OVERVIEW AND DYNAMICS OF IODINE AND BROMINE IN THE ENVIRONMENT .2. IODINE AND BROMINE TOXICITY AND ENVIRONMENTAL HAZARDS

Flooding results in the dissolution of I and Br in soil, enabling rice plants to absorb these elements easily. Therefore the use of forest land and upland field soils for paddy rice cultivation under flooding conditions could induce the widespread occurrence of Reclamation-Akagare disease of rice plants, due to excessive absorption of I. In addition, under these circumstances, rice grain pollution by Br may occur, in which the Br content could exceed the allowable residue level (50 mg/kg air dry wt.). Soil fumigation with methylbromide (MB) resulted in the increase of the Br content in vegetables: in greenhouse cucumbers, the average Br content reached 73 mg/kg fresh wt. (1,660 mg/kg dry wt.) which exceeded the allowable residue level of Br in crops. Application of potassium chloride fertilizer (Br 950 mg/kg dry wt.) increased the Br content of crops to the maximum value of 200 mg/kg dry wt. which was much lower than 5,000 mg/kg dry wt. associated with the application of pesticides (MB, EDB). The Br concentration of the well water in areas with heavy MB and EDB application reached 2.3 mg/L, a value 250 times higher than that recorded in areas with lower doses of the chemicals. Influence of potassium chloride fertilizer on the Br concentration of the well water appeared to be negligible. Findings on the behavior of stable I in the soil-plant system were applied for the estimation of the dynamics of long-lived I-129 (half-life, 1.7 x 10(7) years) in the system and for its radiological assessment.