Remediation of DDT Contaminated Soil: A Field Study

Abstract

<p> Point Pelee National Park in Leamington, Ontario, Canada contained a large component of private farming and recreation until the 1960's. DDT was applied at the park as pest control in the orchards and recreational areas between 1948 and 1960. Recent studies have shown that the compounds DDT, DDE and DDD are highly persistent in the shallow soils of Point Pelee National Park. A laboratory treatability experiment has been effective in the removal of DDT, DDE and DDD from columns packed with soil collected from Point Pelee National Park, using hydroxypropyl-ß-cyclodextrin. Cyclodextrins are microbially produced cyclic oligosaccharides which have a unique hydrophilic shell and a hydrophobic cavity. They are able to form inclusion complexes and aid in the transport of relatively insoluble compounds. A pilotscale field remediation experiment involving the application of hydroxypropyl-ß-cyclodextrin to a Random Latin-Squares design was completed at Point Pelee National Park over the course of five months. Systematic soil sampling and analyses provided DDT, DDE and DDD concentrations throughout the remediation experiment in order to assess the removal efficiency of hydroxypropyl-ß-cyclodextrin. In-Situ volumetric moisture content was monitored throughout the study with a TDR based system. Systematic soil sampling and analyses at the conclusion of the study provided water content, organic matter content, bulk density, porosity, hydraulic conductivity as well as sampling with depth. The application of a hydroxypropyl-ß-cyclodextrin solution did result in a substantial decrease of the concentrations of DDT, DDE and DDD from the surface soil at Point Pelee National Park. By the end of the experiment, the concentration of DDD was consistently below the regulatory limits set by the Ontario Ministry of Environment and Energy for Parkland/Recreational Land-Use. In addition to the observed decrease in concentration, there was a decrease in the degree of variation between the measured concentrations, transport of the mass of DDT, DDE and DDD to depth and an observed tailing effect at late-times. There were also fundamental changes to the system due to the application of the cyclodextrin (HPCD) solution including an increase in moisture content and organic matter, a decrease in infiltration and a corresponding decrease in field saturated hydraulic conductivity. There was no appreciable benefit of the application of a high concentration solution over a low concentration solution due to an observed "clogging" -effect. The results of this study indicates that further research is necessary to determine the extent of vertical mobilization of DDT, DDE and DDD to groundwater and the role of biological matter in the observed fundamental changes responsible for the "clogging" -effect.</p>