# The Impact of Tritium in the Environment
## 4 Biological Effects
\begin{table}
\begin{tabular}{l c c c c} \hline \hline \multirow{2}{*}{**Category of Object**} & \multirow{2}{*}{**Tritium Species**} & \multicolumn{3}{c}{**Confidence Interval**} \\ \cline{3-5}  & & **5\%** & **Average/Recommended** & **95\%** \\ \hline \hline \multirow{2}{*}{Adult body [95]} & HTO & 1.2 & 2.3 & 3.8 \\ \cline{2-5}  & OBT & 2.3 & 5.0 & 11.6 \\ \hline \multirow{2}{*}{Fetus (if orally ingested during pregnancy) [95]} & HTO & 2.1 & 4.4 & 8.1 \\ \cline{2-5}  & OBT & 4.0 & 9.8 & 23.1 \\ \hline \multirow{2}{*}{Blood lymphocytes [96]} & OBT & 1.13 & 2.5 & 3.1 \\ \cline{2-5}  & HTO & 1 & 1 & 2.5 \\ \cline{2-5}  & OBT & 1 & 1 & 2.5 \\ \hline \multirow{2}{*}{Ingestion Dose Coefficients for Adults, Sv-Bq\({}^{-1}\):10\({}^{11}\)} & & & \\ \cline{2-5}  & HTO & 2.1 & 3.9 & 6.6 \\ \cline{2-5}  & OBT & 3.9 & 8.7 & 20 \\ \hline \multirow{2}{*}{Recommended by the ICRP [99]} & HTO & 1.8 & \\ \cline{2-5}  & OBT & 4.1 & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Integrated values of relative biological effectiveness (RBE) and dose coefficients for tritium water (HTO) and organically bound tritium (OBT). Even though the most common and hazardous form of tritium is its aqueous form, organically bound tritium contained in food of plant and animal origins is radiologically more dangerous [100]. In plant organisms, OBT can be formed both through isotopic exchange and photosynthesis. The organic matter of plants consists mainly of the polymer cellulose, which, in turn, consists of D-glucose links [101]. Theoretically, tritium can replace 10 protium atoms: 3 of them are bound to oxygen, and 7 atoms are bound to carbon. The cell membrane of some species of aquatic plants (e.g., kelp) is built mainly of the polysaccharide alginic acid. The alginic acid chain contains three hydroxyl and five alkyl protons. The mobile hydrogen from the hydroxyl groups is easily exchanged for tritium in the tritiated intercellular medium of the sap that washes over plant tissues. Instead, the isotopic exchange of alkyl protons for tritium is much slower. In addition to isotopic exchange, tritium is incorporated into organic matter during photosynthesis. During biological evolution, a mechanism for primarily assimilating the light isotope was formed, as it requires less energy. The interaction between CO\({}_{2}\) and H\({}_{2}\)O under the influence of sunlight in plants leads to the depletion of plant organic matter by deuterium relative to water [102]. It is likely that the isotopic exchange of protium for tritium in the -O-H groups of plant organic matter, depending on the content of the superheavy isotope in the environment, may occur in the opposite direction to the isotopic fractionation in the -C\(\equiv\)H groups due to photosynthesis. When tritium and HTO enter the body, an isotopic exchange occurs between the radionuclide and hydrogen contained in organic structures. The proportion of tritium involved in this exchange is 0.5-4.0%, increasing to 10% with chronic intake of tritium [103; 104]. The incorporation of tritium into organic molecules leads to an increase in the radiation dose by 1.4-1.5 times compared to the dose caused by tritium in the liquid phase of the body [105]. The metabolism of tritium entering the human body in the organically bound form with food is significantly different. Significantly higher rates of incorporation (approximately 10 times) and distribution of OBT in certain body structures are observed when these forms of \({}^{3}\)H are consumed in food compared to the intake of HTO with drinking water. Usually, direct intake and metabolism of OBT is not considered in tritium dosimetry models. At the same time, the dose from the consumption of OBT with food may exceed the dose from an equivalent amount of tritium incorporated in the aqueous form through oral or inhalation intake. The two-component model of tritium metabolism describes the retention of tritium in the bodies of adults and children.