can be readily mobile with low affinities to soil. PuO2CO32− PuO2(CO3)24− PuO2(CO3)36− PuO2 formed from neutralizing highly acidic nitric acid solutions tends to form polymeric PuO2 which is resistant to complexation. Plutonium also readily shifts valences between the +3, +4, +5 and +6 states. It is common for some fraction of plutonium in solution to exist in all of these states in equilibrium. Plutonium is known to bind to soil particles very strongly; see above for an X-ray spectroscopic study of plutonium in soil and concrete. While caesium has very different chemistry to the actinides, it is well known that both caesium and many actinides bind strongly to the minerals in soil. it has been possible to use 134Cs-labeled soil to study the migration of Pu and Cs is soils. It has been shown that colloidal transport processes control the migration of Cs (and will control the migration of Pu) in the soil at the Waste Isolation Pilot Plant. Americium Americium often enters landfills from discarded smoke detectors. The rules associated with the disposal of smoke detectors are very relaxed in most municipalities. For instance, in the UK it is permissible to dispose of an americium containing smoke detector by placing it in the dustbin with normal household rubbish, but each dustbin worth of rubbish is limited to only containing one smoke detector. The manufacture of products containing americium (such as smoke detectors) as well as nuclear reactors and explosions may also release the americium into the environment. In 1999, a truck transporting 900 smoke detectors in France had been reported to have caught fire; it is claimed that this led to a release of americium into the environment. In the U.S., the "Radioactive Boy Scout" David Hahn was able to buy thousands of smoke detectors at remainder prices and concentrate the americium from them. There have been cases of humans being exposed to americium. The worst case was that of Harold McCluskey, who was exposed to an extremely high dose of americium-241 after an accident involving a glove box. He was subsequently treated with chelation therapy. It is likely that the medical care which he was given saved his life; despite similar biodistribution and toxicity to plutonium, the two radioactive elements have different solution-state chemistries. Americium is stable in the +3 oxidation state, while the +4 oxidation state of plutonium can form in the human body. The most common