Risk assessment of heavy metals in soil previously irrigated with industrial wastewater in Shenyang, China

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Abstract

The Zhangshi Irrigation Area (ZIA) in Shenyang, China has been irrigated by industrial wastewater since 1962. Since then, parts of the ZIA have been rezoned for industrial uses, but the remaining area, named Sluice Gate III (SLIII) and Lower Reaches (LR), still occupies 1825 ha. Although land irrigation with industrial wastewater ceased in 1992, a study on heavy metals in soils was carried out to assess the feasibility of agricultural crop cultivation in SLIII and LR. A detailed field investigation was conducted and both total heavy metal concentrations and bioavailable fraction in soil were determined.

The results have highlighted that Cd concentrations in soils still exceed the Environmental Quality Standard for Soil in China (GB15618-1995) grade C standard in SLIII region, and grade B standard in LR. In the SLIII, Zn and Pb concentrations in soil are higher than the grade A standard, although Cu is close the grade A standard. In SLIII the dominant chemical fractions were the exchangeable and carbonatic forms, which represent up to 43% and 35% of the Cd, respectively. The Cd in these two fractionations poses the highest risk for the plant absorption and accumulation. Therefore the SLIII should be abandoned for cultivated crops to prevent the Cd contamination of food chain and any associated hazards to human health.

Introduction

Land irrigation with wastewater has a long history in agricultural areas in China. In China, although the wastewater treatment capacity is 35.785 × 106 t/day, only 40% of total wastewater discharged is treated [1], and some of un-treated wastewater from industries and communities is used for land irrigation. Although wastewater irrigation may increase the agricultural production and farmers’ incomes, many contaminants in municipal and industrial wastewater are sequestered in the soils and consequently pose environmental problems. Heavy metals in wastewater are one of the main causes of soil contamination in China [2], [3]. Chen et al. reported that 45% of wastewater irrigation areas in China are contaminated with heavy metal at the most serious level [4]. Cadmium and lead are the elements most seriously contaminating Chinese soils, with up to 13,000 ha of arable land in 25 regions in 11 provinces polluted by Cd, and the quantity of Cd-contaminated rice reaching 50 million kg in 1999 [4], [5].

Heavy metal contamination of soils through wastewater irrigation is a widespread and serious problem in many countries, for example, in Germany, France and India [6], [7], [8]. The contaminants may transfer into the food chain, in particularly if the contaminants are sequestered in bioavailable forms. Many crops accumulate heavy metals and result in an inexorable rise in the metal content of a farm's production [9], [10]. Food chain translocation of heavy metals is one of the consequences of soils polluted with such elements, and excessive intake of heavy metals is associated with human health problems, e.g. itai–itai disease (caused by excess Cd) and Minamata disease (excess Hg).

The total amount of heavy metals in a soil can be used to quickly assess the condition of a soil through comparison with regulatory guideline values. However, increasingly the bioavailable fraction of heavy metals in soil is deemed essential for risk assessment purposes. Heavy metal mobility and availability in soils is frequently studied with sequential extraction procedures, which allow partitioning the total metal content into different fractionations. For instance, the Tessier method and Testing Programme of the European Commission (formally BCR method) are widely used for sequential extraction to assess metal partitioning in contaminated soils and to predict their environmental risks[11], [12], [13], [14], [15].

In Zhangshi Irrigation Area (hereafter abbreviated to ZIA), the wastewater originates from the industrial districts of Shenyang, and is produced from many industries, including the Shenyang Smelter that produces zinc, lead and a small amount of gold. Land irrigation with wastewater in ZIA commenced in 1962 [16]. At that time in China an emphasis was placed on increasing production of food crops, and consequently many dry-land agricultural regions were converted to paddy farms and wastewater used for irrigation. The wastewater discharged from factories, including the wastewater supplied to ZIA, was largely untreated and contained high levels of heavy metals and other pollutants.

Based on a number of previous studies related to ZIA [16], [17] which narrated the historical perspective and temporal variation in heavy metals in soils across the whole ZIA. The local government decided parts of ZIA (Sluice Gate I and Sluice Gate II areas) were to be used for industrial construction, rather than agriculture. The remaining area, named Sluice Gate III (SLIII) and Lower Reaches (LR), still occupies 1825 ha, and although land irrigation with wastewater has not been practiced for 14 years (having ceased in 1992), the utilization of the land in SLIII and LR is still of concern to governmental authorities and local farmers. Consequently, as part of a National Basic Research Program of China (973 Project) entitled “Forming mechanism of environmental pollution and ecological remediation of contaminated environment in old industrial base in northeastern China” (2004–2009), the aim of the project is to study the consistency of temporal change of metal concentrations in soil and assess the feasibility of agricultural crop cultivation in the SLIII and LR areas. Following risk assessment incorporating aspects of remediation technology [18], [19], [20], [21], [22], the management and remediation options for the ZIA were suggested.

Section snippets

Terrain investigation and sampling

The ZIR is located in the western suburbs of Shenyang (Long. 122°25′–123°48′E and Lat. 41°12′–42°17′N) shown in Fig. 1. Shenyang in northeastern China is the capital city of Liaoning Province, and its boundaries encompass a total area of 8515 km2, and a population of some 6 million. Shenyang is a major communication hub and trade centre in northeast China. It is also one of China's major steel, metal-fabricating and machinery-manufacturing centres.

The field sites of the study were established in

Heavy metal concentrations of soils in ZIA

Cd, Pb, Cu and Zn concentrations of soil in SLIII, LR and control area are shown in Fig. 2. The mean Cd concentration in the 0–20 cm soil layer in SLIII is 1.75 mg kg−1 (n = 21; range 0.42–3.93 mg kg−1). The mean Pb, Cu and Zn concentrations in the 0–20 cm soil layer in SLIII are 40.46 mg kg−1, 32.15 mg kg−1 and 150.10 mg kg−1, respectively. The mean Cd, Pb, Cu and Zn concentrations in the 0–20 cm soil of control area are only 0.10 mg kg−1, 21.60 mg kg−1, 16.88 mg kg−1 and 46.46 mg kg−1, respectively.

A comparison of

Conclusion

From an historical perspective ZIA provided a short-term agricultural and economic success in terms of increased product and farmers’ income, but long-term land irrigation with untreated wastewater has now proven to be the cause of significant soil contamination. The Sluice Gate III and Lower Reaches are the only remaining areas of ZIA and although irrigation with wastewater ceased 14 years ago, the Cd concentration in soil at SLIII area is higher than prescribed by China's grade C standard,

Acknowledgements

The research presented here was supported by National Basic Research Program of China (973 Project 2004B418506) and in part by the Victorian Department of Primary Industries (ORLE Project #08271).

References (29)

  • Q. Wang et al.

    Instances of soil and crop heavy metal contamination in China

    Soil Sediment. Contam.

    (2001)
  • J. Ingwersen et al.

    Modeling the environmental fate of cadmium in a large wastewater irrigation area

    J. Environ. Qual.

    (2006)
  • S. Singh et al.

    Heavy metal load of soil, water and vegetables in peri-urban Delhi

    Environ. Monit. Assess.

    (2006)
  • S.R. Kumar et al.

    Heavy metal contamination of soil and vegetables in suburban areas of Varanasi, India

    Ecotoxicol. Environ. Saf.

    (2007)
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