Reproductive toxicants have a threshold of adversity

This paper surveys the scientific basis for the current threshold approach for reproductive hazard and risk assessment. In some regulatory areas it was recently suggested to consider reproductive toxicants under the stringent linear extrapolation risk assessment paradigm that was developed for genotoxic carcinogens. First, the current risk assessment paradigm for genotoxic carcinogens is addressed, followed by an overview of reproductive toxicology and its threshold dose approach for hazard and risk assessment, the testing procedures for assessing the reproductive toxicity of chemicals, and the derivation of conclusions on their risk assessment and Classification, Labelling and Packaging (CLP). Relevant details of testing methodologies are discussed, such as exposure time windows, parameters determined, and the coverage of the entire reproductive cycle. In addition, the dose-response relationship is considered, illustrated with several examples. It is concluded that the current risk assessment methodology for genotoxic carcinogens is a debatable worst-case scenario and that for risk assessment of reproductive toxicants the threshold dose approach remains valid.