A Fate and Transport Model for 2,3,7,8-tetrachlorodibenzo-p-dioxin in Fly Ash on Soil and Urban Surfaces

ABSTRACT

Quantities of particle-bound 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) that are emitted from elevated stacks during the burning of municipal solid waste settle onto nearby soil and urban surfaces. The quantity and concentration emitted is small, however due to the potential hazard of this very toxic substance means are needed to estimate steady-state concentrations on surfaces. A fate and transport model was developed to quantify the mechanisms known to dissipate TCDD from surfaces. These mechanisms include resuspension by wind, run-off by water, evaporation into air, photochemical reaction and bioturbation.

A transient model was formulated, but the use of constant rates (yearly average) yields a simple algorithm for the TCDD concentration in the growing dust layer. The analytical solution reveals that the TCDD concentration in the dust layer is independent of time and that neither the wind driven particle resuspension rate nor the water run-off rate is needed to yield numerical results. Published rate data on ash-fall, dust-fall, reaction and evaporation along with bioturbation parameters are used to make quantitative estimates of annual average TCDD concentrations on soil and urban surfaces for a Brooklyn, New York site. For a stack emitting ash containing TCDD of concentration 8 ng/g calculated concentrations in surface dust ranged from a high of 0.5 pg/g to a low of 10 fg/g.