Volatility of Organochlorine Insecticides from Soil: I. Effect of Concentration, Temperature, Air Flow Rate, and Vapor Pressure

The volatilization of dieldrin from Gila silt loam as influenced by soil pesticide concentration was determined in the laboratory at two air flow rates at 20 and 30C. The influence of pesticide vapor pressure on volatilization was measured by comparing the volatilization from Gila silt loam of dieldrin with that of lindane and DDT. No net water movement to or from the soil occurred during any of the volatilization processes. The vapor density of the soil-applied pesticide was the main factor controlling volatilization. The rate of volatilization of dieldrin from Gila silt loam increased with increasing soil pesticide concentration until the soil dieldrin concentration reached approximately 25 µg/g. This is the soil dieldrin concentration required to give a maximum saturation vapor density equivalent to that of the pure compound. An increase in temperature of 10C increased the rate of volatilization approximately fourfold. Increasing the rate of air movement over the soil surface from 0.005 to 0.018 mile/hour increased the rate of volatilization twofold. The order of rate of volatilization of three insecticides was: lindane > dieldrin > DDT. This is the same order for increasing vapor pressures of the three insecticides. The increase in rate of volatilization of the three insecticides was less than the increase in saturation vapor density of the pure compounds. This resulted because the concentrations of lindane and dieldrin in the soil rapidly decreased below that required to give a maximum vapor density of the pesticides. The maximum volatilization rates obtained represent potential losses of lindane, dieldrin, and DDT from soils of 202, 22, and 5 kg/ha/year, respectively. The volatilization rates decreased rapidly as soil pesticide concentration decreased. Extrapolation of the laboratory data to field situations suggests that the rate of volatilization could account for a significant proportion of these applied pesticides lost under normal field conditions.