ABSTRACT
Before addressing these issues, we will dene TMEs and present the factors aecting their bioavailability.
In the previous version of this chapter by Hagemeyer and Breckle (2002), the term “heavy metals” was used. at term oen applies a group name for metals and metalloids associated with
environmental pollution. Legal regulations still refer to “heavy metals” as a list of 11 elements with a density higher than ve, soluble at physiological conditions, and relevant in the environmental context: arsenic (which is actually a metalloid), cadmium (Cd), chromium, cobalt (Co), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), tin, vanadium, and zinc (Zn). e term “trace elements” refers to chemical elements that occur in the Earth’s crust in amounts less than 0.1% in mass. Since our review focuses on root responses, we will also consider those metals that are micronutrients, that is to say, which are present as trace amounts in plant organs (<0.01% plant dry weight [DW]) and fulll biological functions. While iron (Fe) is found in abundance in the Earth’s crust (about 5% in mass), it is present only in trace amounts in plant materials. Manganese (Mn) is not considered as a trace element according to the geochemical denition because its abundance reaches the 0.1% threshold, but in the same way as Fe, it is an essential micronutrient.
