# The Impact of Tritium in the Environment
## 1 Introduction  
The use of nuclear energy is expected to play an important role in the near future in the transition towards clean energy (zero emissions goal).  
Tritium, as is widely and globally known, is a radioactive isotope of hydrogen that can be transferred to the environment and to humans mainly via tritium oxide or tritiated water (HTO). It is also generated by the operation and decommissioning of nuclear power plants (including dismantling and spent fuel reprocessing), nuclear incidents, such as Fukushima, Japan, in 2011, radioisotope production and in medical and research applications [1, 2, 3].  
In the future, tritium release is expected to increase through the operation of new nuclear power plants, whether they are fission or fusion reactors [4], because of its production by the neutron activation of \({}^{2}\)H, \({}^{3}\)He, \({}^{6}\)Li, and \({}^{10}\)B [5].  
Tritium is a radioisotope that is extremely mobile in biological systems; it reacts with oxygen, and it rapidly integrates into the biosphere as HTO [1], which has chemical characteristics almost identical to water, from which it is technically extremely difficult to remove. As for its environmental effects, the largest impacts are likely, therefore, to occur only while relatively high activity concentrations of HTO persist.  
Compared to other radionuclides, by taking advantage of these characteristics, tritium can be released into the environment, specifically diluted into water in huge quantities and at low concentrations per year, according to the laws and regulations of the respective countries where nuclear power plants are operated (for example, the Fukushima Daiichi plant will gradually release up to 22 trillion Bq or less of tritium per year over the next 20 to 30 years, a low level compared to the amounts released by nuclear power plants around the world, including those in Europe, North America and other parts of Asia outside of Japan).  
Indeed, tritium is the only radioactive isotope in the triad of hydrogen isotopes that exists for a relatively long time. A soft beta emitter with an average energy of 5.7 keV and a half-life of 12.33 years, it is the most common natural light radioactive isotope. About 200 g of tritium is formed annually in the upper atmosphere under the influence of cosmic radiation, which maintains a natural tritium content in the biosphere at 1.3 \(\times\) 10\({}^{18}\) Bq. Along with its stable analogue, it can migrate quite easily into moisture in the air and water flows and can accumulate as a component of mineral and organic compounds. It is a potential hazard, since it, along with a stable hydrogen isotope, is a component of water and acts as a building block of cellular tissue in living organisms.  
From what has been said, it appears clear that identifying the nature and extent of the problems of tritium or of the materials and/or wastes containing it is a fundamental aspect not only in terms of adequately evaluating the biological impact of tritium and other radionuclides of environmental relevance but also for planning the specific and the necessary actions required for an effective waste management approach under, e.g., disposal conditions. Moreover, the problem of tritium and tritium waste has become particularly critical since the late 70s, primarily due to the development of civil and military nuclear technologies.  
With most of the studies available in the literature referring to the understanding of tritium transport, transfer and dispersion modelling, e.g., during the hydrological cycle, or to the assessment of health impacts resulting from historical operations [6; 7; 8], the present review aims to critically analyze the available literature regarding the biological effects, sources, waste management challenges and environmental consequence of tritium. Existing knowledge gaps are also identified.