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DDT Degradation in Flooded Soil as Related to Temperature¹

ABSTRACT

Raber silt loam was amended with ¹⁴C-labeled DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] and incubated under anaerobic conditions (flooded) at several selected temperatures for 140 days. Soil samples were analyzed for DOT degradation products at intervals during the experiment. DDT degradation rates were temperature dependent, and after 7 days recovery was 80, 64, 44, 10, and 48% at 30, 40, 50, 60, and 70C, respectively. DDT was not degraded at 2C. The first identifiable intermediate product was DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane] followed by DDMU [1-chloro-2,2-bis(p-chlorophenyl)ethylene]. Under these reducing conditions, DDD was not degraded at 30C, but degraded at temperatures of 40C and higher. ¹⁴C activity (applied as ¹⁴C-DDT) remaining in the soil sample after solvent extraction, increased during degradation of the parent compound or of its degradation products. The maximum amount of activity in the non-extractable fraction was found after 140 days in the 60C treatment, and represented 34% of the applied activity; whereas, 49.6% of the activity was extractable, only 15.6% of this was identifiable.

Key Words: DDD • DDE • DDMU • insecticide • persistence • pesticide • anaerobic

¹ Contribution from USDA, ARS, Western Region, P. O. Box E, Ft. Collins, CO 80522, in cooperation with Colorado State Univ. Exp. Stn., Sci. J. Ser. no. 2065.

² Soil Scientist and Chemist, USDA, respectively.

Received for publication July 21, 1975.