Multiscale Assessment of Methylarsenic Reactivity in Soil. 2. Distribution and Speciation in Soil

Shimizu, Masayuki; Arai, Yuji; Sparks, Donald L.

doi:10.1021/es103577e

Cited by 46 publications

(50 citation statements)

References 35 publications

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“…20,21,46,47 Furthermore, arsM copy number was found to be significantly higher in the rhizosphere soil than in the bulk soil and to be enhanced by the addition of rice straw, 36 both suggesting a positive effect of organic substrate addition possibly due to increased food source for the As methylation microbes. Soil flooding was found to enhance As methylation in soil 21,48 and to increase the concentration of DMA in rice grain. 2,3, 49 Because inorganic As is the substrate for methylation, it might be expected that the concentrations of methylated As and inorganic As in soil pore water would correlate with each other.…”

Section: ■ Discussionmentioning

confidence: 96%

Arsenic Methylation in Soils and Its Relationship with Microbial arsM Abundance and Diversity, and As Speciation in Rice

Zhao

Harris

Jia

et al. 2013

Environ. Sci. Technol.

187

125

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Methylation of arsenic in soil influences its environmental behavior and accumulation by plants, but little is known about the factors affecting As methylation. As speciation was determined in the pore waters of six soils from diverse geographical locations over 54 days of incubation under flooded conditions. The concentration of methylated As (monomethylarsonic acid, MMA, and dimethylarsinic acid, DMA) varied from 0 to 85 μg L −1 (0 − 69% of the total As in pore water). Two Bangladeshi paddy soils contaminated by irrigation of As-laden groundwater produced large concentrations of inorganic As but relatively little methylated As. Two contaminated paddy soils from China produced a transient peak of DMA during the early phase of incubation. Methylated As represented considerable proportions of the total soluble As in the two uncontaminated soils from the UK and U.S. The copy number of the microbial arsenite methyltransferase gene (arsM) correlated positively with soil pH. However, pore-water methylated As correlated negatively with pH or arsM copy number, and positively with dissolved organic C. GeoChip assay revealed considerable arsM diversity among the six soils, with 27−35 out of 66 sequences in the microarray being detected. As speciation in rice plants grown in the soils generally mirrored that in the pore water. The results suggest that methylated As species in plants originated from the soil and As methylation in soil was influenced strongly by the soil conditions. ■ INTRODUCTIONArsenic (As) is a ubiquitous contaminant in the environment originating from both natural and anthropogenic sources. Because its biogeochemical behavior and toxicity vary greatly among different chemical species, it is important to understand how the speciation of As changes in the environment and what drives such changes. A particularly important case is the paddy rice system because it is now recognized that rice is a major source of As in the human diet. 1 The anaerobic conditions in paddy soils are conducive to the mobilization of arsenite, 2,3 which is taken up inadvertently by rice roots through the strong uptake pathway for silicic acid. 4 Rice grain contains both inorganic As (arsenate and arsenite) and organic As (mostly dimethylarsinic acid, DMA; occasionally also trace amounts of monomethylarsonic acid, MMA, and tetramethylarsonium). 5−9 As speciation in rice varies widely among different riceproducing regions. Market-basket surveys show that Asian rice generally is dominated by inorganic As with DMA typically accounting for about 20% of the total As. [5][6][7]10 In contrast, rice produced in the U.S. and Europe is more variable in As speciation with many samples containing more organic than inorganic As. 5,7,8,10 It is possible that that this geographical pattern reflects the relative bioavailability of inorganic versus organic As in different paddy environments. 10 Compared with inorganic As, methylated As species are more easily accumulated in rice grain. 10 Although pentavalent methylated As species are ...

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Section: ■ Discussionmentioning

confidence: 96%

Arsenic Methylation in Soils and Its Relationship with Microbial arsM Abundance and Diversity, and As Speciation in Rice

Zhao

Harris

Jia

et al. 2013

Environ. Sci. Technol.

187

125

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“…However, the majority of microorganisms exhibited a relatively limited ability to volatilize As [25]. Besides environmental factors such as organic matter [13,18], moisture content [ 19], pH [ 20], temperature [ 21], Fe(II) and NH 4+ [ 22], internal factors (such as genes encoding As efflux transporters, arsB, etc.) may also limit As volatilization rate of microorganisms.…”

Section: Discussionmentioning

confidence: 99%

“…However, As volatilization, which is dependent on As methylation, is not efficient for most microorganisms except for Arsenicibacter rosenii SM-1 (47.6±18.4%) [9], possibly Prochlorococcus [15,16] and engineered Pseudomonas putida KT2440 (31%) [17]. On the one hand, some environmental parameters such as organic matter [13,18], moisture content [ 19], pH [ 20], temperature [ 21], Fe(II) and NH 4+ [ 22] are able to affect As volatilization efficiency. These parameters might alter the expression level and activity of the gene products of microbial arsMs, which are the genes encoding ArsM, responsible for As methylation, thereby affecting the As methylation rate [ 20].…”

Section: Introductionmentioning

confidence: 99%

Arsenite efflux limits microbial arsenic volatilization

Ke¹,

Kuang²,

Zhao³

et al. 2019

Preprint

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Background: Arsenic (As) methylation is regarded as a potential way to volatize and thereby remove As from the environment. However, most microorganisms conducting As methylation display low As volatilization efficiency as As methylation is limited by As efflux transporters as both processes compete for arsenite [As(III)]. In the study, we deleted arsB and acr3 from Rhodopseudomonas palustris CGA009, a good model organism for studying As detoxification, and further investigated the effect of As(III) efflux transporters on As methylation. Results: Two mutants were obtained by gene deletion. Compared to the growth inhibition rate (IC50) [1.57±0.11 mmol/L As(III) and 2.67±0.04 mmol/L arsenate [As(V)] of wildtype R. palustris CGA009, the As(III) and As(V) resistance of the mutants decreased, and IC50 value of the R. palustris CGA009 ∆arsB mutant was 1.47±0.02 mmol/L As(III) and 2.12±0.03 mmol/L As(V), respectively, and that of the R. palustris CGA009 ∆acr3 mutant was 1.21±0.07 mmol/L As(III) and 1.76±0.12 mmol/L As(V), respectively. The As volatilization rate of R. palustris CGA009 ∆arsB and R. palustris CGA009 ∆acr3 was 7.36 and 10.46 times higher than that of the R. palustris CGA009 at 100.0 µmol/L As(III) when incubated for 12 h, respectively, and 7.21 and 10.30 times higher than that of the R. palustris CGA009 when incubated with 25.0 mol/L As(V), respectively. At 25.0 mol/L As(III), low doses of methylarsonate [MAs(V)] and dimethylarsonate [DMAs(V)] were detected in both the wild type and in the deletion mutant strains. In addition, the content of As(III) in the medium changed significantly with the order being R. palustris CGA009 > R. palustris CGA009 ∆arsB > R. palustris CGA009 ∆acr3, indicating that Acr3 displayed the highest As(III) efflux rate. Conclusion: The results of this study showed that As efflux transporters were shown to be a remarkable intrinsic factor limiting As volatilization efficiency, and As volatilization rate could be significantly improved by deleting genes encoding microbial As efflux transporters. Our study provided an explanation for the often low rate of microbial As methylation and an effective strategy for screening microorganisms with high As volatilization.

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“…The proportion of DMA was higher in the RZ after drainage at harvest than after intermittent drainage (Figure 2). Since DMA is strongly adsorbed on Fe (hydr)oxide [37,38], it can be sequestered in Fe (hydr)oxide in the rhizosphere, including in Fe plaque [22].…”

Section: Oxidation Of As After Drainagementioning

confidence: 99%

Effects of Iron Amendments on the Speciation of Arsenic in the Rice Rhizosphere after Drainage

Yamaguchi

Ohkura

Hikono

et al. 2017

Soils

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Abstract:Applications of iron-(Fe-) bearing materials represent an effective countermeasure for decreasing the dissolution of arsenic (As) in soil under anaerobic conditions. In this study, we investigated the effects of Fe amendments (ferrihydrite-based and zero-valent iron-(ZVI-) based materials) on the speciation of As in rice cultivated soils and root-attached materials including Fe plaque when the soil shifts from anaerobic to aerobic conditions. Rice (Oryza sativa L.) was cultivated in pots filled with soil under continuous flooding conditions, and root distribution in the soil was restricted inside a cylinder made by nylon mesh. Soil and root samples were collected after drainage at different growth stages of the rice plants, which are represented by intermittent drainage and drainage at harvest. The speciation of As was determined by As K-edge X-ray absorption near edge structure (XANES) spectroscopy. The proportion of arsenite did not differ between the bulk soil and root-attached materials including Fe plaque, whereas a larger proportion of dimethylarsinic acid was found in the root-attached materials regardless of the application of Fe amendments. Observation of soil thin-sections showed that the application of Fe amendments caused an increase in Fe (hydr)oxide deposition around the roots as well as on the soil particles. In addition to Fe (hydr)oxide, sulfide was found to be associated with As under anaerobic conditions, notably for the ZVI-amended soil at the time of intermittent drainage. The concentration of As in the soil solution and As uptake by rice grains decreased, while As speciation near the roots was not influenced by the application of Fe amendments. In conclusion, Fe amendments mitigated As dissolution in the soil solution by providing a sorption site for As in bulk soil without altering As speciation near the roots.

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Multiscale Assessment of Methylarsenic Reactivity in Soil. 2. Distribution and Speciation in Soil

Cited by 46 publications

References 35 publications

Arsenic Methylation in Soils and Its Relationship with Microbial arsM Abundance and Diversity, and As Speciation in Rice

Arsenic Methylation in Soils and Its Relationship with Microbial arsM Abundance and Diversity, and As Speciation in Rice

Arsenite efflux limits microbial arsenic volatilization

Effects of Iron Amendments on the Speciation of Arsenic in the Rice Rhizosphere after Drainage

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