TRANSPORT AND FATE OF PESTICIDE iN UNSATURATED NONISOTHERMAL SOIL: EXPERIMENTAL AND NUMERICAL STUDIES FOR BROMOXYNIL OCTANOATE.

Transport of bromoxynil octanoate (3,s-dibromo-4-hydroxy-benzonitrile) and water were
studied experimentally and numerically in closed soil columns. Bromoxynil and water content
distributions in the soil columns were measured. A numerical model was developed based upon
unsteady state movement of water, heat and nonvolatile organic compound (i.e., bromoxynil
octanoate) for simulating the measured data. Loamy sand soil was moisturized then packed in
sealed PVC columns (0.10m diameter and 0.3m long). The average bulk density of soil columns
was 1439 kg/m3. The soil had initial water content of 0.113 m3/m3. The top 0.005 m- layer of soil
column had 0.000272 mol/l of bromoxynil, while the rest of soil column had zero concentration.
The columns were buried vertically within a soil bin such that column surfaces were exposed to
natural radiation of Qassim region, Saudi Arabia. Two soil columns lasted for 14 days. Both
predicted and measured final soil water contents showed nonlinear distributions and similar trends.
The water moved from the upper region (0.05 m thick) toward the cold region at depth O.lm. The
measured and predicted soil water distributions in the lower layer (i.e., 0.1 to 0.3 m) showed small
changes. The predicted and measured bromoxynil concentrations behaved similarly in their &end.
The upper 0.0- 0.15 m was an active layer for degradation and movement of bromoxynil. The
upper 0.0-0.05 m-region possessed lower concentration of bromoxynil while the succeeded region
of 0.05 to 0.15 m possessed the highest concentration. Numerical simulation showed that
increasing the mean temperature resulted more migration of water and bromoxynil from upper
region toward lower region.