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1、J. Geogr. Sci. 2010, 20(1): 135-147 DOI: 10.1007/s11442-010-0135-8 2010 Science in China Press Springer-Verlag Received: 2009-04-24 Accepted: 2009-06-18 Foundation: National Natural Science Foundation of China, No.40701164, No.40730526; Public Project of Ministry of Environmental Protection of China
2、, No.WFLY-2009-1-SK-06-03; National Key Water Program during the 11th Five-Year Plan Period, No.2009ZX07317-006 Author: Sun Chao (1985), specialized in water resource and water environment in urban area. E-mail: *Corresponding author: Bi Chunjuan, E-mail: Assessment on environmental quality of heavy
3、 metals in agricultural soils of Chongming Island, Shanghai City SUN Chao, *BI Chunjuan, CHEN Zhenlou, WANG Dongqi, ZHANG Cui, SUN Yuedi, YU Zhongjie, ZHOU Dong School of Resources and Environmental Science, East China Normal University, Shanghai 200062, China Abstract: The environmental quality of
4、heavy metals (Pb, Cd, Cr, As, Hg) in agricultural sur- face soil of Chongming Island was assessed by national, local and professional standards based on a large scale investigation, in which 28 samples from vegetable plots, 65 samples from paddy fields and 9 samples from watermelon fields were colle
5、cted from whole island area. Results showed that the average concentration of Pb, Cd, Cr, As and Hg was 21.6 mgkg1, 0.176 mgkg1, 69.4 mgkg1, 9.209 mgkg1 and 0.128 mgkg1, respectively. Com- pared with the background value of Shanghai City soil, except for Pb and Cr, all the other heavy metals average
6、 concentrations in Chongming Island agricultural surface soil exceeded their corresponding natural-background values. The concentrations of Cd, As and Hg were 33.0%, 1.2% and 26.3% higher than the background value of Shanghai City, respectively. In addition, inverse distance interpolation (IDW) tool
7、 of GIS was also applied to study the spatial variation of heavy metals. The results indicated that most of agricultural soil quality was good, and the ratio of ecological, good soil, certified soil and disqualified soil were 1.26%, 97.1%, 1.47% and 0.12%, respectively. About 10.1%, 85.7%, 27.0%, 55
8、.4% and 55.2% soil samples exceeded the Pb, Cd, Cr, As and Hg background value of Shanghai City, respectively. Among these three land use type soils, vegetable soil was most seriously polluted by heavy metals, which is probably related to the over-application of pesticides. The annual deposition flu
9、xes of Pb, Cd, As and Hg were 7736 gm2a1, 208 gm2a1, 2238 gm2a1 and 52.8 gm2a1, respectively. Crop straw burning was the important source of heavy metals of atmospheric deposition, and atmospheric deposition contributed a lot to heavy metals in agricultural soil in Chongming Island. Keywords: agricu
10、ltural soil; heavy metals; assessment; Chongming Island 136 Journal of Geographical Sciences 1 Introduction Soil serves as many vital functions in our society, particularly for food production and hu- man health. Therefore, it is very important to protect this resource and ensure its sustainabil- it
11、y. Heavy metals pollution in agriculture soils is of great concern and leads to the functional disorder of soil, interferences with crop growth, and even impair human health through a contaminated food chain. In recent years, studies focused on heavy metals accumulation in agricultural soils have be
12、en reported, mainly including accumulation characteristics (Zheng et al., 2005a, 2005b, 2005c, 2005d; Chen et al., 2005; Guo et al., 2008), spatial distribution (Zheng et al., 2003; Zhao et al., 2007; Hu et al., 2004; Zhu et al., 2006; Zheng et al., 2006; Cheng et al., 2006; Zhang et al., 1997; Mart
13、in et al., 2006; Huang et al., 2003; Hu et al., 2006; Zhao et al., 2007), pollution evaluation (Ma et al., 2006; Chen et al., 2006; Zheng et al., 2006), source identification (Wang et al., 2006; Colqan et al., 2003; Facchinelli et al., 2001) and food security (Cai et al., 2004; Guo et al., 2005; Dud
14、ka et al., 1994). Chongming Island, lying in the estuary of the third biggest river of the world, Yangtze River, is one of the most potential developing spaces of Shanghai. Agriculture is the leading industry of Chongming Island, and farmland in the study area predominantly consists of paddy fields
15、and vegetable plots. The 2004 population census reported that more than 75% of employed people are engaged in agriculture for both subsistence and commercial purpose. However, the high population density and modern agricultural development have put great pressure on the natural and economic resource
16、s. A number of substantial environmental pressures and symptoms of environmental degradation have been identified in recent years. There have been a lot of researches on soil heavy metals contents in the study area. However, these researches mainly focused on a small amount of sampling sites, such a
17、s sampled from tidal flat (Lv et al., 2007), roadside soils (Wang et al., 2007a), river sediments (Wang et al., 2007) and vegetable plot (Wang et al., 2007b, 2007c). Few works was reported about large-scale investigation and study of heavy metals levels in agricultural soils of whole Chongming Islan
18、d. In this paper, by a dense sampling site setting, we try to: firstly, measure the contents of selected heavy metals (Pb, Cr, Cd, As and Hg) of Chongming Island agricul- tural soils; secondly, map the heavy metals distribution character through spatial interpola- tion to identify their spatial patt
19、erns in the region; thirdly, evaluate the agricultural soils quality based on several different evaluation standards; finally, calculate the atmospheric deposition fluxes of individual heavy metals in the study area. The results of this research may be useful for the local government in alleviating
20、heavy metals contamination in the course of rapid development as an eco-island. 2 Materials and methods 2.1 Description of the study area Chongming Island, lying between 121.16121.90E and 31.4531.85N, is located at the intersection zone of the Yangtze River and the East China Sea. Covering about 1.2
21、25103 km2 and increasing about 5 km2 annually because of the deposition of sediments transported by the Yangtze River, the island is the third largest in China and the largest alluvial island in the world. The middle and northeast of the island are higher than the southwest and the east. SUN Chao et
22、 al.: Assessment on environmental quality of heavy metals in agricultural soils of Chongming 137 The island is of subtropical monsoon climate, which is a comfortably warm and humid cli- mate with sufficient rainfall and distinct changes of seasons. The soil types mainly include paddy soil, calcareou
23、s alluvial soil and coastal saline soil. 2.2 Sample collection and analysis A total of 102 samples, 28 samples from vegetable plots, 65 samples from paddy fields and 9 samples from watermelon fields, were collected from Chongming Island agricultural land. In each sampling site, about 810 sub-samples
24、 of topsoil (020 cm) were taken and then mixed thoroughly to obtain a bulk sample. The coordinates of the sample locations were recorded with a portable GPS, and the sampling sites are shown in Figure 1. Figure 1 A sketch map showing the sampling sites Wet and dry atmospheric deposition was collecte
25、d by continuously open containers at Chongming Island by every month from November 2007 to October 2008 to determine the atmospheric deposition fluxes of heavy metals (Pb, Cd, As and Hg). The samples were fil- trated by 0.45 m filter and divided into soluble subsamples (water samples) and insoluble
26、subsamples (particle samples) for Pb, Cd, As and Hg analysis. Sampler consisted of four polyethylene containers pre-cleaned in laboratory then soaked in 10% (v/v) HNO3 for more than 24 h and finally rinsed thoroughly with MilliQ water and air dried. In order not to be influenced by some point source
27、 pollution, human disturbance and soil dust, the sampler was deployed with clear surrounding airspace at a height of 34 m (Morselli et al., 2003). Soil samples were stored in sealed polyethylene (PE) package, and then transported to the laboratory and preserved in a refrigerator. The samples were fr
28、eeze-dried, thoroughly mixed, ground and sifted by 0.125mm sieve for the heavy metals measurement. About 0.25g dried soil sample was weighed out and digested with concentrated HNO3, HF and HClO4 in the microwave oven operating at 0.3106 Pa 6min, 0.6106 Pa 4min, 0.9106 Pa 4min, 1.2106 Pa 3min, 1.5106
29、 Pa 8min and 1.8106 Pa 8min. Subsequently, the concentrations of Cr, Cd and Pb were determined by a Perkin-Elmer AANALYST 800 atomic adsorption spectro- 138 Journal of Geographical Sciences photometer analyzer, and flame law was used for measurement of Cr, graphite stove method for Cd and Pb. The co
30、ncentrations of As and Hg were determined by a Titan AFS9230 atomic fluorescence spectrometer analyzer. Soil particle size was determined by a Beckman Coulter LS13320 laser grain analyzer. Synchronously, a standard soil reagent (GSD-9) was used for quality assurance and qual- ity control (QA/QC). Th
31、e recoveries for the 5 observed heavy metals came up to the stan- dards of quality control. The analysis accuracy was also checked by the duplicated samples, and the standard deviation was less than 10%. The acid employed in sample analysis was guaranteed reagent and all solutions were prepared by u
32、ltrapure water (resistivity 18.2 Mcm). 3 Results and discussion 3.1 Physicochemical characteristics of soil The physicochemical parameters of the agricultural soils in this study are presented in Table 1. The average pH value of the soils was 7.31, ranging from acidic to alkaline (6.018.12). The alk
33、aline soil may be related to the input of atmospheric deposition and various con- struction materials and wastes. The average Eh value of the soils was 18.53, showing that most of the sampled soils were reductive due to 64% soil samples from paddy fields. The average content of TOC was 2.16%. The me
34、an particle size of the soils ranged from 15.90 m to 47.46 m. Table 1 The physicochemical parameters of agricultural soils in Chongming Island Item Parameter Minimum Maximum Arithmetic mean S.D.a C.V.b pH 6.01 8.12 7.31 0.43 0.06 Eh 66.00 55.70 18.53 23.53 1.27 TOC/% 0.37 4.29 2.16 0.74 0.34 Soil Pa
35、rticle size/m 15.90 47.46 27.22 6.39 0.23 a Standard Deviation b Coefficient of Variation 3.2 Statistics of heavy metals contents The descriptive statistics of heavy metals levels in agricultural topsoil in Chongming Island were summarized in Table 2. Table 2 Statistics of heavy metals concentration
36、s in agricultural soils of Chongming Island HMsa Number Skewness Kurtosis B.V.b/ mgkg1 Minimum/ mgkg1 Maximum/ mgkg1 Arithmetic mean/mgkg1 S.D./ mgkg1 C.V. Standard-exceeding ratio/% Pb 99 0.115 0.056 25.47 14.19029.255 21.597 3.0280.140 10.1 Cd 97 0.895 1.464 0.13230.087 0.330 0.176 0.0460.263 85.7
37、 Cr 102 0.301 0.261 75.00 49.81592.261 69.395 8.8540.128 27.0 As 101 0.072 0.459 9.10 2.142 18.373 9.209 3.3540.364 55.4 Hg 96 0.820 0.549 0.10120.000 0.388 0.128 0.0790.618 55.2 a Heavy metals b Background values of Shanghai SUN Chao et al.: Assessment on environmental quality of heavy metals in ag
38、ricultural soils of Chongming 139 The soil background values of Shanghai (Wang et al., 1992) were used as the reference values. The mean contents of all measured heavy metals in soils except Pb and Cr slightly exceeded the reference values. The variation coefficient of Hg (0.618) in soils was relati
39、vely higher than the other heavy metals (from 0.128 to 0.364), which demonstrated that the spatial variation of Hg content in soils was greater. Skewness values indicated that the levels of all measured heavy metals in soils conformed to normal distribution. The background value of soil in Shanghai
40、was ex- ceeded by 10.1% of Pb, 85.7% of Cd, 27.0% of Cr, 55.4% of As and 55.2% of Hg in the soil samples collected from the study area. The standard-exceeding ratio demonstrated the fol- lowing order: Cd As Hg Cr Pb. 3.3 Spatial distributions of heavy metals According to different assessment standar
41、ds, Chongming Island agriculture soil quality was classified into 5 grades based on the pH value and heavy metal levels of all sampled soils. The classification criterions are presented in Table 3. The heavy metals contents of Grade 1, namely ecological grade, are lower than the background values of
42、 soil in Shanghai (Wang et al., 1992). Grade 2, namely superior grade, conforms to Environmental Standard of Safe, Healthy, High Quality Agricultural Products (Shanghai Local Standard, DB31/T 2522000). Grade 3, namely satisfactory grade, conforms to Green Food-Technical Conditions for En- vironmenta
43、l of Area (NY/T3912000). Grade 4, namely certified grade, conforms to Envi- ronmental Requirements for Origin of Non-environmental Pollution Vegetable (NY50102001). Grade 5 is disqualified grade. Table 3 Evaluation standards of soil/mgkg1 Grade pH Pb Cd Cr As Hg 1 Not limited 25.47 0.1323 75.00 9.10
44、 0.1012 2 Not limited 35 0.3 85 13 0.20 7.5 50 0.4 120 20 0.35 7.5 350 0.6 250 25 1.0 250 0.3 150 40 0.3 6.57.5 300 0.3 200 30 0.5 5 7.5 350 0.6 250 25 1.0 According to the potential ecological risk indexes of multiform heavy metals (RI) under different pH values, the soil integrated evaluation was
45、classified into 5 grades. Based on GIS, inverse distance interpolation (IDW) was used to determine the heavy metals spatial distri- bution and to draw the evaluation maps of integrated indexes (Figure 2). 0 11 / nn iiii rrn ii RIETCC = = 140 Journal of Geographical Sciences where RI is the potential
46、 ecological risk indexes of multiform heavy metals; E i ris the poten- tial ecological risk factor of single heavy metal; T i ris the toxic response factor (Pb: 5, Cd: 30, Cr: 2, As: 10, Hg: 40); C i nis the measured value of heavy metals contents; and C0 i is the ref- erence value of heavy metals c
47、ontents (the background values of soil heavy metals in Shang- hai are used as the reference values in the study). Most of agricultural soils were good, and the ratio of ecological soil, superior and satis- factory soil, certified soil and disqualified soil were 1.26%, 97.1%, 1.47% and 0.12%, re- spe
48、ctively (see Figure 2). The ecological soil spread on Chongming Island as some small spots. The superior soil, accounting for 72.11% of the total area, had the widest distribution and largest area. The satisfactory soil mainly distributed in Chenjia Town, Gangyan Town, Shuxin Town, Sanxing Town and
49、some regions of Nongchang. The disqualified soil mainly distributed in Gangyan Town and had the smallest area. According to the content of single heavy metal under different pH values, the soil quality was classified into 5 grades. Based on GIS, inverse distance interpolation (IDW) was used to determine the heavy metals spatial distribution and to draw the evaluation maps of single index (Figure 3). The evaluation and classification maps of single index of agricultu