Isotopic fractionation of tritium in biological systems

Abstract

Isotopic fractionation of tritium is a highly relevant issue in radiation protection and requires certain radioecological considerations. Sound evaluation of this factor is indeed necessary to determine whether environmental compartments are enriched/depleted in tritium or if tritium is, on the contrary, isotopically well-distributed in a given system. The ubiquity of tritium and the standard analytical methods used to assay it may induce biases in both the measurement and the signification that is accorded to the so-called fractionation: based on an exhaustive review of the literature, we show how, sometimes large deviations may appear. It is shown that when comparing the non-exchangeable fraction of organically bound tritium (neOBT) to another fraction of tritium (e.g. tritiated water) the preparation of samples and the measurement of neOBT reported frequently led to underestimation of the ratio of tritium to hydrogen (T/H) in the non-exchangeable compartment by a factor of 5% to 50%. In the present study, corrections are proposed for most of the biological matrices studied so far. Nevertheless, the values of isotopic fractionation reported in the literature remain difficult to compare with each other, especially since the physical quantities and units often vary between authors. Some improvements are proposed to better define what should encompass the concepts of exchangeable and non-exchangeable fractions.

Assimilation and transport of organic bound tritium in an irrigated pine forest

“…Several researchers have delineated exchangeable organically-bound tritium (E-OBT) from nonexchangeable organically-bound tritium (NE-OBT) in their reviews and studies with biota. 5,6,12,13,14,15 They have defined E-OBT as being tritium bound to either O or N whereas NE-OBT was defined as tritium bound to C but the terminology for defining OBT varies widely in the literature. These authors collectively classify tritiated water in tissues as "tissue free water tritium" (TFWT).…”

Levels and behavior of environmental tritium in East Asia

“…The effects of low-dose tritium on the central nervous system of offspring mice and rats have also been reported [12][13][14]. Therefore, environmental tritium has attracted wide attention in radiation protection communities [15][16][17]. In this context, environmental tritium monitoring is not only critical for reviewing and checking the operation status of nuclear facilities but is also helpful for assessing their long-term environmental impacts.…”

Historical record of tritium from tree cores at the Savannah River Site

“…Tritium can also become biologically incorporated and migrate in environmental systems by processes like photosynthesis, respiration, and transpiration in the place of Hparticularly when elevated levels of T are present. [2][3][4] Organic bound tritium (OBT) is found in different chemical forms in the environment, which in high levels, presents a health concern for humans and other biological life that live or consume food in these areas. These forms of OBT have been dened as exchangeable (E-OBT) and non-exchangeable OBT (NE-OBT).…”