Properties of water water isotopes. Naturally occurring water is almost completely composed of the neutron-less hydrogen isotope protium. Only 155 ppm include deuterium ( or D), a hydrogen isotope with one neutron, and fewer than 20 parts per quintillion include tritium ( or T), which has two neutrons. Oxygen also has three stable isotopes, with present in 99.76%, in 0.04%, and in 0.2% of water molecules. Deuterium oxide, , is also known as heavy water because of its higher density. It is used in nuclear reactors as a neutron moderator. Tritium is radioactive, decaying with a half-life of 4500 days; exists in nature
Bioremediation of radioactive waste suitable for transfer to a nuclear waste repository). Phytovolatilization involves the capture and subsequent transpiration of radionuclides into the atmosphere. It does not remove contaminants but releases them in volatile form (less harmful). Despite not having too many applications for radioactive waste, it is very useful for the treatment of tritium, because it exploits plants' ability to transpire enormous amounts of water. The treatment applied to tritium (shielded by air produces almost no external radiation exposure, but its incorporation in water presents a health hazard when absorbed into the body) uses polluted effluents to irrigate phreatophytes. It becomes a system