Heavy metals are indispensable for living organism (microelements: copper, zinc, nickel, chromium) as well as elements whose impact to the humans has not been explored yet (amongst others cadmium, mercury, lead, arsenic). Heavy metals have one common feature. If the permitted content is exceeded, they become toxic to living organisms. Cadmium, mercury and lead are most toxic, and pose threat to human health. On the other hand, they are unnecessary for living organisms. This is the first article in the series of „Issues relating to the environmental contamination with heavy metals”.