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Science of the Total Environm

Sources of heavy metals and polycyclic aromatic hydrocarbons

in urban stormwater runoff

Jeffrey N. Brown, Barrie M. Peake*

Chemistry Department, University of Otago, P.O. Box 56, Dunedin, New Zealand

Received 8 September 2004; accepted 5 May 2005

Available online 12 July 2005

Abstract

Polycyclic aromatic hydrocarbons (PAHs) and heavy metals were measured in road debris collecting in urban areas and in

the suspended sediment (SS) component of runoff from two stormwater catchments in Dunedin, New Zealand. Levels in the

road debris ranged from 119–527 Ag/g for lead, 50–464 Ag/g for copper, 241–1 325 Ag/g for zinc and 1.20–11.6 Ag/g for

A16PAH. The SS from the largely rural catchment (20% urban) had similar concentrations to the road debris, indicating that this

urban material was the main source of the contaminants measured in the stormwater. Similar PAH fingerprint profiles and

isomer ratios indicative of dominant pyrogenic (combustion) sources were also found in these two groups of materials. The SS

from the 100% urban catchment contained 2- to 6-fold higher concentrations of metals and 10-fold greater levels of A16PAH.The higher levels of lead and copper were probably a result of industrial land uses in this catchment, while the additional zinc

was linked to an abundance of zinc-galvanised roofing iron in the catchment’s residential suburbs. The PAH profiles and isomer

ratios were different for this urban catchment and suggested that a disused gasworks was contributing PAHs to the stormwater

runoff.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Stormwater; PAHs; Metals; Fingerprint; Street dust; Gasworks

1. Introduction

Motor vehicle emissions, drips of crankcase oil,

vehicle tyre wear and asphalt road surfaces, are all

diffuse sources of chemical contaminants in urban

0048-9697/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.scitotenv.2005.05.016

* Corresponding author. Tel.: +64 3 479 7927; fax: +64 3 479

7906.

E-mail addresses: jeffbrownnz@hotmail.com (J.N. Brown),

bpeake@alkali.otago.ac.nz (B.M. Peake).

environments. During rainfall, these contaminants

are washed from roofs, roads and other surfaces into

the stormwater system and then discharged into sur-

face waterways and estuarine environments. Heavy

metals (copper (Cu), lead (Pb) and zinc (Zn)) and

polycyclic aromatic hydrocarbons (PAHs) are of par-

ticular concern in such runoff due to their prevalence,

toxicity to aquatic organisms and persistence in the

environment (Hoffman et al., 1984; Borchardt and

Sperling, 1997; Walker et al., 1999). Other diffuse

sources of PAHs and heavy metals include domestic

ent 359 (2006) 145–155

J.N. Brown, B.M. Peake / Science of the Total Environment 359 (2006) 145–155146

fire emissions, the spillage or deliberate dumping of

waste oil and the corrosion of roofing materials. Spe-

cific point sources, such as electroplating workshops,

gasworks and commercial incinerators may also exist

in urban catchments. Contaminant bfingerprintingQ,involving the use of concentration data or ratios of

specific contaminants can allow the potential sources

of these contaminants to be identified (Walker et al.,

1999; Gonzalez et al., 2000; McCready et al., 2000;

Soclo et al., 2000).

Previous work on urban stormwater runoff from

two catchments in Dunedin, New Zealand (Brown,

2002; Brown et al., 2003), indicated that significantly

Fig. 1. Location of catchments sampled within Dunedin City, New Ze

numbered sampling sites are: (1) Portobello Road; (2) Water of Leith; (3)

higher concentrations of A16PAH (sum of the 16

USEPA priority listed PAHs) and heavy metals were

present in the runoff from an urban catchment (Por-

tobello Road, see Fig. 1) as compared to a local river

(Water of Leith) that has 83% of its catchment in rural

land uses but receives stormwater discharges from

several small urban sub-catchments. Surprisingly, cal-

culations of the annual contaminant loading (kg/ha/yr)

from each catchment into the Otago Harbour, Dune-

din, New Zealand, showed that the Portobello Road

catchment exported less suspended sediment (SS) but

considerably more heavy metals and PAHs (up to 20

times more per hectare), even when the data for the

aland and discharged as stormwater into the Otago Harbour. The

St. David Street sub-catchment; (4) Upper Leith.

J.N. Brown, B.M. Peake / Science of the Total Environment 359 (2006) 145–155 147

Water of Leith catchment were normalised to the

urban area of its small urban sub-catchments.

The present study investigated the sources of the

PAHs and heavy metals in the two catchments using

bfingerprintingQ techniques and the likely cause(s) of

the higher pollutant loadings from the Portobello Road

catchment. The contaminant content of the stormwater

SS was determined and then compared to that obtained

from the debris collecting on the city roads and a

number of other possible source materials.

2. Materials and method

2.1. Reagents

Dichloromethane (LR grade) was purified by frac-

tional distillation. Anhydrous sodium sulphate, glass

microfibre filters, Soxhlet extraction thimbles, filtra-

tion glassware, 100 mL screw top glass bottles and

aluminium foil were purified by heating to 450 8C for

N16 h. Other glassware was cleaned by successive

solvent rinsing, soaking in an alkaline detergent bath,

rinsing with distilled water and then air-drying.

Quartz-distilled nitric acid (Q-HNO3) and hydrochlo-

ric acid (Q-HCl) were used for metal analysis. All

plastic and glassware used for metal sampling and

analysis were cleaned via soaking in 25% aqua regia

for 1 week, rinsing three times with de-ionised (Milli-

Q) water, drying in a Class-100 clean-room and then

sealing in double plastic bags.

2.2. Sampling

Stormwater samples were primarily taken from the

underground Portobello Road stormwater drain over 7

storm events from 1998 to 2000 (30 November 1998;

12 April 1999; 4–5 May 1999; 13 September 1999; 3–

5 December 1999; 7 December 2000; 23–29 December

2000). This drain comprises one of the larger storm-

water inputs into the Otago Harbour (Fig. 1) (Brown,

2002). The catchment area (486 ha) is largely flat and

is 100% urban, comprising of mixed residential (55%),

commercial (30%) and light industrial land uses

(15%). Samples were also taken during 1 storm event

(28 March 2001) towards the outlet of the Water of

Leith, a river that drains a large catchment (4 555 ha)

that has a land use composition of approx. 83% rural

and 17% urban (largely residential). Within the Leith

catchment, single samples were also taken towards the

river headwaters at the upper reaches of the urban area

(Upper Leith) and from a stormwater drain (St. David

Street sub-catchment) that discharges into the river

500 m upstream from the principal sampling site.

Sampling was conducted using a combination of

automatic and manual sampling techniques. Most

stormflow samples were collected in 350 mL glass

bottles using an ISCO 6700 autosampler, which was

activated by a Sigma 950 flowmeter when flows

exceeded a pre-determined level. Some PAH storm-

flow samples at the Portobello Road site, and all

samples at the Leith sites, were collected by inserting

a pre-cleaned stainless steel bucket into the flow and

filling clean 2.5 L glass bottles. Samples for metal

analysis from the Leith sites were collected in acid-

washed 1 L polypropylene bottles that screwed into a

plastic sampler which was lowered into the flow.

Baseflow samples at the Portobello Road and Leith

sites were taken manually at times immediately pre-

ceding a sampled storm event.

Samples of debris collecting on city roads were

collected over the same time period as the storm-

water sampling. Samples of street dust were collect-

ed from three separate areas in Dunedin City by

street sweeping trucks (Brown, 2002). The collected

material was tipped out at the truck depot and sam-

ples taken by collecting 15 sub-samples from the

debris pile and then combining them in a clean

container. Suction tankers collected the liquid and

sediments in sumps underlying the roadside storm-

water grates. Composite samples, comprised of sedi-

ments from 20–30 sumps spread evenly throughout

each area, were obtained from six areas covering a

range of land uses within the city (Brown, 2002).

The liquid effluent was sampled prior to being dis-

posed of at the depot and the sediments tipped into a

pile and sampled as above. At the laboratory, the

street dust and sump sediment samples were stirred

and sub-sampled before metal and PAH analysis.

These samples contained coarse winter road grit

(basalt) that was removed using an acid-washed 2

mm plastic sieve. Samples of tanker effluent were

allowed to settle in a refrigerator for 3 days, the

supernatant liquid drained off, and then the remain-

ing fine sediments stirred and sub-sampled. The dry

weights (dw) of the road debris were determined

J.N. Brown, B.M. Peake / Science of the Total Environment 359 (2006) 145–155148

gravimetrically by drying sub-samples at 105 8C to

constant weight.

2.3. Metal analysis

Aliquots (100 mL) of the stormwater samples were

extracted for total (particulate+dissolved) Cu, Pb and

Zn using a Q-HNO3 and Q-HCl acid digestion

(USEPA Method 200.9; (USEPA, 1992)). The dis-

solved metal fraction was isolated by membrane fil-

tration (0.4 Am, Nucleopore 47 mm) of a 50 mL

aliquot of the raw sample and acidified with Q-

HNO3 to 1% for analysis. Analysis for Cu and Pb

was undertaken using graphite furnace atomic absorp-

tion spectroscopy (USEPA, 1992) with Zeeman back-

ground correction (Perkin-Elmer ZL4100 instrument).

Due to higher Zn concentrations, this metal could be

determined using inductively coupled plasma-atomic

emission spectroscopy (ICP-AES, Thermo Jarrell Ash

Atomscan 25 instrument). Standard addition measure-

ments yielded mean recoveries of 98% for Cu, 97%

for Pb and 101% for Zn. Analysis of replicate sam-

ples, one pair for each storm event sampled, yielded

relative standards deviations (RSD) of less than 10%.

Results for procedural and field blanks were below the

detection limits of the present study (0.5 Ag/L for Cu

and Pb, 0.05 mg/L for Zn). Particulate metal concen-

trations were calculated by subtracting the dissolved

metal concentration from the total metal concentration

and then dividing by the concentration of SS (APHA,

1998) in the sample.

Sub-samples (5 g) of the road debris were extracted

using a hot concentrated Q-HNO3 followed by hydro-

gen peroxide digestion and the Cu, Pb and Zn content

determined by ICP-AES (Brown, 2002).

2.4. PAH analysis

Stormwater samples were filtered through 0.7 Amglass microfibre filters (Advantec GF75) to obtain the

particulate (SS-bound) PAHs. The filters were placed

in 100 mL screw top bottles sealed with aluminium foil

and extracted using 15 min cycles on an ultrasonic bath

using three successive 30 mL volumes of dichloro-

methane (Brown, 2002). Methods for the drying and

clean-up of the sample extracts have been described

previously (Brown and Peake, 2003). Two grams of

the road debris samples were dried by mixing with 10 g

anhydrous sodium sulphate, transferred to Soxhlet ex-

traction thimbles and then extracted for 12 h (5–6

cycles/hr) with 300 mL dichloromethane (Holoubek

et al., 1990). The final extract was concentrated to 100

mL on a rotary evaporator prior to clean-up. Sample

extracts were analysed for the 16 USEPA priority

PAHs by HPLC with dual UV/Vis and fluorescence

detection as described previously (Brown, 2002;

Brown and Peake, 2003). The analysed PAHs and

their abbreviations were naphthalene (NAP), acenap-

hthylene (ACY), acenaphthalene (ACE), fluorene

(FL), phenanthrene (PHEN), anthracene (ANT), fluor-

anthene (FLR), pyrene (PYR), benzo[a]anthracene

(BaA), chrysene (CHY), benzo[b]fluoranthene (BbF),

benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP),

dibenz[a,h]anthracene (DBA), benzo[g,h,i]perylene

(BPY) and indeno[1,2,3-cd]pyrene (INP). Detection

limits ranged from 0.01 to 0.1 Ag/g dw. Small amounts

of several PAHs were occasionally detected in the field

and procedural blanks, but were always b5% of the

sample amount. Matrix spikes processed with each

batch of samples showed analytical recoveries in the

range of 73–116% for which the reported concentra-

tions were corrected. The overall effectiveness of the

extraction and analytical procedures were evaluated by

analysing the NIST reference material SRM 1941a.

Extraction via both the Soxhlet (n =2) and ultrasonic

methods (n=4) yielded results that were within an

average of 18% of the certified values and exhibited

good precision (average RSD of 9%).

3. Results and discussion

3.1. Contaminant concentrations

The mean contaminant concentrations are given in

Table 1. The high degree of variability has been

observed previously (Stone and Marsalek, 1996; Gon-

zalez et al., 2000), particularly for the stormwater SS,

which can reflect the variety of contaminant sources

within a catchment and the complex wash-off dynam-

ics of the contaminated materials (Hoffman et al.,

1984; Gonzalez et al., 2000; Krein and Schorer,

2000).

The concentrations and relative abundances

(ZnNPbNCu) of the metals in the street dust, sump

sediment and the tanker effluent solids (Table 1) were

Table 1

Mean concentrations of heavy metals plus PAHs and PAH fingerprinting ratios in the road debris and stormwater suspended sediments (S.D. in

parenthesis)

Source Heavy metals PAHs

n Zn (Ag/g dw) Pb (Ag/g dw) Cu (Ag/g dw) n A16PAH (Ag/g dw) LMW/HMW PHEN/ANT FLR/PYR

Road debris

Street dust 3 528 (206) 289 (89) 129 (79) 3 4.40 (1.45) 0.20 (0.06) 4.89 (1.09) 1.06 (0.01)

Sump sediment 6 424 (304) 262 (167) 179 (145) 6 6.53 (3.81) 0.36 (0.03) 4.34 (0.90) 0.85 (0.60)

Tanker effluent 2 1188 (194) 262 (39) 142 (14) 2 13.13 (1.62) 0.19 (0.07) 3.90 (0.77) 1.03 (0.05)

Water of Leith catchment

Baseflow 3 ND 166 (62) 129 (85) 3 3.50 (1.08) 0.55 (0.48) 10.4 1.05 (0.20)

Stormflow 3 1079 (293) 208 (74) 146 (14) 3 5.69 (1.58) 0.11 (0.01) 4.65 (0.28) 1.10 (0.04)

Upper Leith 1 ND 95 63 1 2.17 0.20 4.55 1.16

St. David St. 1 1274 241 111 1 10.81 0.11 4.09 1.06

Portobello Road catchment

Baseflow 7 4915 (4192) 569 (583) 632 (379) 6 115 (164) 0.15 (0.06) 1.96 (0.21) 0.83 (0.14)

Stormflow 41 5901 (3721) 670 (332) 560 (300) 17 105 (125) 0.19 (0.10) 2.51 (0.98) 1.16 (0.37)

Dec 99 1 2692 613 123 1 157 0.13 3.59 1.13

Dec 00 1 3912 774 546 1 503 0.27 1.68 1.04

ND—not detected as result was less than the method detection limit.

J.N. Brown, B.M. Peake / Science of the Total Environment 359 (2006) 145–155 149

similar to those reported previously for road-derived

debris in North American sites (Stone and Marsalek,

1996; Walker et al., 1999) and for gross bed sediments

from a Parisian combined sewer (Rocher et al., 2004).

The Upper Leith SS contained lower concentrations of

Pb and Cu but no detectable Zn, indicating lower

inputs of road debris into the river at the upper reaches

of the urban area. The SS from the St. David Street

sub-catchment had similar concentrations of these

metals as the road debris, suggesting that the road

debris was their most likely source. The metal content

of the SS from the Water of Leith was not significant-

ly different between the two flow regimes, except for

Zn, which was below the detection limit during base-

flow conditions. During stormflow conditions, the

metals content of the Leith SS was similar to that of

the SS from the St. David Street sub-catchment and of

the road debris, implicating the road debris as the

predominant source of sediments entering the river

during the storm (3.5 mm rain in 1 h). For much larger

storm events, soil wash-off from fields within the

catchment’s rural areas and erosion of river banks

has been shown to contribute large amounts of un-

contaminated sediment to the river, thereby reducing

the metals content of the river borne SS (Reid, 1990).

It is likely that reworking of the contaminated road

debris material residing on the riverbed was respon-

sible for the Pb and Cu concentrations measured

during baseflow conditions. Zinc ions are consider-

ably more soluble than Pb and Cu ions, and while

below the ICP-AES detection limit, their transport in

the dissolved phase during baseflow conditions may

explain the negligible Zn content of the SS in the river

during such conditions as previously observed in an

adjoining urban catchment (Mosley and Peake, 2001).

The SS metal content at Portobello Road (Table 1)

exhibited no differences between flow regimes and

showed the same relative metal abundances of

ZnNPbNCu measured at the Leith (stormflow) and

St. David Street sites and in the road debris. However,

the concentrations of these metals were considerably

higher at Portobello Road but they were still within

the range reported in the literature. For example,

Gromaire-Mertz et al. (1999) measured similar values

for Cu (500 Ag/g), Zn (4 100 Ag/g) and higher values

for Pb (1 800 Ag/g) in runoff SS from a highly

urbanised Paris catchment. Higher traffic densities

and the presence of light industrial land use (including

a small-scale non-ferrous metal foundry, water tap

fabrication plant and a railway carriage manufacturing

yard) may explain the high concentrations of Cu and

Pb in the Portobello Road catchment. The high Zn

J.N. Brown, B.M. Peake / Science of the Total Environment 359 (2006) 145–155150

concentrations are likely to be due to this catchment

containing many densely settled suburbs, whose

roofed area of 30–35% (of the total suburban surface

area) is higher than the typical New Zealand values of

20–25% for residential areas (O. Schmid, Dunedin

City Council, personal communication). Zinc-galva-

nised iron is the predominant roofing material in these

suburbs and can lead to the release of significant

amounts of zinc during rainfall (Gromaire-Mertz et

al., 1999).

The A16PAH concentrations (Table 1) showed

similar patterns to those of the metals. No differences

in A16PAH values were observed between the flow

regimes for either catchment. Concentrations in the SS

collected from the Water of Leith and St. David Street

sites resembled those in the road debris and were

similar in magnitude to the 1.60–4.30 Ag/g dw

reported by Gonzalez et al. (2000) for street runoff

particles from a Parisian catchment. The Water of

Leith and St. David Street results were less than the

20 Ag/g dw value reported recently by Stout et al.

(2004) as being an upper limit typical for surficial

sediments from US urban waterways that are impact-

ed by non-point sources of pollution. However, con-

centrations at Portobello Road were an order of

magnitude higher than those in the Water of Leith

catchment, indicating a higher intensity of urban land

use and/or the possibility of a PAH point source(s)

within the catchment (Stout et al., 2004).

Potential evidence for this additional contaminant

source within the Portobello Road catchment occurred

during the December 1999 and December 2000 storm

events, when extremely high total (particulate+dis-

solved) water concentrations of all species (up to

4 100 Ag/L Pb, 823 Ag/L Cu, 18 550 Ag/L Zn and 1

050 Ag/L A16PAH) were measured in several samples

(Brown, 2002). During the December 1999 event, the

contaminant content of the SS (Table 1) was not

significantly higher than that measured previously.

The probable cause of the high total water concentra-

tions for this event, was in fact unlikely to be an

additional source, but rather maintenance activities

within the stormwater network (prior to the event)

disturbing sediments within the system, resulting in

unusually high levels of SS of 6 685 mg/L during the

event (compared to the mean stormflow concentration

of SS of 53 mg/L) (Brown, 2002). During the De-

cember 2000 event, the concentration of SS of 80 mg/L

was much lower. However, the A16PAH concentration

of the particles of 503 Ag/g dw (Table 1) was five times

higher than the mean for this site and 50 times higher

than that measured in either the road debris or at the

other sites confirming that an additional source(s) of

PAHs was present within the catchment.

3.2. PAH profiles

The relative PAH abundances (hereafter called

profiles) may also be used to investigate sources of

PAHs found in terrestrial and aquatic sediments (Gon-

zalez et al., 2000; McCready et al., 2000). In urban

areas, the principal sources of PAHs are the incom-

plete combustion of fossil fuels or wood (pyrogenic

sources), and spilt oil or petroleum products (petro-

genic sources) (Takada et al., 1991; Ngabe et al.,

2000). Pyrogenic sources, such as the combustion-

derived particles present in urban atmospheric dust,

are depleted in low molecular weight 2–3 ring PAHs

(LMW) and enriched in high molecular weight 4–6

ring PAHs (HMW) (Soclo et al., 2000; Rocher et al.,

2004) leading to LMW/HMW ratios b1. Petrogenic

sources, such as fuel oil or light refined petroleum

products, are dominated by LMW PAHs (Soclo et al.,

2000) and have LMW/HMW ratios N1. Used crank-

case oil, another PAH source in urban areas (Takada et

al., 1991), has a petrogenic profile that becomes

imprinted with a pyrogenic signature as the oil

becomes contaminated through contact with the ex-

haust gases in the engine cylinders (Wang et al.,

2000). Asphalt contains significant amounts of

PAHs and also has a mix of petrogenic and pyrogenic

character (Brandt and De Groot, 2001).

The profiles of the road debris are shown in Fig. 2

together with those of potential sources. The road

debris profiles were dominated by FLR and PYR.

The LMW/HMW ratios of significantly less than

one indicated that pyrogenic sources were predomi-

nant. The street dust profile was a mixture between

that of urban dust and used crankcase oil, although it

was depleted in LMW PAHs possibly as a result of

evaporative losses (MacKenzie and Hunter, 1979).

The sump sediments gave rise to a similar profile

but with a LMW/HMW ratio of 0.36. Combustion-

derived soot particles are present largely as 2–12.5 Amparticles, whereas degraded asphalt particles have

grain sizes in the range of 63–630 Am (Hoffman et

(a) Source Materials

(b) Stormwater

Sump Sediments

0

5

10

15

20

25

NA

P

AC

Y

AC

E FL

PH

EN

AN

T

FL

R

PY

R

B(a

)A

CH

Y

B(b

)F

B(k

)F

B(a

)P

DB

A

BP

Y

INP

NA

P

AC

Y

AC

E FL

PH

EN

AN

T

FL

R

PY

R

B(a

)A

CH

Y

B(b

)F

B(k

)F

B(a

)P

DB

A

BP

Y

INP

NA

P

AC

Y

AC

E FL

PH

EN

AN

T

FL

R

PY

R

B(a

)A

CH

Y

B(b

)F

B(k

)F

B(a

)P

DB

A

BP

Y

INP

NA

P

AC

Y

AC

E FL

PH

EN

AN

T

FL

R

PY

R

B(a

)A

CH

Y

B(b

)F

B(k

)F

B(a

)P

DB

A

BP

Y

INP

LMW/HMW = 0.36

Street Dust

0

5

10

15

20

25

LMW/HMW = 0.20

Used Crankcase Oil

0

5

10

15

20

25

LMW/HMW = 1.23

Asphalt

0

5

10

15

20

25

% Σ

16P

AH

%

Σ16

PA

H

LMW/HMW = 0.52

Portobello STW

0

5

10

15

20

25

LMW/HMW = 0.19

Leith STW

0

5

10

15

20

25

LMW/HMW = 0.11

Portobello BF

0

5

10

15

20

25

LMW/HMW = 0.15

Leith BF

0

5

10

15

20

25

LMW/HMW = 0.55

Urban Dust - SRM 1649a

0

5

10

15

20

25

LMW/HMW = 0.14

Tanker Effluent

0

5

10

15

20

25

LMW/HMW = 0.19

Fig. 2. Relative abundances (FSD) of the 16 PAHs in (a) potential source materials: used crankcase oil (Wang et al., 2000); asphalt (Brandt and

De Groot, 2001); urban dust (SRM 1649a) (King, 1997) and the locally collected road debris; and in (b) the stormwater suspended sediment

during baseflow (BF) and stormflow (STW) conditions.

J.N. Brown, B.M. Peake / Science of the Total Environment 359 (2006) 145–155 151

J.N. Brown, B.M. Peake / Science of the Total Environment 359 (2006) 145–155152

al., 1984; Krein and Schorer, 2000). The larger asphalt

particles are only likely to be mobilised during high

intensity storm events and may become preferentially

enriched in the sumps (Krein and Schorer, 2000),

leading to the sump sediments having a higher

LMW/HMW ratio. The tanker effluent solids had a

similar profile to the street dust, although they had a

lower LMW/HMW ratio, possibly due to an absence

of coarser asphalt particles.

FLR and PYR dominated the profiles for the

stormwater SS (Fig. 2) consistent with the findings

of Ngabe et al. (2000) and Gonzalez et al. (2000).

However, PHEN accounted for less than 10% of the

A16PAH concentration. At Portobello Road, both the

baseflow and stormflow profiles resembled those of

the road dust and tanker effluent solids, but not the

sump sediments, which had a slightly different profile

(more PHEN and PYR) possibly due a greater content

of coarse asphalt particles. The Portobello Road pro-

files were predominately pyrogenic in character as

their mean LMW/HMW ratios are b1 (0.15–0.19).

These values were similar to those reported for Par-

isian combined sewer gross bed solids (0.22–0.26)

(Rocher et al., 2004) and for urban waterway sedi-

ments impacted by stormwater runoff (mean of 0.34)

in the USA (Stout et al., 2004). A minor petrogenic

component was also present at Portobello Road as

indicated by the presence of minor amounts of NAP,

ACY, ACE and FL. This was consistent with the

findings of Bomboi and Hernandez (1991) who

reported that petroleum/oil residues contributed 5–

25% of the PAHs in urban runoff in Madrid, Spain,

with the remainder coming from pyrogenic sources.

Stout et al. (2004) also estimated a petrogenic contri-

bution of 20–30%.

The profiles for the St. David Street and Upper

Leith sites (not shown) were similar to those for the

Water of Leith. The Water of Leith stormflow profile

showed strong pyrogenic character, again similar to

that of the urban dust and street dust. A minor petro-

genic component was present but was lower (LMW/

HMW=0.11) than that found in the Portobello Road

catchment suggesting that contributions from used

crankcase oil and asphalt were lower in the Leith

catchment. However, during baseflows, the Water of

Leith profile had high but very variable levels of NAP,

FL and PHEN and a higher LMW/HMW ratio sug-

gesting greater petrogenic input. This was possibly

due to greater contributions from the urban parts of

the catchment of the oily layer (predominately used

crankcase oil) that floats at the top of the stormwater

sumps.

3.3. PAH fingerprint ratios

The use of bfingerprintQ ratios of the concentrationsof certain isomeric pairs of PAHs provides a less

subjective means to identify PAH sources. Ratios of

PHEN/ANT b10 and FLR/PYR ~1 are indicative of

pyrogenic sources, while ratios of PHEN/ANT N15

and FLR/PYR significantly less than one suggest a

dominance of petrogenic sources (Baumard et al.,

1998). The ratios for the street dust (Table 1) showed

pyrogenic sources were dominant. The values were

similar to those calculated from Christensen et al.

(1999) for highway dust in Milwaukee (PHEN/

ANT=4.82F0.49, FLR/PYR=1.42F0.04) and

street dust from residential Tokyo (FLR/

PYR=1.02F0.14) (Takada et al., 1991). The ratios

for the other forms of road debris were similar to those

of the road dust, except that the sump sediments had a

slightly lower FLR/PYR ratio.

The SS from the Leith during stormflow condi-

tions, as well as the St. David Street and Upper Leith

sites, exhibited ratios similar to those of the road

debris (Table 1). Ratios of 1–5 for PHEN/ANT and

FLR/PYR ~1 are typical of SS in urban stormwater

runoff (Hoffman et al., 1984; Bomboi and Hernandez,

1991; Gonzalez et al., 2000; Stout et al., 2004) and are

indicative of pyrogenic sources, probably dominated

by automobile emissions and used crankcase oil

(Takada et al., 1991; Gonzalez et al., 2000). For the

Leith during baseflow conditions, the PHEN/ANT

ratio of 10.4 was high compared to those for the

other stormwater sampling sites, while the FLR/PYR

ratio was similar. The closest match to any of the

potential source materials was to SRM 1649a-Urban

Dust (PHEN/ANT=11, FLR/PYR=0.99) (King,

1997). Thus, during baseflow conditions, the domi-

nant input of PAHs to the Water of Leith appears to

arise from atmospheric particulate matter.

The PHEN/ANT ratios from Portobello Road site

(Table 1) were lower than those found elsewhere

during the study, indicating that another PAH source

may be present in the catchment. Plotting the values

of PHEN/ANT against FLR/PYR (Fig. 3) allowed this

0

1

2

3

4

5

6

7

0 1 2

FLR / PYR

PH

EN

/ A

NT

Portobello STW

Tanker effluent solids

Street dust

Sump sediments St David St

Leith STW

Portobello BF

Portobello Dec99

Upper Leith

Portobello Dec00

Gasworks sludge Gasworks tar

Fig. 3. PHEN/ANT versus FLR/PYR plot indicating the road debris were the major sources of PAHs in the stormwater. In addition to the road

debris, the gasworks sludge contributed PAHs at the Portobello Road site.

J.N. Brown, B.M. Peake / Science of the Total Environment 359 (2006) 145–155 153

to be investigated further (Baumard et al., 1998). The

values for the street dust and tanker effluent solids

grouped closely with those for the SS from the Leith,

St. David Street and Upper Leith sites, thereby sup-

porting the earlier conclusions that the stormwater

sediments were primarily comprised of these forms

of road debris. The sump sediments, which also had a

higher LMW/HMW ratio, plotted further left at lower

FLR/PYR values. The mean Portobello Road values,

both during baseflow and stormflow conditions, were

some distance away at lower PHEN/ANT values. The

ratios for the two samples from which extremely high

total (particulate+dissolved) water concentrations of

A16PAH were measured are also shown in Fig. 3. The

sample from the December 1999 storm event plots

close to the other stormwater SS, indicating that it was

probably derived from road debris, possibly as a result

of maintenance activities within the stormwater drain-

age system. The December 2000 sample had a similar

FLR/PYR ratio but had the lowest PHEN/ANT ratio

(1.68). A disused gasworks, which are known PAH

sources (Luthy et al., 1994), is located within the

catchment 1 km from the sampling site. The PAH

analyses of sludge and tar from this site (B. Thomson,

Envirosil Ltd., Dunedin, personal communication) are

plotted in Fig. 3. The tar, with its high FLR/PYR ratio

and extremely low PHEN/ANT ratio, plotted some

distance from the other samples. However, the ratios

for the sludge are close to those for the Portobello

Road stormwater SS, in particular the sample taken in

December 2000. Remediation work had occurred at

the gasworks site in 1999/2000 to remove some PAH-

contaminated materials. It is probable that some

sludge entered the stormwater system and was trans-

ported to the sampling site by the storm. The gas-

works may also contribute PAHs on a continuous

basis as shown by the low mean PHEN/ANT ratio

for the baseflow samples. Also, the mean PHEN/ANT

ratio for the stormflow samples at Portobello Road,

while being slightly higher due to the influx of more

typical sediments from the roads, is still lower than

that measured in the Leith catchment.

4. Conclusions

Analysis of the trace metal and PAH content of

stormwater SS, in comparison with that of road debris

from the same catchments, enabled the apportionment

of the contaminant sources in the stormwater. The

road debris, in particular street dust and tanker efflu-

ent solids, were the principal sources of the heavy

metals and PAHs in the stormwater SS from the Water

of Leith catchment. The road debris were also a

significant contributor to the contaminants in the Por-

tobello Road catchment but significantly higher metal

and PAH concentrations suggested that additional

contaminant sources were present. For Cu and Pb,

higher concentrations probably arose from a greater

intensity of urban and industrial land uses within the

catchment. Additional zinc was traced to runoff from

extensive use of zinc-galvanised roofing iron within

J.N. Brown, B.M. Peake / Science of the Total Environment 359 (2006) 145–155154

the catchment’s residential areas. During one storm

event, high PAH and metal concentrations appeared to

be the result of maintenance activities within the

stormwater system disturbing or adding a large

amount of road debris. In another event, where only

PAH concentrations were highly elevated, input of

PAH-rich sludge from a closed gasworks facility

was implicated. This extra source of PAHs was likely

to contribute to PAH levels at all times, as evident

from the Portobello Road SS having different PHEN/

ANT and FLR/PYR ratios than the road debris and

stormwater SS from the Water of Leith catchment.

This additional input was the likely explanation for

the high annual PAH loading from this catchment.

Acknowledgements

The authors express their gratitude to the Dunedin

City Council for material and financial support, the

University of Otago for a Postgraduate Scholarship

and Bridging Grant, and Bill Thomson, Envirosil Ltd.,

for the gasworks PAH testing results.

References

APHA. Standard methods for the examination of water and waste-

water, 20th ed. Washington, DC7 American Public Health As-

sociation; 1998.

Baumard P, Budzinski H, Michon Q, Garrigues P, Burgeot T,

Bellocq J. Origin and bioavailability of PAHs in the Mediterra-

nean Sea from mussel and sediment records. Estuar Coastal

Shelf Sci 1998;47:77–90.

Bomboi MT, Hernandez A. Hydrocarbons in urban runoff: their

contribution to the wastewaters. Water Res 1991;25:557–65.

Borchardt D, Sperling F. Urban stormwater discharges: ecological

effects on receiving waters and consequences for technical

measures. Water Sci Technol 1997;36:173–8.

Brandt HCA, De Groot PC. Aqueous leaching of polycyclic aro-

matic hydrocarbons from bitumen and asphalt. Water Res

2001;35:4200–7.

Brown JN. 2002. Partitioning of chemical contaminants in urban

stormwater. PhD thesis, University of Otago, Dunedin, New

Zealand, p. 266.

Brown JN, Peake BM. Determination of colloidally-associated

polycyclic aromatic hydrocarbons (PAHs) in fresh water using

C18 solid phase extraction disks. Anal Chim Acta

2003;486:159–69.

Brown JN, Peake BM, Robinson D, Schmid O. Partitioning of

chemical contaminants in urban stormwater. 3rd south Pacific

conference on stormwater and aquatic resource protection,

Auckland. New Zealand7 New Zealand Water and Wastes As-

sociation; 2003.

Christensen ER, Rachdawong P, Karls JF, Van Camp RP. PAHs in

sediments: unmixing and CMB modelling of sources. J Environ

Eng 1999;1022–32.

Gonzalez A, Moilleron R, Chebbo G, Thevenot DR. Determination

of polycyclic aromatic hydrocarbons in urban runoff samples

from the bLe MaraisQ experimental catchment in Paris centre.

Polycycl Aromat Compd 2000;20:1–19.

Gromaire-Mertz MC, Garnaud S, Gonzalez A, Chebbo G. Charac-

terisation of urban runoff pollution in Paris. Water Sci Technol

1999;39:1–8.

Hoffman E, Mills G, Latimer JS, Quinn JG. Urban runoff as a

source of polycyclic aromatic hydrocarbons to coastal waters.

Environ Sci Technol 1984;18:580–7.

Holoubek I, Paasivirta J, Maatela P, Lahtipera M, Holoubkova I,

Korinek P, et al. Comparison of extraction methods for polycy-

clic aromatic hydrocarbon determination in sediments. Toxicol

Environ Chem 1990;25:137–54.

King DE. Establishing the credibility of environmental laboratories.

In: Clement RE, Keith LH, Siu KWM, editors. Reference

materials for environmental analysis. Boca Raton7 Lewis Pub-

lishers; 1997. p. 131–86.

Krein A, Schorer M. Road runoff pollution by polycyclic aromatic

hydrocarbons and its contribution to river sediments. Water Res

2000;34:4110–5.

Luthy RG, Dzombak DA, Peters CA, Roy SB, Ramaswami A,

Nakles DV, et al. Remediating tar-contaminated soils at man-

ufactured gas plant sites. Environ Sci Technol 1994;28:

266A–76A.

MacKenzie MJ, Hunter JV. Sources and fates of aromatic com-

pounds in urban stormwater runoff. Environ Sci Technol

1979;13:179–83.

McCready S, Slee DJ, Birch GF, Taylor SE. The distribution of

polycyclic aromatic hydrocarbons in surficial sediments of Syd-

ney Harbour, Australia. Mar Pollut Bull 2000;40:999–1006.

Mosley LM, Peake BM. Partitioning of metals (Fe, Pb, Cu, Zn) in

urban run-off from the Kaikorai Valley, Dunedin, New Zealand.

NZ J Mar Freshw Res 2001;35:615–24.

Ngabe B, Bidleman TF, Scott GI. Polycyclic aromatic hydrocarbons

in storm runoff from urban and coastal South Carolina. Sci Total

Environ 2000;255:1–9.

Reid MR. The marine geochemistry of lead in an urban catchment.

PhD thesis, University of Otago, Dunedin, New Zealand, 1990.

Rocher V, Azimi S, Moilleron R, Chebbo G. Hydrocarbons and

heavy metals in the different sewer deposits in the dLe MaraisTcatchment (Paris, France): stocks, distributions and origins. Sci

Total Environ 2004;323:107–22.

Soclo HH, Garrigues P, Ewald M. Origin of polycyclic aromatic

hydrocarbons (PAHs) in coastal marine sediments: case studies

in Cotonou (Benin) and Aquitaine (France) areas. Mar Pollut

Bull 2000;40:387–96.

Stone M, Marsalek J. Trace metal composition and speciation in

street sediment: Sault Ste Marie, Canada. Water Air Soil Pollut

1996;87:149–69.

Stout SA, Uhler A, Emsbo-Mattingly SD. Comparative evaluation

of background anthropogenic hydrocarbons in surficial sedi-

J.N. Brown, B.M. Peake / Science of the Total Environment 359 (2006) 145–155 155

ments from nine urban waterways. Environ Sci Technol

2004;38:2987–94.

Takada H, Onda T, Harada M, Ogura N. Distribution and sources of

polycyclic aromatic hydrocarbons (PAHs) in street dust from the

Tokyo metropolitan area. Sci Total Environ 1991;107:45–69.

USEPA. Methods for the determination of metals in environmental

samples. Cincinnati7 U.S. Environmental Protection Agency;

1992. 339 pp.

Walker WJ, McNutt RP, Maslanka CA. The potential of urban

runoff to surface sediments of the Passaic River: sources and

chemical characteristics. Chemosphere 1999;38:363–77.

Wang J, Jia CR, Wong CK, Wong PK. Characterisation of polycy-

clic aromatic hydrocarbons created in lubricating oils. Water Air

Soil Pollut 2000;120:381–96.