Figure 1. Location map of Sardinia (a); sampling sites of the collected soils around the root of Pinus halepensis in the contaminated Campo Pisano site (CP) and not-contaminated sites (Santa Margherita: B1; Calamosca: B2; and Fontanamare: B3) (b); location map of the study area (c); details of the sampling points and soil samples collected in the CP-contaminated site: the core-drilled soil samples are indicated by yellow spots (S1, S2 and S3); and the blue spots indicate the soil around the root in contaminated (CP1, CP2 and CP3) and non-contaminated sites (B1, B2 and B3) (d).

Figure 1. Location map of Sardinia (a); sampling sites of the collected soils around the root of Pinus halepensis in the contaminated Campo Pisano site (CP) and not-contaminated sites (Santa Margherita: B1; Calamosca: B2; and Fontanamare: B3) (b); location map of the study area (c); details of the sampling points and soil samples collected in the CP-contaminated site: the core-drilled soil samples are indicated by yellow spots (S1, S2 and S3); and the blue spots indicate the soil around the root in contaminated (CP1, CP2 and CP3) and non-contaminated sites (B1, B2 and B3) (d).

Figure 2. Spectroscopy-scanning Electron Microscopy (SEM) analysis on minerals of the root and the soil around the root of Pinus halepensis samples (CP1, CP2 and CP3); in the soil samples (a–c), and the root surface (d–f).

Figure 2. Spectroscopy-scanning Electron Microscopy (SEM) analysis on minerals of the root and the soil around the root of Pinus halepensis samples (CP1, CP2 and CP3); in the soil samples (a–c), and the root surface (d–f).

Figure 3. Total Zn, Pb and Cd content (mean values and standard deviation) in core-drilled samples at different depths. Total metal content and bioavailable fraction (DTPA extraction) in soil around the roots of Pinus halepensis at Campo Pisano (CP1, CP2 and CP3) and in non-contaminated sites (B1, B2 and B3); non-contaminated soils are indicated with green circles.

Figure 3. Total Zn, Pb and Cd content (mean values and standard deviation) in core-drilled samples at different depths. Total metal content and bioavailable fraction (DTPA extraction) in soil around the roots of Pinus halepensis at Campo Pisano (CP1, CP2 and CP3) and in non-contaminated sites (B1, B2 and B3); non-contaminated soils are indicated with green circles.

Figure 4. Geochemical fractions of Zn, Pb and Cd obtained through BCR sequential extraction: acid-extractable (F1), reducible (F2), oxidizable (F3) and residual fraction (F4) in the soil collected from depth layers of the core samples (S1, S2 and S3) and around the collected Pinus halepensis root samples in Campo Pisano mine tailings (CP1, CP2, and CP3) and in the non-contaminated areas (B1, B2 and B3).

Figure 4. Geochemical fractions of Zn, Pb and Cd obtained through BCR sequential extraction: acid-extractable (F1), reducible (F2), oxidizable (F3) and residual fraction (F4) in the soil collected from depth layers of the core samples (S1, S2 and S3) and around the collected Pinus halepensis root samples in Campo Pisano mine tailings (CP1, CP2, and CP3) and in the non-contaminated areas (B1, B2 and B3).

Figure 5. PCA for the collected soils in deep layers. Elements extracted in F1, F2, F3 and F4 BCR Fractions; the total metal content in soil (T-Zn; T-Pb; T-Cd); the sum of the BCR fractions (SF-Zn; SF-Pb; SF-Cd); electrical conductivity (EC); organic carbon (OC); total nitrogen (T-N); total carbon (T-C) in the uppermost soil samples (S1-1, S2-1 and S3-1) and the deep layers (S1-2, S1-3, S2-2, S2-3, S3-2, S3-3).

Figure 5. PCA for the collected soils in deep layers. Elements extracted in F1, F2, F3 and F4 BCR Fractions; the total metal content in soil (T-Zn; T-Pb; T-Cd); the sum of the BCR fractions (SF-Zn; SF-Pb; SF-Cd); electrical conductivity (EC); organic carbon (OC); total nitrogen (T-N); total carbon (T-C) in the uppermost soil samples (S1-1, S2-1 and S3-1) and the deep layers (S1-2, S1-3, S2-2, S2-3, S3-2, S3-3).

Table 1. The physico-chemical properties of the contaminated soil samples in the different soil depths (S1, S2 and S3); the soil around the roots of Pinus halepensis (CP1, CP2 and CP3); and the non-contaminated soil around the P. halepensis roots (B1, B2 and B3); Number after ± is standard deviation.

Table 1. The physico-chemical properties of the contaminated soil samples in the different soil depths (S1, S2 and S3); the soil around the roots of Pinus halepensis (CP1, CP2 and CP3); and the non-contaminated soil around the P. halepensis roots (B1, B2 and B3); Number after ± is standard deviation.

SoilSoil
Depth
(cm)Soil PropertiesMean Value (mg kg−1)pHEC
(dS m−1)CaCO3 (%)Total
Carbon (%)Total
Nitrogen (%)Organic
Carbon (%)Fe-OxideAl-OxideBulk soil in-depth S1-10–206.812.0552.07 ± 0.78.9 ± 0.10.17 ± 0.011.9 ± 0.110,565.3 ± 301.3160.4 ± 6.2S1-220–284.515.34.05 ± 0.10.71 ± 0.040.010 ± 0.0010.22 ± 0.0129,658.3 ± 3026.0517.2 ± 2.9S1-332–382.329.30.1 ± 0.080.36 ± 0.0010.03 ± 0.010.020 ± 0.00114,920.9 ± 751.93.4 ± 1.7S2-10–207.31.959.4 ± 0.48.3 ± 0.10.04 ± 0.020.35 ± 0.0219,160.8 ± 537.9189.5 ± 10.3S2-237–416.714.237.5 ± 0.55.00 ± 0.050.020 ± 0.00030.020 ± 0.00045909.6 ± 128.6101.5 ± 18.3S2-347–507.611.347.6 ± 0.76.59 ± 0.020.002 ± 0.0010.180 ± 0.00311,498.5 ± 326.837.2 ± 4.9S3-10–206.910.753.6 ± 1.58.6 ± 0.20.15 ± 0.021.5 ± 0.212,334.9 ± 99.6112.9 ± 6.7S3-220–457.111.255.5 ± 0.27.62 ± 0.080.002 ± 0.0010.140 ± 0.00517,411.7 ± 2030.761.2 ± 6.3S3-356–662.519.11.40 ± 0.020.38 ± 0.0050.02 ± 0.010.190 ± 0.00242,948.9 ± 5084.914.3 ± 3.9Bulk soil around the roots of P. halepensisCP1 7.68.349.7 ± 1.79.97 ± 0.050.70 ± 0.080.35 ± 0.039194.4 ± 129.9211.95 ± 7.08CP2 7.72.245.4 ± 1.25.7 ± 0.10.27 ± 0.020.060 ± 0.00218,265.6 ± 159.4112.8 ± 9.8CP3 7.48.841.03 ± 1.038.9 ± 0.20.51 ± 0.030.33 ± 0.0410,936.2 ± 269.4245.6 ± 2.8B1 6.70.30.32 ± 0.021.2 ± 0.20.06 ± 0.010.77 ± 0.07726.8 ± 116.9215.2 ± 14.3B2 7.93.94.07 ± 0.3010.07 ± 0.040.66 ± 0.017.61 ± 0.04992.2 ± 26.82323.9 ± 37.9B3 8.81.119.03 ± 0.503.83 ± 0.080.080 ± 0.0050.78 ± 0.06467.6 ± 62.5195.2 ± 8.4

Table 2. The correlation matrix between BCR fractions and the total metal content in soil (T-Zn; T-Pb; T-Cd), the total metal content in Pinus halepensis root (Zn-R; Pb-R; Cd-R), the bioavailable content of Zn, Pb and Cd (DTPA), the sum of BCR fractions (SF-Zn; SF-Pb; SF-Cd), and the soil characteristics; Correlation (r > 0.8) is significant at the 0.05 level (2-tailed).

Table 2. The correlation matrix between BCR fractions and the total metal content in soil (T-Zn; T-Pb; T-Cd), the total metal content in Pinus halepensis root (Zn-R; Pb-R; Cd-R), the bioavailable content of Zn, Pb and Cd (DTPA), the sum of BCR fractions (SF-Zn; SF-Pb; SF-Cd), and the soil characteristics; Correlation (r > 0.8) is significant at the 0.05 level (2-tailed).

SamplesF1F2F3F4ZnPbCdZnPbCdZnPbCdZnPbCdBulk soil around the roots of P. halepensisT-Zn0.960.860.900.81--0.890.920.930.88-0.80T-Pb0.980.920.940.760.85-0.860.950.970.890.83-T-Cd0.920.950.96-0.92--0.960.940.870.87-Zn-R0.960.98.99-0.95--0.980.990.870.90-Pb-R0.940.990.99-0.97--0.970.970.860.93-Cd-R0.93-0.820.9--0.980.840.880.80--DTPA-Zn 0.83-0.880.80-0.970.88-0.920.850.820.89DTPA-Pb 0.820.83-0.850.87--0.81----DTPA-Cd 0.85-0.890.80-0.980.89-0.930.870.840.90SF-Zn 0.99-0.980.86-0.950.980.970.950.960.960.98SF-Pb 0.960.910.950.730.920.820.870.990.920.940.980.89SF-Cd0.980.920.990.85-0.980.970.940.990.980.960.98pH 0.86------0.840.820.89-0.94EC ------------CaCO30.88-0.800.92-0.980.920.800.940.880.830.94Total C --0.92---------Total N ------------OC ------------Fe-oxide 0.970.800.980.740.820.900.930.980.980.990.94-Al-oxide------------Bulk soil in-depthT-Zn0.85-0.96------0.89-0.90T-Pb------------T-Cd0.86-0.93------0.89-0.94SF-Zn0.970.97.950.81-----0.89-0.91SF-Pb----------0.80-SF-Cd0.90-0.970.80-----0.88-0.93pH---0.85--0.89-----EC------------CaCO3---0.92-0.850.890.830.89---Total C---0.91-0.880.870.850.90---Total N------------OC------------Fe-oxide------------Al-oxide-----0.94-0.920.92---