Submitted to: American Society of Agronomy Abstracts
Publication Type: Abstract only
Publication Acceptance Date: 5/1/2007
Publication Date: 11/4/2007
Citation: Khaokaew, S., Tappero, R.V., Ginder-Vogel, M., Chaney, R.L., Sparks, D.L. 2007. Cadmium Speciation and Release Kinetics in a Thai Paddy Soil Subjected to Varying Redox Regimes. Abstracts of the American Society of Agronomy Annual Meeting, November 4-8, 2007, New Orleans, LA. p. 1302. Interpretive Summary: .
Technical Abstract: Understanding the factors controlling Cd speciation and bioavailability in flooded, drained, and alternate flooded/drained paddy soil will be crucial to developing and implementing best management practices needed for productive agricultural areas. Transformation of Cd species can occur in response to fluctuating soil moisture conditions. Redox potential is a master variable controlling Cd speciation and bioavailability in paddy soils, and soil pH influences the transport and fate of Cd. This research aims to study speciation of Cd and mobility of Cd and Zn under varying redox conditions. Synchrotron X-ray absorption spectroscopy (XAS) at the Advanced Photon Source (APS) was used to investigate Cd speciation in a contaminated paddy soil incubated at redox regimes representative of field conditions (e.g., flooded and drained). Bulk XAS data of the dry soil revealed CdCO3 was the most abundant species in the limed Thai paddy soil (70%). But when the soil was flooded and drained at different moisture contents [FC (~ 34% soil moisture content) and at the point immediately after draining excess water from the soil (~ 67% soil moisture content)], the data revealed changes in Cd speciation. The flooding period and moisture content both affected Cd speciation. For all periods, Cd-humic complexes were the predominant Cd species in the 67% moisture samples while for the FC samples, differences occurred depending on the length of the flooding period. For 1 day and 7 day periods, the major species were Cd-humic complexes, but for 14 day flooding periods, CdCO3 (~70%) was the major Cd species. A stirred-flow reaction chamber was used to investigate Cd and Zn release kinetics from the paddy soil. Kinetic experiments revealed Cd and Zn release from soil was initially rapid followed by a gradual slow release of the metals at longer periods of time.