Soil transport and plant uptake of radio-iodine from near-surface groundwater

This paper describes a 12-month experiment designed to study the extent of upward migration of 125I (as a surrogate for 129I) from near-surface groundwater, through a 50-cm column of soil and into perennial ryegrass. The water table was established at a depth of 45 cm below the soil surface. By 3 months, 125I had migrated about half way up the soil column. After this, it tended to accumulate just above this mid-point, with only very small amounts being transported to the upper 20 cm of soil. This behaviour seemed to be explained well by soil moisture and redox conditions. The experiment indicated that 125I was mobile only within the saturated/low redox zone at the base of the soil column and accumulated in the zone of transition between anoxic and oxic soil conditions. Uptake of 125I by the ryegrass was found to be low.