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nồng độ và các dạng kim loại của Cu, Zn, Pb, Cr trong đất vùng ủy ban tại namning Trung quốc
Geoderma 115 (2003) 101 – 111 www.elsevier.com/locate/geoderma Concentrations and chemical speciations of Cu, Zn, Pb and Cr of urban soils in Nanjing, China Ying Lu a,b,*, Zitong Gong a, Ganlin Zhang a, Wolfgang Burghardt c b a Institute of Soil Science, Academia Sinica, Nanjing 210008, PR China College of Resources and Environmental Science, South China Agricultural University, Guangzhou 510642, PR China c Department of Applied Soil Science, University of Essen, 45141 Essen, Germany Abstract About 150 soil samples from 20 urban and non-urban soil profiles in Nanjing were analyzed for total concentrations of Cu, Zn, Pb and Cr using ICP spectrometry The Cu, Zn, Pb and Cr of 23 urban and non-urban topsoils (A horizon soils) were sequentially extracted into fractions according to the method of Tessier [Anal Chem 51 (1979) 844] Total Cu, Zn, Pb and Cr concentrations of the urban soils were 84.7 (48.1 – 139.7), 66.1 (12.2 – 869.4), 162.6 (57.7 – 851.6) and 107.3 (36.3 – 472.6) mg kgÀ 1, respectively The soils were polluted with Cu, Zn and Cr to some extent and heavily polluted with Pb For 20 urban topsoils, the Cu, Zn, Pb and Cr were dominated by the residual fraction and were least present in exchangeable fraction On average, the order of Cr, Cu in each fraction was residual (92.9%, 66.1%)Horganic (4.2%, 23.4%)>Fe – Mn oxide (2.7%, 5.4%)>carbonate (0.2%, 4.7%)>exchangeable (0.04%, 0.38%), Zn followed the order residual (60.0%)HFe – Mn oxides (19.1%)>carbonate (11.6%)>organic (8.8%)>exchangeable (0.5%), Pb was residual (56.8%)>Fe – Mn oxide (30.9%)Horganic (6.3%)>carbonate (5.2%)>exchangeable (0.8%) The percentage of residual Cu and Zn decreased with the increase of total Cu and Zn concentrations The proportion of residual Pb increased with the increase of total P The mobility and bioavailability of heavy metals were Pb>Zn>Cu>Cr Cu, Zn and Pb were more mobile and bioavailable in the urban than in the nonurban soils; however, Cr was similar D 2003 Elsevier Science B.V All rights reserved Keywords: Heavy metals; Chemical speciations; Urban soils; Nanjing, China * Corresponding author College of Resources and Environmental Science, South China Agricultural University, Guangzhou 510642, PR China Tel.: +86-20-85280295 E-mail address: luying@scau.edu.cn (Y Lu) 0016-7061/03/$ - see front matter D 2003 Elsevier Science B.V All rights reserved doi:10.1016/S0016-7061(03)00079-X 102 Y Lu et al / Geoderma 115 (2003) 101–111 Introduction Heavy metal contamination in urban soils can be harmful to the biota and human beings, and extensive investigations have been carried out recently in some countries and regions (Culbard et al., 1988; Thornton, 1991; Weiss et al., 1994; Chon et al., 1995; Markus and McBrantney, 1996; Chen et al., 1997; Kasimov and Lychagin, 1998; Lavado et al., 1998; Stroganova et al., 1998; Wilcke et al., 1998, 1999) Total analysis may give information concerning possible enrichment of the soil with heavy metals, but it is generally recognized that it is the chemical form of a metal in the soil that determines its mobilization capacity and behavior in the environment Sequential extraction provides information about the differentiation of the relative bonding strength of metal on various solid phases and about their potential reactivity under different physicochemical environmental conditions and is considered useful for evaluating mobility and bioavailability of heavy metals in urban soils (Harrison et al., 1981; Gibson and Farmer, 1986; Ramos et al., 1994; Tack and Verloo, 1995; Wilcke et al., 1998, 1999) Of the various sequential extraction methods available, the one followed most often is that proposed by Tessier et al (1979) China is the largest developing country with the largest population in the world By the end of 1999, China had 668 cities with 376 million urban inhabitants, which is 30.9% of the total population, with an average density of 462 persons kmÀ (State Statistical Bureau and P.R China, 2000) With continuing population growth and rapid economic development of China, the percentage of population living in cities is increasing dramatically and, consequently, the environmental quality of urban soils are becoming more and more important in regards to human health However, very little information is available about heavy metals of urban soils in China (Lu, 2000) The objective of this study was to determine the total Cu, Zn, Pb and Cr concentrations and chemical speciation of urban soils in Nanjing, China Materials and methods 2.1 Description of study area Nanjing city is located in eastern China (31j14V 118j22V and lies at the lower N, E), reaches of the Yangtse River and north subtropical zone, with a history of more than 2000 years and about million inhabitants The average annual temperature of Nanjing city is 16.7 jC with a mean monthly variation ranging from 2.3 jC in January to 29.5 jC in July and the mean annual precipitation is 1239 mm 2.2 Soils Twenty urban soil profiles, distributed in different districts including roadsides, urban parks, residential areas, campuses and vegetable gardens within the urban area, and three non-urban soil profiles nearby the urban area, were randomly selected In all cases, the soils were sampled according to pedogenetic horizons to a depth of about 1.2 m by digging soil profiles Altogether, 138 urban soil and 15 non-urban soil samples were collected The Table Classification and some physicochemical properties of soils in this study Profile Number of Soil groupa no horizons 8 10 11 12 13 14 15 16 17 18 19 20 7 7 a b c b urban park urban park urban park campus campus campus campus campus vegetable garden Tur-Anthric Entisols residential area Tur-Anthric Entisols roadside Tur-Anthric Entisols residential area Tur-Anthric Entisols residential area Tur-Anthric Entisols residential area Hyp-Udic Cambsols urban park Hyp-Udic Cambsols urban park Tur-Anthric Entisols roadside Tur-Anthric Entisols roadside Tur-Anthric Entisols campus Fim-Orthic Anthrosols vegetable garden Arp-Udic Luvisols rural area Fer-Udic Luvisols rural area Fer-Udic Cambsols rural area CEC (cmol (+) kgÀ 1) pHH2O Sand (g kgÀ 1) Silt (g kgÀ 1) Clay (g kgÀ 1) Total P2O5 (g kgÀ 1) 5.08 F 5.96b 11.83 F 10.00 9.12 F 12.97 18.31 F 16.86 11.52 F 6.59 10.01 F 4.03 21.35 F 14.90 12.11 F 4.73 11.00 F 4.34 14.23 F 3.74 15.41 F 1.29 22.07 F 1.98 16.43 F 2.15 17.95 F 3.81 16.09 F 4.57 16.40 F 1.82 16.54 F 1.21 16.98 F 1.12 7.51 F 0.17 8.40 F 0.28 6.79 F 0.47 8.26 F 0.21 8.35 F 0.19 8.45 F 0.25 8.43 F 0.21 8.40 F 0.23 6.93 F 0.96 286.5 F 146.9 255.0 F 92.2 77.6 F 20.3 342.4 F 31.2 308.9 F 38.1 245.7 F 118.9 289.9 F 127.3 216.1 F 33.6 246.3 F 32.4 458.2 F 105.4 522.0 F 55.4 528.3 F 20.5 478.8 F 39.4 478.0 F 22.2 559.8 F 43.4 575.0 F 80.3 615.1 F 35.4 550.4 F 9.6 255.3 F 49.2 223.0 F 53.7 394.1 F 38.2 178.8 F 38.9 213.1 F 35.2 194.6 F 78.5 135.1 F 53.1 168.9 F 15.1 203.3 F 37.0 1.19 F 0.12 1.76 F 0.27 0.92 F 0.16 3.06 F 0.65 2.91 F 0.73 5.20 F 2.21 6.67 F 1.63 7.74 F 2.77 3.45 F 0.64 9.26 F 2.87 21.05 F 1.74 8.48 F 0.51 273.7 F 122.5 514.7 F 43.1 211.6 F 105.0 3.08 F 0.40 28.53 F 7.97 13.44 F 4.10 17.68 F 1.74 18.71 F 1.93 8.06 F 0.25 361.0 F 64.7 8.16 F 0.27 241.4 F 43.5 504.5 F 78.0 514.5 F 38.3 122.3 F 11.1 244.2 F 59.6 3.87 F 0.43 2.42 F 0.81 14.14 F 9.32 18.47 F 1.53 8.40 F 0.17 270.6 F 100.4 522.5 F 32.9 206.8 F 82.8 4.47 F 2.92 36.16 F 10.18 13.63 F 3.51 8.22 F 0.07 505.4 F 189.5 402.1 F 132.1 92.6 F 60.2 4.50 F 0.66 6.76 F 6.76 5.83 F 7.37 19.54 F 13.48 13.35 F 13.71 14.26 F 10.90 9.83 F 7.02 7.59 F 0.86 7.44 F 0.43 8.16 F 0.28 7.99 F 0.17 7.93 F 0.27 7.85 F 0.27 591.2 F 66.6 504.0 F 110.5 468.6 F 113.3 549.8 F 72.2 607.0 F 69.2 532.5 F 100.7 257.2 F 99.7 119.8 F 61.3 127.8 F 59.8 238.9 F 67.7 227.0 F 84.6 365.1 F 130.7 2.04 F 0.24 2.53 F 0.53 3.45 F 1.77 3.96 F 1.41 4.36 F 1.53 1.97 F 1.13 626.2 F 25.8 263.3 F 53.8 304.8 F 26.0 298.8 F 26.0 108.5 F 63.5 30.4 F 6.1 1.32 F 0.24 2.60 F 0.11 0.42 F 0.18 4.68 F 3.32 4.77 F 4.94 6.75 F 7.90 14.83 F 2.24 11.98 F 3.78 13.73 F 2.91 18.12 F 2.21 18.09 F 1.91 22.18 F 5.91 151.6 F 79.6 376.2 F 164.3 403.6 F 151.6 211.3 F 110.1 166.0 F 136.0 102.5 F 36.8 12.91 F 0.96 7.14 F 0.22 75.0 F 8.5 11.02 F 2.66 5.83 F 0.17 556.3 F 94.3 9.64 F 3.00 5.24 F 0.68 664.8 F 24.2 Soil classification was based on Chinese Soil Taxonomy (Gong, 1999) Data in the table stand for mean F standard deviation of each soil profile 103 a Tur-Anthric Entisols Tur-Anthric Entisols Arp-Udic Luvisols Hap-Orthic Gleysols Tur-Anthric Entisols Tur-Anthric Entisols Hyp-Udic Cambsols Hyp-Udic Cambsols Fim-Orthic Anthrosols Organic C (g kgÀ 1) Y Lu et al / Geoderma 115 (2003) 101–111 Locations 104 Y Lu et al / Geoderma 115 (2003) 101–111 horizon numbers of each profile and soil classification are shown in Table Soils were air-dried and ground in an agate mortar to pass through a 2-mm nylon sieve A subsample (10 g) of each soil was further ground to pass through a nylon sieve with 0.15-mm openings 2.3 Soil analyses Soil pH was measured in a 1:2.5 (w/v) ratio of soil to water by a glass electrode Particle size analysis was made using the pipette method (Gee and Bauder, 1986) Organic C was measured using Walkley – Black titration (Nelson and Sommers, 1982) Cation exchangeable capacity (CEC) was determined as described by Chapman (1965) Total P was determined with HClO4 digestion (Olsen and Sommers, 1982) Some physicochemical properties of soils used in the study are given in Table The sequential extraction scheme proposed by Tessier et al (1979) was adopted to partition the heavy metals into five fractions: exchangeable, bound to carbonates, bound to Fe –Mn oxides, bound to organic matter and residual Each fraction was defined as follows: Exchangeable (F1): Soil (2.00 g dry wt.) extracted with 16 ml of pH 7, 1.0 mol lÀ MgCl2 in 100-ml polyethylene centrifuge tubes for h at room temperature with continuous agitation Carbonate (F2): Residue from exchangeable fraction, extracted with 16 ml of pH 1.0 mol lÀ sodium acetate for h at room temperature with continuous agitation Fe– Mn oxide (F3): Residue from carbonate fraction, extracted with 40 ml of 0.04 mol lÀ NH4OHÁHCl in 25% acetic acid (v/v) for h at 96 F jC with occasional agitation Organic (F4): Residue from Fe –Mn oxide fraction, extracted with ml of 0.02 mol lÀ HNO3 and 10 ml of 30% H2O2 adjusted to pH with HNO3 The mixture was heated to 85 F jC for h with occasional agitation A second 6-ml aliquot of 30% H2O2 (pH with HNO3) was then added and the sample was heated again to 85 F jC for h with intermittent agitation After cooling, 10 ml of 3.2 mol lÀ NH4OAc in 20% (v/v) HNO3 was added and the sample diluted to 40 ml and agitated continuously for 30 Residual (F5): Residue from the organic fraction was washed with deionized water, dried in a force-air oven at 40 jC for 24 h, weighed and ground to pass a nylon sieve with 0.15-mm openings A 0.2-g subsample was used for determining Cu, Zn, Pb and Cr contents Total Cu, Zn, Pb and Cr contents in soils and residual fractions were determined by attacking about 0.2000 g of dried soil samples with HNO3 – HF – HClO4 mixture followed by elemental analysis The Cu, Zn, Pb and Cr concentrations of all solutions were determined by ICP (JY38S, Jobin Yvon, France) Results and discussions 3.1 Heavy metal concentrations The concentrations of Cu, Zn, Pb and Cr in urban soils in Nanjing (Table 2) have a wide range of values and have a marked vertical variability in soil profiles The mean Cu Y Lu et al / Geoderma 115 (2003) 101–111 105 Table The Cu, Zn, Pb and Cr contents of urban soils in different zones and background values in Nanjing area and the mean values in China (mg kgÀ 1) Cu Urban park soils range 12.2 – 48.2 mean F S.D 29.2 F 9.1 Campus soils range 23.5 – 869.4 mean F S.D 74.8 F 121.2 Residential area soil range 27.0 – 228.3 mean F S.D 66.4 F 46.4 Roadside soil range 30.9 – 306.9 mean F S.D 117.3 F 83.4 Vegetable garden soil range 30.8 – 54.6 mean F S.D 43.0 F 7.9 All urban soils range 12.2 – 869.4 mean F S.D 66.1 F 84.0 Non-urban soils range 18.30 – 34.35 mean F S.D 25.43 F 4.4 Background value in Nanjing areaa (mean F S.D.) 32.2 F 13 Mean values in Chinab 22.0 a b Zn Pb Cr 57.7 – 143.3 89.3 F 19.1 83.4 – 851.7 170.0 F 117.4 93.9 – 432.7 167.2 F 92.9 80.5 – 769.0 280.3 F 194.3 86.9 – 185.4 120.1 F 32.6 57.7 – 851.6 162.6 F 123.9 41.82 – 127.59 75.15 F 30.8 78.6 F 29.5 100.0 36.3 – 89.9 57.7 F 11.0 58.5 – 472.6 133.2 F 70.0 57.7 – 251.4 99.7 F 47.9 62.0 – 308.5 151.4 F 68.2 74.3 – 101.7 83.62 F 9.44 36.3 – 472.6 107.3 F 62.6 trace – 33.99 17.49 F 11.2 24.8 F 16.3 23.6 49.8 – 117.8 76.1 F 14.8 56.1 – 123.3 84.5 F 11.8 54.7 – 139.7 89.4 F 20.9 48.1 – 118.8 88.6 F 20.3 63.7 – 118.3 92.0 F 16.6 48.1 – 139.7 84.7 F 17.0 6.89 – 76.25 41.89 F 23.6 59.0 F 20 53.9 The Group of Natural Background Values of Soil and Academia Sinica (1979) Liu (1996) concentration is triple the mean value of soils in China and twice as much as the natural background value of soils in the Nanjing area The mean total Zn concentration is greater than the mean value of soils in China and twice as much as the natural background value of soils in the Nanjing area The mean total Pb concentration is four times more than the mean value of soils in China and the natural background value of soils in the Nanjing area The mean total Cr concentration is higher than the mean value of soils in China and the natural background value of soils in the Nanjing area Taking the natural background values + standard deviation as an evaluation criteria (Lu, 1999), 31.9%, 41.3% and 16.7% of urban soils in Nanjing are polluted with Cu, Zn and Cr, respectively Pb concentration in urban soils are higher than pollution evaluation criteria (57.4 mg kgÀ 1), with the exception of several urban park soils The mean concentration of Pb is the highest in the roadside soils and the lowest in the urban park soils; this suggests that the emission from vehicles may be the main source of Pb contamination in urban soils The concentrations of Cu, Zn, Pb and Cr in non-urban soils are much lower than those in urban soils, and are not polluted by Cu, Zn, Pb and Cr Anthropogentic source contributes to elevated levels of Cu, Zn, Pb and Cr concentrations in urban soils, and that soil horizons were scraped, filled, mixed, etc repeatedly can interpret vertical variability of Cu, Zn, Pb and Cr concentrations in urban soil profiles Similar findings ´ˇ were reported by Culbard et al (1988), Chon et al (1995), Sanka et al (1995) and Lavado et al (1998) There are positive correlations among Cu, Zn, Pb and Cr concentrations (Table 3) Significant positive correlation between organic carbon and Cu, Zn, Pb and Cr concentrations suggests that those four metals have strong affinity with organic matter Cu, Zn and Pb concentrations are inversely correlated with clay content and directly correlated 106 Y Lu et al / Geoderma 115 (2003) 101–111 Table Correlation coefficients between Cu, Zn, Pb and Cr contents and urban soil properties (n = 138) pH Cu Zn Pb Cr Organic C Sand Silt Clay Cu Zn Pb Cr 0.124 0.147 0.281** 0.008 0.463** 0.693** 0.578** 0.342** 0.339** 0.455** 0.330** 0.119 À 0.165 À 0.247** À 0.011 À 0.084 À 0.346** À 0.447** À 0.471** À 0.106 1.000 0.838** 0.815** 0.400** 1.000 0.814** 0.404** 1.000 0.355** 1.000 ** Significant at the 0.01 probability level with sand content Cr concentrations have no significant correlation with the contents of sand, silt and clay The results are quite different from natural soils in which the Cu, Zn, Pb and Cr concentrations increased with the increase of clay content (Xu and Yang, 1995; Liu, 1996) Lu (2000) reported that Cu, Zn, Pb and Cr in Nanjing urban soils were mainly originated from anthropogentic input, and soil organic C negatively correlated with clay content, these probably result in different distribution of Cu, Zn, Pb and Cr in particle size fractions of urban soils from natural soils, and the results need be further confirmed 3.2 Heavy metal fractions in topsoils (A horizon soils) Recovery of the heavy metals during the sequential extraction procedure can be judged by comparing the sum of each fraction with the total heavy metal concentrations Recovery is essentially quantitative within the precision of the method Table shows satisfactory agreement between the total concentrations of heavy metals and the sum of the individual fractions There is a good correlation between the sums of the heavy metal fractions and the total concentrations The coefficients for Cu, Zn, Pb and Cr are 0.997, 0.989, 0.990 and 0.986 ( P < 0.01), respectively The Cu, Zn, Pb and Cr fractions expressed as amounts and percentages of the sum of individual chemical fractions are presented in Table The distribution of metals varies greatly among the samples Only very small amounts of Cu, Zn, Pb and Cr are present in the exchangeable fraction, most of which are present in the residual fraction The highest percentage of Cu associated with the residual fraction averages 66.1% and the lowest with exchangeable fraction averages 0.38% An average 4.7%, 5.4% and 23.4% of Cu is associated with the carbonate, Fe – Mn oxide and organic forms, respectively The percentage of Cu fraction follows the order as residualHorganic>Fe– Mn oxides>carbonate>exchangeable In roadside soils, however, the highest amounts of Cu Table Metal recovery from the sequential extraction analysis (all topsoils) (%) Cu Range Mean F S.D Zn Pb Cr 84.4 – 117.0 103.8 F 7.9 81.1 – 118.9 95.5 F 8.5 84.6 – 118.9 104.1 F 9.4 87.1 – 108.9 96.7 F 4.9 Y Lu et al / Geoderma 115 (2003) 101–111 107 Table Cu, Zn, Pb and Cr fractions expressed as percentage of sum of fractions (%) Exchangeable Carbonate Cu urban topsoils range mean F S.D non-urban range topsoils mean F S.D Zn urban topsoils range mean F S.D non-urban range topsoils mean F S.D Pb urban topsoils range mean F S.D non-urban range topsoils mean F S.D Cr urban topsoils range mean F S.D non-urban range topsoils mean F S.D a 0.08 – 0.79 0.38 F 0.17 1.62 – 1.79 1.68 F 0.10 0.22 – 0.86 0.46 F 0.18 0.61 – 2.36 1.30 – 17.22 4.73 F 3.63 0.42 – 1.15 Fe – Mn Oxide Organic Residual 0.07 – 12.83 6.51 – 50.43 20.81 – 86.96 5.39 F 3.65 23.38 F 13.22 66.11 F 17.25 n.d.a – 3.60 1.51 – 5.51 91.72 – 95.12 0.81 F 0.37 1.20 F 2.08 5.72 – 23.46 9.65 – 29.15 11.62 F 5.39 19.10 F 5.48 0.80 – 2.65 3.64 – 5.85 3.29 F 2.04 93.03 F 1.83 4.88 – 14.86 43.39 – 76.94 8.78 F 3.49 60.03 F 11.14 0.82 – 1.86 87.65 – 93.66 1.69 F 0.94 0.43 – 1.27 0.79 F 0.23 2.20 – 3.67 2.00 F 1.04 2.95 – 9.69 5.20 F 1.92 2.49 – 6.37 4.54 F 1.16 20.37 – 42.67 30.93 F 6.65 3.65 – 7.03 1.45 F 0.55 90.33 F 3.06 2.71 – 10.70 45.57 – 66.50 6.33 F 2.56 56.75 F 6.56 4.04 – 6.46 76.82 – 87.61 3.07 F 0.77 n.d – 0.12 0.04 F 0.03 1.60 – 4.31 3.90 F 2.15 n.d – 1.68 0.20 F 0.41 0.11 – 0.34 5.24 F 1.70 n.d – 6.72 2.69 F 1.46 2.15 – 4.81 5.31 F 1.21 2.61 – 6.70 4.16 F 1.19 4.34 – 5.64 82.48 F 5.41 88.70 – 95.40 92.92 F 1.85 87.56 – 91.60 2.52 F 1.55 0.20 F 0.12 3.07 F 1.51 4.81 F 0.72 89.40 F 2.04 Not dectected are associated with the organic fraction with an average of 48.74% and only 31.47% with the residual form, and the proportion of carbonate forms are obviously higher than other urban soils The results are in line with other investigations (Harrison et al., 1981) The percentage of urban soil Zn in exchangeable, carbonate, Fe – Mn oxide and organic fractions averages 0.46%, 11.62%, 19.10% and 8.78%, respectively Most of the total Zn, with an average of 60.03%, is present in the residual fraction The percentage of Zn fractions follows the order residualHFe – Mn oxides>carbonate>organic>exchangeable The Pb in urban soils is mainly associated with residual and Fe – Mn oxide fractions, making up 56.75% and 30.93%, respectively Exchangeable is the lowest, only accounting for 0.79% The percentage of organic and carbonate are 6.33% and 5.20%, respectively The proportion of Pb fractions follows the order residual>Fe – Mn oxideHorganic, carbonate>exchangeable The highest contents of Cr are associated with the residual fractions and average 92.92% Exchangeable, carbonate, Fe –Mn oxide and organic fractions average 0.037%, 0.20%, 2.69% and 4.16%, respectively The amount of Cr in each fraction follows the order residualHorganic>Fe –Mn oxide>carbonate>exchangeable In non-urban topsoils, the residual fraction of Cu, Zn, Pb and Cr accounts for 93.03%, 90.33%, 82.48% and 89.9%, respectively The percentages of Cu, Zn and Pb in the residual fraction are much higher than those in urban topsoils There is no difference in the proportion of Cr in the residual fraction between urban and non-urban topsoils It was reported that anthropogenic inputs, such as atmospheric deposition, street dust, etc., were the main sources of Cu, Zn, Pb and Cr in Nanjing urban soils (Lu, 2000) For atmospheric 108 Y Lu et al / Geoderma 115 (2003) 101–111 deposition and street dust, the major portion of Cu, Zn and Pb were associated with Fe– Mn oxide or organic fraction, with small percentage in residual fraction (Harrison et al., 1981; Gao et al., 1995; Wang et al., 1998), which result in the different distribution of Cu, Zn and Pb fractions between urban soils and non-urban soils The results show a certain similarity between the speciation patterns of Cr for urban and non-urban topsoils and perhaps for the high residual fraction of anthropogenic input Cr such as atmospheric deposition (Gao et al., 1995) The exchangeable fraction was the first to be brought into solution and is considered to be easily available for plant uptake, the carbonate fraction was susceptible to pH changes, the Fe –Mn oxide fraction was unstable under low Eh conditions, the organic fraction could be degraded under oxidizing conditions and the residual fraction was not considered to create a bioavailable pool since it was not expected to be solubilized over a reasonable period of time under natural conditions (Tessier et al.,1979) The amounts of non-residual fractions represent the amounts of active heavy metals (Xu and Yang, 1995) The non-residual fractions of Cu, Zn, Pb and Cr in urban soils average 33.89%, 39.97%, 43.25% and 7.08%, respectively, which suggests that the mobility and bioavailability of the four metals probably declined in the following order: Pb, Zn, Cu and Cr The non-residual fractions of Cu, Zn, Pb and Cr in non-urban soils average 6.7%, 8.7%, 16.5% and 10.1%, respectively Therefore, Cu, Zn and Pb in urban soils have higher mobility and bioavailability than Table Correlation coefficients between percentage of metal fractions and urban topsoil properties (n = 20) Metal Percentage of fractions Total metal pH Organic C CEC Total P Sand Silt Clay Cu 0.418 0.903** 0.505* 0.641** À 0.793** À 0.189 0.788** 0.643** 0.205 À 0.759** 0.279 0.741** À 0.906** 0.357 0.380 0.337 À 0.199 À 0.045 À 0.115 0.148 À 0.343 0.032 0.018 À 0.109 0.077 À 0.502* À 0.033 À 0.107 À 0.195 0.138 À 0.134 0.355 À 0.012 À 0.058 À 0.067 À 0.035 0.284 0.149 À 0.059 À 0.141 0.324 0.165 À 0.465* 0.664** À 0.449* À 0.193 0.607** 0.486* 0.571** À 0.708** 0.373 0.430 À 0.487* 0.639** 0.153 0.037 À 0.139 À 0.232 0.576** À 0.157 0.097 0.255 0.326 0.360 À 0.400 0.174 0.284 0.518* À 0.186 À 0.337 À 0.251 0.063 À 0.758** À 0.045 0.862** 0.013 À 0.097 À 0.167 0.179 0.037 À 0.186 0.617** 0.347 0.645** À 0.696** À 0.295 0.454* 0.368 0.091 À 0.424 À 0.006 0.711** À 0.391 0.222 0.084 0.201 0.572** 0.538* À 0.241 À 0.401 0.075 À 0.451* À 0.084 À 0.523* 0.513* 0.579** À 0.410 À 0.324 À 0.277 0.435 0.110 À 0.533* 0.211 À 0.244 0.052 À 0.153 À 0.477* À 0.538* 0.090 0.476* 0.231 À 0.515* À 0.501* À 0.474* 0.575** À 0.206 À 0.282 À 0.238 0.187 0.198 À 0.126 À 0.576** 0.420 À 0.082 À 0.211 À 0.160 À 0.403 À 0.269 0.308 0.107 Zn Pb Cr exchangeable carbonate Fe – Mn oxide organic residual exchangeable carbonate Fe – Mn oxide organic residual exchangeable carbonate Fe – Mn oxide organic residual exchangeable carbonate Fe – Mn oxide organic residual * Significant at the 0.05 probability level ** Significant at the 0.01 probability level 0.061 À 0.335 À 0.395 À 0.187 0.297 À 0.248 À 0.253 À 0.108 0.202 0.116 À 0.160 À 0.429 0.149 0.134 À 0.043 À 0.106 À 0.045 À 0.365 0.401 0.044 Y Lu et al / Geoderma 115 (2003) 101–111 109 in non-urban soils The mobility and bioavailability of Cr is not significantly different between urban and non-urban soils 3.3 Correlations between Cu, Zn, Pb and Cr fractions and urban soil properties The relationship between the percentage of Cu, Zn, Pb and Cr fractions and urban soil properties was evaluated by simple correlation procedures (Table 6) Total Cu concentration was negatively correlated with the percentage of the residual fraction and positively correlated with the percentage of organic, Fe – Mn oxide and carbonate fraction Total Zn concentration was negatively correlated with the percentage of the residual fraction and positively correlated with the percentage of Fe – Mn oxides and carbonate fractions Total Pb concentration was negatively correlated with the percentage of oxide Pb and positively correlated with the percentage of carbonate Pb The percentages of organic fractions of Cu, Zn, Pb and Cr were correlated with organic C contents Total P content was positively correlated with the percentage of residual Pb and negatively correlated with the percentage of Fe – Mn oxide Pb P concentration in urban soils was much high (Lu et al., 2001a,b) and phosphate could form highly insoluble pyromorphite with Pb (Janet, 1996); therefore, the proportion of residual Pb increased with soil P content The formation of Fe and Mn phosphates, which reduced the absorption and combination of Fe– Mn oxide with Pb, resulted in an inverse correlation of total P content with the percentage of Fe– Mn oxide fraction Conclusions The urban soils in Nanjing were polluted with Cu, Zn and Cr to some extent and heavily polluted with Pb The mean concentration of Pb is the highest in the roadside soils and the lowest in the urban park soils This suggests that the emission from vehicles may be the main source of Pb contamination in urban soils.There was a positive correlation among Cu, Zn, Pb and Cr concentrations Cu, Zn and Pb concentrations were inversely correlated with clay content and directly correlated with sand content Cr concentration had no significant correlation with the contents of sand, silt and clay For urban topsoils, the distribution of metals varied greatly among the samples The Cu, Zn, Pb and Cr were predominately present in the residual fraction The order of Cr, Cu in each fraction was residualHorganic>Fe – Mn oxides>carbonate>exchangeable, the amount of Zn in each fraction followed the order residualHFe – Mn oxides>carbonate>organic>exchangeable and Pb in each fraction was residual>Fe – Mn oxidesHorganic, carbonate>exchangeable The mobility and bioavailability of the four metals declined in the following order: Pb, Zn, Cu and Cr Cu, Zn and Pb were more mobile and bioavailable in the urban than in the non-urban soils; however, Cr was similar The percentage of residual Cu and Zn was negatively correlated with total Cu and Zn concentrations The organic carbon was positively correlated with the percentage of organic Cu, Zn, Pb and Cr fraction The total P content was directly correlated with the percentage of residual Pb and inversely correlated with the percentage of Fe – Mn oxide Pb 110 Y Lu et al / Geoderma 115 (2003) 101–111 Acknowledgements This work was supported by the National Natural Science Foundation of China (grant no 40235054) References Chapman, H.D., 1965 Cation exchangeable capacity In: Black, C.A (Ed.), Methods of Soil Analysis Agronomy, vol Am Soc Agron., Madison, WI, pp 891 – 901 Chen, T.B., Wong, J.W.C., Zhou, H.Y., Wong, M.H., 1997 Assessment of trace metal distribution and contamination in surface soils of Hong Kong Environ Pollut 96, 61 – 68 Chon, H.T., Kim, K.W., Kim, J.Y., 1995 Metal contamination of soils in Seoul metropolitan city, Korea Environ Geochem Health 17, 139 – 146 Culbard, E.B., Thornton, T., Watt, J., Wheatley, M., Moorcroft, S., Thompson, M., 1988 Metal contamination in British urban dusts and soils J Environ Qual 17, 226 – 234 Gao, L.C., Feng, S.P., He, G.H., 1995 Specification of Cu, Zn, Pb in dust of different diameters Res Environ Sci (4), 35 – 39 (in Chinese, with English Abstr.) Gee, G.W., Bauder, J.W., 1986 Particle size analysis In: Klute, A (Ed.), Methods of Soil Analysis: Part Physical and Mineralogical Methods Am Soc Agron., Madison, WI, pp 383 – 411 Gibson, M.J., Farmer, J.G., 1986 Multistep sequential chemical extraction of heavy metals from urban soils Environ Pollut 11, 117 – 135 (series B) Gong, Z.T., 1999 Chinese Soil Taxonomy Science Press, Beijing, China (in Chinese) Harrison, R.M., Laxen, D.P.H., Wilson, S.J., 1981 Chemical association of lead, cadmium, copper, and zinc in street dusts and roadside soils Environ Sci Technol 15, 1378 – 1383 Janet, C.H., 1996 Lead phosphate formation in soils Environ Pollut 93, – 16 Kasimov, N., Lychagin, M., 1998 Heavy metals in urban soils in Russia Symposium 28: Urban and Suburban Soils, Proc World Cong Soil Sci., Montpellier, France ´ Lavado, R.S., Rodrıguez, M.B., Scheiner, J.D., Taboada, M.A., Rubio, G., Alvarez, R., Alconada, M., Zubillaga, M.S., 1998 Heavy metals in soils of Argentina: comparison between urban and agricultural soils Commun Soil Sci Plant Anal 29, 1913 – 1917 Liu, Z., 1996 Microelements in Soils of China Jiangsu Sci and Technol Publishing House, Nanjing, China (in Chinese) Lu, Y.S., 1999 Environmental Evaluation Tongji Univ Press, Shanghai, China (in Chinese) Lu, Y., 2000 The Characteristics and environmental significance of urban soils: a case study for Nanjing city PhD Thesis Institute of Soil Science, Academia Sinica, Nanjing, China (in Chinese, with English Abstr.) Lu, Y., Gong, Z.T., Zhang, G.L., 2001a Features and classification of urban soils in Nanjing Soils 33, 47 – 51 (in Chinese) Lu, Y., Gong, Z.T., Zhang, G.L., 2001b Phosphorus characteristics of urban soil and its relationship with P concentration in groundwater Chin J Appl Ecol 12, 735 – 738 (in Chinese with English Abstr.) Markus, J.A., McBrantney, A.B., 1996 An urban soil study: heavy metals in Glebe, Australia Aust J Soil Res 34, 453 – 465 Nelson, D.W., Sommers, L.E., 1982 Total Carbon, organic carbon, and organic matter In: Page, A.L., Miller, R.H., Keeney, D.R (Eds.), Methods of Soil Analysis, Part 2, 2nd ed Chemical and Microbiological Properties Am Soc Agron, Madison, WI, pp 539 – 579 Olsen, S.R., Sommers, L.E., 1982 Phosphorus In: Page, A.L., Miller, R.H., Keeney, D.R (Eds.), Methods of Soil Analysis, Part 2, 2nd ed Chemical and Microbiological Properties Am Soc Agron., Madison, WI, pp 403 – 407 Ramos, L., Hernandez, L.M., Gonzalez, M.J., 1994 Sequential fractionation of copper, lead, cadmium and zinc ˜ in soils from or near Donana National Park J Environ Qual 23, 50 – 57 ´ˇ Sanka, M., Strnad, M., Vondra, J., Paterson, E., 1995 Sources of soil and plant contamination in an urban environment and possible assessment methods Int J Environ Anal Chem 59, 327 – 343 Y Lu et al / Geoderma 115 (2003) 101–111 111 State Statistical Bureau, P.R China, 2000 China Statistical Yearbook China Statistical Publishing House, Beijing, China (in Chinese) Stroganova, M.N., Myagkova, A.D., Prikofieva, T.V., Skvortsova, I.N., 1998 Soils of Moscow and Urban Environment Moscow Tack, F.M.G., Verloo, M.G., 1995 Chemical speciation and fractionation in soil and sediment heavy metal analysis: a review Int J Environ Anal Chem 59, 225 – 238 Tessier, A., Campbell, P.G.C., Blsson, M., 1979 Sequential extraction procedure for the speciation of particulate trace metals Anal Chem 51, 844 – 851 The Group of Natural Background Values of Soil, Academia Sinica, 1979 The natural background values of some trace elements in the important soil types of Beijing and Nanjing areas Acta Pedol Sin 16, 319 – 328 (in Chinese, with English Abstr.) Thornton, I., 1991 Metal contamination of soils in urban areas In: Bullock, P., Gregory, P (Eds.), Soils in the Urban Environment Blackwell, Oxford, pp 47 – 75 Wang, W.H., Wong, M.H., Leharne, S., Fisher, B., 1998 Fractionation and biotoxicity of heavy metals in urban dusts collected from Hong Kong and London Environ Geochem Health 20, 185 – 198 Weiss, P., Riss, A., Gschmeidler, E., Schentz, H., 1994 Investigation of heavy metal, PAH, PCB patterns and PCCD/F profiles of soil samples from an industrialized urban area (Linz, Upper Austria) with multivariate statistical methods Chemosphere 29, 2223 – 2236 Wilcke, W., Muller, S., Kanchanakool, N., Zech, W., 1998 Urban soil contamination in Bangkok: heavy metal ă and aluminium partitioning in topsoils Geoderma 86, 211 – 228 Wilcke, W., Lilienfein, J., Lima, S.D.C., Zech, W., 1999 Contamination of highly weathered urban soils in ˇ Uberlandia, Brazil J Plant Nutr Soil Sci 162, 539 – 548 Xu, J.L., Yang, J.R., 1995 Heavy Metals in Terrestrial Ecosystem China Environ Sci Press, Beijing, China (in Chinese) ... main source of Pb contamination in urban soils The concentrations of Cu, Zn, Pb and Cr in non -urban soils are much lower than those in urban soils, and are not polluted by Cu, Zn, Pb and Cr Anthropogentic... objective of this study was to determine the total Cu, Zn, Pb and Cr concentrations and chemical speciation of urban soils in Nanjing, China Materials and methods 2.1 Description of study area Nanjing... of Cu, Zn, Pb and Cr concentrations in urban soils, and that soil horizons were scraped, filled, mixed, etc repeatedly can interpret vertical variability of Cu, Zn, Pb and Cr concentrations in