Why is “heavy water” used in nuclear energy, are not potable to drink, even it’s just 1 molecule more than H2O?
In: Chemistry
H2O is the molecule (two hydrogen atoms, one oxygen atom). That is true for ordinary hydrogen, for the deuterium in heavy water, and for tritium. The distinction is in the number of neutrons in the hydrogen nucleus — none for most hydrogen, one for deuterium, two for tritium.
Tritium is already radioactive. We’ll set that aside, although you could have super-heavy or tritiated water and that would pose the additional radiation problems.
Heavy water, meaning the water with the deuterium form of hydrogen, can disrupt some biological processes that are reliant on fine-tuning at the molecular level, because of the significant difference in the weight of the hydrogen caused by adding the neutron. With most isotopes of heavier elements, this is not an issue because the addition of one or two neutrons is insignificant next to the overall mass of the nucleus; but with hydrogen, going from one proton to one proton plus one neutron is a significant mass difference. It can disrupt cell division, cause problems with bone marrow and the digestive tract, or even cause sterility and death in extremely high levels.
Unless you are intentionally setting out to live off the heavy water stored at a nuclear plant, however, this is not really a serious concern. You would have to drink quite a bit of heavy water before the level in your body became high enough to start making you seriously ill. There is actually already a very small proportion of hydrogen atoms in nature that are deuterium, so a tiny fraction of the natural water you drink is already heavy water.
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