Environ Monit Assess (2014) 186:2907–2923 DOI 10.1007/s10661-013-3589-1

Accumulation and risks of polycyclic aromatic hydrocarbons and trace metals in tropical urban soils P. S. Khillare & Amreen Hasan & Sayantan Sarkar

Received: 11 July 2013 / Accepted: 12 December 2013 / Published online: 29 December 2013 # Springer Science+Business Media Dordrecht 2013

Abstract The study deals with the combined contribution of polycyclic aromatic hydrocarbons (PAHs) and metals to health risk in Delhi soils. Surface soils (0– 5 cm) collected from three different land-use regions (industrial, flood-plain and a reference site) in Delhi, India over a period of 1 year were characterized with respect to 16 US Environmental Protection Agency priority PAHs and five trace metals (Zn, Fe, Ni, Cr and Cd). Mean annual ∑16PAH concentrations at the industrial and flood-plain sites (10,893.2±2826.4 and 3075.4 ±948.7 μg/kg, respectively) were ~15 and ~4 times, respectively, higher than reference levels. Significant spatial and seasonal variations were observed for PAHs. Toxicity potentials of industrial and flood-plain soils were ~88 and ~8 times higher than reference levels.

Electronic supplementary material The online version of this article (doi:10.1007/s10661-013-3589-1) contains supplementary material, which is available to authorized users. P. S. Khillare (*) : A. Hasan Environmental Monitoring and Assessment Laboratory, School of Environmental Sciences, Jawaharlal Nehru University, Room number 325, New Delhi 110067, India e-mail: [email protected] S. Sarkar Atmospheric Sciences Research Center, State University of New York, Albany, NY 12203, USA S. Sarkar Wadsworth Center, New York State Department of Health, Albany, NY 12237, USA

Trace metal concentrations in soils also showed marked dependencies on nearness to sources and seasonal effects. Correlation analysis, PAH diagnostic ratios and principal component analysis (PCA) led to the identification of sources such as coal and wood combustion, vehicular and industrial emissions, and atmospheric transport. Metal enrichment in soil and the degree of soil contamination were investigated using enrichment factors and index of geoaccumulation, respectively. Health risk assessment (incremental lifetime cancer risk and hazard index) showed that floodplain soils have potential high risk due to PAHs while industrial soils have potential risks due to both PAHs and Cr. Keywords Polycyclic aromatic hydrocarbons (PAHs) . Trace metals . Principal component analysis . Enrichment factors . Index of geoaccumulation . Delhi

Introduction Polycyclic aromatic hydrocarbons (PAHs) are organic contaminants of high environmental stability that are mainly derived from incomplete combustion and pyrolysis of organic materials (Harrison et al. 1996; Zhang et al. 2009). They originate from anthropogenic sources such as burning of fossil fuels, industrial emissions, and motor vehicle exhausts, and also from primarily natural sources such as forest fires and volcanic activity (Masih and Taneja 2006). Sixteen PAHs have been identified as priority pollutants by the United States Environmental Protection Agency (US EPA) and seven of them

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(benz[a]anthracene, benz[a]pyrene, benz[b]fluoranthene, benz[k]fluoranthene, chrysene, dibenz[a,h]anthracene, and indeno[1,2,3-c,d]pyrene) are considered carcinogenic (US EPA 2002). In turn, the International Agency for Research on Cancer (IARC) has established that benz[a]anthracene and benz[a]pyrene are probable human carcinogens, whereas benz[b]fluoranthene, benz[j]fluoranthene, benz[k]fluoranthene, and indenol[1,2,3-c,d]pyrene are possible human carcinogens (IARC 2004). The environmental occurrence of PAHs has been widely associated with adverse effects on public health (Rost and Loibner 2002). As a consequence of their low water-solubility, low vapour pressure and high degree of association with soil organic matter, PAHs tend to adsorb strongly onto soil particles (Kipopoulou et al. 1999; Orecchio 2010). In fact, most of the environmental burden of PAHs is considered to be due to their presence in soil (approximately 95 %), as opposed to air (approximately 0.2 %) (Smith et al. 1995). Trace metals are needed by organisms in minute amounts for normal biological functions but are highly toxic if present in excess. Detrimental effects of trace metal exposure to humans include oxidative damage, neurological disorders and different forms of cancer (Canfield et al. 2003; Nawrot et al. 2009; IARC 2009). The contribution of trace metals from anthropogenic sources to the soil system is far higher than that from natural ones (Nriagu and Pacyna 1988). Metals are co-emitted with PAHs from a number of anthropogenic sources, such as, vehicular exhausts, industrial emissions, domestic fuel use and solid waste/refuse burning (Sandroni et al. 2003). Co-exposure to PAHs and metals are often associated with greater biological damage (Liu et al. 2010) and as such, there exists a great need for simultaneous characterization of PAHs and trace metals in soils. Uptake of PAHs and metals by food crops grown in contaminated soil poses human health risk (Khillare et al. 2012). This is especially true for the Indian scenario where understanding of PAH and metal distributions in characteristic soil types is still poor, and studies involving simultaneous characterizations of these species are virtually non-existent. The city of Delhi, the capital of India, is home to a population of about 18 million. Its vehicular population (~7.5 million as of 30 September 2012) (Transport Department 2012) is the highest in India and is dominated by gasoline-fuelled vehicles such as two-wheelers (63 %) and private four-wheelers (31 %). A large fraction of the private cars and almost all heavy-duty vehicles run on diesel. Compressed natural gas (CNG) vehicles comprise

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of a miniscule 5 % of the total vehicular fleet. Three coalfired power plants, namely, Badarpur (720 MW), Indraprastha (247.5 MW) and Rajghat (135 MW), along with brick kilns, hot mix plants and industrial units add to the local pollution problem. The Indraprastha power station has been shut down since 2010; however, it was in operation during the course of sampling for this study (2007–2008). There has been a phenomenal growth in the number of small scale industrial units in Delhi from just 26,000 in 1971 to 129,000 in 2000–2001 (Planning Department 2006). In this context, the present study aims to characterize surface soils from three separate land-use regions in Delhi with respect to 16 US EPA priority PAHs and five trace metals (Fe, Zn, Ni Cr and Cd), and to investigate their interdependencies. The main objectives of the present study are: (1) to investigate the spatial and temporal distributions of PAHs and trace metals; (2) to assess the nature and degree of correlation between these species; (3) to identify the major sources contributing PAHs and trace metals in Delhi soils; (4) to assess the degree of soil contamination; (5) to assess the resulting health risks, if any.

Materials and methods Study area Delhi is spread over an area of 1,483 sq km. It is situated at 28°24′17″N to 28°53′N (latitude) and 76°20′37″E to 77°20′37″E (longitude), with a mean altitude of 216 m asl. It is flanked by the Himalayas in the north (at a distance of about 160 km) and the central plains in the south. To the west of Delhi is the Great Indian Desert (Thar) of Rajasthan and cooler hilly regions lie to the northeast. The wind direction in Delhi is usually from the north or northwest, except during the monsoon (July to October) when easterly or southeasterly winds are more common. The summer season extends from March to June with monthly mean temperatures of 32–34 °C while the winter season lasts from November to February with monthly mean temperatures of 12–14 °C. The mean annual rainfall is 714 mm, of which around 80 % is received during the monsoon months. The monsoon season starts in late June and lasts till mid-September with a mean temperature of ~29 °C (varying from ~25 °C on rainy days to ~32 °C during dry spells). The monthly mean rainfalls in Delhi during the

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sampling period (starting from August 2007 through to July 2008) were 216.8, 72.8, 0, 0, 0, 1.8, 0, 0, 31, 136.6, 100.7 and 166.2 mm, respectively (IARI 2013). Description of sampling sites Sampling locations are shown in Fig. 1. Samples were collected from three sites representing different land-use patterns, namely, Palla village (PV, reference site), Wazirpur Industrial Area (WIA, industrial site) and Akshardham (AKS, Yamuna flood plain site). Site 1, PV, is situated in the extreme north (upwind) of Delhi and is far away from any traffic or industrial activities. Sources related to domestic and agricultural activities could be important at this site. Site 2, WIA, is located in north-central Delhi and consists of a large number of unorganized industrial units. The sampling points were located in the midst of various small scale factories, such as steel processing, steel polishing, scrap metal recycling, ferrous and non-ferrous metal smelters, electroplating, and automobile parts manufacture. Site 3, AKS, is situated near Akshardham temple in east Delhi. It is located on the flood plain of river Yamuna having substantial agricultural activities all around. Moderate to high traffic roads are present in the proximity of the site. The Akshardham temple complex present in the vicinity also owns a huge parking space. This site is 2–3 km downwind of the Indraprastha and Rajghat coal-fired power plants. Fig. 1 Map of Delhi showing the sampling sites and major point sources in the study area

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Sample collection Samples were collected for three seasons, namely, monsoon, winter and summer from August 2007 to July 2008. Sampling was done on a monthly basis, i.e., for each season four samples were collected at each site. Seasonal data is reported as the mean of these 4-month samples. Surface soil samples were collected using a stainless steel auger down to a depth of 5 cm. Subsequently, samples were transferred into polyethylene bags, transported to the laboratory and preserved at 4°C till further processing. Samples were dried in the dark, and twigs and stones were removed. Each composite soil sample was comprised of 10–12 sub-samples collected from different points at each site. After homogenization, the soil samples were sieved through a 2mm sieve. Representative samples were obtained after quartering and coning. Chemicals and standards Standard mixture containing 16 PAHs (16 compounds specified in US EPA method 610) and deuterated PAHs internal standard mixture (naphthalene-d8; acenaphthened10; phenanthrene-d10 and chrysene-d12) were procured from Supelco (Bellefonte, PA, USA). All solvents (toluene, n-hexane, acetonitrile, etc.) used for sample processing and analysis were of HPLC grade. High-purity

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deionized water from the Milli-Q system (Millipore, USA) was used in the analysis. Concentrated nitric acid and hydrofluoric acid were of GR grade (Merck India Ltd.). Stock standard solutions of Zn, Fe, Ni, Cr and Cd for each metal were purchased from Reagecon, Ireland. Calibration standards of each metal were prepared by appropriately diluting the stock solutions. Determination of pH and soil texture Soil pH was measured using a 1:2.5 soil solution prepared in deionized water, and soil texture was determined by pipette method using sodium hexametaphosphate solution. Determination of PAHs Detailed protocols used for extraction, concentration, clean-up and analysis of PAHs from soil samples is described elsewhere (Ray et al. 2008; Agarwal et al. 2009). Briefly, soil samples were extracted in toluene by ultrasonic agitation (Sonicator 3000, Misonix Inc., USA). The extracts were centrifuged and then concentrated to 0.5–2 ml (Buchi Rotavapor, Switzerland). PAHs in the concentrated samples were fractionated by a silica gel column, fractions were again concentrated to 0.5–2 ml and solvent exchange was performed. Samples were analyzed on a High Performance Liquid Chromatography (HPLC) system (Waters, USA) equipped with a tunable absorbance UV detector (254 nm) and a Waters PAH C18 column (4.6×250 mm, 5-μm particle size). Quantification of PAHs was done by internal calibration method and PAH identification was performed by comparing their retention times with those of authentic standards. Samples were spiked with internal standard solution prior to extraction to monitor procedural performance and matrix effects. Surrogate compounds were represented for the analyses as follows: Naphthalene-d8 for naphthalene (Naph); Acenaphthened10 for Acenaphthylene (Acy), Acenaphthene (Acen) and Fluorene (Flu); Phenanthrene-d10 for Phenanthrene (Phen), Anthracene (Anth), Fluoranthene (Flan) and Pyrene (Pyr); Chrysene-d12 for Benz[a]anthracene (B[a]A) and Chrysene (Chry); Perylene-d 12 for Benz[b]fluoranthene (B[b]F), Benz[k]fluoranthene (B[k]F), Benz[a]pyrene (B[a]P), Dibenz[a,h]anthracene (DBA), Benz[g,h,i]perylene (B[g]P) and Indeno[1,2,3cd]pyrene (IP).

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Determination of trace metals A microwave sample preparation system (Speedwave™ MWS-3+; Berghof GmbH) was used for the microwave-assisted digestion of soil samples. The microwave digester consists of a 2,450-MHz power system and has a maximum power of 1,450 W. The maximum operable temperature and pressure are 230 °C and 40 bars, respectively. Digestions were carried out in DAP-100 TFM™ vessels equipped with temperature and pressure sensors, screw caps and rupture discs. The reaction vessels were cleaned before each digestion using concentrated HNO3. Samples were prepared by weighing around 0.1 g of soil sample into the vessels followed by addition of 10 ml HNO 3 and 2 ml HF (US EPA 3051A). A predefined programme was chosen to be run (175 °C for 10 min, 210 °C for 20 min and 100 °C for 10 min). After subsequent filtration and volume make-up, the samples were transferred to polypropylene bottles and stored in a refrigerator. For each digestion set, reagent blanks were also digested to examine analytical interferences. A few samples were spiked with known concentrations of standard solution to check recovery efficiencies of the target metals. An Atomic Absorption Spectrometer (Shimadzu AA6800) was used for metal determination. The metals were measured under optimized operating conditions by flame AAS. Quality control The instruments (HPLC and AAS) were calibrated with sets of at least five standards covering the range of concentrations encountered in soil work. The calibration curves were linear in the concentration ranges with linear regression coefficients (R2 > 0.99) for linear least-squares fit of data. Analytical methods were checked for precision and accuracy. All samples were analyzed in triplicates. Relative standard deviations (RSDs) of replicate samples were less than 10 % for both PAHs and metals. PAH and metal concentrations in reagent blanks were often below detection limits, and in other cases were <5 % of real sample concentrations. Recovery efficiencies were tested by spiking six samples (two samples from each site), out of 36 samples, with known concentrations of standard solution prior to extraction. Analytical detection limits of the target PAHs varied from 0.15 to 0.94 μg/kg while those for metals

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varied from 4 μg/l for Cd to 12 μg/l for Ni. Recovery efficiencies of PAHs varied from 78 % to 96 % while those for metals varied from 72 % to 90 %.

Results and discussion

Statistical analysis

Soil texture analysis showed all three sites (PV, WIA and AKS) to have sandy-loam soil. Moreover, soils from all three sites were mildly alkaline in nature with pH values of 7.4–7.9, 7.5–7.7 and 7.6–8.2 for PV, WIA and AKS, respectively. These similarities across sites therefore seem to indicate that soil physico-chemical properties might not influence spatial variations of PAHs and/or trace metals in this study.

Statistical analyses were performed with SPSS 14.0. A two-way analysis of variance (ANOVA) was used to determine seasonal and spatial variations in PAHs and metals. Pearson correlation analysis was used to ascertain correlations between individual PAHs and metals. Principal component analysis (PCA) with varimax rotation and Kaiser normalization was performed to elucidate the possible sources. An eigenvalue >1 was the criterion for choosing factors in PCA and factor scores >0.5 were considered significant. A minimum significance level of 95 % was chosen for all statistical analyses.

Soil physical and chemical properties

Distribution and spatio-temporal variation of PAHs Seasonal mean concentrations of PAHs at different sites are given in Table 1. The annual average ∑16PAH (sum of 16 priority PAHs) concentration was found to be

Table 1 Spatial and temporal variations of PAHs (μg/kg) and metals (mg/kg) in the present study Compound

Naph

PV

WIA

AKS

Monsoon

Winter

Summer

Monsoon

Winter

Summer

Monsoon

Winter

Summer

135.1

136.6

73.1

182

495.6

685.5

412.4

394.8

134.3

Acy

99.7

123.1

58.1

204.9

617.9

678

300.3

390.4

499.7

Acen

153.3

202

86.9

383.2

433.1

595

269

335.2

451.4

Flu

54.9

77.4

38.2

157.6

50

40.1

266.2

236.1

103.4

Phen

32.3

57.3

24.6

293.9

98.9

89

178.4

159

96.7

Anth

7.3

20.3

12.8

166.5

70.3

97.2

162

129.9

54.4

Flan

75.7

119.9

72.4

453.4

342.7

211.7

258.5

224.8

126.7

Pyr

47.8

60.6

27.5

522.6

335.1

301.9

141.7

135.2

58.7

B[a]A

39.9

54.6

32.7

1,058.9

910.5

486.7

165.6

143.7

62.6

Chry

nd

nd

nd

485.2

304.5

223

179

153.3

73.3

B[b]F

26.7

29.4

16.2

269.5

533.9

330

135.4

312.4

91.4 96.7

B[k]F

13.9

18.7

12.5

1,227.8

1,324.9

980.7

113.4

245.5

B[a]P

30.3

41.8

20.8

1,275.1

998.8

511

86.5

173.8

53.9

DBA

nd

nd

nd

2,049.5

3,156.2

1,547.5

133.2

232.9

87.5

B[g]P

nd

nd

nd

932.7

3,092.1

1,170.4

107.6

416

86.4

IP

nd

nd

nd

703.6

875.4

725.4

92.7

354.9

109.3

∑16PAHs

717

941.8

475.7

10,366.5

13,639.8

8,673.2

3,001.9

4,038

2,186.3

∑7carcPAHs

110.8

144.6

82.2

7,069.6

8,104.2

4,804.5

905.9

1,616.5

574.7

Zn

69.9

117

82.6

368.6

669.8

503.8

126

148.6

138.2

Fe

10,043.3

11,466.2

8,052.3

25,588.5

25,983.3

25,553.4

14,199.5

13,144.1

13,615.9

Ni

37.1

65.4

29.2

347.1

1,210.4

1,272.2

103.6

109.1

70.9

Cr

45.1

77.1

55.8

2,172.9

4,538

10,063.4

46

135.3

32.5

Cd

0.12

0.9

1.1

2.6

3

0.5

2.5

0.33

0.5

nd not detected

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highest for the industrial site (WIA) (10,893.2 μg/kg) and lowest for the reference site (PV) (711.5 μg/kg) while that of the flood plain site (AKS) was 3075.4 μg/kg. The mean ∑16PAHs value of industrial site was ~15 times higher than reference and ~3.5 times higher than flood plain. The observed PAHs concentration of industrial site is far higher than 1,002 μg/kg (∑16PAHs) and 4,628 μg/kg (∑15PAHs) at industrial sites of Tarragona County, Spain (Nadal et al. 2004) and Turkey (Bozlaker et al. 2008), respectively, while the observed PAHs concentration of flood plain soil is lower than that reported by Yang et al. (2008) near Mosel river, Germany (24,280 μg/kg, ∑19PAHs). Spatial variations in ∑16PAHs were highly significant (Table 2) showing the importance of land-use patterns in PAH distributions in soil. The reference site was found to be dominated by low molecular weight (two- and three-ring, LMW) PAHs, which implies lower contributions from anthropogenic activities. On the other hand, predominance of high molecular weight (four-, five- and six-ring, HMW) PAHs are known to indicate the presence of pyrogenic sources (Wang et al. 2007). Soil of site WIA was dominated by HMW PAHs, especially B[a]A, B[k]F, B[a]P, DBA, B[ghi]P and IP, which is the characteristic of industrial soils (Wang et al. 2007). The comparatively lesser concentration of PAHs at site AKS may be due to the fact that large undisturbed agricultural fields are present here. This site is situated downwind of Indraprastha and Rajghat coal fired power plants and high values of Flu, Phen, Anth, Flan, Pyr and B[a]A observed here might possibly indicate some influence of industrial coal combustion, for which these species are known markers (Duval and Friedlander 1981). Seasonal variation of ∑16PAHs were also highly significant (Table 2) and followed a common trend of winter > monsoon > summer at all the sites. Lowest PAH concentrations in summer might be due to a greater degree of volatilization of semi-volatile PAHs (Bozlaker et al. 2008) from the soil and enhanced photochemical

decomposition rates in the atmosphere (Hong et al. 2007; Odabasi et al. 1999; Lee and Tsay 1994) resulting in lesser deposition. On the other hand, dominance of PAHs in winter season could be traced to the increased atmospheric stability, higher emissions (biomass, wood and coal burning), and reduced atmospheric reactivity of PAH compounds (European Commission 2001) leading to higher rates of deposition onto soils. PAHs profile The annual means of the sum of seven carcinogenic PAHs (∑ 7 c arc PAHs) were 112.5, 6,659.4 and 1,032.4 μg/kg for PV, WIA and AKS, respectively. The annual mean of ∑7 carcPAHs of industrial site was ~6 times higher than the flood plain site and ~59 times higher than the reference site. The percentage contributions of ∑7 carcPAHs to ∑16PAHs were 16 %, 61 % and 34 % for sites PV, WIA and AKS, respectively. The ring wise percentage composition of PAHs for different sites is shown in Fig. 2. The percentage contribution of twoand three-ring PAHs to ∑16PAHs at site PV was 65 %. High concentrations of LMW PAHs especially Naph and Acy are indicative of long-range transport (Hautala et al. 1995). At site PV, no six-ring PAHs were detected, which might point to negligible contributions by vehicular sources at this site. The industrial site, on the other hand, was dominated by five- and six-ring PAHs with 44 % and 23 % contributions, respectively, suggesting predominantly local pyrogenic sources. Site AKS was characterized by the dominance of two- and three-ring species with a combined contribution of 49 %, followed by four-ring (19 %), five-ring (19 %) and six-ring (13 %) species. High concentrations of LMW species at this site might again suggest impacts of long-range transport and low-temperature combustion processes while the presence of five- and six-ring species possibly indicates local pyrogenic inputs, presumably vehicular emissions. The PAH profile at this site is, thus, essentially mixed in nature.

Table 2 Results of two-way ANOVA tests on PAHs and trace metal concentrations observed in the present study

Site Season Site×Season NS

∑16PAHs

Zn

Fe

229.6***

94.1***

44.8*** NS

Ni

Cr

Cd

129.3***

130.2***

7.5**

12.3***

6.2**

0.2

14.7***

23.1***

20.3***

3.7**

4.0**

0.1NS

15.0***

23.4***

8.7***

not significant; *p<0.05; **p<0.01; ***p<0.001

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Fig. 2 Ring-wise distribution of PAHs at different sites

Levels and distribution of trace metals The seasonal average trace metal concentrations at each site are summarized in Table 1 while their annual average concentrations are shown in Fig. 3. All metals except Fe showed significant seasonal variation (Table 2). Concentrations of these metals were generally highest in the winter, which suggests that greater emissions in the cold season and near-source deposition of pollutants due to calm atmospheric conditions are important factors controlling their seasonal variation. Metal smelting (Cd, Zn), oil combustion (Ni), coal combustion (Cd, Ni, Zn) and vehicular emissions (Cd, Cr, Zn, Ni) are important sources of these metals (Pacyna and Pacyna 2001; Birmili et al. 2006; Lin et al. 2005). The absence of significant seasonal variation in Fe concentrations is possibly due to the fact that Fe is predominantly crustal and does not have important anthropogenic sources having a strong seasonality. Understandably, all metals exhibited significant spatial variations (Table 2) with highest concentrations at the industrial site. The concentration of Zn was found to be within the Fig. 3 Annual average concentrations of trace metals at the study sites. Concentrations of Cd have been plotted on the secondary axis. Error bars show (±) 1 standard deviation

permissible limit of Indian standards, i.e., 300–600 μg/g (Awashthi 2000). Zinc is very mobile in soil, its range of concentration varied from 62.6 to 870.8 mg/kg for different seasons and different soils in the present study. High concentrations of Ni at the industrial site could be due to electroplating operations, battery manufacture and residual oil combustion in the nearby area (HPA 2008–2009). Cadmium sources in the industrial soil may include alloy making, Ni–Cd batteries, welding and soldering, and electroplating of other metals (HPA 2011). The annual average concentration of Cr was 5591.4 mg/kg for site WIA, 71.3 mg/kg for site AKS and 59.3 mg/kg for site PV. The exceptionally high concentration of Cr at the industrial site is possibly due to the presence of chrome based industries (especially chrome plating) in the vicinity of the sampling locations. The observed concentrations of Cd, Cr and Zn at flood plain site AKS were found to be comparable with values reported by Mehra et al. (1998) (1.3, 59.6 and 100 mg/kg for Cd, Cr and Zn, respectively) at E2 site (downwind of Rajghat and Indraprastha Power plants) which is near site AKS. Also, the N3 site described by Mehra et al. (1998)

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is near site PV and the reported values were comparable with those observed at site PV in this study. The average concentration of Cr, Ni and Zn at site WIA was found to be far higher than those reported from Thane – Belapur Industrial development area, Mumbai, India (Krishna and Govil 2005), i.e., 521.3 mg/kg for Cr, 183.6 mg/kg for Ni and 191.3 mg/kg for Zn. Interspecies correlations Correlation analysis performed between individual PAHs and trace metals are summarized in Tables S1, S2, and S3. Significant correlations between known tracers might indicate presence of a particular source. For example, high correlations between LMW PAHs (Naph, Acy, Acen) might suggest low-temperature combustion processes and/or atmospheric transport and deposition. Certain HMW species (Flu, Anth, Flan, Pyr, B[a]A, Chry) are known markers of coal combustion while certain others (B[b] F, B[k]F, DBA, B[g]P, IP) are considered tracers of vehicular emissions. Associations of these PAHs with corresponding metal tracers might be indicative of specific sources. Results of the analysis suggested that coal/wood combustion and atmospheric transport might be possible sources affecting PV, whereas coal combustion, traffic and industrial sources could be important at AKS and WIA. It is, however, important to mention here that significant correlations do not necessarily imply a common emission source for PAHs and metals since certain sources such as industrial activities involve fuel combustion as well as the use trace metals as processing materials. It should also be stressed at this point that correlation analysis provides only a preliminary understanding of sources that might be affecting a site and inferences thus derived are subject to confirmation by receptor modeling. Source identification Molecular diagnostic ratios of PAHs Molecular diagnostic ratios of PAHs were used for preliminary identification of sources. Combustion processes and release of uncombusted petroleum products are the two main sources of anthropogenic PAHs found in the environment (Yan et al. 2009). The ratios of Anth/Anth+Phen <0.1 indicates petrogenic source and >0.1 indicates combustion source of PAHs (Zhang et al. 2006). On the other hand, Flan/Flan+Pyr ratio <0.4 suggests petrogenic sources

Environ Monit Assess (2014) 186:2907–2923

of PAHs, values >0.5 are the characteristics of grass, wood or coal combustion and ratios between 0.4 and 0.5 are indicative of liquid fossil fuel combustion (Yunker et al. 2002). The ratio of B[a]A/B[a]A+Chry >0.35 suggests PAHs origin by combustion processes and values <0.2 are indicative of petrogenic sources. Values between 0.2 and 0.35 indicate mixed origin. IP/IP+ B[g,h,i]P ratios >0.5 are indicative of grass, wood and coal combustion (Bucheli et al. 2004; MaliszewskaKordybach et al. 2008), ratios <0.2 imply petroleum and between 0.2 and 0.5 indicates combustion of liquid fossil fuel (vehicles and crude oil) (Yunker et al. 2002). The ratios of Flan/Flan+Pyr (0.68 ± 0.05) and Anth/Anth+Phen (0.27±0.09) indicate that grass, wood or coal combustion are the major PAH sources at site PV. Ratios of Anth/Anth+Phen and BaA/BaA+Chry at site WIA were found to be 0.43±0.07 and 0.71±0.03, respectively, which represents pyrogenic and coal, grass and wood combustion sources. The values of Flan/Flan+Pyr and IP/IP+BgP were 0.46±0.04 and 0.34±0.09, respectively, which shows liquid fossil fuel combustion as the major PAH source. At site AKS, the values of Flan/Flan+Pyr (0.65±0.02), Anth/Anth+Phen (0.43±0.05), IP/IP+BgP (0.49±0.05) and BaA/BaA+ Chry (0.48±0.01) indicate pyrogenic and liquid fossil fuel combustion as the main sources of PAHs. Principal component analysis Three factors accounted for 93 % variability in the data at PV (Table 3). Factor 1 accounted for 69.7 % of total variance and was loaded with Naph, Acy, Acen, Flu, Phen, Flan, Pyr, B[a]A, B[a]P, Ni and Fe. High concentration of LMW PAHs might be due to long range transport (Meharg et al. 1998; Yang et al. 1991). Flu, Phen, Flan, Pyr and B[a]A are markers of coal combustion. So, factor 1 seems to represent long range transport and coal combustion sources. Factor 2 accounted for 15.9 % of total variance and was loaded with Anth, Flan, Zn, Ni, Cr and Cd, which might possibly indicate agricultural waste and refuse burning (Samara et al. 1994; Agarwal et al. 2009). Factor 3 explained 7.4 % of variance and was laden with Naph, Acy, Acen, Flu, Flan, BbF, BkF and Fe, which possibly represents a wood combustion source (Khalili et al. 1995). For WIA, four factors accounted for 99.6 % variability in the data. Factor 1 accounted for 51.3 % of the total variance and was highly loaded with Flu, Phen, Anth, Flan, Pyr, B[a]A, Chry, B[a]P and B[k]F. The presence of Phen, Anth, Flan, Pyr, B[a]A, Chry and B[a]P near

Environ Monit Assess (2014) 186:2907–2923

2915

Table 3 Results of principal component analysis (varimax rotation with Kaiser Normalization) at the study sites PV Species

PC1

WIA PC2

PC3

PC1

AKS PC2

PC3

PC4

PC1

Naph

0.69

0.64

Acy

0.84

0.52

Acen

0.83

0.53

Flu

0.76

0.51

0.93

Phen

0.86

0.94

0.98

0.81

0.46

0.94

0.96

0.53

0.58

0.89

Anth Flan

0.53

Pyr

0.94

B[a]A

0.92

0.45

0.8 0.44

0.9

0.36 0.95

0.99

0.95

0.33

0.98 0.92

0.35

0.49

0.95

0.96

0.34

0.59

0.81

0.3

0.95

0.83

0.39

0.41

0.91

DBA

0.97

0.47

0.88

B[g]P

0.95

IP

0.88

B[b]F

0.96 0.44

B[k]F B[a]P

0.84

0.94

Zn

0.39

Fe

0.84

Ni

0.64

0.54

Cr

0.44

0.79

Cd

0.96

0.82 0.45

0.77

PC4

0.95

0.79

Chry

PC3

0.69

0.99 0.37

PC2

0.4

0.98 0.41

0.57

0.51 0.44

0.35

0.53

0.99 0.69

0.93

0.99

0.99

0.43

0.34

0.43

0.52

0.8

0.91

0.94

0.51

0.33

0.82

0.91

0.34 0.32

Eigen values

7.82

4.03

3.96

8.68

5.89

4.37

1.98

8.49

7.23

2.77

2.43

% of variance

45.98

23.72

23.32

41.33

28.03

20.82

9.42

40.41

34.43

13.20

11.57

Cumulative %

45.98

69.71

93.02

41.33

69.36

90.18

99.60

40.41

74.83

88.03

99.60

Only factor loadings ≥0.3 are shown and loadings ≥0.5 are in bold

industrial areas has been previously reported (Nadal et al. 2004). On the other hand, Phen, Anth, Flan, Pyr, B[a]A and Chry are known to be released from coal combustion (Khalili et al. 1995; Pacyna and Pacyna 2001; Lin et al. 2005). So, factor 1 represents coal combustion and industrial sources. Factor 2 accounted for 29.5 % of the total variance and comprised of B[b]F, B[k]F, DBA, B[g]P, IP, Zn and Cd. B[b]F and B[k]F are markers of heavy duty diesel vehicles (Kulkarni and Venkataraman 2000) while DBA, B[g]P and IP are markers of gasoline vehicle emission (Bixiong et al. 2006; Larsen and Baker 2003). Zinc and Cd are also known markers of vehicular emissions. So, Factor 2 clearly represents vehicular emissions. Factor 3 explained 11.4 % of the total variance and was heavily loaded with Naph, Acy, Acen, Cr and Ni. Fresh liquid fuels (petrogenic sources) are usually abundant in low molecular weight PAHs. So, high loadings of

Naph, Acy and Acen might point towards fresh fuel spills. Sources of Ni could be steel and other Ni alloy production and electroplating while Cr could be contributed by chrome industries and metal smelting activities. Factor 3 thus represents industrial sources. Factor 4 accounted 7.2 % of total variance and was loaded with Zn and Fe. The main sources of Zn and Fe are crustal dust, brake-wear and tire-wear particles (Adachi and Tainosho 2004; Birmili et al. 2006).So, factor 4 represents crustal and vehicular sources. Four factors were extracted for AKS, which accounted for 99.6 % variability in the data. Factor 1 accounted for 55.9 % of total variance and was highly loaded with Naph, Flu, Phen, Anth, Flan, Pyr, B[a]A, Chry and Cd. Flu, Phen, Anth, Flan, Pyr, Chry and B[a]A are known markers of coal combustion (Khalili et al. 1995). It is also known that Cd is mainly contributed by coal and fossil

2916

Environ Monit Assess (2014) 186:2907–2923

fuels combustion (HPA 2011; Fishbein 1981). Therefore, factor 1 seems to represent coal combustion as the probable source. Factor 2 explained 24.3 % of total variance and was highly loaded with B[b]F, B[k]F, B[a]P, DBA, B[g]P, IP and Cr, which suggests vehicular emissions as the major source in this case (Kulkarni and Venkataraman 2000; Yang et al. 1998; Harrison et al. 1996; Guo et al. 2003). Factor 3 explained 12.5 % of total variance and was loaded with Zn, Fe and Ni. Both Zn and Fe are important constituents of crustal dust and vehicular abrasion emissions. Diesel oil is an important source of Ni (Fishbein 1981). Factor 4 accounted for 6.7 % of total variance and was loaded with Acy and Acen. These PAHs are known to be transported atmospherically. This factor thus possibly represents the impacts of transported pollutants.

39.9, 3,517.8 and 326.3 μg/kg, respectively. The total B[a]Peq concentration for industrial and flood plain sites were found to be ~88 and ~8 times higher than the reference value. This is especially of concern since a large variety of vegetables that cater to the needs of Delhi are grown in the Yamuna flood plains. The uptake of PAHs by plants has been investigated in many studies (Wild et al. 1992; Voutsa and Samara 1998; Kipopoulou et al. 1999; Jones et al. 1989). Due to their lipophilic nature, PAHs may accumulate in vegetation (Jones et al. 1989; Jones 1991; Wild and Jones 1992). The carcinogenic potency of PAHs was found to be elevated during winter as compared to other seasons at all the sites.

Soil toxicity assessment

The index of geoaccumulation (Igeo) was used to determine the pollution status of soil by comparing the present concentrations with preindustrial levels (Loska et al. 1997, 2002, 2003). It was calculated using the equation

B[a]P-equivalent concentrations To estimate the toxicity potential of PAHs, Benz[a]pyrene–equivalent concentrations (B[a]Peq) were used. Toxic equivalency factors (TEFs) relative to B[a]P as given by Tsai et al. (2004) were used to calculate the B[a]Peq of individual PAHs. The total B[a]Peq concentration was calculated as Total B½aŠPeq ¼

X i

ðC i  TEFi Þ;

Fig. 4 Season-wise total B[a]Peq concentrations (μg/ kg) for three different sites. Also shown are the site-wise annual average values

BaP(eq) concentration (ug/kg)

where Ci is the concentration of an individual PAH and TEFi is the corresponding toxic equivalency factor. Figure 4 shows the season-wise and annual average B[a]Peq concentrations at the sites. The annual average B[a]Peq concentrations of sites PV, WIA and AKS were

Index of geoaccumulation

I geo ¼ log2 ðC n =1:5βn Þ; where Cn is the measured concentration of element n in the examined environment, βn is the measured geochemical background value of element n in average shale (Turekian and Wedephol 1961) and the factor 1.5 is used to compensate for the natural fluctuation in the contents of the given substance in the environment and to adjust for very small anthropogenic influences. Table 4 shows the Igeo values for heavy metals at different sites. Based on Muller (1981) classification, the reference site and the flood plain site falls in the category of

10000

1000 Monsoon Winter

100

Summer Average

10

1 PV

WIA

Sampling Sites

AKS

Environ Monit Assess (2014) 186:2907–2923 Table 4 Geoaccumulation index and enrichment factor values for heavy metals in soil of different sites

Metals

2917

EF

Igeo PV

WIA

AKS

Zn

–0.7±0.3

1.8±0.5

−0.1±0.4

Fe

−2.9±0.2

1.5±0.3

−2.4±0.4

Ni

−1.3±0.6

3.0±1.0

−0.2±0.5

Cr

−1.3±0.5

5.1±1.0

Cd

0.1±1.5

1.8±1.3

PV

WIA

AKS

4.5±0.9

9.9±2.4

5.0±0.5

3.0±1.0

25.4±11.9

4.8±0.9

−1.2±1.0

3.2±1.1

114.2±71.1

2.8±1.9

0.7±1.4

11.9±11.0

12.4±6.9

12.4±11.1

Enrichment factors

"practically uncontaminated" soil for all the studied metals except Cd, which exhibited values pertaining to the category of "uncontaminated to moderately contaminated". The industrial site can be classified as "moderately contaminated", "very heavily contaminated", "moderately to heavily contaminated", and "practically uncontaminated" for Cd and Zn, Cr, Ni, and Fe respectively.

Enrichment factors (EFs) were used to get an idea about the contribution of anthropogenic sources to a particular element by standardizing the examined element in relation to a reference element (Loska et al. 1997). It was calculated by using the formula (Buat-Menard and Chesselet 1979)

EF ¼ ½C n ðsampleÞ=C ref ðsampleފ=½Bn ðbackgroundÞ=Bref ðbackgroundފ;

in this study. Table 4 shows the EF values for heavy metals at different sites. Based on contamination categories associated with calculated EFs given by Sutherland (2000), PV soils can be classified as "moderately enriched" with respect to all the studied metals except Cd, which was "significantly enriched". For WIA, Zn and Cd were found to be "significantly enriched", whereas Ni had "very high enrichment" and Cr had "extremely high enrichment". The high EFs of Cr and Zn at WIA site were comparable

where Cn is the concentration of element n in the examined environment, Cref is the concentration of a reference element in the examined environment, Bn is the concentration of element n in the background environment and Bref is the concentration of a reference element in the background environment. The Fe content of the earth's crust has not been disturbed by anthropogenic activities (Dragovic et al. 2008) and its concentration in the crust shows very low variability. For this reason, Fe was chosen as the reference element Table 5 Parameters used in the incremental lifetime cancer risk assessment

Exposure variable Body weight (kg) −1

Child

Adult

References

15

70

US EPA (1989) US EPA (1991)

Exposure frequency (day year )

350

350

Exposure duration (years)

6

24

US EPA (2001)

Inhalation rate (m3 day−1)

10

20

Wang et al. (2011)

Soil intake rate (mg day−1)

200

100

US EPA (2001)

Dermal exposure area (cm2)

2800

5700

US EPA (2001)

Dermal adherence factor (mg cm−2 h−1) Dermal absorption fraction

0.2

0.07

US EPA (2001)

0.13

0.13

US EPA (2001)

Averaging life span (years)

70×365=25,550

70×365=25,550

US EPA (1989)

Particle Emission factor

1.36×109

1.36×109

US EPA (2001)

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Environ Monit Assess (2014) 186:2907–2923

Table 6 Risk of cancer due to human exposure to PAHs at PV, WIA and AKS Sites

Adult ILCRing

Children ILCRinh

ILCRder

Cancer Risk

ILCRing

ILCRinh

ILCRder

Cancer Risk

PV

1.37E−04

1.06E−08

2.43E−04

3.79E−04

1.91E−04

3.70E−09

2.38E−04

4.29E−04

WIA

1.21E−02

9.35E−07

2.14E−02

3.35E−02

1.68E−02

3.27E−07

2.10E−02

3.78E−02

AKS

1.12E−03

8.68E−08

1.99E−03

3.11E−03

1.56E−03

3.03E−08

1.95E−03

3.51E−03

with the results obtained by Srinivasa et al. (2010) at Jajmau and Unnao industrial areas, India. Dasaram et al. (2011) also reported moderate enrichment of Zn, Ni and Cr at Patancheru industrial area, Hyderabad, India while Yaylali-Abanuz (2011) observed extremely high enrichment of Cd and Cr in soils around the Gebze industrial area in Turkey. EFs for metals such as Zn and Cd at the flood plain site (AKS) were "significantly enriched", whereas Ni and Cr were "moderately enriched". Kaushik et al. (2009) reported similar results for Cr and Cd in Yamuna sediments from Haryana, India. Grygar et al. (2013) also reported enrichments of Cr, Cu, Ni, Zn and Pb in soils from the Jizera floodplain in Czech Republic. Overall, results obtained from EF analyses are similar to those obtained from the analyses of Igeo values. Health risk assessment The age specific potential cancer risks of human exposure to soil PAHs of reference, industrial and flood plain areas of Delhi was assessed using incremental lifetime cancer risk (ILCR) for ingestion, dermal and inhalation exposure (US EPA standard model) (US EPA 1991; Chen and Liao 2006; Wang 2007). Table 5 shows the parameters used in the ILCR assessment. In regulatory Table 7 Reference doses for each element and pathways (Ferreira-Baptista and De Miguel 2005) Metals

Oral RfD

Dermal RfD

Inhal. RfD

Cd

1.00E−03

1.00E−05

1.00E−03

3.00E−03

6.00E−05

2.86E−05

Cd cancer Cr

6.30E+00

Cr cancer Ni

4.20E+01 2.00E−02

5.40E−03

2.00E−02

3.00E−01

6.00E−02

3.00E−01

Ni cancer Zn

Inhal SF

8.40E−01

terms, an ILCR between 10−6 and10−4 indicates potential risk, an ILCR greater than 10−4 denotes potentially high risk and an ILCR of 10−6 or less denotes virtual safety (Liao and Chiang 2006). The result of risk of cancer due to human exposure to PAHs at sites PV, WIA and AKS is shown in Table 6.The ILCR via dermal contact and ingestion pathway ranged between 10−2 and 10−4 at sites PV, WIA and AKS while due to inhalation pathways, it was between10−7 and 10−9. Exposure via inhalation was found negligible when compared with dermal and ingestion pathways, as also found by Wang et.al. (2011). Health risk for children was observed to be greater than that of adults and was mainly contributed by ingestion and dermal routes. In the present study, the total cancer risk was found to be higher than the acceptable level of risk. Calculation of the exposure of humans to metals in reference, industrial and flood plain areas of Delhi was done by the model developed by US Environmental Protection Agency (US EPA 1996). It was assumed that the total non-cancer risk can be calculated for each element by summing the individual risks calculated for all of the three exposure pathways: ingestion, inhalation and dermal while for Cd, Cr and Ni, the carcinogens, the risk through inhalation pathway was considered as total risk. It was assumed that after inhalation the absorption of particle-bound toxicants will result in similar health effects as via ingestion; so, for Cd, Ni and Zn, the toxicity values considered for the inhalation route are corresponding oral reference doses and slope factors (Ferreira-Baptista and De Miguel 2005). Hazard quotient (HQ) or non-carcinogenic health effects were assessed by dividing ADD for each element and exposure pathway by the corresponding reference doses (Table 7). For carcinogens, ADD was multiplied by the corresponding slope factor to yield cancer risk. It was

AKS

WIA

Cd

PV

3.25E−02

Cr

Cr cancer

6.28E−04

6.47E−03

5.02E−04

9.24E−08

9.52E−07

2.22E−07

3.94E−02

2.55E+00

1.51E−03

3.45E−07

9.50E−06

2.35E−03

6.46E−02

4.08E−07

4.18E−04

2.71E−02

2.77E−03

6.03E−08

4.42E−07

1.43E−07

4.10E−04

3.01E−03

9.70E−04

2.23E−03

4.30E−06

3.28E−05

2.06E−04

1.75E−01

1.61E−05

3.27E−04

3.79E−04

1.85E−03

2.80E−06

1.52E−05

1.33E−04

3.53E−02

6.33E−04

6.51E−03

1.71E−03

2.77E+00

2.36E−03

6.49E−02

3.15E−03

2.94E−02

4.13E−04

3.02E−03

1.10E−03

HI=∑HQ

6.03E−07

1.60E−08

1.40E−09

4.73E−05

1.60E−07

2.57E−09

5.02E−07

7.43E−09

8.99E−10

Carcinogenic risk

3.04E−01

5.86E−03

6.04E−02

1.41E−02

2.38E+01

2.19E−02

6.03E−01

2.59E−02

2.53E−01

3.83E−03

2.81E−02

9.06E−03

HQing

HQder

HQing

HQinh

Children

Adult

Zn

Ni cancer

Ni

Cd cancer

Cd

Cr cancer

Cr

Zn

Ni cancer

Ni

Cd cancer

Cd

Cr cancer

Cr

Zn

Ni cancer

Ni

Cd cancer

Metals

Sites

Table 8 Non carcinogenic and carcinogenic risks due to human exposure to metals at PV, WIA and AKS

1.17E−03

2.16E−07

2.22E−06

5.17E−07

9.19E−02

8.05E−07

2.22E−05

9.52E−07

9.75E−04

1.41E−07

1.03E−06

3.33E−07

HQinh

3.64E−03

7.04E−06

5.37E−05

3.38E−04

2.86E−01

2.63E−05

5.36E−04

6.21E−04

3.03E−03

4.59E−06

2.49E−05

2.17E−04

HQder

3.09E−01

5.87E−03

6.05E−02

1.44E−02

2.42E+01

2.19E−02

6.04E−01

2.65E−02

2.57E−01

3.83E−03

2.81E−02

9.27E−03

HI=∑HQ

1.41E−06

3.73E−08

3.26E−09

1.10E−04

3.72E−07

6.00E−09

1.17E−06

1.73E−08

2.10E−09

Carcinogenic risk

Environ Monit Assess (2014) 186:2907–2923 2919

2920

assumed that risks were additive. HQ for each pathway was summed to generate the hazard index (HI). HI <1indicates no significant risk of non-carcinogenic effects, while HI >1indicates a probability of adverse non carcinogenic effects to be caused (US EPA 2001). The result of risk assessment due to metals is shown in Table 8. For non-carcinogenic effects the health risk due to metal exposures is higher in children than in adults with ingestion and dermal routes being the main contributors. HI of Cr was greater than 1 at site WIA and the general trend of HIs for different metals was Cr>Ni>Cd>Zn. The carcinogenic risk levels of Cr, Ni and Cd at all three sites were found less than 10−6 which denotes safe levels except for Cr at site WIA, which showed a risk between 10−6 and 10−4 As with HIs, the carcinogenic risks for children were found to be higher than those for adults.

Conclusions Industrial and flood plain soils in Delhi showed ~15 times and ~4 times, respectively, higher PAHs contamination than a reference site, while corresponding carcinogenic potencies of PAHs were found to be ~88 and ~8 times higher, respectively. All trace metals exhibited highest concentrations at the industrial site and lowest at the reference site. PAHs and trace metals exhibited strong seasonal and spatial variations. The use of correlation analysis, PAH isomer pair ratios and ultimately PCA led to the identification of coal combustion, industrial, vehicular, atmospheric transport and biomass combustion sources of the target pollutants. The industrial soil was found to be highly contaminated with Ni and Cr, and to a lesser extent, by Zn and Cd. Floodplain and reference soils were moderately enriched with the target metals; however, the accumulation was not significant. Both flood plain and industrial area were found to have ILCR >10−4, denoting potentially high risk. For non cancer risk, the HIs for adult and children at the sites decreased as follows: Cr>Ni>Cd>Zn. The carcinogenic risk levels of Cr, Ni and Cd at all three sites were at the safe level except for Cr at the industrial site. Overall, this study establishes a baseline and provides the first indications of the interrelationships between PAHs and trace metals in Delhi soils and the sources impacting them.

Environ Monit Assess (2014) 186:2907–2923 Acknowledgments The authors gratefully acknowledge the anonymous reviewers for their comments and suggestions to improve the manuscript.

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