Metals in the Life of Man*

Abstract

The importance of metals in the life of mankind has generally been thought of as beginning with the bronze age, about 2000 years before Christ when men discovered that by mixing tin and copper (probably known as early as 5000 B.C.), a beautiful, durable, gleaming, new material became available to them to enrich their art, to implement their trade and industry as well as to enable them to fashion more destructive instruments of war. Actually, metals were vital factors in man's life many millions of years earlier. They have been an essential part of all cellular metabolism since the most primitive life began. Most of them are present as trace elements--those that constitute less than 0.01 per cent of the organism (1)mand since capabilities for measuring metals beyond parts per million have only recently been available, it is difficult to estimate how many may be present in the human body. Their action. except when present in overwhelming concentrations, is largely through their influence on enzymes: acting catalytically, as co-enzymes or as structural components of the enzyme system. In some, the metals are firmly bound, in others they come and go readily with changes in the chemical environment. Since a large number of the body's enzymes, perhaps S0 per cent, are metallo enzymes, they constitute a most important area of influence in human metabolism. Until recent years, the clinician has been concerned primarily with heavy metals such as arsenic, lead and mercury and more recently cadmium, cobalt and nickel. It appears likely that a far more important area for study than heavy metal poisoning is that of the essential metals whose range of concentration within the cell may be critical and narrow. These metals, unlike their fellow nutrients, the vitamins, cannot be synthesized and the cell is utterly dependent on its environment for their supply, By the same token, an excess in the environment may present as great a problem since both excesses and deficiencies can kill. An early pioneer in the study of the biological role of metals was a physician, Dr. Henry A. Schroeder. Some 20 years before his death, he left a practice and teaching position in St. Louis. acquired a few acres of rocky soil atop a mountain in Vermont and built the first laboratory for the exclusive study of the role of trace elements in health and disease. Designed to raise animals in an environment free of metals, it was constructed without nails. Building materials were analyzed for lead and cadmium. Polyethylene and acrylic plastics were used throughout (2). In order that contamination from the atmosphere be prevented, the laboratory was pressurized from within, and air was brought in from the forest through large conduits equipped with electrostatic filters. All visitors were excluded from its animal rooms and all persons entering were required to wear special clothing. Here, Dr. Schroeder exhaustively studied the occurrence of 20 trace elements in food, water, soil, vegetation and animal and human tissues