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Heavy metals in wheat grain: Assessment of potential healthrisk for inhabitants in Kunshan, China

Mingli Huanga,b, Shenglu Zhoub,⁎, Bo Sunc, Qiguo Zhaoc

aCollege of Resources and Environment of China Agriculture University, Beijing 100193, ChinabSchool of Geographic and Oceanographic Sciences of Nanjing University, Nanjing 210093, ChinacInstitute of Soil Science, the Chinese Academy of Sciences, Nanjing 210008, China

A R T I C L E I N F O

⁎ Corresponding author. Tel.: +86 25 83592681E-mail address: zhousl@nju.edu.cn (S. Zho

0048-9697/$ – see front matter © 2008 Elsevidoi:10.1016/j.scitotenv.2008.07.004

A B S T R A C T

Article history:Received 22 April 2008Received in revised form28 June 2008Accepted 2 July 2008Available online 13 August 2008

Heavy metals (HMs) may cause deleterious effects on human health due to the ingestion offood grain grown in contaminated soils. Concentrations of HMs (Hg, As, Cr, Cu, Ni, Pb, Zn andCd) in wheat grains were investigated in different areas of a developed industry city inSoutheastChina (Kunshancity), and their potential risk tohealthof inhabitantswasestimated.The results showed that concentrations of HMs in the top soil (0–15 cm) were in this order:ZnNCrNNiNPbNCuNAsNHgNCd. The Zn, Cr, Ni Cd and Hg concentrations of several soilsamples exceeded thepermissible limits ofChina standard. In addition, concentrationsofHMsin wheat grain decreased in the order of ZnNCuNPbNCrNNiNCdNAsNHg. There were 1, 6 and10 wheat samples whose Zn, Pb and Cd concentrations were above the permissible limits ofChina standard, respectively. In relation to non-carcinogenic risks, Hazard Quotient (HQ) ofindividual metal presented values inside the safe interval. However, health risk due to theadded effects of eight HMswas significant for rural children and rural adults, but not for urbanadults and urban children. HQ (individual risk) and HI (Hazard Index of aggregate risk) todifferent inhabitants due to HMs followed the same sequence of: country childrenNcountryadultsNurban childrenNurban adults. Amongst the HMs, potential health hazards due to As,Cu, Cd and Pb were great, and that due to Cr was the minimum. It was suggested to pay moreattention on the potential added threat of HMs to the health of country inhabitants (bothchildren and adults) through consumption of wheat in Kunshan.

© 2008 Elsevier B.V. All rights reserved.

Keywords:Health riskHeavy metalWheat grainKunshan

1. Introduction

Heavy metals (HMs) are the most dangerous contaminantsfor environment and human beings (Bradl, 2005). Onceexcessive HMs enter in the soil, water or air, it may causehazards to human health through consumption of foodcrops cultivated in these contaminated environments (Zhaoet al., 2002; Wang et al., 2003). Ingestion of contaminatedfood is one of the main routs through which HMs enter thehuman body (Lacatusu et al., 1996; Järup, 2003; Grasmückand Scholz, 2005).

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er B.V. All rights reserved

For human body, certain HMs are essential for the biologicalsystems as structural and catalytic components of proteins andenzymes like zinc (Zn) and copper (Cu), and others arecontaminants such as cadmium (Cd), arsenic (As), mercury(Hg), lead (Pb), chromium (Cr), nickel (Ni) and so on (Somers,1974; Mushtakova et al., 2005). However, excessive retention ofeither kind of HMs in the environment imposes health risk tohuman. For instance, HMs induce toxic effect on human bloodneutrophils (Mushtakova et al., 2005), As, Cd, Pb and Hg areendocrine-disrupting chemicals (Dyer, 2007). HMs of relevanceto human health induces genomic instability (Coen et al., 2001).

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Both Pb and Hg are neurotoxic and there is a risk of develop-mental problems following exposure (Myers et al., 1997). Studyshowed that the most affected group of inhabitants by HMs ischildren (Lacatusu et al., 1996). Therefore, Food and AgricultureOrganization (FAO) and Word Health Organization (WHO),United States Environment Protection Agency (US EPA) andother regulatory bodies of other countries strictly regulate theallowable concentrations or maximum permitted concentra-tions of toxic HMs in foodstuffs (FAO/WHO, 1984; US EPA, 2000).

Potential health risk due to HMs can be assessed bycarcinogenic or non-carcinogenic assessing methods. Non-cancer risk assessment methods based on Hazard Quotient(HQ) and Hazard Index (HI) are set by United States Environ-mental Protection Agency (US EPA, 1989). These methods haverecentlybeenusedandprovedtobevalidanduseful (Chienetal.,2002;Wang et al., 2005; Zheng et al., 2007), so it is also applied inthis study. In general, potential food exposure routes of HMsinclude ingestion of fish and shellfish, meat and game, dairy,eggs and vegetables (US EPA, 1989), but little attention was paidon the consumption of grain crop (Chien et al., 2002; Nadal et al.,2004; Wang et al., 2005; Zheng et al., 2007; Chary et al., 2008). Infact, however, grain crop is almost themaximum ingestion foodin one's daily diet all around the world (Caussy et al., 2003), andalso one kind of lifetime consumption (Nadal et al., 2004).

In recent decades, with the rapid development of industry,agriculture, traffic and transportation, and mining industries,HM contamination is becoming serious in some regions,especially in developing countries (Jung and Thornton, 1997;Spiegel, 2002; Muchuweti et al., 2006). In China, the geologicalbackground levels of HMs are low, but with the activity ofhumans, soil, water, air, and plants were polluted by HMs insome cases and even affect human health through the food

Fig. 1 –Sampling points of wheat gra

chain (Cheng, 2003). Human health risk from consuming cropsgrown in contaminated environment was widely present inthe environment due to natural and anthropogenic emissions(Cui et al., 2005).

HMs in soil in the rapid economic development regions ofsouth Jiangsu province have attracted extensive attention ofmany researchers. Panet al. (1999) studied theavailable formsofHMs in soil environment in the south of Jiangsu province. Sunet al. (2004) assessed the concentration of HMs in the soil of thebasic farmland of Kunshan. Recent study (Wan et al., 2005)showed that some of the concentrations of HMs (Hg, As, Cr, Cu,Ni, Pb, Zn and Cd) in soil were higher than their backgroundvalues set by State Environmental Protection Administration ofChina (1995). Little attention is given, however, to concentra-tions ofHMs in grain crops and their possible deleterious effectson human health in Kunshan. So, in this study, wheat grainsamples in different locations of Kunshan were collected, toanalyze concentrations of HMs (Hg, As, Cr, Cu,Ni, Pb, Zn andCd)inwheat grain and to estimate the risk of adverse health effectsof HMs through ingestion of wheat in Kunshan.

2. Materials and methods

2.1. Study site and sampling

Kunshan, which is in the southeast of Jiangsu province, belongto Yangzi River Delta which is the most developed area inChina (Fig. 1). Kunshan is only 50 km far away from Shanghaimunicipality which is the biggest city in China. The total areaof Kunshan is 927 km2, and the population 600 thousand.Kunshan is a traditional agriculture area experienced in a

in on paddy soil (▲) in Kunshan.

Table 1 – Concentrations of HMs (mg kg−1) in soil

HMs Range Median Permission limits ofChinese standardsa

Zn 59.32-1064.12 98.575 200–250 (n=2)b

Cu 18.07-61.88 26.000 50–100 (n=0)Pb 12.34-48.13 28.630 250–300 (n=0)Cr 46.58-162.96 67.415 150–200 (n=1)Ni 24.67-56.67 35.835 40–50 (n=4)Cd 0.099-1.007 0.160 0.3 (n=2)As 8.63-20.95 12.005 30–40 (n=0)Hg 0.10-0.81 0.213 0.3–0.5 (n=6)

a Permissible limits of different HMs in agricultural soil set byEnvironment Protection Administration of PRC (1995).b Values in the parenthesis is the number of samples whichconcentrations of HMs exceeded the background value orpermissible limits. The same below.

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remarkable development of economy since the early 1990s. In2005, gross domestic production (GDP) of Kunshan amountedto 75 billion Yuan, and ranked first among all counties inChina. Per capita GDP achieved 113 thousand Yuan. Chemicaland electronic industries have become the pillar industries ofthe economy in this area. Previous study showed that thecontribution of textile, chemical, printed circuit board manu-facturing and building materials industries are 45.73% of thetotal contamination in Kunshan (Liu et al., 2005a). Further-more, area of arable land in 2005 (21.06 thousand ha) was only45.9% of that in 2000 (45.92 thousand ha). Under thesecircumstances, the environmental threat and possible healtheffects due to HMs are becoming more and more serious withthe intensive activities of industry and agriculture.

The hypsography is flat in Kunshan. The general physiog-nomic characteristic is high in the south and low in the north(Fig. 1). Most plains are covered with Quaternary Sediments,most of which are fluvial and lacustrine sediments. Paddy soilis prominent, which accounts for 93.8% of the total area of soil(blank area in Fig. 1). Humid soil distribute sporadically in thenorthwest and southwest of Kunshan (Fig. 1). Soils of fortysampling locations are all paddy soil (The Soil Survey Office ofKunshan county, 1984).

Forty sampling points were selected in different agricul-tural areas in Kunshan (Fig. 1) in May 2006 just before wheatharvest. These wheat fields were near different industryplants, which included chemical, printing and dying, breedingand metallurgy and plating industries that are prevalent inKunshan. Paired soil and wheat grain were sampled from atleast five distinct samples taken in a 10 ×10 block for everywheat field. Soil samples were taken with a 5 cm diameterstainless steel auger on the 0–15 cm layer, and were placed inplastic bags and brought back to laboratory. Wheat ears werecollected at the same time.

2.2. Soil analyses

The collected soil samples were air-dried and sieved through a2-mm polyethylene sieve to remove stones and plant roots.Soil pHwasmeasured in suspension (soil: water: 1:2.5) with pHglass electrodes (Lu, 2000). Organic carbon contents in soilwere determined by the method of potassium bichromate(Institute of Soil Science, CAS, 1978). Laser Grain-size Analyzerwas used to analyze soil mechanical composition.

The soil samples were ground with wooden roller by handuntil fine particles (b0.149 mm) were obtained. Soil sampleswere digested using HCl-HNO3 for the determination of thetotal concentrations of Hg and As with the method ofReduction Gasification — Atomic Fluorescence Spectroscopy(AFS) (Zhu et al, 2002). A 0.25 g subsample of soil samples weredigested in a mixture of HF-HNO3-HClO4 acid for Cd determi-nation with graphite furnace atomic absorption spectrometer(GF-AAS), and other elements (Cu, Ni, Pb, Zn, Cr) withInductively Coupled Plasma-atomic Emission Spectrometry(ICP-AES) (Liu, 1996).

2.3. Wheat grain analyses

Air dried wheat ears were threshed with a wooden tool. Grainsamples were washed with tap water to remove any attached

particles, rinsed three times with distilled water, and oven-dried at 38 °C till constant weight. Dried samples were groundusing a stainless steel grinder (b0.25 mm) for HM analysis. Aportion of the dry wheat grain powder material was digested ina mixture of HNO3 and HClO4 (Thompson and Walsh, 1983),then total concentration of Cd and Pbwere determinedwithGF-AAS and those of Cr, Cu, Ni, Zn with ICP-AES. Those sampleswhere the ICP-AES was insufficiently sensitive, concentrationsof metals were determined by a GF-AAS. Ground grain sampleswere digested in a mixture of HNO3–HClO4–H2SO4 acid for totalHg and As determination with AFS (AF-640) according tostandard analytical procedures.

2.4. Analytical quality

Quality control measures in analyzing procedure were takento confirm the accuracy of the analytical data. Two certifiedreference soils and two reference plant materials weredigested in a similar manner to the soil and wheat grainsamples for quality control and to monitor any instrumentvariability. The reference soils included GBW 07405 (GSS-5)and GBW 07408 (GSS-8), respectively (China National Centerfor Standard Materials). The certified plant materials werewheat (GBW10011) and tea (GBW 07605 (GSV-4)). In everyanalytical batch, 10% samples of all were analyzed repeatedlyto ensure the precision and accuracy of analysis. Internalreference standard materials and reagent blanks were alsoused in the process of analysis to ensure the precision.

3. Results and discussion

3.1. Soil

In general, the soil was slightly acidic (6.6), and pH of the soilranged from 5.3 to 7.8. Median value of organic matter (OM)was 3.04%, and ranged from 1.95% to 4.43%. The soils reportedmoderate cation exchange capacity (CEC) (18.29) which rangedbetween 14.8 and 28.8 cmol kg−1. Data of eight HMs in the soilalong with permissible Chinese standards are presented inTable 1. The standard values of different HMs (varied with soil

Fig. 2 –The consumption rates of wheat among urban andrural inhabitants in Kunshan.

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pH) were promulgated by Environment Protection Adminis-tration of PRC (1995) to protect soil environment and agri-culture production (Table 1).

Concentrations of HMs of forty soil samples varied verymuch. So median value of HMs concentration were presentedin Table 1. Variability (Coefficient of variance, CV is 116%) of Znconcentration in soils were high, showing a remarkable effectof environmental input on Zn concentration in soil. CV of Cdand Hg in soils were 78% and 49%, respectively. Concentrationof As is more stable than others in soil.

Median concentrations of eight HMs in soil were all lowerthan permission limits of Chinese standards. However, a fewsamples presented higher concentrations of Zn, Cr, Ni, Cd andHg than thepermissible limits ofChinese standards. Thereweresix soil samples which have higher Hg concentration than thestandardvalue, and four forNi, two forCd andZnandone for Cr.Concentrations of Cu, Pb and As of all forty soil samples wereunder their permissible value of Chinese standard.

3.2. Wheat grain

Concentrations of Hg, As, Cr, Cu, Ni, Pb, Zn and Cd in wheatgrain, tolerance limits of Chinese standards and Bioconcen-tration Factor (BCF) are exhibited in Table 2. BCF is a commonparameter often used in the study of environmental contam-inations (Sjöström et al, 2008; Sipter et al, 2008). BCF is the ratioof concentration of HM in wheat grain and that in soil (Eq. (1)).

BCF ¼ Cp=Cs ð1Þ

Cp: the concentration of HM in wheat grain; Cs is the

concentration of HM in soil.

Astheessentialmicronutrients forplant (Rameshetal., 2004;Lin and Wu, 1994; Marschnar, 1995), Zn and Cu were the mostabundant metals in wheat grains. In 40 sampling locations,concentrations of Zn in wheat grains ranged from 12.06 to80.32 mg kg−1, and that of Cu ranged from 2.43 to 6.83 mg kg−1.Median concentrations of both Zn and Cu in wheat grains werenot above the tolerance limits of Chinese standards (Table 2),only one sample showed a higher level of Zn than the tolerancelimit (50 mg kg−1), and none for Cu (10 mg kg−1). The highconcentrationofZn inwheatgrainwas related to that insoil and

Table 2 – Concentrations of HM (mg kg−1 dry wt.) in wheatgrain in Kunshan

HMs Range Median Tolerancelimits ofChinese

standards a

Bioconcentrationfactor (median)

Zn 12.06-80.33 27.781 50 (n=1) 0.273Cu 2.43-6.83 5.229 10 (n=0) 0.201Pb 0.017-1.158 0.177 0.4 (n=6) 0.007Cr 0.027-0.799 0.108 1 (n=0) 0.002Ni 0.043-0.637 0.148 1 (n=0) 0.004Cd 0.006-0.179 0.055 0.1 (n=10) 0.347As 0.029-0.086 0.038 0.7 (n=0) 0.003Hg 0.003-0.006 0.003 0.02 (n=0) 0.016

a Tolerance limits of different HMs in food (Ni limit in margarine)set by Ministry of Health of PRC.

the high value of BCF of Zn from soil towheat grain (0.278). Thisresult is consistent with that of Wang et al. (2005) who foundhigh BCF of Zn for vegetables and fish. Comparing with that ofZn, BCF of Cu was lower, which is about 0.192.

Concentration of Pb was higher than those of Ni and Cr inwheat grain (Table 2), however, quite the contrary in the soil.Comparing with BCF of Ni and Cr, that of Pb was higher, whichwas significantly lower than that for carrot (Samøe-Petersenet al., 2002; Pendergrass andButcher, 2006). This result stronglyagreed with the observation of Gigliotti et al. (1996) who foundCr andPb are lessmobile in cornplants. Variationsof Pb,Ni andCr concentrations in wheat grains were considerably largerthan those in soil, suggesting those HMs in grain may beaffected by such environmental factors as emissions fromprintworks and electroplating plants in Kunshan (Liu et al.,2005a). In special, Pb concentrations of 6 grain samplesexceeded the Chinese tolerance limits of 0.4 mg kg−1. Childrenare more sensitive to Pb comparing with adults (NationalAcademy of Sciences, 1993), so more attention should be paidto the possible damaging effects of Pb in wheat grain onchildren's health.

Range of Cd concentration in wheat grain (0.006 to0.179 mg kg−1) was much bigger than that of As (Table 2). BCFof Cd was 0.413, which was higher than those of any othermetals examined. It was noticeable that Cdwas considered as avery dangerous substance for human health at the long term(Nordberg, 1996; de Burbure et al., 2006). Therefore, the risks ofCd for health should be highlighted by its high toxicity andmobility from soil to wheat grain. In contrast, BCF of As (0.003)was much lower than those of other HMs, which is consistentwith the result of Liu et al. (2005b) who found the BCF of As incrops are considerably lower than those of Cd, Zn, Cu and Pb.The small BCF of As may be impact by water solubility of As insoil (Grisson et al., 1999).

Concentration of Hg was minimal in wheat grain, rangingfrom 0.003 to 0.006 mg kg− , which is observably lower thanthat in vegetables (Wang et al., 2005). Variation of Hg in wheatgrain was much lower than that in soil. BCF of Hg was 0.0176,and no sample showed higher Hg concentration than theChinese tolerable limits (0.02 mg kg−1).

Table 3 – HQ of individual HM for different exposure populations

HMs Hg As Cr Cu Ni Pb Zn Cd

Urban adults 1.3×10−2 1.5×10−1 8.7×10−5 1.6×10−1 9.0×10−3 5.3×10−2 1.1×10−1 6.5×10−2

Urban children 1.5×10−2 1.7×10−1 9.5×10−5 1.7×10−1 9.7×10−3 5.8×10−2 1.2×10−1 7.2×10−2

Rural adults 2.6×10−2 3.0×10−1 1.7×10−4 3.0×10−1 1.7×10−2 1.0×10−1 2.2×10−1 1.3×10−1

Rural children 2.9×10−2 3.3×10−1 1.9×10−4 3.3×10−1 1.9×10−2 1.1×10−1 2.4×10−1 1.4×10−1

Fig. 3 –HQ of HMs for different exposure populations.

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3.3. Health risk of consuming wheat grain

3.3.1. Daily intake of wheat grainIt was reported that 90.02 kg staple food were consumed by anaverage urban inhabitant and 174.63 kg by a rural inhabitant inKunshan in 2004 (Kunshan Statistic Bureau, 2005). Accordingto the study of Hu et al (2004), wheat grain accounted about30% of the staple food in the diet of inhabitants in Jiangsuprovince. So, it can be calculated that the daily intake of wheatfor an urban adult was about 74 g per day, and that for a ruraladult was 144 g per day in Kunshan (Fig. 2). The daily intake ofwheat for children (0–6 years old) is assumed to be 1/3 of thatfor adults, so those for an urban child and a rural child were24.7 g per day and 47.8 g per day, respectively. It is shown fromFig. 2 that the daily intake of wheat for inhabitant (adults orchildren) in country is almost two times of that for those inurban area.

3.3.2. Risk of individual HMThe potential non-cancer risk for individual HM is expressedas hazard quotient (HQ) (US EPA, 1989)

HQ ¼ CDI=RfDo ð2Þ

CDI mg=kg d dayð Þ ¼ CF� IR� EF� EDBW� AT

ð3Þ

In which, Chronic Daily Intake (CDI) is exposure expressedasmass of a substance contacted per unit bodyweight per unittime, averaged over a long period of time (a lifetime in thispaper); RfDo is the oral reference dose (mg kg−1 day−1). Units ofCDI and RfDo are same. (US EPA, 1989). CF is the medianconcentration of HM in wheat grain (mg kg−1); IR is theingestion rate of wheat grain (kg person−1 day−1), showed inFig. 2; EF is exposure frequency (365 days year−1); ED is theexposure duration (70 years for adults and 6 years for childrenare assumed in this study), equivalent to the average lifetime(Bennett et al., 1999); BW is the average bodyweight (61.6 kg foradults (Yuan et al, 2007), and 18.7 kg for 0–6 years old childrenare presumed (Xu, 2001)), and AT is the averaging exposuretime for non-carcinogenic effects (ED×365 days year−1). If theCDI exceeds this threshold (i.e., if HQ exceeds unity), theremaybe concern for potential non-cancer effects. As a rule, thegreater the value of HQ above unity, the greater the level ofconcern.

The RfDo is an estimation of a daily exposure to the humanpopulation that is likely to be without an appreciable risk ofdeleterious effects during a lifetime. RfDo were based on3×10−4, 3×10−4, 1.5, 4×10−2, 2×10−2, 0.3 and 1×10−3 mg kg−1

day−1 for Hg, As, Cr, Cu, Ni, Zn and Cd, respectively (US EPA,

2000). The US EPA has not established an RfDo for Pb (US EPA,2004), so RfDo for Pb used in this paper was 4.0×10−3 mg kg−1

calculated from the tolerable weekly Pb intake limit (25 µg kg−1

body weight) recommended by the FAO/WHO for adults (FAO/WHO, 1984; Ostapczuk et al., 1987).

Results of HQ for individual element were shown in Table 3.For different exposure population, HQ of individual HMwere allbelow 1, which means that the daily intake of individual metalthrough the consumption of wheat grain would be unlikely tocause adversehealth effects for Kunshan inhabitants. The valueof HQ in wheat grain was much smaller than that in fish orvegetables studiedbyothers (Chienetal., 2002;Wangetal., 2005;Zheng et al., 2007). It can also be shown from Table 3 that HQ ofindividualmetal for children ishigher than that for adults eitherin city or country, which is coincidence with previous studies(Nadal et al., 2004; Zheng et al., 2007) found. Consequences ofHQs of every metal for different exposure populations were inthe same order of: Country childrenNCountry adultsNUrbanchildrenNUrban adults. There was a big discrepancy of HQamong different HMs. HQ of Cu and As are the biggest, rangingfrom 0.15 to 0.33. HQ of Crwas the lowest, whichmay be relatedto its high RfDo of 1.5 mg kg−1. The non-cancer HQ followingexposure to Cr was less than 0.0002 for all populations. Wanget al. (2005) also found that HQ of Cr in the consumption ofvegetables and fish is minimal, comparing with that of Cu, Zn,Pb, Cd and Hg.

Fig. 4 –Contribution of HM to integrative risk.

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3.3.3. Aggregate risks for multiple HMsTo assess the overall potential for non-carcinogenic effectsposed by more than one HM, a hazard index (HI) approach hasbeen developed based on EPA's Guidelines for Health RiskAssessment of Chemical Mixtures (US EPA, 1986). The hazardindex is equal to the sum of the hazard quotients, as describedin Eq. (4) (US EPA, 1989).

HI ¼X

HQ ¼ CDI1=RfDO1 þ CDI2=RfDO2 þ :::þ CDIi=RfDOi ð4Þ

When the hazard index exceeds unity, there may beconcern for potential health effects. It is very interesting thatalthough there is no single metal exposure exceeds its RfDo,but the potential risk due to the added risk of all HMs throughthe consumption of wheat grain is significant for ruralchildren and rural adults, but not for urban children andurban adults in Kunshan (Fig. 3). HI of rural adults and childrenwere 1.09 and 1.20, indicating that it is likely for exposedcountry inhabitants (both adults and children) to experienceadverse health effects.

HI was 0.56 for urban adults and 0.62 for urban childrenrespectively (Fig. 3), which were lower than 1. That is, urbaninhabitants were not likely to be hurt by HMs throughconsuming wheat grain. However, if potential health risks ofHMs through other exposure routs are considered, total HMswill be likely to pose potential health risks to urbaninhabitants in this area. Because vegetables and fish oftencarried high concentrations of HMs in the diet of inhabitants(Chien et al., 2002; Nadal et al., 2004; Wang et al., 2005; Zhenget al., 2007).

In contrast, contributions of As and Cu to integrative riskwere the biggest for different receptor population, and bothwere more than 25% (Fig. 4). High potential risk due to As andCu may be related to waste water released from metallurgyand chemical plants in Kunshan area. So diseases related to Asand Cu should be paid more attention in Kunshan. HQ of Zn,Cd and Pb attributed to total HI are 19.8%, 11.6% and 9.4%,respectively. The risk contribution from Hg and Ni are 2.4%and 1.6%. That from Cr is minimal, only accounts for 0.015%,

which may be related to the high RfDo of Cr (1.5 g kg−1). Wanget al. (2005) also found that contribution of Cr to integrativerisks (HI) is minimal through consumption of vegetables andfish in Tianjin.

4. Conclusions

The investigation in the fast industrializing city, Kunshan,showed the concentrations ofmetals inwheat grain decreasedin the order of ZnNCuNPbNCrNNiNCdNAsNHg. Although themedian concentrations of HMs in soil andwheat grainwere alllower than the permissible limits of Chinese standards, thereare still a few soil and wheat grain samples presented highconcentrations of HMs. It was noticeable that 1, 6 and 10wheatsamples presented higher concentrations of Zn, Pb and Cdthan their permissible limits of China standard, respectively.The discrepancies in the concentrations of heavy metals atdifferent locations suggested that the environmental influ-ence differ very much amongst eight HMs.

The possible health risk from individual HM was notnotable, but the aggregate risks of eight heavy metals forcountry inhabitants (both children and adults) are more than1, indicating crucial attention should be paid on the potentialhealth risk of heavymetals through the consumption of wheatgrain. Sequences of HQ (individual risk) and HI (aggregaterisks) due to eight heavy metals are the same, that is CountrychildrenNCountry adultsNUrban childrenNUrban adults. Fordifferent exposure populations, contributions of As and Cu tothe aggregate risks of HMs were the biggest, which may berelated waste water released from metallurgy and chemicalplants in Kunshan. Contribution of Cr was minimal.

As the estimated intake of heavy metals in the presentwork does not include the contribution of other foods thatmay constitute further contamination sources the populationsubjected, further investigation should be focused on dis-covering the levels of heavy metals in other medium likevegetables, fish, eggs, milk, meat, table water and air, also onthe occurrence of diseases linked to heavy metals, andcontribution of different sources to the heavy metal pollutionin soil–crop system in this area.

Acknowledgments

This paper is done according to the work of the first author'sPhD dissertation conducted in Nanjing University. This workis supported by grants from the project of Basic ResearchDevelopment Project of China (Grant No. 2002CB410810) andthe project of Ecological geochemical survey of land in Jiangsuprovince (No. 20031230008 and 200312300009203) (Coopera-tive project of China Geological Survey and the People'sGovernment of Jiangsu Province). Authors are grateful to Prof.Fusuo Zhang for the valuable suggestion on the manuscript,and Dr. Bo Liu, Xiaolan Zhong and Fuqiang Liao, and MScShusi Qi (Nanjing University) for the sampling and pre-treatment work. We also thank senior experimenter ZhaoliLiu (Institute of Soil Science, the Chinese Academy ofSciences, Nanjing, China) for his help in the process ofanalysis.

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