Conclusion
The heavy metal concentrations and indices of pollution/ contamination varied greatly in soils over the world, and many various indices of pollution confirmed and verified major contributions from anthropogenic activities. Indices of soil pollution/contamination were divided into two groups: individual indices and total complex indices. It is evident that the metal pollution of soils reflects many factors (historical development, land use, industrialization processes, growing trend of population density, climate conditions, biogeography, etc.). This review provides analyses of soil pollution/contamination by heavy metals and summarizes the pollution sources; 20 different indices of heavy metal pollution were reviewed and classified into single indices and total complex indices of pollution/ contamination. This review also contains classification of indices of pollution in the context of complex assessment of soil quality. The soil is one of the most important components of ecosystems in relation to human health; therefore, it is essential that the soil quality has been included in environmental quality management on a worldwide. The assessment of soil pollution and evaluation of soil quality have to be still monitored over the world.
