**3. Chemical fractionation of heavy metals from sediments**

In order to obtain information about mobility and potential toxicity of heavy metals or their potentially dangerous effects on the environment, it is necessary to implement a methodology that determines speciation or fractionation of those metals in sediments [19]. Different schemes of chemical fractionation [20] have


#### **Table 2.**

*Sequential chemical extraction methodology from Tessier 1979.*

*Mobility of Heavy Metals in Aquatic Environments Impacted by Ancient Mining-Waste DOI: http://dx.doi.org/10.5772/intechopen.98693*

been used to identify and quantify concentrations of heavy metals and metalloids present in different fractions. However, the sequential extraction that suggests Tessier 1979, is one of the most used. Each fraction or extract corresponds to the metals associated with water or reagent (acid), Tessier method suggested five chemical fractions: exchangeable fraction (F1), fraction of carbonates (F2), reducible fraction or oxyhydroxides of Fe and Mn (F3), Oxidizable fraction or organic matter and sulfides (F4) and residual fraction (F5) that are extracted with different reagents, under different physicochemical conditions (**Table 2**) [20–22].
