TR 068 – Assessment Factors in Human Health Risk Assessment (Updated by TR No. 86)

TR 068 : Assessment Factors in Human Health Risk Assessment (Updated by TR No. 86) | August 1995

This Technical Report reviews the background to the role of 'Assessment Factors' (AFs) in Human Health Risk Assessment. The use of these factors is described in the context of the overall Risk Assessment and risk management process. The disparity between AFs contained or implicit within the approaches to Risk Assessment which have developed separately for occupational and non occupational situations is pointed out.

The Reports sets out to recommend a scientifically based approach to the use of Afs in Health Risk Assessment which will allow consistency across the entire spectrum of human exposure. The Task Force considered that any such approach should be capable of general applicability while enabling justifiable distinctions to be made between occupational and non-occupational situations. It should also draw clear distinctions between the scientific and non-scientific aspects of the Risk Assessment/Risk Management process. A number of criteria for acceptability are proposed.

Three existing approaches developed principally for non-occupational situations are reviewed in some detail, as is the generic approach to the setting of occupational exposure limits. The scientific basis for the factors used in these approaches is explored. None of these approaches is regarded as meeting the criteria for general acceptability and the Task Force decided to develop a new approach, utilising the best elements of those currently available.

The Report defines the scientific elements which are considered to be relevant to the Risk Assessment process and these are reviewed in some detail. The basis in the scientific literature for specific numerical ranges and default values for each of the component elements of the overall AF is explored.

An approach is recommended which provides a method of deriving the best scientific estimate of a human no adverse effect level which is referred to in this report as the Predicted No Adverse Effect Level (PNAEL). An important feature of this approach is the need to establish the route and duration of exposure to which the PNAEL refers before attempting to derive factors, since these may vary for different routes or exposure durations. For each element of the approach, ranges and/or default values for the numerical factors involved are recommended.

The approach permits justifiable distinctions to be made between occupational and non-occupational situations and, being solely based on scientific considerations, is properly the province of the risk assessor. The risk assessor will make an estimate of the degree of scientific uncertainty involved in the process and it is recommended that due allowance be made for this uncertainty by the risk assessor and the risk manager together. Any further, non-scientific factors which the risk manager considers to be relevant may then be taken into account. The overall process should thus enable clear distinctions to be made between scientific and non-scientific elements.