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Fang X, Colina Blanco AE, Christl I, Le Bars M, Straub D, Kleindienst S, Planer-Friedrich B, Zhao FJ, Kappler A, Kretzschmar R. Simultaneously decreasing arsenic and cadmium in rice by soil sulfate and limestone amendment under intermittent flooding. Environ Pollut 2024; 347:123786. [PMID: 38484962 DOI: 10.1016/j.envpol.2024.123786] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2023] [Revised: 02/22/2024] [Accepted: 03/12/2024] [Indexed: 03/19/2024]
Abstract
Water management in paddy soils can effectively reduce the soil-to-rice grain transfer of either As or Cd, but not of both elements simultaneously due to the higher mobility of As under reducing and Cd under oxidizing soil conditions. Limestone amendment, the common form of liming, is well known for decreasing Cd accumulation in rice grown on acidic soils. Sulfate amendment was suggested to effectively decrease As accumulation in rice, especially under intermittent soil flooding. To study the unknown effects of combined sulfate and limestone amendment under intermittent flooding for simultaneously decreasing As and Cd in rice, we performed a pot experiment using an acidic sandy loam paddy soil. We also included a clay loam paddy soil to study the role of soil texture in low-As rice production under intermittent flooding. We found that liming not only decreased rice Cd concentrations but also greatly decreased dimethylarsenate (DMA) accumulation in rice. We hypothesize that this is due to suppressed sulfate reduction, As methylation, and As thiolation by liming in the sulfate-amended soil and a higher share of deprotonated DMA at higher pH which is taken up less readily than protonated DMA. Decreased gene abundance of potential soil sulfate-reducers by liming further supported our hypothesis. Combined sulfate and limestone amendment to the acidic sandy loam soil produced rice with 43% lower inorganic As, 72% lower DMA, and 68% lower Cd compared to the control soil without amendment. A tradeoff between soil aeration and water availability was observed for the clay loam soil, suggesting difficulties to decrease As in rice while avoiding plant water stress under intermittent flooding in fine-textured soils. Our results suggest that combining sulfate amendment, liming, and intermittent flooding can help to secure rice safety when the presence of both As and Cd in coarse-textured soils is of concern.
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Affiliation(s)
- Xu Fang
- Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, CHN, ETH Zurich, CH-8092, Zurich, Switzerland.
| | - Andrea E Colina Blanco
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440, Bayreuth, Germany
| | - Iso Christl
- Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, CHN, ETH Zurich, CH-8092, Zurich, Switzerland
| | - Maureen Le Bars
- Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, CHN, ETH Zurich, CH-8092, Zurich, Switzerland
| | - Daniel Straub
- Quantitative Biology Center (QBiC), University of Tuebingen, 72076, Tuebingen, Germany; Cluster of Excellence: EXC 2124: Controlling Microbes to Fight Infection, Tuebingen, 72076, Germany
| | - Sara Kleindienst
- Microbial Ecology, Department of Geosciences, University of Tuebingen, 72076, Tuebingen, Germany; Now: Department of Environmental Microbiology, Institute for Sanitary Engineering, Water Quality and Solid Waste Management (ISWA), University of Stuttgart, Stuttgart, 70569, Germany
| | - Britta Planer-Friedrich
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440, Bayreuth, Germany
| | - Fang-Jie Zhao
- College of Resources and Environmental Sciences, Nanjing Agricultural University, 210095, Nanjing, China
| | - Andreas Kappler
- Cluster of Excellence: EXC 2124: Controlling Microbes to Fight Infection, Tuebingen, 72076, Germany; Geomicrobiology, Department of Geosciences, Tuebingen University, 72076, Tuebingen, Germany
| | - Ruben Kretzschmar
- Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, CHN, ETH Zurich, CH-8092, Zurich, Switzerland
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Colina Blanco AE, Higa Mori A, Planer-Friedrich B. Widespread occurrence of dimethylmonothioarsenate (DMMTA) in rice cakes: Effects of puffing and storage. Food Chem 2024; 436:137723. [PMID: 37862982 DOI: 10.1016/j.foodchem.2023.137723] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Revised: 09/29/2023] [Accepted: 10/08/2023] [Indexed: 10/22/2023]
Abstract
Thioarsenates have recently been detected in rice and rice-based products, with particularly high contents in puffed rice cakes. Here, we show that puffing rice can cause almost complete transformation of dimethylarsenate (DMA) to dimethyldithioarsenate (DMDTA) and dimethylmonothioarsenate (DMMTA). Analysis of puffed rice cakes after 3 months of non-sealed storage at room temperature showed transformation of DMDTA mainly into DMMTA. From a food safety perspective, this likely represents an increased risk because DMMTA is highly cytotoxic and misidentified as non-regulated DMA by routine acid extractions. Analysis of 80 commercial puffed rice cakes confirmed widespread occurrence of thioarsenates. The sum of non-regulated, but potentially toxic DMMTA and DMDTA reached values up to 537 µg·kg-1 and 241 µg·kg-1 for generic and infant-labeled rice cakes, respectively. Our results highlight the importance of better understanding (de)thiolation processes along the rice cake-production chain and potentially revising current thresholds set for iAs to include DMMTA and DMDTA.
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Affiliation(s)
- Andrea E Colina Blanco
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440 Bayreuth, Germany.
| | - Alejandra Higa Mori
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440 Bayreuth, Germany.
| | - Britta Planer-Friedrich
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440 Bayreuth, Germany.
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Colina Blanco AE, Pischke E, Higa Mori A, Kerl CF, Clemens S, Planer-Friedrich B. In Planta Arsenic Thiolation in Rice and Arabidopsis thaliana. Environ Sci Technol 2023; 57:21846-21854. [PMID: 38093687 DOI: 10.1021/acs.est.3c06603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2023]
Abstract
Inorganic and methylated thioarsenates have recently been reported to form in paddy soil pore waters and accumulate in rice grains. Among them, dimethylmonothioarsenate (DMMTA) is particularly relevant because of its high cytotoxicity and potential misidentification as nonregulated dimethylarsenate (DMA). Studying DMMTA uptake and flag leaf, grain, and husk accumulation in rice plants during grain filling, substantial dethiolation to DMA was observed with only 8.0 ± 0.1, 9.1 ± 0.6, and 1.4 ± 0.2% DMMTA remaining, respectively. More surprisingly, similar shares of DMMTA were observed in control experiments with DMA, indicating in planta DMA thiolation. Exposure of different rice seedling varieties to not only DMA but also to arsenite and monomethylarsenate (MMA) revealed in planta thiolation as a common process in rice. Up to 35 ± 7% DMA thiolation was further observed in the shoots and roots of the model plant Arabidopsis thaliana. Parameters determining the ratio and kinetics of thiolation versus dethiolation are unknown, yet, but less DMA thiolation in glutathione-deficient mutants compared to wild-type plants suggested glutathione concentration as one potential parameter. Our results demonstrate that pore water is not the only source for thioarsenates in rice grains and that especially the currently nonregulated DMA needs to be monitored as a potential precursor of DMMTA formation inside rice plants.
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Affiliation(s)
- Andrea E Colina Blanco
- Environmental Geochemistry Group, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440 Bayreuth, Germany
| | - Erik Pischke
- Plant Physiology, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Alejandra Higa Mori
- Environmental Geochemistry Group, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440 Bayreuth, Germany
| | - Carolin F Kerl
- Environmental Geochemistry Group, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440 Bayreuth, Germany
| | - Stephan Clemens
- Plant Physiology, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Britta Planer-Friedrich
- Environmental Geochemistry Group, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440 Bayreuth, Germany
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4
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Kerl CF, Basallote MD, Käberich M, Oldani E, Cerón Espejo NP, Colina Blanco AE, Cánovas CR, Nieto JM, Planer-Friedrich B. Consequences of sea level rise for high metal(loid) loads in the Ría of Huelva estuary sediments. Sci Total Environ 2023; 873:162354. [PMID: 36822435 DOI: 10.1016/j.scitotenv.2023.162354] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Revised: 02/13/2023] [Accepted: 02/16/2023] [Indexed: 06/18/2023]
Abstract
Ría of Huelva, located in southwestern Spain, is a highly metal(loid)-contaminated estuary system where sediments are exceeding action limits in an increasing order for Cd, Zn, Pb, Cu, and As. With a predicted sea level rise over the next 50 years, the estuary will be subject to flooding with brackish water or seawater. To evaluate the risk of metal(loid) mobilization under future climate scenarios, different locations along the estuary were sampled at different depths. Samples were flooded with river water, brackish water, and seawater under different short- and long-term laboratory setups. Potential metal(loid) mobilization showed that water quality standards for As, Pb, Zn, Ni, Cu, and Cd could be exceeded upon seawater flooding. However, metal(loid) mobilization was not predictable solely based on sediment loads. The driving factors for cation and anion mobility were identified to be mainly pH under low salinity and competitive desorption under high salinity conditions. Further drivers such as wave movement or labile C input in C-limited systems were found to enhance metal(loid) mobilization. Long-term flooding of intact sediment cores revealed that sea level rise will have different effects on the estuary system depending on duration of flooding. Short-term flooding in the near future will first affect alkaline sediments and enhance currently low cation mobilization, while anion mobilization due to reductive Fe dissolution will remain high. Once acidic sediments further inland are flooded with seawater, highest contaminant mobilization can be expected as high salinity will further enhance already high cation mobilization under acidic pH. Long-term flooding with seawater will neutralize the sediment pH and limit cation mobilization compared to acidic pH. However, the contaminant load stored in the estuary is so high that, extrapolating data obtained, mobilization could last for >1000 years, e.g. for As, Pb, and Al.
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Affiliation(s)
- Carolin F Kerl
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - M Dolores Basallote
- Department of Earth Sciences & Research Center on Natural Resources, Health and the Environment (RENSMA), University of Huelva, Huelva 21071, Spain
| | - Merle Käberich
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Erica Oldani
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Nathalia P Cerón Espejo
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Andrea E Colina Blanco
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Carlos Ruiz Cánovas
- Department of Earth Sciences & Research Center on Natural Resources, Health and the Environment (RENSMA), University of Huelva, Huelva 21071, Spain
| | - José Miguel Nieto
- Department of Earth Sciences & Research Center on Natural Resources, Health and the Environment (RENSMA), University of Huelva, Huelva 21071, Spain
| | - Britta Planer-Friedrich
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany.
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5
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Fang X, Christl I, Colina Blanco AE, Planer-Friedrich B, Zhao FJ, Kretzschmar R. Decreasing arsenic in rice: Interactions of soil sulfate amendment and water management. Environ Pollut 2023; 322:121152. [PMID: 36731739 DOI: 10.1016/j.envpol.2023.121152] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Revised: 12/13/2022] [Accepted: 01/23/2023] [Indexed: 06/18/2023]
Abstract
Accumulation of inorganic arsenic (iAs) and dimethylarsenate (DMA) in rice threatens human health and rice yield, respectively. We studied the yet unclear interactions of soil sulfate amendment and water management for decreasing As accumulation in rice grain in a pot experiment. We show that soil sulfate amendment (+200 mg S/kg soil) decreased grain iAs by 44% without clearly increasing grain DMA under intermittent flooding from booting stage to maturation. Under continuous flooding during this period, sulfate amendment decreased grain iAs only by 25% but increased grain DMA by 68%. The mechanisms of sulfate amendment effects on grain iAs were not explained by porewater composition or in-planta As sequestration but were allocated to the rhizosphere. Grain iAs closely correlated with As in the root iron-plaque (r = 0.92) which was effectively decreased by sulfate amendment and may have acted as an iAs source for rice uptake. Although both sulfate amendment and intermittent flooding substantially increased porewater DMA concentrations, it was the continuous flooding, irrespective of sulfate amendment, that resulted in rice straighthead disease with 47-55% less yield and 258-320% more DMA in grains than intermittent flooding. This study suggests that combining soil sulfate amendment and intermittent flooding can help to secure the quantity and quality of rice produced in As-affected areas. Our results also imply the key role of rhizosphere processes in controlling both iAs and DMA accumulation in rice which should be elucidated in the future.
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Affiliation(s)
- Xu Fang
- Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, ETH Zurich, Zurich, CH-8092, Switzerland.
| | - Iso Christl
- Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, ETH Zurich, Zurich, CH-8092, Switzerland
| | - Andrea E Colina Blanco
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, Bayreuth, 95440, Germany
| | - Britta Planer-Friedrich
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, Bayreuth, 95440, Germany
| | - Fang-Jie Zhao
- College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, 210095, China
| | - Ruben Kretzschmar
- Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, ETH Zurich, Zurich, CH-8092, Switzerland
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6
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Planer-Friedrich B, Kerl CF, Colina Blanco AE, Clemens S. Dimethylated Thioarsenates: A Potentially Dangerous Blind Spot in Current Worldwide Regulatory Limits for Arsenic in Rice. J Agric Food Chem 2022; 70:9610-9618. [PMID: 35901520 DOI: 10.1021/acs.jafc.2c02425] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Arsenic (As) occurrence in rice is a serious human health threat. Worldwide, regulations typically limit only carcinogenic inorganic As, but not possibly carcinogenic dimethylated oxyarsenate (DMA). However, there is emerging evidence that "DMA", determined by routine acid-based extraction and analysis, hides a substantial share of dimethylated thioarsenates that have similar or higher cytotoxicities than arsenite. Risk assessments characterizing the in vivo toxicity of rice-derived dimethylated thioarsenates are urgently needed. In the meantime, either more sophisticated methods based on enzymatic extraction and separation of dimethylated oxy- and thioarsenates have to become mandatory or total As should be regulated.
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Affiliation(s)
- Britta Planer-Friedrich
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Carolin F Kerl
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Andrea E Colina Blanco
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Stephan Clemens
- Plant Physiology, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
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7
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Pischke E, Barozzi F, Colina Blanco AE, Kerl CF, Planer-Friedrich B, Clemens S. Dimethylmonothioarsenate Is Highly Toxic for Plants and Readily Translocated to Shoots. Environ Sci Technol 2022; 56:10072-10083. [PMID: 35759640 DOI: 10.1021/acs.est.2c01206] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Arsenic is one of the most relevant environmental pollutants and human health threats. Several arsenic species occur in soil pore waters. Recently, it was discovered that these include inorganic and organic thioarsenates. Among the latter, dimethylmonothioarsenate (DMMTA) is of particular concern because in mammalian cells, its toxicity was found to exceed even that of arsenite. We investigated DMMTA toxicity for plants in experiments with Arabidopsis thaliana and indeed observed stronger growth inhibition than with arsenite. DMMTA caused a specific, localized deformation of root epidermal cells. Toxicity mechanisms apparently differ from those of arsenite since no accumulation of reactive oxygen species was observed in DMMTA-exposed root tips. Also, there was no contribution of the phytochelatin pathway to the DMMTA detoxification as indicated by exposure experiments with respective mutants and thiol profiling. RNA-seq analysis found strong transcriptome changes dominated by stress-responsive genes. DMMTA was taken up more efficiently than the methylated oxyarsenate dimethylarsenate and highly mobile within plants as revealed by speciation analysis. Shoots showed clear indications of DMMTA toxicity such as anthocyanin accumulation and a decrease in chlorophyll and carotenoid levels. The toxicity and efficient translocation of DMMTA within plants raise important food safety issues.
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Affiliation(s)
- Erik Pischke
- Plant Physiology, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Fabrizio Barozzi
- Plant Physiology, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Andrea E Colina Blanco
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Carolin F Kerl
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Britta Planer-Friedrich
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
| | - Stephan Clemens
- Plant Physiology, Bayreuth Center for Ecology and Environmental Research (BayCEER), University of Bayreuth, D-95440 Bayreuth, Germany
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Abstract
Inorganic and methylated thioarsenates have recently been reported to contribute substantially to arsenic (As) speciation in paddy-soil pore waters. Here, we show that thioarsenates can also accumulate in rice grains and rice products. For their detection, a method was developed using a pepsin-pancreatin enzymatic extraction followed by chromatographic separation at pH 13. From 54 analyzed commercial samples, including white, parboiled and husked rice, puffed rice cakes, and rice flakes, 50 contained dimethylmonothioarsenate (DMMTA) (maximum 25.6 μg kg-1), 18 monothioarsenate (MTA) (maximum 5.6 μg kg-1), 14 dimethyldithioarsenate (DMDTA) (maximum 2.8 μg kg-1), and 5 dithioarsenate (DTA) (maximum 2.3 μg kg-1). Additionally, we show that the commonly used nitric acid extraction transforms MTA to arsenite and DMMTA and DMDTA to dimethylarsenate (DMA). Current food guidelines do not require an analysis of thioarsenates in rice and only limit the contents of inorganic oxyarsenic species (including acid-extraction-transformed MTA), but not DMA (including acid-extraction-transformed DMMTA and DMDTA).
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Affiliation(s)
- Andrea E Colina Blanco
- Department of Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440 Bayreuth, Germany
| | - Carolin F Kerl
- Department of Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440 Bayreuth, Germany
| | - Britta Planer-Friedrich
- Department of Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BAYCEER), University of Bayreuth, 95440 Bayreuth, Germany
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Kerl CF, Schindele RA, Brüggenwirth L, Colina Blanco AE, Rafferty C, Clemens S, Planer-Friedrich B. Methylated Thioarsenates and Monothioarsenate Differ in Uptake, Transformation, and Contribution to Total Arsenic Translocation in Rice Plants. Environ Sci Technol 2019; 53:5787-5796. [PMID: 31033272 DOI: 10.1021/acs.est.9b00592] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Methylated and inorganic thioarsenates have recently been reported from paddy fields besides the better-known oxyarsenates. Methylated thioarsenates are highly toxic for humans, yet their uptake, transformation, and translocation in rice plants is unknown. Here, hydroponic experiments with 20 day old rice plants showed that monomethylmonothioarsenate (MMMTA), dimethylmonothioarsenate (DMMTA), and monothioarsenate (MTA) were taken up by rice roots and could be detected in the xylem. Total arsenic (As) translocation from roots to shoots was higher for plants exposed to DMMTA, MTA, and dimethylarsenate (DMAV) compared to MMMTA and monomethylarsenate (MMAV). All thioarsenates were partially transformed in the presence of rice roots, but processes and extents differed. MMMTA was subject to abiotic oxidation and largely dethiolated to MMAV already outside the plant, probably due to root oxygen loss. DMMTA and MTA were not oxidized abiotically. Crude protein extracts showed rapid enzymatic reduction for MTA but not for DMMTA. Our study implies that DMMTA has the highest potential to contribute to total As accumulation in grains either as DMAV or partially as DMMTA. DMMTA has once been detected in rice grains using enzymatic extraction. By routine acid extraction, DMMTA is determined as DMAV and thus escapes regulation despite its toxicity.
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Affiliation(s)
- Carolin F Kerl
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER) , University of Bayreuth , D-95440 Bayreuth , Germany
| | - Ruth Alina Schindele
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER) , University of Bayreuth , D-95440 Bayreuth , Germany
| | - Lena Brüggenwirth
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER) , University of Bayreuth , D-95440 Bayreuth , Germany
| | - Andrea E Colina Blanco
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER) , University of Bayreuth , D-95440 Bayreuth , Germany
| | - Colleen Rafferty
- Plant Physiology, Bayreuth Center for Ecology and Environmental Research (BayCEER) , University of Bayreuth , D-95440 Bayreuth , Germany
| | - Stephan Clemens
- Plant Physiology, Bayreuth Center for Ecology and Environmental Research (BayCEER) , University of Bayreuth , D-95440 Bayreuth , Germany
| | - Britta Planer-Friedrich
- Environmental Geochemistry, Bayreuth Center for Ecology and Environmental Research (BayCEER) , University of Bayreuth , D-95440 Bayreuth , Germany
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