Lens design in the EU or for anything marketing to the EU has had to change due to ingredient
restrictions, including radioactive or toxic. Some excellent lenses have disappeared from new mfg
due to this. The classic dye transfer color prining process used a Thorium mordant. Some of us have
substituted uranyl nitrate (lab grade yellowcake). Can cause a customs issue in certain cases, but 100g per purchase is really silly to question, because it would take shiploads of the stuff to make
a dirty bomb.