Guidance of the Scientific Committee on a request from EFSA related to Uncertainties in Dietary Exposure Assessment Request No EFSA-Q-2004-019 Adopted on 14 December 2006

The Scientific Committee has been asked by the European Food Safety Authority (EFSA) to advise on harmonisation of risk assessment methodologies in the fields falling within its mission. This opinion addresses the issue of scientific uncertainties in dietary exposure assessment. Every dietary exposure assessment is affected by scientific uncertainties and it is important for assessors to characterise the extent of uncertainty, so that it can be taken into account by risk managers. Many exposure assessments follow standard screening procedures that are intended to produce conservative estimates of exposure. These screening assessments do not require an analysis of uncertainty on every occasion, provided that they include appropriate conservative assumptions and default values to take account of uncertainty. The Scientific Committee recommends that each Panel considers reviewing whether this requirement is satisfied by the assumptions and default values used in screening assessments in its area of work. If screening assessments indicate exceedance (or in the case of nutrients, failure to attain) health-based guidance values, then more refined assessments may be needed. Some evaluation of uncertainty is required in all refined assessments. The Scientific Committee recommends that dietary exposure assessments should start with a systematic examination of potential sources and types of uncertainty, to maximise the likelihood that important uncertainties are recognised. The use of tables is suggested to help with this task. The Scientific Committee recommends a tiered approach to analysing uncertainties. Each uncertainty in an assessment may be analysed at one of three tiers: qualitative, deterministic or probabilistic. Bearing in mind that it is not practical to treat all uncertainties quantitatively, initially, all significant uncertainties may be analysed qualitatively. This may be sufficient, if the outcome is clear enough for risk managers to reach a decision. Otherwise, those uncertainties that appear critical to the outcome may be analysed deterministically or probabilistically. Communicating uncertainty to other scientists, risk managers and wider audiences is a key challenge. A tabular format is proposed to facilitate qualitative evaluation and communication of uncertainties. Treating the most significant uncertainties at higher tiers progressively refines the characterisation of uncertainty, and provides an increasingly clear picture of the likelihood of exceeding (or in the case of nutrients, failure to attain) a health-based guidance value. It is important to communicate the strengths of the exposure assessment (what is known) as well as the uncertainties, and also to discuss the uncertainty affecting exposure compared to that affecting other parts of the overall risk assessment (e.g. toxicity). The aim should be to provide a balanced picture of what is known and what is uncertain, and avoid giving an exaggerated impression of either certainty or uncertainty. Sources and types of uncertainty affecting areas of dietary exposure assessment in the work of EFSA are reviewed in Annex 2. They illustrate the relevance of the approaches discussed in this opinion and provide a starting point for use in assessments by EFSA Panels. It would be premature to give prescriptive guidance on which specific approaches to use for dealing with uncertainty in dietary exposure assessment until more experience is gained with their use in this field. The Scientific Committee therefore recommends that EFSA Panels identify which approaches appear promising for their particular needs and context, and review the usefulness and application to their work. The Scientific Committee strongly encourages the Panels to incorporate the systematic evaluation of uncertainties in their risk assessments and to communicate this clearly in their opinions.