Introduction

Abstract

The term ‘heavy metal’has become entrenched in the literature of environmental pollution; its use, however, is not entirely satisfactory. Examination of the periodic table of elements reveals that some 84 of the currently known elements can be regarded as metals although the distinction between metals and non-metals is not always a sharp one (e.g. Vouk, 1979). One of the commonest definitions of ‘heavy metal’is a metal with a density of greater than 5 g cm⁻³ (e.g. Passow et al., 1961). Sixty-nine elements fall into this category, of which 16 are synthetic elements not found in nature. Despite this relatively clear, unambiguous definition of heavy metals, a great deal of confusion appears in the literature where authors have been uncritical in their use of the term and have included light metals, heavy metals and metalloids. Nieboer and Richardson (1980) and Phipps (1981) have reviewed this problem and emphasised the lack of agreement between different authors. Luckey et al. (1975), for example, discussed the toxicology of virtually all the metals in a book specifically entitled ‘Heavy Metal Toxicity…’. A further complication is that, even if the definition of a density greater than 5 g cm⁻³ is used, this includes both the lanthanides and the actinides as heavy metals; these groups of elements are not generally accepted to be ‘heavy metals’when their chemistry is considered.