|Spencer, William - 5310-20-05 (COLLABORATOR)|
|Singh, Gulab - U.C. RIVERSIDE|
|Farmer, Walt - U.C. RIVERSIDE|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 4, 1994
Publication Date: N/A
Interpretive Summary: DDT and some of it's metabolites are highly persistent in soil. Although DDT is no longer used, soil residues remain in many areas of the US with p,p'-DDE making up the major proportion of the total DDT residue in such soils. In 1971, an experiment was conducted to evaluate management practices to reduce total DDT residues in a field containing high amounts of residual DDT. The experimental site was revisited in 1994 to determine residual soil concentrations of DDT isomers and their metabolites in soil and their movement into the atmosphere. Concentrations of all the DDT isomers decreased since 1971, but the remaining total DDTR residue in the surface varied from 10 to 28% of their amounts in 1971. Soil concentrations of DDT were higher in deep plowed plots and were lowest in plots which had previously been flooded in 1971. Air concentrations and volatilization flux indicated that small amounts of DDT isomers and metabolites, particularly p,p'-DDE continue to move into the atmosphere from the soils containing DDT residues. The finding that the DDT isomers are continuing to volatilization from the soil surface has implications for long range transport of DDT and for its transport to above ground plant parts as well as potential exposure to animals and humans in the area of DDT contaminated soils.
Technical Abstract: In 1971, an experiment was conducted in a field containing high amounts of residual DDT to evaluate deep plowing, followed by flooding, with and without organic matter applications, as soil and water management tools to reduce total DDT residues and to preferentially degrade the residual DDT to DDD. The experimental site was revisited in 1994 to determine residual soil concentrations of DDT isomers and their metabolites in soil, soil dust, and the atmosphere. Also, volatilization flux measurements were made to evaluate rates of movement into the atmosphere. Soil concentrations of all DDT isomers and metabolites had decreased in all plots with p,p'-DDE the major component of the total remaining residues (DDTR). The total DDTR residues in the surface 75 cm varied from 10 to 28% of their amounts in 1971. Highest concentrations were found in the deep plowed, unflooded plots. Deep plowing evidently increased DDT persistence by placing it deeper into the soil profile which protected it from degradation and volatilization. Concentrations of all isomers were lower in the previously flooded plots. Degrading DDT under reducing conditions brought about by flooding lessened or prevented the formation of DDE in the soil thus ultimately reducing its redistribution into the environment. Significant concentrations of both o,p' and p,p'-DDE and DDT were detected in the atmosphere above the plots. Irrigating the soil with 20 mm water dramatically increased the volatilization flux of all the DDT isomers and metabolites, particularly p,p'-DDE. The finding that DDT isomers continue to volatilize from the soil surface has implications for long range transport of DDT and possible health implications from exposure to humans or animals through the air route.