contamination and risk assessment of metals in road-deposited sediments in a medium-sized city of...

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Contamination and risk assessment of metals in road-deposited sediments in a medium-sized city of China Bo Bian a,b,n , Cheng Lin c , Hai suo Wu a,b a Jiangsu Provincial Academy of Environmental Science, 241 Fenghuang West Street, Nanjing, Jiangsu Province 210036, China b Jiangsu Province Key Laboratory of Environmental Engineering, 241 Fenghuang West Street, Nanjing, Jiangsu 210036, China c Terracon Consultants, Inc., 2201 Rowland Avenue, Savannah, GA 31404, USA article info Article history: Received 4 August 2014 Received in revised form 20 October 2014 Accepted 21 October 2014 Keywords: Road-deposited sediment (RDS) Metals Contamination Health risk Different land uses Particle sizes abstract Road-deposited sediment (RDS) is a valuable environmental medium for characterizing contamination of metals in urban areas and the associated risks to human health. A total of 62 RDS samples were collected for metal test in four urban areas in a medium size city in eastern China. The areas that represented different land uses consisted of intense trafc area (ITA), commercial area (CA), residential area (RA), and riverside park area (RPA). The effects of particle size and different land uses on metal contamination and health risk were the major focus in this study. The test results showed that RDS in ITA appeared to have higher metal content, enrichment factor (EF), ecological risk index (RI), and the non-cancer and cancer risks than in the other areas. The metal contamination and health risk increased inversely with particle size. The particles less than 63 μm were found to be most critical in development of metal contamination and health risk. The EF was measured to be greater than 2.0 in the four areas, indicating a moderate enrichment. The measured RI ranged between 50 and 200, indicating considerable to moderate risks. The non-cancer risk for children was high in the four areas but was low for adults in all test areas except in ITA. The cancer risk of Cr for children was high in all test areas. Based on the test results, the con- tamination control and management for metals in RDS shall focus on the effects from such factors as particles ( o63 μm) and the land use for intense trafc (ITA). & Elsevier Inc. All rights reserved. 1. Introduction Road-deposited sediment (RDS) is a potentially toxic medium as it contains such pollutants as metals and hydrocarbons, origi- nated from a wide range of non-point sources including wet and dry deposition, vehicle exhausts, vehicle and road wear, de-icing operations, accidents, abrasion of construction materials and soil erosion (Kim and Sansalone, 2008; Yunker et al., 2002). RDS on impervious ground surface tends to accumulate more pollutants and thus the associated surface runoff carries a higher pollutant load (Jartun et al., 2008). RDS that is enriched with toxic metals has been blamed for the cause of a variety of health problems (Zheng et al., 2010). Therefore, a proper understanding of RDS contamination is crucial to urban environmental quality and hu- man health. Metals in RDS are of major concern because of their toxicity and non-degradability (Wei and Yang, 2010; Kong et al., 2011). The RDS quantity, particulate size, and particulate mobility are important factors for the assessment of metal pollution in public health. Fine RDS tends to contain a high percentage of metals. Sansalone and Buchberger (1997) indicated that the highest concentrations of Zn, Cu and Pb were associated with particles smaller than 250 μm. Murakami et al. (2005) concluded that RDS with particle size less than 100 μm were most signicant in the pollution of surface runoff. The contamination of metals in RDS can be assessed with dif- ferent methods (Liu et al., 2008; Shi et al., 2010; Wei and Yang, 2010) which include (1) enrichment factor (EF), (2) Nemerow synthetic pollution index (PIN), and (3) potential ecological risk index (RI). Most of studies employing these methods focused on the pollutant distribution of RDS; however, the effects of particle size of RDS on contamination of metals and health risk were not considered (Yuen et al., 2012; Cao et al., 2014). RDS particle sizes have a direct impact on health risk. For example, the ner particles tend to be easier for transportation and more detrimental to hu- man health; particles smaller than 66 μm can be easily blown Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ecoenv Ecotoxicology and Environmental Safety http://dx.doi.org/10.1016/j.ecoenv.2014.10.030 0147-6513/& Elsevier Inc. All rights reserved. n Corresponding author at: Jiangsu Provincial Academy of Environmental Science, 241 Fenghuang West Street, Nanjing, Jiangsu Province 210036, China. Fax: þ86 25 86535962 . E-mail address: [email protected] (B. Bian). Ecotoxicology and Environmental Safety 112 (2015) 8795

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Page 1: Contamination and risk assessment of metals in road-deposited sediments in a medium-sized city of China

Ecotoxicology and Environmental Safety 112 (2015) 87–95

Contents lists available at ScienceDirect

Ecotoxicology and Environmental Safety

http://d0147-65

n Corr241 FeFax: þ8

E-m

journal homepage: www.elsevier.com/locate/ecoenv

Contamination and risk assessment of metals in road-depositedsediments in a medium-sized city of China

Bo Bian a,b,n, Cheng Lin c, Hai suo Wu a,b

a Jiangsu Provincial Academy of Environmental Science, 241 Fenghuang West Street, Nanjing, Jiangsu Province 210036, Chinab Jiangsu Province Key Laboratory of Environmental Engineering, 241 Fenghuang West Street, Nanjing, Jiangsu 210036, Chinac Terracon Consultants, Inc., 2201 Rowland Avenue, Savannah, GA 31404, USA

a r t i c l e i n f o

Article history:Received 4 August 2014Received in revised form20 October 2014Accepted 21 October 2014

Keywords:Road-deposited sediment (RDS)MetalsContaminationHealth riskDifferent land usesParticle sizes

x.doi.org/10.1016/j.ecoenv.2014.10.03013/& Elsevier Inc. All rights reserved.

esponding author at: Jiangsu Provincial Acadenghuang West Street, Nanjing, Jiangsu6 25 86535962 .ail address: [email protected] (B. Bian).

a b s t r a c t

Road-deposited sediment (RDS) is a valuable environmental medium for characterizing contamination ofmetals in urban areas and the associated risks to human health. A total of 62 RDS samples were collectedfor metal test in four urban areas in a medium size city in eastern China. The areas that representeddifferent land uses consisted of intense traffic area (ITA), commercial area (CA), residential area (RA), andriverside park area (RPA). The effects of particle size and different land uses on metal contamination andhealth risk were the major focus in this study. The test results showed that RDS in ITA appeared to havehigher metal content, enrichment factor (EF), ecological risk index (RI), and the non-cancer and cancerrisks than in the other areas. The metal contamination and health risk increased inversely with particlesize. The particles less than 63 μmwere found to be most critical in development of metal contaminationand health risk. The EF was measured to be greater than 2.0 in the four areas, indicating a moderateenrichment. The measured RI ranged between 50 and 200, indicating considerable to moderate risks. Thenon-cancer risk for children was high in the four areas but was low for adults in all test areas except inITA. The cancer risk of Cr for children was high in all test areas. Based on the test results, the con-tamination control and management for metals in RDS shall focus on the effects from such factors asparticles (o63 μm) and the land use for intense traffic (ITA).

& Elsevier Inc. All rights reserved.

1. Introduction

Road-deposited sediment (RDS) is a potentially toxic mediumas it contains such pollutants as metals and hydrocarbons, origi-nated from a wide range of non-point sources including wet anddry deposition, vehicle exhausts, vehicle and road wear, de-icingoperations, accidents, abrasion of construction materials and soilerosion (Kim and Sansalone, 2008; Yunker et al., 2002). RDS onimpervious ground surface tends to accumulate more pollutantsand thus the associated surface runoff carries a higher pollutantload (Jartun et al., 2008). RDS that is enriched with toxic metalshas been blamed for the cause of a variety of health problems(Zheng et al., 2010). Therefore, a proper understanding of RDScontamination is crucial to urban environmental quality and hu-man health.

my of Environmental Science,Province 210036, China.

Metals in RDS are of major concern because of their toxicity andnon-degradability (Wei and Yang, 2010; Kong et al., 2011). The RDSquantity, particulate size, and particulate mobility are importantfactors for the assessment of metal pollution in public health. FineRDS tends to contain a high percentage of metals. Sansalone andBuchberger (1997) indicated that the highest concentrations of Zn,Cu and Pb were associated with particles smaller than 250 μm.Murakami et al. (2005) concluded that RDS with particle size lessthan 100 μm were most significant in the pollution of surfacerunoff.

The contamination of metals in RDS can be assessed with dif-ferent methods (Liu et al., 2008; Shi et al., 2010; Wei and Yang,2010) which include (1) enrichment factor (EF), (2) Nemerowsynthetic pollution index (PIN), and (3) potential ecological riskindex (RI). Most of studies employing these methods focused onthe pollutant distribution of RDS; however, the effects of particlesize of RDS on contamination of metals and health risk were notconsidered (Yuen et al., 2012; Cao et al., 2014). RDS particle sizeshave a direct impact on health risk. For example, the finer particlestend to be easier for transportation and more detrimental to hu-man health; particles smaller than 66 μm can be easily blown

Page 2: Contamination and risk assessment of metals in road-deposited sediments in a medium-sized city of China

Fig. 1. Map of study areas and sampling locations.

B. Bian et al. / Ecotoxicology and Environmental Safety 112 (2015) 87–9588

away by a breeze (De Miguel et al., 1997). The fine particles (e.g.PM2.5) can penetrate deep into the respiratory system, after whichthey are retained and absorbed by the body. In addition, fineparticles have the longer atmospheric residence time than coarseparticles and the ability of long-range transport (Prabhakar et al.,2014; Gugamsetty et al., 2012; Sorooshian et al., 2012). The fineparticles may enter the human body through dermal contact, in-halation, and ingestion exposures to environmental media. Assuch, it is also important to conduct health risk assessment toestimate the severity of the pollution and develop an effective riskmitigation program (Qu et al., 2012). One of the important para-meters for health risk assessment is hazard quotient (HQ) whichwas developed by the US Environmental Protection Agency(USEPA) and has been widely used to characterize the non-cancerrisk (Mari et al., 2009).

The RDS research is often conducted at the city scale. A citycommonly consists of areas of different land uses which exhibittheir own characteristics; and these characteristics affect the dis-tribution and pollution level of the RDS directly or indirectly.Health risks of metals in soil and urban dust have been evaluatedin many different cities, such as Luanda, Angola (Ferreira-Baptistaand De Miguel, 2005), Shanghai, China (Shi et al., 2011) Nanjing,China (Liu et al., 2014), Beijing, China (Zhao and Li, 2013) and Xi'an,China (Lu et al., 2014). However, these studies did not evaluate theeffects of particle sizes on the health risk, partly because of thelack of systematic multi-pathway health risk analyses (Cao et al.,2014). In general, the literature review indicates that it is sig-nificant to incorporate the RDS grain size distribution into theassessment of contamination of metals in RDS and the potentialhealth risk (Zhao and Li, 2013; Zhu et al., 2008).

The objective of this paper was to assess contamination andhealth risk of metals in RDS in Zhejiang City, a medium size city inChina. Within a city, the areas that are developed for different landuses may be subjected to different levels of RDS contamination. Assuch, RDS was collected from the four areas for different land usesincluding intense traffic area (ITA), commercial area (CA), re-sidential area (RA), and riverside park area (RPA). The particle sizedistribution of RDS and metal concentrations were analyzed. Dif-ferent methods were employed to assess the metal contaminationand health risk. Eventually, the study in this paper intends toaddress the three questions: (1) effects of particle size distributionon the concentrations of metals in RDS, (2) effects of particle sizedistribution on contamination and health risk of metals in RDS,(3) effects of different land uses on contamination and health riskof metals in RDS.

2. Material and methods

2.1. Study area and RDS sampling

Zhenjiang City is located on the fertile Yangtze River delta ineastern China, where the Yangtze River and the man-made Beij-ing-Hangzhou Grand Canal meet. The city is approximately260 km north of Shanghai. RDS samples were collected on theroads in the four urban areas in Zhenjiang: intense traffic area(ITA), commercial area (CA), residential area (RA), and riversidepark area (RPA) as indicated in Fig. 1. The samples in the CA werecollected near the major roads with the traffic of 2561 people perhour. In the RA that was a relatively old neighborhood, the roadswere used as a temporary car parking area with the traffic volumeof 651 peoples per hour, 121 cars per hour, and 306 motorcyclesper hour. The RPA was located near one of the main roads in thecity. The roads in the ITA had hourly traffic of 1438 vehicles, 18.6%of which were heavy duty trucks. The sampling areas representedfour different land uses in a medium size city, featuring different

population density, traffic density, energy consumption, streetcleaning methods, distributions of industries, and ground surfaceconditions. A total of 62 samples were collected at locations usinga random sampling strategy as to adequately cover the four areasas presented in Fig. 1. The sampling occurred after the roads werecleaned and was located on the road side within 1 m from the curbbecause metals such as Pb, Cd, and Zn tended to accumulate inRDS as a result of airborne redistribution by automobiles (Momaniet al., 2002). Each sample, which weighed between 60 and 500 g,was collected from an area of 1 m2 using a clean plastic dustpanand a brush. The samples were stored separately in self-sealingplastic bags and transported back to laboratory for subsequentanalyses. In the meantime, to obtain the background levels ofmetals, soil samples were also collected in the relatively pristineareas adjacent to the sampling areas.

2.2. Sample analysis

The samples were dried for 48 h at a temperature of 105 °C andthen cooled to room temperature in a dark place for furtherfractionation and chemical analysis. Metal concentrations are

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B. Bian et al. / Ecotoxicology and Environmental Safety 112 (2015) 87–95 89

typically measured for bulk samples with grain size less than2 mm because particles coarser than 2 mm are insignificant intransporting adsorbed metals in urban systems. Therefore, thesamples were first sieved through a 2 mm nylon mesh to removecoarser materials and large plant roots. The remainder of thesamples were further sieved into different size fractions. De-pending on the particle size, the RDS can be classified as differentsoil types (Folk, 1974): 1000–2000 μm (very coarse sand), 500–1000 μm (coarse sand), 250–500 μm (medium sand), 125–250 μm(fine sand), 63–125 μm (very fine sand), 54–63 μm (silt and clay)and o54 μm (clay). The sieved fractions were weighed the daythe samples were collected and then stored in desiccators prior tochemical analysis.

A small portion of the sample (approximately 0.3 g) was placedin a polypropylene vessel (speed wave MWS-3þ). A mixture ofguaranteed reagent (6 ml of 90% HNO3, 3 ml of 75% HClO4, and3 ml of 78% HF) was added to the vessel to digest the sample. Theresiduals were redissolved in a plastic bottle with 10 ml HCl (1:1)and diluted with 25 ml of deionised water. Concentrations of Cu,Pb, Zn, Cr and Ni were determined using an atomic absorptionspectrophotometer. Quality control methods involving the collec-tion of field duplicates and using control standards and duplicateswere employed. Approximately 5% of the samples were used asthe internal and external control samples. The precision wasnearly 90% with a confidence level of 95%.

2.3. Pollution assessment methods

2.3.1. Enrichment factor (EF)Enrichment factor (EF) is widely used to assess the pollution

levels of metals in dust (Lu et al., 2009). This factor is used tomeasure trace elements that are enriched or reduced relative to aspecific source. It can also be used to determine the source ofmetals e.g. originated from human activities or from natural pro-venance, and to assess the degree of anthropogenic influence(Meza-Figueroa et al., 2007). EF is calculated by

⎡⎣ ⎤⎦⎡⎣ ⎤⎦

=C C

C CEF

/

/ (1)

x ref

x ref

sample

Background

where Cx is the concentration of metals; Cref is the concentration ofreference metal. The risk criteria based on EF of degree of metalspollution may be classified into five categories: EFo2 (minimal),EF¼2–5 (moderate), EF¼5–20 (significant), EF¼20–40 (veryhigh),and EF440 (extremely high).

2.3.2. Potential ecological risk index (RI)Potential ecological risk index (RI) is another useful factor for

assessing the contamination of metals in RDS. It represents thesensitivity of biological community to the toxic substance andindicates the potential ecological risk caused by the overall con-tamination. Given the toxicity of metals and environmental re-sponses, RI can be calculated as follows (Hakanson, 1980):

∑= ERI (2)ri

=CC

C (3)fi

i

ni

= ×E T C (4)ri

ri

fi

where Eir is the monomial potential ecological risk factor; Tir is themetal toxic factor, with the standardized Tir being 5 for Pb, Cu, andNi, 2 for Cr, and 1 for Zn; Cif is the metal pollution factor; Ci is theconcentration of metals; and Cin is a reference value for metals. In

this study, Cin was taken as the background values of the pristinesoils around the city. The risk criteria based RI may be classifiedinto four categories: RIr50 (low risk), 50o RIr100 (moderate),100oRIr200 (considerable), and RI4200 (high).

2.4. Health risk assessment

The health risk assessments of children and adults in RDS wereperformed in accordance with Technical Guidelines for Risk As-sessment of Contaminated Sites (Ministry of Environmental Pro-tection the People's Republic of China, 2014). Three exposurepathways were considered for the assessment: direct ingestion ofsubstrate particles, inhalation of dust particles, and dermal ab-sorption of metals in RDS. The average daily dose (ADD)(mg kg�1 day�1) of an element via the three exposure pathwayscan be estimated by Eqs. (5), (6), and (7), respectively:

= × × ××

CADD

IngR EF EDBW AT (5)ing

= × × ×× ×

CADD

InhR EF EDPEF BW AT (6)inh

= × × × × ××

C EF EDADD

SA AF ABSBW AT (7)derm

where C is the concentration of metals in RDS (mg kg�1); IngR isthe ingestion rate (mg day�1); InhR is the inhalation rate(m3 day�1); PEF is the inhalation factor for the respirable particles(m3 kg�1); SA is the surface area of the skin exposed to pollutants(cm2), AF is the skin adherence factor in mg (cm2 h)�1; ABS is thedermal absorption factor; EF is the exposure frequency(days year�1); ED is the exposure duration (year); BW is the bodyweight (kg); and AT is the average time (day).

The body weights of children and adults, BW, was obtainedthrough the questionnaire-based exposure survey. The other ex-posure parameters, such as the IngR and SA, were obtained fromthe published data (Zimová et al., 2011; Gržtić, 2008; Lai et al.,2010). The calculated average daily doses of metals (ADD) in eachexposure pathway were subsequently divided by the corre-sponding reference dose (RfD) (mg kg�1 day�1) to yield a hazardquotient (HQ) for the assessment of non-cancer risk, whereas theADD was multiplied by the corresponding slope factor (SF)(mg kg�1 day�1) to assess the cancer risk. The InternationalAgency for Research on Cancer (IARC) has defined the risk cate-gories of metals. The metals of Pb, Zn, Cu, Mn, Cr, and Cd are an-ticipated to develop non-cancer risk, while the metals of Cr, Cd, As,Ni and Co are considered to have potential cancer risk. The SF, RfD,RfC, GIABS (gastrointestinal absorption factor used for calculatingSF) were estimated based on Technical Guidelines for Risk Assess-ment of Contaminated Sites (Ministry of Environmental Protectionthe People's Republic of China, 2014). Moreover, to assess theoverall potential non-cancer risk caused by more than one che-mical element, the HQ calculated for each metal was summed(assuming additive effects) and expressed as a Hazard Index (HI). IfHI was greater than 1, the non-cancer risk was significant; other-wise, the non-cancer risk was insignificant. If there were multiplepathways, a total exposure Hazard Index (HIt) was used to char-acterize the non-cancer risk. Hazard Index (HIt) could be used tocommunicate the non-cancer risks through different pathways,which is expressed using Eqs. (8) and (9) as follows (USEPA,2011a):

∑=HI HQ (8)n

1

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B. Bian et al. / Ecotoxicology and Environmental Safety 112 (2015) 87–9590

∑=HIt HI (9)n

1

Cancer risk (CR) is a probability than an individual develops acancer from lifetime exposure to carcinogenic hazards. Cancer risk(CR) and total cancer risk can be evaluated using Eqs. (10) and (11)

Fig. 2. Metal concentrations in RDS (a) variations of metal concentrations versus differenbars represent the standard deviation; CA¼ commercial area; RPA¼ riverside park are

= ×CR ADD SF (10)

∑=TCR CR (11)1

k

where ADD is the chronic daily intake (mg kg�1 day�1), SF is theslope factor (kg day�1 mg�1). The acceptable or tolerable risk forregulatory purposes is within the range of 10�6–10�4.

t land uses and (b) variations of metal concentrations with grain size fraction. Errora; RA¼ residential area; and ITA¼ intense traffic area.

Page 5: Contamination and risk assessment of metals in road-deposited sediments in a medium-sized city of China

Fig. 3. The enrichment factor (EF) of metals in RDS (a) in different areas (b) in different size particles, and (c) the generalized EF of metals. Error bars represent the standarddeviation; ITA¼ intense traffic area; CA¼ commercial area; RA¼ residential area; and RPA¼ riverside park area.

B. Bian et al. / Ecotoxicology and Environmental Safety 112 (2015) 87–95 91

If there were multiple carcinogenic contaminants, cancer risk foreach carcinogen and exposure pathway was added. Cancer risk ran-ging between 1.0�10�6 and 1.0�10�4 (i.e. one occurrence in onemillion people and one in 10,000 people) is considered acceptable tohuman's health (Lim et al., 2008). In this study, both non-cancer risk(using HIt) and cancer risk methods were used to assess health risksdue to the exposure to RDS in different areas of Zhenjiang.

2.5. Statistical analysis

The statistical analysis and multiple regression analysis wereperformed using the commercial software, SPSS (16.0), to evaluatethe uncertainties associated with the calculation process andparameters selection.

Page 6: Contamination and risk assessment of metals in road-deposited sediments in a medium-sized city of China

a

b

Fig. 4. The potential ecological index (RI) of metal in RSD (a) in different areas(b) in different particle sizes. Error bars represent the standard deviation. ITA¼intense traffic area; CA¼ commercial area; RA¼ residential area; and RPA¼ riv-erside park area.

B. Bian et al. / Ecotoxicology and Environmental Safety 112 (2015) 87–9592

3. Results

3.1. Effects of particle size and different land uses on metalconcentrations in RDS

Particle size distribution of RDS in the four areas for differentland uses was analyzed using the procedures outlined previously.The results were expressed as mean mass percentages for differentsize factions and are summarized in the paper (Zhu et al., 2008).The mean RDS size decreased in the four areas from RPA, RA, ITA,to CA. The majority of RDS was composed of particles smaller than250 μm which accounted for approximately 60–85% by weight.Mean concentrations of five metals (i.e. Zn, Pb, Cu, Cr and Ni) inRDS from the four areas were measured and are depicted in Fig. 2a.It can be seen that among all metals measured, Zn appeared tohave a higher maximum mean concentration (i.e. 687 mg kg�1)than the other metals (i.e. Pb, Cu, Cr and N) that had the maximummean concentrations of 589, 158, 129 and 125 mg kg�1 respec-tively. For the different land uses, RDS in ITA and CA contained thehighest and lowest mean metal concentrations respectively whileRDS in RPA and RA contained moderate amount of metals. More-over, ITA had two metals with high concentrations (i.e. Zn and Pb)while the other areas contained only one metal (i.e. Zn) with highconcentrations.

Fig. 2b shows the distribution of individual metal in differentsize particles in different areas. The distribution of metals in dif-ferent size particles was similar in the four areas. In general, thecoarser particles in RDS had lower metal concentrations andgreater variability. The highest concentrations were found in theparticles of less than 63 μm. In addition, coarse particles in RDStended to have a great heterogeneity; for example, metal con-centration in particles (o63 μm) was almost twice that in coarseparticles, which could explain their high metal concentrationvariability relative to their low metal concentration. The aboveobservation is believed to be associated with the higher specificsurface area in finer particles.

3.2. Assessment of metal contamination in RDS

The contamination and ecological risks of metals in RDS wereassessed using enrichment factor (EF) and potential ecological riskindex (RI). The EF is an index to contamination risk of individualmetals and was calculated for each RDS sample and comparedwith the background values of the corresponding metal in localsoil (China National Environmental Monitoring Center, 1990). TheAl was chosen as the reference metal (Turner and Simmonds,2006). As seen in Fig. 3a, the mean EF of Zn, Pb, Cu and Ni in RDS inthe four areas was greater than 2 but that of Cr was less than 2.Overall, the EF values for all metals decreased in the four areas inthe order of ITA, RPA, RA, and CA. RDS particle sizes also played animportant role in assessing contamination levels. Fig. 3b indicatesthe effects of particle size on the enrichment of metals (Zn, Pb, Cu,Cr, and Ni). The EF of Cr was less than 2 for all particle sizesmeasured (i.e. o2000 μm), indicating insignificant enrichment.The particles that contained moderate enrichment levels of Cu andNi (2oEFr5) were smaller than 1000 μm in CA, RPA and RA. Theparticles that had significant enrichment levels of Zn and Pb(5oEFr20) were smaller than 2000 μm for all four areas. Fig. 3balso indicates that the coarser particles (450–2000 μm)had agreater EF range and smaller enrichment than the smaller particles(o63 μm). Fig. 3c indicates the generalized EF values for eachmetal based on the results in the four areas. The calculated EF forthe metals followed the descendent order of Pb, Zn, Cu, Ni, and Cr.According to the contamination criteria, Zn and Pb were a sig-nificant pollutant in RDS, Cu and Ni were a moderate pollutant,whereas Cr was an insignificant pollutant.

As compared with EF, RI is an integrated index that considersnot only concentration of metals, but also the toxicity of metals.The calculated RI of RDS metals contamination in different areas ispresented in Fig. 4a. In general, ITA had the largest RI, followed byRA, RPA, and CA. According to risk criteria, RDS in ITA had con-siderable risk and RDS in the other three areas had moderate risk.Among the five metals assessed (Zn, Pb, Cu, Cr, and Ni), Pb wasfound to pose the major risk to the urban ecological system inZhenjiang. Fig. 4b indicates RI increased inversely with particlesize. Additionally, the moderate risk occurred in the particle sizessmaller than 2000 μm and the considerable risk appeared in theparticle sizes smaller than 450 μm. These results indicated thatmetals in RDS had potentially considerable to moderate ecologicalrisk in Zhenjiang. Further work as presented subsequently is todetermine human health risk of metals in different size RDS par-ticles, particularly in fine particles.

3.3. Health risk assessment

As discussed previously, the total exposure Hazard Index (HIt)was used for the assessment of non-cancer risk. The measured HItfor children and adults in the four areas is presented in Fig. 5a.From the figure, the mean HIt for children (i.e. HIt¼3.541) wasmore than six times that for adults (HIt¼0.61o1), indicating thatchildren suffered a much higher risk than adults by exposing toRDS. Fig. 5a also indicates that the mean HIt for children washighest in ITA, followed by in RA, CA, and RPA. Per criteria, themean HIt for children all exceeded the safe level in the four areas.The mean HIt for adults in the four areas decreased in the order of

Page 7: Contamination and risk assessment of metals in road-deposited sediments in a medium-sized city of China

a

b

Fig. 5. The total hazard index (HIt) for child and adult after exposure to metalscontamination in RDS (a) in areas for different land uses and (b) in different sizeparticles, ITA¼ intense traffic area; CA¼ commercial area; RA¼ residential area;and RPA¼ riverside park area.

a

b

Fig. 6. Cancer risk (CR) for child exposed to metal contamination in RDS (a) risk ofCr (b) risk of Ni. ITA¼ intense traffic area; CA¼ commercial area; RA¼ residentialarea; and RPA¼ riverside park area.

B. Bian et al. / Ecotoxicology and Environmental Safety 112 (2015) 87–95 93

ITA, RA, CA, and RPA and only RDS in ITA had a potential non-cancer risk for adults. This result indicated that sweepers and taxidrivers might be at a health risk due to the long-term exposure toRDS on the intense traffic roads. Fig. 5b shows the mean HIt forchildren and adults as a function of particle sizes. The mean HIt forchildren was measured to be greater than 1 but was less than 1 foradults. The particles (with sizes smaller than 63 μm) can easily bere-suspended into the atmosphere by wind, affecting the atmo-spheric environmental quality. The particles(o63 μm) may re-main airborne for a long period (De Miguel et al., 1997), which caneasily enter the respiratory system by inhalation, threatening hu-man's health.

Another important factor to assess health risk is cancer risk.The cancer risk to children due to metal contamination in RDS wasdetermined herein and the results are presented in Fig. 6. From thefigure, cancer risk of Cr was 1.0�10�4 and thus exceeded thehealth limit; in contrast, cancer risk of Ni was less than 1.0�10�4

and thus satisfied the requirement of health. The mean cancer riskof Cr and Ni for children in the four areas decreased in the order ofITA, RPA, RA, and CA. The above results showed a good agreementwith those in a previous study in these areas (Cao et al., 2014).

4. Discussion

Based on our test results, particle size had a significant effect onthe deposit of metals in RDS. In general, the metal concentrations

decreased inversely with particle size. The highest concentrationsof metals were found in particles smaller than 63 μm. Guna-wardana et al. (2014) indicated that approximate 60% of the metalsoccurred in particles smaller than 150 μm with 33% in particlessmaller than 75 μm. Sutherland (2003) reported that the particlesize less than 63 μmwas significant in accommodating metals and38% of Pb occurred in this range of particle sizes. Zhao et al. (2010)found that particle sizes between 62 and 105 μm were the mostimportant for the deposit of metals. In general, our results agreedwith the findings of Sutherland (2003) that the particles with thesize less than 63 μm played a crucial role in accumulating metalsin RDS.

The four areas for different land uses appeared to have differentparticle size distributions, especially the fine contents. Variationsof particle size distribution of RDS in different areas may be relatedto the inability of rotary brush street sweepers in picking up finedust particles (e.g. clay and silt) (Kidwell-ross, 2003). In general,ITA and RPA had a relative high metal contents as compared withRA and CA. The riverside park area (RPA) and residential area (RA)were cleaned more frequently than the intense traffic area (ITA)and hence the coarse particles (e.g. sands) were more likely to beremoved from these two areas. Moreover, the RPA was moresubjected to erosion than the CA and ITA. The eroded soils wereeasily trapped by the ground in the RPA consisting of pebbles,which resulted in a significant amount of particles(o63 μm) inRPA. As the particle size decreased below 150 μm, content of clay

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minerals increased. The clay minerals tended to have a high spe-cific surface area and effective cation exchange capacity, andtherefore a high metal adsorption. Moreover, RPA was located inthe old urban area, adjacent to busy traffic roads and RDS in theRPA had a relative high organic carbon content. Metal concentra-tion has been found to correlate with the clay and organic carboncontents (Sansalone and Buchberger, 1997). As such, like ITA, theRPA accumulated RDS with relatively high concentrations of me-tals. The RDS in ITA was measured to have higher EF than the otherareas test results, indicating ITA was most susceptible to metalpollution. RDS consisted of the minerals derived from naturalsources such as quartz, albite, microcline, chlorite, and muscovite,of which a significant amount were related to traffic related ac-tivities. Tyre wear particles were a RDS of considerable concernbecause they were typically amorphous and had complex shapesand morphology as well as high porosity (Gunawardana et al.,2012). The significant amount of traffic related particles contributeto pollutant retention as a result of the increased capacity of ad-sorption and cation exchange (Eisma, 1981). Another type of RDSwith potential contamination concerns was traffic-relatednon-exhaust emissions which had a potential of the enrichment of Cr,Cu, Ni, Pb and Zn (Apeagyei et al., 2011; Gunawardana et al., 2014).The non-exhaust emissions could cause significant heavy metalcontamination with the rapid increase of traffic volume and con-gestion in urban areas (Wei and Yang, 2010; Yuen et al., 2012). Assuch, metal pollution resulting from non-exhaust traffic emissionsshould receive attentions during contamination control, especiallyat crossroads.

The use of different methods for assessment of metal con-tamination and risk helps to minimize uncertainties induced byusing a single method (Zhao and Li, 2013). The enrichment factor(EF) measured only the total concentration of individual metalsand assessed the degree of anthropogenic influence and back-ground enrichment of metals. The potential ecological risk index(RI) is an integrated factor that indicates not only concentration ofmetals, but also toxicity of metals. Based on the RI results, ITA andRA had higher metal risk than the other two areas. Similar to theresults of EF, RI measurement also indicated that RDS in ITA had ahigher risk of metal contamination than the other areas. As such,the methods used to assess the contamination risk (i.e. EF and RI)generally agree with each other. Since metals in RDS typically havecharacteristics of toxicity and non-degradability, posing threats tothe environmental and public health, the human health risk wasalso evaluated. The health risk assessment focused on non-cancerrisk for children and adults and cancer risk for children. Based onthe test results, the non-cancer risk for children was high in thefour areas but was relatively low for adults in all four areas exceptin ITA. The cancer risk of Cr to children was also high. The non-cancer risk was highest in ITA but lowest in RPA. The cancer risk ofCr and Ni in RDS was highest in ITA but lowest in CA. In general,the health risk assessment also revealed RDS in ITA had a higherhealth risk than in the other areas. As such, the different methodsemployed herein generally led to consistent results for assessingcontamination and health risk in areas for different land uses. Theeffects of particle size played a key role in containment of metalsin RDS and thus contamination risks to environments (e.g. air,water, etc.,) and human health. RDS with fine grain sizes tended toaccumulate high metal contents. Particles smaller than 63μmweremost significant as they carried the largest portion of metals inRDS and posed the highest contamination risk. This type of par-ticles was easy for transportation and could easily enter the re-spiratory system by inhalation, adversely affecting human health.As discussed previously, the particles (o63 μm) were typically ofhigh specific surface area and high capacity of cation exchange andadsorption and therefore had a high capacity of retaining metals.

These results implied that smaller particles and the ITA warrantedmore attentions during contamination control and management.

5. Conclusions

(1)

Among all metals measured ( Zn, Ni, Cr, Pb, and Cu), Zn ap-peared to have the highest mean concentration of687 mg kg�1. The RDS in ITA was found to have the highestmean concentrations of metals. The metal concentration gen-erally increased inversely with particle size with the highestmetal concentrations occurred in particles less than 63 μm.

(2)

The environmental contamination risk of metals in RDS wasassessed using enrichment factor (EF) and potential ecologicalrisk index (RI). Based on the measured mean EF, Zn and Pbwere of significant enrichment in RDS whereas Cu and Ni wereof moderate enrichment in RDS. The measured EF and RI in-dicated that the ITA was more susceptible to metal con-tamination than the other areas.

(3)

The non-cancer risk for children was high in the four areas butwas relatively low for adults in the four areas except in ITA.The cancer risk of Cr was significant for children. In general thenon-cancer risk was highest in ITA but lowest in RPA while thecancer risk was highest in ITA and lowest in CA. RDS withsmall grain size tended to develop high health risk, especiallyfor particles smaller than 63 μm.

(4)

The findings from this study implied that particles (o63 μm)and intense traffic activities played a critical role in con-tamination of metals in RDS and potential health risk. Thecontamination control and management need to address theconcerns associated with these two factors.

Acknowledgment

The authors are grateful for the financial supports for this studyprovided by the Natural Science Fund Project in Jiangsu Province(BK2012883) and the National Water Pollution Control and Man-agement Technology Major Projects (Grant no. 2012ZX07506-001).

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