# Potentially Toxic Trace Elements in the Urban Soils of Santiago de Compostela (Northwestern Spain)
## 3 Results
### Trace Element Concentrations and Influence of Land Use and Lithology  
The total concentrations of the six trace elements considered in all the soils are shown in Table 3. Figures 1 and 2 show these concentrations grouped by land use and lithology, along with ANOVA results for the influence of land use and lithology, whereas their spatial distribution is shown in Figure 3. Table 4 presents correlations between trace elements contents and soils physicochemical properties.  
\begin{table}
\begin{tabular}{l c c c c c c} \hline
**Soil** & **Pb** & **Cu** & **Zn** & **Ni** & **Cr** & **As** \\ \hline
1 & \(72\pm 3\) & \(188\pm 5\) & \(197\pm 9\) & \(91\pm 20\) & \(172\pm 22\) & \(20\pm 6\) \\
2 & \(40\pm 6\) &  
==WARNING: Truncated because of repetitions==
4 & \(-\)0.6 & 0.6 & \(-\)0.4 & 0.1 & 1.1 & \(-\)0.4 & 2 \\
5 & \(-\)0.4 & \(-\)0.8 & \(-\)0.6 & \(-\)1.9 & \(-\)1.0 & \(-\)0.9 & 0 \\
6 & \(-\)1.2 & 0.4
+++  
In order to obtain further insights about the pollution levels of the soils, we have compared trace element concentrations to regional background values and to generic reference levels as established in the regulations for polluted soils (Table 2), with the results of this comparison summarized in Figure 4. In the case of Zn, 25 out of 55 soils exceeded the normal background values in soils of the region, but only three soils surpassed the generic reference level (GRL) for ecosystem protection, only one exceeded also the GRL set for other uses and none of the soils surpassed the levels established for urban or industrial use. Most soils exceed the background values for Pb concentrations (39 soils, 75% of the total). Among these, 21 soils surpassed the GRL for ecosystem protection, of which 15 also exceeded the urban use GRL and only one surpassed the GRL for industrial use. For Cu, 28 out of 55 soils present concentrations over the background values: of these, concentrations in 22 soils surpass the GRL for ecosystem protection and in six cases also exceed the GRL for urban use. None of the soils surpassed the Cu thresholds set for industrial use. Regarding Cr concentrations, only 11 soils surpass the lithological background established in the regulation: those soils also surpassed the levels for ecosystem protection and other uses, of which four surpassed the GRL for urban use, and none of the soils surpassed the thresholds set for industrial use. In the case of Ni, only two soils presented concentrations higher than the background set in the regulations and none of the soils surpassed other protection  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Igeo**} & & & & & \\ \cline{2-7}
**Soil** & **Pb** & **Cu** & **Zn** & **Ni** & **Cr** & **As** & **Soil Class** \\ \hline
20 & 1.2 & 0.1 & 0.1 & \(-\)1.3 & \(-\)0.1 & \(-\)0.2 & 2 \\
21 & 2.6 & 0.6 & \(-\)0.2 & \(-\)2.4 & \(-\)0.9 & \(-\)0.3 & 3 \\
22 & \(-\)  
levels for contamination. Finally, arsenic concentrations in seven soils exceed the regional background, among which six also exceed all levels of protection for urban or industrial use (GRL values are set at the same value, 50 mg kg\({}^{-1}\), for the three uses).  
Overall, comparison of total concentrations to GRLs shows that no soil would be considered polluted by the Spanish Law (element concentration > 100 times the corresponding GRL), but an important number of the soils present contaminant levels that would require further investigation of risk assessment: 35 soils (64 % of the total) exceeded the level set for other uses for at least one element, 25 soils (45% of the studied soils) the urban use levels, and seven soils (13% of studied soils) the levels for industrial use (most of these because of As concentrations).