Seasonal mass balance of halogens in simulated rice paddies

Halogens released from soil reservoirs to the atmosphere play important roles in atmospheric chemistry, including ozone loss and aerosol formation. Closed system experiments to determine controlling factors in halogen movement between the pedosphere, hydrosphere, terrestrial biosphere, and atmosphere are needed. This paper presents results from a closed system experiment on simulated rice paddies. It was observed that most water-extractable (bioavailable), halogens were swept downward from the surface during the initial watering pulse (similar to50, 70, and 75% of chloride, bromide, and iodide in unadulterated soils). Soil halogens were sequestered by rice plants with 28, 4, and 24% of the remaining bioavailable chlorine, bromine, and iodine processed by the plant tissue by the end of the season. Of the bioavailable halogens taken into the rice plant, less than 1% of chlorine or bromine is volatilized as a methyl halide while over 90% of iodide is emitted as gaseous CH3I.