*3.2. Potential Ecological Risks*

According to the single-factor ecological hazard coefficient calculation formula, combined with the toxicity response coefficient of heavy metal elements to calculate the Ei value, the single-factor potential ecological hazard coefficient formula is as follows:

$$\mathbf{E\_{Hg}} = \left(\mathbf{T\_{Hg}} \times \mathbf{C}\right) / \mathbf{C\_0} \tag{1}$$

where EHg is the potential ecological risk factor of Hg, THg is the toxic response factor of Hg, C is the concentration of Hg, C<sup>0</sup> is the concentration of Hg in the background. In this study, the T of Hg was 40 [47]. Hakanson proposed that the highest value of heavy metals in sediments before industrialization was used as a reference value [48]. In the process of practical application, the potential ecological risk assessment of sedimentary river bottoms is used as a reference value, but when the risk assessment object is extended to the soil, The selection of the reference value is not uniform. Considering the characteristics of the study area and the collected soil samples, this work selects the background value of heavy metals in uncontaminated soil in the area [49,50] as the reference value for evaluation. See Tables 1 and 2.

**Table 1.** Toxicity coefficients of Hg and its reference values.


**Table 2.** Potential ecological risk coefficient and classification of ecological risk degree.

