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Faculty for Biology, Chemistry, and Earth Sciences

Environmental Geochemistry Group - Prof. Dr. Britta Planer-Friedrich

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Master Thesis

Effect of sulfate fertilization on Arsenic speciation in paddy soil pore water and rice grains

Aya Bouallegue (07/2019-04/2021)

Support: Britta Planer-Friedrich, Carolin Kerl

Rice is known to accumulate arsenic (As), which constitutes a potential risk to human health. Although sulfate (S)- fertilization was reported to alleviate As accumulation in rice, its effect on As behavior in the pore-water and rice is still not well understood especially under different water managements. Further, the effects of such paddy field managements on the behavior of contaminants (As, Cd, Pb, Sb) and essential micronutrients (Cu, Fe, Mn, Mo, Ni, Zn) are still little investigated. In this study, As concentration and speciation besides concentrations of other metal(loid)s in the pore-water and rice grains were investigated in a two-year mesocosm experiment using two different paddy soils (Fornazzo and Veronica). The study comprised eight treatments; continuously flooding (CF2017) vs. delayed flooding (DF), CF2018 vs. alternate wetting and drying (AWD) conditions, and either with S-addition or not. The results showed that S-fertilization significantly decreased the concentrations of metal(loid)s, As and inorganic As (iAs) in the pore-water and rice grains but promoted As methylation and thiolation with a stronger effect on Veronica compared to Fornazzo. Uptake of dimethylarsenate (DMA) appeared, however, to be controlled by pore-water pH independent of S-addition and water management. Delayed flooding showed the beneficial effect of decreasing Cd accumulation in rice, but was also associated with a slight decrease in Mn and Zn uptake. Sulfate fertilization with DF conditions, lowered As and further decreased grain Cd, Mo, Mn and Zn contents. The opposite effect was noticed for AWD, which decreased As and increased Cu and Mn contents, yet, increased Cd accumulation. Sulfate fertilization with AWD conditions, further decreased As accumulation, while the uptake of Cu and Mo was lower and Cd was higher compared to single S and AWD. None of the treatments significantly affected Fe, Ni, Pb or Sb accumulation. Rice cultivation under S-fertilization and DF conditions appeared to be the best field management in simultaneously alleviating both As and Cd accumulation in rice.

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