2238 © IWA Publishing 2011 Water Science & Technology | 63.10 | 2011

Seasonal influence on urban dust PAH profile and toxicity

in Sydney, Australia

Rupak Aryal, Bivek Baral, Saravanamuthu Vigneswaran, Ravi Naidu

and Paripurnanda Loganathan

ABSTRACT

Road dust is one of the major threats to the urban environment due to wash-off of dust to the

surrounding catchments during wet weather period. The dust contains wide range of toxic

contaminants such as heavy metals, polycyclic aromatic hydrocarbons (PAHs) and endocrine

disrupting chemicals. Among the toxic contaminants, PAHs are of environmental concern due to

their potential carcinogenic and mutagenic effect besides endocrine disruptive behaviour. Eighteen

road dust samples from Sydney were collected in different time periods for a year and analysed for

16 US EPA PAHs. Total PAHs content range in the dust was 9–105 μg/g. Total and individual PAH

contents were highest in the finest size fraction (<75 μm) and in winter compared to the other

seasons. The PAH profiles in the different particle sizes were similar but different between the four

seasons. The concentrations of higher molecular weight PAHs (4- and 5-rings) were much greater

than the concentrations of lower molecular weight PAHs (2- and 3-rings). Toxicity equivalency factor

application showed that the longer the dry weather period the higher the total PAHs content and

toxicity in the dust.

doi: 10.2166/wst.2011.504

Rupak AryalSaravanamuthu Vigneswaran (corresponding

author)Paripurnanda LoganathanFaculty of Engineering and Information

Technology,University of Technology,Sydney, NSW, 2007,AustraliaE-mail: s.vigneswaran@uts.edu.au

Bivek BaralDepartment of Mechanical Engineering,The University of Auckland,Auckland,New Zealand

Ravi NaiduCRCCARE, Adelaide, SA,Australia

Key words | polycyclic aromatic hydrocarbons, toxicity, urban dust

INTRODUCTION

Non-point pollution is considered as one of the major contri-buting sources of polycyclic aromatic hydrocarbons (PAH)to the urban environment. Among the different non-point

sources, road dust is one of the major sources. PAHs areusually generated from incomplete combustion of organicssuch as petroleum and coal, tire abrasion and road asphaltleaching. In roads, the major source of PAHs is the vehicular

exhaust (Pengchai et al. ) although atmospheric depo-sition also accounts for some PAHs input. With vehicularmovement, the deposited dust is re-suspended and re-mobi-

lized. During this process, the dust is exposed tohydrophobic PAHs and get adsorbed on it. Because thefiner particles have high surface area, high content of

organic matter and able to easily resuspend, PAHs are accu-mulated more in finer particles (Hoffman et al. ; Krein &Schorer ). During wet weather period, the PAHsenriched dust is dislodged from the road surface and carried

along with stormwater which may enter the aquatic environ-ment. PAHs being toxic it deteriorates water quality (Fosteret al. ).

The study of PAHs in different particle sizes of road dustexpands our knowledge of its distribution in particle sizes aswell as their ease of transport and toxicity to the receiving

water. The magnitude of the toxicity of total PAHs in dustdepends on the nature of the individual PAH and its concen-tration (Swartz et al. ). The total and individual PAHcontents depend on several factors such as traffic density,

weather, dust sizes and nature of traffic etc. According toLee et al. (), 3- and 4-ring PAHs formation is largely con-tributed by heavy duty vehicles. Similarly, Pengchai et al.() reported that low molecular weight PAHs were ident-ified in diesel vehicle exhaust. Krein & Schorer ()studied PAHs pollution in road runoff in Germany and

reported that there was a good relationship between molecu-lar size of PAH and dust grain size. They found that small3-ring molecules were enriched in the fine sand fraction.

Sydney is one of the largest cities in Australia with a

population of 4 million. Large population and high urbanactivities have resulted in dense traffic in the city. However,data concerning PAHs species and their concentration in

2239 R. Aryal et al. | Urban dust PAH profile and toxicity in Sydney Water Science & Technology | 63.10 | 2011

the road dust of Sydney is not available. This study aimed to

investigate the PAHs in road dust in different particle sizesin different seasons in Sydney. This study also investigatethe relationship between dry weather period and total

PAHs as well as its toxicity using toxicity equivalencyfactor (TEF).

EXPERIMENTAL METHODS

Study area

A long term road dust sampling was carried out by collectingroad dust samples from Broadway, Sydney every 4 weeks

using brooms and pan. The collected dust sample weresieved into three different size fractions (<75, 75–150 and150–300 μm) using stainless steel mesh sieve. The fractio-nated dust samples were dried in an oven at 105 WC to

remove water content in the sample. The dried sampleswere placed in desiccator for 24 h followed by storage inrefrigerator till further analysis. Traffic density in the road

was more than 50,000 per day to and from Sydney CentralBusiness District according to Road Traffic Authority(RTA ).

Chemical analysis

The samples were treated with a solvent mixture of dichloro-methane and methanol (5:1 by volume) to extract 16 USEPAPAH. Three internal standards (phenanthrene-d10,chrysene-d12, and perylene-d12) were also analysed in par-

allel with the test samples to correct the recovery rate ofthe sample analysis. The mixtures were then subjected tosonification for 25 min (50% cycles, 160 W) for extraction

of PAHs. The extracts were filtered through a glass fiberfilter (GF-75, Advantec). The filtrates were concentrated byevaporation to dryness at a temperature of less than 40 WC.

The dried extracts were finally dissolved in a dichloro-methane solution and PAHs in the solution were analyzedusing gas chromatography-mass spectrometry (GC/MS

Hewlett Packard HP6890 GC coupled with HP 5973 massselective detector) with a capillary column (30 m × 0.25 μminternal diameter) HP-5. Trace Analysis (5% HP ME Silox-ane) were conducted by injecting 1 μL volume. GC/MS

was operated in selected ion monitoring mode usinghelium as a career gas. The oven temperature was kept con-stant at 40 WC for 3 min and then increased to 250 WC at a rate

of 20 WC/min. The temperature was held constant for 10 minand finally increased to 300 WC, at a rate of 22 WC/min, and

held steady for 4 min. The following 16 PAHs were quanti-

fied: naphthalene, acenaptylene, acenapthene, fluorene,anthracene, phenanthrene, fluoranthene, pyrene, benzo(a)-anthracene, chrysene, benzo(k)fluoranthene, benzo(b)fluor-

anthene, benzo(a)pyrene, indeno-(1,2,3-cd)pyrene, dibenz(a,h)- anthracene, and benzo(ghi)perylene.

Toxicity evaluation method

PAHs have been considered to be carcinogenic or muta-genic. The toxicity of the total PAHs identified in the roaddust samples were evaluated using a relative toxicity value

of individual PAH proposed by Nisbet & LaGoy ().The toxicities of the 16 USEPA PAH were assigned valuesrelative to BaP which was assigned a value of 1 in the

TEF system. The toxic equivalent concentration (TEQ) ofeach road dust sample was calculated by summing the pro-ducts of each individual PAH concentration and it’s TEF,

as follows:

TEQ ¼X

(CixTEFi)

where TEQ is the toxic equivalent concentration, Ci is the

concentration of PAHi, and TEFi is the toxicity equivalencyfactor of PAHi.

RESULTS AND DISCUSSION

Particle size distribution

Road dust contains wide range of particle sizes. Sartor et al.() measured the particle size distribution in dry deposited

road dust and reported that 15% of particulate matter wereless than 104 μm, 28% were between 104 and 246 μm, 25%between 246 and 840 μm, 8% between 846 and 2000 μm,

and 24% larger than 2,000 μm whereas Shaheen ()found that about 10% of the particles were less than 75 μm,32% between 75 and 250 μm, 24% between 250 and

420 μm, 19% between 420 and 850 μm and 15% between850 and 3,350 μm.

Ball et al. () measured the particle size distributionsin road dust and found that 10–30% of the particles were in

the finer fraction (<200 μm). The mean diameter of particu-lates was approximately 70 μm while the 10 and 90percentile diameters were approximately 16 and 189 μm,

respectively. On the average, 34% of the fine sedimentscollected were less than 43 μm.

Table 1 | Individual and total PAHs content (μg/g) in road dust

PAH Max Min Std dev

Na 0.33 0.00 0.11

Acy 0.35 0.03 0.09

Ace 2.72 0.11 0.89

Fl 0.94 0.01 0.36

Ph 2.43 0.19 0.67

An 1.01 0.08 0.26

Flu 19.18 1.63 4.89

Py 16.64 1.17 4.37

B(a)An 11.73 1.69 2.93

Ch 11.96 0.96 3.02

B(k)Fl 16.16 1.15 3.93

B(b)Fl 8.71 0.42 2.69

B(a)Py 5.65 0.54 1.54

IPy 7.65 0.52 2.08

dB(ah)An 1.68 0.02 0.46

B(ghi)Pe 3.65 0.17 1.10

Total 105.41 8.72 26.45

2240 R. Aryal et al. | Urban dust PAH profile and toxicity in Sydney Water Science & Technology | 63.10 | 2011

Figure 1 illustrates the particle size distribution in road

dust in four seasons in three different size fractions in thecurrent study. The size fractions of the particles in the dustwere estimated from a size smaller than 300 μm. Among

the three fractions, fine particles (<75 μm) accounted for 7–13%, 75–150 μm accounted for 26–33% and >150–300 μmfraction accounted for 54–65%. These results are similar tothose of Ball et al. () and Shaheen ().

PAHs in road dust

Many studies have shown an influence of particle size onPAH accumulation in road dust. Aryal () reportedhigher PAHs content in smaller particles (<63 μm) than in

coarser particles. The total PAHs content (12 PAHs) in par-ticles smaller than 45 μm was 3.3–15 μg/g compared to thecontent in soil of 0.84–0.85 μg/g. Total PAHs in particles

larger than 106 μm was low and in the range of 0.14–0.37 μg/g. Pathirana et al. () studied the distribution ofPAHs in an urban roadway system in Australia and reportedthat PAHs were widely distributed in leaf litter exhibiting

the highest concentration of 1254 ng/g total wet weightwhich was several fold higher than the concentration insoil (471 ng/g). They found that PAH content in the soil,

leaf litter and vegetation declined exponentially with dis-tance from the roadway, soil depth and vegetation heightrespectively.

Table 1 shows the maximum and minimum concen-trations of individual and total PAHs in the current study.The total PAHs concentration ranged from 8.7 to 105.4 μg/g

with a standard deviation of 26.4 μg/g.Figure 2 shows the total PAHs in the three size fractions

in the four seasons. Among the four seasons, the highest

Figure 1 | Road dust particle size distribution in (a) autumn, (b) winter, (c) spring, (d) summer

PAHs content was observed in winter followed by autumn,summer and spring. The PAHs contents in size fractions<75, 75–150 and 150–300 μm were 9.4–118, 10.4–88.3 and64.2–9.6 μg/g, respectively. The major reasons for having

high concentration of PAHs in finer fraction are theirhigher surface area, enriched organic contents and theirsuspension and remobilization in the atmosphere.

Tasdemir & Esen () found that the concentrationand deposition levels of individual and total PAHs areaffected by the composition and strength of the emissions,

.

Figure 2 | Total PAHs in (a) autumn, (b) winter, (c) spring, (d) summer.

2241 R. Aryal et al. | Urban dust PAH profile and toxicity in Sydney Water Science & Technology | 63.10 | 2011

the turbulence and the removal process type. The PAHswith 2- to 4-membered rings are mainly in gaseous phaseand some of them are bound to finer particles (Harrison

et al. ; Cousins & Jones ; Wang et al. ) whereasPAH with 5- and 6-rings are mainly present in the particularphase due to their low volatility (Tremolada et al. ).

Particles with increased atmospheric exposure havehigher PAHs content with low molecular weights (Leeet al. ; Vardar & Noll ). Vehicular type and fueltype also affects the individual and total PAHs. According

to Lee et al. (), abundance of PAHs with high molecularweights increases with increasing light duty vehicles volume.Similarly, Pengchai et al. () reported that the enrich-

ment of low molecular weight PAH contents with respectto diesel vehicle exhaust and enrichment of high molecularweight PAHs mainly emanating from gasoline vehicle

exhaust. An interesting relationship between PAHs and par-ticle sizes were observed by Krein & Schorer () in astudy of road runoff and its contribution to river sediment

in Hunsruck Mountains, Germany. Their study of PAHs indifferent particle sizes showed a relationship betweenPAHs molecular size and dust grain size. In street runoff,they found small 3-ring molecules enriched in the fine

sand fraction.Figure 3 shows the profiles of individual PAHs in differ-

ent particle sizes in the four seasons. PAHs profiles in

different particle sizes were relatively similar whereas thefour seasons showed differences in PAHs profile. Many ofthe individual PAHs contents were higher in the finer size

fraction compared to the coarser fraction. It can be assumed

that when the particles are deposited and remobilized sev-eral times the remobilization extent is higher for finerparticles.

Similar result was obtained in Winterthur road, Switzer-land (Aryal et al. ). Different PAHs profiles in differentseasons led these authors to assume that PAHs emission and

degradation were governed by local weather conditions.Among the PAHs, higher molecular weights PAHs wererelatively abundant during winter and autumn. Low temp-erature and low wind speed may have favoured the

enrichment of PAHs in winter and autumn.Figure 4 shows the distribution of PAHs in terms of ring

sizes. Among the 16 PAHs the lower molecular weights

PAHs (2- and 3-rings) had relatively low contribution tothe total PAHs. The 4-ring PAHs followed by 5-ring PAHshad higher contribution.

Toxicity of PAHs in road dust

Toxicity equivalency factor (TEF) values proposed by Nisbet &LaGoy () were used to calculate toxic equivalent con-

centration (TEQs) of PAHs of the road dusts. It rangedfrom 1.6 to 25.3 μg/g with standard deviation 7.0 μg/g(Figure 5). The accumulation of road dust during winter con-tained relatively high concentrations of high molecular

weight PAHs, which had high TEF values. Another impor-tant factor responsible for the increase in TEQ was the dryweather period. Increase of dry weather period increased

accumulation of PAHs in the particles. Figure 5 shows therelationship of total PAHs with dry weather period and

Figure 4 | PAHs distribution according to ring sizes in four seasons. (a) <75 μm, (b) 75–

150 μm, (c) 150–300 μm.

Figure 5 | Relationship between TEQ and total PAH content and between dry weather

period and total PAH content.

Figure 3 | PAH profile in size fractions in (a) autumn, (b) winter, (c) spring, (d) summer.

2242 R. Aryal et al. | Urban dust PAH profile and toxicity in Sydney Water Science & Technology | 63.10 | 2011

TEQ. Linear regression showed good correlations for total

PAH with dry weather period (R2¼ 0.8459) and TEQ(R2¼ 0.6579). Increase of TEQ values with dry weather

period was mainly due to accumulation of higher molecular

weight PAHs. Dong & Lee () also observed similar TEQrelationship in road dust in Ulsan, South Korea.

CONCLUSIONS

Road dust samples collected from Sydney, Australia for a

year showed that the dust size ranges were 7–13% in<75 μm, 26–33% in 75–150 μm and 54–65% in 150–300 μm. The total PAHs was in the range of 9–105 μg/gwith standard deviation of 26.4 μg/g. The finer fraction con-

tained higher PAH content. Individual profiles of PAHs inthe three size fractions were almost similar indicating homo-geneous distribution of PAHs in all fractions. Out of the four

seasons, winter had the highest PAHs content. Among thePAHs, 4- and 5-rings contributed 83–90% of the total

2243 R. Aryal et al. | Urban dust PAH profile and toxicity in Sydney Water Science & Technology | 63.10 | 2011

PAHs. Total PAHs and dry weather period as well as total

PAHs and toxicity showed good linear relationships witheach other (R2¼ 0.85 and 0.66). This indicated dry weatherperiod can help to evaluate PAHs load as well as PAHs can

evaluate the toxicity.

ACKNOWLEDGEMENT

This study is supported by CRC CARE Australia under theproject On-site remediation of micropollutants from storm-water for reuse (Project number 2-5-07-07/08).

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