## 2 Materials and Methods
### Evaluation Methods
#### 2.3.4 Health Risk Assessment  
This study utilized the U.S. Environmental Protection Agency's methodology to develop a risk assessment model for evaluating human cancer and non-cancer risks. It assessed the health risks of eight heavy metals in the soil of the study area. Human exposure to heavy metals in soil occurs through three main pathways: inhalation (_inh_), ingestion (_ing_), and dermal contact (_derm_). The carcinogenic and non-carcinogenic risks from the three exposure pathways were calculated as follows [38; 39]:  
\[ADD_{inh}=\frac{C_{i}\times IRI\times E\times ED}{BW\times AT\times PEF} \tag{6}\]  
\[ADD_{ing}=\frac{C_{i}\times IRg\times FI\times EF\times ED}{BW\times AT}\times 1 0^{-6} \tag{7}\]  
\[ADD_{derm}=\frac{C_{i}\times SA\times AF\times ABS\times EF\times ED}{BW\times AT }\times 10^{-6} \tag{8}\]  
The lifetime average daily dose (\(LADD\)) for each exposure pathway is calculated using Equations (9)-(11) to assess the cancer risk from long-term exposure to soil heavy metals.  
\[LADD_{inh}=\frac{C_{i}\times FI\times EF}{LT\times PEF}\times\left(\frac{IR_{ Chid}\times ED_{child}}{BW_{child}}+\frac{IR_{adult}\times ED_{adult}}{BW_{adult}}\right) \tag{9}\]  
\[LADD_{ing}=\frac{C_{i}\times FI\times EF}{LT}\times\left(\frac{IR_{SG_{Child} }\times ED_{child}}{BW_{child}}+\frac{IR_{Bad}\times ED_{adult}}{BW_{adult}} \right)\times 10^{-6} \tag{10}\]  
\[LADD_{derm}=\frac{C_{i}\times EF\times ABS}{LT}\times\left(\frac{SA_{child} \times ED_{child}\times AF_{child}}{BW_{child}}+\frac{SA_{adult}\times ED _{adult}\times AF_{adult}}{BW_{adult}}\right)\times 10^{-6} \tag{11}\]  
Non-carcinogenic hazards are characterized by a term known as the hazard quotient (\(HQ\)), which is assessed by comparing the exposure level over a specific period to the reference dose (\(RfD\)) for individual pollutants over a similar exposure period. The \(HQ\) is a dimensionless number that indicates the probability of adverse effects from environmental hazard exposure. It is defined as follows:  
\[HQ=\frac{ADD}{RfD} \tag{12}\]  
The cumulative non-carcinogenic risk of \(k\) heavy metals across all pathways is expressed as the hazard index (\(HI\)).  
\[HI=\sum_{k=1}^{n}HQ_{k}=\sum_{k=1}^{n}\left(\frac{ADD_{inh}}{RfD_{inh}}+\frac {ADD_{ing}}{RfD_{ing}}+\frac{ADD_{derm}}{RfD_{derm}}\right)_{k} \tag{13}\]  
An \(HI\) value less than 1.0 is considered to pose no carcinogenic risk, with the degree of hazard increasing as the \(HI\) value rises. For carcinogens, the risk is estimated as the incremental probability of an individual developing cancer over a lifetime due to exposure to potential carcinogens, called the lifetime cancer risk (\(LCR\)). The slope factor (\(SF\)) is a carcinogenic potency factor that directly converts the estimated \(LADD\) to \(LCR\).  
\[LCR=LADD\times SF \tag{14}\]  
The total lifetime cancer risk (\(TLCR\)) for an individual is calculated based on the contributions of \(k\) heavy metals across all pathways, as shown in the following Formula (15).  
\[TLCR=\sum_{k=1}^{n}LCR_{k}=\sum_{k=1}^{n}\left(LADD_{inh}\times SF_{inh}+LADD_{ ing}\times SF_{ing}+LADD_{derm}\times SF_{derm}\right)_{k} \tag{15}\]  
Tables S1 and S2 list the definitions, units, and reference values of all parameters used in Equations (6)-(15). The reference values for these parameters are based on the research of [PERSON] et al. [38], [PERSON] et al. [39], [PERSON] et al. [40] and [PERSON] et al. [41]. According to U.S. EPA regulations, a maximum acceptable target cancer risk level of \(1\times 10^{-6}\) is set. \(LCR\) and \(TLCR\) values ranging from \(1\times 10^{-6}\) to \(1\times 10^{-4}\) are considered to represent low-risk levels, those from \(1\times 10^{-4}\) to \(1\times 10^{-3}\) are considered moderate risk, and values above \(1\times 10^{-3}\) are regarded as unacceptable by most international regulatory agencies [38].