The past three decades have seen a emarkable advance in the appreciation of the significant role played by the so-called ‘trace metals’ in the health and productivity of plants. the actions of metal ions, both ‘essential’ and ‘toxic’ has been studied. Lead: The presence of indigenous lead in the earth’s crust at concentrations averaging 16μg/g soil
(De Treville, 1964), its recent deposition near highways and other pollutant sources (Koeppe, 1977), and the knowledge that lead is highly toxic to various physiological processes have brought into focus over the last 15–20 years the question of the effects of lead on higher plants. Cadmium: The absorption of cadmium (Cd) by plants
has not been extensively studied until recently. The World Health Organization (WHO) (1972) has proposed a maximum tolerable intake not to exceed 400–500 μg Cd/week. Copper: It was formerly employed as bronze (a copper-tin alloy) for the production of utensils, weapons and ornaments, but Today, the main use of copper is in the form of its various alloys, many of which are of great importance in the electrical industry. Zinc: In many parts of the world Zn deficiency is a common phenomenon, often occurring in economically important crops. Nickel: nickel was not recognized for a further hundred years but analysed a wide range of plant, animal and soil
samples for nickel, widely present in these materials and may therefore function as essential elements. Also there is considerable information published concerning the environmental effects of some of the toxic metals, for example, mercury. However, there is a growing need to extend our knowledge to encompass the other elements in the Periodic Table which may exhibit an unrecognized toxicity to living organisms. as Aluminium, & other similar elements. Also some of the metalloids as Arsenic, selenium and antimony.