Technical Report No. 157
Katherine W. Pringle, Clark C.K. Liu, Richard E. Green
DBCP (dibromochloropropane) has been used as a soil fumigant for nematode control for decades by the Hawaii pineapple industry. Recent detection (parts-per-trillion range) of the fumigant in potable well water has spurred a study of the behavior of DBCP in its Hawaiian environment. A volatile trapping apparatus was developed which proved to be highly efficient in capturing volatilized DBCP. Rates of DBCP volatilization from water were established for variations in air flow rate, temperature, and DBCP solution concentration. Measurements of cumulative DBCP volatilized at three solution concentrations indicated the applicability of Henry’s law for solution concentrations up to 35 ug/ml. A soil cell, patterned after that developed by Spencer and associates, was used to determine volatilization rates for DBCP mixed uniformly in surface soils from the Wahiawa series of 0’ahu and the Maile series of Hawaii Island. The effect of Wahiawa soil-water content on DBCP volatilization (without water loss) was evaluated at water contents of 2.3, 8.5, 13.5, and 31.6% by volume. DBCP vapor flux was lower at 2.3% water content than at higher water contents for the first three days, possibly because of higher adsorption on the very dry soil. An untreated 0.02 m thick soil layer placed above DBCP-treated soil greatly retarded DBCP volatilization during the first two days. The calculated effective liquid-vapor diffusion coefficient, De, for Wahiawa soil increased with soil water content from 6.1 x 10-4 cm2/s at 2.3% water content to 2.6 x 10-3 cm2/s at 31.6% water content.