Adsorption and desorption of iodine by various Chinese soils I. Iodate Jiu-Lan Dai a,b , Min Zhang a, * , Yong-Guan Zhu b a College of Environment and Resource, Shandong Agricultural University, Tai’an 271018, China b Research Center for Eco-environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China Received 19 August 2003 Abstract In order to assess the adsorption of iodate by different soils from China, a series of batch experiments were conducted. It was found that soils rich in iron oxide had high affinity for iodate. Iodate adsorption isotherms could be well fitted with both Langmuir and Freundlich equations. Iodate adsorption by 20 different soils from China revealed that iodate adsorption was significantly correlated with soil organic matter negatively and positively with free iron oxide contents. At initial concentration of 4 mg I L  1 , iodate adsorption ranged between 9 and 34 mg kg  1 soil. No correlation between iodate adsorption and cation exchange capacity and soil pH was found. For a single soil, there was a significant linear relationship between the amounts of iodate adsorbed and desorbed, but for a group of different soils, the relationship between the amounts of iodate adsorption and desorption followed a nonlinear relationship, the deviation mainly occurred at high adsorption side. The relationship between K d and free aluminum oxide and free iron oxide contents showed an exponential relationship for various soils with exception of the soil from Hetian in Xinjiang. D 2003 Elsevier Ltd. All rights reserved. Keywords: Adsorption; Desorption; Iodine; Iodate; Soil; China 1. Introduction Iodine is an essential element for human and animals. It has been well established that environmental iodine defi- ciency can cause a number of health problems known as iodine deficiency disorders (IDD), such as goiter, spontane- ous abortion or sterility (Ahuka and Geelhoed, 1997) and mental retardation (Delange et al., 2001). It has been estimated that around 1570 million people in the world are at the risk of IDD, with 650 million suffering from goiter (14% of the world population) (Delange, 1998). Apart from the visual symptom of iodine deficiency-goiter, it is gener- ally held that iodine deficiency may cause a loss of up to 10 IQ points per person across the community (Stewart et al., 2003). Supplementation of I in salts has been proven to be a useful approach to eliminating IDD in many parts of the world, but the actual effectiveness may depend on a number of environmental and socioeconomic factors in a particular region. The use of iodized salt has been promoted in China from early 1980s; however, IDD remains a major health problem in remote areas such as Xinjiang Province. In these regions, I intake by the population is inherently low because there is generally less I in soil and drinking water than in coastal regions. Iodine deficiency in Xinjiang, China is further exacerbated by two factors. Firstly, the ethnic mi- nority people in Xinjiang prefer the rock salt that is available free of charge. Secondly, Chinese cooking methods using oil at high temperature may result in substantial loss of I via volatilization (Zhang et al., 2000). A recent survey in Xinjiang showed that about 23% of children aged between 8 and 10 had goiter (XJDCC, 2000). It is therefore sug- gested that approaches to improving human iodine nutrition other than salt iodination may be necessary for some regions taking into consideration of socioeconomic and environ- mental factors (Zhu et al., 2003). Iodine supplementation through the food chain has recently been attempted in Xinjiang, for example by the irrigation of paddy soil with iodized water to reduce I deficiency (Cao et al., 1994). 0160-4120/$ - see front matter D 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.envint.2003.10.007 * Corresponding author. Tel.: +86-10-6293-6940; fax: +86-10-6293- 3563. E-mail address: mzhang@sdau.edu.cn (M. Zhang). www.elsevier.com/locate/envint Environment International 30 (2004) 525 – 530