8 - Multimedia pathways

Summary

Summary

Whereas the classical air pollutants are harmful only via inhalation, persistent pollutants such as toxic metals are also harmful after entering the food chain. This is an important pathway, because the total population dose due to ingestion can easily be an order of magnitude larger than the dose via inhalation. Note that the geographic range of the analysis must be even larger than for atmospheric dispersion, because most food is transported over large distances, often worldwide. This chapter describes several approaches for estimating ingestion doses. Even though the detail about dispersion in the environment is exceedingly complex and difficult to model, some shortcuts are possible if one can find the right data for the relation between total emissions and total population dose under steady-state conditions. Thus one can carry out calculations of total population dose that are far simpler and probably more reliable than detailed site-specific models. That is the case for dioxins, the subject of Section 8.2. The pathways for mercury are complex, and because of its long residence time in the atmosphere it is dispersed over the entire hemisphere. But with data for the global emissions and the global ingestion dose, one can again obtain a simple model for the global health impact, as described in Section 8.3. In Section 8.4 we present a more detailed model, based on transfer factors between different environmental compartments that have been published by USEPA. The key result is the intake fraction, defined as the fraction of the emitted pollutant mass that will be inhaled or ingested by a human being. Results for impacts and damage costs of toxic metals can be found in Section 8.5.