You may be referring to the 2006 assassination of Alexander Litvinenko by a pellet of polonium-210. What killed him was acute radiation syndrome, not heavy metal poisoning. Polonium-210 has a half-life of ~138 days, whereas radium-226 (the most common natural isotope) has a half-life of 1600 years. Naturally occurring uranium and thorium are nowhere as radioactive. Natural uranium can sometimes be found in granite used for counter-tops, as included pitchblende. U-238 is often used as radiation shielding, notwithstanding its own (small) radioactivity.
You may be referring to the 2006 assassination of Alexander Litvinenko by a pellet of polonium-210. What killed him was acute radiation syndrome, not heavy metal poisoning. Polonium-210 has a half-life of ~138 days, whereas radium-226 (the most common natural isotope) has a half-life of 1600 years. Naturally occurring uranium and thorium are nowhere as radioactive. Natural uranium can sometimes be found in granite used for counter-tops, as included pitchblende. U-238 is often used as radiation shielding, notwithstanding its own (small) radioactivity.