Holding Times and Preservation for Environmental Radiochemical Samples: An Evaluation of ISO Standard Guidelines

The condition of a sample taken and stored before analysis is an important aspect in analytical measurements including in the field of environmental radiochemistry. The validity of the result from the test depends heavily on the sample integrity; a sample that is not well preserved might not be a true representative of what has been sampled. For example, the radionuclides in a water sample might be adsorbed by the wall of the container during transport and storage. This study summarises a range of shelf-life tests performed by SOCOTEC nuclear laboratory. Our studies suggest that the integrity of freshwater samples can be preserved for up to 1½ year when filtered and acidified for the analyses of gamma emitting radionuclides and at least 6 months for actinides. Tritium, either in its natural non-acidified state or acidified, can be stored for at least 3 years. For a minimum loss of the transuranium actinides, filtration and acidification should occur within 3 to 7 days of sampling. Cooling the samples during transport and interim storage is advised to suppress bacterial and algal growth.