The most diffusive chemicals occurring in soil are heavy metals, pesticides, petroleum
hydrocarbons, polychlorobiphenyl (PCBs), dibenzo-p-dioxins/dibenzofurans (PCDD/Fs).
Heavy metals from anthropogenic sources are widely spread in the environment and most
of them finally reach the surface soil layers. Heavy metals can enter the soil from different
sources, such as pesticides, fertilizers, organic and inorganic amendants, mining, wastes and
sludge residues (Capri & Trevisan, 2002). In contrast to harmful organic compounds, heavy
metals do not decompose and do not disappear from soil even if their release to the
environment can be restricted (Brusseau, 1997).