210 Environmental Geochemistry and Health

We invite presentations on the environmental fate of contaminants and their impact on human and environmental health. Transdisciplinary contributions are encouraged, especially those examining the rock-soil-water-human nexus at all scales with strong public outreach or societal impact.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 302A

Connections between surface hydrology and climate on the sulfur cycle in rice paddies, arsenic uptake and accumulation in rice

Paper number: 210-6
Program: Technical Sessions
Time: 2:55 PM – 3:10 PM

Authors

Abstract

Rice is the most consumed staple in the world. Rice grows in paddy soils that are periodically inundated. This flooding is a critical factor in controlling redox chemistry in rice paddies and modulates the aqueous concentrations of many elements in the porewater and rice.  Sulfate reduction has long been recognized as a critical variable in rice health, with excess sulfide being toxic to the plant. This leads to rice actively oxidizing the rhizosphere by introducing oxygen from roots. Thioarsenic complexes form in rice paddies and are important to uptake and translocation to the grain, even when iron is oxidized in the rhizosphere.  Few studies have evaluated the connection between surface water conditions and rice paddy geochemistry in detail, and none have done it at scale.  In this research, we fuse participatory science involving more than 100 farms with detailed hydrologic and geochemical characterization to examine how transient flooding impacts sulfur cycling in Cambodian rice paddies, and how it affects the timing and extent of arsenic release from soils and accumulation in rice plants. We then use reactors containing soils to study the reduced S species formed from rapid sulfate reduction. Our results indicate that arsenic concentrations increase much more rapidly in paddies than overall iron reduction. This rapid release from solids is attributed to the formation of thioarsenate complexes that are weakly retained by soil minerals that retain inorganic arsenate or arsenite. This effect can be tracked across the wider landscape by monitoring the physical environment with remote sensing. High-resolution (~5m) remote sensing of soil moisture records flooding history of rice plants and shows clear relationships with the extent of arsenic accumulation in rice. These factors indicate that rapid sulfur cycling, and the factors that affect it, should be considered when developing strategies to reduce arsenic accumulation in rice.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414866

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