195
classification. Therefore, the IAEA typically uses a much simpler classification
scheme based on texture and organic matter content (IAEA 2009, 2010). For uranium, a classification scheme that takes account of pH as well as texture has been
found to be useful (see Sect. 2).
In evaluating impacts on non-human biota, it is not possible to address all possible taxa. Therefore, approaches have been developed based on the use of reference
organisms (Larsson 2004) or reference animals and plants (RAPs) (ICRP 2007,
2008). In either case, the definitions are similar. Thus, a RAP is defined as a hypothetical entity, with the assumed basic biological characteristics of a particular type
of animal or plant, as described to the generality of the taxonomic level of Family,
with defined anatomical, physiological and life-history properties, that can be used
for the purposes of relating exposure to dose, and dose to effects, for that type of
living organism. In this context, the IAEA (2014) has produced a handbook on estimating transfers to wildlife that is similar to its handbook on estimating transfers to
human foodstuffs (IAEA 2010) and is based on a reference organism concept. The
use of a reference organism approach is appropriate to evaluating both the radiological and chemotoxic impacts of uranium.
Models used to simulate the transport of uranium and its progeny in the environment for assessment purposes may be very simple, e.g. they may involve no more
than a 1D vertical representation of advection and dispersion in the soil column,
with uptake by plants estimated using an empirically derived ratio between the concentration in plants and the concentration in the underlying soil (Thorne 2012,
2014). However, much more complex models may also be used, e.g. 3D coupled
representations of water flow, sediment movement and contaminant transport in a
surface-water catchment (Bosson et al. 2010). The level of complexity of the assessment model should be matched to the significance of the environmental issue being
addressed (e.g. spatial extent and degree to which uranium concentrations are
increased above typical background or baseline values) and the need for assurance
that the key factors controlling the transport of uranium in the environment are
included in the model, so that the robustness of the results obtained can be determined. In some situations, specific aspects may need to be investigated through
detailed modelling, in order that a simplified assessment approach can be derived
and/or justified (IAEA 2018).
Assessment models are often empirical in nature, i.e. with parameter values
based on observed relationships between different environmental media, but without explicit consideration of the processes giving rise to those relationships. Also, in
the past, assessment approaches have typically been deterministic, using point estimates of the various parameters. However, there is now an increasing use of probabilistic approaches, with input parameter values selected from specified probability
density functions.
In the following sections of this chapter, more detailed consideration is given to
the quantification of environmental transfer processes and to the assessment of
radiological and chemotoxic impacts of uranium once concentrations in environmental media have either been measured or modelled.
Assessment Modelling and the Evaluation of Radiological and Chemical Impacts…
classification. Therefore, the IAEA typically uses a much simpler classification
scheme based on texture and organic matter content (IAEA 2009, 2010). For uranium, a classification scheme that takes account of pH as well as texture has been
found to be useful (see Sect. 2).
In evaluating impacts on non-human biota, it is not possible to address all possible taxa. Therefore, approaches have been developed based on the use of reference
organisms (Larsson 2004) or reference animals and plants (RAPs) (ICRP 2007,
2008). In either case, the definitions are similar. Thus, a RAP is defined as a hypothetical entity, with the assumed basic biological characteristics of a particular type
of animal or plant, as described to the generality of the taxonomic level of Family,
with defined anatomical, physiological and life-history properties, that can be used
for the purposes of relating exposure to dose, and dose to effects, for that type of
living organism. In this context, the IAEA (2014) has produced a handbook on estimating transfers to wildlife that is similar to its handbook on estimating transfers to
human foodstuffs (IAEA 2010) and is based on a reference organism concept. The
use of a reference organism approach is appropriate to evaluating both the radiological and chemotoxic impacts of uranium.
Models used to simulate the transport of uranium and its progeny in the environment for assessment purposes may be very simple, e.g. they may involve no more
than a 1D vertical representation of advection and dispersion in the soil column,
with uptake by plants estimated using an empirically derived ratio between the concentration in plants and the concentration in the underlying soil (Thorne 2012,
2014). However, much more complex models may also be used, e.g. 3D coupled
representations of water flow, sediment movement and contaminant transport in a
surface-water catchment (Bosson et al. 2010). The level of complexity of the assessment model should be matched to the significance of the environmental issue being
addressed (e.g. spatial extent and degree to which uranium concentrations are
increased above typical background or baseline values) and the need for assurance
that the key factors controlling the transport of uranium in the environment are
included in the model, so that the robustness of the results obtained can be determined. In some situations, specific aspects may need to be investigated through
detailed modelling, in order that a simplified assessment approach can be derived
and/or justified (IAEA 2018).
Assessment models are often empirical in nature, i.e. with parameter values
based on observed relationships between different environmental media, but without explicit consideration of the processes giving rise to those relationships. Also, in
the past, assessment approaches have typically been deterministic, using point estimates of the various parameters. However, there is now an increasing use of probabilistic approaches, with input parameter values selected from specified probability
density functions.
In the following sections of this chapter, more detailed consideration is given to
the quantification of environmental transfer processes and to the assessment of
radiological and chemotoxic impacts of uranium once concentrations in environmental media have either been measured or modelled.
Assessment Modelling and the Evaluation of Radiological and Chemical Impacts…