Evaluation of Iodide and Iodate for Adsorption–Desorption Characteristics and Bioavailability in Three Types of Soil Chunlai Hong & Huanxin Weng & Ghulam Jilani & Ailan Yan & Huiping Liu & Zhiyong Xue Received: 27 September 2011 /Accepted: 4 October 2011 /Published online: 27 October 2011 # Springer Science+Business Media, LLC 2011 Abstract Adsorption–desorption of iodine in two forms, viz., iodide (I - ) and iodate (IO 3 - ), in three types of soil were investigated. The soils were: red soil developed on Quaternary red earths (REQ)— clayey, kaolintic thermic plinthite Aquult, Inceptisol soil (IS) and alluvial soil (AS)—Fluvio-marine yellow loamy soil. The isothermal curves of iodine adsorption on soils were described by Langmuir and Freundlich equation, and the maximum adsorption values (y m ) were obtained from the simple Langmuir model. As compared with the iodide, the iodate was adsorbed in higher amounts by the soils tested. Among three soils, the REQ soil adsorbed more iodine (I - and IO 3 - ) than the IS and AS. The distribution coefficient (K d ) of iodine in the soils decreased exponen- tially with increasing iodine loading concentration. Desorption of iodine in soil was increased correspond- ingly with increasing adsorption values. The REQ soil had a greater affinity for iodine than the IS and AS at the same iodine loadings. In the pot experiment cultivated with pakchoi (Brassica chinensis L.) and added with two exogenous iodine sources, the iodide form was quickly taken up by pakchoi and caused more toxicity to the vegetable. The rate of iodine loss from soil was higher for iodide form as compared with the iodate. The iodine bioavailability was the highest but the persistence was the weakest in AS among the three soils tested, and the REQ soil showed just the opposite trend to that of the AS soil. This study is of theoretical importance to understand the relationship between iodine adsorption–desorption char- acteristics and their bioavailability in different soils and it also has practical implications for seeking effective alternatives of iodine biofortification to prevent iodine deficiency disorders. Keywords Iodide and iodate . Adsorption–desorption isotherms . Bioavailability . Pakchoi Introduction For human health, iodine is considered an essential microelement. Iodine deficiency disorder (IDD) is one of the most common and preventable health hazards [3, 17]. Nearly one billion people (remarkably in developing countries) suffering from IDD are thought to result from the lack of iodine in diet [44]. The IDD may cause diseases like endemic goiter, cretinism, and fetal abnormalities (Delong and Leslse, [10,25]). The relationship of the geochemistry of iodine in the rocks, soil, water, sea, and atmosphere with the incidence of IDD is one of the exciting research topics that is now creating global interest among scientists. Iodine deficiency in China, particularly in the western parts of the country, is severe. Although the use of iodized salt has been promoted nationwide in China since early 1980s, iodine deficiency remains a major health issue of C. Hong : Z. Xue Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China C. Hong : H. Weng (*) : A. Yan : H. Liu Institute of Environment and Biogeochemistry, Zhejiang University, Hangzhou 310027, China e-mail: spring76212@yahoo.com.cn H. Weng e-mail: gswenghx@zju.edu.cn G. Jilani Department of Soil Science, PMAS Arid Agriculture University, Rawalpindi 46300, Pakistan Biol Trace Elem Res (2012) 146:262–271 DOI 10.1007/s12011-011-9231-6