Tritium Determination at Trace Level: Which Strategy to Determine Accurately HTO and OBT in Environmental Samples?

Focusing on environmental tritium levels, measurements have been made for several natural water and leaf samples from an area where no tritium industrial discharge was known to occur. Therefore, to obtain sufficiently accurate data tritium was determined from large samples. Moreover, tritium measurement at environmental level requires appropriate methodology to avoid any contamination. Both tissue free water tritium (TFWT) and organically bound tritium (OBT) were determined for biological samples and compared to preliminary or literature data. In this paper, the authors describe both:

• a mobile extraction water device allowing therefore to realise the extraction step under the sampling site conditions to get rid of any contamination.
  
• a sensitive method for low level non-exchangeable OBT determination by a combination of a suitable sample treatment, a large capacity combustion apparatus and low background liquid scintillation spectrometry. Then, owing to validate this approach the authors give an application of this methodology to the determination of both fractions determined on tree leaves originating from the lower Rhone valley. The results demonstrate both the suitability of the procedure as tritium concentration in leaves and natural waters exhibit environmental level concentration and also that the OBT background in the studied area is very close to the one measured in the south west of France.