Introduction

This chapter introduces students to the basic toxicology associated with ionising radiation, beginning with some definitions of underlying processes and the terms that we use to describe them. The unique nature of radionuclides requires quite a different approach to their toxicology from that applied to stable elements, although certain shared concepts, such as threshold toxicity, are noted and cross-referenced with other chapters. In this chapter, we are concerned with the potentially toxic nature of the radionuclides themselves, while recognising that they share the same chemical toxicity as the respective stable element. For example, at the molecular level, radioactive 210Pb has the same toxicity as its stable counterpart 207Pb. This fact, of course, forms the rationale for the use of radioisotopes as tracers in biochemistry, physiology, and ecology. With the assumption that the radioactive element behaves in the same way as its stable isotopes, the passage and the dynamics of numerous substances through various components of the ecosystem can be traced. This aspect of radionuclides is not dealt with in this chapter.

Before the adverse health effects of radiation exposure were fully recognised, deliberate exposure to radioisotopes often formed part of therapies for a variety of ailments. It was not until after intense nuclear weapons testing programmes in the 1950s and 1960s together with accumulated information from victims of the two wartime nuclear detonations that the full extent of harmful effects began to be fully understood. Even then, this realisation took many years to develop.