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Volatilization of Lindane and DDT from Soils¹

ABSTRACT

Four soils ranging in texture from a loamy sand to a clay were amended separately with ¹⁴C-labeled lindane and DDT to give a concentration of 10 ppm. Pesticide volatilization was determined each day for three consecutive drying cycles at 30C and 55C by liquid scintillation counting of trapped pesticide vapors. Soils were initially wetted to bar suction and dried by passing dry air over the soil surface.

Neither pesticide was volatilized at either temperature after the soils contained less than a monolayer of water. Since these soils became dry at different times during the 14-day drying cycle, two factors were important in describing pesticide volatilization. First, the rate of pesticide loss was constant for each soil in the moisture range from bar to 15 bars. Second, since essentially the same amount of water was lost from each soil per day until dryness, the pesticides were volatilized over a longer period of time from the finer textured soil than from the coarser textured soils. A mechanism is proposed.

Volatilization rates for DDT and lindane from soil containing moisture greater than 15 bars tension were dependent on temperature, adsorptive characteristics of the soil, and concentraction of the pesticide (lindane). For lindane and DDT at 30C, the rate of volatilization from soil was in the order Valentine loamy sand > Hand loam > Raber silty clay loam > Promise clay.

Degradation of lindane to PCCH occurred at 30C and 55C. After three wetting and drying cycles at 55C, the amount of DDT converted to DDE ranged from 6.7% for Valentine loamy sand to 21.2% for the Raber silty clay loam.

¹ Contribution from the Northern Plains Branch, Soil & Water Conservation Research Division, ARS, USDA, in cooperation with Colorado Agr. Exp. Sta., Scientific Journal Series no. 1466. Presented before Div. S-3, Soil Sci. Soc. of America, Nov. 11, 1968, at New Orleans, La.

² Research Soil Scientist and Chemist, respectively, Ft. Collins, Col.

Received for publication November 10, 1969. Accepted for publication March 9, 1970.