INTRODUCTION

Cadmium and zinc are chemically similar (Cotzias and others, 1961; Cotton and Wilkinson, 1966). They therefore compete with one another for a variety of ligands (Pulido and others, 1966a; Gunn and others, 1968). Because cadmium is considered to have only adverse effects in biological systems (Friberg and others, 1971) and zinc is an essential nutrient (Sandstead, 1973), the significance of their competitive interactions for health merits investigation.

In this paper we will examine the hypothesis that competition between zinc and cadmium for biological ligands has important implications for health.

ZINC AND CADMIUM IN THE ENVIRONMENT

Cadmium is a relatively rare element. Its average concentration in the Earth’s crust is about 0.5 ppm (Heindl, 1970). In nature it is closely associated with zinc (Friberg and others, 1971). The zinc:cadmium ratio of most minerals and soils ranges from 100:1 to 12,000:1 (Bowen, 1966; Schroeder and others, 1967).

In the United States, cadmium is obtained commercially only as a by-product during the processing of zinc-bearing ores (Heindl, 1970). Its production has risen steadily during the past three decades (Moulds, 1969). This growth can be described by the equation y = 0.21x – 1.81, where y represents the annual production in millions of pounds and x is the year minus 1900.

Sixty percent (8 million pounds in 1968) of the cadmium produced each year is used for electroplating (Heindl, 1970), and products plated with cadmium are widely used throughout the United States (Flick and others, 1971). Such cadmium-plated products and cadmium-containing materials may be . . .