THE ROLE OF GROUNDWATER-SURFACE WATER INTERACTION ON PESTICIDE PERSISTENCE AND DEGRADATION PATHWAYS

Historical DDT use at Point Pelee National Park in Ontario, Canada has left a legacy of contamination that remains throughout much of the Park. The degradation half-lives are longer than expected and both concentrations and proportions of DDT, DDE and DDD vary significantly. Long term water level fluctuations in Lake Erie and the marsh at Point Pelee National Park cause periodic flooding and a higher water table in adjacent areas. The groundwater-surface water interaction changes the biogeochemical processes affecting degradation pathways and concentrations of DDT, DDE, and DDD. This was attributed to changes in the redox conditions associated with changes in soil hydrology on the biogeochemistry of DDT degradation. In the years when the marsh and groundwater levels are high, the adjacent area is flooded and soil water contents are high. Lower concentrations of residual DDT and lower proportions of DDE to DDT were found adjacent to the marsh. Conversely, higher concentrations of residual DDT and higher proportions of DDE to DDT were found at the higher elevation locations of the sand dune environment.