Multiple Issues Surrounding the Feasibility of LCA Impact Assessment 971210
The presentation evaluates the feasibility for life-cycle impact assessment to yield accurate, useful results for sound decision-making. The evaluation raises feasibility issues based on (1) inherent scale issues, e.g., spatial and temporal discontinuities, between LCA and most environmental processes; (2) disparities between LCA threshold and dose-response assumptions and actual environmental processes; (3) extensive use of value-based subjective judgment and opinion to create environmental categories, equivalency models, and scores; and (4) the current lack of systems to indicate whether real and relevant differences are identified. All of these issues limit or constrain the decisions that can be made solely from LCA. The origins of these issue lie in procedures and calculations that are fundamental to life-cycle inventory: data collection and aggregation across multiple system operations, allocation rules for emissions and resources, and data normalization to a study functional unit. These operations remove spatial, temporal, and other considerations, resulting in significant interpretive limitations. In addition, although often presented as a technical or scientific process, extensive value-based subjective judgments are employed throughout impact assessment. Some of these judgments compromise or conflict with scientific knowledge, e.g., when independent processes or compounds are aggregated into a numerical score. There is a significant range and mix of these scale issues, process assumptions, and subjective judgments. For example, the most useful results may be for global, long lived processes with known mechanisms. Problematic areas involve transient or local processes, those measured by biological parameters, e.g., biodiversity habitat and toxicity, and those involving independent mechanisms. As a result, one cannot quantify or predict actual environmental impacts using LCA. In some cases, current practices can generate a hazard estimate that may be useful to guide pollution prevention and resource conservation strategies. Otherwise, various scores often have no substantive support for their relevance. The evaluation helps to identify and track these issues to improve interpretation of LCA impact assessment results and suggests that a significant level of caution is needed in using LCA results for decision-making.