ABSTRACT
The main threats to human health from heavy metals are associated with exposure to lead, cadmium, mercury, and arsenic (arsenic is a metalloid, but is usually classi-ed as a heavy metal). These metals have been extensively studied and their effects on human health regularly are reviewed by international bodies such as the World Health Organization (WHO) and International Agency for Research on Cancer (IARC). There is no clear denition of what a heavy metal is; density is in most cases taken to be the dening factor. Heavy metals are thus commonly dened as those having a specic density of more than 5 g/cm3.
