Polycyclic Aromatic Hydrocarbons in PM 2.5 and PM10 From Industrial Area of Odisha, India: Sources, Atmospheric Transport and Health Risk Assessment

In this study we aim to assess 16 priority PAHs enlisted by the US Environmental Protection Agency in PM 2.5 and PM 10 for the rst time from industrial areas of Odisha State in India. During 2017–2018, bimonthly sampling of PM 10 and PM 2.5 were carried out for 24 hours by respirable dust sampler and PM 2.5 sampler respectively, in the industrial and mining areas of Jharsuguda (n = 2) and Angul (n = 4) during the pre-monsoon, monsoon and post monsoonal seasons. Highest average concentration of ∑ 16 PAHs in PM 2.5 was observed during post monsoon (170 ng/m 3 ) followed by pre-monsoon (17–89 ng/m 3 ; avg, 48 ng/m 3 ) and monsoonal season (2–40 ng/m 3 ; avg, 16 ng/m 3 ), respectively. Similar trend of ∑ 16 PAHs levels in PM 10 was seen with higher levels during post monsoon (116–471 ng/m 3 ; avg, 286 ng/m 3 ) followed by pre-monsoon (avg, 81 ng/m 3 ) and monsoon seasons (27 ng/m 3 . Diagnostic ratios BaA/(BaA + Chry), Phe/(Phe + Ant) and Flt/(Flt + Pyr) and principal component analysis (PCA) suggest diesel, gasoline and coal combustion are the major contributors for atmospheric PAHs pollution in Odisha. Back trajectories analysis revealed that PAHs concentration was affected majorly by air masses originating from the northwest direction traversing through central India. Toxic equivalents (TEQs) ranged between 0.24 to 94.13 ng TEQ/m 3 . In our study incremental lifetime cancer risk (ILCR) ranged between 10 − 5 and 10 − 3 representing potential cancer risk.


Introduction
Polycyclic aromatic hydrocarbons (PAHs) are of major concern due to their carcinogenicity, genotoxicity and ubiquitous nature. PAHs can be majorly formed during incomplete combustion (pyrolysis) or high temperature pyrolytic processes of organic materials and combustion of fossil fuels (Chen et al., 2007).
They are pervasive environmental pollutants that are characterized by their hazardous carcinogenic and mutagenic potential (Carreras et al., 2013;McGrath et al., 2007). PAHs have received increased attention in recent years due to their diverse sources and their ubiquitous presence in all the environmental components (air, soil, and water) not only in developing but also in developed countries. The primary sources of PAHs are of anthropogenic origin viz., motor vehicle exhaust, petroleum re neries, heating in power plants, combustion of refuse, deposition from sewage, oil/gasoline spills, tobacco smoke, barbeque smoke and coke production (Christensen and Bzdusek, 2005; Moon et al., 2006). The US Environmental Protection Agency (USEPA) published a list of 16 priority PAHs in 1995. This list was expanded in 2008 to 28 priority compounds that present a serious hazard for human health (Ravindra et al., 2008). Benzo(a)pyrene (5-ring PAH) is the most commonly measured PAHs and is used as an indicator of carcinogenic hazard in polluted environments. Moreover PAHs with a larger number of aromatic rings are mostly bound to particulate matter associated with urban emissions (Possanzini et al., 2004). With the rapid social and economic development over the past several decades, air pollution due to PAHs has been both serious and widespread in India. The highest concentrations of atmospheric PAHs can be found in urban environments due to increasing vehicular tra c, coal combustion for power generation and low dispersion of the atmospheric pollutants (Caricchia et al., 1999). PM 10 and PM 2.5 are 25 to 100 times thinner than a human hair and can travel into the respiratory tract, penetrate deep into the lungs and even into the blood stream and cause severe health damage. Research shows that every 10 µg/m 3 increase in PM 2.5 , increases all-cause mortality between 3-26 %, chances of childhood asthma by 16 %, chances of lung cancer by 36% and heart attacks by 44 % (Airveda, 2017).
The state of Odisha has a tropical climate, characterized by high temperature and humidity, medium to high rainfall and mild winters. Serious air pollution in the industrial areas of Odisha over the past decade has attracted much attention. In India, studies were mainly carried out in large cities but no detailed study has been reported from Odisha despite the fact that the city is surrounded by multifarious industries of small, medium and large scales along with several coal mines. Hence, in the year 2017-2018 we took the rst attempt to monitor atmospheric PAHs in PM 2.5 and PM 10 in the industrial cities in the state of Odisha and the major objectives of this study were to (i) monitor 16 USEPA enlisted priority PAHs in two major industrial areas of Odisha viz., Angul and Jharsuguda during, summer or pre-monsoon (March -May), monsoon (June -September) and winter or post-monsoon (October -January) (ii) identify the probable sources by applying principal component analysis (PCA) and diagnostic ratios, (iii) identify the origin of air mass by Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) Model's back-trajectory analysis (iv) assess the potential health risk posed by particulate-bound PAHs using USEPA health risk assessment model.

Sample collection
During all the seasons from March 2017 to January 2018 i.e., summer or pre-monsoon (March -May), monsoon (June -September) and winter or post -monsoon (October -January), twice in each season PM 2.5 and PM 10 sampling were conducted at Angul (from four substations) and Jharsuguda (from two substations), in the state of Odisha, India (Fig. 1). A total of 36 PM 2.5 samples and 108 PM 10 samples were collected during this sampling campaign. From Angul-Talcher, 24 PM 2.5 and 72 PM 10 samples were collected (for six times 3 samples were collected from each location of 4 sub-stations). From Jharsuguda, 12 PM 2.5 and 36 PM 10 samples (twice 3 samples were collected from each location of 2 substations) were collected. Details of sampling locations are given in Table S1 of supporting information (SI). The PM 2.5 samples were collected using ne dust sampler (Envirotech APM − 550) which operated at a ow rate of 16.67 L/min for 24 h to collect particle bound PAHs in PTFE Filter paper. PM 10 sampler (Envirotech, APM 460 NL, India) was used with a ow of 0.9-1.1 L/min to collect particle bound PAHs in 20.3 x 25.4 cm glass ber lter (EPM 2000). Each sample for PM 10 was collected in three shifts (8 Hourly basis) in 24 h to avoid pressure drop due to loading of particulate matter on lter paper After 24 hours (h), the samples were taken and wrapped with aluminum foil and stored in desiccators.
The sample lters were stabilized in a temperature and humidity-controlled incubator before and after collection at 25 ± 1°C and 52 ± 1 % relative humidity for 24 h.. All the lters were weighed using an electronic microbalance (Sartorius T-114) before analysis. Filter papers wrapped in aluminium foils and stored at -20°C prior to analysis. Filter papers were desiccated for 24 h before taking initial weight prior to the sampling. In the same manner nal weight for lter papers were taken after sample collection.

Sample extraction and clean up
Exposed lter paper was cut into small pieces in a 250 mL beaker. Ultrasonic extraction was conducted using 100 mL of toluene and was repeated for three times. The extracted samples were then ltered using Whatman lter paper and were pooled together. The pooled extracts were reduced to ~ 1mL using rotary evaporator with water bath (temp below 40 0 C).
Clean-up was performed using silica gel column having length of 200 mm and inner diameter (ID) of 0.5 cm. Slurry of 3g deactivated silica gel (60-100 mesh size) in cyclohexane was poured into the column.
Conditioning was performed using toluene followed by cyclohexane. Samples were passed drop-wise and eluted using cyclohexane. Further, 30 mL of cyclohexane were added to the column to elute all organics of interest. Pooled samples were reduced to 1 mL and store in a dark and cool place.

Instrumental analysis
Sixteen priority PAHs were analysed using Agilent 7820A gas chromatograph coupled with Agilent 19091, J-413, 325 0 C capillary column (30 m × 0.32 mm × 0.25µm). 2 µL of each sample was injected in splitless mode. High purity 99.999% nitrogen was used as the carrier gas, with a ow rate of 1 mL/min. The temperature of the injector and transfer lines were 250 0 C and 300 0 C respectively. The initial oven temperature was set at 120 0 C for 2 min, increased to 300 0 C at a rate of 7 0 C/min and then maintained for 10 min. The concentrations of 16 PAHs were quanti ed according to their elution orders as follows;

Quality assurance and control
The analytical method was based on the USEPA Method TO-13. Field blanks, lter blanks and solvent blanks were analyzed by the same procedure as the samples and it was ensured that there were no signi cant background interferences. The quanti cations were performed using the internal standard method. For quality control check SRM urban dust No 1649a was used to check recovery. Recovery % was between 75-130 % and is presented in details in SI Table S2

Cancer Risk Assessment
Incremental lifetime cancer risk (ILCR) exposure to carcinogenic PAHs (BaA, Chry, BkF, BbF, BaP, Ind, and DbA) were estimated by using the lifetime average daily dose (LADD) and the cancer slope factor (CSF).
The LADD is the intake quantity of a known pollutant with a potential to cause adverse health effects when absorbed into the body over a period of time (Jamhari et al., 2014). In this study, the LADD and the ILCR were computed for infants (0-1 year), children (2-5 years), children (6-12 years), and adults (19-75 years). The LADDs through the inhalation (LADD inh ), ingestion (LADD ing ), and dermal (LADD derm ) pathways were estimated using where C = concentration of PAHs (ng/m 3 ); ED = exposure duration (days); BW = body weight of the exposed group (kg); AT = averaging time (days), ET = exposure time (h/day); IngR = ingestion rate (mg/day); InhR = inhalation rate (m 3 /day); SA = surface area of the skin exposed to pollutants (cm 2 ); AF = skin adherence factor (mg/cm 2 /day); ABS = dermal absorption factor; EF = exposure frequency (days/year); CSF = cancer slope factor (mg − 1 kg day) and CF = unit conversion factor (C = 10 − 6 ). The values of these parameters are taken from a previous study (Morakinyo et (Table 1). In both sites, the overall trend of PAHs pollution was observed as post monsoon > pre monsoon > monsoon (SI Table S4 and S5). Concentration of ∑ 16 PAHs in Odisha during post monsoon was 3 folds higher than pre monsoon and 10 folds higher than monsoon. PM 2.5 bound PAHs were signi cantly different (p < 0.05) between three seasons (SI Table S8 ). Furthermore, signi cant difference of individual PAHs between different seasons were observed in all the stations (p < 0.05).The overall mean concentration for all the seasons for ∑ 16 PAHs in PM 2.5 in industrial regions of Odisha was slightly lower than Zhengzhou  (Table S6). Overall range of ∑ 16 PAHs in PM 10 (Table S7).

Seasonality and back trajectory analysis
HYSPLIT back trajectories analysis were performed over both Angul and Jharsuguda (Fig. 2)  Ocean and Arabian Sea. Interestingly, Cluster 2 and 3 together constituted less than 10 % of the total PAHs and carcinogenic PAHs in both PM 2.5 and PM 10 . Thus, this cluster was affected mostly by localized emission sources from 12 hours journey over Odisha. This hypothesis has been further supported by wind rose showing the exact wind direction (Fig. 2b). Between 4 to 9 % frequency of highspeed wind were coming between North-West and North. Winds with a speed of 10-15 m/s were coming from the South and South-West directions. Figure 2c shows Cluster 1, which contributed about one third of total back trajectories that came from Arabian Sea via Maharashtra and Chhattisgarh during the winter season and traversed from west and from a height below 500 m AGL.
Over Jharsuguda, wind rose showed 10 m/s to > 15 m/s winds (with 1.6-6.4 % frequency) from the west (Fig. 2d). Over Jharsuguda, most of the trajectories (Cluster 2) arose from the industrial regions of Indo-Gangetic plain and we suspect the possibility of long range atmospheric transport from such emission regions. Thus, this cluster can be associated with a mixer of long-range transport and local pollution sources mainly from vehicular and industrial sources. Cluster 2 (50 %) was traversing during speci c dates (21st March, 21st November, 21st December) during winter and pre-monsoon seasons of 2017 originating from north and North-West along the Indo -Gangetic plain (Fig. 2e). These months constituted nearly 80 to 85 % of total PAHs and carcinogenic PAHs in PM 2.5 and PM 10 . It originated from the Arabian Sea and crossed over the states, Maharashtra and Chhattisgarh for 3 days before ending in this sampling site. Wind rose indicates high wind speed coming from North and North-West directions (Fig. 2b). In 2017, on 26th May, the 3rd cluster (17 %) originating from south and south-west i.e. the Bay of Bengal and can be used to track local sources pollution especially from vehicles and local industries. The maximum transfer of PAHs air parcel was observed during the winter season (November, December) followed by pre-monsoon (March) over both Angul and Jharsuguda sites. This winter season atmospheric transport might be caused by western disturbance, which brings the pollutant from industrial areas of Indo-Gangetic plains to the study area.

Source apportionment
PAHs can be classi ed by the number of aromatic rings such as two rings (Nap), three rings (Acy, Ace, Flu,  (Table S4) and Angul (Table S5).
PAHs have been used as tracers to distinguish between diverse sources (Lodovici et al., 2003;Vasconcellos et al., 2003). For the source apportionment, various diagnostic ratios were combined with principal component analysis to arrive at a suitable source type for a speci c group of PAHs. Diagnostic ratios of PAHs are usually an effective way to identify sources because they exhibit the characteristics of speci c sources, but they should be used carefully because some of them are variable in different ambient conditions due to the reactivity of some PAH species, such as the photolytic decomposition of BaP ( (Table S14) and Angul (Table S15) for different seasons. Figure 4 shows distribution of total PAHs and carcinogenic PAHs for different seasons.

Inhalation Risk
Page 14/23 The estimated LADD values of carcinogenic PAHs in PM2.5 and PM 10 for different age groups are presented in the Fig. 5. It can be observed from the gure that during the post monsoon season ILCR was higher in both PM 2.5 and PM 10 ( Fig. 5)  Angul. During the post monsoon season ILCR was high in both PM 2.5 and PM 10 across all age groups.
The risk was highest in children in the age group of 2-4 years. In our study ILCR for both PM 2.5 and PM 10 ranged between 10 − 5 and 10 − 3 representing potential cancer risk to signi cant cancer risk.  territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.  SupportingInformation25012021PC.doc