RELATIONSHIP BETWEEN SOIL-SOIL-SOLUTION DISTRIBUTION COEFFICIENTS OF 125I AND 127I IN PASTURE SOIL.

Area of Science:

• Environmental Science
• Radiochemistry
• Soil Science

Background:

• Understanding iodine (I) behavior in soil is crucial for assessing radionuclide transport, especially near nuclear facilities.
• Soil-iodine distribution coefficients (Kd) quantify the partitioning between soil and soil solution, influencing iodine mobility.
• Previous studies suggested power-law relationships between iodine Kd and soil organic carbon (C) content.

Purpose of the Study:

• To measure depth profiles of native 127I and exogenous 125I distribution coefficients (Kd) in pasture soils.
• To investigate the relationships between iodine Kd, soil 127I concentration, organic C concentration, and organic C Kd (C-Kd).
• To compare findings with previous studies on iodine-C-Kd relationships.

Main Methods:

• Soil samples were collected from a pasture near a nuclear fuel reprocessing plant.
• Depth profiles of 127I-Kd and 125I-Kd were measured.
• Concentrations of 127I, organic C, and C-Kd were analyzed in relation to depth.

Main Results:

• Depth profiles of 125I-Kd and 127I-Kd showed similar trends.
• Low 127I concentrations and Kd values indicated iodine migration beyond 10 cm depth.
• Exponential functions, not power functions, described the relationships between both 125I-Kd and 127I-Kd and C-Kd.

Conclusions:

• Soil organic matter plays a significant role in the soil profile transport of iodine.
• The binding of native 127I in the upper soil layers is stronger than exchangeable with exogenous 125I.
• Observed exponential relationships between iodine Kd and C-Kd differ from previous power-law findings, warranting further investigation.