Sensitivity study of an OCDD environmental fate screening model in soils in the presence of PCP wood-preserving oil.

In order to better understand the fate of polychloro dibenzo-p-dioxins and furans (PCDD/Fs) in soils around pentachlorophenol (PCP) treated poles, a model was developed to assess the influence of wood-preserving oil and PCP on the vertical migration of octachloro-dibenzo-p-dioxin (OCDD). Simulations were performed for three soil types: sand, clay and organic. OCDD fate was modeled in the absence of co-contaminant and in the presence of oil with or without 5% (w/w) PCP. A variance propagation study was conducted to evaluate the model sensitivity to a small variation in input parameters, to determine the uncertainty on the migration depth modeled for each soil, and to understand the variability of this migration observed between different soil types. The model predicts a different OCDD fate depending on the soil type with a significant migration in the case of sand and an absence of migration in the case of organic soil. No migration is predicted in the absence of co-contaminants and a migration depth of 7-600 cm is predicted in the presence of oil (with and without PCP). Model sensitivity also depends on the soil type: the predicted OCDD migration depth is, respectively, 22 cm+/-10 cm for organic soils, 71 cm+/-20 cm for clay and 566 cm+/-200 cm for sand after 60 days of emissions from a class 3, 12.2m long pole. Even if the input parameters have a significant uncertainty due to the lack of available data, the model results seem reliable as a first approximation to screen an eventual PCDD/F migration.