HEAVY METAL CONTENT OF DIFFERENT VEGETABLES GROWN IN URBAN GARDEN SOILS OF SZEGED
Zsuzsanna Szolnoki*, Andrea Farsang
University of Szeged, Department of Physical Geography and Geoinformatics 6722 Szeged, Egyetem str. 2-6. *e-mail: szolnoki@geo.u-szeged.hu
SUMMARY
Urban soils are not only the recipients of anthropogenic heavy metals, these soils can easily become the source of these toxic and potentially toxic elements. The consumption of vegetables grown in contaminated urban gardens can be an important exposure pathway of residents to these non-degradable pollutants, because heavy metals can enter the plants and thus the food chain.
We investigated the heavy metal content of soil samples and different vegetable types derived from 20 vegetable gardens of Szeged in order to assess the possible harmful effects of home-produced vegetable consumption.
The investigated garden soils of Szeged can generally be considered to be unpolluted, but anthropogenic enrichment of copper is evident in these soils. The investigated leafy vegetables (lettuce, sorrel, spinach) accumulated significantly more arsenic, zinc and cadmium, than the analyzed root vegetables (onion, carrot), but none of the analyzed vegetables samples grown in these urban sols had so high cadmium or led concentrations which would be above the threshold limit (maximum limit in food products).
1. INTRODUCTION
Concentrations of heavy metals are often higher in urban soils than those in rural soils around the cities, reflecting several metal inputs arising from anthropogenic activities (heavy traffic, industrial emission, waste disposal, domestic heating etc.) (Thornton, 1991). Among urban soils, garden soils are recipients of further metal load from cultivation (using pesticides containing metals, mixing compost as well as organic and artificial fertilizers into the soil etc.) (Csathó, 1994). Heavy metals are of particular concern due to their long residence time in the soils and their toxicity to humans (Kabata-Pendias and Pendias, 2001). Taken up by plants, these toxic substances may enter the food chain in significant amounts. Therefore, people could be at risk of adverse health effects from consuming vegetables and fruits grown in urban soils containing elevated metal concentrations.
The aim of this study was to determine the heavy metal content of garden soils in Szeged and of different vegetable types grown in these soils in order to assess the possible harmful effects derived from consumption of vegetables grown in urban garden soils.
2. MATERIALS AND METHODS
We collected composite topsoil (0–10 cm) samples (N=20) and different vegetables (lettuce, sorrel, spinach, carrot, and onion) (N=35) from 20 vegetable gardens in Baktó, a district on the outskirts of Szeged, Hungary.
After laboratory preparation, the soil samples were digested with aqua regia whereas the edible parts of the vegetable samples were digested in concentrated nitric acid in a microwave oven and then the concentrations of heavy metals and As were measured by inductively coupled plasma optical emission spectrometer (ICP-OES).
3. RESULTS AND DISCUSSION
The mean concentration of all the studied metals was below the Hungarian pollution limit value1(PLV) in the soil samples, whereas the maximum concentrations of As, Cd, and Cu were above the PLV (Table 1). Furthermore, mean concentration of Cu was significantly higher than the background concentration2 (BC), which was indicative of the anthropogenic impacts on the soil Cu status (Table 1). Generally, the metal contents ofvegetable garden soils reflected no significant metal contamination, except for Cu.
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The highest concentrations were measured in the case of Zn followed by Cu, Ni, and Cr, whereas concentrations of Cd, Pb, and Co were the lowest in the analyzed vegetables (Table 2). Concentrations of As, Zn and Cd were significantly higher in leafy vegetables than in root vegetables (Table 2). Nevertheless, Cd and Pb concentrations (converted to fresh weight based on the moisture content) in all the analyzed vegetable samples were below the maximum concentration limit values established for these metals in foodstuffs by the European Commission (Commission Regulation (EC) no. 1881/2006).
4. CONCLUSIONS
The soils of the studied vegetable gardens of Szeged can generally be considered to be unpolluted, but the anthropogenic enrichment of Cu is evident in these soils. The leafy vegetables of the analyzed vegetables accumulate significantly more As, Zn and Cd than the root vegetables. Nevertheless, none of the vegetables grown in these garden soils have so high Cd or Pb concentrations which would be above the threshold limit (maximum limit in foodstuffs), these vegetable are suitable for human consumption, so consuming root and leafy vegetables grown in the studied urban gardens do not pose any threat on human health.
ACKNOWLEDGMENT
This research was supported by theEuropean Unionand theState of Hungary, co-financed by the European Social Fundin the framework of TÁMOP-4.2.4.A/ 2-11/1-2012-0001 ‘National Excellence Program’.
REFERENCES
1 Risk substance, with due regard in the case of the geological medium to the full range of soil functions and the sensitivity of groundwater to pollution. Pollution limit values are defined by the Joint Decree No. 6/2009. (IV. 14) KvVM-EüM-FVM
2 Representative value, typical concentration of a particular substance reflecting natural, or close to natural, conditions in the soil. Background concentrations are defined by the Joint Decree No. 10/2000. (VI. 2) KöM-EüM-FVM-KHVM
Csathó, P. (1994): A környezet nehézfém szennyezettsége és az agrártermelés. MTA-TAKI, Budapest
Kabata-Pendias, A., Pendias, H. (2001): Trace Elements in Soils and Plants. (third ed.) CRC press, Boca Raton Thornton, I. (1991): Metal contamination of soils in urban areas. In: Bullock, P., Gregory, P.J. (Eds.), Soils in the Urban Environment. Blackwell, Oxford, pp. 47–75.
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