HEAVY METALS AND HEAVY-METAL ANTAGONISTS: INTRODUCTION

People continue to be exposed to heavy metals in the environment. Metals contaminate water and food in some areas. Metals also leach from eating utensils and cookware. The emergence of the industrial age and large-scale mining brought occupational diseases caused by various toxic metals. Metallic constituents of pesticides and even therapeutic agents (e.g., antimicrobials) have been additional sources of hazardous exposure. The burning of fossil fuels containing heavy metals, the addition of tetraethyl lead to gasoline, and the increase in industrial applications of metals have made environmental pollution the major source of heavy-metal poisoning. The first part of this chapter covers the toxic properties of lead, mercury, arsenic, and cadmium, as well as radioactive heavy metals, and treatment of the consequences of toxic exposure to these metals. The second part of the chapter covers the chemical properties and therapeutic uses of several heavy-metal antagonists.

Heavy metals exert their toxic effects by combining with one or more reactive groups (ligands) essential for normal physiological functions. Heavy-metal antagonists (chelating agents) are designed specifically to compete with these groups for the metals and thereby prevent or reverse toxic effects and enhance the excretion of metals. Heavy metals, particularly those in the transition series, may react in the body with ligands containing oxygen (¾OH, ¾ COO-, ¾ OPO₃H^-, >CO), sulfur (¾SH,¾S¾S¾), and nitrogen (¾NH₂ and >NH). The resulting metal complex (or coordination compound) is formed by a coordinate bond in which both electrons are contributed by the ligand.