Pharmacology and toxicology of heavy metals: Silver

LIKE silver, gold has been known and used by man for thousands of years. It is mentioned many times in the early books of the Old Testament (e.g. Gen. 2 : 11; Gen. 13 : 2; Ex. 25 : 11), and was used as a decorative metal by the ancient Egyptians prior to 3400 ac. The gold used in these early periods was placer gold, obtained by washing sand or gravel, and was made into jewelry or other articles by hammering (Rickard, 1932). The early method of recovering alluvial gold particles from sand by the use of animals skins is believed to have been the inspiration of the story of Jason and the golden fleece (Hoover and Hoover, 1950). The melting of gold as a means of its recovery and its use in the manufacture of articles was accomplished about 3000 BC (Hoover and Hoover, 1950). Apart from its value as a precious metal for jewelry and as a monetary standard, gold is used in the manufacture of selected delicate instruments, and has some application in art and photography. Gold is found throughout the world in relatively pure form in lodes and placer deposits, as well as in impure form in many base metal ores, particularly in deposits of copper and silver. It is recovered as a by-product of the isolation of magnesium and bromine from sea water. Jones (1970) has recently published an extensive review of the gold content of water, plants, and animals. Although the number of samples in this study was not great, some estimate of environmental distribution of gold can be made from the report. Sea water and fresh ground waters contain the element in the range of 0.001-44.0 ng/l. Using neutron-activation analysis, Jones gave a mean value of 0.05 ng/l for the concentration in sea water. Plant ash has an average of 7 mg/kg and a maximum value of 36 mg/kg which is much greater than that found in the earth's crust. These data suggest that gold is concentrated by plants, but there are no data on the possibility of concentration of gold in land or marine animals. It may well be that there is a source of gold for plants not derived from the soil in which they are grown. One such source may be the fly ash from incinerators and power plants, since the Bureau of Mines has shown that levels of gold in fly ash over metropolitan Washington, D.C. is in the range of 0.02-0.05 oz/ton, or about 1.5 mg/kg. Gold has found its way into medical practice through the observations of Robert Koch, who, in the late nineteenth century, showed that low concentrations of gold salts adversely affected the tubercle bacillus. Gold salts were thereafter used sporadically to treat tuberculosis and syphilis without much success. However, during this time gold compounds were also used to treat arthritis and lupus erythematosus, which at that time were thought to be due to the tubercle bacillus (Goodman and Gilman, 1965). In 1929, Forestier published a report on gold therapy for rheumatoid arthritis which is considered to be the basis for present interest in this subject. Gold compounds are still an important group of drugs in the armamentarium of the rheumatologist, as is evident from the review of Freyberg (1966). Radioactive colloidal gold preparations are used to treat certain malignancies involving ascites, and they are also used as diagnostic tools in liver scanning.