In this study the Impact Pathway Approach (IPA) was used to calculate the external costs associated with
indirect exposure, via topsoil ingestion, to atmospheric emissions of lead (Pb) from a waste-to-energy
plant in Denmark. Three metal-specific models were combined to quantify the atmospheric dispersion
of lead, its deposition and accumulation in topsoil, and the increase in blood lead concentration for
children resulting from lead intake via topsoil ingestion. The neurotoxic impact of lead on children was
estimated using a lead-specific concentration-response function that measures impaired cognitive
development in terms of IQ points lost per each incremental mg/dl of lead in blood. Since IQ loss during
childhood can be associated with a percent decrease in expected lifetime earnings, the monetary value of
such an impact can be quantified and the external costs per kg of lead emitted from the plant were then
calculated. The costs of indirect exposure calculated over a time horizon of 100 years, for the subpopulation
of children of 0e3 years, and discounted at 3%, were in the range of 15e30 V/kg. Despite
the continued accumulation of lead in topsoil resulting in increasing future indirect exposure, the results
indicate that costs associated with this exposure pathway are of the same order of magnitude as costs
associated with direct exposure via inhalation, calculated at 45e91 V/kg. Moreover, when the monetary
value of future impacts is discounted to the present, the differences between the two exposure pathways
are diminished. Finally, setting a short time horizon reduces the uncertainties but excludes part of the
costs of indirect exposure from the assessment.