantly higher than on horizontal surfaces (p<0.01). DISCUSSION: Our soil analysis indicates that arsenic does not migrate laterally but accumulates under elevated platforms at levels that can exceed the soil guideline. Dislodgeable arsenic values varied greatly and were not a useful predictor of soil arsenic (R2 = 0.0015).     

Response of Pepper Plants (<Emphasis Type="Italic">Capsicum annum</Emphasis> L.) on Soil Amendment by Inorganic and Organic Compounds of Arsenic

The influence of soil contamination by inorganic and organic arsenic compounds on uptake, accumulation, and transformation of arsenic in pepper (Capsicum annum L.) was investigated in greenhouse pot experiments under controlled conditions. Pepper plants were cultivated in substrate amended by aqueous solutions of arsenite, arsenate, methylarsonic acid (MA), and dimethylarsinic acid (DMA) applied individually into cultivation substrate at concentrations of 15 mg As per kg of substrate. The plant availability of the arsenicals increased in the order arsenite = arsenate < MA < DMA. The highest arsenic concentrations were found in roots followed by stems, leaves, and fruits regardless of arsenic compound applied. In the control samples of pepper fruits, As(III), As(V), and DMA were present (25%, 37%, and 39% of the water-extractable arsenic). In control stems + leaves and roots, As(V) was the major compound (63% and 53% in a phosphate buffer extract) followed by As(III) representing 33% and 42%. Additionally, low concentrations (not exceeding 5%) of DMA and MA were detected as well. In all the soils analyzed after the first harvest of pepper fruits, arsenate was the dominating compound followed by arsenite. Methylarsonic acid, methylarsonous acid, and DMA were present at varying concentrations depending on the individual soil treatments. In the treated plants, the arsenic compounds in plant tissues reflected predominantly the extractable portions of arsenic compounds present in soil after amendment, and this pattern was more significant in the first part of vegetation period. The results confirmed the ability of generative parts of plants to accumulate preferably organic arsenic compounds, whereas in the roots and aboveground biomass, mainly inorganic arsenic species are present. Evidently, the source of soil arsenic contamination affects significantly the extractable portions of arsenic compounds in soil and subsequently the distribution of arsenic compounds within the plants.     

Arsenic contamination in food-chain: transfer of arsenic into food materials through groundwater irrigation

Arsenic contamination in groundwater in Bangladesh has become an additional concern vis-à-vis its use for irrigation purposes. Even if arsenic-safe drinking-water is assured, the question of irrigating soils with arsenic-laden groundwater will continue for years to come. Immediate attention should be given to assess the possibility of accumulating arsenic in soils through irrigation-water and its subsequent entry into the food-chain through various food crops and fodders. With this possibility in mind, arsenic content of 2,500 water, soil and vegetable samples from arsenic-affected and arsenic-unaffected areas were analyzed during 1999-2004. Other sources of foods and fodders were also analyzed. Irrigating a rice field with groundwater containing 0.55 mg/L of arsenic with a water requirement of 1,000 mm results in an estimated addition of 5.5 kg of arsenic per ha per annum. Concentration of arsenic as high as 80 mg per kg of soil was found in an area receiving arsenic-contaminated irrigation. A comparison of results from affected and unaffected areas revealed that some commonly-grown vegetables, which would usually be suitable as good sources of nourishment, accumulate substantially-elevated amounts of arsenic. For example, more than 150 mg/kg of arsenic has been found to be accumulated in arum (kochu) vegetable. Implications of arsenic ingested in vegetables and other food materials are discussed in the paper.     

Relative bioavailability and bioaccessibility and speciation of arsenic in contaminated soils

Background: Assessment of soil arsenic (As) bioavailability may profoundly affect the extent of remediation required at contaminated sites by improving human exposure estimates. Because small adjustments in soil As bioavailability estimates can significantly alter risk assessments and remediation goals, convenient, rapid, reliable, and inexpensive tools are needed to determine soil As bioavailability.Objectives: We evaluated inexpensive methods for assessing As bioavailability in soil as a means to improve human exposure estimates and potentially reduce remediation costs.Methods: Nine soils from residential sites affected by mining or smelting activity and two National Institute of Standards and Technology standard reference materials were evaluated for As bioavailability, bioaccessibility, and speciation. Arsenic bioavailability was determined using an in vivo mouse model, and As bioaccessibility was determined using the Solubility/Bioavailability Research Consortium in vitro assay. Arsenic speciation in soil and selected soil physicochemical properties were also evaluated to determine whether these parameters could be used as predictors of As bioavailability and bioaccessibility.Results: In the mouse assay, we compared bioavailabilities of As in soils with that for sodium arsenate. Relative bioavailabilities (RBAs) of soil As ranged from 11% to 53% (mean, 33%). In vitro soil As bioaccessibility values were strongly correlated with soil As RBAs (R² = 0.92). Among physicochemical properties, combined concentrations of iron and aluminum accounted for 80% and 62% of the variability in estimates of RBA and bioaccessibility, respectively.Conclusion: The multifaceted approach described here yielded congruent estimates of As bioavailability and evidence of interrelations among physicochemical properties and bioavailability estimates.     

Sources of Arsenic and Fluoride in Highly Contaminated Soils Causing Groundwater Contamination in Punjab,Pakistan

Highly contaminated groundwater, with arsenic (As) and fluoride (F⁻) concentrations of up to 2.4 and 22.8 mg/L, respectively, has been traced to anthropogenic inputs to the soil. In the present study, samples collected from the soil surface and sediments from the most heavily polluted area of Punjab were analyzed to determine the F⁻ and As distribution in the soil. The surface soils mainly comprise permeable aeolian sediment on a Pleistocene terrace and layers of sand and silt on an alluvial flood plain. Although the alluvial sediments contain low levels of F, the terrace soils contain high concentrations of soluble F⁻ (maximum, 16 mg/kg; mean, 4 mg/kg; pH > 8.0). Three anthropogenic sources were identified as fertilizers, combusted coal, and industrial waste, with phosphate fertilizer being the most significance source of F⁻ accumulated in the soil. The mean concentration of As in the surface soil samples was 10.2 mg/kg, with the highest concentration being 35 mg/kg. The presence of high levels of As in the surface soil implies the contribution of air pollutants derived from coal combustion and the use of fertilizers. Intensive mineral weathering under oxidizing conditions produces highly alkaline water that dissolves the F⁻ and As adsorbed on the soil, thus releasing it into the local groundwater.     

In vivo assessment of arsenic bioavailability in rice and its significance for human health risk assessment

BACKGROUND: Millions of people worldwide consume arsenic-contaminated rice; however, little is known about the uptake and bioavailability of arsenic species after arsenic-contaminated rice ingestion. OBJECTIVES: In this study, we assessed arsenic speciation in greenhouse-grown and supermarket-bought rice, and determined arsenic bioavailability in cooked rice using an in vivo swine model. RESULTS: In supermarket-bought rice, arsenic was present entirely in the inorganic form compared to greenhouse-grown rice (using irrigation water contaminated with sodium arsenate), where most (approximately 86%) arsenic was present as dimethylarsinic acid (organic arsenic). Because of the low absolute bioavailability of dimethylarsinic acid and the high proportion of dimethylarsinic acid in greenhouse-grown rice, only 33 +/- 3% (mean +/- SD) of the total rice-bound arsenic was bioavailable. Conversely, in supermarket-bought rice cooked in water contaminated with sodium arsenate, arsenic was present entirely in the inorganic form, and bioavailability was high (89 +/- 9%). CONCLUSIONS: These results indicate that arsenic bioavailability in rice is highly dependent on arsenic speciation, which in turn can vary depending on rice cultivar, arsenic in irrigation water, and the presence and nature of arsenic speciation in cooking water. Arsenic speciation and bioavailability are therefore critical parameters for reducing uncertainties when estimating exposure from the consumption of rice grown and cooked using arsenic-contaminated water.     

Growth and reproduction of the earthworm Eisenia fetida after exposure to leachate from wood preservatives

Wood preserved with chromated copper arsenate (CCA) and alkaline copper quaternary (ACQ) was mixed with artificial rainwater, to generate leachates containing As, Cr and Cu. Then, leachates were applied to two soils at rates of 13-169 mg As kg(-1) soil (dry weight basis), 12-151 mg Cr kg(-1) and 10-216 mg Cu kg(-1). Metal bioavailability was evaluated after 28 days using the earthworm Eisenia fetida (Savigny). Metal concentrations in earthworm tissue ranged from negligible to 80 mg As kg(-1) (dry weight basis), 89 mg Cr kg(-1) and 90 mg Cu kg(-1), which appeared to be non-lethal to E. fetida. There was less Cu available to earthworms in the Courval soil (pH 7.8) than the Chateauguay soil (pH 6.8), but earthworm growth and reproduction were not affected by exposure to Cu from ACQ-treated wood. In contrast, earthworms exposed to As, Cr and Cu from the CCA-treated wood gained weight more quickly in the Courval soil (1.3-21 mg g(-1) initial biomass days) than in the Chateauguay soil (0.2-7.8 mg g(-1) day(-1)), but fewer than 20% of the cocoons deposited by the faster-growing earthworms hatched by the end of the 56 days ecotoxicology test. It appeared that E. fetida can allocate more energy to growth than reproduction, delaying cocoon development and hatching in some situations. Further information is needed on the soil factors that may induce such behavior, as it can affect the interpretation of results from the earthworm ecotoxicology test.     

Phytoextraction and phytofiltration of arsenic

Arsenic, a ubiquitous contaminant in groundwater and soils, is currently drawing much public attention. Arsenic-contaminated soils can be cleaned up via phytoextraction-the use of plants to extract the arsenic from soil and transport it into aboveground tissues. Arsenic removal from polluted soils can be carried out using hyperaccumulator ferns like the Chinese brake fern Pteris vittata, which accumulates very high concentrations of the element in aboveground tissues. The capacity of the plant to take up large concentrations of arsenic, even at low levels in soil, illustrates efficient bioaccumulation. The possibility of using Pteris ferns to remove arsenic from water by phytofiltration has been proposed.     

Arsenic speciation and effect of arsenate inhibition in a Microcystis aeruginosa culture medium under different phosphate regimes

To assess the ecological impact of arsenic pollution during cyanobacterial blooms, As speciation and cyanobacterial growth in phosphate-modified Microcystis aeruginosa cultures treated with arsenate were investigated under laboratory conditions. Marked growth inhibition was observed when arsenate was added. The inhibition effect of 1?μM arsenate was lower than that of 10?μM arsenate. Increasing phosphate supply (0-175?μM) in the medium decreased the inhibition of As. In the medium, arsenate, arsenite, and dimethylarsenicals (DMA) occurred under phosphate-deprivation (0?μM) and phosphate-excess (175?μM) conditions. However, only arsenate and DMA were detected under phosphate-limited (1?μM) and phosphate-rich (10?μM) conditions. Moreover, arsenite and DMA concentrations had significantly positive correlation with the biomass production of M. aeruginosa in the existence of phosphate. Arsenic speciation was more significantly affected by phosphate levels than arsenate concentrations. Recovery of total As content in M. aeruginosa culture medium increased with the increasing phosphate supply. The duration of arsenate contamination in the culture of M. aeruginosa had no influence on the variation of As species but affected the concentration of them in the medium under the phosphate-excess condition. This demonstrated that the effect of M. aeruginosa on As speciation was not related to the duration of As contamination under the phosphate-excess condition.     

Greenhouse study on the phytoremediation potential of vetiver grass, Chrysopogon zizanioides L., in arsenic-contaminated soils

The purpose of this greenhouse study was to assess the capacity of vetiver grass to accumulate arsenic from pesticide-contaminated soils of varying physico-chemical properties. Results indicate that vetiver is capable of tolerating moderate levels of arsenic up to 225 mg/kg. Plant growth and arsenic removal efficiency was strongly influenced by soil properties. Arsenic removal was highest (10.6%) in Millhopper soil contaminated with 45 mg/kg arsenic, which decreased to 4.5 and 0.6% at 225 and 450 mg/kg, respectively. High biomass, widespread root system and environmental tolerance make this plant an attractive choice for the remediation of soils contaminated with moderate levels of arsenic.     

Determination of monomethylarsonous acid, a key arsenic methylation intermediate, in human urine

In this study we report on the finding of monomethylarsonous acid [MMA(III)] in human urine. This newly identified arsenic species is a key intermediate in the metabolic pathway of arsenic biomethylation, which involves stepwise reduction of pentavalent to trivalent arsenic species followed by oxidative addition of a methyl group. Arsenic speciation was carried out using ion-pair chromatographic separation of arsenic compounds with hydride generation atomic fluorescence spectrometry detection. Speciation of the inorganic arsenite [As(III)], inorganic arsenate [As(V)], monomethylarsonic acid [MMA(V)], dimethylarsinic acid [DMA(V)], and MMA(III) in a urine sample was complete in 5 min. Urine samples collected from humans before and after a single oral administration of 300 mg sodium 2,3-dimercapto-1-propane sulfonate (DMPS) were analyzed for arsenic species. MMA(III) was found in 51 out of 123 urine samples collected from 41 people in inner Mongolia 0-6 hr after the administration of DMPS. MMA(III )in urine samples did not arise from the reduction of MMA(V) by DMPS. DMPS probably assisted the release of MMA(III) that was formed in the body. Along with the presence of MMA(III), there was an increase in the relative concentration of MMA(V) and a decrease in DMA(V) in the urine samples collected after the DMPS ingestion.     

Arsenic drinking water exposure and urinary excretion among adults in the Yaqui Valley, Sonora, Mexico

The objective of this study was to determine arsenic exposure via drinking water and to characterize urinary arsenic excretion among adults in the Yaqui Valley, Sonora, Mexico. A cross-sectional study was conducted from July 2001 to May 2002. Study subjects were from the Yaqui Valley, Sonora, Mexico, residents of four towns with different arsenic concentrations in their drinking water. Arsenic exposure was estimated through water intake over 24 h. Arsenic excretion was assessed in the first morning void urine. Total arsenic concentrations and their species arsenate (As V), arsenite (As III), monomethyl arsenic (MMA), and dimethyl arsenic (DMA) were determined by HPLC/ICP-MS. The town of Esperanza with the highest arsenic concentration in water had the highest daily mean intake of arsenic through drinking water, the mean value was 65.5 microg/day. Positive correlation between total arsenic intake by drinking water/day and the total arsenic concentration in urine (r = 0.50, P < 0.001) was found. Arsenic excreted in urine ranged from 18.9 to 93.8 microg/L. The people from Esperanza had the highest geometric mean value of arsenic in urine, 65.1 microg/L, and it was statistically significantly different from those of the other towns (P < 0.005). DMA was the major arsenic species in urine (47.7-67.1%), followed by inorganic arsenic (16.4-25.4%), and MMA (7.5-15%). In comparison with other reports the DMA and MMA distribution was low, 47.7-55.6% and 7.5-9.7%, respectively, in the urine from the Yaqui Valley population (except the town of Cocorit). The difference in the proportion of urinary arsenic metabolites in those towns may be due to genetic polymorphisms in the As methylating enzymes of these populations.     

Hair and toenail arsenic concentrations of residents living in areas with high environmental arsenic concentrations

Surface soil and groundwater in Australia have been found to contain high concentrations of arsenic. The relative importance of long-term human exposure to these sources has not been established. Several studies have investigated long-term exposure to environmental arsenic concentrations using hair and toenails as the measure of exposure. Few have compared the difference in these measures of environmental sources of exposure. In this study we aimed to investigate risk factors for elevated hair and toenail arsenic concentrations in populations exposed to a range of environmental arsenic concentrations in both drinking water and soil as well as in a control population with low arsenic concentrations in both drinking water and soil. In this study, we recruited 153 participants from areas with elevated arsenic concentrations in drinking water and residential soil, as well as a control population with no anticipated arsenic exposures. The median drinking water arsenic concentrations in the exposed population were 43.8 micro g/L (range, 16.0-73 micro g/L) and median soil arsenic concentrations were 92.0 mg/kg (range, 9.1-9,900 mg/kg). In the control group, the median drinking water arsenic concentration was below the limit of detection, and the median soil arsenic concentration was 3.3 mg/kg. Participants were categorized based on household drinking water and residential soil arsenic concentrations. The geometric mean hair arsenic concentrations were 5.52 mg/kg for the drinking water exposure group and 3.31 mg/kg for the soil exposure group. The geometric mean toenail arsenic concentrations were 21.7 mg/kg for the drinking water exposure group and 32.1 mg/kg for the high-soil exposure group. Toenail arsenic concentrations were more strongly correlated with both drinking water and soil arsenic concentrations; however, there is a strong likelihood of significant external contamination. Measures of residential exposure were better predictors of hair and toenail arsenic concentrations than were local environmental concentrations.     

Arsenate sorption on two Chinese red soils evaluated with macroscopic measurements and extended X-ray absorption fine-structure spectroscopy

Arsenic sorption is the primary factor that affects the bioavailability and mobility of arsenic in soils. To elucidate the characteristics and mechanisms of arsenate, As(V), sorption on soils, a combination of sorption isotherms, zeta potential measurements, and extended X-ray absorption fine-structure (EXAFS) spectroscopy was used to investigate As(V) sorption on two Chinese red soils. Arsenate sorption increased with increasing As(V) concentration and was insensitive to ionic strength changes at pH 6.0. Arsenate, mainly as H2AsO4- in soil solution at pH 6.0, was strongly sorbed mainly through ligand exchange by the two soils. The sorption capacity was affected by the iron and aluminum mineral contents in the soils. The zeta potential measurements showed that As(V) sorption lowered the zeta potential and the points of zero charge of the soils. The EXAFS data indicate that adsorbed As(V) forms inner-sphere complexes with bidentate-binuclear configurations, as evidenced by an As-Fe bond distance of 3.28 +/- 0.04 A and an As-Al bond distance of 3.17 +/- 0.03 A. The two As(V) complexes were stable at different As(V) loadings, whereas the proportions were related to the aluminum and iron mineral contents in the soils. This study illuminated the importance of inclusion of microscopic and macroscopic experiments to elucidate sorption behavior and mechanisms.     

Total arsenic accumulation in yabbies (Cherax destructor Clark) exposed to elevated arsenic levels in Victorian gold mining areas, Australia

Arsenic is a proven carcinogen often found at high concentrations in association with gold and other heavy metals. The freshwater yabby, Cherax destructor Clark (Decapoda, Parastacidae), is a ubiquitous species native to Australia's central and eastern regions, with a growing international commercial market. However, in this region of Australia, yabby farmers often harvest organisms from old mine tailings dams with elevated environmental arsenic levels. Yabbies exposed to elevated environmental arsenic were found to accumulate and store as much as 100 microg/g arsenic in their tissues. The accumulation is proportional to the concentration of arsenic in the sediment and is high enough to be of concern for people who eat the yabbies. A comparison of arsenic levels in wild and lab-fed animals also was performed. Although there was no significant difference in the level of arsenic in the various organs of the wild animals, the animals purchased from a yabby farm showed a significantly higher arsenic concentration in their hepatopancreas (3.7 +/- 0.9 microg/g) compared to other organs (0.6-1.8 microg/g). Furthermore, after a 40-d exposure to food containing 200 to 300 microg/g inorganic arsenic, arsenate (As[V])-exposed animals showed a significant increase in tissue-specific arsenic accumulation, whereas arsenite (As[III])-exposed animals showed a lower, nonsignificant increase in As uptake, primarily in the hepatopancreas. These results have important implications for yabby growers and consumers alike.     

Occurrence,speciation analysis and health risk assessment of arsenic in Chinese mitten crabs (Eriocheir sinensis) collected from China

Arsenic (As) is a major hazardous element in natural environments, and arsenic pollution is becoming an issue of concern worldwide. The more toxic inorganic arsenic, such as trivalent arsenite As(Ⅲ) and pentavalent arsenate As(Ⅴ), which normally can transform to organic arsenic compounds, such as arsenobetaine (AsB), arsenocholine (AsC), monomethyl arsenic acid (MMA), dimethyl arsenic acid (DMA), trimethyl arsenic acid (TMA), arsenosugars and arsenolipids. In this study, a total of 2130 individuals of Chinese mitten crabs were collected from seven locations and mixed to 71 samples. Total arsenic and six major species (AsC, AsB, DMA, MMA, As (Ⅲ), and As (Ⅴ)) were determined by inductively coupled plasma mass spectrometry (ICP-MS) and high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS), respectively. The target hazard quotient (THQ) was utilized to evaluate the human health risk. The total arsenic concentration and totals for the six arsenic forms are 0.25–1.66 mg/kg and 0.05–1.19 mg/kg wet mass, respectively. Except for HH and LH, the six arsenic species concentrations accounted for more than 50.0 % of the total arsenic. The less toxic AsB is the most predominant in crabs, comprising 50.0 %–90.0 % of the sum of six types of arsenic. The more toxic inorganic arsenic only range from 0.01 to 0.21 mg/kg wet mass, much less than the limit content of 0.50 mg/kg inorganic As in crustacea. The THQ values of inorganic arsenic through the consumption of Chinese mitten crabs are estimated, and the values are all less than 1, indicating that intaking Chinese mitten crabs collected from China will not cause an appreciable hazard risk to human health.     

Influence of soil properties and aging on arsenic phytotoxicity

Bioavailability of As varies among soils, and this needs to be taken into account during environmental risk assessment. Using a standardized barley root elongation assay, we investigated the phytotoxicity of arsenate added to 16 European soils that varied widely in their physicochemical properties. The effective concentrations of As causing 10% (EC10) and 50% (EC50) inhibition were estimated based on the concentrations of total added As or As extracted with 0.05 M (NH4)2SO4 or 0.05 M NH4H2PO4. In addition, four soils were used to evaluate changes in arsenate phytotoxicity over a three-month period. The EC10s and EC50s of added As varied from 4.2 to 206.7 mg/kg and from 26.6 to 458.2 mg/kg, respectively. Multiple-regression analysis showed that the variability in the EC10 and EC50 was largely (>89%) explained by the contents of amorphous Mn oxide and clay and, to a lesser extent, Fe oxide, indicating that arsenate adsorption was a key factor controlling its bioavailability. Neither (NH4)2SO4 nor NH4H2PO4 extraction could explain arsenate phytotoxicity independently of soil properties. Furthermore, arsenate phytotoxicity decreased significantly after aging for three months, although the extent of aging differed among soils. This aging effect should be taken into account during the risk assessment.