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

Characterizing the Role of Hydrologic Conditions on Rice Arsenic Variability

Paper number: 210-5
Program: Technical Sessions
Time: 2:40 PM – 2:55 PM

Authors

Abstract

Rice is a globally important staple crop, providing 20% of the calories consumed worldwide.  However, as a result of the distinct environmental conditions in which rice is typically grown and the unique physiology of the plant, rice is highly susceptible to the uptake and accumulation of arsenic into its grain.  Arsenic is toxic to both the rice plant itself and to humans that consume the contaminated grain.  Arsenic mobilization from soils and sediments is strongly dependent on redox chemistry and thus characterizing the environmental factors which influence rice paddy redox conditions (e.g., soil moisture levels and flooding frequency) is important to understanding what drives arsenic uptake into rice.

 

To address these questions we sampled over 150 rice fields across Cambodia and have multiple harvest years of data for more than 50 of these fields.  Here we present measurements of rice grain arsenic and stable isotopes (C, N, O) along with field-based and remotely sensed measurements of soil moisture and flooding to identify how hydrologic conditions influence rice grain development and arsenic uptake.  Notably, we find that fields which have experienced frequent flooding in recent decades have substantially less year-to-year variability in rice grain arsenic than those flooded less frequently.  In light of our findings connecting rice paddy hydrologic history to arsenic uptake into the rice grain we examined the use of rice grain stable isotopes as a proxy for the hydrologic conditions in which the rice was grown.  We find that rice grain stable isotopes of carbon and oxygen are a reliable recorder of the soil moisture and flooding conditions experienced by the plant over the course of the growing season.  Our isotopic findings provide a tool for identifying past hydrologic conditions without direct observation, which is of particular use in samples of unknown origin (e.g., rice purchased from a market, historic/archaeological samples of rice).  Taken together our work reveals the importance of long-term flooding conditions on temporal variability in rice grain arsenic and provides isotopic insights into rice paddy hydrologic history, findings which further our understanding of arsenic uptake into rice and may prove useful in developing strategies to mitigate future exposures.

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

doi: 10.1130/abs/2025AM-412056

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