Heavy metals
Heavy metals: a group of metals with an atomic mass greater than 50 (Pb, Cd, Ni, Cr, Zn, Cu, Hg), which may exert toxic effects at certain concentrations
Source: "GOST R 17.4.3.07-2001. Environmental protection. Soils. Requirements for the properties of sludge from wastewater when used as fertilizers"
(adopted and put into effect by the Decision of the Russian State Standard from 23.01.2001 No. 30-st)
"Heavy metals" means those metals, or in some cases metalloids, which are stable and have a density greater than 4.5 g/cubic cm, and their compounds
Source: "PROTOCOL ON HEAVY METALS TO THE 1979 CONVENTION ON LONG-RANGE TRANSPORT OF POLLUTANTS"