Ferrihydrite Reduction Increases Arsenic and Uranium Bioavailability in Unsaturated Soil

Authors

Arindam Malakar, University of Nebraska - LincolnFollow
Michael Kaiser, University of Nebraska - LincolnFollow
Daniel D. Snow, University of Nebraska-LincolnFollow
Harkamal Walia, University of Nebraska - LincolnFollow
Banajarani Panda, University of Nebraska-Lincoln
Chittaranjan Ray, University of Nebraska-LincolnFollow

ORCID IDs

Arindam Malakar https://orcid.org/0000-0001-6704-8891

Chittaranjan Ray https://orcid.org/0000-0002-1731-2030

Date of this Version

2020

Document Type

Article

Citation

Published in Environmental Science & Technology 54 (2020), pp 13839−13848.

https://dx.doi.org/10.1021/acs.est.0c02670

Comments

Copyright © 2020 American Chemical Society. Used by permission

Abstract

Redox driven mobilization and plant uptake of contaminants under transiently saturated soil conditions need to be clarified to ensure food and water quality across different irrigation systems. We postulate that solid-phase iron reduction in anoxic microsites present in the rhizosphere of unsaturated soil is a key driver for mobilization and bioavailability of contaminants under nonflooded irrigation. To clarify this, two major crops, corn and soybean differing in iron uptake strategies, were grown in irrigated synthetic soil under semiarid conditions with gravimetric moisture content ∼12.5 ± 2.4%. 2-line ferrihydrite, which was coprecipitated with uranium and arsenic, served as the only iron source in soil. Irrespective of crop type, reduced iron was detected in pore water and postexperiment rhizosphere soil confirming ferrihydrite reduction. These results support the presence of localized anoxic microsites in the otherwise aerobic porous bulk soil causing reduction of ferrihydrite and concomitant increase in plant uptake of comobilized contaminants. Our findings indicate that reactive iron minerals undergo reductive dissolution inside anoxic microsites of primarily unsaturated soil, which may have implications on the mobility of trace element contaminants such as arsenic and uranium in irrigated unsaturated soils, accounting for 55% of the irrigated area in the US.

Includes supplemental materials.