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Home ›› About Speciation ›› Speciation News

Thioarsenate Formation in Rice Plants: A Comprehensive Study on Arsenic Uptake, Accumulation, and Speciation

(01.02.2024)

A group of researchers from the University of Bayreuth investigated the uptake, accumulation and speciation of arsenic by rice plants. Their results indicate that thioarsenate species are formed within the plant.

Background:

Arsenic, a known environmental contaminant, exists in various species, including inorganic forms like arsenite (iAsIII) and arsenate (iAsV), as well as organic forms such as monomethyl arsenic (MMA), dimethyl arsenic (DMA), trimethyl arsenic (TMA), arsenobetaine (AsB), arsenocholine (AsC), arsenosugar (AsS), and arsenolipids (AsLs). The toxicity of arsenic species varies, with inorganic forms generally posing higher risks than their organic counterparts. Due to these differences, accurate risk assessments for arsenic-contaminated food rely on speciation analysis.

Rice, cultivated in paddy fields under reducing conditions, is known to accumulate more arsenic from the soil than other cereals. In this context, understanding arsenic speciation in rice is crucial. In particular, inorganic arsenic poses health risks, leading to global monitoring efforts. However, recent studies have identified the presence of inorganic and methylated thioarsenates in rice paddy pore waters, formed through the activity of sulfate-reducing bacteria. Thioarsenate behaviour in plant tissues remains poorly understood, raising concerns about potential health implications.

Figure: Thioarsenates

The new study:
Researchers from the University of Bayreuth (Germany) conducted an in-depth investigation into thioarsenate distribution in rice plants. The study aimed to compare the uptake, accumulation, transport, translocation, and species transformation of rice plants exposed to dimethylmonothioarsenate (DMMTA) or DMA during the grain filling stage.

Methodology:
The study utilized the rapid life cycle model cultivar Kitaake (ssp. japonica). Exposure levels to DMMTA or DMA were carefully selected to identify minor species without inducing plant toxicity. Various plant parts, including flag leaves, panicles, grains, and husks, were analysed using robust extraction and speciation techniques.

Results and Insights:
When comparing total arsenic accumulation in rice plants exposed to DMMTA or DMA, panicles exposed to DMMTA exhibited a two-fold higher total arsenic content in leaves and grains, suggesting greater mobility of DMMTA in rice plants. Surprisingly, speciation results indicated DMMTA accumulation in DMA-exposed plants, implying its generation within the plant. The study also revealed in planta thiolation as a common process in rice, observed not only with DMA but also with arsenite and monomethylarsenate (MMA).

Conclusion:
The authors underscore the importance of monitoring currently non-regulated DMA as a potential precursor to DMMTA formation within rice plants. This comprehensive study sheds light on the complex dynamics of thioarsenate formation, emphasizing the need for continued research and regulatory consideration in arsenic monitoring programs for rice products.

The original publication

A.E. Colina Blanco, E. Pischke, A. Higa Mori, C.F. Kerl, S. Clemens, B. Planer-Friedrich, In Planta Arsenic Thiolation in Rice and Arabidopsis thaliana, Environ. Sci. Technol., 57/51 (2023) 31846-54. DOI: 10.1021/acs.est.3c06603

Related Studies:

A.E. Colina Blanco, A. Higa Mori, B. Planer-Friedrich, Widespread Occurrence of Dimethylmonothioarsenate (DMMTA) in Rice Cakes: Effects of Puffing and Storage. Food Chem., 436 (2024) No. 137723. DOI: 10.1016/j.foodchem.2023.137723

Britta Planer-Friedrich, Carolin F. Kerl, Andrea E. Colina Blanco, Stephan Clemens, Dimethylated Thioarsenates: A Potentially Dangerous Blind Spot in Current Worldwide Regulatory Limits for Arsenic in Rice, J. Agric. Food Chem., 70/31 (2022) 9610–9618. DOI: 10.1021/acs.jafc.2c02425

J. Dai, Z. Tang, A.X. Gao, B. Planer-Friedrich, P.M. Kopittke, F.J. Zhao, P. Wang, Widespread Occurrence of the Highly Toxic Dimethylated Monothioarsenate (DMMTA) in Rice Globally. Environ. Sci. Technol., 56/6 (2022) 3575−3586. DOI: 10.1021/acs.est.1c08394

E. Pischke, F. Barozzi, A.E. Colina Blanco, C.F. Kerl, B. Planer-Friedrich, S. Clemens, Dimethylmonothioarsenate Is Highly Toxic for Plants and Readily Translocated to Shoots. Environ. Sci. Technol., 56/14 (2022) 10072−10083. DOI: 10.1021/acs.est.2c01206

A.E. Colina Blanco, C.F. Kerl, B. Planer-Friedrich, Detection of Thioarsenates in Rice Grains and Rice Products. J. Agricult. Food Chem., 69/7 (2021) 2287–2294. DOI: 10.1021/acs.jafc.0c06853

J. Dai, C. Chen, A.X. Gao, Z. Tang, P.M. Kopittke, F.J. Zhao, P. Wang, Dynamics of Dimethylated Monothioarsenate (DMMTA) in Paddy Soils and Its Accumulation in Rice Grains. Environ. Sci. Technol., 55/13 (2021) 8665−8674. DOI: 10.1021/acs.est.1c00133

J. Wang, C.F. Kerl, P. Hu, M. Martin, T. Mu, L. Brüggenwirth, G. Wu, D. Said-Pullicino, M. Romani, L. Wu, B. Planer-Friedrich, Thiolated Arsenic Species Observed in Rice Paddy Pore Waters. Nat. Geosci., 13 (2020) 282−287. DOI: 10.1038/s41561-020-0533-1

C.F. Kerl, T.B. Ballarant, B. Planer-Friedrich, Iron Plaque at Rice Roots: No Barrier for Methylated Thioarsenates. Environ. Sci. Technol., 53 (2019) 13666−13674. DOI: 10.1021/acs.est.9b04158

B. Moe, H. Peng, X. Lu, B. Chen, L.W.L. Chen, S. Gabos, X. Li, X.C. Le, Comparative Cytotoxicity of Fourteen Trivalent and Pentavalent Arsenic Species Determined Using Real-Time Cell Sensing. J. Environ. Sci., 49 (2016) 113−124. DOI: 10.1016/j.jes.2016.10.004

W.R. Cullen, M. Fricke, Q. Liu, X. Lu, H. Peng, X. Yan, Q. Zhang, H. Sun, X.C. Le, A. McKnight-Whitford, A. Popowich, X.C. Le, Methylated and Thiolated Arsenic Species for Environmental and Health Research - A Review on Synthesis and Characterization. J. Environ. Sci., 49 (2016) 7−27. DOI: 10.1016/j.jes.2016.11.004

Y.T. Kim, H. Lee, H.O. Yoon, N.C. Woo, Kinetics of Dimethylated Thioarsenicals and the Formation of Highly Toxic Dimethylmonothioarsinic Acid in Environment. Environ. Sci. Technol., 50/21 (2016) 11637−11645. DOI: 10.1021/acs.est.6b02656

H. Naranmandura, M.W. Carew, S. Xu, J. Lee, E.M. Leslie, M. Weinfeld, X.C. Le, Comparative Toxicity of Arsenic Metabolites in Human Bladder Cancer EJ-1 Cells. Chem. Res. Toxicol., 24/9 (2011) 1586−1596. DOI: 10.1021/tx200291p

D. Wallschläger, J. London, Determination of Methylated Arsenic-Sulfur Compounds in Groundwater. Environ. Sci. Technol., 42/1 (2008) 228−234. DOI: 10.1021/es0707815

H.R. Hansen, A. Raab, M. Jaspars, B.F. Milne, J. Feldmann, Sulfur-Containing Arsenical Mistaken for Dimethylarsinous Acid [DMA(III)] and Identified as a Natural Metabolite in Urine: Major Implications for Studies on Arsenic Metabolism and Toxicity. Chem. Res. Toxicol., 17/8 (2004) 1086−1091. DOI: 10.1021/tx049978q

K.T. Suzuki, B.K. Mandal, A. Katagiri, Y. Sakuma, A. Kawakami, Y. Ogra, K. Yamaguchi, Y. Sei, K. Yamanaka, K. Anzai, M. Ohmichi, H. Takayama, N. Aimi, Dimethylthioarsenicals as Arsenic Metabolites and Their Chemical Preparations. Chem. Res. Toxicol., 17/7 (2004) 914−921. DOI: 10.1021/tx049963s