ABSTRACT
Metals are a ubiquitous class of agents both in the natural environment and in the workplace. There are numerous natural and artificial forms of metals. The common occurrence of metals in the human environment is dictated both by their wide natural distribution and by their intensive use in an ever-growing number of industrial processes (1). Clearly, the use of metals has been critical to the progress of human civilization and they are intensely used by modern society. However, metallic agents, once concentrated in the biosphere, generally persist and are not broken down by natural forces, at least not beyond the elemental form. Unlike many products of human enterprise, the use of metal products generally does not consume the innate, natural material. Beyond this, most metals are only sparingly recycled, with a few notable exceptions. Environmental persistence in combination with intensive use by modern society has, over the years, concentrated metals within the human environment. This trend continues generally unabated and provides ample opportunity for human exposure to metals. Thus, human exposure to metals and metal compounds is clearly inevitable. Be-yond this, metal exposure, by nature, is always to a multitude of metals and metal compounds and never to a single metallic agent.
