B. J. HOWARD* AND N. A. BERESFORD

ABSTRACT

Over the past decade the international community has recognised the need to demonstrate that wildlife populations are protected from environmental releases of radioactivity as well as humans. Frameworks and models for such assessments have been developed and are continuously being tested and improved. In this chapter, the basic elements of an assessment for radiation exposure of wildlife are outlined, including the current methods used to estimate environmental radionuclide transfer and the resulting doses. The methods used to derive benchmarks based on radiation effects data, against which estimated doses can be compared, are described. Since it is impossible to quantify transfer and doses for all species, the approaches use representative groups such as ‘‘reference organisms’’ including the Reference Animals and Plants of the International Commission on Radiological Protection (ICRP). The current approaches used for wildlife have some commonalities with those used for humans, but with some notable differences. Organisms tend to be considered as homogenous, simplified geometric shapes with the whole organism absorbed dose rate being estimated; the majority of available effects data are expressed on the basis of whole organism dose rates. Transfer is often quantified by predicting the whole organism activity concentration from that in the environmental media such as soil, water or air. Protection is focused on

* Corresponding author

Issues in Environmental Science and Technology, 32 Nuclear Power and the Environment Edited by R. E. Hester and R. M. Harrison © Royal Society of Chemistry 2011

Published by the Royal Society of Chemistry, www. rsc. org

populations rather than individuals, and therefore some approaches used for

the assessment of chemicals pollutants are also being adopted for

radionuclides.

1 Introduction

Man-made radionuclides are emitted from the nuclear fuel cycle into the atmosphere in gaseous discharges and into aquatic ecosystems via liquid discharges. Radionuclides can be transferred from air, soil, water and sediment to organisms. Liquid discharges input radionuclides into water bodies from which they can be transferred to sediment, which is the major sink in aquatic systems. Gaseous discharges are deposited onto both plant and soil surfaces, and soil is the major reservoir for most radionuclides in the terrestrial envir­onment. To illustrate various issues in the chapter, we will concentrate on a few radionuclides: 60Co, 90Sr, 137Cs, 239+240Pu, 241Am and 131I. Noble gases, which are discharged in comparatively high amounts, are not important in dose terms, due to their low environmental transfer and dose coefficients (see the predicted dose rates presented by Copplestone et al.).1

In this chapter, we describe the major terrestrial pathways for radionuclides released during the nuclear fuel cycle, with a focus on wildlife rather than the human food chain. We briefly describe the approaches being used and devel­oped to demonstrate protection of wildlife from releases of radioactivity into the environment. Key differences in the approaches to predicting environ­mental transfer between the human food chain and environmental assessment methods for wildlife will be highlighted. More detailed information on this topic can be accessed at http://www. ceh. ac. uk/protect.

The major factors affecting the extent of transfer of radionuclides to organisms are briefly described. In many recent radiological documents, the term ‘‘non-human’’ biota has been used for organisms other than humans. This term is rarely used in ecotoxicology and other areas of environmental protec­tion. Here we use the term ‘‘wildlife’’ which encompasses wild plants, undo­mesticated animals and organisms such as fungi and bacteria (i. e. the potential objects of environmental protection).

The degree of internal exposure arising from man-made radionuclides in the environment depends on the environmental behaviour of the radionuclides emitted. The environmental mobility of different radionuclides varies con­siderably. Radionuclides with a potentially high environmental mobility include 131I, 134/137Cs, 90Sr, 14C, 3H, 35S, whereas those with low environmental mobility include 239/240Pu and 241Am. Many different factors affect environ­mental mobility and the extent to which radionuclides are transferred into organisms. We briefly describe a range of these processes but as an example focus on those which are most important in determining transfer to wildlife.