Dynamics of iodine, bromine, and chlorine in soil

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Abstract
The effect of the moisture content, temperature, and pH on the dissolution ratios of iodine, bromine, and chlorine (triad) from Japanese soils which contain large amounts of iodine and bromine was examined, (i) Soil moisture level was the most important environmental factor affecting the dissolution ratio. The dissolution ratios of iodine and bromine which were lowest under the non-flooded conditions and ranged from 40 to 60% of the water saturation level, increased by 2–3 orders when the soil had been flooded, (ii) The dissolution ratios of the triad were in the order of iodine≪bromine≪chlorine under non-flooded conditions. (iii) The dissolution ratios of iodine and bromine were lowest at pHs 4.0-5.5. (iv) The dissolution ratios of iodine and bromine were lowest in the soil temperature range of 5-30°C and — 5-15°C, respectively, both ratios gradually increasing with the increase of the temperature. When the air-dried soil was frozen at — 20°C, the dissolution ratio of iodine increased markedly, and that of bromine increased only gradually. However, when the non-flooded soil was frozen, the dissolution ratios of both elements did not increase, (v) The dissolution ratio of chlorine was always constant and higher than those of iodine and bromine under all the conditions of moisture, pH, and temperature tested, (vi) It is assumed that the native iodine and bromine in soil flow out in large amounts due to flooding, or drought, especially flooding and that these large amounts are absorbed by plants or run off from the soil within a very short time, (vii) The water exudation method was very convenient for collecting the soil solution, and could be used even when the soil moisture content was low. The concentrations of the triad expressed as ppm in dry soil in the soil previously incubated by this method were almost the same as the values obtained by the centrifugation method.

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