Effect of soil moisture on chlorine deposition

The effect of soil moisture on chlorine (Cl2) deposition was examined in laboratory chamber experiments at high Cl2 exposures by measuring the concentration of chloride (Cl−) in soil columns. Soil mixtures with varying amounts of clay, sand, and organic matter and with moisture contents up to 20% (w/w) were exposed to ≈3 × 104 ppm Cl2 vapor. For low water content soils, additional water increased the reaction rate as evidenced by higher Cl− concentration at higher soil moisture content. Results also showed that the presence of water restricted transport of Cl2 into the soil columns and caused lower overall deposition of Cl2 in the top 0.48-cm layer of soil when water filled ≈60% or more of the void space in the column. Numerical solutions to partial differential equations of Fick's law of diffusion and a simple rate law for Cl2 reaction corroborated conclusions derived from the data. For the soil mixtures and conditions of these experiments, moisture content that filled 30-50% of the available void space yielded the maximum amount of Cl2 deposition in the top 0.48 cm of soil.