This presentation aimed to give a broad overview of what is currently understood about how ionizing radiation affects plants and animals, with emphasis on observations made in natural environments rather than controlled laboratory conditions. It also outlined the additional knowledge needed to establish reliable protection standards and to better assess compliance with those standards.

The discussion summarized key conclusions from past intentional and accidental exposure studies involving both plant communities and wildlife, including insights into differences in radiosensitivity and the factors that influence those differences. It also highlighted the limitations of many existing experiments, particularly challenges in interpreting ecological relevance and applying results to environmental protection guidelines. 

The ability of affected plant systems and animal populations to recover during or after exposure was examined, and traditional endpoints—such as mortality and reproductive success—were reviewed, while questioning whether they truly represent the most sensitive or ecologically meaningful indicators of radiation impact.  

Major gaps in our understanding of radiation effects on ecosystems were identified, along with specific types of studies that are still needed. These research needs were grouped into areas such as dosimetry, effect endpoints, and dose–response characterization. For instance, in dosimetry, further work is required to determine which species should be considered key indicators, to improve dose modeling for spatial and temporal variability, and to clarify relative biological effectiveness for different types of damage. 

It is already known that biological changes, including genomic alterations, can occur at dose rates far lower than those that visibly affect reproduction. The critical question is whether these subtle effects have consequences for populations—either immediately or in future generations—and under what circumstances such impacts might occur. Additionally, many species and ecosystem types have never been experimentally exposed to controlled photon sources or to radioactive contamination that creates highly uneven dose distributions. 

Finally, there remains very little understanding of how chemical stressors or other environmental pressures might interact with long-term radiation exposure, and whether such combined stresses intensify, reduce, or otherwise alter ecological outcomes.

For many years, industry, government regulators, and the general public have examined the environmental consequences of both regulated and unregulated activities. Historically, the prevailing approach has been to assume that safeguarding human health would automatically protect the environment as well.

In the United States, the overall system for environmental oversight has strengthened over time through clearer federal policy, a more structured national regulatory framework, improved coordination among agencies, revised rulemaking processes, and better communication from federal regulators. 

This discussion outlines the tools and strategies used in the United States to establish and maintain environmental protection, emphasizing the importance of transparency and active participation from stakeholders. It also highlights how international organizations can support global progress by helping build shared understanding and consensus on environmental protection principles.

In environmental radiation protection, significant knowledge gaps remain regarding long-term, low-level exposures—those typically experienced by organisms affected by radioactive releases. For any given radionuclide and ecosystem, several factors shape these exposures: (i) radionuclides exist in multiple chemical forms depending on the physical and chemical conditions of the environment; (ii) their transfer between environmental components can alter these forms, affecting mobility and bioavailability; and (iii) various non-radioactive pollutants are often present simultaneously.

In such complex, multi-pollutant settings, the biological effects of ionizing radiation may be intensified or diminished, depending on interactions with other contaminants. Chronic low-level exposures can trigger toxic effects that differ from those observed after short-term, high-dose exposure, due to long-term accumulation within cells and tissues that can localize in specific cellular or subcellular targets. Understanding these mechanisms is particularly critical for internal exposure to radionuclides, as localized accumulation can increase both radionuclide concentration and the effective dose, combining chemical and radiological toxicity.

  This forms the central focus of the ENVIRHOM research program, recently launched by IRSN. Following a summary of the experimental approach and initial results with phytoplankton and uranium, this study reviews the current knowledge on uranium in freshwater systems and highlights the challenges faced when attempting an Ecological Risk Assessment (ERA) from either a chemical or radiological perspective. The findings underscore the need for future research to clarify the relationship between chemical toxicity and radiotoxicity in cases of internal contamination. The ultimate goal is to align ecological risk assessments with human health risk evaluations for both radioactive and conventional pollutants.

Fifteen organizations, including regulatory bodies, research institutes, and industry partners across seven European countries—Finland, France, Germany, Norway, Spain, Sweden, and the UK—are collaborating on the FASSET (Framework for Assessment of Environmental Impact of Ionising Radiation) project. The initiative seeks to develop methods and tools for evaluating the effects of radiation on wildlife and ecosystems, with the ultimate goal of supporting environmental protection measures. The project is funded by the European Union under the 5th Framework Programme and is scheduled to conclude in October 2003.

The project is organized into four main work packages (WPs). WP2 focuses on assessing seven representative European ecosystems: three aquatic (marine, brackish, freshwater) and four terrestrial (semi-natural areas including pastures, agricultural lands, wetlands, and forests). A set of candidate reference organisms has been identified based on expert evaluation of exposure scenarios within these ecosystems. These reference organisms act as surrogates for real biota in natural habitats, serving as starting points for the development of dosimetric models in WP1 and for integrating existing knowledge on ecological relevance and biological effects.
The selection of reference organisms is further analyzed to justify their use and evaluate their suitability across different environmental scenarios, considering factors such as radionuclide transfer, internal and external dose estimates, ecological significance, and observed biological effects. 

WP3 addresses broad “umbrella” effects that occur at the individual level but may influence populations or higher organizational levels. Four key categories are considered: 

  1.Morbidity – changes in health, fitness, or overall well-being. 
  2.Mortality – deaths directly attributable to radiation. 
  3.Reproductive success – changes in the number of offspring produced. 
  4.Scorable cytogenetic effects – molecular or chromosomal alterations. 

A comprehensive database is being compiled, integrating literature data for multiple organism groups across these four effect categories, including evaluation of the suitability of data for determining relative biological effectiveness (RBE) for different types of radiation.

  Finally, findings from the three work packages—exposure, dosimetry, and effects—will be synthesized into a unified framework for environmental impact assessment. WP4 draws on ecotoxicological approaches used for other hazardous substances to guide this process. The framework is designed to support regulators, demonstrate compliance, and facilitate communication with stakeholders, decision-makers, and the general public.

Several radionuclide transfer models, each tailored to different ecosystems, will be employed to calculate both external and internal radionuclide concentrations. These calculations will also enable the conversion of environmental and internal concentrations into absorbed dose rates. In this process, the relative biological effectiveness (RBE) of various radiation types will be taken into account, allowing the development of suitable radiation weighting factors (wr) for the organisms, endpoints, and dose rates being studied.

The models are based on unit deposition for scenarios of acute exposure and steady-state conditions, as well as radionuclide flux for dynamic models, such as those applied to waste repositories. Work on these models has already begun and is expected to be completed by the end of the project in autumn 2003.

In the initial phase of the project, external exposure assessments were focused on organisms living in terrestrial environments. Analytical methods recently applied, such as the point-source dose distribution function, provide reliable results in media with relatively uniform densities, such as aquatic systems. However, in terrestrial habitats where materials and densities vary considerably, these analytical approaches introduce significant uncertainties.

To improve estimates of external exposure, Monte Carlo simulations were conducted for various reference organisms. Simplified geometric models of the organisms, such as cylinders and ellipsoids, were used. The outer layers of the skin and fur, composed of non-active tissue, provide some shielding; however, this effect is mainly relevant for D-, E-, and low-energy J-emitters. 

To account for the influence of radionuclide distribution in the soil, simulations were run for different scenarios: planar sources on the soil surface, sources buried at 5 cm and 20 cm depths, and a uniform volume source extending to 50 cm depth. Calculations were performed for monoenergetic J-radiation with energies of 50 keV, 300 keV, 662 keV, 1 MeV, and 3 MeV. 

For example, the dose conversion factor (DCF) for a mole exposed to a planar J-source on the soil surface demonstrates two clear trends: the DCF increases with higher J-energy and decreases with greater depth of the organism, due to the shielding effect of the overlying soil. This shielding effect is particularly pronounced at lower energies.