**4. Contents of heavy metal soluble forms and reaction of surface horizon (0 - 20 cm) of soils in green belts adjacent to selected transportation routes in the city of Poznań (western Poland)**

Anthropopressure affects physical, biological and chemical properties of soil. Soils in urban areas, located along transportation routes, are exposed to heavy metal pollution, originating from substances produced during combustion of fuels, abrasion of road surfaces and tires, granular materials falling onto the ground during transport, etc. [24, 36]. Platinum metals, which have been employed in production of car catalysts, reach environment and cause contamination of soil, plants and water [84]. Moreover, chemical substances used in winter to eliminate black ice (e.g. sodium or calcium chlorides) as well as deposition of dusts and water migration of elements contribute to soil degradation and deterioration of plant growth conditions. In urban areas strong alkalization of soil is frequently observed, which significantly reduces contents of soluble forms of metallic components [12, 27, 74].

According to the Ordinance of the Minister of the Environment of 9 September 2002 on soil quality standards and land quality standards currently binding in Poland (the Journal of Law Dziennik Ustaw no. 165, item 1359), soil category B comprises soils in urbanized areas, for which the admissible heavy metal level (mg kg-1 dry matter) in the upper 0 - 30 cm layer is Ni 100, Cd 4, Pb 100 and Cr 150, respectively.

Legal regulations pertain to total heavy metal contents in soils; however, many authors claim that it is not always a direct indicator of their bioavailability [44]. In the opinion of Gorlach and Gambuś [53], the most appropriate measure is to assess soil contents of soluble forms of trace elements, as they may be absorbed by plants.

The aim of the studies conducted by the authors was to determine what amounts of soluble forms of heavy metals are available for plants in the 0 - 20 cm layer of soil in green areas located in the vicinity of selected transportation routes in the city of Poznań, Poland. Collected soil samples were tested for soil reaction and contents of selected heavy metals (cadmium, lead, chromium and nickel, classified as metallic micronutrients, essential elements at the same time having a negative effect on plants when found in greater amounts).

#### **Material and methods**

Soil samples from green areas were collected in October 2012 in the vicinity of transportation routes in the city of Poznań, Poland. Forty five streets were selected for analyses and soil samples were collected using an Egner sampling stick from a 0 - 20 cm layer at a distance of 0.5 - 2.0 m from the roadway. Along each analyzed street 4 bulk samples were collected, comprising 15 individual samples (4 x 15 = 60 individual samples). Heavy metals (Cd, Pb, Cr and Ni) were extracted from soil using Lindsay's solution containing in 1 dm3: 5 g EDTA (ethylenediaminetetraacetic acid), 9 cm3 25% NH4OH solution, 4 g citric acid and 2 g Ca(CH3COO)2·2H2O. Next they were assayed by flame atomic absorption spectroscopy (FAAS) with an AAS 3 Zeiss apparatus. Active acidity expressed in pH (H2O) was determined by potentiometry (soil : water = 1:2), [50].

Results were analyzed determining their minimum, maximum and mean values (in the case of pH its logarithmic value was considered), standard deviation, coefficients of variation and empirical distribution for individual chemical parameters. Mean results of chemical analyses are presented in Table 3, while stem-and-leaf displays are given in Figs. 1 - 2.

In these analyses soil pH fell within the range of 4.32 – 8.26, while its coefficient of variation was as low as 9% (Table 3). For most plants optimal soil reaction is pHH2O 6.0 – 6.5. Only 2.2% soils had a highly acid reaction (at pH 4.3 – 5.0), whereas a vast majority had an alkaline reaction pH>7.4 (46.7% soil samples) and a neutral reaction (37.8%), comprising jointly 84.5% samples (Figure 1). Elevated soil pH is connected with an excessive content of alkaline ions, i.e. calcium, magnesium, sodium and potassium. Alkalization of urban soils may result e.g. from the use of salts such as sodium chloride to remove black ice from roadways, as well as strongly alkalizing dusts (containing e.g. CaO, MgO, Na2O, K2O), being by-products of carbon com‐ bustion to heat houses [27, 74]. In turn, Kleiber [74] to a much greater degree suggests strong alkalization of soil (pH in H2O up to 10.95) as a factor having a potentially negative effect on plant growth and development.

granular materials falling onto the ground during transport, etc. [24, 36]. Platinum metals, which have been employed in production of car catalysts, reach environment and cause contamination of soil, plants and water [84]. Moreover, chemical substances used in winter to eliminate black ice (e.g. sodium or calcium chlorides) as well as deposition of dusts and water migration of elements contribute to soil degradation and deterioration of plant growth conditions. In urban areas strong alkalization of soil is frequently observed, which significantly

According to the Ordinance of the Minister of the Environment of 9 September 2002 on soil quality standards and land quality standards currently binding in Poland (the Journal of Law Dziennik Ustaw no. 165, item 1359), soil category B comprises soils in urbanized areas, for which the admissible heavy metal level (mg kg-1 dry matter) in the upper 0 - 30 cm layer is Ni

Legal regulations pertain to total heavy metal contents in soils; however, many authors claim that it is not always a direct indicator of their bioavailability [44]. In the opinion of Gorlach and Gambuś [53], the most appropriate measure is to assess soil contents of soluble forms of

The aim of the studies conducted by the authors was to determine what amounts of soluble forms of heavy metals are available for plants in the 0 - 20 cm layer of soil in green areas located in the vicinity of selected transportation routes in the city of Poznań, Poland. Collected soil samples were tested for soil reaction and contents of selected heavy metals (cadmium, lead, chromium and nickel, classified as metallic micronutrients, essential elements at the same time

**Material and methods** Soil samples from green areas were collected in October 2012 in the vicinity of transportation routes in the city of Poznań, Poland. Forty five streets were selected for analyses and soil samples were collected using an Egner sampling stick from a 0 - 20 cm layer at a distance of 0.5 - 2.0 m from the roadway. Along each analyzed street 4 bulk samples were collected, comprising 15 individual samples (4 x 15 = 60 individual samples). Heavy metals (Cd, Pb, Cr and Ni) were extracted from soil using Lindsay's solution containing in 1 dm3: 5 g EDTA (ethylenediaminetetraacetic acid), 9 cm3 25% NH4OH solution, 4 g citric acid and 2 g Ca(CH3COO)2·2H2O. Next they were assayed by flame atomic absorption spectroscopy (FAAS) with an AAS 3 Zeiss apparatus. Active acidity expressed in pH (H2O) was determined

Results were analyzed determining their minimum, maximum and mean values (in the case of pH its logarithmic value was considered), standard deviation, coefficients of variation and empirical distribution for individual chemical parameters. Mean results of chemical analyses are presented in Table 3, while stem-and-leaf displays are given in Figs.

In these analyses soil pH fell within the range of 4.32 – 8.26, while its coefficient of variation was as low as 9% (Table 3). For most plants optimal soil reaction is pHH2O 6.0 – 6.5. Only 2.2% soils had a highly acid reaction (at pH 4.3 – 5.0), whereas a vast majority had an alkaline reaction pH>7.4 (46.7% soil samples) and a neutral reaction (37.8%), comprising jointly 84.5% samples

reduces contents of soluble forms of metallic components [12, 27, 74].

having a negative effect on plants when found in greater amounts).

100, Cd 4, Pb 100 and Cr 150, respectively.

580 Environmental Risk Assessment of Soil Contamination

by potentiometry (soil : water = 1:2), [50].

1 - 2.

trace elements, as they may be absorbed by plants.

In the opinion of Klimowicz and Melke [75], in urban areas traffic-related pollution is more dangerous than industrial pollution, since it is spread in relatively large amounts, at low heights, in the respiration zone of humans, animals and plants. Relief features, distance from a roadway and intensity of vehicle traffic have a decisive effect on the contents of heavy metals in soils adjacent to transportation routes in urban green areas. In the soil found at the car market in Słomczyn near Warsaw (one of the biggest car markets in Poland) contents of zinc, lead and copper are as follows (in mg kg-1 d.m.): the car sale point Zn at 612.3, Pb at 397.8 and Ni at 94.5, while at the spare part sale point and warehouse they are: Zn at 679.1, Pb at 420.4 and Ni at 114.0, respectively [115].

Soil pollution with heavy metals is typically assessed on the basis of total contents of elements [44]. Those authors claimed that this assessment should be supplemented with an analysis of heavy metal contents directly available to living organisms.

This study consisted in the determination of contents of soluble heavy metal forms (Table 3). Cadmium content in soils fell within the range of 0.16 – 0.42 mg Cd dm-3 and it was of relatively limited variability (CV=17.50%). As many as 55.1 % samples contained this heavy metal at <0.21 - 0.26 mg Cd dm-3 (Figure 2). Bach [9] in soils of green areas adjacent to transportation routes in the city of Krakow, Poland found contents of soluble cadmium forms to range from 0.21 to 1.54 mg kg-1 d.m. soil. In most tested soils Bach [9] recorded cadmium content from 0.4 to 0.8 mg kg-1 d.m. soil. According to Kabata-Pendias and Pendias [67], natural total cadmium content (the so-called background) in Polish soils is 0.3 mg Cd kg-1 d.m.

Lead content ranged from 0.79 to 42.96 mg Pb dm-3, at the same time being highly variable depending on the location (CV=110.78%). As many as 84.4% tested soils had low contents of this heavy metal (up to 9.22 mg Pb dm-3), while samples with 42.96 mg Pb dm-3 accounted for 2.2.% (Figure 2). A low lead content (max. up to 4.3 mg Pb dm-3) was reported in his study by Kleiber [74]. Lead content (soluble forms) in soils adjacent to transportation routes in the city of Krakow ranged from 11.1 up to 142.8 mg kg-1 d.m. soil, of which the highest proportion (53%) comprised soils with its contents from 40 to 80 mg Pb kg-1 d.m. soil. Mean content of bioavailable Pb forms in soils of allotment gardens located in the right-bank Warsaw was 332.7 mg kg-1 d.m. [41].

The primary source of lead pollution in soils (adjacent to transportation routes) up to 2005 was connected with tetraethyl lead, commonly added to gasoline as an antiknock agent [62]. In turn, the authors of this chapter in their analyses recorded a low content of soluble lead content in the surface soil layer in areas adjacent to transportation routes in the city of Poznań, Poland. No lead pollution in soils adjacent to exit routes leading from Poznań was detected by Hofman and Wachowski [62].

In turn, chromium content ranged from 0.26 to 0.67 mg Cr dm-3. The coefficient of variation for chromium was similar to that calculated for nickel, amounting to CV 22.34%. The greatest proportion (44.4%) of soils was found within the range of chromium contents from < 0.36 to 0.46 mg Cr dm-3 (Figure 2). Results of analyses conducted by Bach [9] indicate that the content of chromium (soluble forms) in soils in areas adjacent to transportation routes in the city of Krakow ranged from trace values to 10.23 mg Cr kg-1 d.m.

The recorded nickel content ranged from 0.43 to 1.25 mg Ni dm-3. The variability of levels for this metal was relatively medium-ranged (CV=23.19%). Most of soil samples (84.4%) were characterized by nickel contents falling within the range of values from < 0.43 to 0.63 mg Ni dm-3 (Figure 2). In soils found in green areas adjacent to transportation routes in Krakow, Poland the content of nickel soluble forms ranged from 1.07 to 6.38 mg kg-1 d.m. soil [9]. In contrast, in soils collected from allotment gardens located in right-bank Warsaw the mean content of bioavailable nickel forms was 28.4 mg kg-1 d.m. [41].

Environmental pollution with heavy metals constitutes a serious problem in some regions of Poland. According to Dmochowski et al. [41], high emissions of heavy metals originating from a dense network of transportation routes with high intensity vehicle traffic causes their accumulation in soils and crops produced in allotment gardens located in Praga Południe, the right-bank district of Warsaw, Poland.

In the opinion of Heck et al. [59], introduction of advanced catalytic systems, containing platinum, rhodium and palladium and constituting a source of environmental pollution also for soils in areas adjacent to transportation routes makes their monitoring a necessary practice. In the nearest future it will be required to create an effective system of environmental pollution monitoring.


Continuous and Induced Phytoextraction — Plant-Based Methods to Remove Heavy Metals from Contaminated Soil http://dx.doi.org/10.5772/57257 583

No lead pollution in soils adjacent to exit routes leading from Poznań was detected by Hofman

In turn, chromium content ranged from 0.26 to 0.67 mg Cr dm-3. The coefficient of variation for chromium was similar to that calculated for nickel, amounting to CV 22.34%. The greatest proportion (44.4%) of soils was found within the range of chromium contents from < 0.36 to 0.46 mg Cr dm-3 (Figure 2). Results of analyses conducted by Bach [9] indicate that the content of chromium (soluble forms) in soils in areas adjacent to transportation routes in the city of

The recorded nickel content ranged from 0.43 to 1.25 mg Ni dm-3. The variability of levels for this metal was relatively medium-ranged (CV=23.19%). Most of soil samples (84.4%) were characterized by nickel contents falling within the range of values from < 0.43 to 0.63 mg Ni dm-3 (Figure 2). In soils found in green areas adjacent to transportation routes in Krakow, Poland the content of nickel soluble forms ranged from 1.07 to 6.38 mg kg-1 d.m. soil [9]. In contrast, in soils collected from allotment gardens located in right-bank Warsaw the mean

Environmental pollution with heavy metals constitutes a serious problem in some regions of Poland. According to Dmochowski et al. [41], high emissions of heavy metals originating from a dense network of transportation routes with high intensity vehicle traffic causes their accumulation in soils and crops produced in allotment gardens located in Praga Południe, the

In the opinion of Heck et al. [59], introduction of advanced catalytic systems, containing platinum, rhodium and palladium and constituting a source of environmental pollution also for soils in areas adjacent to transportation routes makes their monitoring a necessary practice. In the nearest future it will be required to create an effective system of environmental pollution

**(H2O)**

 28 czerwca 56 r. 7.67 0, 49 0, 23 14, 81 0, 31 Aleje Niepodległości 7.58 0, 51 0, 28 10, 74 0, 33 Aleje Solidarności 7.37 0, 58 0, 27 3, 36 0, 49 Arciszewskiego 7.30 0, 48 0, 20 6, 55 0, 41 Armii Poznań 7.72 0, 59 0, 21 42, 96 0, 55 Biskupińska 7.76 0, 52 0, 23 2, 18 0, 46 Dolna Wilda 8.26 0, 44 0, 18 4, 00 0, 38 Droga Dębińska 7.37 0, 48 0, 23 6, 76 0, 34

**Contents (mg kg-1 d.m.) Ni Cd Pb Cr**

Krakow ranged from trace values to 10.23 mg Cr kg-1 d.m.

content of bioavailable nickel forms was 28.4 mg kg-1 d.m. [41].

right-bank district of Warsaw, Poland.

**No. Street pH**

monitoring.

and Wachowski [62].

582 Environmental Risk Assessment of Soil Contamination



**Table 3.** Contents of soluble forms of heavy metals and soil reaction in the surface soil layer (0 - 20 cm) in green areas adjacent to selected transportation routes in the city of Poznań, Poland Coefficient of variation (%) 9,0 23.19 17.50 110.78 22.32

Standard deviation 0,65 0.14 0.04 6.64 0.10

Figure 1. The stemplot for pH (H2O) of soil in green areas located near to routes in Poznan **Figure 1.** The stemplot for pH (H2O) of soil in green areas located near to routes in Poznan

Continuous and Induced Phytoextraction — Plant-Based Methods to Remove Heavy Metals from Contaminated Soil http://dx.doi.org/10.5772/57257 585

**No. Street pH**

584 Environmental Risk Assessment of Soil Contamination

Content

Content

**The**

**number of cases**

**(H2O)**

 Słowiańska 6.87 0, 63 0, 23 5, 31 0, 29 Stablewskiego 7.55 0, 57 0, 23 3, 28 0, 46 Starołęcka 7.12 0, 63 0, 29 6, 01 0, 53 Stróżyńskiego 7.53 0, 49 0, 23 2, 71 0, 46 Szpitalna 4.32 0, 82 0, 23 11, 84 0, 50 Umultowska 6.79 1, 25 0, 42 3, 03 0, 65 Widłakowa 7.41 0, 50 0, 22 2, 07 0, 45 Witosa 7.09 0, 48 0, 21 6, 07 0, 43 Wojska Polskiego 6.53 0, 69 0, 26 9, 48 0, 39 Zwierzyniecka 7.64 0, 52 0, 23 2, 49 0, 40

36 Słowiańska 6.87 0,63 0,23 5,31 0,29 37 Stablewskiego 7.55 0,57 0,23 3,28 0,46 38 Starołęcka 7.12 0,63 0,29 6,01 0,53 39 Stróżyńskiego 7.53 0,49 0,23 2,71 0,46 40 Szpitalna 4.32 0,82 0,23 11,84 0,50 41 Umultowska 6.79 1,25 0,42 3,03 0,65 42 Widłakowa 7.41 0,50 0,22 2,07 0,45 43 Witosa 7.09 0,48 0,21 6,07 0,43 44 Wojska Polskiego 6.53 0,69 0,26 9,48 0,39 45 Zwierzyniecka 7.64 0,52 0,23 2,49 0,40

mean 7.22 0.59 0.25 6.00 0, 47 minimum 4.32 0.43 0.16 0.79 0, 26 maximum 8.26 1.25 0.42 42.96 0, 67

Standard deviation 0,65 0.14 0.04 6.64 0.10 Coefficient of variation (%) 9,0 23.19 17.50 110.78 22.32

4,3‐5,0 5,0‐6,0 6,0‐6,7 6,7‐7,4 7,4‐8,5

**Class left half‐open ranges**

mean 7.22 0.59 0.25 6.00 0,47 minimum 4.32 0.43 0.16 0.79 0,26 maximum 8.26 1.25 0.42 42.96 0,67

37,8% 46,7%

Standard deviation 0, 65 0.14 0.04 6.64 0.10 Coefficient of variation (%) 9, 0 23.19 17.50 110.78 22.32

**Table 3.** Contents of soluble forms of heavy metals and soil reaction in the surface soil layer (0 - 20 cm) in green areas

**pH**

Figure 1. The stemplot for pH (H2O) of soil in green areas located near to routes in Poznan

2,2% 2,2% 11,1%

**Figure 1.** The stemplot for pH (H2O) of soil in green areas located near to routes in Poznan

adjacent to selected transportation routes in the city of Poznań, Poland

**Contents (mg kg-1 d.m.) Ni Cd Pb Cr**

Figure 2. The stemplot for content of heavy metals in soil of green areas located near to routes in Poznan **Figure 2.** The stemplot for content of heavy metals in soil of green areas located near to routes in Poznan

#### **4.1. Concluding remarks**

Based on analyses of soils collected from green areas located in the vicinity of selected transportation routes in the city of Poznań, Poland in most examined locations an alkaline reaction pH >7.4 (46.7% soil samples) and a neutral reaction (37.8%) were found, which may significantly affect habitat conditions for plants.

Moreover, most tested soil samples contained low amounts of soluble forms of cadmium, lead, chromium and nickel.
