# The Impact of Tritium in the Environment
## 4 Biological Effects
The wide difference in experimentally and scientifically grounded assessments, which reach more than five orders of magnitude, as well as different individual dose criteria (40 to 1000 \(\upmu\)Sv\(\cdot\)y\({}^{-1}\)) is due to the fact that tritium drinking water limits around the world vary by a factor of more than 700, i.e., from 100 Bq\(\cdot\)dm\({}^{-3}\), as recommended by the EU \begin{table}
\begin{tabular}{l l l l} \hline \hline \multirow{2}{*}{**Exposure Route**} & \multirow{2}{*}{**Tritium Species**} & \multicolumn{2}{c}{**Dose Factor [Sv-Bq\({}^{-1}\)]**} \\ \cline{3-4}  & & **Adults 1** & **Children (\(\leq\)1 y)** \\ \hline \multirow{3}{*}{Inhalation} & Tritiated water HTO (from air) & 1.8 \(\times\) 10\({}^{-11}\) & 1.1 \(\times\) 10\({}^{-10}\) \\ \cline{2-4}  & Tritiated gas (hydrogen) HT & 1.8 \(\times\) 10\({}^{-15}\) & 4.8 \(\times\) 10\({}^{-15}\) \\ \cline{2-4}  & Tritiated methane CH\({}_{3}\)T & 1.8 \(\times\) 10\({}^{-13}\) & 4.8 \(\times\) 10\({}^{-13}\) \\ \cline{2-4}  & Organically bonded tritium (OBT) & 4.1 \(\times\) 10\({}^{-11}\) & 4.8 \(\times\) 10\({}^{-11}\) \\ \hline \multirow{2}{*}{Oral ingestion} & Tritiated water HTO (aqueous specie) & 1.8 \(\times\) 10\({}^{-11}\) & 4.8 \(\times\) 10\({}^{-11}\) \\ \cline{2-4}  & Organically bonded tritium (OBT) & 4.2 \(\times\) 10\({}^{-11}\) & 1.2 \(\times\) 10\({}^{-10}\) \\ \hline \hline \end{tabular} \({}^{\dagger}\) Factors are equal for workers (Annex A1 and B1) and members of the public (Annex F1 and H1, [58]).  
\end{table} 
Table 3: Dose factors recommended by the ICRP [58]. Recent radiobiological studies [8] showed that the dangers of tritium ingestion have been previously underestimated; it is probably several times more dangerous than \(\beta\) exposure to \({}^{137}\)Cs, and it is considerably more dangerous when ingested in amniotic fluid. The relative biological effectiveness (RBE) for tritium was determined in the range of 1-3 [62; 63], and it was two orders of magnitude higher for 1-3% tritiated liquid, which can reach DNA. This means that the degree of health damage due to \(\beta\) radiation from tritium is assumed to be quantitatively equal to that from \(\gamma\)-rays; \(\beta\)-rays may even contribute more to the exposure per unit energy than \(\gamma\)-rays. The latter is especially effective for low doses [84]. A study of the effect of tritium water on peripheral blood lymphocytes allowed for determining the relative biological effectiveness (RBE) in the range of 2.12-2.8 [85; 86; 87]. The term RBE was introduced for the integrated assessment/comparison of the absorbed dose from different types of radioactivity and can be determined as the ratio of absorbed doses required to produce the same biological end point, using a reference radiation level and a comparison radiation level for given end point [88; 89; 90]:  
\[\text{RBE}=Dose_{reference\ radiation}/Dose_{test\ radiation} \tag{10}\]  
The basis for comparing the RBE from low-energy beta radiation with a short travel time and high-energy gamma radiation is the degree of damage caused by radioactive exposure to a body organ or the body as a whole. However, at the microscopic level, exposure occurs in two main ways: by gamma radiation and by beta radiation. For gamma radioactivity, the released high energy of the photoelectron is distributed over a large distance with a relatively low density. That is, absorbing many photons, the organ is irradiated evenly at the macroscopic level. The energy of tritium beta particles is distributed over a shorter distance with a higher intensity, leaving a significant space between individual tracks. However, since the HTO is distributed evenly in the organ, uniform irradiation also occurs at the macroscopic level. However, the uniform exposure is due to the propagation of the tritium nuclide itself and not to the overlapping of beta particle tracks in a wide range.