Quantitative risk assessment of stack emissions from municipal waste combustors

Multi-pathway risk assessment (MRA) is a tool for evaluating the possibility of adverse effects to human health that may result from contaminant releases from municipal solid waste combustors (MWCs) and other sources of air pollution. An MRA attempts to model the movement of pollutants within the environment to various points at which they may be contacted by people, beginning with inhalation of contaminated air and continuing with indirect pathways such as food chain exposures that entail contaminant transfer and accumulation through several media. MRAs of MWCs date back to the mid-1980s, and are rooted in methods developed to assess the consequences of radionuclide releases from nuclear power generation. A detailed example of a typical MRA is presented that follows the classic four-stage risk assessment paradigm (Valberg et al., 1995). MRA methods, however, continue to be enhanced and refined by recent research. A number of current risk assessment topics are explored that are new to traditional MRAs and may serve to re-focus our collective efforts. The purpose of and demands on MRAs must be considered. A philosophical shift toward placing greater realism in MRAs underscores the importance of uncertainties inherent to risk estimates. Tools such as probabilistic risk assessment techniques must be developed and endorsed so that decision-makers may intelligently utilize the information provided by MRAs.