Fate of Cadmium and Arsenic Under Engineered Physico-Chemical Gradients in the Soil-Water-Rice Nexus

Rice is a staple food for half the world's population. Despite its importance, the yield and quality of rice are threatened by arsenic and cadmium uptake from soil. Rice will uptake and concentrate arsenic when it is grown under conventional soil flooding, because arsenic is released into the water from biogeochemical reactions in the soil. This process can happen even when soil arsenic concentrations are low. Although minimizing soil flooding can decrease arsenic contamination of rice and even save water resources, doing so can increase rice grain uptake of cadmium from the soil. The goal of this research project is to develop methods that simultaneously limit rice uptake of both arsenic and cadmium. Manganese(II) is less toxic to plants than cadmium or arsenic and has been recently shown to share a root transport pathway with cadmium. Therefore, it should be possible to exploit the geochemical characteristics of manganese to decrease uptake of cadmium into the plant via engineered soil electrochemistry. This research project takes a multidisciplinary approach that incorporates geochemistry and plant biology methods and also will utilize resources at the NSF-funded Rice Investigation, Communication, and Education (RICE) Facility. This work will help train and foster the professional development of the next generation of STEM professionals to tackle the grand challenge of a sustainable food supply. Additional outreach efforts to high schools will increase scientific literacy of students and hopefully interest them in STEM careers.<br/><br/>Rice is often the first food consumed by infants and is also a staple food for half of the global population. However, the yield and quality of rice are threatened by the uptake of toxic arsenic and cadmium during the soil flooding process integral to rice cultivation. Although arsenic cycling has been well studied over the last two decades, cadmium cycling and uptake by rice is less well understood. The hypothesis behind this research project is that controlling manganese(II) availability can provide an engineered solution to limit cadmium and arsenic uptake by rice. The specific objectives of this project are 1) to understand the role of increasing manganese(II) availability in decreasing cadmium uptake by rice in simple hydroponic systems; 2) to evaluate the impact of engineered redox states on dissolution, plant uptake, and localization of metal(loid)s including manganese, iron, cadmium, and arsenic, in rice plants grown in rice paddy mesocosms; and 3) to compare traditional redox measurements to novel techniques for quantifying indicators of reduction in soil (IRIS) films. IRIS film technology will be evaluated as a low-cost means for farmers to know when to drain their fields in order to restrict rice uptake of toxic metalloids. The outcomes of this research will transform the ability of rice agronomists, wetland scientists, farmers, and other stakeholders to prevent toxic metal uptake and thereby safeguard the food supply of billions of people. The results of this study should be applicable to many other plants beyond rice, because many plants also accumulate cadmium.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.