Trace elements in soils and food chains of the Balkan region

Abstract

The present review summarizes the available data on the concentration of trace elements (TEs) in soils and their availability to plants with a view to reflect the quality and safety of food and fodder crops. Most soils in western Balkan countries are not contaminated. However, soils around industrial centers and historical mining sites do create concern for food and feed safety. Also high concentrations of TEs are related to their geochemical original. For example, ultrabasic rocks and serpentinites in western Serbia and western Bosnia are very rich in chromium, nickel, magnesium, iron (Fe), and cobalt, and cover an area of 5200 km². High TE concentrations caused by anthropogenic activities are also reported. In vineyard soils in Croatia, concentrations of cadmium, copper (Cu), and zinc (Zn) were much higher than their background concentrations. On the other hand, TE deficiency in plants is also prevalent in the regions. For example, Zn and Fe deficiencies in eastern parts of Croatia and northern parts of Serbia, Cu deficiency in pasture and sheep's blood at Nisici Plateau of Bosnia and Herzegovina, and selenium (Se) deficiency almost in the whole region have been observed. Therefore, information on TEs' behavior and soil factors affecting their mobility and availability is highly needed in order to separate the areas of contamination and then propose agrotechnical measures to protect the entry of TEs into the food chain. Research is also required to assess the influence of agronomic management on TE supply to plants and for achieving a better utilization of essential TEs. Concentrations of Se in wheat in Serbia are so low that if people were fed exclusively with wheat, their daily requirements for Se would not be met. There is also a need for full implementation of new food safety regulations in the Balkan countries in accordance with the legislations of the European Union.

Keywords:

• Bioavailability
• Bosnia and Herzegovina
• Croatia
• feed plants
• food plants
• Serbia

Introduction

In recent years, there has been a shift in all European countries, including the Balkan countries, from the importance of the quantity of food toward the quality and safety of food and fodder crops, with an emphasis on nutritional value and the absence of unhealthy elements. The need for information related to the quality and safety of food crops in the Balkan countries is even more strongly felt because the system of monitoring the quality of the whole food chain in these countries is still under development, and a comprehensive and systematic research on these aspects is rather limited (Djarmati, 2005; Vidojević & Manojlović, 2007). Moreover, this region has had very specific environmental pollution problems due to the burning and destruction of industrial and military targets during the war, which has resulted in the release of a number of chemicals into the environment (Djogo et al., 2003; Đurić et al., 2007; Radenkovic et al., 2008).

In some areas of the Balkans, the contamination of soil and plant materials with toxic trace elements (TEs) has been reported. The contamination of plants with cadmium (Cd) and lead (Pb) in the vicinity of mines was found in Bosnia and Herzegovina (BIH; Zenica and Kakanj) and Serbia (the Rudnik mountain; Goletić, 1999; Jakovljević & Antić-Mladenović, 2000). Similarly, high concentrations of iron (Fe), manganese (Mn), Pb, and zinc (Zn) were found in the soils of metallurgic areas of Olovo and Vareš in BIH (Medjedović, 1999; Alijagić and Šajn, 2006) and the high acidity of soils in this area enhanced the uptake of TEs by the herbaceous plant species growing in this region (Mededović, 1999). In Croatia, high concentrations of copper (Cu) and chromium (Cr) in the soils in industrial areas of Rijeka and around Bakar Bay were observed (Prohić et al., 1997). On the other hand, TE deficiency in plants has also been found in some areas of the Balkans, for example Zn and Fe deficiencies in eastern parts of Croatia (Kovacevic et al., 1988; Jug et al., 2008) and northern parts of Serbia (Marić et al., 1967), Cu deficiency in pasture and sheep's blood at Nisici Plateau (BIH; Muratović et al., 2005), and selenium (Se) deficiency in almost whole Balkan region (Maksimović et al., 1992; Antunović et al., 2005; Muratović et al., 2007) have been observed.

Essential and toxic TEs enter the food chain through soil enriched with them by weathering of geological materials or through contamination caused by industrial activities, consumption of petrol, waste deposition, and use of compost and other waste materials as fertilizers (Adriano, 2001; Kabata-Pendias & Mukherjee, 2007). Some of the TEs, Cu, Zn, Mn, Fe, molybdenum (Mo), boron (B), and nickel (Ni) are essential for plant growth. However, these elements can become toxic to plants at high concentrations. Other TEs such as Cd, Pb, Cr, Ni, mercury (Hg), and arsenic (As) are toxic even at low concentrations. Some TEs, such as cobalt (Co), Se, and iodine (I), are not essential for plants’ growth but are required by animals and humans (He et al., 2005).

The uncontrolled input of TEs is undesirable because once accumulated in the soil, they can be taken up by plants and they enter the food chains, entailing a serious risk to animal and human health (McLaughlin & Singh, 1999; Wilkinson et al., 2003). On the other hand, microelements, essential for animal and human nutrition, if deficient may cause substantial metabolic disorders (impairments of physical growth, immune system, cognitive development, and increase of anemia and maternal mortality; Welch & Graham, 2000). As a consequence of low level of Se in parent material in Serbia, low concentrations of Se in soils and food are reflected in very low Se status of both domestic animals and human population. In some areas, extremely low Se values were found in serum and scalp hair, approaching those in the low-Se belt in China (Maksimović et al., 1992). It is assumed that very low Se status of human population could be a risk factor in the etiology of endemic nephropathy and urinary tract tumors in endemic areas (Maksimović et al., 1992).

High total concentration of TEs in soil usually implies higher probability of TEs entering the food chain and also a higher probability that they can affect the environment and cause other ecological problems (Kabata-Pendias & Pendias, 1992). However, the mobility and uptake of metals depend not only on the total concentrations of the elements in the soil, but plant uptake is also the result of competition among plant roots, microorganisms and soil solution and solid phases of soil for the available fractions of the total element (McLaughlin et al., 1998). The electrochemical properties of the solid phase directly influence the behavior of soil elements, especially in both soil solution composition and in the bioavailability of these elements (Charlatchka & Cambier, 2000; Kabata-Pendias & Mukherjee, 2007).

As information about the bioavailability of essential and toxic TEs in soils of the Balkan region is generally scarce, the objective of this paper is to summarize the available data to obtain a general picture of the concentration and accumulation of TE in soils and plants, and to assess the contribution of bioavailable forms of TE in soil toward the quality and safety of food and fodder crops.

Geographic and geologic description of the area

Serbia, BIH, and Croatia are countries in the Balkans, a historical and geographical region of southeastern Europe, and in the Pannonian Plain, a region of central Europe (Croatia and Serbia; Figure 1). The area is characterized by great heterogeneity of geological base, climate, vegetation, and paedo-fauna, resulting in the formation of extremely heterogenic soils.

Figure 1.  The main metallogenic provinces in Croatia, Bosnia and Herzegovina, and Serbia, and locations of investigated sites. Locations: 1 – Zlatibor (Serbia); 2 – Sv. Jakob (Croatia); 3 – Istrian Penninsula (Croatia); 4 – Sinjsko polje (Croatia); 5 – Velika Morava River Valley (Serbia); 6 – Rudnik (Serbia); 7 – Dugi Rat (Croatia); 8 – Zenica, Vareš, and Iliaš (Bosnia and Herzegovina); 9 – Petrovo (BIH); 10 – Industrial areas (Serbia); Tuzla (BIH); Luke (BIH); 13 – Banja Luka (BIH); 14 – NW Croatia; 15 – Srem (Serbia); 16 – Banat (Serbia); 17 – Bačka (Serbia); 18 – Nišava (Serbia); 19 – Pozega (Croatia); 20 – Goč (Serbia); 21 – Divčibare (Serbia); 22 – Sava Basin (Croatia); 23 – Drava Basin (Croatia).

The Balkan Peninsula represents a rather complex geological and geochemical feature: diverse magmatic, metamorphic, and sedimentary formations, and large geotectonic units: (1) Neogene-Quaternary Pannonian Basin toward north; (2) two organogenic belts – the Dinaride and Carpatho-Balkanides; (3) Vardar Zone; and (4) Serbo-Macedonian Mass, between Carpatho-Balkanides and the Dinarides (Dangić & Dangić, 2007). This area is also comprised of two magmatic, metallogenic provinces: (1) Pb–Zn–Sb deposits occurring in the Dinarides, Vardar Zone, and Serbo-Macedonian Mass; and (2) Cretaceous Cu–Mo deposits occurring in the Carpatho-Balkanides. Limestone is a predominant formation in diverse sedimentary, metamorphic and magmatic rocks in Serbo-Macedonian Mass. In both of these provinces, there are a number of ore deposits that contain high amounts of TEs (Dangić & Dangić, 2007).

Agricultural land in Serbia covers ~66% of the total area. Arable land dominates by far the greatest areas under agricultural production (65%; Vidojević & Manojlović, 2007). Serbia can be divided into three major regions: (1) Vojvodina Province, a large area in the north containing fertile plains drained by the Danube and other rivers; (2) central Serbia, a hilly and densely populated area with the Morava River basin as a particularly fertile region; and (3) mountainous regions of western and eastern Serbia. Since June 1999, the southern part of Serbia, AP Kosovo and Metohija, has been under the jurisdiction of UN Interim Administration Mission in Kosovo (UNMIK) and is not covered by this study.

The territory of BIH is mainly a hilly mountainous region, with 50% of agricultural land and only <20% under intensive agriculture, most of it in lowland river valleys. However, nearly 538,500 ha, 20% of the agricultural land, has suffered some degree of environmental damage caused by erosion, fertility loss, loss of agricultural land through mining, road construction, and human settlement industry. This area has also suffered TE pollution by traffic power stations and war damage (Custovic, 2005).

Croatia covers 5.7 million ha, of which 3.2 million ha is under agriculture (56%). The Pannonian region is the largest and most important agricultural region in Croatia. However, the area of agricultural land per capita is the highest in the mountainous region, because of pastures and intensive depopulation (Bašić, 2005).

Trace elements in soil

Overview of data in the entire region

Under natural soil-forming conditions, TE content of soil originates from the parent rock. However, inputs of TEs through human activities have increased in the past decades. Mean concentration and range of TEs in soils of Balkan in comparison with their concentration in world's soils are shown in Table I. Although there are some variabilities in the concentration of TEs between various areas of the Balkans, the average values of TEs in the soils of the Balkan countries correspond to mean TE concentrations in world's soils (Xie & Lu, 2000). The results of large-scale investigations in Croatia (Miko et al., 2001; Halamić et al., 2003; Romić & Romić, 2003), BIH (Marković et al., 2006; Federal Institute of Agropedology, 2007), and Serbia (Protic et al., 2005; Antonović & Mrvić, 2008; Nešić et al., 2009) have shown that most of the investigated soils are not contaminated with TEs. However, moderate soil contamination has been noticed on a number of micro-locations caused by either geochemical factors or industrial and agricultural activities.

Table I. Mean concentrations and range (in brackets) of some trace elements in soils (mg kg⁻¹).

		South-Eastern Europe's soils
Elements	World's soils	Northwestern Croatia (n = 293)	South Dalmacia, Croatia (n = 404)	Croatia, urban soils (n = 331)	Banja Luka, rural area, BIH (n = 159)	Vojvodina, Serbia (n = 1600)	Srem, Serbia (n = 250)	South Backa, Serbia (n = 145)	Nišava catchment, Serbia (n = 345)
As	9.36	10.0 (1.8–52.7)	16.0 (1.8–52.7)	NA	12.5 (2.53–82.5)	2.19 (0.30–13.0)	8.40 (1.76–21.9)	10.3(3.26–33.1)	10.6 (1.30–114)
Cd	0.06	NA	NA	0.66 (0.25–3.85)	0.40 (0.08–2.17)	<2	0.43 (0.05–1.50)	0.20 (0.03–2.36)	1.19 (0.05–4.20)
Cr	20–200	83.0 (32–524)	126 (15–2200)	NA	42.2 (16.2–170)	30.0 (5.33–86.1)	37.9 (7.11–128)	44.8 (17.9–61.2)	24.3 (0.60–121)
Co	10–40	12.0 (2.0–38.0)	17.0 (2.0–38.0)	NA	21.0 (6.43–50.3)	NA	14.1 (3.81–35.5)	12.4 (5.29–17.3)	NA
Cu	20	26 (5–248)	67 (6–923)	20.8 (4.30–183)	29.0 (8.61–105)	17.1 (1.85–388)	27.3 (2.49–345)	26.5 (7.83–151)	19.1 (0.10–213)
Hg	0.03	0.094 (0.01–4.53)	NA	NA	0.60 (0.07–1.24)	NA	NA	NA	0.16 (0.01–1.54)
Pb	10–150	34 (15–382)	52 (9–220)	25.9 (1.00–139)	29.5 (7.49–98.1)	17.2 (3.0–73.5)	26.8 (7.11–115)	24.4 (7.26–286)	22.1 (0.10–139)
Mo	1–5	NA	NA	NA	NA	NA	NA	NA	NA
Ni	40	42 (13–427)	84 (7–288)	49.5 (1.00–282)	50.7 (14.9–396)	14.8 (1.78–62.7)	52.0 (9.28–255)	35.6 (14.9–58.5)	18.3 (0.10–61.0)
Se	0.20	NA	NA	NA	NA	NA	NA	NA	NA
Zn	10–300	92 (28–974)	113 (16–491)	77.9 (15.2–277)	79.9 (38.1–216)	60.3 (10.7–203)	64.4 (5.85–294)	74.4 (22.1–74.4)	38.4 (0.10–147)
Fe (g kg^−1)		32.8 (6.0–64.3)	39.4 (4.3–350)	27 (5.85–51.7)	NA	NA	27.1 (6.59–276)	NA	NA
Mn		622 (131–5619)	971 (96–2563)	613 (79.2–1282)	1370 (249–4093)	NA	644 (75.4–2937)	NA	NA
B		NA	NA	NA	NA	3.49^a (<0.01–15.9)	NA	NA	NA
Reference	Xie and Lu (2000)	Miko et al. (2001)	Miko et al. (2001)	Romić and Romić (2003)	Marković et al. (2006)	Ubavić et al. (1993)	Nešić et al. (2008)	Nešić et al. (2009)	Antonović and Mrvić (2008)
BIH – Bosnia and Herzegovina; NA – Not analyzed. ^aExtracted by 1 M HCl.

Geogenic anomalies in the entire region

Soils derived from parent materials abundant with TE often contain a high concentration of TEs. Ultrabasic rocks and serpentinites in western Serbia and western Bosnia, very rich in Cr, Ni, magnesium, Fe, and Co, cover an area of more than 5200 km² (Komatina, 2004), and they are also distributed in Croatia (Miko et al., 2001). According to Maksimović (1975), the contents of TEs in peridotites from Serbia and Bosnia were: Cr, 260–5000 mg kg⁻¹; Ni, 750–4000 mg kg⁻¹; Ti, 10–1250 mg kg⁻¹; V, 10–210 mg kg⁻¹; Co, 60–275 mg kg⁻¹; Mn, 300–1400 mg kg⁻¹; and Hg, 0.014 mg kg⁻¹ on average. Because ultrabasic rocks and serpentinites are extremely poor in other essential TEs, we expect high concentrations of Cr, Ni, and Pb in soils, water, and plants, but very low concentrations of biologically important microelements (Komatina, 2004). Indeed, extremely high concentrations of Ni and Cr and high concentrations of Fe, Mn, and Co were measured in soil samples from 13 locations on the Zlatibor mountain (Serbia) (Jakovljević & Stevanović, 2004; Table II). A high concentration of diethylenetriaminepentaaceticacid (DTPA)-extractable Ni (on average 181 mg kg⁻¹) caused high Ni accumulation in plants (see Table V). A considerable concentration of Cr was also measured in hay samples from that region (Stevanović et al., 2004; Table V).

Table II. Trace element concentrations in soils and their sources in areas with enchanced levels (mean and range in brackets; mg kg⁻¹).

Location, source of contamination, and reference	n	Cu	Zn	Pb	Cd	Ni	Cr	Hg	As	Co	Mn	Mo
Zlatibor (Serbia), geochemical (Jakovljević & Stevanović, 2004)	13	17. 0(10–54)	64. 0(43–153)	41. 0(30–54)	0. 6(0.5–1.0)	1456(700–2770)	599(210–975)	0. 03(0.02–0.05)	1. 9(1.2–2.9)	88. 0(20–134)	1486(420–2130)	NA
Zlatibor (Serbia), geochemical (Dragović et al., 2008)	174	8. 64(4.6–13.4)	21. 8(6.6–40.3)	41. 5(1.2–71.5)	1. 42(0.01–3.6)	320(3.4–771)	46. 3(0.01–260)	NA	NA	NA	953(206–1742)	NA
Sv. Jakob (Croatia), geochemical (Durn et al., 1999)	100	40.0±44. 0(5.0–377)	664± 1318(12–9125)	2693± 4790(9–18,188)	11.7± 26(0.25–189)	NA	NA	0.42±0. 34(0.06–1.83)	NA	NA	NA	NA
Istrian Penninsula (Croatia), geochemical (Miko et al., 1999)	45	NA	85.5± 39(40–200)	54.9± 32(18–150)	NA	57.3±41. 0(20–300)	86.4±28. 0(10–140)	NA	NA	NA	NA	NA
Sinjsko polje (Croatia), geochemical (Miko et al., 1999)	42	NA	172.6± 86(61–506)	58.9± 18(21–113)	NA	128±62. 0(43–330)	145.5±41. 0(67–278)	NA	NA	NA	NA	NA
Istra (Croatia), geochemical/anthropogenic (Prohić et al., 1997)	440	(15–361)	(40–626)	(30–720)	NA	NA	50–350	NA	NA	NA	NA	NA
V Morava river valley (Serbia), geochemical/anthropogenic (Jakovljević et al., 1997)	30	33.3±7.8	110±43.8	63.9±51.3	0.20±0.01	114±52.3	57.6–19.3	0.06±0.03	13.2±6.2	16.9±3.7	773±191	NA
V. Morava and Jasenica River Valleys and Rudnik (Serbia), geochemical/anthropogenic (Jakovljević & Antić-Mladenović, 2000)	17	56.8±11. 4(5–71.5)	141± 18(46–375)	148± 48(29.5–945)	0.82±0. 22(0.25–4.5)	189±33. 9(3.5–465)	187±46. 9(17.5–615)	NA	17.1±4. 25(5.3–86.6)	19.5±1. 74(4–32)	896±47. 5(440–1240)	NA
Dugi Rat (Croatia), ex-ferrochromium smeltery (Orešcanin et al., 2006)	10	44±14.7	415±461	76.8±86.4	NA	315±147	15,990±10,610	NA	NA	NA	24,050±10,610	NA
Zenica, Vareš and Ilijaš (BIH), metallurgic area (Alijagić & Šajn, 2006)	6	NA	(361–2434)	(267–918)	(1.5–3.5)	(114–187)	(161–271)	(0.51–5.4)	(31–91)	(16–34)	(1284–3704)	(1.8–5.5)
Zenica (BIH), metallurgic area (Alijagić, 2007)	62	53(11–92)	202(46–474)	122(19–384)	0. 78(0.3–1.8)	122(47–329)	156(34–555)	0. 22(0.05–2.97)	32. 0(11–117)	22. 0(5.0–37)	14, 240(6520–30,900)	0. 77(0.30–1.9)
Petrovo (BIH), geochemical/exposed to war activities (Đurić et al., 2007)	6	(10.7–34.1)	(51.9–339)	(9.46–197)	(1.09–3.19)	(40.6–2055)	(32.3–541)	NA	NA	NA	NA	NA
Industrial areas (Serbia), industrial (Slavkovic et al., 2004)	59	40.0±56. 4(4.0–348)	103±53. 9(34.6–268)	37.7±66. 8(1.6–436)	1.3±0. 5(0.6–3.0)	66.6±66. 9(13.7–239)	33.7±25. 1(8.8–119)	NA	10.3±1. 1(7.5–13.2)	NA	349± 206(87.5–1028)	NA
Pancevo (Serbia), industrial (Markovic et al., 2003)	6	(65.0–159)	NA	NA	NA	(37.5–55.0)	(17.5–34.0)	NA	NA	(2.0–10.0)	NA	NA
Tuzla (BIH), coal-fired power plants (Dellantonio et al., 2008)
Plane	18	49±16	82±29	22±5	0.2±0.1	368±158	228±87	NA	24±9.2	33±8.4	NA	0.4±0.2
Dreznik	37	46±16	80±17	18±2.7	0.3±0.10	418±170	323±131	NA	23±10	35±9.8	NA	0.5±0.26
Divkovci I	10	44±16	73±31	24±7.9	0.4±0.26	327±147	177±41	NA	12±8.5	29±11	NA	NA
Luke (BIH), anthropogenic (road) (Federal Institute of Agropedology, 2007)	28	36. 6(21.7–47.7)	71. 4(54–101)	94. 6(37.3–142.8)	4. 7(2.6–10.4)	NA	NA	NA	NA	21. 4(11.2–33.6)	1108(538–1556)	NA
Banja Luka (BIH), anthropogenic (Marković et al., 2006)	5	151(25.2–630)	222(73.0–803)	56. 9(16.9–205)	2. 0(0.27–8.72)	138(41.4–426)	89. 4(31.9–300)	(ND–3.34)	26. 9(8.59–86.1)	24. 0(16.3–34.7)	1243(1033–1480)	NA
Northwest Croatia, anthropogenic (vineyard) (Romić et al., 2004)	67	368± 191(29.8–700)	114±93. 7(56–420)	36.6±7. 55(19.8–53.9)	2.2±0. 71(0.62–4.57)	52.7±19. 5(20–158)	67.6± 18(42.6–134)	NA	NA	NA	573± 210(228–1253)	NA
NA – not analysed; ND – not detected; BIH – Bosnia and Herzegovina.

Besides ultrabasic rocks, the diverse mineral reserves, especially in the territories of eastern Serbia, central Serbia, northeast Bosnia, and central Bosnia, caused a local contamination of nearby vegetation, soil and water. Copper ore deposits occur predominantly in the east Serbian sector of the Carpatho-Balkanides (the Bor metallogenic zone). The most significant area for Pb–Zn ore is the Kopaonik metallogenic district. Additional Pb and Zn deposits and occurrences are located in the Ljubisnje and Bjelasica regions, with associated gold (Au), silver (Ag), Cu, bismuth (Bi), and Cd. In northeast Bosnia, from Srebrenica to Maglaj, Zavidovići, and Teslić, there are breakthroughs of tertiary igneous rocks that are associated with occurrences of Zn, Pb, Sb, Ag, Bi, As, Fe, and other minerals (Midžić & Silajdžić, 2005a, b). As Balkan countries have a long tradition of the exploitation of ores and minerals, and there are many mines on TE deposits (Cu, Pb, Zn, and Sb in Serbia; Fe, Mn, Pb, and Zn in BIH; and Al, Fe, Pb, and Cu in Croatia), geogenic and anthropogenic influences on soil contamination with TEs are frequently mixed in the areas close to the mines, which is why it is discussed in the following section.

Anthropogenic anomalies in the entire region

Mines and metallurgic activities are common sources of soil contamination with TEs. In the process of opening the mines and exploration, TEs are exposed, spread over the mining area and cause the soil of that area to be contaminated. Old and modern Pb–Zn mines are frequent sources of Pb and Zn environmental contamination in the Balkan region: Vareš and Srebrenica in BIH (Alijagić & Šajn, 2006; Alijagić, 2007), and Veliki Majdan, Rudnik, etc., in Serbia (Dangić & Dangić, 2003). The historic Pb–Ag mining site “Sv. Jakob” (Mt. Medvednica near Zagreb, Croatia) was also identified as source of soil contamination with Pb, Zn, Cd, and Hg (Durn et al., 1999; Table II).

The highest contamination with Cu in Serbia was observed in the vicinity of metal mines Bor and Majdanpek (Bulajić et al., 1999; Environmental Protection Agency, 2006). As a consequence of mines processing and emission of TEs, concentrations of Cu in soils in the vicinity of Cu mine Bor amount to 375–490 mg kg⁻¹, depending of the soil type (Bulajić et al., 1999). The transformation of sulfur gases (SO₂ and SO₃), emitted due to mine processing, to H₂SO₄ causes soil acidification and low pH. A high total concentration of Cu in the soil (433 mg kg⁻¹) and a very low pH value of the soil (2.07), resulted in a high concentration of Cu extracted by ethylenediaminetetraacetic acid (EDTA; 41.2 mg kg⁻¹) (Antonijević & Marić, 2008).

In the vicinity of the ex-ferrochromium smeltery Dugi Rat, Croatia, concentrations of TEs in the soil, particularly Cr and Mn, were 56 times higher in relation to normal background soil (Orešcanin et al., 2006; Table II). Slag material, fly and bottom ash, was highly enriched with Cr, Mn, and Ni. There was a significant Cr uptake by vegetation growing on the contaminated soil; Cr reached a 14-fold enrichment in comparison with the background values (the vegetation growing over the pristine soil).

Potential contamination with As was observed in the region of metal mines Bor and in the surrounding coal mine Resava (Serbia; Environmental Protection Agency, 2006). High concentrations of As were found in many samples of coal, suspended particles, and leaching water. Arsenic was present in lignite from Obrenovac (Serbia) in the concentration of 1705 µg g^–1 (Simonović, 2003), in fly ash from 5- and 13-year-old deposit site 111 and 84.6 µg g^–1, respectively (Mitrović et al., 2008). Increased concentrations of As were also measured in the above-ground parts of Festuca rubra and Festuca epigejos (2.22–2.91 mg kg⁻¹) grown at an ash deposition site (Mitrović et al., 2008).

Coal combustion accounts for 60% of the total primary energy supply in BIH and for 40% in the whole of the Balkan region (Dellantonio et al., 2008). Coal combustion residues contain large concentrations of easily soluble salts and are potentially enriched with TEs (Simonović, 2003) and radionuclides (Vuković et al., 1996). Dellantonio et al. (2008) reported moderate contamination of ash with Cr, Ni, and to a lesser extent, with As, Cu, and Zn. Cover soil, used to grow plants to prevent the spreading of ash particles via wind erosion, often contains high total concentrations of TEs (Pavlovic et al., 2004; Djurdjević et al., 2006; Mitrović et al., 2008; Dellantonio et al., 2008; Table II).

As a result of the use of leaded petrol, high concentrations of Pb in soils near frequently used crossroads and highways were measured at a number of locations in BIH, Serbia and Croatia. The analysis of 76 soil samples taken at four localities (Luke, Donja Zimca, Mioca, and Gradina) along the Zenica-Sarajevo M-17 road in 2004 (Federal Institute of Agropedology, 2007) showed a considerable number of samples with high concentrations of TEs (Table II). The highest soil contamination caused by Pb, Cd, and Mn was noticed at locality Luke (Table II). Similar concentrations of Pb, Cd, and Mn were measured not only in samples from urban areas of Banja Luka, BIH (Marković et al., 2006), but also in Serbia (Vratuša & Anastasijević, 1999; Vasin et al., 2004) and Croatia (Prohić et al., 1997; Romić & Romić, 2003).

The concentration of Cd in <2% of the samples of the investigated area in Eastern Serbia was higher than 3 mg kg⁻¹ (Environmental Protection Agency, 2006), which is the upper limit for agricultural soils according to Serbian regulations (Official Gazette RS, 1994). It is believed that besides the geochemical origin, high content of this element found in the soils can be caused by anthropogenic contamination, such as industrial and mining activities, phosphate fertilizers, and organic solids (manure and sewage sludge). However, according to Bogdanovic et al. (1999), the application of increasing rates of P fertilizer (22, 44, and 66 kg P ha^–1) during a 30-year period did not significantly affect the concentration of Cd in Chernozem soil at Rimski Šancevi, near Novi Sad (Serbia), compared to the unfertilized control plot, because Cd addition through fertilizers ranged only from 0.24 to 0.71 g Cd ha^–1 year^–1.

Concentrations of Cu in vineyard soils in the region which are higher than their background concentrations may be associated with long-time intensive fertilization and protection of grapevine (Orešcanin et al., 2003; Romić et al., 2004; Table II). Copper salts (Bordeaux mixture, Ca(OH)₂+CaSO₄) have been widely applied as fungicides against mildew of grapevine.

Regions of deficiency

Most of the soils from the Balkan region inherited very low concentrations of Se from parent materials (Table III). For example, extremely low Se concentrations, on average 0.046 mg kg⁻¹, were found in magmatic rocks from Serbia (Maksimović et al., 1986); Se concentration decreases from basic and ultra basic to acid and neutral rocks (Dangić et al., 1989); and lowest Se concentrations are recorded in sandstone and limestone. The metamorphic rocks of Serbia have lower Se concentrations than magmatic and sedimentary rocks (average 0.028 mg kg⁻¹; Jović et al., 1995). In most of the soil samples from different areas in Balkan, the concentration of Se was in the range of 0.024–0.45 mg kg⁻¹ (Table III; Maksimović et al., 1992; Jakovljević et al., 1995a; Čuvardić, 2000, 2003). Soils containing less than 0.5 mg kg⁻¹ of total Se are considered as deficient in this element.

Table III. Concentration of selenium in soils of some SEE countries (mean and range; mg kg⁻¹).

Location	n	Mean value	Range	Reference
Srem and Banat, Vojvodina (Serbia)	46	0.250	0.110–0.450	Čuvardić (2003)
Vojvodina (Serbia)	7	0.106	0.024–0.194	Čuvardić (2000)
Serbia	140	0.200	0.079–0.439	Maksimović et al. (1992)
Northern Pomoravlje (Sebia)	43	0.240	0.120–0.440	Jakovljević et al. (1995a)
Alluvial soil	18	0.250	0.120–0.440	Jakovljević et al. (1995a)
Brown forest soil	14	0.200	0.140–0.320	Jakovljević et al. (1995a)
Smonitza	4	0.170	0.130–0.200	Jakovljević et al. (1995a)
Meadow soil	4	0.330	0.280–0.430	Jakovljević et al. (1995a)
Hidromorphic black soil	2	0.170	0.190–0.260	Jakovljević et al. (1995a)
Chernozem	1	0.170	–	Jakovljević et al. (1995a)
Medjumurje, Podravina, Slavonija (Croatia)	1	0.180	–	Antunović et al. (2005)
Požega Valley (Croatia)	4	0.038	0.020–0.048	Gavrilović and Matešić (1987)
Zeta Valley (Montenegro)	25	0.280	0.200–0.410	Jakovljević et al. (1995b)
Northern BIH	9	0.453	0.319–0.677	Muratović et al. (2007)
BIH – Bosnia and Herzegovina.

The distribution of total Se in different soil types shows that somewhat higher Se concentrations are to be found in meadow soils, while the highest variation was recorded in the case of alluvial soils (Table III; Jakovljević et al., 1995a). A significant correlation was found not only between total Se and soil organic matter but also between Se and many TEs (Pb, Zn, Co, Ni, As, and Cr), which indicates that the geochemistry of these elements in parent material and soil is very similar (Adriano, 2001). Croatia, mostly northern and eastern (Medumurje, Podravina and Slavonija) are also areas of Se deficiency (Gavrilović, 1982; Popijac & Prpić-Majić, 2002; Antunović et al., 2005). A severe deficiency of Se was evident in soils of eastern Slavonia (0.18 mg kg⁻¹ Se in soil; Antunović et al., 2005), particularly in the Požega valley (0.038 mg kg⁻¹ Se soil; Gavrilović & Matešić, 1987). Relatively low concentrations of total Se have also been measured in soils of the Zeta Valley in Montenegro (average 0.28 mg kg⁻¹ Se soil), where total Se showed a significant correlation with organic matter in topsoil (Jakovljević et al., 1995b). In BIH, concentrations of total Se measured in the soil on three family farms from the northern part of the country ranged from 0.32 to 0.68 mg kg⁻¹ Se (Table III; Muratović et al., 2007). As total Se concentrations were on the limits for Se deficient soils (0.5 mg kg⁻¹ Se, Mayland et al., 1989), Se concentrations in forage grown on the investigated soils were very low.

Zinc and Fe deficiencies have been found to be the most widespread micronutrient deficiencies worldwide, because nearly 50% of the soils cultivated for cereal production globally have low levels of plant available Zn (Cakmak, 2009), while Fe deficiency occurs in 30% of the cultivated soils in the world (Vose, 1982). Zinc and Fe deficiencies, caused by high pH values of calcareous soils, have also been noticed in eastern parts of Croatia (Jug et al., 2008) and the Serbian part of the Pannonian valley (Vojvodina). This survey in Croatia showed a gradient with increasing values of soil pH leading to increasing deficiency of microelements from west toward the east (mostly Zn and Fe deficiencies).

Results obtained from 56 soils from Vojvodina, used in vegetable production, showed that 37% of the samples had less than critical concentration of 1 mg kg⁻¹ of DTPA-extractable Zn (Čuvardić et al., 1993). In Vojvodina, more than 55% of arable soils have concentrations of CaCO₃ higher than 5%; consequently 58% of arable soils can be considered alkaline (Vasin, 2008), which can have a negative effect on TEs availability.

TEs bioavailability in soils

Total TE concentration in soil is not always a good predictor of the amounts of TEs which can be taken up by the plants and thus entered into the food chain because TEs are present in the soil in different forms and are more or less available to plants. TEs in soluble or weakly adsorbed pools are regarded as more available than TEs in strongly adsorbed and occluded forms (Kennedy et al., 1997). Many of the soil's physical, chemical, biological, and plant factors, and their interactions affect TEs availability. Also, the availability of TEs depends on their own characteristics and on the origin of TEs in soil. According to Kabata-Pendias and Pendias (1992), TEs in polluted soils tended to be more available than elements in uncontaminated soils. Jakovljević et al. (1997), dealing with two slightly contaminated soils (Cambisol and Fluvisol), from the Velika Morava River Valley (Serbia), reported that the least extractable elements were Cr and As (by 0.1 M HCl) with only 3.2 and 4.4% of their total concentrations, respectively. On the other hand, Mn and Cd were 40 and 100% extractable, respectively, and hence the most soluble ones. Therefore, Mn and Cd can easily enter the food chain or be transported through the soil profile to the ground water. Copper, Hg, Pb, and Co fell in the 27–28% range whereas the extractability of Ni and Zn was between 13 and 14.5%. It was found that the extractability of Ni and Pb increases rapidly where total values exceed 80 mg kg⁻¹, which can indicate that soils are contaminated. Factorial analysis elucidated a relationship of total concentrations of Zn and Cd with pH value of the soil, and indicated a possibility of their easy mobilization even with minor changes in soil acidity (Antic et al., 2006). High extractability of Pb (37.8% in average, 8.72–50.3% of total Pb) was also recorded in 20 samples from soils in the wider area of Sarajevo (Muhić-Šarac, 1999). As total Pb concentration in soils was on average 274 mg kg⁻¹ (59.3–833 mg kg⁻¹), a considerable part of Pb (13.1–215 mg kg⁻¹, in average 97.8 mg kg⁻¹) was extractable; therefore Pb could be a risk factor for both the food chain and the environment. However, as Pb uptake as well as transport in the plant are limited, the real risk in a polluted area is probably soil dust on grass for feeding animals rather than the plant uptake route.

Jakovljević and Stevanović (2004) reported high natural total concentrations of Fe, Mn, Co, Ni, and Cr in soils from Zlatibor Mountain formed on the serpentinite (Table II). In most cases, moderately acid soil pH increased the availability of investigated TEs, particularly Ni (64–372 mg kg⁻¹). This resulted in high concentrations of Ni (2–32 mg kg⁻¹) in the grass samples (Stevanović et al., 2004), especially high in one sample (443 mg kg⁻¹ Ni; see Table V).

Orešcanin et al. (2003) reported highly significant correlations between concentrations of TEs in the soil, measured in the 1 M NH₄OAc, and the grape samples from the wine producing area of Vrbnik on the island of Krk (Croatia). The concentration of the exchangeable fraction of Cu compared with the total Cu ranged from 12 to 83% of total, with a mean value of ~60%. High concentrations of total and available Cu were related to a long-term use of blue vitriol as a fungicide. Although intensive agricultural production in this area almost doubled the concentration of total Cu compared to the background level determined at Krk, due to a low translocation of Cu from root to grapes, concentrations of Cu in the grape and wine are lower than the threshold values (see Table X). The available concentration of Cr varied from 4 to 31% of total Cr, with a mean value of 15%. In most samples, the other TEs were present in an exchangeable fraction in <10% of the total concentration (Orešcanin et al., 2003).

In most samples from the Balkan region, the concentrations of the essential TEs were at adequate levels to satisfy plant requirements (Muhić-Šarac, 1999; Jakovljević & Stevanović, 2004). However, the concentrations of EDTA-extractable Zn in 33% of the samples from Chernozem soil from Vojvodina, the most important agricultural area in Serbia, were below the critical limit for plant growth (Manojlović et al., 1986). Similar results were obtained for DTPA-extractable TEs from 56 soils from Vojvodina, used in vegetable production, where 37% of the samples had less than a critical concentration of 1 mg kg⁻¹ available Zn (Čuvardić et al., 1993; see section “Regions of deficiency”).

Zinc and Fe deficiencies, caused by high pH values of calcareous soils, have also been noticed in eastern parts of Croatia (Jug et al., 2008). It is well known that acidic pH increases the solubility of Zn and other cationic TEs, while anionic species such as Se are more soluble in basic soils. However, Čuvardić et al. (1997) reported a very low concentration of water-soluble Se (traces to 0.013 mg kg⁻¹ Se) in 46 soil samples from Srem and Banat region (Vojvodina, Serbia) used for vegetable production, due to a low total Se concentration in the soils (ranged from 0.11 to 0.45 mg kg⁻¹), despite slightly alkaline soil pH and significant dependence of concentrations of water-soluble Se on soil pH (r=0.37, p < 0.01) and on CaCO₃ (r=0.79, p < 0.05) reported for these soils.

Effects of TEs on plants and food chain

TEs affect plant, animal and human growth and reproduction, in a twofold manner. In soil, deficiency of essential TEs not only reduces crop productivity, but low TE concentrations in plant feed and food also adversely affect animal and human health and well-being (Marschner, 1995; Kabata-Pendias & Mukherjee, 2007). On the other hand, the accumulation of toxic TEs in the soil and plants can cause a yield reduction of growing plants as well as metabolic disorders in animals and humans (Adriano, 2001).

TEs in plants for animal feed

Essential trace elements

Micronutrient deficiencies in plants are becoming increasingly important globally. Intensive cultivation of high-yielding crops with heavy applications of N, P, and K fertilizers has led to the occurrence of micronutrient deficiencies in many countries (Cakmak, 2002). Zinc and Fe deficiencies, caused by high pH values of calcareous soils, have been noticed in eastern parts of Croatia and Serbian part of Pannonian valley (Vojvodina; see section “Regions of deficiency”). However, in Vojvodina, plant response to Zn fertilization is only connected to Zn-sensitive crops (corn in certain years, Abd Elnaim & Manojlović, 1984; Ubavić et al., 1984; grapes, fruit crops, Marić et al., 1967). Moreover, plant response to Zn deficiency is genetically determined and significant differences among 121 corn genotypes in eastern Slavonia (Croatia) were found for all TEs studied (B, Cu, Fe, Mn, and Zn) except Ni (Brkić et al., 2004). For example, the grain concentration ranges for Zn and Fe were 11.9–33.2 and 11.0–60.7 mg kg⁻¹ dry matter (DM), respectively.

According to Gupta and Gupta (2005), livestock requirements for Zn are much greater than the levels of Zn that are sufficient in crop yields. Concentrations of Zn in alfalfa samples from Vojvodina (Čuvardić et al., 2006) and grass samples from Divcibare region, Serbia (Krstić et al., 2008), are variable to a large extent (Table IV), and therefore the concentrations of Zn in some of the samples were below the critical deficiency level and below dietary requirements for ruminants (20 mg kg⁻¹ DM; Underwood & Suttle, 1999). Zinc requirements for pigs and poultry are even greater (Table IV). However, concentrations of Fe in grass, corn, and alfalfa from a few locations in Croatia and Serbia were somewhat higher than plant requirements but were within the values proposed by Gupta and Gupta (2005).

Table IV. Comparison of sufficient levels of micronutrients in crops and feeds for livestock (mg kg⁻¹).

Nutrient	Location	Level in crops in WB	Sufficient levels in crops^a	Sufficient levels in feeds for livestock^a
Cu	Vojvodina (Serbia)	Alfalfa 0.1–8.3^d	Alfalfa 6–12	Sheep 6–10
	Goč (Serbia)	Grass 2–6.6^b	Timothy 4–8	Post-weaning pigs 50–60
	Serbia	Grass 2–12.2^c	Pasture grasses 5–12
	Divčibare (Serbia)	Grass 2.92–9.77^e
	Zlatibor (Serbia)	Grass 1.8–7^h
	Nisici plateau (BIH)	Grass 0.56–0.72^i
	Vojvodina (Serbia)	Corn 1.6–1.6^d
	Eastern Croatia	Corn 0.5–3.4^g
Co	Vojvodina (Serbia)	Alfalfa 0.01–0.15^d	Alfalfa, Timothy 0.012–0.032	Ruminants 0.1
	Goč (Serbia)	Grass 0.04–0.12^b		Sheep 0.07
	Zlatibor (Serbia)	Grass 0.1–1.0^h
	Vojvodina (Serbia)	Corn <0.1–0.16^d
Fe	Vojvodina (Serbia)	Alfalfa 20–271^d	Alfalfa 35–50	Leghorn chicken 60–80
	Goč (Serbia)	Grass 104–603^b	Timothy 23–47	Broiler chicks 80
	Divcibare (Serbia)	Grass 81–232^e
	Zlatibor (Serbia)	Grass 95–710^h
	Vojvodina (Serbia)	Corn 284–306^d
	Eastern Croatia	Corn 11–60.7^g
Mn	Vojvodina (Serbia)	Alfalfa 0.1–46^d	Alfalfa 31–49	Poultry, Chicks 50
	Goč (Serbia)	Grass 16–54^b	Timothy 34–53	Ruminants 40
	Divčibare (Serbia)	Grass 26–133^e
	Zlatibor (Serbia)	Grass 20–115^h
	Vojvodina (Serbia)	Corn 3.2–3.2^d
	Eastern Croatia	Corn 4.7–14.8^g
Zn	Vojvodina (Serbia)	Alfalfa 0.08–26.3^d	Alfalfa, Ryegrass 12–28	Pigs 50–100
	Goč (Serbia)	Grass 23–46^b	Crotolana anagyroides 10	Dairy cattle, Bulls 50
	Divčibare (Serbia)	Grass 4.01–38.91^e		Poultry 35–65
	Zlatibor (Serbia)	Grass 12–30^h
	Vojvodina (Serbia)	Corn 22–65^d
	Eastern Croatia	Corn 11.9–33.2^g
Se (µg kg^−1)	Divčibare (Serbia)	Grass 0.013–0.022^e	10–2000^j	30–50^k
	Vojvodina (Sebia)	Corn 25.5–40.5^f
	Central region (Serbia)	Corn 22.1–31.1^f
	South region (Serbia)	Corn 12.5–21.0^f
	Sava Basin (Croatia)	Corn meal 114±80.0^l
	Drava Basin (Croatia)	Corn meal 38.1±1.0^l
	Požega Valley (Croatia)	Corn <10^m
B	Zlatibor (Serbia)	Grass 14–25^h	Alfalfa >15^n
	Eastern Croatia	Corn 0.5–6.0^g
Ni	Eastern Croatia	Corn 0.1–1.0^g	20–30^o	50–60^o
BIH – Bosnia and Herzegovina. ^aGupta and Gupta (2005), ^bDanon and Jakovljevic (1989), ^cDanon and Jakovljevic (1992), ^dČuvardić et al. (2006), ^eKrstić et al. (2008), ^fMihaljev et al. (2003a), ^gBrkić et al. (2004), ^hStevanović et al. (2004), ^iMuratović et al. (2005), ^jKabata-Pendias and Pendias (1992), ^kUnderwood and Suttle (1999), ^lKlapec et al. (2004), ^mGavrilović and Matešić (1987), ^nMengel and Kirkby (1987), ^oSauerbeck (1982).

Copper is an important microelement for normal functioning of numerous processes in the animal organism. Very variable concentrations of Cu in grass samples were measured at some locations in the Balkan region (Danon & Jakovljević, 1992; Stevanović et al., 2004; Krstić et al., 2008; Table IV). However, in the majority of the grass samples, the concentrations of Cu were lower than the suggested critical level for pasture grass of 5 mg kg⁻¹ DM (Gupta & Gupta, 2005), and was also not sufficient to supply the nutritive requirements of domestic animals. Copper requirements for various classes of livestock range 3 mg kg⁻¹ for ruminants, 6–10 mg kg⁻¹ for sheep and 50–60 mg kg⁻¹ for post-weaning pigs (Gupta & Gupta, 2005). In central Bosnia, the results also indicated a low level of Cu in pasture (Table IV; Muratović et al., 2005). Low levels of Cu in sheep's blood (0.39 mg kg⁻¹) confirm this deficiency. As the total Cu concentration in the soil was 19.4 mg kg⁻¹ on average, it is possible that the interaction with other TEs or sulfur in the soil or in the plants caused Cu deficiency. A Cu:Mo ratio above 1–3 in feed is considered critical for Mo-induced Cu deficiency (hypocuprosis) in ruminants (Underwood & Sutlle, 1999). High concentrations of Mo in a leguminous fodder crop, Medicago sativa (12.5 mg kg⁻¹), grown on cover soil of the coal ash landfill in Tuzla (BIH) resulted in Cu:Mo ratio of 1.25 (Dellantonio et al., 2008).

Manganese: according to Kabata-Pendias and Pendias (1992), a normal range of Mn for most plant species is 20–300 mg kg⁻¹. Most of the grass samples from Serbia and BIH had adequate levels of Mn for plant nutrition, although values in the deficient range of Mn (below 15–25 mg kg⁻¹ for most crops according to Kabata-Pendias and Mukherjee [2007]) were found at some locations in Vojvodina (Table IV). However, nutrient requirements for poultry and chicks, of 50 mg kg⁻¹ Mn, can be met with Mn supplementation.

Cobalt is a non-essential element for higher plants but is required for N₂-fixing bacteria in the nodules of leguminous plants. In most of the samples, the concentrations of Co are at an adequate level required by animals. According to Gupta and Gupta (2005), a sufficient level in the diet is 0.07 mg kg⁻¹ Co for sheep and 0.1 mg kg⁻¹ for ruminants.

Boron is an essential TE. Fertilization with B positively affects the yield of sugar beet in Vojvodina (Serbia) in certain years (Manojlović, 1987). On the other hand, high concentrations of soil B can seriously affect the growth and yield of many crop species, particularly in arid and semiarid environments. Therefore, the level of available B in the soil must be taken into account when making decisions on the application of B. High concentrations of B are also related to the emission and deposition of ash particles from coal fired heat and power plants. Plant growth on ash is often reduced by concentrations of B and accumulation of As, Mo, and Se in plants in quantities considered hazardous to animals. For example, concentrations of B in seeded and naturally recolonized plants grown at an ash deposition site of thermal electrical plant in Obrenovac, ranged from 11.2 to 180 mg kg⁻¹ (Pavlović et al., 2004), and from 56 to 97.2 mg kg⁻¹ DW for above-ground parts of F. rubra and F. epigejos (Mitrović et al., 2008). The concentration of B in M. sativa grown on a coal ash landfill in Tuzla (BIH) was 120 mg kg⁻¹, the concentrations in native vegetation were even higher (260 mg kg⁻¹ in Populus nigra, 450 mg kg⁻¹ in Salix caprea and 1122 mg kg⁻¹ in Salix alba; Dellantonio et al., 2008). According to Kabata-Pendias and Pendias (1992), in plants, excessive or toxic values of B range from 50 to 200 mg kg⁻¹. Concentrations >800 mg kg⁻¹ B are considered toxic for livestock (Underwood & Suttle, 1999).

Croatia, mostly its northern and eastern parts (Medjumurje, Podravina, and Slavonija) and Serbia are areas of Se deficiency (Gavrilović, 1982; Popijac & Prpić-Majić, 2002). A severe deficiency of Se, particularly evident in soils of eastern Slavonia (0.18 mg kg⁻¹ Se soil; Antunović et al., 2005), consequently affected feed and foodstuff (Popijac & Prpić-Majić, 2002). However, Se levels are lower in cornmeal samples from the Drava river basin (38.1 µg kg⁻¹) than the Sava basin (114.2 µg kg⁻¹; Klapec et al., 2004; Table IV). However, in Serbia Se level in corn was lowest (17.8 µg kg⁻¹) in the southern region of the country, in the central region of the country, the average was 25.6 µg kg⁻¹ Se and the highest level of Se (36.6 µg kg⁻¹) was found in the northern part of Vojvodina (Mihaljev et al., 2003a). Jakovljević et al. (1995a) reported lower Se concentrations in wheat, corn, and beans on alluvial soil (12, 4, and 10 µg kg⁻¹, respectively) than on brown forest soil (19, 21, and 20 µg kg⁻¹, respectively). All these concentrations are very low and they can cause health problems in animals or humans that consume such feed and food. Selenium levels of below 50 µg kg⁻¹ are characterized as a lower than normal level in feed (Kubota et al., 1967). In young sheep, two Se responsive diseases are recognized; one a myopathy in lambs, white muscle disease, and the other a syndrome of lowered productivity ranging in severity from poor wool production to a clinical condition known as Se responsive unthriftiness (Andres et al., 1999). However, an occurrence of Se deficiency disorders in animals in the Balkan region is restricted to grazing ruminants that have little or no access to concentrated feed (Gavrilović & Matešić, 1987; Antunović et al., 2010), since regulations (in Serbia Official Gazette SRY, 2000; Official Gazette RS, 2010) prescribe mandatory supplementation of animals with Se throw feed mixtures. Although the regulated levels (0.1–0.3 mg kg⁻¹ feed, depends on category of animals) are only aimed at preventing deficiency diseases, they significantly raise the Se concentration in animal products (Klapec et al., 1998).

Toxic trace elements

Contamination of grass and natural vegetation with toxic TEs has occasionally been reported in the Balkan region. However, in most of the analyzed grass, corn and alfalfa samples from Serbia and BIH, the concentrations of toxic TEs are far below the maximum allowed concentration (MAC) for animal feed (Official Gazette RS, 2010; Table V).

Table V. Mean and range (in brackets) of toxic trace element concentrations in crops and feeds for livestock reported by various studies.

Crop	Location	n	Cd (mg kg^−1)	Pb (mg kg^−1)	Hg (mg kg^−1)	As (mg kg^−1)	Cr (mg kg^−1)	Ni (mg kg^−1)	Reference
Alfalfa	Vojvodina (Serbia)	12	0.03 (0.02–0.04)	0.55 (0.35–0.82)	0.53 (0.01–1.33)	0.15 (0.10–0.33)	NA	NA	Čuvardić et al. (2006)
Corn	Vojvodina (Serbia)	12	0.02 (0.02–0.03)	0.35 (0.20–0.52)	<0.01	0.41 (0.10–0.90)	NA	NA	Čuvardić et al. (2006)
Grass^a	Zlatibor (Serbia)	9	0.12 (0.12–0.12)	1.90 (1.0–2.7)	NA	NA	8.1 (2.0–25.7)	65 (2.3–443)	Stevanović et al. (2004)
Grass	Kakanj (BIH)	4^b	(0.01–0.02)	(0.11–0.36)	NA	NA	NA	NA	Muratović et al. (2002)
		4^a	(0.01–0.02)	(0.11–0.29)	NA	NA	NA	NA	Muratović et al. (2002)
Plants^c	Rudnik, V Morava (Serbia)	17	0.4 (0.25–1.5)	9.7 (3–88.5)	NA	0.3 (0.03–1.83)	16.2 (7–34)	8.9 (2.5–21.5)	Jakovljević and Antić-Mladenović (2000)
MAC			0.5	10	0.2	0.5	–	–	Official Gazette RS (2010)
NA – not analyzed; BIH – Bosnia and Herzegovina; MAC – maximum allowed concentration. ^aHay from meadows; ^bgreen mass from meadows; ^cmostly alfalfa.

Among all TEs, Pb is the most frequent environmental pollutant and one of the most common TE causes of poisoning in farm animals. Lead availability in the soil is usually very low and therefore the main form of plant contamination with Pb is air pollution. The mobility of Pb in the plant is also very low (Mengel & Kirkby, 1987). Lead contamination of herbaceous plants along the roads or in urban areas is common (Vratuša & Anastasijević, 1999). Animals grazing near roads where vehicles are using leaded petrol develop increased Pb concentrations in their blood, due to the uptake from both pasture and soil (Ward et al., 1978). Concentrations of Pb in herbaceous plants, taken along the roads from 18 settlements in Serbia were in the range from 12.2 to 147.7 mg kg⁻¹ Pb, and above the limits (10 mg kg⁻¹) allowed by Serbian law (Official Gazette RS, 2010), despite the total concentrations of Pb in soils, which were below MAC for soil (100 mg kg⁻¹ Pb; Vratuša & Anastasijević, 1999).

Lead mines can also be a source of Pb pollution. Although the availability of Pb in the soil is usually low because of strong retention in most soils (Kabata-Pendias & Mukherjee, 2007), herbaceous and native plants grown on historical mining sites could accumulate high concentration of Pb, and other toxic TEs, due to high total concentrations of these elements in most soils. Consequently, herbaceous and native plants grown on these contaminated sites present a hazard to grazing animals. For example, a high concentration of Pb in the soil and in scarce vegetation cover was measured in the broad area of Pb and Zn mines Olovo and Vareš (Medjedović, 1999). Besides the high total concentration of Pb in the soil, high acidity of the soil also enhanced the absorption of TEs by the plants in this region. The highest concentration of Pb (range 101–561 mg kg⁻¹) was measured in herbaceous plants (Plantago media, Achillea milefolium and Thymus serpyllum); then in grass (16.5 mg kg⁻¹ for fresh and 34.8 mg kg⁻¹ Pb for hay); and the lowest concentrations of Pb were found in seedlings of Picea abies (0.94 mg kg⁻¹) and Abies alba (4.70 µg kg⁻¹). According to Medjedović (1999), low accumulation of Pb by coniferous plants, might be explained by the development of exotrophic mycorrhiza on the root system. The uptake and storage of Pb in ectomycorrhizal sheets around the roots inhibited the uptake of the TE into the root cells. Jakovljević and Antić-Mladenović (2000) have reported that plants grown on slightly contaminated soils in Serbia (alluvial soil from the Morava River valley and soil near a Pb mine, on the Rudnik Mountain) in most of the samples had a normal range of TEs for plant materials. However, concentrations of Pb and Cd in two samples were above critical limits for animal food (Official Gazette RS, 2010). Concentrations of Pb were 88.5 mg kg⁻¹ Pb in hay from natural pasture in the vicinity of the Pb mine, and 13.5 mg kg⁻¹ Pb in an alfalfa sample from the soil with high total (945 mg kg⁻¹) and available (260 mg kg⁻¹) concentrations of Pb. As the critical limit for food and animal feed is 10 mg kg⁻¹ Pb (Official Gazette RS, 2010), grass should not be used for grazing or for any kind of animals feed.

Unlike Pb and other TEs, the transport of Cd and Ni to above-ground parts of the plants after uptake is quite fast (Petrović & Kastori, 1994). Moreover, as translocation of Ni from the root occurs rapidly, the accumulation of Ni in a young plant's parts, even in the reproduction organs, in many plant species is common. However, the translocation of Cd to the generative organs is fair and therefore, the accumulation of Cd in the seed or the fruit is rare, even in more highly contaminated soils (Leita et al., 1993). Compared to other TEs, Cd is unique in that it reaches concentrations in crops (to human and animal consumers) to levels which are toxic to humans and animals but not phytotoxic (McLaughlin et al., 2000). According to Maksimović et al. (2007), high concentrations of Cd and Ni (0.1 mM Cd and Ni) caused severe changes in root morphology and anatomy of young maize plants (e.g. shortened and thicker less root branches with an enhanced number of root hairs) as well as in plant essential metal composition although such severe symptoms did not appear on the shoots.

Plant species differ in their ability to accumulate Cd. Yarrow (A. millefolium L.), plant species known as Cd accumulator, accumulated higher concentrations of Cd (1.5 mg kg⁻¹) than alfalfa, grass and other crops (0.25–0.5 mg kg⁻¹) grown at the same locations (Jakovljević & Antić-Mladenović, 2000). Radanovic et al. (2002) reported that concentrations of Cd in St. John's wort (Hypericum perforatum L.) and yarrow, collected from different localities in Yugoslavia and Republic Srpska, decreased exponentially (r = –0.77, p < 0.05 for yarrow and r = –0.58, p < 0.05 for St. John's wort) with the increase of the soil's pH value. Cadmium concentration in St. John's wort was mostly above the limit of 0.5 mg kg⁻¹ Cd when the soil's pH value (in KCl) was lower than 5.9, and 4.5 for yarrow. A higher Cd content in the yarrow herb, and especially in St. John's wort herb from acidic soils, points to the significance of control of Cd content in raw materials collected in the wild but also to the necessity to avoid such soils for the cultivation of such species.

High concentrations of Cr and Ni in plant materials are undesirable, and known as potentially toxic. The most obvious symptom of the phytotoxic effect of Ni is chlorosis, which is possibly induced by Fe deficiency. There is no proof of the irreplaceable role that Ni plays in plant metabolism. However, a favorable effect of small quantities of this element on plant growth has been recorded (Kabata-Pendias & Pendias, 1992). Chromium (as CrIII) is an essential TE in animal-based agricultural systems while CrVI has been shown to be carcinogenic. Normal concentrations of Ni and Cr are 0.1–0.5 mg kg⁻¹ DM (Kabata-Pendias & Pendias, 1992), while values above 30–50 mg kg⁻¹ DM are considered potentially harmful. In Serbia and other South Eastern European (SEE) countries, there is a special interest in monitoring Ni and Cr concentrations in plants, because many soils developed on serpentinite contain these two TEs in high concentrations (even above 1000 mg kg⁻¹; Jakovljević & Antić-Mladenović, 1997). Concentrations of mobile Ni (extraction with 1 M HCl) from serpentinite rankers from Serbia were 200–600 mg kg⁻¹ (Dordević et al., 2005). Concentrations of Ni higher than usual (2.5–21.5 mg kg⁻¹ Ni) were found in most of the alfalfa (M. sativa) and yarrow (A. millefolium) samples (80%) taken from soils with high concentrations of total Ni, alluvial soils from the Morava River valley and soils from the Rudnik mountain (Table V; Jakovljević & Antić-Mladenović, 2000). High concentrations of Ni and Cr were also found in grass grown on serpentinite ranker on the Zlatibor mountain (Table V; Stevanović et al., 2004), particularly high in one of the samples (443 mg kg⁻¹ Ni). However, high variability in the concentration of Ni in grass samples from different locations is a result of a different distribution of grass species at each location. Some plant species can tolerate high concentrations of Ni and have the ability to accumulate Ni in their organs in large quantities. For example, grass species from family Allyssum accumulated 100 times more Ni (4728 mg kg⁻¹) than other species from the same location (Stevanović et al., 2004).

Herbaceous and native plants grown on historical mining sites could accumulate high concentrations of Cr and other toxic TEs and therefore pose a serious hazard for grazing animals. For example, Orešcanin et al. (2006) noted a 14-fold enrichment in the concentration of Cr in grass grown in the vicinity of an ex-ferrochromium smelter Dugi Rat (Croatia) compared to a non-exposed region, 11 years after the production had ceased.

TEs in plants for food with respect to regulations and daily requirements

Arsenic, Cu, Cd, Fe, Hg, Pb, and Zn are considered potentially toxic in the human diet by the joint Food and Agriculture Organization/World Health Organization Codex Alimentarius Commission (2005), with As (as arsenite) being carcinogenic (Ybanez & Montoro, 1996). An intake of relatively low doses of these elements over a long period can lead to malfunction of organs and chronic toxicity.

The Serbian legislation (Official Gazette RS, 2011) sets maximum levels for Pb, Cd, Hg, and As as 0.2, 0.2, 0.05, and 0.5 mg kg⁻¹ DM, respectively (Table VI), in wheat grain, very important foodstuff in Serbian diet. For example, the average daily consumption figures for bread, wheat flour, pasta, and bakery products were about 270, 42, 8, and 5 g/person, respectively, in 2002 (Škrbić & Čupić, 2005). The results of a nation-wide survey on TEs levels in Serbia, for the 2002 harvest (Table VI), showed that mean and median concentrations of all 443 samples from 52 locations lay below the maximum limits according to the Serbian legislation and also below the maximum level given by Commission Regulation (EC) 1881/2006 (Table VII). However, it should be stressed that in some samples (Table VI) the concentrations of Pb, Cd, Hg, and As were higher than the threshold values set by Serbian Regulations (2011). Similar mean concentrations of essential and potentially toxic TEs in wheat samples from Serbia (Table VI) were also found by other authors (Zivkov-Baloš et al., 2000; Kastori et al., 2002; Škrbić & Onjia, 2007). Those values correspond to TE concentrations in wheat samples from Austria (Sager & Hoesch, 2005).

Table VI. Mean and range (in brackets) of trace element concentrations in wheat grain reported by various studies (on dry weight basis).

Location	n	Cd (µg kg^−1)	Pb (µg kg^−1)	Hg (µg kg^−1)	As (µg kg^−1)	Cu (mg kg^−1)	Zn (mg kg^−1)	Fe (mg kg^−1)	Mn (mg kg^−1)	Reference
Vojvodina (Serbia)	12	33.9 (16–60)	<50 (<50–65)	<1	1.08 (<0.5–1.08)	4.06 (3.2–5.01)	52.5 (30–90)	40.5 (30.6–89.6)	26.3 (22.3–30.9)	Zivkov-Baloš et al. (2000)
R Šančevi, Vojvodina (Serbia)	16	14 (ND–20)	135 (ND–304)	<1	19 (ND–154)	4.6 (4.2–5.1)	21.8 (16.8–30.6)	47.6 (43.3–55.8)	45.9 (41.7–47.4)	Kastori et al. (2002)
(Serbia)	52	28.8 (5.1–72)	137 (34.3–379)	7.0 (<0.1–54.8)	55.4 (<20–90.6)	4.1 (3.0–6.1)	23.8 (20.2–29.3)	53.5 (47.0–60.7)	33.9 (27.1–41)	Škrbić and Čupić (2005)
(Serbia)	14	38.3 (2.4–252)	366 (74.8–1099)	6.24 (<0.3–57.6)	82.7 (<50–162)	5.30 (3.61–7.64)	33.2 (26.6–44.3)	80.7 (51.7–165)	50.9 (37–88.4)	Škrbić and Onjia (2007)
MAC		0.2	0.2	0.05	0.5					Official Gazette RS (2011)
ND – Not detected. MAC – maximum allowed concentration (mg kg^−1).

Table VII. Maximum levels for heavy metals in foodstuffs – cereals, vegetables, and fruit.

	Maximum level (mg kg^−1 FW)
	Serbian regulation (Official Gazette RS, 2011)				Commission regulation (EC) 1881/2006
Product	Pb	Cd	Hg	As	Pb	Cd
Cereals^a	0.2	0.1	0.05	0.5	0.2	0.1
Rice and buckwheat	0.4/0.4^c	0.2/0.1^c	0.05/0.03^c	0.5	0.2	0.2
Soybean	0.2	0.2	0.1	1.0	0.1	0.2
Vegetables^b	0.1^d	0.05/0.1^d	0.02	0.3	0.1^d	0.05/0.1^d
Brassica, leafy vegetables, fresh herbs and fungi	0.3	0.2	0.02	0.3	0.3	0.2
Fungi	1 (5)	1	0.5 (3)	1
Fruit (excluding berries and small fruits)	0.1	0.05	0.02	0.3	0.1
Berries and small fruits	0.2	0.05	0.02	0.1	0.2
Fruit and vegetable dried	3	0.3	0.1	0.5
^aExcluding buckwheat, legumes, and pulces. ^bExcluding brassica, leafy vegetables, fresh herbs, and fungi. ^cLevel for flour values refers to cereals, flour, and cereal products. ^dLevel for peeled potatoes.

If concentrations of TE in wheat samples given in Table VI are compared with the daily requirements reported by Leblanc et al. (2005) (cited by Kabata-Pendias & Mukherjee, 2007), which should ensure an adequate supply with nutrient elements, it can be seen that wheat supplies adequate amounts of Cu, Mn, and Zn. However, exclusive feeding with wheat would lead to severe deficiencies in Se (Table VIII). A very low level of Se has also been reported for different cereals and fruit and vegetable species grown in Croatia and Serbia (Table IX). An extremely low Se concentration (18 µg kg⁻¹) was measured in wheat from Croatia, grown in the central part of the region where animal seleno-deficiency occurred (Gavrilović & Matešić, 1987). A higher Se concentration was measured in white wheat flour from the Sava and Drava basins, particularly the Sava, due to higher total Se content in the soil and/or availability (Klapec et al., 2004). In Serbia, a somewhat higher concentration of Se was found in Vojvodina, then in central and western parts of the country (Mihaljev et al., 2003b), but in all cases inadequate to satisfy daily Se requirements. There is no record in Serbia of a specific disease in humans caused by Se deficiency. However, a serious Se deficiency in rural inhabitants could be a major risk factor in the development of Balkan Nephropathy and high incidence of Urinary Tract Tumors in endemic areas (Maksimović et al., 1992).

Table VIII. Nutritional levels of trace elements.

Trace element (unit)	Nutritional value, lowest threshold intake^a	Toxicological value, upper level^b	Cereals^c (mg kg^−1)	Cereals containing daily needs (kg) (lowest threshold intake)^f	Cereals containing toxicological daily values^g (kg)
Cu (mg)	0.6	10–35	3.2–7.64	0.19–0.08	7.03–2.94
Mn (mg)	0.75	–	22.3–88.4	0.03–0.01	–
Mo (µg)	17.5	600	201–418^d	0.09–0.04	2.99–1.43
Ni (µg)	–	600	224–468^d	–	2.68–1.28
Se (µg)	20	150–300	34.6^e	0.58	4.33–8.67
Zn (mg)	4–5	25–60	16.8–90	0.24–0.04	1.48–0.67
^a,bNutritional and toxicological daily reference values established for adults by various organisms (Leblanc et al., 2005; adopted by Kabata-Pendias & Mukherjee, 2007). ^cAverage of data for TE concentrations in wheat grain given in Table VI. ^dµg kg^−1, Kastori et al. (2002). ^eµg kg^−1, Mihaljev et al. (2003a). ^fCalculated on the bases of nutritional value, lowest threshold intake (a) and concentration of TE in cereals (c). ^gCalculated on the bases of toxicological value, upper level (b) and concentration of TE in cereals (c).

Table IX. Concentration of selenium in cereals, fruit, and vegetables in SEE (µg kg⁻¹).

Crop	n	Location	Mean value	Range	Reference
Wheat		Vojvodina (Serbia)	34.6		Mihaljev et al. (2003a)
	31	Vojvodina (Serbia)	25.3±7.2		Maksimović et al. (1992)
	14	West Serbia	15.0±14.8		Maksimović et al. (1992)
	58	Serbia	20.5±12.4	3.6–65.5	Maksimović et al. (1992)
	14	Croatia	<10.0–18.0		Gavrilović and Matešić (1987)
	3	Koprivnica (Croatia)		22.0–62.0	Popijač & Prpić-Majić (2002)
Wheat flour, white	4	Sava Basin (Croatia)	58.5±5.1		Klapec et al. (2004)
	3	Drava Basin (Croatia)	56.3±4.4		Klapec et al. (2004)
		Croatia	69.0		Matešić et al. (1981)
Barley		Vojvodina (Serbia)	32.4		Mihaljev et al. (2003a)
Oats		Vojvodina (Serbia)	77.8		Mihaljev et al. (2003a)
Rye		Vojvodina (Serbia)	70.7		Mihaljev et al. (2003a)
Apple	2	Sava Basin (Croatia)	8.8±1.6		Klapec et al. (2004)
	2	Drava Basin (Croatia)	7.8±0.2		Klapec et al. (2004)
Grape	2	Sava Basin (Croatia)	12.9±3.6		Klapec et al. (2004)
	2	Drava Basin (Croatia)	8.9±0.0		Klapec et al. (2004)
Walnut	2	Sava Basin (Croatia)	46.1±15.5		Klapec et al. (2004)
Garlic	23	Vojvodina (Serbia)	24.9±24	2.2–85.5	Maksimović et al. (1992)
	43	West and central Serbia	7.7±6.6	2.1–36.1	Maksimović et al. (1992)
	66	Serbia	13.7±17	2.1–85.5	Maksimović et al. (1992)
	2	Sava Basin (Croatia)	34.2±5.1		Klapec et al. (2004)
	1	Drava Basin (Croatia)	57.6		Klapec et al. (2004)
Cabbage, fresh	2	Sava Basin (Croatia)	66.1±5.6		Klapec et al. (2004)
	2	Drava Basin (Croatia)	8.3±0.5		Klapec et al. (2004)
Potato	3	Sava Basin (Croatia)	9.5±1.3		Klapec et al. (2004)
	2	Drava Basin (Croatia)	7.2±0.8		Klapec et al. (2004)

Concentrations of toxic and potentially toxic TEs, detected in vegetables and grapes from different regions in Croatia and Serbia, are shown in Table X. However, there is a certain variability in TE concentrations between samples from different locations in Croatia and Serbia, as well as between different species. It is obvious that somewhat higher concentrations of TEs in crops were measured in urban or industrial areas than in rural areas. If measured concentrations of TEs are compared to the European Union (EU) directive (EC 1881/2006), with the exception of the concentrations of Pb and Cd in potato (Vitali et al., 2007), grapes at some locations close to a thermal electrical plant (Bešlić et al., 2005) and Brassicacae in the urban area of Zagreb (Bošnir & Puntarić, 1997), all others are below maximum limits (Directive EU 1881/2006; Table VII).

Table X. Mean and range (in brackets) of trace element concentrations in vegetables and fruit reported by various studies (fresh weight).

Crop and location	N	Cd (µg kg^−1)	Pb (µg kg^−1)	Hg (µg kg^−1)	As (µg kg^−1)	Cu (mg kg^−1)	Zn (mg kg^−1)	Fe (mg kg^−1)	Ni (mg kg^−1)	Reference
Brassicacae, Zagreb (Croatia)	81	NA	454^a (19–1871)	NA	NA	NA	NA	NA	NA	Bošnir and Puntarić (1997)
Vegetables (Croatia)	60	(14.9–42.3)	(11.1–73.8)	NA	NA	NA	NA	NA	NA	Blanuša and Jureša (2001)
Cabbage (Croatia)	20	10.3 (6–27)	24 (ND–284)	ND	NA	0.32 (0.17–0.62)	2.25 (0.97–4.27)	NA	NA	Vitali et al. (2007)
Potato (Croatia)	20	28 (5–63)	96 (10–380)	11 (ND–40)	ND	1.81 (1.02–2.98)	5.33 (2.64–14.1)	NA	NA	Vitali et al. (2007)
Potato (Serbia)	12	(<20–70)	<10	NA	ND	NA	NA	(<4–4.3)	(<0.1–2.8)	Kovacevic et al. (2002)
Grapes, Obrenovac (Serbia)	4	(ND–20)	155 (90–240)	(ND–10)	NA	NA	1.44 (0.76–2.49)	7.43 (5.59–9.41)	5.53 (5.59–9.41)	Bešlić et al. (2005)
Grapes, Vrbnik (Croatia)	31	NA	4.5 (ND–21)	NA	0.8 (ND–4.9)	0.12 (0.05–0.53)	0.07 (0.005–0.21)	0.08 (0.01–0.20)	0.003 (ND–0.01)	Orešcanin et al. (2003)
NA – not analyzed; ND – not detected. ^aMedian.

It is important to emphasize that, in order to harmonize MAC for TEs with the EU regulations, Croatia adopted new standards in 2005 (Public Health Regulation 16/05) and Serbia in 2011 (Official Gazette RS, 2011). That resulted in a decrease of MAC for Pb, Cd, and As for most of the food products (Table VII). All the countries in the region have passed laws on food safety and with the adoption of all by-law directives the harmonization with European regulations will be complete. However, the regulations are not fully implemented.

There is a lack of data on concentrations of TEs in foodstuff from BIH. Goletić (1999) reported enhanced concentrations of Cd, Pb, Cu, and Fe in carrot, onion, lettuce, and spinach grown in the vicinity of the ironworks in Zenica (BIH; Table XI), caused by high concentrations of these TEs in the soil and atmospheric deposits. Concentrations of TEs were highly increased and far above normal concentrations, regardless of crop species (Goletić, 1999). However, concentrations of Cd and Pb in investigated crops differ depending on plant species. It is well known that leafy vegetables are prone to accumulating high concentrations of TEs. Indeed, in the area of Zenica's ironworks, the concentrations of TEs were higher in lettuce and spinach than in onion and carrot (Table XI).

Table XI. Mean and ranges (in brackets) of trace element concentrations in vegetables, sediments, and soil at the area of ironwork in Zenica, BIH (dry weight) (Goletić, 1999).

Crop	n	Cd (mg kg^−1)	Pb (mg kg^−1)	Cu (mg kg^−1)	Fe (mg kg^−1)
Carrot	9	1.35 (1.15–1.65)	1.53 (1.0–2.0)	1.07 (1.0–2.0)	39.5 (19.5–75.0)
Onion	9	2.77 (2.52–2.90)	5.93 (5.0–6.80)	2.10 (1.0–3.80)	30.2 (26.0–43.0)
Lettuce	9	4.02 (3.90–4.16)	16.0 (11.5–18.4)	11.6 (9.40–15.0)	459 (373–578)
Spinach	9	2.04 (1.80–2.22)	6.93 (4.5–9.75)	21.2 (20.5–22.0)	438 (409–471)
Sediments^a (mg m^–2 day^–1)	9	0.003 (0.001–0.003)	0.13 (0.02–0.31)	0.01 (0.001–0.02)	3.54 (1.32–6.78)
Soil (mg kg^−1)	9	6.70 (6.16–8.10)	82.2 (62.1–130)	56.8 (38.7–74.8)	44,160 (34,233–53,846)
BIH – Bosnia and Herzegovina. ^aAtmospheric deposits.

Accumulation of TEs in the soil

Annual TE inputs to agricultural land in Serbia from different sources and respective outputs are summarized in Table XII. The details of calculations are explained in the table. There is a general lack of representative nation-wide data for several parameters which are necessary to make a precise assessment of a mass balance of TEs. However, in most cases, the presented data indicate more than 10 times of higher input of TEs to agricultural land than their output. That is partly caused by high values for dry and wet TE deposition, which were measured at sites localized in urban areas. Because of low fertilizer consumption (~80 kg of active matter per hectare of agricultural land), the inputs of most of the TEs by fertilizers are low, except for the increased inputs of Cr, Mn, and Cu, which is a consequence of a high distribution of these TEs in some fertilizer products (Milinović et al., 2008; Stevanović et al., 2009). A highly positive balance of TEs on agricultural land has lead to the accumulation of TEs, which can harmfully affect the food chain as well as terrestrial and aquatic environments. This can be a problem particularly in urban areas.

Table XII. Estimated average inputs of trace elements to agricultural land in Serbia, output and balance (g ha^–1 year^–1).

Source	Cr	Cd	Ni	Pb	Mn	Cu	Zn	As
Input of trace elements	25.7–117	1.79–49.7	17.1–145	26.6–458	531–2660	266–538	561–9081	1.55–6.04
Atmospheric deposition
Dry deposition^a	5.0–30.2	0.15–69.5	8.29–95.7	0.69–376	97.5–326		21.0–8034
Wet deposition^b	–	1.21–1.77	7.94–9.15	21.2–65.9	70.1–76.9	177–213	461–704
Mineral fertilizers^c	0.73–63.5	0.18–2.90	1.09–18.0	1.27–10.9	1.90–1738^d	2.13–177^d	0.82–67.4^e	0.16–2.09^f
Animal manure^g	20.0–23.0	0.25–0.60	5.49–22.7	3.42–5.25	362–519	86.9–148	78.5–276	1.39–3.95
Output of trace elements
Removal by crops^h	0.29–0.54	0.06–0.82	0.32–1.53	0.65–6.22	10.5–290	4.76–25.0	0.32–294	0.32–2.95
Balance	25.4–116	1.73–50.2	16.8–144	25.9–452	521–2370	261–513	561–8787	1.22–3.09
^aOn the basis of average annual values in a network of 23 urban air sampling units (Institute of Public Health of Serbia “Dr Milan Jovanovic Batut”, 2009). ^bAverage for two experimental stations (Republic Hydrometerological Service of Serbia, 2009). Based on data from Statistical Yearbook of Serbia (2009) and TE concentrations in fertilizers given by ^cStevanović et al. (2009), ^dMilinović et al. (2008), ^eBogdanovic et al. (1999), and ^fSager (1997). ^gBased on data from Statistical Yearbook of Serbia (2009) and TE values given by Nicholson et al. (2003), Bolan et al. (2004), and Kabata-Pendias and Pendias (1992). ^hBased on data from Statistical Yearbook of Serbia (2009) and TE values shown in Tables IV–VI.

Regulations on TEs in soils and fertilizers

The current legislation in most countries utilizes total metal concentrations as a simple index of hazard in contaminated soils. In some European countries, for example in Croatia, metal limits based on pH criteria are used, recognizing that pH is the major factor affecting metal availability (Official Gazette RC, 2001, 2010). The Serbian legislation regulates maximum permissible concentrations of TEs in the soil (Official Gazette SFRY, 1994), fertilizers, and substrates as well as maximum quantities of TEs that can enter the soil with fertilizers (Official Gazette RS, 2009). In Croatia, Official Gazette RC (2010) regulates the use of sewage sludge and biosolids for agricultural production. In BIH, the control of the quality of soils and fertilizers is also defined by state regulations (Official Gazette BIH, 2009). However, monitoring of the soil quality with respect to TEs in this region is mostly related only to industrial and urban areas.

Research perspectives

Comprehensive studies and constant monitoring of soil and foodstuff are necessary in order to protect the food chain from toxic TEs; to enhance the food quality by supplying not only the essential plant micronutrients but also by supplying elements that are non-essential for plant growth but are essential for animals and humans. Research is also needed to assess the influence of agronomic management on TE supply to plants in order to achieve better utilization of TEs. Furthermore, a screening programme of plant genotypes for finding those less sensitive to micronutrients deficiency and B toxicity is highly required. There is also a need to harmonize the legislation in all SEE countries with that of the EU and to implement threshold and toxicity levels.

Acknowledgements

This study is part of the project “Improving nutritional quality and safety of food and fodder crops in South Eastern Europe (SEE) countries” (Project 5) under the Norwegian Programme “Institutional collaboration between academic institutions in Agriculture, Forestry and Veterinary Medicine in Norway and Bosnia and Herzegovina, Croatia, Serbia and Montenegro”. The financial and technical assistance from the project is gratefully acknowledged.