Radioactive Times: LLRC Journal

Tritium: an unconsidered hazard

report from Radioactive Times Volume 3, Number 1, March 1999 (content not updated)

Tritium, a form of hydrogen, represents a unique radioactive hazard for a number of reasons. The molecule is very small and can diffuse through almost every type of containment. It can easily enter the human body, as tritiated water, by inhalation and ingestion, even through the skin. Because of its extremely small decay energy, 5.6keV, one hundreth the energy of a Caesium-137 decay, the nuclear risk agencies consider Tritium to carry very little risk. Accordingly, and since Tritium is one of the two most embarrassing nuclear power pollutants, the recent Euratom Directive has relaxed the threshold for authorization requirement from 400Bq/kg to 2.5 million Bq/kg.

The easy movement of Tritium through the body means that its biological half-life is low, so it is generally rapidly excreted. A number of recent critiques of the risk models focus on the risk from the retained fraction resulting from reaction between Tritium and Carbon-Hydrogen bonds. There has also been a suggestion that the higher number of atoms per Sievert dose resulting from the low decay energy makes Tritium a Second Event hazard. Since there may be several atoms in one cell at low dose, it is possible for sequential hits to the same cell to occur in a short period and interfere with induced cell repair. However, there is another possible biochemical mechanism which has been generally overlooked.

Hydrogen bound to Oxygen, Sulphur, Nitrogen and Phosphorus in bio-molecules is the basis of the mechanism (called hydrogen bonding) which causes weak bridges between adjacent enzyme structures in living systems. It is the tertiary structure, the gross shape of these huge molecules like insulin and haemoglobin, that gives them their biological activity. These hydrogens are easily exchanged by Tritium in tritiated water, HTO.

The decay of the bound Tritium atom converts it to a Helium atom, which cannot bind to the adjacent atom. The chemical bond fails and the adjacent Oxygen, Nitrogen or other atom becomes very reactive and attaches itself to the nearest atom, tying the huge enzyme up in knots and destroying its activity. Since these enzymes have literally thousands of atoms in them, their inactivation or destruction by one Tritium decay is a massive amplification mechanism for harm from this substance.

The mechanism, called ‘transmutation’ has been acknowledged but dismissed by NCRP for DNA base mutation effects. But since the number of Bequerels per Sievert for Tritium is so high, the number of Tritium atoms in a cell at low exposure will also be high, and the further amplification of harm to tertiary proteins by this transmutation mechanism is an unconsidered route for cell damage and mutation.

A Review of Tritium effects is to be found in Health Physics Vol 65 (6), 593-733 (1993); Transmutation effect see Krasin, J. Molecular. Biol. 105(445) (1976)

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