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Volatility of DDT Residues in Soil as Affected by Flooding and Organic Matter Applications¹

ABSTRACT

In a field experiment, flooding with and without organic matter additions was evaluated as a means of preferentially degrading residual DDT and thereby changing the ratio of the various isomers and metabolites volatilizing from the soil surface. Flooding for a 7-week period, either with or without manure or alfalfa (Medicago sativa L.) meal applications, effectively degraded DDT isomers, primarily to the respective DDD isomers, but had little effect on DDE isomers. Both flooding and organic matter decreased the volatility even when soil concentrations were not affected, apparently because of increased adsorption of the compounds by added organic matter or by organic matter in the soil altered by flooding. The data indicate that minor changes in vapor concentration ratios were accomplished by flooding and organic matter additions, but regardless of treatment, the major constituent evaporating from the surface was p,p'-DDE. To accomplish significant changes in volatilization patterns, it will be necessary to use such management practices before a major part of the DDT has been degraded to DDE. However, flooding and organic matter treatments will ultimately decrease the total quantity of DDE volatilizing from residual DDT in soils over long-time periods because of their effectiveness in degrading DDT to DDD instead of DDE.

Key Words: pesticide degradation • pesticides • vapor density • DDE • DDD

¹ Contribution from the Western Region, Agricultural Research Service, USDA, and the California Agr. Exp. Sta., Riverside.

² Soil Scientist, Chemist, USDA, Assistant Chemist and Staff Research Associate, Univ. of California, Riverside, respectively.

Received for publication April 20, 1973.