Speciation analysis of low-level tritium in marine organisms

Tritium in the marine organisms is present as both tissue-free water tritium (TFWT) and organically bound tritium (OBT). OBT has longer biological retention than TFWT and is more important for radiological impact assessment. Accurate OBT quantification remains difficult because of low activity levels, complex organic matrices, residual TFWT interference, and impurities in combustion water that can affect LSC measurement. Thus, reliable speciation methods are required for assessing tritium exposure risks in marine organisms.

In this work, we developed a method for tritium speciation analysis. TFWT was separated by freeze-drying, while OBT was converted to tritiated water through oxidation combustion and rapidly purified using ion-exchange resin. The separation procedure for OBT was investigated, and the optimal combustion program was recommended, in which slow carbonization at 330-450 °C ensured stable combustion and efficient decomposition of protein- and lipid-rich tissues. With optimized protocol, an overall ∼95% recovery of OBT in combustion process was achieved and a maximum of ∼5 g of dried fish or shrimp sample can be treated. AG501-X8 mixed bed ion-exchange resin removed over 99% of major inorganic ions and reduced chemiluminescence interference. Tritium recovery during purification remained at about 93%, supporting reliable LSC measurements.

By optimizing high-temperature oxidation and resin purification, this study improves the feasibility of OBT determination in small amounts of biological sample, supporting more reliable tritium monitoring and environmental risk assessment.