31-13 Characterizing the Mobilizable Arsenic Pool in Cambodian Rice Paddy Soils Through a Series of Rapid Soil Incubations and Digestions

Session: Environmental Geochemistry and Health (Posters)

Poster Booth No.: 39

Presenting Author:

Alexandra Lim

Authors:

Lim, Alexandra¹, Stahl, Mason Odell², Chambial, Sienna³, Casassa, Amelia⁴, Lawless, Keith⁵, Phin, Samnang⁶, Phan, Kongkea⁷, Phan, Samrach⁸, Coleman, Eva⁹, Thompson, Emma¹⁰, Tran, My-Thu¹¹, Sousa, Daniel¹², Kothandaraman, Chellam¹³, Halpert, Eden¹⁴, Bostick, Benjamin C.¹⁵

(1) Geosciences, Union College, Schenectady, NY, USA, (2) Geosciences, Union College, Schenectady, NY, USA, (3) Geosciences, Union College, Schenectady, NY, USA, (4) Geosciences, Union College, Schenectady, NY, USA, (5) Geosciences, Union College, Schenectady, NY, USA, (6) Water Innovation Lab, Cambodia, (7) Water Innovation Lab, Cameroon, (8) Water Innovation Lab, Cambodia, (9) Geography, San Diego State University, San Diego, CA, USA, (10) Geography, San Diego State University, San Diego, CA, USA, (11) Geography, San Diego State University, San Diego, CA, USA, (12) Geography, San Diego State University, San Diego, CA, USA, (13) Barnard College, New York, NY, USA, (14) Lamont Doherty Earth Observatory, Columbia University, Palisades, NY, USA, (15) Lamont Doherty Earth Observatory, Columbia University, Palisades, NY, USA,

Abstract:

Inorganic arsenic (As) is a carcinogenic metalloid that is found naturally in soils worldwide. Rice is highly susceptible to accumulating As within its grain due to the plant's unique physiology and the environmental conditions under which it is grown. In particular, the flooding of rice paddies can lead to anaerobic conditions that drive the reductive dissolution of arsenic-bearing iron oxides in the soils. Once As is mobilized from the soil, it can be taken up by the rice crop and accumulate in the grain.

Arsenic uptake into the rice crop reduces yields and poses serious health risks to those who consume the grain. However, there are difficulties in predicting rice grain As levels, which depend on the complex interactions of environmental factors, including rice paddy hydrology, climate, and soil properties. These factors result in highly variable As levels in soil and rice grain. Further complicating predictions of grain As is the fact that rice grain As levels are poorly correlated to bulk soil As concentrations. The ability to predict which fields have the potential for high As in rice grains is critical for mitigating As exposure.

This limited relationship between bulk soil As levels and rice grain As may be in part driven by variation in how solid-phase As is partitioned within the soil (e.g., weakly or strongly adsorbed, incorporated in mineral phases). To better understand this disconnect, we conducted a series of rapid laboratory incubations and rapid soil digestions on over 150 fields across a wide range of settings in Cambodia. Due to Cambodia’s largely traditional farming practices, which use minimal inputs (e.g., chemical fertilizers, herbicides, and irrigation), Cambodia provides a window into how environmental conditions affect As mobilization and uptake into rice. For Cambodians, As intake through rice is a significant health concern because of high As concentrations and their reliance on rice for over 60% of their caloric intake. In this study, we connect our soil incubations and digestions with rice grain As levels measured on these same fields. We find that these rapid and easy-to-implement methods shed light on As partitioning in the soil and the potential of a given rice paddy to produce high-As rice grain.

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