Differences in human hazard assessments of existing chemicals by different evaluation organizations and their scientific backgrounds

<p>Toxicity evaluations of existing chemical substances have been conducted by domestic and foreign risk assessment organizations. Ideally, evaluations should be based on human data, but in many cases, the use of epidemiological data is difficult due to confounding factors such as mixed exposure to other substances and smoking. In such cases, the hazard assessment for human health, especially for carcinogenicity, is conducted based on the results of toxicity studies using laboratory animals, and a major point of concern, i.e. the existence or non-existence of a threshold for carcinogenicity, is judged based on genotoxicity data. For example, acrylonitrile has been evaluated as a genotoxic substance with no threshold for carcinogenesis in many evaluation reports, as well as in the Evaluation of Human Health Effects II of the Chemical Substances Control Law in 2016. On the other hand, the ECHA RAC Opinion 2018 stated that although acrylonitrile cannot be concluded as being non-mutagenic, it can be assigned a carcinogenicity threshold. In this study, we summarized the evaluation purposes and the differences in the toxicity data emphasized by different organizations. As a result, it was found that even in the latest scientific papers, there are still some fluctuations in the evaluation because of lacking elucidation of mutagenicity and carcinogenicity mechanisms. Thus, continue efforts to clarify the details of toxicological mechanisms are required for an accurate assessment of human health effects of chemicals chronically exposed via the environment.</p>