Using a non-toxic precursor, we created a green chemical synthesis for colloidal spheres with a core@shell structure having a silica core and an iron oxide shell (SiO2@FexOy). Our synthesis pathway enabled an iron oxide shell formation with a 9 ± 6 nm thick shell onto colloidal silica spheres (ca. 700 nm). SiO2@FexOy particles reduced A549 cell viability and induced DNA damage. SiO2@FexOy particles showed the potential for removing fluoride from water.