# Risk Assessment of Soil Heavy Metals in the Jiahe River Basin of Yantai City, China
## 4 Discussion  
### Comparison Between GB15618-2018 and Pollution Indices  
In GB15618-2018, the screening and intervention risk values are given for five elements (i.e., Cr, Hg, As, Pb, and Cd), and only screening values are listed for three elements (i.e., Cu, Ni, and Zn). However, other heavy metals such as Co, V, and Mn are not mentioned in GB15618-2018. Therefore, a comparison was made between GB15618-2018 and the four pollution indices C\({}_{f}\), Er, EF, and I\({}_{geo}\), mainly for the five elementsCr, Hg, As, Pb, and Cd. This comparison aims to identify a suitable assessment method for other heavy metals in this area. In comparisons between GB15618-2018 and C\({}_{\rm f}\), Pb and Hg were at the background level (the lowest level) in GB15618-2018, while Pb was at a considerable risk level and Hg was at a very high risk level (the highest level) in C\({}_{\rm f}\). Therefore, the assessment results are inconsistent for Pb and Hg. The method of C\({}_{\rm f}\) is not suitable in this area. In comparisons between GB15618-2018 and Er, Hg was at the background level (the lowest level) in GB15618-2018 but at a very high risk level (the highest level) in Er. Cd was at the screening level (the medium level) in GB15618-2018 but at a very high risk level (the highest level) in Er. Therefore, the assessment results are inconsistent for Hg and Cd. Furthermore, Er cannot be used for Ni, Co, V, and Mn due to the lack of toxic-response factor values. These results indicate that the Er method is also unsuitable in this area. In comparisons between the three levels in GB15618-2018 and the five levels of EF, five metals (i.e., Cr, Hg, As, Pb, and Cd) were not at the highest risk level. Therefore, no clear inconsistency was found in the results of these two methods. However, Mn could not be assessed because it was used as the immobile element. The assessment results may be different if another element is used as the immobile element. These results indicate that the EF method does not meet our aims in this area. In comparisons between the three levels of GB15618-2018 and the seven levels of I\({}_{\rm geo}\), the five metals Cr, Hg, As, Pb, and Cd were not at the highest risk level. Therefore, no clear inconsistency was found in the results of GB15618-2018 and I\({}_{\rm geo}\). When the first two levels in I\({}_{\rm geo}\) were viewed as one level (I\({}_{\rm geo}\)\(\leq\) 1) corresponding to the background level in GB15618-2018, Pb was at the background level in GB15618-2018 and also at the background level in I\({}_{\rm geo}\), except for two samples. Hg was at the background level in GB15618-2018 and at the background level in I\({}_{\rm geo}\), except for five samples. Cr was at the background level except for two samples in GB15618-2018 and one in I\({}_{\rm geo}\). Cd and As were mainly at the background level, with some outliers in the results for both GB15618-2018 and I\({}_{\rm geo}\). When the last two levels in I\({}_{\rm geo}\) were viewed as one level (4 \(<\) I\({}_{\rm geo}\)) corresponding to the intervention level in GB15618-2018, the five metals (i.e., Cr, Hg, As, Pb, and Cd) were not at the intervention level. When the middle three levels in I\({}_{\rm geo}\) were viewed as one level (1 \(<\) I\({}_{\rm geo}\)\(\leq\) 4) corresponding to the screening level in GB15618-2018, the assessment results were basically consistent between GB15618-2018 and I\({}_{\rm geo}\) for the five metals. Cu, Ni, and Zn were mainly at the background level in GB15618-2018, except for 18, 2, and 2 samples, respectively. With the three merged levels of I\({}_{\rm geo}\), Cu, Ni, and Zn were also mainly at the background level, except for 14, 3, and 3 samples, respectively. In summary, the I\({}_{\rm geo}\) method can be selected as a suitable method in this area to evaluate the risk of heavy metals, whether or not they are mentioned in GB15618-2018. Here, we suggest an idea that the risk of heavy metals can be evaluated using the criteria in GB15618-2018 with I\({}_{\rm geo}\) as a supplement for metals without criteria.