When a large fraction of water (> 50%) in higher organisms is replaced by heavy water, the result is cell dysfunction and death. The human body naturally contains deuterium equivalent to about five grams of heavy water, which is harmless. This difference increases the strength of water's hydrogen–oxygen bonds, and this in turn is enough to cause differences that are important to some biochemical reactions. Nevertheless, the various differences in deuterium-containing water (especially affecting the biological properties) are larger than in any other commonly occurring isotope-substituted compound because deuterium is unique among heavy stable isotopes in being twice as heavy as the lightest isotope. In its pure form, it has a density about 11% greater than water, but is otherwise physically and chemically similar. The weight of a heavy water molecule, however, is not substantially different from that of a normal water molecule, because about 89% of the molecular weight of water comes from the single oxygen atom rather than the two hydrogen atoms. Where this article uses heavy water, though, it means DĢO. It is 99.75% enriched by hydrogen atom-fraction-meaning that 99.75% of the hydrogen atoms are of the heavy type however, heavy water in the Gold Book sense need not be so highly enriched. For instance, the heavy water used in CANDU reactors is a highly enriched water mixture that contains mostly deuterium oxide DĢO, but also some hydrogen-deuterium oxide (HDO) and a smaller amount of ordinary hydrogen oxide HĢO. Thus heavy water as defined by the Gold Book includes hydrogen-deuterium oxide (HDO) and other mixtures of DĢO, and HDO in which the proportion of deuterium is greater than usual. For comparison, ordinary water (the "ordinary water" used for a deuterium standard) contains only about 156 deuterium atoms per million hydrogen atoms, meaning that 0.0156% of the hydrogen atoms are of the heavy type. The term heavy water as defined by the IUPAC Gold Book can also refer to water in which a higher than usual proportion of hydrogen atoms are deuterium rather than protium. The additional neutron makes a deuterium atom roughly twice as heavy as a protium atom.Ī molecule of heavy water has two deuterium atoms in place of the two protium atoms of ordinary "light" water. 7.6 Metabolic rate testing in physiology and biologyĭeuterium is a hydrogen isotope with a nucleus containing a neutron and a proton the nucleus of a protium (normal hydrogen) atom consists of just a proton.5.3 Heavy water radiation contamination confusion.
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