Why only pulmonary, digestive and cutaneous cell lines are used? We know that the liver and the brain can be a good target.

Given the limited budget, the JA had to concentrate on primary target tissues of MN exposure by inhalation, oral, and skin routes. The liver and the kidneys will eventually be exposed at least in oral exposure and the brain at least by inhalation. However, MN doses in these organs will be lower than in the organs selected in the JA, and a sound study would probably require a long-term exposure to reach toxicologically adequate organ doses. Developing genotoxicity assays for the secondary target organs would be a great challenge requiring basic research and cannot be the scope of a Joint Action (but rather of research projects).