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Salinity and Persistent Toxic Substances in Soils from Shanghai, China
Pedosphere 19(6): 779–789, 2009 ISSN 1002-0160/CN 32-1315/P c 2009 Soil Science Society of China Published by Elsevier Limited and Science Press
Salinity and Persistent Toxic Substances in Soils from Shanghai, China∗1 SHI Gui-Tao1,2 , CHEN Zhen-Lou1,∗2 , XU Shi-Yuan1 , YAO Chun-Xia1 , BI Chun-Juan1 and WANG Li1 1 Key Laboratory of Geographic Information Science of Ministry of Education, East China Normal University, Shanghai 200062 (China) 2 Polar Research Institute of China, Shanghai 200136 (China)
(Received October 18, 2008; revised September 10, 2009)
ABSTRACT Some farmland soils in Shanghai had high salinity levels, suggesting secondary salinization of the soils. The soil problems in Shanghai were studied, including the salinity and nitrate nitrogen (NO − 3 -N) concentrations, heavy metal pollution characteristics, and organochlorine pesticide (OCP) residual levels and polycyclic aromatic hydrocarbon (PAH) contents. Accumulation of NO− 3 -N in vegetable soils was the most significant among different functional soils. Heavy metal pollution was significant in the samples collected from the sewage-irrigated land and roadside. The identification of the metal sources through multivariate statistical analysis indicated that Pb, Zn, Cu and Cr in urban soils were from the traffic pollutants; excessive application of fertilizer and irrigation were the main reasons for the metal pollution in agricultural soils; Ni in the observed soils was controlled by parent soils. OCPs could still be detected in farmland soils but degraded greatly in last 20 years after prohibition of their usage. PAHs with 2–3 rings were the main components in industrial soils. The concentrated PAHs in the investigated soils were likely from petroleum and coal combustion. Key Words:
heavy metal, OCP, PAH, salinity, soil environment
Citation: Shi, G. T., Chen, Z. L., Xu, S. Y., Yao, C. X., Bi, C. J. and Wang, L. 2009. Salinity and persistent toxic substances in soils from Shanghai, China. Pedosphere. 19(6): 779–789.
INTRODUCTION Soil provides the nutrition for plants and also acts as a recipient of undesirable materials. Human health and environmental quality are strongly dependent on the soil quality (Simpson, 1996; De Kimple and Morel, 2000). With accelerated urbanization and industrialization, urban soils have been disturbed severely due to dense human activities, and contaminants have been accumulated significantly in the soils. Pollutants in soils can be transported to surrounding media as well as remote environmental components via different approaches, e.g., runoff, food chain and volatilization (Chen et al., 1997; Barra et al., 2005); thereby contaminant-enriched soils are the secondary pollution sources by re-emission (Harner et al., 2001). Among the persistent toxic substances (PTS) in soils, heavy metals and persistent organic pollutants (POPs) are the predominant components. Urban soils are known to have high heavy metal levels (Manta et al., 2002), and varied sources, such as industrial production, vehicle exhaust, and waste disposal, could be the contributions (Kock and Rotard, 2001; Sheets et al., 2001). The significant accumulation of heavy metals in urban soils could affect the construction of green-lands, urban environmental quality and people’s health via contact with the polluted soils (Nevin, 2000). In addition, heavy metals (e.g., Cr, Zn, Pb, Cd and Ni) could accumulate in farmland soils at toxic levels as a result of long-term ∗1 Project
supported by the National Natural Science Foundation of China (Nos. 40730526 and 40701164), the National Maritime Bureau of China (Nos. HAD1 and HAD2), and the Shanghai Tongji Gao Tingyao Environmental Science and Technology Development Foundation of China. ∗2 Corresponding author. E-mail: [email protected].
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application of untreated wastewaters (Chary et al., 2008). The toxic metals in the sewage-irrigated soils could be transferred through food chains and consequently cause adverse health effects on human potentially (Chary et al., 2008). As a widespread pollutant, POP contamination has become a global problem. There are 12 substances for global action in the Stockholm Convention on POPs, including 8 pesticides, 2 industrial chemicals, and 2 byproducts (Wang et al., 2005). As a big agricultural country, China increased foodstuff output largely depending on extreme usage of pesticides. Organochlorine pesticides (OCPs), e.g., hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs), constitute 80% of the total pesticides produced between 1950s and 1970s and their high usage resulted in high HCHs/DDTs residual levels in some regions of China (Wei et al., 2007). A large quantity of chemical fertilizer was used in farmlands for promoting productivity, and the value for Shanghai was 613 kg ha−1 in 2006, which was much higher than that of the developed countries (Shanghai Statistical Bureau, 2007). As a result, excessive salinity (e.g., nitrate and nitrite) was accumulated in soils. It is reported that vegetables are the primary dietary source (more than 80%) of nitrate of human being (White, 1975). So, salinity in soils could harm human health potentially by food chains. Moreover, a high residue of salinity could limit the growth of crops, constrain agricultural productivity, and in severe case, lead to the abandonment of agricultural soils (Ghollarata and Raiesi, 2007). Based on the aforementioned facts, it is significant to study the soil problems in Shanghai in detail. The objectives of this study are as follows: (1) the salinity and nitrate nitrogen (NO− 3 -N) concentrations in different functional soils were measured; (2) heavy metal pollution characteristics in soils were analyzed and their main sources were identified by the aid of multivariate statistical analysis; and (3) OCP residual levels in farmland soils and polycyclic aromatic hydrocarbon (PAH) contents in industrial soils were determined. MATERIALS AND METHODS Site description and sampling Shanghai is located in the east coast of China, with the center at 31.14◦ N and 121.29◦ E, and the Yangtze River flows into the East China Sea along its north. The city has a total area of 6 340.5 km2 , 0.06% of China’s total territory. At the end of 2005, the population reached more than 17 million (NPFPCC, 2006). The soil types of Shanghai mainly include paddy soil, fluvo-aquic soil, coastal saline soil and yellow-brown soil, which belong to 4 soil groups, 7 subtypes, 24 soil genus and 95 soil species (Xu, 2004). At present, Shanghai is a city where economy and urban construction development is the fastest in China. Large population and dense industrial activities have discharged a tremendous amount of waste to the urban environment. Fig. 1 shows the discharge of waste water and gas in recent years (Shanghai Statistical Bureau, 2007). In general, the amount of discharged wastes had been increasing
Fig. 1
Discharge of waste water and gas from 2000 to 2006 in Shanghai.
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steadily since 2000 except waste water emissions during the years of 2001–2003, and the decrease of waste water was probably due to the three-year (2000–2002) environmental action plan in Shanghai. Sampling sites are illustrated in Fig. 2. For the measurement of salinity and ions, 122 soil samples were collected from the farmlands of Pudong, Nanhui, Jinshan and Fengxian. Twenty four profiles in the farmlands were conducted, and soils in the depth of 0–20, 20–40 and 40–60 cm at each profile were collected. In all, 236 soil samples were collected from seven different functional soils for the determination of NO− 3 -N. To understand the contamination characteristics of heavy metals, 191 urban soils from small towns (Fengjing, Songjiang and Zhujiajiao), urban parks and roadside (along Yan’an road, which traverses Shanghai) were collected. In all, 46 agricultural soils were collected from farmlands in Songjiang and Pudong. In addition, 21 soil samples were collected from two industrial zones, and contents of 16 US EPA (Environmental Protection Agency) priority pollutant PAHs were determined. For anonymity, the two industrial zones were assigned the codes A and B. The residual levels of HCHs and DDTs were measured in 202 samples collected from farmlands.
Fig. 2
Sketch map of the study area and soil sampling sites.
All the observed soil samples were collected with a stainless steel spatula, and four subsamples of surface soils (0–10 cm) were taken and then mixed thoroughly to obtain a bulk sample (about 1 kg) for each sampling site. All the collected samples were kept in Ziploc bags to avoid contamination; subsequently, the samples were transported to the laboratory and preserved under freezing conditions. Sample preparation and analysis The soil samples were air-dried, thoroughly mixed, ground to pass through a 1.0-mm sieve for the determination of salinity and ions, and through a 0.125-mm sieve for the measurement of heavy metals and POPs. The soils passed through a 1.0-mm sieve were treated with distilled water at a soil to water ratio of 1:5 (w/v) in a plastic bottle. The bottle was tightly capped, shaken at 150 r min−1 for 5 min, and the mixture was filtered with suction. Total soluble salts in the filtrate were measured by the mass of the residue after the evaporation of solution, K+ and Na+ concentrations by flame photometry, Ca2+ −1 and Mg2+ by atomic absorption spectrophotometry, NO− CaCl2 (1:10 3 by the method of 0.01 mol L 2− of soil to CaCl2 solution) with continuous flow analysis, SO4 by turbidimetry with BaCl2 using a SHIMADZU UV/V Spectrometer (Shimadzu, Kyoto, Japan), Cl− by titration with AgNO3 , and CO2− 3 and HCO− by double indicator titration (Lu, 2000). 3 Soil samples for determining heavy metal levels were digested with concentrated HNO3 , HF and HClO4 in a microwave oven operating at 0.3 MPa 3 min, 0.6 MPa 2 min, 1.0 MPa 2 min, 1.5 MPa 2 min, and 2.0 MPa 6 min. A Perkin-Elmer AANALYST800 atomic adsorption spectrophotometer analyzer (Perkin-Elmer, Waltham, MA, USA) was employed for the determination of Pb, Zn, Cu, Cr, Cd, and Ni. A series of soil/sediment standards were used for quality assurance and quality control (QA/QC),
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and these were GSS-6 and GSD-9 geochemical reference materials, which were supplied by the National Research Center for Certified Reference Materials of China. The recoveries for the observed metals were between 90% and 110%. The accuracy analysis was also checked by the duplicated samples, and the standard deviation ranged within 5%. The blank determinations were also performed in triplicate throughout all the experiment. Organochlorine pesticides were extracted from soil samples with dichloromethane and PAHs with dichloromethane/acetone (v/v = 1:1) mixture in an ultrasonic extractor. Terphenyl was used as internal standard for analysis of PAHs, and 2,4,5,6-tetrachloro-m-xylene and decachlorobiphenyl for OCPs. Volume was reduced after extraction under a gentle nitrogen stream at ambient temperature, and fractionation was achieved on silica gel column. The column is made of pyrex glass, 500 mm long with 11 mm diameter. Silica of 10.0 g was weighed into a glass container, and 0.3 mL of deionized water was added. The silica gel was homogenized overnight after vigorous shake, activated at 130 ◦ C for 24 h, and cooled down in a dessicator. Organochlorine pesticides in the samples were measured by gas chromatography with electron capture detector (Agilent6890N, Agilent, Santa Clara, CA, USA) and PAHs by high performance liquid chromatography with fluorescence detection (Agilent1200, Agilent, Santa Clara, CA, USA). The recoveries for OCPs and PAHs were 35%–90% and 64%–106%, respectively. Statistical analysis Multivariate statistical analyses of the data were carried out by means of the Origin and SPSS software packages. The essence of principal components analysis (PCA) is converting the variables under investigation into factors or principal components (PCs) so that correlation among the original variables can be minimized. In this study, data were log-transformed prior to PCA to reduce the influence of high values. Bartlett sphericity test and Kaiser-Meyer-Olkin test indicated that the normalized data were suitable for PCA. Varimax with Kaiser normalization rotation was applied to increase the variances of the factor loadings across variances for each factor. In addition, the correlations between the original variables are presented in the form of nonparametric Pearson correlation coefficients. RESULTS AND DISCUSSION Salinity in farmland soils The salinity and ion concentrations in farmland soils in the suburbs of Shanghai are listed in Table I. All the average salinity contents in the observed districts except Pudong were under salinization standard (Zu, 1986). In general, salinity content less than 2.0 g kg−1 can not affect the normal growth and development of crops. However, the maximum salinity contents were all above the standard, indicating some soils are unfavorable for the plant growth. Anions in the investigated soils were predominated − − 2+ , Na+ . In general, ion levels in the soils by SO2− 4 , Cl , NO3 , whereas cations were mainly by Ca − 2− from Pudong and Nanhui, especially NO3 and SO4 , were higher than the other two districts. The correlations between the levels of salinity and ions were analyzed, and the results indicated that there (r = 0.89), Cl− (r = 0.71), and NO− were significant correlations between salinity levels and SO2− 4 3 (r = 0.79) concentrations at the 0.01 level, namely, the soil salinization levels in Shanghai were controlled by these three anions. The three anions are partly from the parent materials, but they mainly originate from auxiliary or transformation components of chemical fertilizer (Yao, 2005). Therefore, the secondary salinization of suburban soils is mainly related to improper application of fertilizer. The salinity and ion concentrations in the depth of 0–20 cm were higher than those in the depth of 20–40 and 40–60 cm (Fig. 3), which agrees well with the reports for other regions (Rhoades et al., 1992; De Pascale and Barbieri, 1997). In suburbs of Shanghai, an increasing quantity of chemical fertilizer is used to increase the yield of foodstuff, which leads to soil secondary salinization, especially in the greenhouse. However, high evaporation of freestanding irrigation and no dilution of precipitation also contribute to the salinization (Shimojima et al., 1996; Lagreid et al., 1999; Janmaat, 2004).
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TABLE I Salinity and ion concentrations in farmland soils of Shanghai Region
Parameter
Salinity
NO− 3
HCO− 3
C1−
SO2− 4
Pudong
Minimum Maximum Average SDa) Minimum Maximum Average SD Minimum Maximum Average SD Minimum Maximum Average SD
0.53 7.12 3.57 2.23 0.49 8.02 1.92 1.94 0.22 3.73 1.23 1.10 0.65 3.27 1.56 0.72
0.01 0.93 0.31 0.31 0.01 0.73 0.17 0.19 0.01 0.42 0.12 0.13 0.01 0.19 0.06 0.05
0.01 0.20 0.03 0.06 0.01 0.02 0.01 0.00 0.01 0.02 0.01 0.00 0.01 0.02 0.01 0.00
0.03 0.57 0.23 0.17 0.05 0.53 0.18 0.13 0.04 0.39 0.14 0.09 0.04 0.35 0.14 0.10
g kg−1 0.19 2.58 1.09 0.95 0.21 3.78 0.78 0.96 0.10 1.16 0.33 0.27 0.09 1.79 0.35 0.41
Nanhui
Jinshan
Fengxian
a) Standard
Ca2+
Mg2+
K+
Na+
0.06 0.80 0.37 0.26 0.03 0.56 0.20 0.16 0.03 0.49 0.15 0.13 0.01 0.22 0.08 0.07
0.02 0.34 0.14 0.12 0.01 0.56 0.14 0.15 0.02 0.08 0.04 0.02 0.01 0.13 0.05 0.03
0.01 0.28 0.11 0.11 0.03 0.58 0.11 0.14 0.00 0.06 0.02 0.02 0.01 0.11 0.03 0.02
0.06 0.91 0.30 0.28 0.06 0.42 0.20 0.11 0.06 0.29 0.16 0.07 0.06 0.29 0.13 0.06
deviation.
Fig. 3 Salinity and ion concentrations in soil profiles of farmlands in Shanghai. A, B, C, D, E, F, G, H and I represent − 2− − 2+ , Mg2+ , K+ and Na+ , respectively. Salinity, NO− 3 , HCO3 , Cl , SO4 , Ca Fig. 4 NO− 3 -N concentrations in different functional surface soils. 1–7 represent greenhouse vegetable land, open vegetable land, traditional vegetable land, residential district land, woodland, park soil and paddy field, respectively. − Levels of NO− 3 -N in different functional soils are shown in Fig. 4. The results showed that NO3 -N concentrations differed significantly among various functional soils. Especially, NO− 3 -N concentrations in residential district soil, forest soil, park soil and paddy soil were low, about one order magnitude lower than those in vegetable soils. The use of high levels of chemical fertilizer may be the direct contribution to the high concentrations of NO− 3 -N in vegetable soils (Liang and MacKenzie, 1994). The utilization ratio of nitrogen by vegetable is relatively low. Because most vegetables are nitrophile crops, excessive nitrogenous fertilizer is used in vegetable land for promoting productivity. Sometimes, the quantity of the used fertilizer is several times higher than the actual requirement. Therefore, surplus of nitrogen was accumulated in the soils.
Heavy metals in soils The descriptive statistics of heavy metal contents in urban soils are summarized in Table II. The heavy metal background values of soils in Shanghai (Wang, 1992) are used as references to check the
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heavy metal contamination. The average contents of heavy metals except Ni greatly exceeded the reference values. Meanwhile, the mean levels of Zn were above the trigger concentration, the recommended mean of Zn in soils used for recreation and agriculture (ICRCL, 1987). In general, the accumulation processes of heavy metals in the soils of small towns and parks were similar, which were much lower than those in roadside soils. TABLE II Heavy metal contents in urban soils of Shanghai Region Small towns (n = 117)
Urban parks (n = 44)
Roadside (n = 30)
Parameter Average Maximum Minimum SDb) Average Maximum Minimum SD Average Maximum Minimum SD
Background valuec) Trigger concentrationd) a) Not
analyzed;
b) Standard
deviation;
Cu
Zn
48.60 492.44 9.52 53.42 44.57 151.74 23.12 27.63 80.78 138.79 27.43 26.66
303.13 1 812.50 0.88 325.51 198.54 1 025.65 102.45 144.93 452.20 895.71 141.71 208.01
28.59 130
83.68 300
c) Cited
from Wang (1992);
Cr mg 86.52 711.98 3.31 95.98 77.01 163.70 25.53 30.80 153.31 233.26 97.17 34.17 75.00 600 d) Cited
Pb
Cd
Ni
48.26 253.68 1.40 42.58 55.06 174.35 26.39 32.49 93.61 192.38 13.72 48.68
0.32 2.10 0.08 0.29 0.40 0.67 0.19 0.13 0.70 3.66 0.21 0.64
NAa) NA NA NA 31.17 65.70 4.95 15.27 31.09 51.85 14.70 9.64
25.47 500
0.13 1.0
31.19 70
kg−1
from ICRCL (1987).
The loadings of measured metal contents in the coordinate system of three PCs are illustrated in Fig. 5a. The observed heavy metals were well represented by the first three PCs, which constituted 80% of the total variance. Three heavy metal groups were clearly distinguished in urban soils. Pb, Zn, Cu, and Cr were highly loaded in PC1, which constituted 53.01% of the total variance. There were significant correlations between their levels in urban soils (Table III), which imply that these four metals in urban soils originate from similar pollution sources, such as the deposition of aerosol particles emitted by vehicular traffic (Bullock and Gregory, 1991; Cyrys et al., 2003; Gray et al., 2003). Ni showed a higher value in the third component (PC3), and the mean level of Ni in the soils was comparable to the background value (Table II). Therefore, it can be concluded that the parent materials of soils control Ni content. In PC2, Cd showed a higher value, distinguishing itself from the other heavy metals. This reflects different anthropogenic or geogenic sources and possible pathways of accumulation from the other five investigated metals.
Fig. 5 Three-dimensional plot loadings (PC1, PC2 and PC3) of heavy metals in urban (a) and farmland soils (b) by principal component (PC) analysis.
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TABLE III Pearson correlative coefficients of heavy metals in urban and farmland soils of Shanghai Soil
Heavy metal
Cu
Zn
Cr
Urban
Cu Zn Cr Pb Cd Ni Cu Zn Cr Pb Cd Ni
1
0.673** 1
0.501** 0.607** 1
1
0.212 1
0.740** 0.418* 1
Farmland
Pb 0.508** 0.580** 0.578** 1
0.200 −0.022 0.288 1
Cd 0.241* 0.161 0.259* 0.104 1 −0.022 0.342* 0.038 0.118 1
Ni 0.158 0.232* 0.151 0.322** 0.078 1 −0.075 0.453 0.146 0.320 −0.152 1
*,**Significant at P = 0.05 and P = 0.01 levels, respectively.
Heavy metal contents in agricultural soils are illustrated in Fig. 6. In general, farmland soils had lower heavy metal contents than urban soils, and the metal accumulation processes in sewage-irrigated soils were the most significant among the observed samples. Metal contents in the farmland soils were lower than grade 2 of soil standard, which are recommended means of heavy metal limits in agricultural soils in China, and comparable to the background values in Shanghai (Wang, 1992). However, all the investigated elements except Cr and Pb in sewage-irrigated soils were above the soil standards and much higher than the soil background values.
Fig. 6 Heavy metal contents in different functional soils of Shanghai. Error bars represent standard deviations of heavy metals.
The heavy metal sources of sewage-irrigated soils were specific compared with other functional soils. In detail, the observed land was irrigated by wastewater in 1970s–1980s. Another fact is that the sediment of urban river was used in the investigated land in 1970s. As a result, heavy metals in sewageirrigated soils were especially high. The heavy metals in farmland soils could be classified into three groups (Fig. 5b). PC1 was dominated by Cu and Cr, and there was a strong correlation between them (Table III). It can be concluded that they are from the same source. Fig. 6 showed that the variation coefficient of Cr was relatively low, indicating that the homogeneous source dominated. In addition, Cr content was higher than the background value, so the parent material is not the major source. From the previous works, atmospheric deposition would be the major contribution (Manno et al., 2006; Sabin et al., 2006). The loadings of Pb and Ni levels in PC2 were 0.699 and 0.927, respectively, and the contents of the two elements were slightly lower than the background values (Fig. 6). Hereby, PC2 represents the parent materials of soils influencing metal contents. Cd and Zn showed high values in PC3, combined
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with the better correlation of the two metals. Furthermore, contents of both the elements were much higher than the background values, different from the other elements in farmland soils. It is well known that fertilizer is a major source of heavy metals in farmland, especially the toxic element Cd from the phosphate fertilizer (Mulla et al., 1980). Thus, it is found that utilization of chemical fertilizer is the main source of Cd and Zn. POP contents in soils Residual levels of OCPs in farmland soils are shown in Fig. 7. The residual mean of HCHs (α-, β-, γand δ-HCH) was 4.41 μg kg−1 with a range of 0.03 to 17.3 μg kg−1 . In terms of spatial distribution, HCH average content in Songjiang (6.77 μg kg−1 ) was the highest, which was followed by Qingpu, Jinshan, Minhang, and Fengxian. DDT (p,p -DDT, p,p -DDD, and p,p -DDE) contents ranged between 1.00 and 64.70 μg kg−1 in the observed soils, with a mean of 20.30 μg kg−1 . Among the average contents of DDTs in the five study regions, the maximum was present in Minhang and the minimum was in Qingpu. It was noticeable that the contents of DDTs were 2–10 times HCHs in the study districts, and the difference is associated with the historical soil use and different degradation rates of OCPs (Shi et al., 2005).
Fig. 7 Residual levels of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) in farmland soils of Shanghai. Error bars represent standard deviations. Fig. 8 Residual levels of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) in farmland soils in different years of Shanghai. The data of 1980s are from Wang (1991).
Compared with OCP contents (HCHs of 1.17 μg kg−1 and DDTs of 11.57 μg kg−1 ) in industrial soils (Xie, 2006), the concentrations of HCHs and DDTs in farmland soils were higher (Fig. 7). This indicated that the large amount of OCP usage during 1960s–1970s led to the enrichment of HCHs and DDTs in farmland soils. The temporal variation of OCP residual levels in farmland soils is shown in Fig. 8. The results indicated that the concentrations of HCHs and DDTs in farmland soils decreased significantly with the values in this paper being 25% and 17%, respectively, of the mean levels in 1980s. The difference of OCP levels implies that since the use of OCPs was banned for agriculture soils in 1983 in China, most of the OCPs have been removed or degraded in the soil. Contents of 16 US EPA priority pollutant PAHs in soils from two industrial zones are shown in Table IV. The PAHs in soils were dominated by 2–3 ring components, specifically, fluorene and phenanthrene for zone A, naphthalene and acenaphthylene for zone B. In general, both components and total PAH concentrations in zone A were much lower than those in zone B. The intervention value of total PAHs (40 mg kg−1 ) is the maximum tolerable concentration above which remediation is required (van Volkshuiswesting, 2000), and the mean content of total PAHs in B-zone soils was above the intervention value, corresponding to serious contamination.
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TABLE IV Contents of US EPA (Environmental Protection Agency) priority pollutant polycyclic aromatic hydrocarbons (PAHs) in industrial soils of Shanghai PAH
Zone B (n = 12)a)
Zone A (n = 9) Range
Mean mg
NDb) –8.90 ND–0.20 NAc) ND–19.00 ND–34.30 ND–5.60 ND–7.80 ND–4.30 NA ND–1.70 ND–1.00 ND–0.80 ND–0.80 ND–0.60 ND–1.40 ND–1.50 ND–81.90
Naphthalene (Nap) Acenaphthylene (Acy) Acenaphthene (Ace) Fluorene (Flu) Phenanthrene (Phe) Anthracene (Ant) Fluoroanthracene (Fla) Pyrene (Pyr) Benzo[a]anthracene (BaA) Chrysene (Chr) Benzo[b]fluoranthene (BbF) Benzo[k]fluoranthene (BkF) Benzo[a]pyrene (BaP) Dibenzo[a,h]anthracene (DAH) Benzo[g,h,i]perylene (BGP) Indeno[1,2,3-c,d]pyrene (InP) Total a) Cited
from Zhao (2006);
b) Not
detectable;
c) Not
1.11 0.03 NA 4.12 4.07 0.70 1.32 0.92 NA 0.42 0.21 0.20 0.28 0.07 0.26 0.23 13.94
Range
Mean
0.15–90.29 0.33–60.51 ND–22.38 0.002–12.13 0.004–2.59 0.008–2.05 0.08–12.05 0.09–34.02 0.0005–24.76 0.04–18.21 0.09–4.97 0.1–5.04 0.002–12.21 0.003–50.87 ND–7.61 0.002–2.87 3.95–246.28
18.28 11.62 3.40 1.83 0.56 0.44 2.80 7.50 4.39 3.49 1.64 1.39 3.09 5.52 1.55 0.48 67.96
kg−1
analyzed.
The differences of PAHs in the soils over the two zones may be associated with the different industrial activities. In detail, the industries in zone A are mainly manufacturing, whereas chemical industries are predominant in zone B. PAHs could be derived from several different sources, e.g., petrogenic, pyrogenic, or biogenic (Tolosa et al., 2004), and the high levels of PAH in B-zone soils could be attributed to chemical factory pollutants. In addition, PAH ratios could be the indicators of PAH source (Yunker et al., 2002). The ratio of Flu/(Flu+Pyr) in zone A was 0.8 (> 0.5), which indicates that pyrogenic source (e.g., coal combustion) is predominant. In zone B, the ratio of Flu/Flu+Pyr was 0.2 (< 0.5), suggesting that petrogenic source is predominant. The low molecular weight to high molecular weight (LMW/HMW) is another index that can be used to assess the various sources of PAHs, such as residue of oils, combustion/maturation of organic mater, petrogenic/pyrolytic origin pollution. The values of LMW/HMW in B-zone soils were higher than 1, indicating the residue of the oils (Soclo et al., 2000). CONCLUSIONS Some of the farmland soils had a secondary salinization trend in Shanghai. The anions in the study − and NO− soils were mainly SO2− 4 , Cl 3 , which were correlated well with the salinity content. The -N in vegetable soils was related to excessive application of nitrogen significant accumulation of NO− 3 fertilizer. Soils from sewage-irrigated land and roadside had higher heavy metals, whereas the contents for farmland soils were relatively low, comparable to the background values. Based on the results of multivariate statistical analysis, Pb, Zn, Cu, and Cr in urban soils were from the traffic pollutants. However, human activities, i.e., chemical fertilizer application and irrigation, contributed to the heavy metals in agricultural soils. In addition, Ni in urban soils and Pb and Ni in farmland soils with low concentrations were influenced by weathering materials from parent soils. HCHs and DDTs could still be detected in farmland soils. Nevertheless, the residues of both HCHs and DDTs in this study were much lower than those in 1980s due to the prohibition of their production and usage since early 1980s. Petrogenic and pyrogenic sources were the main contributions of concentrated PAHs in the industrial soils.
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Some works have been done on soil quality in Shanghai. However, the researches on POPs in soils of Shanghai are still deficient. Most of the available data are focused on a few OCPs, with little or no data on other organic pollutants, such as chlorophenol, atrazine, phthalate esters, PCDD/Fs, etc. Furthermore, the migration and transformation of pollutants in different interfaces (e.g., atmospheresoil, soil-plant and water-sediment) arouse less concern. Therefore, further work is still needed to ravel POP pollution as well as the migration and transformation of PTS in soils. REFERENCES Barra, R., Popp, P., Quiroz, R., Bauer, C., Cid, H. and von T¨ umpling, W. 2005. Persistent toxic substances in soils and waters along an altitudinal gradient in the Laja River Basin, Central Southern Chile. Chemosphere. 58(7): 905–915. Bullock, P. and Gregory, P. J. (eds.). 1991. Soils in the Urban Environment. Blackwell Scientific Publications, Oxford. Chary, N. S., Kamala, C. T. and Raj, D. S. S. 2008. Assessing risk of heavy metals from consuming food grown on sewage irrigated soils and food chain transfer. Ecotox. Environ. Safe. 69(3): 513–524. Chen, T. B., Wong, J. W. C., Zhou, H. Y. and Wong, M. H. 1997. Assessment of trace metal distribution and contamination in surface soils of Hong Kong. Environ. Pollut. 96(1): 61–68. Cyrys, J., Stolzel, M., Heinrich, J., Kreyling, W. G., Menzel, N., Wittmaack, K., Tuch, T. and Wichmann, H.-E. 2003. Elemental composition and sources of fine and ultrafine ambient particles in Erfurt, Germany. Sci. Total Environ. 305: 143–156. De Kimple, C. R. and Morel, J.-L. 2000. Urban soil management: A growing concern. Soil Sci. 165(1): 31–40. De Pascale, S. and Barbieri, G. 1997. Effect of soil salinity and top removal on growth and yield of broadbean as green vegetable. Sci. Hortic. 71: 147–165. Ghollarata, M. and Raiesi, F. 2007. The adverse effects of soil salinization on the growth of Trifolium alexandrinum L. and associated microbial and biochemical properties in a soil from Iran. Soil Biol. Biochem. 39: 1699–1702. Gray, C. W., McLaren, R. G. and Roberts, A. H. C. 2003. Atmospheric accessions of heavy metals to some New Zealand pastoral soils. Sci. Total Environ. 305: 105–115. Harner, T., Bidleman, T., Jantunen, L. and Mackay, D. 2001. Soil-air exchange model of persistent pesticides in the United States cotton belt. Environ. Toxicol. Chem. 20: 1612–1621. Inter-Departmental Committee on the redevelopment of Contaminated Land (ICRCL). 1987. Guidance on the Assessment and Redevelopment of Contaminated Land. Department of the Environment, London. pp. 59–83. Janmaat, J. 2004. Calculating the cost of irrigation induced soil salinization in the tungabhadra project. Agr. Econ. 31(1): 81–96. Kock, M. and Rotard, W. 2001. On the contribution of background sources to the heavy metal content of municipal sewage sludge. Water Sci. Technol. 43: 67–74. Lagreid, M., Bockman, O. C. and Kaarstad, O. 1999. Agriculture, Fertilizers and the Environment. CABI publishing, New York. Liang, B. C. and MacKenzie, A. F. 1994. Changes of soil nitrate-nitrogen and denitrification as affected by nitrogen fertilizer on two Quebec soils. J. Environ. Qual. 23(3): 521–525. Lu, R. K. (ed.). 2000. Analytical Methods of Soil Agrochemistry (in Chinese). China Agricultural Science and Technology Press, Beijing. pp. 87–98. Manno, E., Varrica, D. and Dongarr, G. 2006. Metal distribution in road dust samples collected in an urban area close to a petrochemical plant at Gela, Sicily. Atmos. Environ. 40(3): 5929–5941. Manta, D. S., Angelone, M., Bellanca, A., Neri, R. and Sprovieri, M. 2002. Heavy metals in urban soils: A case study from the city of Palermo (Sicily), Italy. Sci. Total Environ. 300: 229–243. Mulla, D. J., Page, A. L. and Ganje, T. J. 1980. Cadmium accumulation and bioavailability in soils from long term phosphorus fertilization. J. Environ. Qual. 9: 408–412. National Population and Family Planning Commission of China (NPFPCC). 2006. Shanghai: The Resident Population. Available online at http://www.chinapop.gov.cn/rkzh/rk/tjzlzg/t20060320 57335.htm. Nevin, R. 2000. How lead exposure relates to temporal changes in IQ, violent violence, and unwed pregnancy. Environ. Res. 83: 1–22. Rhoades, J. D., Kandiah, A. and Mashali, A. M. 1992. The Use of Saline Waters for Crop Production. Irrigation and Drainage Paper. FAO, Rome. Sabin, L. D., Lim, J. H., Venezia, M. T., Winer, A. M., Schiff, K. C. and Stolzenbach, K. D. 2006. Dry deposition and resuspension of particle-associated metals near a freeway in Los Angeles. Atmos. Environ. 40: 7528–7538. Shanghai Statistical Bureau. 2007. Shanghai Statistical Yearbook 2007. Available online at http://www.stats-sh.gov.cn/ 2004shtj/tjnj/tjnj2007.htm. Sheets, R. W., Kyger, J. R., Biagioni, R. N., Probst, S., Boyer, R. and Barke, K. 2001. Relationship between soil lead and airborne lead concentrations at Springfield, Missouri, USA. Sci. Total Environ. 271: 79–85. Shi, Y. J., Guo, F. F., Meng, F. Q., Lu, Y. H., Wang, T. Y. and Zhang, H. 2005. Temporal trend of organic chlorinated pesticides residues in soils of orchard, Beijing. Acta Sci. Circum. (in Chinese). 25(3): 313–318.
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Shimojima, E., Yoshioka, R. and Tamagawa, I. 1996. Salinization owing to evaporation from bare-soil surfaces and its influences on the evaporation. J. Hydrol. 178: 109–136. Simpson, T. 1996. Urban soils. In McCall, G. J. H., De Mulder, E. F. J. and Marker, B. R. (eds.) Urban Geoscience. AGID Special Publication, Rotterdam. pp. 35–60. Soclo, H. H., Garrigues, P. H. and Ewald, M. 2000. Origin of polycyclic aromatic hydrocarbons (PAHs) in coastal marine sediments: Case studies in Cotonou (Benin) and Aquitaine (France) areas. Mar. Pollut. Bull. 40: 387–396. Tolosa, I., de Mora, S., Sheikholeslami, M. R., Villeneuve, J.-P., Bartocci, J. and Cattini, C. 2004. Aliphatic and aromatic hydrocarbons in coastal Caspian Sea sediments. Mar. Pollut. Bull. 48: 44–60. van Volkshuiswesting, M. 2000. Intervention Values and Target Values: Soil Quality Standards. Annex A. Ministry of Housing, Spatial Planning and Environment; Directorate-General for Environmental Protection; Department of Soil Protection, Febrero, The Netherlands. pp. 8–14. Wang, T. Y., Lu, Y. L., Zhang, H. and Shi, Y. J. 2005. Contamination of persistent organic pollutants (POPs) and relevant management in China. Environ. Int. 31: 813–821. Wang, Y. (ed.). 1992. The Backgrounds of Soil Environment in Shanghai (in Chinese). China Environmental Science Press, Beijing. Wang, Y. G. (ed.). 1991. Pollution of Agro-Environment in Shanghai (in Chinese). Shanghai Science & Technology Press, Shanghai. Wei, D., Kameya, T. and Urano, K. 2007. Environmental management of pesticidal POPs in China: Past, present and future. Environ. Int. 33(7): 894–902. White, J. W. Jr. 1975. Relative significance of dietary sources of nitrate and nitrite. J. Agr. Food Chem. 23(5): 886–891. Xie, H. Y. 2006. Distributions of polychlorinated biphenyls and organochlorine pesticides in one of representative chemical industrial zone of Shanghai (in Chinese). M.S. Dissertation, Shanghai Jiaotong University. Xu, S. Y. 2004. Atlas of Shanghai Urban Physical Geography (in Chinese). China Map Press, Shanghai. Yao, C. X. 2005. Environmental effect of fertilizer employing on dry farmland in Shanghai suburbs (in Chinese). Ph. D. Dissertation, East China Normal University. Yunker, M. B., Macdonald, R. W., Vingarzan, R., Mitchell, R. H., Goyette, D. and Sylvestre, S. 2002. PAHs in the Fraser River basin: a critical appraisal of PAH ratios as indicators of PAH source and composition. Org. Geochem. 33: 489–515. Zhao, W. C. 2006. Distribution characteristics of polycyclic aromatic hydrocarbons (PAHs) in the environmental media in an industrial zone of Shanghai (in Chinese). M.S. Dissertation, Shanghai Jiaotong University. Zu, K. Q. 1986. Soils (in Chinese). China Science and Technology Press, Beijing.
Salinity and Persistent Toxic Substances in Soils from Shanghai, China∗1 SHI Gui-Tao1,2 , CHEN Zhen-Lou1,∗2 , XU Shi-Yuan1 , YAO Chun-Xia1 , BI Chun-Juan1 and WANG Li1 1 Key Laboratory of Geographic Information Science of Ministry of Education, East China Normal University, Shanghai 200062 (China) 2 Polar Research Institute of China, Shanghai 200136 (China)
(Received October 18, 2008; revised September 10, 2009)
ABSTRACT Some farmland soils in Shanghai had high salinity levels, suggesting secondary salinization of the soils. The soil problems in Shanghai were studied, including the salinity and nitrate nitrogen (NO − 3 -N) concentrations, heavy metal pollution characteristics, and organochlorine pesticide (OCP) residual levels and polycyclic aromatic hydrocarbon (PAH) contents. Accumulation of NO− 3 -N in vegetable soils was the most significant among different functional soils. Heavy metal pollution was significant in the samples collected from the sewage-irrigated land and roadside. The identification of the metal sources through multivariate statistical analysis indicated that Pb, Zn, Cu and Cr in urban soils were from the traffic pollutants; excessive application of fertilizer and irrigation were the main reasons for the metal pollution in agricultural soils; Ni in the observed soils was controlled by parent soils. OCPs could still be detected in farmland soils but degraded greatly in last 20 years after prohibition of their usage. PAHs with 2–3 rings were the main components in industrial soils. The concentrated PAHs in the investigated soils were likely from petroleum and coal combustion. Key Words:
heavy metal, OCP, PAH, salinity, soil environment
Citation: Shi, G. T., Chen, Z. L., Xu, S. Y., Yao, C. X., Bi, C. J. and Wang, L. 2009. Salinity and persistent toxic substances in soils from Shanghai, China. Pedosphere. 19(6): 779–789.
INTRODUCTION Soil provides the nutrition for plants and also acts as a recipient of undesirable materials. Human health and environmental quality are strongly dependent on the soil quality (Simpson, 1996; De Kimple and Morel, 2000). With accelerated urbanization and industrialization, urban soils have been disturbed severely due to dense human activities, and contaminants have been accumulated significantly in the soils. Pollutants in soils can be transported to surrounding media as well as remote environmental components via different approaches, e.g., runoff, food chain and volatilization (Chen et al., 1997; Barra et al., 2005); thereby contaminant-enriched soils are the secondary pollution sources by re-emission (Harner et al., 2001). Among the persistent toxic substances (PTS) in soils, heavy metals and persistent organic pollutants (POPs) are the predominant components. Urban soils are known to have high heavy metal levels (Manta et al., 2002), and varied sources, such as industrial production, vehicle exhaust, and waste disposal, could be the contributions (Kock and Rotard, 2001; Sheets et al., 2001). The significant accumulation of heavy metals in urban soils could affect the construction of green-lands, urban environmental quality and people’s health via contact with the polluted soils (Nevin, 2000). In addition, heavy metals (e.g., Cr, Zn, Pb, Cd and Ni) could accumulate in farmland soils at toxic levels as a result of long-term ∗1 Project
supported by the National Natural Science Foundation of China (Nos. 40730526 and 40701164), the National Maritime Bureau of China (Nos. HAD1 and HAD2), and the Shanghai Tongji Gao Tingyao Environmental Science and Technology Development Foundation of China. ∗2 Corresponding author. E-mail: [email protected].
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application of untreated wastewaters (Chary et al., 2008). The toxic metals in the sewage-irrigated soils could be transferred through food chains and consequently cause adverse health effects on human potentially (Chary et al., 2008). As a widespread pollutant, POP contamination has become a global problem. There are 12 substances for global action in the Stockholm Convention on POPs, including 8 pesticides, 2 industrial chemicals, and 2 byproducts (Wang et al., 2005). As a big agricultural country, China increased foodstuff output largely depending on extreme usage of pesticides. Organochlorine pesticides (OCPs), e.g., hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs), constitute 80% of the total pesticides produced between 1950s and 1970s and their high usage resulted in high HCHs/DDTs residual levels in some regions of China (Wei et al., 2007). A large quantity of chemical fertilizer was used in farmlands for promoting productivity, and the value for Shanghai was 613 kg ha−1 in 2006, which was much higher than that of the developed countries (Shanghai Statistical Bureau, 2007). As a result, excessive salinity (e.g., nitrate and nitrite) was accumulated in soils. It is reported that vegetables are the primary dietary source (more than 80%) of nitrate of human being (White, 1975). So, salinity in soils could harm human health potentially by food chains. Moreover, a high residue of salinity could limit the growth of crops, constrain agricultural productivity, and in severe case, lead to the abandonment of agricultural soils (Ghollarata and Raiesi, 2007). Based on the aforementioned facts, it is significant to study the soil problems in Shanghai in detail. The objectives of this study are as follows: (1) the salinity and nitrate nitrogen (NO− 3 -N) concentrations in different functional soils were measured; (2) heavy metal pollution characteristics in soils were analyzed and their main sources were identified by the aid of multivariate statistical analysis; and (3) OCP residual levels in farmland soils and polycyclic aromatic hydrocarbon (PAH) contents in industrial soils were determined. MATERIALS AND METHODS Site description and sampling Shanghai is located in the east coast of China, with the center at 31.14◦ N and 121.29◦ E, and the Yangtze River flows into the East China Sea along its north. The city has a total area of 6 340.5 km2 , 0.06% of China’s total territory. At the end of 2005, the population reached more than 17 million (NPFPCC, 2006). The soil types of Shanghai mainly include paddy soil, fluvo-aquic soil, coastal saline soil and yellow-brown soil, which belong to 4 soil groups, 7 subtypes, 24 soil genus and 95 soil species (Xu, 2004). At present, Shanghai is a city where economy and urban construction development is the fastest in China. Large population and dense industrial activities have discharged a tremendous amount of waste to the urban environment. Fig. 1 shows the discharge of waste water and gas in recent years (Shanghai Statistical Bureau, 2007). In general, the amount of discharged wastes had been increasing
Fig. 1
Discharge of waste water and gas from 2000 to 2006 in Shanghai.
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steadily since 2000 except waste water emissions during the years of 2001–2003, and the decrease of waste water was probably due to the three-year (2000–2002) environmental action plan in Shanghai. Sampling sites are illustrated in Fig. 2. For the measurement of salinity and ions, 122 soil samples were collected from the farmlands of Pudong, Nanhui, Jinshan and Fengxian. Twenty four profiles in the farmlands were conducted, and soils in the depth of 0–20, 20–40 and 40–60 cm at each profile were collected. In all, 236 soil samples were collected from seven different functional soils for the determination of NO− 3 -N. To understand the contamination characteristics of heavy metals, 191 urban soils from small towns (Fengjing, Songjiang and Zhujiajiao), urban parks and roadside (along Yan’an road, which traverses Shanghai) were collected. In all, 46 agricultural soils were collected from farmlands in Songjiang and Pudong. In addition, 21 soil samples were collected from two industrial zones, and contents of 16 US EPA (Environmental Protection Agency) priority pollutant PAHs were determined. For anonymity, the two industrial zones were assigned the codes A and B. The residual levels of HCHs and DDTs were measured in 202 samples collected from farmlands.
Fig. 2
Sketch map of the study area and soil sampling sites.
All the observed soil samples were collected with a stainless steel spatula, and four subsamples of surface soils (0–10 cm) were taken and then mixed thoroughly to obtain a bulk sample (about 1 kg) for each sampling site. All the collected samples were kept in Ziploc bags to avoid contamination; subsequently, the samples were transported to the laboratory and preserved under freezing conditions. Sample preparation and analysis The soil samples were air-dried, thoroughly mixed, ground to pass through a 1.0-mm sieve for the determination of salinity and ions, and through a 0.125-mm sieve for the measurement of heavy metals and POPs. The soils passed through a 1.0-mm sieve were treated with distilled water at a soil to water ratio of 1:5 (w/v) in a plastic bottle. The bottle was tightly capped, shaken at 150 r min−1 for 5 min, and the mixture was filtered with suction. Total soluble salts in the filtrate were measured by the mass of the residue after the evaporation of solution, K+ and Na+ concentrations by flame photometry, Ca2+ −1 and Mg2+ by atomic absorption spectrophotometry, NO− CaCl2 (1:10 3 by the method of 0.01 mol L 2− of soil to CaCl2 solution) with continuous flow analysis, SO4 by turbidimetry with BaCl2 using a SHIMADZU UV/V Spectrometer (Shimadzu, Kyoto, Japan), Cl− by titration with AgNO3 , and CO2− 3 and HCO− by double indicator titration (Lu, 2000). 3 Soil samples for determining heavy metal levels were digested with concentrated HNO3 , HF and HClO4 in a microwave oven operating at 0.3 MPa 3 min, 0.6 MPa 2 min, 1.0 MPa 2 min, 1.5 MPa 2 min, and 2.0 MPa 6 min. A Perkin-Elmer AANALYST800 atomic adsorption spectrophotometer analyzer (Perkin-Elmer, Waltham, MA, USA) was employed for the determination of Pb, Zn, Cu, Cr, Cd, and Ni. A series of soil/sediment standards were used for quality assurance and quality control (QA/QC),
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and these were GSS-6 and GSD-9 geochemical reference materials, which were supplied by the National Research Center for Certified Reference Materials of China. The recoveries for the observed metals were between 90% and 110%. The accuracy analysis was also checked by the duplicated samples, and the standard deviation ranged within 5%. The blank determinations were also performed in triplicate throughout all the experiment. Organochlorine pesticides were extracted from soil samples with dichloromethane and PAHs with dichloromethane/acetone (v/v = 1:1) mixture in an ultrasonic extractor. Terphenyl was used as internal standard for analysis of PAHs, and 2,4,5,6-tetrachloro-m-xylene and decachlorobiphenyl for OCPs. Volume was reduced after extraction under a gentle nitrogen stream at ambient temperature, and fractionation was achieved on silica gel column. The column is made of pyrex glass, 500 mm long with 11 mm diameter. Silica of 10.0 g was weighed into a glass container, and 0.3 mL of deionized water was added. The silica gel was homogenized overnight after vigorous shake, activated at 130 ◦ C for 24 h, and cooled down in a dessicator. Organochlorine pesticides in the samples were measured by gas chromatography with electron capture detector (Agilent6890N, Agilent, Santa Clara, CA, USA) and PAHs by high performance liquid chromatography with fluorescence detection (Agilent1200, Agilent, Santa Clara, CA, USA). The recoveries for OCPs and PAHs were 35%–90% and 64%–106%, respectively. Statistical analysis Multivariate statistical analyses of the data were carried out by means of the Origin and SPSS software packages. The essence of principal components analysis (PCA) is converting the variables under investigation into factors or principal components (PCs) so that correlation among the original variables can be minimized. In this study, data were log-transformed prior to PCA to reduce the influence of high values. Bartlett sphericity test and Kaiser-Meyer-Olkin test indicated that the normalized data were suitable for PCA. Varimax with Kaiser normalization rotation was applied to increase the variances of the factor loadings across variances for each factor. In addition, the correlations between the original variables are presented in the form of nonparametric Pearson correlation coefficients. RESULTS AND DISCUSSION Salinity in farmland soils The salinity and ion concentrations in farmland soils in the suburbs of Shanghai are listed in Table I. All the average salinity contents in the observed districts except Pudong were under salinization standard (Zu, 1986). In general, salinity content less than 2.0 g kg−1 can not affect the normal growth and development of crops. However, the maximum salinity contents were all above the standard, indicating some soils are unfavorable for the plant growth. Anions in the investigated soils were predominated − − 2+ , Na+ . In general, ion levels in the soils by SO2− 4 , Cl , NO3 , whereas cations were mainly by Ca − 2− from Pudong and Nanhui, especially NO3 and SO4 , were higher than the other two districts. The correlations between the levels of salinity and ions were analyzed, and the results indicated that there (r = 0.89), Cl− (r = 0.71), and NO− were significant correlations between salinity levels and SO2− 4 3 (r = 0.79) concentrations at the 0.01 level, namely, the soil salinization levels in Shanghai were controlled by these three anions. The three anions are partly from the parent materials, but they mainly originate from auxiliary or transformation components of chemical fertilizer (Yao, 2005). Therefore, the secondary salinization of suburban soils is mainly related to improper application of fertilizer. The salinity and ion concentrations in the depth of 0–20 cm were higher than those in the depth of 20–40 and 40–60 cm (Fig. 3), which agrees well with the reports for other regions (Rhoades et al., 1992; De Pascale and Barbieri, 1997). In suburbs of Shanghai, an increasing quantity of chemical fertilizer is used to increase the yield of foodstuff, which leads to soil secondary salinization, especially in the greenhouse. However, high evaporation of freestanding irrigation and no dilution of precipitation also contribute to the salinization (Shimojima et al., 1996; Lagreid et al., 1999; Janmaat, 2004).
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TABLE I Salinity and ion concentrations in farmland soils of Shanghai Region
Parameter
Salinity
NO− 3
HCO− 3
C1−
SO2− 4
Pudong
Minimum Maximum Average SDa) Minimum Maximum Average SD Minimum Maximum Average SD Minimum Maximum Average SD
0.53 7.12 3.57 2.23 0.49 8.02 1.92 1.94 0.22 3.73 1.23 1.10 0.65 3.27 1.56 0.72
0.01 0.93 0.31 0.31 0.01 0.73 0.17 0.19 0.01 0.42 0.12 0.13 0.01 0.19 0.06 0.05
0.01 0.20 0.03 0.06 0.01 0.02 0.01 0.00 0.01 0.02 0.01 0.00 0.01 0.02 0.01 0.00
0.03 0.57 0.23 0.17 0.05 0.53 0.18 0.13 0.04 0.39 0.14 0.09 0.04 0.35 0.14 0.10
g kg−1 0.19 2.58 1.09 0.95 0.21 3.78 0.78 0.96 0.10 1.16 0.33 0.27 0.09 1.79 0.35 0.41
Nanhui
Jinshan
Fengxian
a) Standard
Ca2+
Mg2+
K+
Na+
0.06 0.80 0.37 0.26 0.03 0.56 0.20 0.16 0.03 0.49 0.15 0.13 0.01 0.22 0.08 0.07
0.02 0.34 0.14 0.12 0.01 0.56 0.14 0.15 0.02 0.08 0.04 0.02 0.01 0.13 0.05 0.03
0.01 0.28 0.11 0.11 0.03 0.58 0.11 0.14 0.00 0.06 0.02 0.02 0.01 0.11 0.03 0.02
0.06 0.91 0.30 0.28 0.06 0.42 0.20 0.11 0.06 0.29 0.16 0.07 0.06 0.29 0.13 0.06
deviation.
Fig. 3 Salinity and ion concentrations in soil profiles of farmlands in Shanghai. A, B, C, D, E, F, G, H and I represent − 2− − 2+ , Mg2+ , K+ and Na+ , respectively. Salinity, NO− 3 , HCO3 , Cl , SO4 , Ca Fig. 4 NO− 3 -N concentrations in different functional surface soils. 1–7 represent greenhouse vegetable land, open vegetable land, traditional vegetable land, residential district land, woodland, park soil and paddy field, respectively. − Levels of NO− 3 -N in different functional soils are shown in Fig. 4. The results showed that NO3 -N concentrations differed significantly among various functional soils. Especially, NO− 3 -N concentrations in residential district soil, forest soil, park soil and paddy soil were low, about one order magnitude lower than those in vegetable soils. The use of high levels of chemical fertilizer may be the direct contribution to the high concentrations of NO− 3 -N in vegetable soils (Liang and MacKenzie, 1994). The utilization ratio of nitrogen by vegetable is relatively low. Because most vegetables are nitrophile crops, excessive nitrogenous fertilizer is used in vegetable land for promoting productivity. Sometimes, the quantity of the used fertilizer is several times higher than the actual requirement. Therefore, surplus of nitrogen was accumulated in the soils.
Heavy metals in soils The descriptive statistics of heavy metal contents in urban soils are summarized in Table II. The heavy metal background values of soils in Shanghai (Wang, 1992) are used as references to check the
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heavy metal contamination. The average contents of heavy metals except Ni greatly exceeded the reference values. Meanwhile, the mean levels of Zn were above the trigger concentration, the recommended mean of Zn in soils used for recreation and agriculture (ICRCL, 1987). In general, the accumulation processes of heavy metals in the soils of small towns and parks were similar, which were much lower than those in roadside soils. TABLE II Heavy metal contents in urban soils of Shanghai Region Small towns (n = 117)
Urban parks (n = 44)
Roadside (n = 30)
Parameter Average Maximum Minimum SDb) Average Maximum Minimum SD Average Maximum Minimum SD
Background valuec) Trigger concentrationd) a) Not
analyzed;
b) Standard
deviation;
Cu
Zn
48.60 492.44 9.52 53.42 44.57 151.74 23.12 27.63 80.78 138.79 27.43 26.66
303.13 1 812.50 0.88 325.51 198.54 1 025.65 102.45 144.93 452.20 895.71 141.71 208.01
28.59 130
83.68 300
c) Cited
from Wang (1992);
Cr mg 86.52 711.98 3.31 95.98 77.01 163.70 25.53 30.80 153.31 233.26 97.17 34.17 75.00 600 d) Cited
Pb
Cd
Ni
48.26 253.68 1.40 42.58 55.06 174.35 26.39 32.49 93.61 192.38 13.72 48.68
0.32 2.10 0.08 0.29 0.40 0.67 0.19 0.13 0.70 3.66 0.21 0.64
NAa) NA NA NA 31.17 65.70 4.95 15.27 31.09 51.85 14.70 9.64
25.47 500
0.13 1.0
31.19 70
kg−1
from ICRCL (1987).
The loadings of measured metal contents in the coordinate system of three PCs are illustrated in Fig. 5a. The observed heavy metals were well represented by the first three PCs, which constituted 80% of the total variance. Three heavy metal groups were clearly distinguished in urban soils. Pb, Zn, Cu, and Cr were highly loaded in PC1, which constituted 53.01% of the total variance. There were significant correlations between their levels in urban soils (Table III), which imply that these four metals in urban soils originate from similar pollution sources, such as the deposition of aerosol particles emitted by vehicular traffic (Bullock and Gregory, 1991; Cyrys et al., 2003; Gray et al., 2003). Ni showed a higher value in the third component (PC3), and the mean level of Ni in the soils was comparable to the background value (Table II). Therefore, it can be concluded that the parent materials of soils control Ni content. In PC2, Cd showed a higher value, distinguishing itself from the other heavy metals. This reflects different anthropogenic or geogenic sources and possible pathways of accumulation from the other five investigated metals.
Fig. 5 Three-dimensional plot loadings (PC1, PC2 and PC3) of heavy metals in urban (a) and farmland soils (b) by principal component (PC) analysis.
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TABLE III Pearson correlative coefficients of heavy metals in urban and farmland soils of Shanghai Soil
Heavy metal
Cu
Zn
Cr
Urban
Cu Zn Cr Pb Cd Ni Cu Zn Cr Pb Cd Ni
1
0.673** 1
0.501** 0.607** 1
1
0.212 1
0.740** 0.418* 1
Farmland
Pb 0.508** 0.580** 0.578** 1
0.200 −0.022 0.288 1
Cd 0.241* 0.161 0.259* 0.104 1 −0.022 0.342* 0.038 0.118 1
Ni 0.158 0.232* 0.151 0.322** 0.078 1 −0.075 0.453 0.146 0.320 −0.152 1
*,**Significant at P = 0.05 and P = 0.01 levels, respectively.
Heavy metal contents in agricultural soils are illustrated in Fig. 6. In general, farmland soils had lower heavy metal contents than urban soils, and the metal accumulation processes in sewage-irrigated soils were the most significant among the observed samples. Metal contents in the farmland soils were lower than grade 2 of soil standard, which are recommended means of heavy metal limits in agricultural soils in China, and comparable to the background values in Shanghai (Wang, 1992). However, all the investigated elements except Cr and Pb in sewage-irrigated soils were above the soil standards and much higher than the soil background values.
Fig. 6 Heavy metal contents in different functional soils of Shanghai. Error bars represent standard deviations of heavy metals.
The heavy metal sources of sewage-irrigated soils were specific compared with other functional soils. In detail, the observed land was irrigated by wastewater in 1970s–1980s. Another fact is that the sediment of urban river was used in the investigated land in 1970s. As a result, heavy metals in sewageirrigated soils were especially high. The heavy metals in farmland soils could be classified into three groups (Fig. 5b). PC1 was dominated by Cu and Cr, and there was a strong correlation between them (Table III). It can be concluded that they are from the same source. Fig. 6 showed that the variation coefficient of Cr was relatively low, indicating that the homogeneous source dominated. In addition, Cr content was higher than the background value, so the parent material is not the major source. From the previous works, atmospheric deposition would be the major contribution (Manno et al., 2006; Sabin et al., 2006). The loadings of Pb and Ni levels in PC2 were 0.699 and 0.927, respectively, and the contents of the two elements were slightly lower than the background values (Fig. 6). Hereby, PC2 represents the parent materials of soils influencing metal contents. Cd and Zn showed high values in PC3, combined
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with the better correlation of the two metals. Furthermore, contents of both the elements were much higher than the background values, different from the other elements in farmland soils. It is well known that fertilizer is a major source of heavy metals in farmland, especially the toxic element Cd from the phosphate fertilizer (Mulla et al., 1980). Thus, it is found that utilization of chemical fertilizer is the main source of Cd and Zn. POP contents in soils Residual levels of OCPs in farmland soils are shown in Fig. 7. The residual mean of HCHs (α-, β-, γand δ-HCH) was 4.41 μg kg−1 with a range of 0.03 to 17.3 μg kg−1 . In terms of spatial distribution, HCH average content in Songjiang (6.77 μg kg−1 ) was the highest, which was followed by Qingpu, Jinshan, Minhang, and Fengxian. DDT (p,p -DDT, p,p -DDD, and p,p -DDE) contents ranged between 1.00 and 64.70 μg kg−1 in the observed soils, with a mean of 20.30 μg kg−1 . Among the average contents of DDTs in the five study regions, the maximum was present in Minhang and the minimum was in Qingpu. It was noticeable that the contents of DDTs were 2–10 times HCHs in the study districts, and the difference is associated with the historical soil use and different degradation rates of OCPs (Shi et al., 2005).
Fig. 7 Residual levels of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) in farmland soils of Shanghai. Error bars represent standard deviations. Fig. 8 Residual levels of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) in farmland soils in different years of Shanghai. The data of 1980s are from Wang (1991).
Compared with OCP contents (HCHs of 1.17 μg kg−1 and DDTs of 11.57 μg kg−1 ) in industrial soils (Xie, 2006), the concentrations of HCHs and DDTs in farmland soils were higher (Fig. 7). This indicated that the large amount of OCP usage during 1960s–1970s led to the enrichment of HCHs and DDTs in farmland soils. The temporal variation of OCP residual levels in farmland soils is shown in Fig. 8. The results indicated that the concentrations of HCHs and DDTs in farmland soils decreased significantly with the values in this paper being 25% and 17%, respectively, of the mean levels in 1980s. The difference of OCP levels implies that since the use of OCPs was banned for agriculture soils in 1983 in China, most of the OCPs have been removed or degraded in the soil. Contents of 16 US EPA priority pollutant PAHs in soils from two industrial zones are shown in Table IV. The PAHs in soils were dominated by 2–3 ring components, specifically, fluorene and phenanthrene for zone A, naphthalene and acenaphthylene for zone B. In general, both components and total PAH concentrations in zone A were much lower than those in zone B. The intervention value of total PAHs (40 mg kg−1 ) is the maximum tolerable concentration above which remediation is required (van Volkshuiswesting, 2000), and the mean content of total PAHs in B-zone soils was above the intervention value, corresponding to serious contamination.
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TABLE IV Contents of US EPA (Environmental Protection Agency) priority pollutant polycyclic aromatic hydrocarbons (PAHs) in industrial soils of Shanghai PAH
Zone B (n = 12)a)
Zone A (n = 9) Range
Mean mg
NDb) –8.90 ND–0.20 NAc) ND–19.00 ND–34.30 ND–5.60 ND–7.80 ND–4.30 NA ND–1.70 ND–1.00 ND–0.80 ND–0.80 ND–0.60 ND–1.40 ND–1.50 ND–81.90
Naphthalene (Nap) Acenaphthylene (Acy) Acenaphthene (Ace) Fluorene (Flu) Phenanthrene (Phe) Anthracene (Ant) Fluoroanthracene (Fla) Pyrene (Pyr) Benzo[a]anthracene (BaA) Chrysene (Chr) Benzo[b]fluoranthene (BbF) Benzo[k]fluoranthene (BkF) Benzo[a]pyrene (BaP) Dibenzo[a,h]anthracene (DAH) Benzo[g,h,i]perylene (BGP) Indeno[1,2,3-c,d]pyrene (InP) Total a) Cited
from Zhao (2006);
b) Not
detectable;
c) Not
1.11 0.03 NA 4.12 4.07 0.70 1.32 0.92 NA 0.42 0.21 0.20 0.28 0.07 0.26 0.23 13.94
Range
Mean
0.15–90.29 0.33–60.51 ND–22.38 0.002–12.13 0.004–2.59 0.008–2.05 0.08–12.05 0.09–34.02 0.0005–24.76 0.04–18.21 0.09–4.97 0.1–5.04 0.002–12.21 0.003–50.87 ND–7.61 0.002–2.87 3.95–246.28
18.28 11.62 3.40 1.83 0.56 0.44 2.80 7.50 4.39 3.49 1.64 1.39 3.09 5.52 1.55 0.48 67.96
kg−1
analyzed.
The differences of PAHs in the soils over the two zones may be associated with the different industrial activities. In detail, the industries in zone A are mainly manufacturing, whereas chemical industries are predominant in zone B. PAHs could be derived from several different sources, e.g., petrogenic, pyrogenic, or biogenic (Tolosa et al., 2004), and the high levels of PAH in B-zone soils could be attributed to chemical factory pollutants. In addition, PAH ratios could be the indicators of PAH source (Yunker et al., 2002). The ratio of Flu/(Flu+Pyr) in zone A was 0.8 (> 0.5), which indicates that pyrogenic source (e.g., coal combustion) is predominant. In zone B, the ratio of Flu/Flu+Pyr was 0.2 (< 0.5), suggesting that petrogenic source is predominant. The low molecular weight to high molecular weight (LMW/HMW) is another index that can be used to assess the various sources of PAHs, such as residue of oils, combustion/maturation of organic mater, petrogenic/pyrolytic origin pollution. The values of LMW/HMW in B-zone soils were higher than 1, indicating the residue of the oils (Soclo et al., 2000). CONCLUSIONS Some of the farmland soils had a secondary salinization trend in Shanghai. The anions in the study − and NO− soils were mainly SO2− 4 , Cl 3 , which were correlated well with the salinity content. The -N in vegetable soils was related to excessive application of nitrogen significant accumulation of NO− 3 fertilizer. Soils from sewage-irrigated land and roadside had higher heavy metals, whereas the contents for farmland soils were relatively low, comparable to the background values. Based on the results of multivariate statistical analysis, Pb, Zn, Cu, and Cr in urban soils were from the traffic pollutants. However, human activities, i.e., chemical fertilizer application and irrigation, contributed to the heavy metals in agricultural soils. In addition, Ni in urban soils and Pb and Ni in farmland soils with low concentrations were influenced by weathering materials from parent soils. HCHs and DDTs could still be detected in farmland soils. Nevertheless, the residues of both HCHs and DDTs in this study were much lower than those in 1980s due to the prohibition of their production and usage since early 1980s. Petrogenic and pyrogenic sources were the main contributions of concentrated PAHs in the industrial soils.
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