Abstract
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.
Highlights
Langmuir sorption maximum of whole soil (WS) was 19.8 mg kg-1
There are some structural differences between HA used in agriculture and indigenous soil humic substances, it is clear that the existing functional groups are similar
The effects of soil organic matter (SOM) and HA, both of which can regulate to some extent I cycle in soil environment, on adsorption/desorption properties of iodide on an Aridisol were investigated
Summary
Langmuir sorption maximum of WS was 19.8 mg kg-1. Freundlich isotherm parameters were n= 0.89 and Kf= 2.165. The reaction between I and HA has not been clearly demonstrated since most of the studies had used complex aerosols-like environments consisting of other I-reactive components These complexities can be explained as follows: the HA-I complex is mainly reduced towards reactive intermediates such as I2 or HOI; followed by electrophilic substitution reactions with electron donor groups on HA (Francois 1987). The effects of SOM and HA, both of which can regulate to some extent I cycle in soil environment, on adsorption/desorption properties of iodide on an Aridisol were investigated. For this purpose, adsorption isotherms and desorption ratio of iodide by WS and OMF soil treated with two doses of HA were obtained
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