Research Article Received: 7 August 2013
Revised: 29 November 2013
Accepted article published: 4 December 2013
Published online in Wiley Online Library: 15 January 2014
(wileyonlinelibrary.com) DOI 10.1002/jsfa.6515
Heavy metals in agricultural landscapes as hazards to human and ecosystem health: a case study on zinc and cadmium in drainage channel sediments Radovan Savic,a Gabrijel Ondrasekb∗ and Jasmina Josimov-Dundjerskia Abstract BACKGROUND: In agricultural systems, heavy metals pose severe risks to the health of soil–plant–animal–human continuum. Drainage channels, as integral components of agricultural landscapes, contain sediment material that can be both a source and a sink of metals and other toxic/persistent elements due to its highly reactive interfaces and strong binding affinity. The drainage channel network in a case study area of Vojvodina (Serbia) is not appropriately protected from contamination, nor is it maintained regularly (e.g. by desilting), thus endangering and potentially decreasing the ecological value of surrounding water and agricultural land resources, i.e. exposing food production to potential contaminants. In this study (2004–2012), Cd and Zn concentrations were analysed in 100 samples from 46 drainage channels sediments spread along the areas of the most intensive agricultural land use in Vojvodina. RESULTS: Among the samples measured, 5% had Cd and 14% had Zn concentrations above the maximally permitted levels, indicating that some drainage channel sections have been exposed to different point and non-point source pollutants. The maximum detected concentrations of the analysed elements were >50% (Zn) and were as much as 11-fold (Cd) higher than their remediation values. CONCLUSION: There is a strong need for the establishment of qualitative monitoring of channel sediment media in agroecosystems closely linked with complex pollution sources (intensive agriculture, industry, urban zones). c 2013 Society of Chemical Industry Keywords: drainage channels; sediments; trace elements; food production; cadmium; zinc
INTRODUCTION
466
Some channels and/or their sections of the studied area (Vojvodina, Serbia), are exposed to different diffuse or point contamination sources leached from the surrounding arable land area (fertilisers, pesticides) or released directly to the melioration drainage system channel networks (industrial or municipal effluents, etc.)1 (Fig. 1). Given specific hydro-technical properties of the drainage system such as relatively low land slopes and low water velocities and flows, over time a significant portion of sediment materials has been created along the drainage channel network.2,3 Under such circumstances, sediment material can generally be defined as an essential dynamic and active solid phase of hydro-ecosystems which poses very strong adsorption potential, representing at the same time a sink and a source of toxic and persistent anthropogenic components.4,5 Unfavourable influences of sediment media are exposed to residential biota, in particular channel networks as well as surrounding areas along channels that usually serve for deposition of sediment materials after desilting of the channel.6,7 Besides, these influences can be manifested in the form of overloading of channel sediments with potentially toxic trace elements, as one of the most dominant environmental contaminants8,9 (Fig. 1). J Sci Food Agric 2015; 95: 466–470
In this study, particular attention was dedicated to zinc (Zn) and cadmium (Cd) concentrations in ameliorative drainage channel sediments in Vojvodina near highly productive agricultural land areas. Namely, the main emitters of excessive amounts of trace metals to environment have been industry, urbanisation and intensive agriculture (Fig. 1). The cycling of Zn/Cd through agricultural eco-systems is complex and influenced by different factors, including soil pH, organic matter content, soil salinity and many other factors.10 However, recent studies suggest agriculture on metal-contaminated land can increase a risk of toxic and nonessential elements such as Cd entering the human food chain at the expense of some essential metals such as Zn.11–13
∗
Correspondence to: Gabrijel Ondrasek, University of Zagreb, Faculty of Agriculture, Svetosimunska 25, 10000 Zagreb, Croatia. E-mail: [email protected]
a University of Novi Sad, Faculty of Agriculture, Trg Dositeja Obradovica 8, Novi Sad, Serbia b University of Zagreb, Faculty of Agriculture, Svetosimunska 25, 10000, Zagreb, Croatia
www.soci.org
c 2013 Society of Chemical Industry
Hazards of heavy metals in agro-ecosystems
www.soci.org
Figure 1. The most common inputs (full arrows) and outputs (dashed arrows) of metals in agro-ecosystems (adapted after Ondrasek and Rengel10 and references therein).
MATERIAL AND METHODS
J Sci Food Agric 2015; 95: 466–470
RESULTS AND DISCUSSION During the investigation period, channels of the study area were exposed to different external influences. Among others, channels that were more exposed to the impact of different pollutants – in terms of either the number of pollutants that are discharged into them in used water or the type of pollution – were also selected. The largest part of the catchment area for the investigated channels represents agricultural arable land, but some channel sections are situated alongside urban or industrial areas, collecting untreated municipal and/or industrial waste waters3 (Fig. 1). The observed channels have relatively low hydraulic properties, with an average depth of 1–1.5 m and water flow mostly up to 1 m3 s−1 . The observed Zn and Cd belong to a wide group of trace metal elements that can be found in drainage channel sediments in high concentrations and thus significantly damage the environmental conditions.23–25 They can remain in the environment for an extremely long time, imposing biotoxic and other adverse effects.26–28 Their presence in the sediments can be natural or more often of anthropogenic origin.2,3 Their negative effects occur instantly after inflow into the waters or cumulatively by deposition onto sediments. By desilting sediment materials (in practice mostly to surrounding croplands), trace metals reach edible crop tissues, that is, the human food chain, relatively easily.21,27,29 Recently, it was demonstrated that bio-geochemistry of Zn and Cd may vary distinctly in relatively homogenous environmental conditions (e.g. very similar pH, temperature and organic matter content), thus influencing mobility and availability, i.e. toxicity of Zn/Cd in the soil–plant–animal continuum.10 For instance, the soil mobility and plant uptake of Cd and Zn are strongly dependent on their chemical speciation and distribution in the rhizosphere, principally on concentration of free metal forms (Cd2+ , Zn2+ ), although some inorganic and organic metallo-complexes (e.g. cadmium–chlorides, cadmium–fulvic acid complexes) may also need to be considered from the standpoint of food safety and security.27
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Vojvodina is spread over a total of 2.15 million ha, of which over 75% is predominantly arable, and lowland areas, very susceptible to the formation of deposits material in natural or artificial hydro-systems such as drainage channels. Of the total agricultural land of 1.61 Mha, around 98% (1.58 Mha) represent arable land areas (crops and gardens) with a domination of cereals (66%, or 1.04 Mha) rather than industrial (22%, or 0.35 Mha) and vegetable/forage crops (10%, or 0.16 Mha), whereas the rest of 2% (31 600 ha) are orchards and vineyards.14 The total length of the drainage channel network in Vojvodina is over 20 000 km, which is equivalent to 10 m per ha.3 Sediment samples were collected from drainage channels in Vojvodina area (46◦ 11 to 44◦ 37 N; 18◦ 51 to 21◦ 34 E) in the period from 2004 to 2012, immediately before the regular desilting operations. The main part of the analysed channel sections was overspread along the arable agricultural land areas, and the remaining part passed very close to urban and industrial zones, collecting untreated municipal/industrial wastewaters and effluents, as well as drained (leached) waters from arable fields (Fig. 2). At each location at least two sediment samples were taken. In total, 100 sediment samples from 46 channel locations (Fig. 2) were analysed for Cd and Zn concentrations. All sediment samples were collected from the bottom of the channels in a disturbed state by using bottom dredge, and then analysed in the accredited soil laboratory of the Institute of Field and Vegetable Crops, Novi Sad. Sediment samples were formed by deposition of mostly mineral materials, created in situ over 5 years (an expected period for desilting in the study area) as a layer of 0.2–0.5 m thickness. During the sampling a water depth in analysed channels varied between of 0.5 and 1.0 m. Total Cd and Zn concentrations in sediment samples were determined by microwave-assisted digestion in accordance with the USEPA Method 3051A15 using a Milestone Ethos 1 microwave sample preparation system (Milestone Srl., Sorisole (BG) - Italy). Analyses were subsequently performed using inductively coupled plasma–optical emission spectroscopy (ICP-OES) (Varian Vista Pro-axial; Varian Inc., Varian Australia Pty Ltd., Mulgrave, Victoria). Quality control was carried out periodically using the The Institute for Reference Materials and Measurements (IRMM) Bureau Communautaire de Reference (BCR) reference materials CRM-141R
and CRM-142R. Recoveries were within ±10% of the certified values. Potential toxicity due to possible excess concentrations of heavy metals was assessed according to the criteria given by the regulations on limit values of pollutants in surface- and groundwaters and sediments listed in the Official Gazette Republic of Serbia16 (Table 1). Basic principles and reference values which are stipulated in the Official Gazette Republic of Serbia16 are almost identical to the criteria used for sediment classification in the Netherlands17 and very similar to some other classifications.18–20 For instance, the terms for prescribed reference values of trace metals in sediments are defined as follows: (1) ‘target value’ is a reference value for pollutant concentration in sediment below which negative impacts on the environment are negligible and represents a long-term sediment quality goal; (2) ‘maximum allowed concentration (MAC)’ is the concentration of a single pollutant or group of pollutants above which negative impacts on the environment are probable; and (3) ‘remediation value’ is the reference value for pollutant concentration in sediments above which there is a risk to aquatic ecosystems and human and animal health which is not acceptable. In sediment samples descriptive statistics as well as correlation matrices (for Zn, Cd and some other metal elements – Cr, Ni, Cu, Pb)21,22 were determined using the Statistica software package (StatSoft Releases Version 12; StatSoft, Inc., Tulsa, Oklahoma).
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R Savic, G Ondrasek, J Josimov-Dundjerski
Figure 2. A map of the studied area with all sampling points, sampling points within urban/industrial zones and at locations where Cd and Zn concentrations in sediments were above the maximum allowed concentration (MAC). Table 1. Limit values for sediment status and quality assessment16 and descriptive statistics for cadmium and zinc concentrations in observed drainage channel sediments (n = 100) Limit values Trace metal (mg kg−1 ) Cadmium Zinc
Target value
MAC
0.8 140
6.4 430
Statistical values Remediation value 12 720
Min
Max
Mean
0.0 11.9
134.7 1084.0
4.04 202.74
SD 16.33 235.07
MAC, maximum allowed concentration.
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Results obtained in studies of the properties of channel sediments in Vojvodina confirmed the excessive presence of observed Cd and Zn in some drainage channels; that is, their total concentrations were significantly above the MAC or even above the remediation value, with potential risk for the environmental conditions (Fig. 2). In the observed channel sediments, high Cd concentrations (21.7–134.7 mg kg−1 ) were recorded in 5% of samples (Fig. 3). Generally, Cd varied in the range of MAC
TV
14% > MAC
800
RV
600 MAC
400
TV
200
0
0 0
20 40 60 80 Number of samples (%)
100
0
20 40 60 80 Number of samples (%)
100
Figure 3. Cd and Zn concentrations in the channel sediments in relation to the critical values (RV, remediation value; MAC, maximum allowed concentration; TV, target value) (n = 100).
J Sci Food Agric 2015; 95: 466–470
As
(Zn and)
(Cd and)
Ni Pb Cu Cr Zn Cd 10
8 6 4 2 0 2 4 Coincidence of Cd and Zn with other trace metals (Number of samples %)
6
Figure 4. The co-occurrence of Cd and Zn and some other trace elements (As, Ni, Pb, Cu and Cr) at concentrations above the maximum allowed concentration (MAC).
Table 2. Correlation matrix (Pearson) between Cd and Zn and concentrations of some other trace metals (n = 100) Parameter Cd Zn
Cd — 0.40∗
∗ Significant: α = 0.05, df
Zn
Cr ∗
0.40 —
∗
0.84 0.36
Ni
Cu
0.33 0.33
0.36 0.78∗
Pb 0.63∗ 0.61
= n − 2, P < 0.0001.
Most of the analysed sediment samples have very low contents of observed metals, lower than the target value or MAC. These concentrations are at the natural background level and do not pose a special threat to the environment, so desilting of sediment media from channels and their deposition in the surrounding area can be performed without any special protective measures. However, due to the relatively high concentrations of heavy metals in sediments in some sections and subsequent interactive processes (e.g. metallo-complexation) that occur in water and sediments, unfavourable effects such as substantial enrichment of cropped topsoils by metals, can be expected in the case of sediment desilting and deposition in surrounding agricultural areas.
CONCLUSIONS Results obtained in this study confirmed the excessive concentration of Cd (>MAC in 5% of samples) and Zn (>MAC in 7% and > remediation value in 7% of samples) in some drainage
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Topola, Kikinda (two samples), Pancevo and Ruma (Fig. 2). The elevated element contents recorded in the sediment samples of those places can be attributed to various anthropogenic sources such as industrial facilities, i.e. their effluents, as well as the absence of municipal/industrial waste water treatment plants on this area. The results show that the content of analysed metals was below the target value in most sediment samples, that is, in about 50% of samples for Cd and about 60% of samples for Zn (Fig. 3). A significant number of samples showed concentrations of the analysed elements above the target value, but still below MAC (46% of samples for Cd and 25% of samples for Zn). Therefore, it can be concluded that the observed concentrations of Cd in 95% of samples for Cd and Zn in 86% of samples for Zn do not represent a potential threat to the environment (Fig. 2). Also, analysis of the occurrence of excessive Cd and Zn concentrations indicated the typical situation in which these elements usually occur not alone (singly) in the sediment samples in concentrations above MAC but together with higher concentrations of some other metals (Fig. 4). The coincidence of Cd and Zn with some other observed metals in channel sediments in concentrations above MAC is shown in Fig. 4. For instance, it was confirmed that in concentrations above MAC, Cd often occurs together with Cr (in all five samples) and Zn (in three samples). Excessive Zn concentrations in sediments most often coincide with high Cu (nine samples), Cr, and Ni contents (for six samples) (Fig. 4). In general, excessive (above MAC) concentrations of Cu (range, 116–347 mg kg−1 ; MAC = 110 mg kg−1 ), Cr (range, 282–11540 mg kg−1 ; MAC = 240 mg kg−1 ), Ni (range, 44.1–829 mg kg−1 ; MAC = 44 mg kg−1 ), and Pb (322 mg kg−1 ; MAC = 310 mg kg−1 ) were recorded in 17%, 14%, 10% and 1% of observed sediment samples, respectively (data not shown). All excessive concentrations of observed trace elements exceeded their levels in uncontaminated pedospheres,10 i.e. were two orders of magnitude higher (e.g. Cr) or greater compared to their abundance in the continental lithosphere,30,31 confirming contamination processes in channel sediments. For all sediment samples, not just those with high trace metal concentrations, correlations of observed Cd, Zn, and some other trace metals are given in Table 2. The strongest correlations are identified between concentrations of Cd and Cr (correlation coefficient r = +0.84 high correlation) and Cd and Pb (r = +0.63 moderate correlation), while Zn is most strongly correlated with Cu (r = +0.78 high correlation) and Pb (r = +0.61 moderate correlation) (Table 2). Detected positive correlation between different trace elements is one of very reliable indication of their mutual sources.10,21,22
www.soci.org channel sediments. Also, significant positive correlation between Cd and Zn (and some other trace metals) indicate their mutual origin, such as industrial/municipal waste waters and effluents on this area. Sediments contaminated with metals may pose serious problems for water management, agriculture and the environment in general. Therefore, it can be concluded that a real need for the establishment of continuous quality monitoring of sediment media exists. Monitoring should be focussed primarily on the channels that are exposed to the influence of various point sources and diffuse pollutants. Detailed research should determine the type and intensity of excessive sediment pollution and the reasons for it. After that the inflow of untreated industrial and municipal wastewater should be limited and controlled and measures to reduce the influence of the spread of diffuse pollution should be implemented.
ACKNOWLEDGEMENTS This study was partly supported by the Basileus Project funded by ¨ the European Union. We are very grateful to Dr Thomas Doring as well as an anonymous reviewer for their valuable discussions, comments and suggestions.
REFERENCES 1 Dragovic S, Maksimovic L, Pantelic S and Pantelic P, History of Drainage and Irrigation in Vojvodina – The Province of Serbia and Montenegro. Integrated Land and Water Resources Management in History. German Water History Association, Siegburg, Germany, pp. 133–150 (2005). 2 Savic R, Maksimovic L, Cimpeanu S, Bucur D, Ondrasek G, Vasin J, et al., Hazardous and harmful substances in sediments of the Jegricka stream. J Food Agric Environ 11:1152–1156 (2013). 3 Savic R, Belic A and Pantelic S, Comparative review of sediment properties from drainage canals. Pol J Environ Stud 22:849–859 (2013). 4 Heise S and Forstner U, Risk assessment of contaminated sediments in river basins – Theoretical considerations and pragmatic approach. J Environ Monit 9:943–952 (2007). 5 Forstner U and Salomons W, Trends and challenges in sediment research 2008: The role of sediments in river basin management. J Soils Sediments 8:281–283 (2008). 6 Netzband A, Sediment management – An essential element of river basin management plans. J Soils Sediments 7:117–132 (2007). 7 Salomons W, Linking soils, sediments and catchment ecosystems. J Soils Sediments 8:67–68 (2008). 8 Yang Z, Wang Y, Shen Z., Niu J and Tang Z, Distribution and speciation of heavy metals in sediments from the mainstream, tributaries, and lakes of the Yangtze River catchment of Wuhan, China. J Hazard Mater 166:1186–1194 (2009). 9 Singh BR, Gupta SK, Azaizeh H, Shilev S, Sudre D, Song WY, et al., Safety of food crops on land contaminated with trace elements. J Sci Food Agric 91:1349–1366 (2011). 10 Ondrasek G and Rengel Z, The role of soil organic matter in trace elements bioavailability and toxicity, in Abiotic Stress Responses in Plants: Metabolism, Productivity and Sustainability, ed. by Ahmad P and Prasad MNV. Springer, New York, pp. 403–423 (2012).
R Savic, G Ondrasek, J Josimov-Dundjerski 11 Audry S, Schafer J, Blanc G and Jouanneau J, Fifty-year sedimentary record of heavy metal pollution (Cd, Zn, Cu, Pb) in the Lot River reservoirs (France). Environ Pollut 132:413–426 (2004). 12 Lair GJ, Gerzabek MH and Haberhauer G, Retention of copper, cadmium and zinc in soil and its textural fractions influenced by long-term field management. Eur J Soil Sci 58:145–1154 (2007). 13 De Vries W, Romkens PFAM and Bonten LTC, Spatially explicit integrated risk assessment of present soil concentrations of cadmium, lead, copper and zinc in the Netherlands. Water Air Soil Pollut 191:199–215 (2008). 14 Statistical Office of the Republic of Serbia, Agriculture 2009, Bulletin 523, Belgrade (2010). 15 US Environmental Protection Agency (US EPA), Microwave Assisted Acid Digestion of Sediments, Sludges, Soils, and Oils, Method 3051a, 2nd edition, Revised 2007. US EPA, US Government Print Office, Washington DC (1997). 16 Official Gazette, Republic of Serbia, Regulation on limit values for pollutants in surface and ground waters and sediments, and the deadlines for their achievement. 50. Regulation number 1343, Belgrade, Serbia, pp. 10–16 (2012) 17 Kelderman P, Pollution sources and abatement measures for dredged sediments in the city of Delft (The Netherlands). Eur Water Manag Online 04:1–13 (2002). 18 Burton GA, Sediment quality criteria in use around the world. Limnology 3:65–75 (2002). 19 De Temmerman LO, Hoenig M and Scokart PO, Determination of ‘normal’ levels and upper limit values of trace elements in soils. J Plant Nutr Soil Sci 147:687–694 (2007). 20 Sekabira K, Origa HO, Basamba A, Mutumba G and Kakudidi E, Assessment of heavy metal pollution in the urban stream sediments and its tributaries. Int J Environ Sci Technol 7:435–446 (2010). 21 Ekengele NL, Myung CJ, Ombolo A, Ngounou N, Ekodeck G and Mbome L, Metals pollution in sediments from river Mingoa, Cameroon. Geosci J 12:337–347 (2008). 22 Ruilian YU, Xing Y, Yuanhui Z, Gongren HU and Xianglin TU, Heavy metal pollution in inter-tidal sediments from Quanzhou Bay, China. J Environ Sci 20:664–669 (2008). 23 Baran S, Oleszczuk P, Lesiuk A and Baranowska E, Trace metals and polycyclic aromatic hydrocarbons in surface sediment samples from the Narew river (Poland). Pol J Environ Stud 11:299–305 (2002). 24 Awofolu OR, Mbolekwa Z, Mtshemla V and Fatoki OS, Levels of trace metals in water and sediments from Tyume River and its effects on an irrigated farmland. Water SA 31:87–94 (2005). 25 Alexakis D, Diagnosis of stream sediment quality and assessment of toxic element contamination sources in East Attica, Greece. Environ Earth Sci 63:1369–1383 (2011). 26 Beg KR and Ali S, Chemical contaminants and toxicity of Ganga River sediment from up and down stream area at Kanpur, Am J Environ Sci 4:362–366 (2008). 27 Ondrasek G, Romic D, Rengel Z, Romic M and Zovko M, Cadmium accumulation by muskmelon under salt stress in contaminated organic soil. Sci Tot Environ 407:2175–2182 (2009). 28 Kelderman P, Sediment pollution, transport, and abatement measures in the city canals of Delft, the Netherlands. Water Air Soil Pollut 223:4627–4635 (2012). 29 Martin CW, Heavy metal storage in near channel sediments of the Lahn River, Germany. Geomorphology 61:275–285 (2004). 30 Taylor SR and MacLennan SM, The Continental Crust: Its Composition and Evolution. Blackwell, Oxford (1985). 31 McLennan SM, Relationships between the trace element composition of sedimentary rocks and upper continental crust. Geochem Geophys Geosys 2:2000GC000109 (2001).
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J Sci Food Agric 2015; 95: 466–470
Revised: 29 November 2013
Accepted article published: 4 December 2013
Published online in Wiley Online Library: 15 January 2014
(wileyonlinelibrary.com) DOI 10.1002/jsfa.6515
Heavy metals in agricultural landscapes as hazards to human and ecosystem health: a case study on zinc and cadmium in drainage channel sediments Radovan Savic,a Gabrijel Ondrasekb∗ and Jasmina Josimov-Dundjerskia Abstract BACKGROUND: In agricultural systems, heavy metals pose severe risks to the health of soil–plant–animal–human continuum. Drainage channels, as integral components of agricultural landscapes, contain sediment material that can be both a source and a sink of metals and other toxic/persistent elements due to its highly reactive interfaces and strong binding affinity. The drainage channel network in a case study area of Vojvodina (Serbia) is not appropriately protected from contamination, nor is it maintained regularly (e.g. by desilting), thus endangering and potentially decreasing the ecological value of surrounding water and agricultural land resources, i.e. exposing food production to potential contaminants. In this study (2004–2012), Cd and Zn concentrations were analysed in 100 samples from 46 drainage channels sediments spread along the areas of the most intensive agricultural land use in Vojvodina. RESULTS: Among the samples measured, 5% had Cd and 14% had Zn concentrations above the maximally permitted levels, indicating that some drainage channel sections have been exposed to different point and non-point source pollutants. The maximum detected concentrations of the analysed elements were >50% (Zn) and were as much as 11-fold (Cd) higher than their remediation values. CONCLUSION: There is a strong need for the establishment of qualitative monitoring of channel sediment media in agroecosystems closely linked with complex pollution sources (intensive agriculture, industry, urban zones). c 2013 Society of Chemical Industry Keywords: drainage channels; sediments; trace elements; food production; cadmium; zinc
INTRODUCTION
466
Some channels and/or their sections of the studied area (Vojvodina, Serbia), are exposed to different diffuse or point contamination sources leached from the surrounding arable land area (fertilisers, pesticides) or released directly to the melioration drainage system channel networks (industrial or municipal effluents, etc.)1 (Fig. 1). Given specific hydro-technical properties of the drainage system such as relatively low land slopes and low water velocities and flows, over time a significant portion of sediment materials has been created along the drainage channel network.2,3 Under such circumstances, sediment material can generally be defined as an essential dynamic and active solid phase of hydro-ecosystems which poses very strong adsorption potential, representing at the same time a sink and a source of toxic and persistent anthropogenic components.4,5 Unfavourable influences of sediment media are exposed to residential biota, in particular channel networks as well as surrounding areas along channels that usually serve for deposition of sediment materials after desilting of the channel.6,7 Besides, these influences can be manifested in the form of overloading of channel sediments with potentially toxic trace elements, as one of the most dominant environmental contaminants8,9 (Fig. 1). J Sci Food Agric 2015; 95: 466–470
In this study, particular attention was dedicated to zinc (Zn) and cadmium (Cd) concentrations in ameliorative drainage channel sediments in Vojvodina near highly productive agricultural land areas. Namely, the main emitters of excessive amounts of trace metals to environment have been industry, urbanisation and intensive agriculture (Fig. 1). The cycling of Zn/Cd through agricultural eco-systems is complex and influenced by different factors, including soil pH, organic matter content, soil salinity and many other factors.10 However, recent studies suggest agriculture on metal-contaminated land can increase a risk of toxic and nonessential elements such as Cd entering the human food chain at the expense of some essential metals such as Zn.11–13
∗
Correspondence to: Gabrijel Ondrasek, University of Zagreb, Faculty of Agriculture, Svetosimunska 25, 10000 Zagreb, Croatia. E-mail: [email protected]
a University of Novi Sad, Faculty of Agriculture, Trg Dositeja Obradovica 8, Novi Sad, Serbia b University of Zagreb, Faculty of Agriculture, Svetosimunska 25, 10000, Zagreb, Croatia
www.soci.org
c 2013 Society of Chemical Industry
Hazards of heavy metals in agro-ecosystems
www.soci.org
Figure 1. The most common inputs (full arrows) and outputs (dashed arrows) of metals in agro-ecosystems (adapted after Ondrasek and Rengel10 and references therein).
MATERIAL AND METHODS
J Sci Food Agric 2015; 95: 466–470
RESULTS AND DISCUSSION During the investigation period, channels of the study area were exposed to different external influences. Among others, channels that were more exposed to the impact of different pollutants – in terms of either the number of pollutants that are discharged into them in used water or the type of pollution – were also selected. The largest part of the catchment area for the investigated channels represents agricultural arable land, but some channel sections are situated alongside urban or industrial areas, collecting untreated municipal and/or industrial waste waters3 (Fig. 1). The observed channels have relatively low hydraulic properties, with an average depth of 1–1.5 m and water flow mostly up to 1 m3 s−1 . The observed Zn and Cd belong to a wide group of trace metal elements that can be found in drainage channel sediments in high concentrations and thus significantly damage the environmental conditions.23–25 They can remain in the environment for an extremely long time, imposing biotoxic and other adverse effects.26–28 Their presence in the sediments can be natural or more often of anthropogenic origin.2,3 Their negative effects occur instantly after inflow into the waters or cumulatively by deposition onto sediments. By desilting sediment materials (in practice mostly to surrounding croplands), trace metals reach edible crop tissues, that is, the human food chain, relatively easily.21,27,29 Recently, it was demonstrated that bio-geochemistry of Zn and Cd may vary distinctly in relatively homogenous environmental conditions (e.g. very similar pH, temperature and organic matter content), thus influencing mobility and availability, i.e. toxicity of Zn/Cd in the soil–plant–animal continuum.10 For instance, the soil mobility and plant uptake of Cd and Zn are strongly dependent on their chemical speciation and distribution in the rhizosphere, principally on concentration of free metal forms (Cd2+ , Zn2+ ), although some inorganic and organic metallo-complexes (e.g. cadmium–chlorides, cadmium–fulvic acid complexes) may also need to be considered from the standpoint of food safety and security.27
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Vojvodina is spread over a total of 2.15 million ha, of which over 75% is predominantly arable, and lowland areas, very susceptible to the formation of deposits material in natural or artificial hydro-systems such as drainage channels. Of the total agricultural land of 1.61 Mha, around 98% (1.58 Mha) represent arable land areas (crops and gardens) with a domination of cereals (66%, or 1.04 Mha) rather than industrial (22%, or 0.35 Mha) and vegetable/forage crops (10%, or 0.16 Mha), whereas the rest of 2% (31 600 ha) are orchards and vineyards.14 The total length of the drainage channel network in Vojvodina is over 20 000 km, which is equivalent to 10 m per ha.3 Sediment samples were collected from drainage channels in Vojvodina area (46◦ 11 to 44◦ 37 N; 18◦ 51 to 21◦ 34 E) in the period from 2004 to 2012, immediately before the regular desilting operations. The main part of the analysed channel sections was overspread along the arable agricultural land areas, and the remaining part passed very close to urban and industrial zones, collecting untreated municipal/industrial wastewaters and effluents, as well as drained (leached) waters from arable fields (Fig. 2). At each location at least two sediment samples were taken. In total, 100 sediment samples from 46 channel locations (Fig. 2) were analysed for Cd and Zn concentrations. All sediment samples were collected from the bottom of the channels in a disturbed state by using bottom dredge, and then analysed in the accredited soil laboratory of the Institute of Field and Vegetable Crops, Novi Sad. Sediment samples were formed by deposition of mostly mineral materials, created in situ over 5 years (an expected period for desilting in the study area) as a layer of 0.2–0.5 m thickness. During the sampling a water depth in analysed channels varied between of 0.5 and 1.0 m. Total Cd and Zn concentrations in sediment samples were determined by microwave-assisted digestion in accordance with the USEPA Method 3051A15 using a Milestone Ethos 1 microwave sample preparation system (Milestone Srl., Sorisole (BG) - Italy). Analyses were subsequently performed using inductively coupled plasma–optical emission spectroscopy (ICP-OES) (Varian Vista Pro-axial; Varian Inc., Varian Australia Pty Ltd., Mulgrave, Victoria). Quality control was carried out periodically using the The Institute for Reference Materials and Measurements (IRMM) Bureau Communautaire de Reference (BCR) reference materials CRM-141R
and CRM-142R. Recoveries were within ±10% of the certified values. Potential toxicity due to possible excess concentrations of heavy metals was assessed according to the criteria given by the regulations on limit values of pollutants in surface- and groundwaters and sediments listed in the Official Gazette Republic of Serbia16 (Table 1). Basic principles and reference values which are stipulated in the Official Gazette Republic of Serbia16 are almost identical to the criteria used for sediment classification in the Netherlands17 and very similar to some other classifications.18–20 For instance, the terms for prescribed reference values of trace metals in sediments are defined as follows: (1) ‘target value’ is a reference value for pollutant concentration in sediment below which negative impacts on the environment are negligible and represents a long-term sediment quality goal; (2) ‘maximum allowed concentration (MAC)’ is the concentration of a single pollutant or group of pollutants above which negative impacts on the environment are probable; and (3) ‘remediation value’ is the reference value for pollutant concentration in sediments above which there is a risk to aquatic ecosystems and human and animal health which is not acceptable. In sediment samples descriptive statistics as well as correlation matrices (for Zn, Cd and some other metal elements – Cr, Ni, Cu, Pb)21,22 were determined using the Statistica software package (StatSoft Releases Version 12; StatSoft, Inc., Tulsa, Oklahoma).
www.soci.org
R Savic, G Ondrasek, J Josimov-Dundjerski
Figure 2. A map of the studied area with all sampling points, sampling points within urban/industrial zones and at locations where Cd and Zn concentrations in sediments were above the maximum allowed concentration (MAC). Table 1. Limit values for sediment status and quality assessment16 and descriptive statistics for cadmium and zinc concentrations in observed drainage channel sediments (n = 100) Limit values Trace metal (mg kg−1 ) Cadmium Zinc
Target value
MAC
0.8 140
6.4 430
Statistical values Remediation value 12 720
Min
Max
Mean
0.0 11.9
134.7 1084.0
4.04 202.74
SD 16.33 235.07
MAC, maximum allowed concentration.
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Results obtained in studies of the properties of channel sediments in Vojvodina confirmed the excessive presence of observed Cd and Zn in some drainage channels; that is, their total concentrations were significantly above the MAC or even above the remediation value, with potential risk for the environmental conditions (Fig. 2). In the observed channel sediments, high Cd concentrations (21.7–134.7 mg kg−1 ) were recorded in 5% of samples (Fig. 3). Generally, Cd varied in the range of MAC
TV
14% > MAC
800
RV
600 MAC
400
TV
200
0
0 0
20 40 60 80 Number of samples (%)
100
0
20 40 60 80 Number of samples (%)
100
Figure 3. Cd and Zn concentrations in the channel sediments in relation to the critical values (RV, remediation value; MAC, maximum allowed concentration; TV, target value) (n = 100).
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As
(Zn and)
(Cd and)
Ni Pb Cu Cr Zn Cd 10
8 6 4 2 0 2 4 Coincidence of Cd and Zn with other trace metals (Number of samples %)
6
Figure 4. The co-occurrence of Cd and Zn and some other trace elements (As, Ni, Pb, Cu and Cr) at concentrations above the maximum allowed concentration (MAC).
Table 2. Correlation matrix (Pearson) between Cd and Zn and concentrations of some other trace metals (n = 100) Parameter Cd Zn
Cd — 0.40∗
∗ Significant: α = 0.05, df
Zn
Cr ∗
0.40 —
∗
0.84 0.36
Ni
Cu
0.33 0.33
0.36 0.78∗
Pb 0.63∗ 0.61
= n − 2, P < 0.0001.
Most of the analysed sediment samples have very low contents of observed metals, lower than the target value or MAC. These concentrations are at the natural background level and do not pose a special threat to the environment, so desilting of sediment media from channels and their deposition in the surrounding area can be performed without any special protective measures. However, due to the relatively high concentrations of heavy metals in sediments in some sections and subsequent interactive processes (e.g. metallo-complexation) that occur in water and sediments, unfavourable effects such as substantial enrichment of cropped topsoils by metals, can be expected in the case of sediment desilting and deposition in surrounding agricultural areas.
CONCLUSIONS Results obtained in this study confirmed the excessive concentration of Cd (>MAC in 5% of samples) and Zn (>MAC in 7% and > remediation value in 7% of samples) in some drainage
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Topola, Kikinda (two samples), Pancevo and Ruma (Fig. 2). The elevated element contents recorded in the sediment samples of those places can be attributed to various anthropogenic sources such as industrial facilities, i.e. their effluents, as well as the absence of municipal/industrial waste water treatment plants on this area. The results show that the content of analysed metals was below the target value in most sediment samples, that is, in about 50% of samples for Cd and about 60% of samples for Zn (Fig. 3). A significant number of samples showed concentrations of the analysed elements above the target value, but still below MAC (46% of samples for Cd and 25% of samples for Zn). Therefore, it can be concluded that the observed concentrations of Cd in 95% of samples for Cd and Zn in 86% of samples for Zn do not represent a potential threat to the environment (Fig. 2). Also, analysis of the occurrence of excessive Cd and Zn concentrations indicated the typical situation in which these elements usually occur not alone (singly) in the sediment samples in concentrations above MAC but together with higher concentrations of some other metals (Fig. 4). The coincidence of Cd and Zn with some other observed metals in channel sediments in concentrations above MAC is shown in Fig. 4. For instance, it was confirmed that in concentrations above MAC, Cd often occurs together with Cr (in all five samples) and Zn (in three samples). Excessive Zn concentrations in sediments most often coincide with high Cu (nine samples), Cr, and Ni contents (for six samples) (Fig. 4). In general, excessive (above MAC) concentrations of Cu (range, 116–347 mg kg−1 ; MAC = 110 mg kg−1 ), Cr (range, 282–11540 mg kg−1 ; MAC = 240 mg kg−1 ), Ni (range, 44.1–829 mg kg−1 ; MAC = 44 mg kg−1 ), and Pb (322 mg kg−1 ; MAC = 310 mg kg−1 ) were recorded in 17%, 14%, 10% and 1% of observed sediment samples, respectively (data not shown). All excessive concentrations of observed trace elements exceeded their levels in uncontaminated pedospheres,10 i.e. were two orders of magnitude higher (e.g. Cr) or greater compared to their abundance in the continental lithosphere,30,31 confirming contamination processes in channel sediments. For all sediment samples, not just those with high trace metal concentrations, correlations of observed Cd, Zn, and some other trace metals are given in Table 2. The strongest correlations are identified between concentrations of Cd and Cr (correlation coefficient r = +0.84 high correlation) and Cd and Pb (r = +0.63 moderate correlation), while Zn is most strongly correlated with Cu (r = +0.78 high correlation) and Pb (r = +0.61 moderate correlation) (Table 2). Detected positive correlation between different trace elements is one of very reliable indication of their mutual sources.10,21,22
www.soci.org channel sediments. Also, significant positive correlation between Cd and Zn (and some other trace metals) indicate their mutual origin, such as industrial/municipal waste waters and effluents on this area. Sediments contaminated with metals may pose serious problems for water management, agriculture and the environment in general. Therefore, it can be concluded that a real need for the establishment of continuous quality monitoring of sediment media exists. Monitoring should be focussed primarily on the channels that are exposed to the influence of various point sources and diffuse pollutants. Detailed research should determine the type and intensity of excessive sediment pollution and the reasons for it. After that the inflow of untreated industrial and municipal wastewater should be limited and controlled and measures to reduce the influence of the spread of diffuse pollution should be implemented.
ACKNOWLEDGEMENTS This study was partly supported by the Basileus Project funded by ¨ the European Union. We are very grateful to Dr Thomas Doring as well as an anonymous reviewer for their valuable discussions, comments and suggestions.
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