2.7.3. Geo-accumulation Index (*Igeo*)

The geo-accumulation indexes (*Igeo*) of elements were calculated to identify the degree of contamination and to compare it with the pre-industrial level [45]. This method classifies the pollution level of elements in terms of seven enrichment classes. It is calculated using the following formula:

$$I\_{\text{geo}} = \text{Log}\_2 \frac{\mathbb{C}\_n}{1.5 \ B\_n} \tag{6}$$

where *Igeo* is the geo-accumulation index, *Cn* is the measured concentration of an element (mg/kg) in the sample, *Bn* is the geochemical background value of an element (mg/kg) and 1.5 is the factor used for lithological variations of elements.

Seven classes and contamination intensity are given for *Igeo*: *Igeo* ≤ 0 (uncontaminated), 0 < *<sup>I</sup>geo* ≤ 1 (uncontaminated to moderately contaminated), 1 < *<sup>I</sup>geo* ≤ 2 (moderately contaminated), 2 < *<sup>I</sup>geo* ≤ 3 (moderately to strongly contaminated), 3 < *<sup>I</sup>geo* ≤ 4 (strongly contaminated), 4 < *<sup>I</sup>geo* ≤ 5 (strongly to extremely contaminated) and *<sup>I</sup>geo* > 5 (extremely contaminated) [45].
