Environ Manage (2007) 40:719–726 DOI 10.1007/s00267-007-0073-0
Determination and Evaluation of Cadmium, Copper, Nickel, and Zinc in Agricultural Soils of Western Macedonia, Greece A. Papadopoulos Æ C. Prochaska Æ F. Papadopoulos Æ N. Gantidis Æ E. Metaxa
Received: 27 February 2007 / Accepted: 23 April 2007 Ó Springer Science+Business Media, LLC 2007
Abstract The objective of this study was to determine the levels of major phytotoxic metals—including cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn)—in agricultural soils of Western Macedonia, Greece. We also wanted to determine the possible relationships among elements and between soil properties and elemental concentrations. Surface soil samples, n = 570, were collected and analyzed. The results of the elemental analysis showed that the mean metal concentrations were consistent with reported typical concentrations found in Greek agricultural soils in the cases of Zn and Cu. Cd exhibited lower and Ni higher mean concentrations than the typical levels reported in the literature. Metal concentrations in the majority of the examined samples (>69%) were found to be higher than the respective critical plant-deficiency levels. However, only 0.4% and 0.2% of the analyzed soil samples, respectively, exhibited Cd and Ni concentrations higher than the levels that cause plant toxicity, as referenced by other investigators. These results suggest that the soils studied can be considered as unpolluted with respect to the examined food-chain metal contaminants. However, the levels of the metal concentrations in some of the soil samples, and the low correlation of the metals with soil properties, suggest an anthropogenic rather that lithogenic origin. Keywords Greece Heavy metals Soil properties Western Macedonia
A. Papadopoulos (&) C. Prochaska F. Papadopoulos N. Gantidis E. Metaxa Soil Science Institute of Thessaloniki, National Agricultural Research Foundation, Greece, 57001 Thermi, Thessaloniki, Greece e-mail:
[email protected]
Introduction General concern about heavy metals getting into the human food chain has been frequently expressed (Krantz & Dorevitch 2004). The basis for this concern is the gradual spread of heavy metals into agricultural soils through industrial and urban activity. The metals that have received the most attention are cadmium (Cd), copper (Cu), nickel (Ni), zinc (Zn), and lead (Pb). Of these, Cu, Ni, and Zn are phytotoxic at high concentrations (i.e., they decrease plant growth). Cu is also toxic to certain livestock. Cd and Pb are food-chain contaminants, although only Cd can readily enter the food chain by way of plant uptake. Cd is more plant-available in soils than most metals, and uptake by humans or animals is not restricted by plant phytotoxicity. Pb, in contrast, is insoluble in soil and is not readily taken up by plants. The major pathway in which Pb enters the human food chain is direct ingestion of Pb-contaminated soil or -containing materials (Notten et al. 2005). Agricultural practices are frequently a source of heavy-metal contamination (Kabata-Pendias 1995). The intensification of agriculture, encouraged by the Common Agricultural Policy (CAP) in Europe since the 1050s, has resulted in the incorporation of several types of pollutants to soil, such as heavy metals, because of the excess use of agrochemicals (Van Camp et al. 2004). These soils have also been influenced by other pollutant activities, such as aerial fallout from industrial activities (e.g., fly ashes produced by lignite-fired power plants). These plants are the main source of electricity in Greece, and four thermal power stations with >4000 MW total installed capacity are located in the prefecture of Kozani, in western Macedonia, Greece, which includes the agricultural municipality of Servia. The concentrations of the trace elements of environmental concern in the fly ashes are of great importance because fly ash is
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mixed with overburden and interbedded sediments and subsequently used as landfill. So far, a large number of papers (Foscolos et al. 1989, Arditsoglou et al. 2004) have only tackled the presence of trace elements in the fly ashes. However, only a limited amount of reported data exist on the evaluation of food-chain contaminants in each of the 14 municipalities of the prefecture of Kozani (Gerouki et al. 2000). This lack of reported data is strongly related to difficulties in evaluating soil contamination by heavy metals. For instance, there is no consensus regarding the criteria for concentration of heavy metals that could be hazardous to plant, animal, or human life. Similarly, no governmental regulation specifies the maximum metal concentrations in nonhazardous wastes for land applications, except in the case of sewage sludge (86/278/EEC). This normative also fails to take into account soil characteristics, it cannot be applied in other countries, and it does not consider all the legal possibilities. Therefore, it is important to establish background concentrations of trace metals for soils occurring within a region and to document systematic variation in concentrations according to soil classes and properties (Kabata-Pendias & Pendias 1992, Chen et al. 2001). Knowledge of the heavy-metal content in soils as well as the origin of these levels are priority objectives in the European Union. According to the European Thematic Strategy for Soil Protection, which was published at the start of 2002 by the European Communities Commission, the characterization of the content and source of heavy metals in soils is necessary to establish quality standards that allow the detection of sampling sites affected by pollution on a regional level. The goals of the present study were (1) to determine the levels of major phytotoxic metals (Cd, Cu, Ni, and Zn) in 570 representatives of Servia’s municipality surface soil and (2) to determine possible relationships among elements and between soil properties and elemental concentrations.
Materials and Methods Study Area The municipality of Servia is situated in the eastern part of the prefecture of Kozani, which is located in western Macedonia, Greece. Servia covers a total area of 400 km2. The cultivated zone covers an area of 90 km2, although the site studied covered an area of 124 km2 (Fig. 1). Servia consists of flat sections with slopes with grades between 0% and 5% and mountain areas with elevations of 200 to 800 m higher than sea level and with harsh slopes with grades of 40% to 60%. The land is influenced by a Mediterranean climate, with an average annual rainfall of 500 mm/y and an annual average temperature approxi-
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mately 13°C. The area is subjected to weak to moderate winds that blow mostly from the north and cause no severe effects to the majority of the area’s cultivations. These cultivations consist of cereals (covering 87.9% of the total cultivation area), fruit-bearing trees (3.8% of the total cultivation area), vineyards (1.7% of the total cultivation area), gardening (1.1% of the total cultivation area), and fallow land (33.348 km2). The largest lignite-power station in Greece, named Aghios Demetrios (1500 MW), produces >30% of Greece’s power requirements and is located only 6 km from the northern boundaries of Servia Municipality and 10 km from the first sampling sites. The amount of fly ash released annually into the atmosphere from the Aghios Demetrios power station is nearly 3 kilo tones (Triantafyllou 2003). The majority of the fly ash arrested by the electrostatic filters is stockpiled in open areas before being taken to a land fill or disposed of in specific mounds. Suspension of the finest fly ash fractions (typically of particles with diameters up to 60 lm) might be a source of fugitive dust in the local atmosphere (Arditsoglou et al. 2004). Another significant particle source is fugitive dust originating from the mining process, including emissions from mining equipment, translocation of soil or coal, vehicle traffic on unpaved roads, and transportation and deposition of lignite and lignite ash. Fugitive dust generated from the previously operations primarily affects the areas closest to the mines and power stations, as found in the study area (Triantafyllou 2003). Soil Sampling In the present study, land resource information was acquired by recent orthophotomaps, as well as topographic maps, of Servia that were published in 1987 with a scale of 1:5.000. Samples, n = 570, of surface soil horizons (0 to 30 cm) were collected by augering. When a sample was taken, its accurate position was noted using global positioning software (packages Arc GIS 8.1 and Arc View 3.2). The samples were taken every 300 m. All samples were air dried, ground, and stored in hermetically sealed polyethylene bags before analysis. Physicochemical Analysis The soil samples were subjected to the following determinations: (1) soil pH using a 1:1 water-to-soil ratio (Peech 1965); (2) electrical conductivity of the saturation extract based on the preparation of a saturated paste with distilled water (Bower & Wilcox 1965); (3) percentage of equivalent calcium carbonate as measured by a Bernard calcimeter; (4) soil texture using the Bouyoucos hydrometer method (Bouyoucos 1962, Soil Survey Staff 1992); (5) soil
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Fig. 1 Location of the study area and soil sampling sites
P using the Olsen extraction method (Olsen et al. 1954); (6) soil K using the ammonium acetate–extraction method (Knudsen et al. 1982); (7) organic matter (OM) content by the Walkley-Black wet-digestion procedure (Nelson & Sommers 1982); and (8) Zn, Cu Cd, and Ni extraction using diethylenetriaminepentaacetic acid (DTPA) according to the method described by Lindsay and Norvell (1978). Such extraction provides more information about metal availability and tends to correlate with metal uptake by plants (Hooda & Alloway 1994). After the extraction, the samples were filtered (Whatman 42) to make a volume of up to 20 ml. The filtrates were stored in polypropylene bottles at 4°C until measured. The metals were determined by flame atomic absorption spectroscopy (FAAS; PerkinElmer Analyst 2000). The detection limits by FAAS for the analysed metals were 0.002 lg ml–1 for Zn and Cu; 0.01 lg ml–1for Cd; and 0.006 lg ml–1 for Ni. To assess the quality of applied methodology and the determination by FAAS matrix, interferences were checked using techniques of standard addition. No matrix interferences were observed for the determination of the studied metals. Statistical Analysis All statistical analyses were performed using software SPSS 8.0 (Cary, NC), which presents the maximum and
minimum value, statistical and SEM, and SD skewness and kurtosis. The Kolmogorov–Smirnov (KS) test was used for the confirmation of normal distribution of the data populations. Bivariate correlation analysis using Pearson’s product moment correlation coefficient was used to establish the relationships between the concentrations of heavymetal and soil properties and among the heavy metals themselves.
Results and Discussion The soils of the study area were developed in recent alluvial deposits or in calcareous parent materials. According to Soil Taxonomy (Soil Survey Staff 1992), 87.3% of the soils are classified as Entisols, 40.63% as Inceptisols, and 3.43% as Alfisols. The frequency and the percentages of the main soil textural classes found in the studied soils are listed in Table 1. Additional soil characteristics are listed in Table 2. These soils are generally characterised by a sandy loam texture, slightly alkaline pH, electrical conductivity (EC) 0.7 mg kg–1. In addition, only one soil sample (0.2%) exhibited Ni concentrations >15 mg kg–1, which has been reported to cause slight chlorosis to various plants (Khalid & Tinsley 1980; Heale & Ormrod 1982). Nevertheless, it has been reported that Ni
Table 2 Descriptive statistics of the soil properties Variable
Symbol
Unit
Descriptive statistics Mean
Std
Statistic
SEM
Sand content
S
%
54.21
0.53
Silt content
Si
%
28.40
Clay content
C
%
17.40
pH
pH
–
Electrical conductivity
EC
OM
Min
Max
Skewness
Kurtosis
KS test
–0.227
0.519
12.58
25.20
90.40
0.166
0.25
5.91
6.00
44.00
–0.346
0.638
0.067
0.42
10.03
1.60
47.60
0.484
–0.087
0.045
7.36
0.04
0.91
4.32
8.33
7.36
0.04
0.000
DS m–1
0.62
0.02
0.42
0.12
4.32
3.55
19.76
0.000
OM
%
1.52
0.04
0.85
0.11
6.78
1.88
8.87
0.000
Carbonates content Available P
CaCO3 P
% mg kg–1
19.70 22.09
0.78 0.77
18.72 18.46
0.00 1.58
76.60 172.02
0.707 1.88
–0.474 22.11
0.000 0.000
Available K
K
Mg kg–1
162.79
4.66
111.27
10.00
1200.00
3.28
20.91
0.000
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Table 3 Descriptive statistics of the heavy metal content Heavy metal
Symbol
Unit
Descriptive statistics Mean Statistic
SEM
–1
Std
Min
Max
Skewness
Kurtosis
KS test
Zinc
Zn
mg kg
1.34
0.05
1.14
0.10
8.62
2.603
Copper
Cu
mg kg–1
1.63
0.09
2.05
0.21
23.01
6.78
57.27
9.425
0.000 0.000
Cadmium
Cd
–1
mg kg
0.07
0.004
0.08
0.00
0.75
4.78
29.65
0.000
Nickel
Ni
mg kg–1
2.85
0.10
2.38
0.08
15.74
2.22
6.12
0.000
Table 4 DTPA-extractable soil metal concentrations (mg kg–1) Heavy Typical mean concentrations metal in Greek agricultural soilsa
Percentages greater than the typical Greek concentrations In Greek agricultural soils (%)
In this work (%)
Critical Percentages greater than levelb critical level In Greek agricultural soils (%)
Toxicity Percentages greater than level toxicity level
In this work (%)
In Greek agricultural soils (%)
In this work (%)
Zn
1.26
35
38
0.6
81
80
>100c
0
0
Cu
1.49
33
34
0.2
96
100
>75d
0
0
Cd
0.13
38
7
0.07
68
69
>0.7e
0
0.4
Ni
1.38
36
76
0.1
98
98
>15c,d
0
0.2
a
National Agricultural Research Foundation 2004
b
Tandon & Roy 2004 Khalid & Tinsley 1980
c d
Heale & Ormrod 1982
e
Prokop et al. 2003
absorption by plants is inhibited by the presence of Cu and Zn and that Cu also has an inhibitory effect on Cd uptake by plants (Kabata-Pendias & Pendias 1992). Considering this, along with the fact that Zn, Cu, Cd, and Ni concentrations were found to be higher than the typical (general) critical level (Table 4) in 80%, 100%, 70%, and 98%, respectively, of the analyzed soil samples, an efficient in the soil–plant system of these metals could be inferred. Correlation analysis was used to analyze similarities between paired data (Table 5). OM showed a positive linear relation with all the analyzed elements, apart from Cu, because of the high affinity of these metals to soil OM (Morera et al. 2001). Furthermore, humic substances in organic soils can serve as strong reducing and complexing agents and can influence the processes controlling mobilization of many toxic metals (Gough et al. 1996). The formation of stable Cu complexes with humic substances can explain why no significant correlation of extractable Cu with OM content was found (Kabbata-Pendias & Pendias 1992). The clay content exhibited a positive relation with Ni and Cd and a negative one with Zn, which is positively correlated with the sand content, because of the higher
availability of Zn that is absorbed by sandy soils. The magnitude of Ni correlation with clay content suggests that this soil component is an important sink of Ni in the studied soils, which is consistent with the data published by Chen et al. (1999). Soil pH correlated more strongly with Ni because soil pH controls Ni concentration in soils (Gupta & Gupta 1998). In fact, Berrow and Burridge (1979) reported that an increase of soil pH from 4.5 to 6.5 decreased the Ni content of oats grain by a factor of approximately 8. This justifies the negative correlation of pH and Ni in the examined soils. EC showed a linear relation only with Zn content. The substitution of Na in the exchange positions can produce desorption and higher mobility of Zn. This result may suggest a higher bioavailability of Zn in some soils with salinity problems (Kabbata-Pendias & Pendias 1992). Soil carbonate content is only related to Cd because of the higher affinity of Cd to react with carbonates producing CdCO3 (Kabata-Pendias & Pendias, 1992). Available P was shown to correlate well with Zn and poorly with Cd, which could be because of the presence of these heavy metals in contaminants, such as P fertilizer
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Table 5 Correlation coefficients, (r), of elemental concentrations with soil properties and among elemental concentrations Soil properties S
Si
C
pH
EC
OM
CaCO3
P
K
Zn
Cu
Cd
S
1
Si
–0.622** 1
C
–0.887** 0.191** 1
pH
–0.486** 0.170** 0.509** 1
EC
NS
NS
OM
NS
0.125** NS
NS
1
CaCO3
–0.348** 0.107*
0.373** 0.526**
NS
0.141** 1
P
NS
NS
NS
0.142** 0.358** NS
K
0.225**
0.132** 0.204** 0.195**
0.116** 0.432** 0.161** 0.427** 1
Zn
0.114**
NS
–0.106* NS
0.140** 0.174** NS
0.269** 0.181** 1
Cu
NS
NS
NS
0.089*
NS
NS
NS
Cd
NS
NS
0.103*
0.133**
NS
0.157** 0.155** 0.097*
0.252** 0.197** 0.138** 1
Ni
–0.224** –0.092* 0.336** –0.142** NS
0.254** NS
0.177** NS
NS
0.120** NS –0.084*
Ni
1
NS
1
NS
0.112** 0.125** 1 NS
0.145** 1
C = clay content; NS = not significant; S = sand content; Si = silt content ** Correlation is significant at the 0.01 level * Correlation is significant at the 0.05 level
(Prokop et al. 2003). The same applies for the correlation of available K with all of the analyzed metals. Finally, a significant correlation was found among Zn, Cu, and Cd, although Ni was found to be correlated only with Cd. This suggests that the metals have a similar origin and that cultivated soils were contaminated simultaneously by these heavy metals. The levels of the metals in some of the examined samples, and the small magnitude of correlation coefficients obtained from the correlation analysis between the metals and the soil properties, indicate an anthropogenic rather than lithogenic origin of these metals. This is because lithogenic metals show higher correlation with soil properties (Chen et al. 1999). Nevertheless, this inconsistent pattern of heavy-metal concentration is a common phenomenon observed in soils. It has been reported by other investigators who did not observe any consistent relation between heavy-metal concentrations and clay content, OM, carbonate content, pH, and EC (Chlopecka et al. 1996).
Conclusion The results obtained in this work increase our knowledge of heavy-metal contents and their possible source in the agricultural soils of Servia Municipality in Western Macedonia, Greece. From the present investigation, it was discovered that the mean DTPA-extractable concentration levels of four major phytotoxic metals (Cd, Cu, Ni, and Zn) in 570 representative samples of Servia’s municipality
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surface soil were greater than the critical level for plant deficiency in the majority of the examined samples (>69%). Although only 0.4% and 0.2% of the analyzed soil samples exhibited Cd and Ni concentrations, respectively, these levels were higher than those suggested by other investigators to cause plant toxicity. The small magnitude of correlation coefficients between the analyzed metals and soil properties suggest that these elements originated from anthropogenic sources, such as fertilizers, automotive emissions, and coal-burning emissions from the lignite power station located close to the area of investigation. The last source is more probable for Ni because its value exceeded the typical levels found in Greek agricultural soils in 76% of the examined soil samples. Furthermore, according to the data reported by other investigators, Ni is contained in high concentrations in the fly ash produced by Kozani’s power stations. These results highlight the need for establishing soil-quality standards for heavy metals to declare soils affected by human-induced pollution. However, to separate natural from anthropogenic factors influencing trace-element concentrations in soils, normalization of the data based on weather- or leach-resistant reference elements is needed. Further knowledge about other municipalities of the prefecture of Kozani, to which the investigation is expected to be expanded in the near future, would enlarge and improve the basis for proposing agricultural soil-quality standards at regional levels according to the European Strategy for Soil Protection. Acknowledgments The authors acknowledge that this investigation was carried out as part of the integrated soil mapping of the agri-
Environ Manage (2007) 40:719–726 cultural soils of Kozani’s prefecture. Financial support was provided by the Hellenic Ministry of Macedonia-Thrace.
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