**b. Heavy metals and trace elements toxic for plants**

Although some preliminary results regarding soil pollution due to heavy metals, organic compounds and salinity have been already described [1, 7, 11, 12] here we examine this issue in detail. All 57 soil samples were subjected to inductively coupled plasma optical emission spectometry (ICP-OES) to determine pseudototal (after prior extraction with nitric and perchloric acids, 4:1 [13]) and bioavailable (after prior extraction with ammonium acetate + EDTA using the method [14]) concentrations of Al, Mn, Zn, Cu, Pb, Cr and Ni. In addition, total As concentrations were determined by X-ray fluorescence in 48 samples. Total Hg levels were determined using an Advanced Mercury Analyser (AMA-254, LECO Company, Czeck Republic) according to the procedure described by [15] in 34 selected samples of the 57 soil samples collected [16].

Tables 4 and 5 provide the metal and trace element concentrations detected in the capping soil and discharge area samples. We also examined total Al and Mn levels: Al concentrations in the landfill ranged from 8123 to 50747 mg kg-1, and Mn concentrations from 205 to 7432 mg kg-1. In the rubble tips, concentration ranges were higher for Al and lower for Mn. Given the alkaline nature of the soils, these elements are not considered hazardous for plant populations and are therefore not included in the tables.

The sites showing the highest levels of all elements occurred on the landfill's slopes and these showed an uneven spatial distribution. However, the most contaminated sites were simulta‐ neously polluted by all elements. The percentage of a metal found in its bioavailable form was also highly variable. Despite being poorly mobile, Pb showed high bioavailability percentages. Cd was also highly bioavailable. Most variation was shown by Zn and Cu. The metals appearing in lowest concentrations were Cr and Ni.

Apart from the trace element bioavailability study conducted according to the method of [14], we performed a more exhaustive analysis of metal bioavailability in the soil samples. To this end, we undertook sequential extraction by the BCR method optimized by [17]. Sequential extraction serves to indicate the fractions of each metal that are bioavailable (F1: exchangeable), reducible (F2: bound to oxyhydroxides), oxidizable (F3: bound to organic matter) and residual (F4). Given that it is the landfill proper that shows the higher concentrations of these metal pollutants, 5 sites were selected representing platform, slope and discharge zones showing variable concentrations of these types of pollutant. The sites were selected according to their known distributions of metals; we have preserved the numbers assigned to their collection sites. Table 6 provides total concentrations of each metal in each sample calculated as the sum of all fractions. The reader may find the percentages of each metal found in each fraction in Figure 4.

The Complex Nature of Pollution in the Capping Soils of Closed Landfills: Case Study in a Mediterranean Setting http://dx.doi.org/10.5772/57223 207

The results of these determinations in each soil sample are provided in Tables 2 and 3. All results are provided to highlight the huge variation existing for each factor. pH varied from 7.0 to 8.5, given the alkaline nature of the surrounding soils used to cap the landfill. The distributions of all variables failed to vary significantly between the landfill proper and rubble

Although some preliminary results regarding soil pollution due to heavy metals, organic compounds and salinity have been already described [1, 7, 11, 12] here we examine this issue in detail. All 57 soil samples were subjected to inductively coupled plasma optical emission spectometry (ICP-OES) to determine pseudototal (after prior extraction with nitric and perchloric acids, 4:1 [13]) and bioavailable (after prior extraction with ammonium acetate + EDTA using the method [14]) concentrations of Al, Mn, Zn, Cu, Pb, Cr and Ni. In addition, total As concentrations were determined by X-ray fluorescence in 48 samples. Total Hg levels were determined using an Advanced Mercury Analyser (AMA-254, LECO Company, Czeck Republic) according to the procedure described by [15] in 34 selected samples of the 57 soil

Tables 4 and 5 provide the metal and trace element concentrations detected in the capping soil and discharge area samples. We also examined total Al and Mn levels: Al concentrations in the landfill ranged from 8123 to 50747 mg kg-1, and Mn concentrations from 205 to 7432 mg kg-1. In the rubble tips, concentration ranges were higher for Al and lower for Mn. Given the alkaline nature of the soils, these elements are not considered hazardous for plant populations

The sites showing the highest levels of all elements occurred on the landfill's slopes and these showed an uneven spatial distribution. However, the most contaminated sites were simulta‐ neously polluted by all elements. The percentage of a metal found in its bioavailable form was also highly variable. Despite being poorly mobile, Pb showed high bioavailability percentages. Cd was also highly bioavailable. Most variation was shown by Zn and Cu. The metals

Apart from the trace element bioavailability study conducted according to the method of [14], we performed a more exhaustive analysis of metal bioavailability in the soil samples. To this end, we undertook sequential extraction by the BCR method optimized by [17]. Sequential extraction serves to indicate the fractions of each metal that are bioavailable (F1: exchangeable), reducible (F2: bound to oxyhydroxides), oxidizable (F3: bound to organic matter) and residual (F4). Given that it is the landfill proper that shows the higher concentrations of these metal pollutants, 5 sites were selected representing platform, slope and discharge zones showing variable concentrations of these types of pollutant. The sites were selected according to their known distributions of metals; we have preserved the numbers assigned to their collection sites. Table 6 provides total concentrations of each metal in each sample calculated as the sum of all fractions. The reader may find the percentages of each metal found in each fraction in

**b. Heavy metals and trace elements toxic for plants**

206 Environmental Risk Assessment of Soil Contamination

tips.

samples collected [16].

Figure 4.

and are therefore not included in the tables.

appearing in lowest concentrations were Cr and Ni.


**Table 3.** pH, organic matter (OM, %), nitrogen (N, %), pseudo-total concentration (T) of nutrient elements (mg kg-1) and percentage of exchangeable fraction (E) in soil samples collected from rubble tips.


**Table 4.** Pseudo-total concentration (T) of trace elements (mg kg-1) and percentage of bioavailable fraction (B) in soil samples collected from landfill proper. nd: not detected; -: not analyzed. Reference levels for alkaline soils according to Spanish law (RD1310/1990), \*As Dutch reference level.

The Complex Nature of Pollution in the Capping Soils of Closed Landfills: Case Study in a Mediterranean Setting http://dx.doi.org/10.5772/57223 209

**Sampling point Zn Cu Pb Cd Cr Ni As Hg T B T B T B T B T B T B**

G-23 9491 23 4593 3 4421 50 93 35 531 0.9 231 1.1 271 11 G-24 137 20 14 18 19 70 0.0 3.2 2.2 8.7 1.5 n.d 0.0 G-45 148 2.1 8.9 13 28 8.2 0.0 7.3 0.6 5.6 4.1 14 - G-46 147 2.1 38 17 35 48 0.0 2.2 2.3 12 4.0 22 - G-47 126 3.8 12 14 11 43 0.0 4.7 1.1 9.9 3.4 n.d - G-48 175 5.3 43 16 22 40 0.0 18 0.6 21 3.4 n.d -

G-6 640 22 1916 21 132 29 0.0 256 0.1 35 2.5 119 0.3 G-8 13029 27 1055 8.1 12689 23 185 34 269 1.7 86 1.9 282 4.0 G-11 3247 20 240 11 579 51 10 67 154 0.6 43 2.0 n.d 0.5 G-16 10777 25 748 9.3 5734 38 142 41 150 3.0 42 2.6 n.d 3.0 G-17 17416 26 1313 8.5 12612 28 308 37 242 1.5 60 2.2 n.d 4.9 G-18 22992 28 1804 9.4 18136 30 306 36 298 1.8 80 3.7 685 4.2 G-19 5190 25 125 14 1198 47 29 52 40 3.3 15 2.6 n.d 0.2 G-20 1085 2.6 18 9.4 106 12 0.3 64 9.8 0.5 9.0 0.9 12 0.0 G-21 129 9.0 11 21 18 37 0.0 3.5 1.4 7.0 1.7 13 0.0 G-22 168 9.3 14 20 25 53 0.0 9.1 0.8 8.8 1.8 23 0.0 G-39 17830 76 1445 20 12555 68 190 60 587 2.2 210 2.5 492 -

G- 3 A 61 2.2 9.1 14 18 59 0.0 2.3 12 5.1 9.2 - - G- 3 F 69 4.6 31 6.2 8.1 40 0.0 9.2 3 5.2 7.0 - - G-9 12632 25 1181 10 7179 37 257 48 236 2.4 90 2.1 306 2.4 G-10 15184 33 1493 13 10085 48 155 42 504 2.2 206 2.2 n.d 3.3 G-37 559 66 20 25 28 61 0.0 3.8 4.7 8.5 5.9 15 0.0 G-38 108 18 15 24 23 65 0.0 15 1.0 7.4 6.7 19 0.0

G- 2 A 528 17 36 27 117 36 0.0 6.6 6.1 8.6 5.1 - - G- 2 F 366 14 35 18 64 28 0.0 5.7 4.9 7.3 5.5 - - G- 4 A 577 19 882 27 149 29 0.0 110 0.1 156 1.5 - - G- 4 F 477 19 1260 26 139 19 0.0 153 0.2 213 1.5 - - G-7 2417 33 151 27 290 48 2.5 86 9.5 3.4 34 8.9 54 0.3 Ref. (pH"/>7) 450 210 300 3 150 112 29\* 1.5

**Table 4.** Pseudo-total concentration (T) of trace elements (mg kg-1) and percentage of bioavailable fraction (B) in soil samples collected from landfill proper. nd: not detected; -: not analyzed. Reference levels for alkaline soils according to

*Platform*

208 Environmental Risk Assessment of Soil Contamination

*Slope*

*Foot of slope*

*Discharge zones*

Spanish law (RD1310/1990), \*As Dutch reference level.


**Table 5.** Pseudo-total concentration (T) of trace elements (mg kg-1) and percentage of bioavailable fraction (B) in soil samples collected from rubble tips. nd: not detected; -: not analyzed. Reference levels for alkaline soils according to Spanish law [18], \*As Dutch reference level.

The results of these tests prompt the following conclusions. Cd and Zn showed highest percentages in the bioavailable fraction. In the case of Cd, this finding is of major concern given its high concentration in the soils examined and this situation has been also described by [19]. Arsenic shows the highest residual percentage and thus its available levels are low. The bioavailable fraction of Cu is fairly low, while remaining fractions vary according to the soils. The behavior of Pb was more irregular among the different soils. In general, the residual fraction was low. The organic matter fraction was variable being greatest at site 18. Its bioavailable fraction was very high at site 39, which is worrying given the high concentration of this heavy metal at this site.


**Table 6.** Total concentration of trace elements (mg kg-1) in soils selected for conducting the sequential fractionation

**Figure 4.** Percentage of metal content that is in each fraction

Clearly the presence of very high concentrations of trace elements and heavy metals is a problem for the establishment of plant populations, worsened by the fact that the sites of highest concentrations coincide with zones of intense slope. In effect, zones corresponding to samples 17 and 18, along with 10 and 39, are naked slopes with practically no plant cover in comparison with surrounding zones.
