Metal contamination of soils and crops affected by the Chenzhou lead/zinc mine spill (Hunan, China)
Introduction
Mining activity is a chief source of metals entering into the environment. In the process of mining exploitation and ore concentrating, mine tailing and wastewaters are created, and dust is emitted. This results in the surrounding environment being severely polluted. The most serious problem is that of spilled mine tailing. Since 1970, there have been 35 reported major mine tailing dam failures around the world resulting in significant soil and river pollution and the loss of more than 500 lives (Macklin et al., 2003). In 2000 alone, there were a total of five reported accidents (in China, Romania, Sweden, and USA; Macklin et al., 2003).
In China, on August 25th, 1985, the mine tailing dam of Chenzhou lead/zinc mine (Hunan, southern China) collapsed because of heavy rain. In that disaster, a strip of farmland about 400 m in wide on both sides of the Dong River channel was covered with an about 15-cm-thick layer of black sludge. After the collapse of the dam, an emergency soil clean-up procedure was quickly carried out in some places. The toxic sludge and a major portion of the contaminated soil surface were mechanically removed. Nevertheless, most of the contaminated farmlands are still covered with spills and a part of these contaminated farmlands are cultivated at present.
Crops can uptake toxic elements through their roots from contaminated soils, and even leaves can absorb toxic elements deposited on the leaf surface. Queirolo et al. (2000) found that corn and potatoes (+skin), growing in a volcano-influenced location of Talabre (Northern Chile), contain very high arsenic concentration in the edible parts (1.85 and 0.86 mg kg−1 fresh weight, respectively), exceeding the National Standard of Chile for arsenic (0.5 mg kg−1) by approximately 400% and 180%, respectively.
Chronic lower level intakes of toxic elements have damaging effects on human beings and other animals (Ikeda et al., 2000), since there is no efficient mechanism for their elimination, and the detrimental impact becomes apparent only after several years of exposure (Bahemuka and Mubofu, 1999). Consuming food contaminated by Pb, Hg, As, Cd and other metals can seriously deplete body stores of Fe, vitamin C and other essential nutrients, leading to decreased immunological defenses, intrauterine growth retardation, impaired psycho-social faculties and disabilities associated with malnutrition (Iyengar and Nair, 2000). Türkdogan et al. (2003) found that the high concentrations of metals (Co, Cd, Pb, Mn, Ni and Cu) in fruit and vegetables in Van region of Eastern Turkey are related to the high prevalence of upper gastrointestinal (GI) cancer rates. Lacatusu et al. (1996) reported that the soil and vegetables polluted with Pb and Cd in Copsa Mica and Baia Mare, Romania, significantly contributed to decreased human life expectancy within the affected areas, reducing average age at death by 9–10 years.
In Chenzhou Pb/Zn mine area (Fig. 1), previous investigations have shown that soil and waters were severely polluted by heavy metals (Zeng et al., 1995, Zeng et al., 1997). It is therefore anticipated that crops grown in this area cannot be free from metals pollution. Thus far, there still has been very little published information on the uptake of toxic elements by cereal, vegetables and pulses in the Chenzhou Pb/Zn mine affected area after the mine tailing dam collapse. The objective of this paper is; (1) to quantify the content of metal in soil and crops; (2) to investigate the degree of pollution and the daily intake amount of toxic elements through foods; (3) to identify the relationship between accumulation of toxic elements by plants and the extent of soil contamination; (4) to assess the long-term effects on the environment surround.
Section snippets
Description of the sampling sites
Chenzhou lead/zinc mine is located about 10 km east of Chenzhou city, Hunan Province, southern China (Fig. 1). In 1988, the annual production capacity was 4,855 tons of lead, 4,869 tons of zinc, 300 tons of tungsten, 87 tons of bismuth, 200 tons of molybdenum, 2.33 tons of sulfur and 15.42 tons of silver. More than 3800 workers were engaged in the mining, smelting, and transport services associated with the mining activities, which continue at full speed today.
The Dong River runs through this
Physical–chemical characteristics of soil samples
Descriptive statistics of physical–chemical characteristics of the soils are presented in Table 2. The REF soil is acidic (pH 4.7). Soils at SZY are weakly acidic, with about 80 % of the soils having pH values lower than 5.6. Most soils at GYB are alkaline, about 70 % of the soil pH values are higher than 7.0. Although a large variability is observed among the individual samples soils from JTC, the mean pH value is nearly neutral.
Mean organic matter and organic carbon contents of the soils
Long-term effect on soil physical–chemical characteristics and metal concentrations
Comparing the pH values of soils from the four sites and those history data in the literature (pH values range from 5.12 to 5.89, Zeng et al., 1997), the pH values of soils from GYB and one soil sample from JTC (see Table 2) are evidently raised (pH>6.0), and a wide range of variation is found between these samples. This situation may be the result of the addition of lime to the soil to stabilize toxic metal mobility. The large variations on the other parameters (OM, OC, N, CEC, etc.) may be
Conclusion
This field study indicates that the physical–chemical properties of soils obviously change due to the different farming styles implemented by individual farmers. The effects of leaching extraction and plant extraction of metals from soils are quite weak. Soils and crops are still severely contaminated with As, Cd, Zn, Pb and Cu in the mine spills contaminated area of Chenzhou Pb/Zn mine (Hunan province, southern China). The extent of contamination was in the order: GYB>SZY>JTC. Arsenic and
Acknowledgements
The authors thank Carole Boucayrand, Frederic Candaudap, Michel Valladon and Remi Freydier from the Laboratoire des Mécanismes de Transfert en Géologie (Toulouse, France) who brought their help in clean room and during ICP-MS analytical work. The authors also thank Adrienne Miller (Lorain County Community College, USA) for her editing help. This work benefits from the Chinese–French cooperation project support (project no. PRA E 00-04) and Hongyu LIU benefits from the CSC (China Scholarship
References (25)
- et al.
Heavy metals in edible green vegetables grown along the sites of the Sinza and Msimbazi Rivers in Dar es Salaam, Tanzania
Food Chem.
(1999) - et al.
Arsenic in soil and vegetation of contaminated area in southern Tuscany (Italy)
J. Geochem. Explor.
(2004) Ecological impact and remediation of contaminated sites around lead smelters in Poland
J. Geochem. Explor.
(1995)- et al.
Heavy metal distribution in some French forest soils: evidence for atmospheric contamination
Sci. Total Environ.
(2003) - et al.
Urban population exposure to lead and cadmium in east and south-east Asia
Sci. Total Environ.
(2000) - et al.
The long term fate and environmental significance of contaminant metals released by the January and March 2000 mining tailing dam failures in Maramures County, upper Tisa Basin, Romania
Appl. Geochem.
(2003) - et al.
Arsenic round the world: a review
Talanta
(2002) Toxic metals in sewage sludge-amended soils: has promotion of beneficial use discounted the risks?
Adv. Environ. Res.
(2003)- et al.
Total arsenic, lead, and cadmium levels in vegetables cultivated at the Andean villages of northern Chile
Sci. Total Environ.
(2000) - et al.
Survey of arsenic and other heavy metals in food composites and drinking water and estimation of dietary intake by the villagers from an arsenic-affected area of West Bengal, India
Sci. Total Environ.
(2003)
Effect of Ni and As on radish tuber cultivated on artificially polluted soils
Eur. J. Soil Biol.
Multielement concentrations in vegetable species grown in two typical agricultural areas of Greece
Sci. Total Environ.
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Present address: Department of Environmental Science and Engineering, Hunan University, Changsha, 410082 China.