Evaluating the effect of rain on the fate of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) accumulated in polluted trees in Amman, Jordan

Abstract

Open combustion of solid waste is one of the main sources of the emission of dioxin and dioxin-like compounds (DLCs). Ambient dioxin will eventually undergo depositions on soils and tree leaves. Pine trees have shown an ability to store dioxin in their needles allowing biomonitoring of dioxin atmospheric concentrations. Infiltration can transport dioxin to greater depths into the ground, on one hand, while vaporization can allow dioxin to return back to the atmosphere on the other. Several studies evaluated the migration of dioxin between two compartments; however, few studies have attempted to understand the fate of non-conservative PCDDs and PCDFs in an unsteady state system of more than two mediums. This study focused on the transportation of dioxin between polluted trees and the underlying soil through the effect of rain water. For approximately 10 years, pine trees in this study have been exposed to emissions generated by the open combustion of municipal solid waste (MSW) from a fixed location. Soil samples located further from the point source had generally lower dioxin concentrations. Dioxin concentrations were correlated to distance from the source using least square regression. Soil samples below contaminated trees had dioxin concentrations 10–35% greater than the calculated measurements for the same spots using the regression model. By detecting these spikes in concentrations, it was possible to identify pools of dioxin found directly under the contaminated trees—indicating a rinsing effect of rain water on the stored dioxin on the trees' needles.