## 3 Results and Discussion
### Health Risk Assessment  
It can be seen from Table 6 that the order of daily average exposure doses of nine kinds of heavy metals, for children and adults, was Mn > Zn > Cu > V > Pb > Cr > Ni > Co > Cd. The order of non-carcinogenic exposure doses of children and adults was \(\text{ADD}_{\text{ing}}>\text{ADD}_{\text{dem}}>\text{ADD}_{\text{inh}}\). The exposure doses of the hand-oral intake route accounted for a relatively high proportion of the total exposure dose, reaching 99.05%  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{3}{*}{**Factor**} & \multicolumn{3}{c}{**Initial Eigenvalues**} & \multicolumn{3}{c}{**Before Rotation**} & \multicolumn{3}{c}{**After Rotation**} \\ \cline{2-9}  & \multirow{2}{*}{**Eigenvalues**} & \multicolumn{2}{c}{**Variance**} & \multicolumn{2}{c}{**Accumulative**} & \multicolumn{2}{c}{**Variance**} & \multicolumn{2}{c}{**Accumulative**} & \multicolumn{2}{c}{**Continuity**} & \multicolumn{2}{c}{**Eigenvalues**} & \multicolumn{2}{c}{**Percentage**} & \multicolumn{2}{c}{**Accumulative**} \\  & & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **Rate (\%)** & **(\%)** & **(\%)** \\ \hline
1 & 3.733 & 41.479 & 41.479 & 3.733 & 41.479 & 41.479 & 3.119 & 34.658 & 34.658 \\
2 & 2.222 & 24.600 & 66.169 & 2.222 & 24.600 & 66.169 & 2.236 & 24.843 & 59.502 \\
3 & 1.018 & 11.309 & 77.478 & 1.018 & 11.309 & 77.478 & 1.618 & 17.977 & 77.478 \\
4 & 0.618 & 6.866 & 84.344 & & & & & \\
5 & 0.435 & 4.836 & 89.180 & & & & & \\
6 & 0.373 & 4.141 & 93.321 & & & & & \\
7 & 0.257 & 2.851 & 96.71 & & & & & \\
8 & 0.216 & 2.401 & 98.572 & & & & & \\
9 & 0.128 & 1.428 & 100.000 & & & & & \\ \hline \hline \end{tabular} Extraction method: principal component analysis; rotation method: maximum variance rotation.  
\end{table}
Table 4: Eigenvalues and cumulative contribution rates obtained from a heavy metal factor analysis of road dust in Yangxin County.  
Figure 4: Cluster analysis of heavy metals in the dust.  
and 98.67%. Obviously, the hand-oral intake route was the most important route of road dust exposure [65; 66; 67]. The exposure dose of children to road dust was higher than that of adults, indicating that children were more threatened by road dust [68; 69; 70]. The results were consistent with those reported in other studies [71; 72].  
The non-carcinogenic risks of heavy metals in road dust, through three exposure routes, was V \(>\) Mn \(>\) Pb \(>\) Cr \(>\) Co \(>\) Cu \(>\) Zn \(>\) Cd \(>\) Ni. The order of non-carcinogenic risk was HQ\({}_{\text{ing}}\) \(>\) HQ\({}_{\text{dem}}\) \(>\) HQ\({}_{\text{mh}}\). The results showed that no significant non-carcinogenic risk was found for all measured heavy metals in the study areas since the HQi and HI values were \(<\)1 [36; 73]. The non-carcinogenic risk of children was higher than that of adults but lower than the allowable limit. Adults' health risks were relatively low [74; 75; 76]. The maximum single non-carcinogenic risk of the three exposure routes was 0.068, indicating that road dust did not pose a non-carcinogenic risk to adults. However, the possibility that these metals may cause serious health effects through their accumulation in body tissues still exists.  
In terms of carcinogenic risk, the order of carcinogenic risk of the four carcinogenic elements was Cr \(>\) Co \(>\) Ni \(>\) Cd. The range of carcinogenic risk in the study area was \(1.1\times 10^{-9}\)-9.19 \(\times\) 10\({}^{-7}\), while lower than 1 \(\times\) 10\({}^{-6}\) was the accepted. However, there were still some deficiencies in the current risk assessment research. For example, the soil background value was used to replace the lack of surface dust background value; there were other potentially toxic metals (e.g., Sb, Fe, As, etc.) and organic pollutants (e.g., polycyclic aromatic hydrocarbons, microplastics, etc.) in the dust, which have not been evaluated [77; 78]. Therefore, more research on other pollutants is needed in the future.