REQUIREMENTS AND TOXICITY OF ESSENTIAL TRACE-ELEMENTS, ILLUSTRATED BYZINC AND COPPER

Early signs of toxicity of essential trace elements are important. Som e trace elements are available over-the-counter (OTC) and/or are prese nt at industrial waste sites. Physicochemically similar trace elements compete for ligands, impairing functions, which is exemplified by the zinc-copper antagonism described long ago by Van Campen, Hill and Mat rone, and Klevay. Intestinal absorption of copper is inhibited by zinc . Thus risk of copper deficiency is increased when the molar ratio of zinc to copper (Zn:Cu) is high. As shown by experiments, copper defici ency can occur in humans. Manifestations include decreased erythrocyte copper-zinc superoxide dismutase, increased low-density-lipoprotein c holesterol, decreased high-density-lipoprotein cholesterol, decreased glucose clearance, decreased methionine and leucine enkephalins, and a bnormal cardiac function. Calculation of a preliminary reference dose for OTC zinc that assumed high bioavailability and uncertain copper in takes established 9 mg as a safe amount for 60-kg adults.