The fuel efficiency and durability of diesel technology are particularly desirable in the transportation and construction industries. Concerns about the health effects of diesel particulate emissions have led to progressively stricter emission standards, which can be met only through new technologic advances and fuel modifications. The cerium-based fuel additive Eolys, used in conjunction with a particulate filter, is one of the approaches being considered. However, this additive will result in emissions of cerium compounds and an increase in cerium in the ambient air and soil. HEI developed this report to provide a qualitative assessment of the possible health risk of cerium used as a fuel additive.