Tritium is radioactive hydrogen. It is generated
in nature by the interaction between cosmic rays and the atmosphere. The
average natural concentration of tritium in environmental waters has been
estimated to range from 3.2 to 24 picocuries per liter of water. Although
naturally occurring on Earth, significant amounts of tritium are also
generated by human activity, including the operation of nuclear power
plants, the manufacture of nuclear weapons, and atomic bomb testing. In
fact, releases of tritium from nuclear power plants to the atmosphere
have reached as high as tens of thousands of curies in one year, and releases
to bodies of water have measured as high as tens of millions of picocuries
The current U.S. Environmental Protection Agency standard for permissible
levels of tritium in drinking water is 20,000 picocuries per liter.
Please note: permissible does not mean safe.
Nuclear power plants routinely and accidentally release tritium into the
air and water as a gas (HT) or as water (HTO or 3HOH). No economically
feasible technology exists to filter tritium from a nuclear power plant’s
gaseous and liquid emissions to the environment. Therefore, the U.S. Nuclear
Regulatory Commission does not require that it be filtered.
The NRC allows a licensee to release an amount of tritium that could
result in a radiation dose to a member of the public of up to 100 millirem
(one millisievert) per year --- in planned air and water effluents (Title
10, Code of Fedl. Regs., Part20.1301). The NRC translates one million
picocuries of tritium per liter as the equivalent of 50 millirem/year
(10 CFR Part 20, Introductory Notes to Appendix B, Table 2, Column 2).
Please note: Table 2 lists concentrations in “microcuries per
millileter.” For example, 1E-3 µCi/ml equals one million
picocuries per liter.
Tritium has a half-life of 12.3 years. A radioactive material gives off
hazardous radiation for at least ten half-lives.
Tritium emits radioactive beta particles. Once tritium is inhaled or swallowed,
its beta particles can bombard cells. If a particle zaps a DNA molecule
in a cell, it can cause a mutation. If it mutates a gene important to
cell function, a serious disease may result. Just as water containing
ordinary hydrogen and oxygen is a component of all living cells, tritiated
water can also be incorporated into the cells of the body. Tritium incorporated
into the DNA of plants and animals is referred to as organically bound
tritium (OBT). Organically bound tritium can deliver damaging radiation
doses for a much longer time than ingested tritiated water or inhaled
tritiated water vapor. Research indicates that tritium can remain in the
human body for more than ten years.
Routine releases and accidental spills of tritium from nuclear power plants
pose a growing health and safety concern. Exposure to tritium has been
clinically proven to cause cancer, genetic mutations and birth defects
in laboratory animals. In studies conducted by Lawrence Livermore Laboratory
in 1991, a comprehensive review of the carcinogenic, mutagenic and teratogenic
effects of tritium exposure revealed that tritium packs 1.5 to 5 times
more relative biological effectiveness (RBE), or biological change per
unit of radiation (one rad or 0.01 gray), than gamma radiation or X-rays.
Tritium: Health Consequences
NIRS fact sheet. July 2006
For examples of the growing body of evidence about tritium’s toxicity
and for information about accidents involving tritium contamination, see
the documents and links below:
[RELEASES, LEAKS AND SPILLS]
--- [SCIENTIFIC ABSTRACTS] --- [LINKS]
Hazard Report by Dr. Ian Fairlie for Greenpeace looks at radioactive hydrogen
releases from reactors with a focus on Canadian heavy water reactors.