| Summary: | The aim of this thesis is the development of a framework for the systematic appraisal and communication of uncertainty in incinerator and landfill human health risk assessments. This aspiration has been in response to finding a limited and ambiguous use of the term 'uncertainty', a lack of consensus in its definition and nomenclature, and its perfunctory review in risk assessmentsI.n the light of the need for such a framework, implications of its introduction are discussed. Guided by the literature and data collected from the field, the development of the framework progressed in three phases. First, the general concept was analysed - immediate and wider goals were set, the target audience identified, the context of use determined, the elements of the framework defined and the needs and requirements of the target audience considered, giving rise to a set of criteria to guide its development. The second phase included the proposal of an initial framework, which would appraise and communicate uncertainty. In drafting the framework, the thesis explored the fundamental context in which uncertainty is placed, drew on the strengths of past definitions and classification schemes to redefine it and suggested a more comprehensive classification scheme which finds practical application in the proposed framework. A second interaction with the field enabled the refinement of the first version and production of a more robust, second version of the framework. Supported by case studies of both incinerator and landfill risk assessments, the third phase of the research involved the application of the framework as "scenarios of use' and its integrity discussed in terms of the set of heuristics developed in the concept analysis. The intention of the introduction of the proposed framework is to increase the transparency of risk assessments, which in turn could establish their reliability and trustworthiness, aid decision-making and allow for its management and subsequent refinement of the risk assessment practice. Although these are achieved to a certain degree, structural and methodological issues stemming from the complex and multidisciplinary nature of uncertainty, the intricacy of risk assessments and the unfamiliarity of the target audience with the fundamental concepts of uncertainty and the framework itself, resulted in both functionality and usability being compromised to a certain extent. Suggestions for future research are made.
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