The STAR project finished on 31st July 2015 - page no longer being updated
Key Question: 'Are existing ecological protection criteria sufficiently robust to protect populations and ecosystems from ecologically-relevant low doses?'
Radioactive decay is accompanied by the emission of high energy radiation. Radioactive decay occurs when a nucleus changes from a higher to a lower energy state, and occurs at a rate which is described by a decay constant. When radiation interacts with biological tissues it causes excitation and ionisation of atoms. The effects of dissipating radiation energy in a tissue include:
- temperature increase
- the breaking of chemical bonds
- biological effects
In SI units, the unit of absorbed dose is the Gray (Gy), where one Gy = one Joule of absorbed energy per kg material (J/kg).
DNA is the primary target for the induction of biological effects from radiation in all living organisms. There are broad similarities in radiation responses of different organisms, and wide differences in their radiation sensitivity. For instance,the range in lethality from acute exposure to radiation varies by three to four orders of magnitude with mammals being among the most sensitive and viruses being among the most radio-resistant. A briefing document providing a general overview of the biological effects of ionising radiation and useful references can be downloaded from here.
Benchmarks for radiological protections of the environment
Approaches have been developed to asses if wildlife is protected from anthropogenic sources of ionising radiation. For use within these approaches various dose rates have been proposed by different organisations which are intended to protect populations. Benchmark values generally fall into two types:
Screening values; where exceeding the values mean that additional analyses and/or work are needed to better understand and quantify the risk (as developed under the previous EC EURATOM projects ERICA and PROTECT. These are frequently used in tiered risk assessment schemes and serve primarily as a trigger for further investigation. Legally binding criteria or standards that must be met in accordance with a given regulation (for example as Environmental Quality Standards (EQSs) under the EC Water Framework Directive or USDOEs dose rate limits for wildlife). In these cases, exceeding the values may result in legal or regulatory action.
Within ICRP Publication 108 the ICRP has recently produced Derived Consideration Reference Levels (DCRLs) for each of theirReference Animals and Plants (RAPs). The DCRLs are defined as a (order of magnitude) band of dose rate within which there is likely to be some chance of deleterious effects of ionising radiation occurring to individuals of that type of RAP (derived from a knowledge of expected biological effects for that type of organism). The ICRP is now working on guidance to show how to use the DCRLs in assessments. A general overview of the derivation and application of benchmarks for application in radiological assessments of the environment can be downloaded from here.
Ecologically relevant low dose effects - key strategic question for STAR
New ways of thinking about radioecology and approaches, in collaboration with other environmental sciences, are emerging. The new approaches stress that to properly determine contaminant effects we must address the realistic environmental conditions in which organisms are actually exposed.The conditions under which most contaminant research is conducted are often not directly relevant to real exposure conditions (see text box) and this and greatly increase the uncertainties associated with environmental risk assessments.
The overarching objective in this workpackage is to enhance the scientific robustness of ecological protection criteria and their applicability as protection benchmarks. This will be achieved by addressing two specific objectives:
- To identify (for a limited number of taxonomic groups) how different life history characteristics (e.g. longevity, age-specific fertility, age at first reproduction) influence the propagation of radiological effects from individuals to populations; and to test (for two radiation types (α and γ) and two species which we have not yet selected) the ability of omics tools, and Dynamic Energy Budget concepts, to enhance understanding of:
- How radiosensitivity at the molecular and individual levels mechanistically link to impacts on individuals and populations;
- How dose characteristics (e.g. radiation type, targeted organs) influence the biological efficiency of radiological damage, by identifying the metabolic pathways that produce individual trait disturbances.
In designing and conducting the experiments we will carry out to answer these questions we will work with experts from ecotoxicology both from within the STAR partner organisations and also via consultation workshops with external experts.This workpackage will work closely with the workpackage on Radiation Protection in a Mixed Contaminant Context
- A methodology to obtain transparently derived and scientifically grounded ecological group-specific protection criteria (following recommendations from the PROTECT project and the ICRP
- Ecologically group specific protection criteria
- An understanding of the mode of actions of different radiation types
- Assessment of the applicability of omics fingerprints as predictive, early, markers for effects at higher biological levels
- An understanding of the metabolic mode of actions of radiation exposure at the individual level (using biokinetics and the Dynamic Energy Budget approach)
- Knowledge to help extrapolate radiation effects from the metabolic to whole-organism level and from one radiation type to another
- Deliverable 5.1
- Laboratory radiation effects studies. See here for a summary.
- Deliverable 5.2
- Life history traits, radiosensitivity and population modeling: methods to extrapolate from individual endpoints to population dynamics. See here for the summary.
- ICRP Committee 5 which is concerned with radiological protection of the environment, the DCRL values were published in ICRP Publication 108
- ERICA project
- EURATOM project which, amongst other activities, derived a generic screening dose rate for wildlife using approaches adopted from the assessment of chemicals
- Deliverable 5 papers by Garnier-Lapace and Garnier-Lapace, Anderson and Howard are especially relevant to this workpackage of STAR.
- PROTECT project and its Deliverable reports
- IAEA EMRAS II Working group 6 which has a number of sub groups: investigating the relationships between exposures to ionising radiation and effects on flora and fauna; updating dose-effects databases assessing population models; considering multi-stressors.
This workpackage is co-ordinated by Jacqueline Garnier Laplace of IRSN.