Considering the Environment When Applying the System of Radiological Protection: Part 1 Broadening the Reference Animals and Plants Approach and Related Derived Consideration Reference Levels

Abstract

This publication broadens the Reference Animals and Plants (RAP) and Derived Consideration Reference Levels (DCRL) approach outlined in Publication 108. It introduces a methodology for establishing additional DCRLs at higher taxonomic levels to complement the existing DCRLs which are defined at the family level. A transparent, data-driven approach for assessing the effects of ionising radiation on non-human species in their natural environment is described. By integrating comprehensive radiation effects data, documented models, and considering the underlying assumptions, the methodology enhances transparency, reproducibility, and improves the ability of assessors to address complex environmental impact assessments. The broadened RAP approach extends beyond the twelve RAP families defined in Publication 108 by incorporating higher taxonomic levels such as class, phylum, and broad non-human species groups (vertebrates, invertebrates, and plants). This expansion improves the representativeness and applicability of the RAP approach in radiological environmental impact assessments. The approach applies two statistical models: the Acute-to-Chronic Transformation of Radiation Effects (ACTR) model, which extrapolates chronic effects from acute data, and the Endpoint Sensitivity Distribution (ESD) model, which synthesises chronic and acute effects data across taxonomic groups. The additional DCRLs are derived using the 5 th percentile of the ESD, with a multi-criteria Extrapolation Factor (EF) applied to establish the lower boundary, and accounting for data gaps and uncertainties. As simple guidance, the DCRLs (family) from Publication 108 are the benchmarks recommended for environmental impact assessments. The additional DCRLs introduced in this publication provide complementary reference points, particularly in cases where dose rates approach or exceed DCRL Family values. This broadened approach where benchmarks can be used in conjunction, is especially relevant for complex impact assessments, such as evaluations of large facilities, post-accident scenarios, and protected ecosystems. It also allows flexibility in applying different ESD percentiles to identify an acceptable level of protection in consultation with stakeholders or to incorporate site-specific data for refined assessments.

Irrespective of the DCRLs used, the guidance from Publication 124 applies: the lower boundary of the relevant DCRL should be applied in planned exposure situations, while in existing exposure scenarios or post-accident long-term assessments, DCRLs help guide optimisation of radiological protection of non-human species. Additionally, in emergencies, at the time where the focus shifts to environmental recovery, the acute ESD models for classes or phyla, or broad species groups can support stakeholder discussions providing retrospective information on the likely ecological consequences of radiation exposure. By broadening the RAP approach, this publication strengthens the scientific basis for environmental radiological protection, facilitates stakeholder engagement, and contributes to support decision-making in environmental impact assessments. The additional DCRLs at higher taxonomic levels introduced in this publication provide an important complement in complex cases as it offers the possibility of a more refined assessment and a transparent evaluation of the level of confidence. The methodology and underpinning data enable assessors to adapt their assessments to specific contexts, make informed judgments, and reduce uncertainties in evaluating radiation impact or risk to non-human species. Further guidance on the application of the DCRLs within the system of radiological protection will be provided as Part 2 in this series of publications ‘Considering the Environment When Applying the System of Radiological Protection Part 2: Integration within the system, including practical use of Derived Consideration Reference Levels’.