2.7.2. Enrichment Factor (EF)

Enrichment factor (*EF*) was evaluated to determine the degree of anthropogenic factors on trace elements accumulation in the soil. It reflects the disturbance degree of human activities on the natural environment [44]. *EF* is calculated as follows:

$$EF = \frac{\left(\frac{\mathbb{C}\_i}{\mathbb{C}\_{ref}}\right)sample}{\left(\frac{\mathbb{B}\_i}{\mathbb{B}\_{ref}}\right)background}} \tag{5}$$

where *Ci* is the concentration of trace elements in the sample; *Cref* is the concentration of reference element in the sample; *Bi* is the background value of interest element and *Bref* is the background value of reference elements in the study area. Fe was selected as the reference element for this study because Fe is a major sorbent and it is a quasi-conservative tracer of natural elements in fluvial and coastal sediments [12]. Wuhan soil background was used as the reference. The following EF class were given for elements; *EF* < 2, 2 ≤ *EF* < 5, 5 ≤ *EF* < 20, 20 ≤ *EF* < 40 and *EF* ≥ 40 indicated low, moderate, significant, very high and extremely high enrichment factor, respectively.
