Heavy metals in soils and their environmental significance

Modern civilization is completely dependent on a large range of metals for all aspects of daily life. There is a long history of association between metals and human development (Encyclopedia Britannica, 1980). Copper has been used since about 8000 b.c., initially as native copper, but smelting of copper from oxide ores is thought to date from about 6000 b.c. Lead was used before 5000 b.c., zinc and mercury by about 500 b.c., and nickel in alloys by 200 b.c. Cadmium was discovered comparatively recently (1817). The chronology of the environmental impact of heavy metals has been assessed by examination of cores from sediments (Muller, 1981), ice (Murozumi et al., 1969), and peat (Chamberlain, 1983). A peak in lead usage was noted at the time of the Roman Empire; metal use accelerated during the Industrial Revolution of the nineteenth century, and since then heavy metals have become ‘essential’ to modern society because of the range of metal products used. All-time usage of Cd, Cu, Pb, Ni, and Zn has been estimated to have been 0.5, 307, 241, 17, and 250 × 109 kg, respectively (Nriagu, 1979). The estimated total (all-time) and annual amounts of these metals dispersed through the atmosphere are presented in Table 1. This enormous input into the atmosphere is increased by liquid effluents and direct deposition of solid wastes onto land and into water.