  At the basis of most risk assessments aimed at determining the long-term
trends in changes in the activity of radionuclides in the environment and thus
exposure to ionizing radiation, various concepts of half-lives are used,
particularly: biological, environmental (ecological) and effective one. There
is a clear lack of consensus on the terminological level and, more importantly,
on the methodological level regarding the determination of these half-lives.
This manifests by a divergent methodology and the existence of two main, but
contradictory concepts. In the first, empirically determined half-life is
referred to as environmental or biological. The effective half-life is
extrapolated at a later stage after taking into account the physical decay. In
the second concept, the effective half-life is the one empirically determined
and the remaining half-lives can be extrapolated after correction for physical
decay. As both concepts seems to be incompatible with each other, the aim of
this work was to thoroughly analyze their theoretical assumptions, conditions,
strengths and weaknesses and to define the conditions that must be met in order
to enable comparison of the results obtained with the use of two separate
concepts. In case of the environmental components the suggested approach is to
empirically determine the effective half-life, and subsequently, to extrapolate
the environmental and/or biological half-lives.
