Iodine in the Environment Revisited. An Evaluation of the Chemical- and Physico Chemical Processes possibly Controlling the Migration Behaviour of Iodine in the Terrestrial Environment

The report gives an overview of the environmental cycle of iodine, especially focussing on the possible reactions being responsible for the retention of iodine in the terrestrial environment. During the last two decades evidence for the presence of iodine in soil as organically bound has been presented. The major part of inorganic iodine in the terrestrial environment will, under physical and chemical conditions normally prevailing, exist as iodide. No evidence for a direct reaction between iodide and organic material has been presented, whereas strong support for the engagement of microbial activity in the formation of organic iodine compounds in soil has been obtained. Incorporation of iodine in humic substances as a result of enzymatic catalysis, involving an enzyme of the peroxidase group appears reasonable. It is concluded that microbiological activity involving extracellular enzymes most probably is resonsible for the possible retention of iodine in the terrestrial environment. It is suggested that these reactions in detail should be studied experimentally.