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

The translocation of iodine (I) from soil to food chain is largely  determined by its adsorption/desorption reaction in soils. In this  study, the effects of commercial humates (HA) applied on an Aridisol  and indigenous soil organic matter (SOM) on the adsorption and  desorption of iodide were investigated. For this reason, 1% and 3%  HA (w/w) were incorporated into the whole soil (WS) and organic  matter free (OMF) soil samples. Then soil samples were equilibrated  with 0, 2, 4, 6, 8 and 10 mg L-1 iodide solution prepared in 0.01 molar CaCl2 for 40 h. The sorption data were better described by Langmuir isotherm (R2= 0.938) than Freundlich isotherm (R2= 0.763).  The  Langmuir sorption maximum of WS was 19.8 mg kg-1. Freundlich  isotherm parameters were n= 0.89 and Kf= 2.165. Sorption maximum  of OMF soil significantly increased up to 35.5 mg kg-1. HA  applications reduced iodide sorption maximum of both WS and  organic OMF soil samples. Desorption rate of the WS ranged between  0-15.3% whereas it decreased 0-0.65% upon removal OM. HA  treatments, in general, reduced the desorption rates. However,  increasing HA application resulted in higher desorption ratio in both  WS and OMF soils. Consequently, either SOM or HA has preeminent  role in the adsorption-desorption chemistry in soils.