Effect of Soil Organic Matter and Humates on Adsorption and Desorption Chemistry of Iodide in an Aridisol

Abstract

The translocation of iodine (I) from soil to food chain is largelydetermined by its adsorption/desorption reaction in soils. In thisstudy, the effects of commercial humates (HA) applied on an Aridisoland indigenous soil organic matter (SOM) on the adsorption anddesorption of iodide were investigated. For this reason, 1% and 3%HA (w/w) were incorporated into the whole soil (WS) and organicmatter free (OMF) soil samples. Then soil samples were equilibratedwith 0, 2, 4, 6, 8 and 10 mg L-1 iodide solution prepared in 0.01 molarCaCl2 for 40 h. The sorption data were better described by Langmuirisotherm (R2= 0.938) than Freundlich isotherm (R2= 0.763). TheLangmuir sorption maximum of WS was 19.8 mg kg-1. Freundlichisotherm parameters were n= 0.89 and Kf= 2.165. Sorption maximumof OMF soil significantly increased up to 35.5 mg kg-1. HAapplications reduced iodide sorption maximum of both WS andorganic OMF soil samples. Desorption rate of the WS ranged between0-15.3% whereas it decreased 0-0.65% upon removal OM. HAtreatments, in general, reduced the desorption rates. However,increasing HA application resulted in higher desorption ratio in bothWS and OMF soils. Consequently, either SOM or HA has preeminentrole in the adsorption-desorption chemistry in soils.