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Soil pH and Metallic Amendment Effects on DDT Conversion to DDE¹

ABSTRACT

Highs oil pH resulted in greater conversion of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) to 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) in both nonamended and MgO-amended soils. The conversion of DDT continued throughout the experimental time of up to 32 months to a maximum of 15% of total residues as DDE. DDT was converted to DDE in both moist and dry soils above pH 7. The predominant conversion mechanism in moist soils appears to be microbial, whereas chemical conversion appears to be dominant in dry soils. Soils amended with MgO required pH values of near 10 before DDT conversion became significant. CaCO₃, a dolomitic lime, Fe₂O₃, or Al₂O₃ applied to soils with a wide range of pH values did not enhance DDT conversion to DDE. Laboratory experiments indicate that the liming of soils containing DDT is not a practical means of converting DDT to DDE.

Key Words: lime • organochlorine insecticides • degradation • persistence

¹ Contribution from Agricultural Environmental Quality Institute, Agr. Res. Cent., ARS, USDA, Beltsville, Md. 20705.

² Soil Scientist and Horticulturist, ARS, USDA, Beltsville, Md.

³ Professor of Chemistry, Virginia State College, Petersburg, Va.

Received for publication September 18, 1972.