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Probabilistic Risk Assessment - Theory and Reality (MO4/6) Conceptual failings of probabilistic risk assessment. Santillo, D.1, Johnston, P.1, 1 Greenpeace Research Laboratories, University of Exeter, Exeter, United Kingdom ABSTRACT- At first sight, the application of probabilistic risk assessment to the regulation of chemicals and other environmental stressors is an attractive concept. Born out of engineering disciplines, such assessments appear to provide objective, quantitative measures of both the nature and likelihood of adverse impacts at levels of organization from organismal to whole ecosystems. As such, they are understandably attractive to decision-makers. However, the transition across disciplines from engineering into ecological and ecotoxicological domains is a substantial "leap of faith". Considerable uncertainties are attached to the scale of the hazards and the chemical exposures involved, which the probabilistic approach recognises and attempts to address. Nonetheless, there are numerous other dimensions in which significant confounding factors may exist, some of which will inevitably remain unidentified and, therefore, fall outside the scope of the assessment. Probabilistic models cannot effectively address non-random uncertainty, or bias. These can influence the design and framing of risk assessments and consequently lead to judgmental errors vastly greater than those arising from random data uncertainty alone. Moreover, the existence of pathways, receptors and endpoints which are not recognized by risk assessment design further compromises reliability. While seemingly providing a reliable tool for decision-making, therefore, probabilistic risk assessment can foster a false sense of security. More precautionary decision-making, e.g. the control of hazardous chemicals on the basis of their inherent propensity to cause harm, is often derided as "unscientific", though in truth it has a firm basis in science and the ability to deliver a higher level of protection to the environment and public health. It is essential, therefore, that such precautionary elements remain a central component of the developing strategies for chemical regulation within the European Union. Key words: uncertainty, risk assessment, ecotoxicology, precaution |
