# The Impact of Tritium in the Environment
## 4 Biological Effects
RSC (relative source contribution) is the relative contribution of water consumption to the degree of exposure, estimated at 0.6. UF (uncertainty factor) is a complex uncertainty factor (assumed to be 100) that includes intra- and interspecies extrapolations of human variability, resistance to subchronic and chronic exposure, and other aspects of \begin{table}
\begin{tabular}{l l l} \hline \hline
**Material** & \(\mathrm{E}\) **(\(\beta\)) 5.7 keV** & \(\mathrm{E}\) **(\(\beta\)) 18.6 keV** \\  & **(Average)** & **(Maximum)** \\ \hline T\({}_{2}\), gas, 0 \({}^{\circ}\)C, 101, 325 Pa & 2.4 \(\times\) 10\({}^{-3}\) & 3.2 \(\times\) 10\({}^{-2}\) \\ \hline Air, 0 \({}^{\circ}\)C, 101, 325 Pa & 3.6 \(\times\) 10\({}^{-4}\) & 4.5 \(\times\) 10\({}^{-3}\) \\ \hline Water, soft tissues, oils & 4.2 \(\times\) 10\({}^{-7}\) & 5.2 \(\times\) 10\({}^{-6}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Penetration range, m, of a beta particle into materials depending on its energy [54, 55]. uncertainty, while IR (ingestion rate) is the level of drinking water consumption, which is 1 dm\({}^{3}\cdot\)day\({}^{-1}\) for children and 2 dm\({}^{3}\cdot\)day\({}^{-1}\) for adults. The calculated value of the \"safe\" concentration of tritium (C\({}_{2}\)) is 7.8 \(\times\) 10\({}^{6}\) and 2.2 \(\times\) 10\({}^{6}\) Bq\(\cdot\)dm\({}^{-3}\) for adults and children, respectively. Radiation protection assumes that any exposure to radiation is associated with a certain level of risk. The WHO recommendations are based on a linear relationship between exposure and risk, with no threshold below which there is no risk. An individual dose criterion (IDC) of 0.1 mSv/year reflects a very low level of risk that is not expected to result in any detectable adverse health effects. The nominal risk factor used to assess the lifetime risk of fatal cancer arising from radiation exposure to the public is 0.05 per Sv (5 \(\times\) 10\({}^{-8}\) per \(\upmu\)Sv). It was found that the risk of fatal and severe non-fatal cases from a dose of 0.1 mSv (100 \(\upmu\)Sv) per year is 10\({}^{-5}\) to10\({}^{-4}\) per year, or about 6 \(\times\) 10\({}^{-4}\) over a lifetime (70 years). If the dose of radioactivity from drinking water is below the WHO-recommended level of 0.1 mSv/year, the water is considered safe for human consumption from a radiological point of view [71]. To calculate the equivalent and effective dose from different radionuclides depending on the way they enter the body, the ICRP periodically publishes updated dose coefficients (dose per unit of exposure) (Table 3) [71]. These data also allow for solving the opposite issue, i.e., calculating the limits of radionuclide incorporation from the atmospheric air by inhalation and water and food by oral ingestion. As already mentioned, due to the low energy of beta particles, unlike, for example, gamma-emitters, tritium does not cause external irradiation. The limit for the tritium content in water can be calculated similarly to the previous Equation (7):  
\[\text{C}_{3}=\frac{\text{IDC}}{\text{EP}\times\text{DF}\times\text{WIR}} \tag{9}\]  
where IDC is the WHO-recommended individual dose criterion, which is equal to 1.0 \(\times\) 10\({}^{-4}\) Sv\(\cdot\)y\({}^{-1}\), and DF is the dose factor of 1.8 \(\times\) 10\({}^{-11}\) Sv\(\cdot\)Bq\({}^{-1}\), which was determined in the official ICRP publication 119 according to the modern model of radionuclide metabolism based on the energy characteristics of beta particles emitted by tritium, radiological parameters, radiation weighting, and other factors. The calculated value of the tritium limit in drinking water (C\({}_{3}\)) is 7610 and 4280 Bq\(\cdot\)dm\({}^{-3}\) for adults and children, respectively (Table 3).