Air contains a large number of particulates. A small fraction of the particulates present in the air is metallic particles. The metallic particles are present in the air of mercury, lead, cadmium, chromium, beryllium, aluminum metals, nickel, arsenic, vanadium, zinc, iron, and tin. All the metallic particles are poisonous to some extent to all living things such as human beings, animals, and plants. Some are less toxic whereas others are more toxic. Though the amounts of metallic particles in the air are quite low even then some of the metallic particles including lead and mercury are extremely harmful to the living organisms because they get concentrated in their bodies over a period of time.
The metallic particles are released into the environment by various industrial processes, transport vehicles, and agricultural processes. The particles of metals such as mercury, cadmium, and zinc are released into the environment during the refining of copper, lead, zinc, steel, manufacture, and use of pesticides, fungicides, cosmetics, phosphatic, and fertilizers. The two metallic particles which are extremely harmful to human beings are those of lead and mercury.
The lead particles are released into the air by the exhausts of motor vehicles because their fuel (petrol) contains a lead compound called ‘’tetraethyl lead’’. The industries engaged in lead mining, extraction, and purification of lead, manufacture of lead alloys and paints also contaminate the environment with lead particles. Lead is a cumulative poison and keeps on accumulating in the tissues of the human body and in the leaf tissues of plants.