HEAVY METALS CONTAMINATION IN VEGETABLES GROWN IN URBAN AND METAL SMELTER CONTAMINATED SITES IN AUSTRALIA ANTHONY GEORGE KACHENKO∗ and BALWANT SINGH Faculty of Agriculture, Food and Natural Resources, Ross Street Building A03, The University of Sydney, New South Wales 2006, Australia (∗ author for correspondence, e-mail:
[email protected], Tel. +61-2-9351-2917, Fax: +61-2-9351-5108)
(Received 11 November 2004; accepted 28 July 2005)
Abstract. Dietary exposure to heavy metals, namely cadmium (Cd), lead (Pb), zinc (Zn) and copper (Cu), has been identified as a risk to human health through the consumption of vegetable crops. This study investigates the source and magnitude of heavy metal contamination in soil and vegetable samples at 46 sites across four vegetable growing regions in New South Wales, Australia. The four regions Boolaroo, Port Kembla, Cowra and the Sydney Basin were a mix of commercial and residential vegetable growing areas. The extent of metal contamination in soils sampled was greatest in regions located in the vicinity of smelters, such as in Boolaroo and Port Kembla. Soil metal concentrations decreased with depth at these two sites, suggesting contamination due to anthropogenic activities. Cadmium, Pb and Zn contamination was greatest in vegetables from Boolaroo, and Cu concentrations were greatest in vegetables sampled from Port Kembla. At Boolaroo, nearly all the samples exceeded the Australian Food Standards maximum level (ML) (0.01 mg kg−1 fresh weight) of Cd and Pb in vegetables. Over 63% of samples exceeded international food standard guidelines set by the Commission of the European Communities and the Codex Alimentarius Commission. All vegetables sampled from Cowra, which is a relatively pristine site had Cd and Pb levels below the Australian and international food standards guideline values. This study suggests that the Australian guideline values are more conservative in defining the ML for Cd and Pb in vegetable crops. This investigation highlights the increased danger of growing vegetables in the vicinity of smelters. Keywords: contamination, transfer coefficients, guidelines, heavy metals, uptake
1. Introduction The implications associated with metal (embracing metalloids) contamination is of great concern, particularly in agricultural production systems. Metals most often found as contaminants in vegetables include As, Cd and Pb. These metals can pose as a significant health risk to humans, particularly in elevated concentrations above the very low body requirements (Gupta and Gupta, 1998). The contamination of agricultural soils is often a direct or indirect consequence of anthropogenic activities (McLaughlin et al., 1999). Sources of anthropogenic metal contamination in soils include - urban and industrial wastes; mining and smelting of non ferrous metals and metallurgical industries (Singh, 2001). Commercial Water, Air, and Soil Pollution (2006) 169: 101–123
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and residential vegetable growing areas are often located in urban areas, and are subject to anthropogenic contamination. Fernandez–Turiel et al. (2001) found elevated levels of heavy metals in urban soils located within the vicinity of a Pb smelter in Lastenia, Argentina. The heavy metals found at elevated concentrations were Pb (31–8714 mg kg−1 ), Cd (0.27–30.68 mg kg−1 ), Cu (21–242 mg kg−1 ) and Zn (44–4637 mg kg−1 ). A study of urban soil contamination by Beavington (1973) found elevated levels of Cu (343 mg kg−1 ) in the industrial area of Wollongong, New South Wales (NSW), Australia. Other sources of anthropogenic contamination include the addition of manures, sewage sludge, fertilizers and pesticides to soils, with a number of studies identifying the risks in relation to increased soil metal concentration and consequent crop uptake (Whatmuff, 2002; McBride, 2003). Both commercial and residential growing areas are also subject to atmospheric pollution, in the form of metal containing aerosols. These aerosols can enter the soil and be absorbed by vegetables, or alternatively be deposited on leaves and adsorbed. Studies of vegetables grown in locations close to industry have reported elevated levels of heavy metals. Vousta et al. (1996) studied the impact of atmospheric pollution from industry on heavy metal contamination in vegetables grown in Greece. The results of the study indicated significantly higher levels of metal accumulation in leafy vegetables as compared with root vegetables. This partitioning of Cd is well known, with accumulation of greater concentrations in the edible leafy portions of crops, than the storage organs or fruit (Jinadasa et al., 1997; Lehoczky et al., 1998). Both Cd and Pb are considered as the most significant heavy metals affecting vegetable crops. In Australia and New Zealand, the maximum level (ML) of Cd and Pb allowable in vegetable crops has been set by the Australian and New Zealand Food Authority (ANZFA) (ANSTAT, 2001). For Cd the ML is 0.1 mg kg−1 fresh weight (FW) for all vegetable types. The ML of Pb is also 0.1 mg kg−1 FW for all vegetable types excluding Brassicas (0.3 mg kg−1 FW). The Commission of the European Communities (2001) and the Codex Alimentarius Commission (2001, 2004) sets similar levels of Cd and Pb for vegetable crops. Both organisations set the ML for Cd as 0.2 mg kg−1 FW for leafy vegetables and fresh herbs, 0.1 mg kg−1 for stem and root vegetables and 0.05 mg kg−1 for the remaining ungrouped vegetables. For Pb, both organizations set the ML of 0.3 mg kg−1 FW for brassicas, leafy vegetables and herbs, and 0.1 mg kg−1 FW for all remaining vegetables. The level of Cd in vegetables of commercial growing regions located within the Sydney Basin has been extensively studied (Jinadasa et al., 1997). To our knowledge, there are no systematic published studies on metals contamination in Australian vegetable growing regions, particularly in urban and metal smelter contaminated sites. In this study we investigated the concentrations of As, Cd, Cu, Pb and Zn in both soil and vegetable crops within vegetable growing regions of NSW, Australia; and evaluated their contamination status with respect to Australian and international food standard guidelines.
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Figure 1. Location of sampling regions.
2. Materials and Methods 2.1. SAMPLING
SITES
Soil and plant samples were collected from 46 sites within four regions across NSW, Australia (Figure 1). There were 24 sites sampled in the Sydney Basin, 11 in Boolaroo, 6 in Port Kembla and 5 in the Cowra region. The sites were a mixture of commercial vegetable farms and private residential vegetable gardens. The regions of Boolaroo and Port Kembla (both residential) were within close proximity to industrial sites. The region of Boolaroo is located 140 km north of Sydney, NSW. The region was host to a Pb–Zn smelter located in the centre of Boolaroo which had been in operation since 1897, ceasing operations in September 2003. Tam and Singh (2004) suggested that the smelter is the primary source of soil heavy metal contamination in the immediate region surrounding the smelter. The region of Port Kembla is situated 80 km south of Sydney, NSW, and was home to a Cu smelter (which ceased operation in July 2003), steelworks and fertilizer plant among other smaller industry. Previous studies have indicated soil contamination, primarily in the nearby urban areas surrounding the Cu smelter (Beavington, 1973). At Port Kembla and Boolaroo, sampling sites were within a 3 km radius of the smelter and representative of soil metal concentrations observed in previous studies. The remaining two regions, Sydney Basin (residential and commercial) and Cowra (commercial) have no obvious point source of pollution. The sites in the Sydney Basin are located in the metropolitan city of Sydney and may have diffused pollution from manufacturing industries, the application of sewage sludge and other waste
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materials. The agricultural region of Cowra is located approximately 300 km west of Sydney and has minimal contamination from anthropogenic sources, and can be considered as relatively pristine. 2.2. SOIL
AND PLANT SAMPLING
A total of 113 soil samples and 138 plant samples were collected from 46 sites in the four regions. A transect of 5 × 5 m was selected at random at each site from which both soil and vegetable samples were collected. From each transect two composite soil samples were collected with a stainless steel auger, at 0–30 cm (n = 69) and at 60–90 cm (n = 44) depths. Each composite soil sample (1 kg) was taken from 5 thoroughly mixed subsamples taken at random locations within the transect. At commercial vegetable growing sites two transects were sampled to account for site variability among soil samples. At the second transect only topsoil samples were collected. Soil texture varied from sand to loam, sandy clay loam to heavy clay. According to The Australian Soil Classification system (Isbell, 1996), soils in the Boolaroo region included Brown/Yellow Chromosols, Yellow Kandosols and Brown/Yellow Dermosols. Soils sampled in Cowra comprised of Red/Brown Chromosols and Red/Brown Dermosols and from Port Kembla included Brown Chromosols and Brown Dermosols. Greatest variation in soil types was observed in soils sampled from the Sydney Basin, and included; Red/Brown Chromosols, Yellow Brown Dermosols, Aeric Podosols, Yellow Brown Kandosols and Yellow Brown Kurosols. The edible portions of 2 plants (e.g. leafy, root, fruit) were randomly sampled from each transect. Leafy vegetables were preferred for sampling since past research shows that they accumulate heavy metals at a greater capacity than other vegetables (Jinadasa et al., 1997; Lehoczky et al., 1998). The number of plant samples collected from the Sydney Basin was 82, from Boolaroo 22, Port Kembla 18, and Cowra 16 (Table II). The vegetables sampled include 56 lettuce (Lactuca sativa L.), 44 spinach (Spinacia oleracea L.), 8 cabbage (Brassica oleracea L.), 6 leek (Allium porrum L.), 4 rhubarb (Rheum rhabarbarum L.) and 2 beetroot (Beta vulgaris). Herbs sampled included 14 parsley (Petroselinum crispum var. crispum) and 4 mint (Mentha spicata L.). 2.3. SOIL
ANALYSIS
The soil samples were air-dried, mechanically ground using a stainless steel roller and sieved to obtain
