The most harmful heavy metals in our atmosphere are cadmium, lead and mercury. Humans are responsible for some of these emissions. The largest sources of emissions into the air are the combustion of fossil fuels, industrial processes and road transport, which are all the result of human activity. As metals are stable environmental contaminants, they tend to accumulate in the biosphere and are stored in soils and sediments.
Heavy metals are also natural components of the Earth's crust.
They cannot be degraded or destroyed. To a small extent they enter our bodies via food, drinking water and air. However, at higher concentrations they can lead to poisoning. Several metals such as lead, cadmium, cobalt, nickel and alkyl mercury compounds have an effect on haematopoiesis and can lead to blood disorders. The liver, the kidneys, the circulatory system and the nervous system may also be affected.