A confidence index for Toxicity Reference Value to inform risk assessors and managers about the quality of the value
Abstract
Toxicological Reference Values (TRVs) are developed to protect humans exposed at chemical substances via the environment either by oral or inhalation routes. These values are derived by different international agencies or organisms and used in risk assessment. It is important for risk assessors and managers who will analyze and use the conclusions of the risk assessment to understand the robustness and the degree of uncertainties of the TRV. The level of confidence in a TRV depends of several parameters used at each step of the construction of a TRV (selection of the critical effect, the dose and endpoint used for value derivation and uncertainty factors). Some organisms, such as US EPA or RIVM, attribute a confidence index to the value they have developed while others do not. In order to homogeneously inform risk assessors on the quality of values developed a confidence index could be proposed. This index may also help assessors to chose a TRV, if several values are available. To develop this index, the main parameters influencing quality of a TRV were identified and structured by groups of key elements. Various criteria are defined corresponding to three main categories: key studies, calculating of the value and consideration of uncertainty factors. A group of expert has analyzed these criteria and case studies with various substances are performed. A confidence index with four levels corresponding to high, medium, moderate and low confidence is proposed.