Street Dust—Bound Polycyclic Aromatic Hydrocarbons in a Saudi Coastal City: Status, Profile, Sources, and Human Health Risk Assessment

Polycyclic aromatic hydrocarbons (PAHs) in street dust pose a serious problem threatening both the environment and human health. Street dust samples were collected from five different land use patterns (traffic areas TRA, urban area URA, residential areas REA, mixed residential commercial areas MCRA and suburban areas SUA) in Jeddah, a Saudi coastal city, and one in in Hada Al Sham, a rural area (RUA). This study aimed to investigate the status, profile, sources of PAHs and estimate their human health risk. The results revealed an average concentration of total PAHs of 3320 ng/g in street dust of Jeddah and 223 ng/g in RUA dust. PAHs with high molecular weight represented 83.38% of total PAHs in street dust of Jeddah, while the carcinogenic PAH compounds accounted 57.84%. The highest average concentration of total PAHs in street dust of Jeddah was found in TRA (4980 ng/g) and the lowest in REA (1660 ng/g). PAHs ratios indicated that the principal source of PAHs in street dust of Jeddah is pyrogenic, mainly traffic emission. Benzo(a)anthracene/chrysene (BaA/CHR) ratio suggests that PAHs in street dusts of Jeddah come mainly from emission of local sources, while PAHs in RUA might be transported from the surrounding urban areas. The estimated Incremental Lifetime Cancer Risk (ILCR) associated with exposure to PAHs in street dusts indicated that both dermal contact and ingestion pathways are major contributed to cancer risk for both children and adults. Based on BaPequivalence concentrations of total PAHs, ILCRIngestion, ILCRdermal and cancer risk values for children and adults exposed to PAHs in street dust of different areas in Jeddah were found between 10−6 and 10−4, indicating potential risk. The sequence of cancer risk was TRA > URA > MCRA > SUA > REA. Only exposure to BaP and DBA compounds had potential risk for both children and adults.


Introduction
Surface street dust particles are considered to be one of the most important sources of fine aerosols in urban atmospheres and can become easily airborne through wind dispersion [1][2][3]. Atmospheric aerosols and their contaminants from anthropogenic sources finally settle on the surfaces by atmospheric dry and/or wet deposition, and are then transferred to the surface of the soil or incorporated into the surface dusts. The chemical contents of the surface road dust is related to atmospheric particulate content and their chemical composition in both road dust and airborne particulate are similar [4]. Vehicle exhaust, tire dust, spillages and leaks from vehicles, road surface erosion material and vegetative plant fragments, garden soil, and litter are the sources of deposited

Sample Collection
Gentle sweeping motions using plastic brushes and dustpans were used to collect the surface street dust samples, especially fine dust [54]. A total of 87 surface street dust samples were collected from five different land use patterns in Jeddah and a rural area in Hada Al Sham. Street dust samples were collected during September 2017 on weekdays. Approximately 300 gm of surface street dust on impenetrable surfaces of the paved roads among 8-m radius circle were collected from each land use type. Brushes and dustpans were cleaned after each sampling. Bags, wrapped with solvent (nhexane)-rinsed aluminum foil, were used to store the collected street dust samples. They were sealed in polyethylene bags and transported to the lab. The samples were set in a desiccator to remove wetness. The coarse impurities of the samples such as cigarette buts, small gravel, plastic waste, metal scraps, and broken construction debris were removed using 1.0 mm mesh nylon sieves. Then, the remaining part of the sample was homogenized, sieved through a <63 µm particle size sieve and stored in small self-sealing plastic bags in a refrigerator until analysis.

Sample Collection
Gentle sweeping motions using plastic brushes and dustpans were used to collect the surface street dust samples, especially fine dust [54]. A total of 87 surface street dust samples were collected from five different land use patterns in Jeddah and a rural area in Hada Al Sham. Street dust samples were collected during September 2017 on weekdays. Approximately 300 gm of surface street dust on impenetrable surfaces of the paved roads among 8-m radius circle were collected from each land use type. Brushes and dustpans were cleaned after each sampling. Bags, wrapped with solvent (n-hexane)-rinsed aluminum foil, were used to store the collected street dust samples. They were sealed in polyethylene bags and transported to the lab. The samples were set in a desiccator to remove wetness. The coarse impurities of the samples such as cigarette buts, small gravel, plastic waste, metal scraps, and broken construction debris were removed using 1.0 mm mesh nylon sieves. Then, the remaining part of the sample was homogenized, sieved through a <63 µm particle size sieve and stored in small self-sealing plastic bags in a refrigerator until analysis.

Extraction of PAHs
A known weight (2 gm) of the surface street dust samples were Soxhlet extracted for 16 h [55]. A mixture of acetone/dichloromethane/n-hexane (1:1:1, v/v/v) was used for extraction. The extracted organic part was concentrated using a rotary evaporator, and cleaned-up according to Park et al. [56]. The collected eluent from the clean-up procedure was concentrated and exchanged to 1 ml hexane and stored frozen (−10 • C) until analysis.

Analysis of PAHs
Gas chromatography (GC)/flame ionization detector (FID) was used for determination the concentration of PAH compounds, using PAH standards. One microliter (µL) of extract was withdrawn from the samples, including blanks, and injected into a Hewlett-Packard (HP6890, Agilent, Santa Clara, CA, USA) gas chromatograph (GC), fitted with a flame ionization detector (FID). A HP-5 capillary column was used with hydrogen as carrier gas. The concentrations of the target PAH compounds were quantified by an external standard solution of 15 PAH compounds (PAH mixture, Supelco, Inc., St. Louis, MO, USA). To check the reliability of the obtained results, Quality assurance/quality control (QA/QC) including reagent blanks, analytical standards, standard spike recoveries, GC/FID calibration and detection limits were employed. Based on the drift in retention times and responses of PAH compounds in the standard calibration mixture injection, the GC/FID was checked daily. PAH mixture standards contained 15 compounds (Supelco, Inc., St. Louis, MO, USA) were used for preparation of the calibration curve to quantify the concentrations of the target PAH compounds. For all measured PAHs, the relative standard deviation of the replicated analyses of the calibration standard ranged from 4% to 6%. The average recovery of each PAH ranged from 70% to 108% for the 15 measured PAH compounds. The detection limit of each PAH compounds ranged from 0.048 ng/g to 0.376 ng/g.

Carcinogenic Potency of PAHs (BaP equi )
According to the TEFs proposed by Nisbet and LaGoy [64], the quantities of carcinogenic potency of PAH compounds in the surface street dust were calculated as benzo(a)pyrene equivalence (BaP equi ). The reference chemical was BaP, the most toxic PAH and was assigned a value of one [68,69]. BaP equi was calculated by using the following equation: where, C is the concentration of individual PAH compounds; TEF is the corresponding individual equivalency factor for PAH compounds [64]. Then, the cancer potency of the total PAHs in the surface street dust was estimated by the summation of calculated cancer potency relative to BaP for all PAHs.

Carcinogenic PAHs (CPAHs) Determination
According to the International Agency for Research on Cancer [70] and USEPA [71], carcinogenic PAH compounds (CPAHs) of the 15 PAHs examined in this study are BaA + CRY + BbF + BaP + DBA + IND. The CPAHs was calculated as the percentage composition of carcinogenic PAHs to other PAHs [14].

Incremental Lifetime Cancer Risk (ILCR)
To evaluate the health risk assessment for children and adults exposed to PAHs in surface street dust, the USEPA standard models (residential scenario) [8,44,[65][66][67] were used. Local residents are exposed to PAHs in the surface street dust through three main exposure pathways including: (1) direct ingestion, (2) inhalation through mouth and nose, and (3) dermal absorption. The carcinogenic risk was calculated for each PAH compounds in street dust by the summation of the individual risks calculated for the three exposure pathways. The cancer risk for total PAHs carcinogenic risk was computed by summing the individual PAH risks for each PAH compounds for the three exposure pathways. BaP equi was used for risk assessment calculation. ILCR in terms of inhalation, dermal contact and direct ingestion was calculated based on the following equations: 6 (2) Carcinogenic risk = ILCR ingestion + ILCR inhalation + ILCR dermal (5) where the ILCR is incremental lifetime cancer risk, CS the concentration of the PAH compounds in surface street dust based on toxic equivalent of BaP using the TEF, CSF the carcinogenic slope factor (mg/kg/day), BW the body weight (kg), AT the average life span (years), EF the exposure frequency (day/year), ED the exposure duration (years), IR Inhalation the inhalation rate (m 3 /day), IR Ingestion the soil intake rate (mg/day), SA the dermal surface exposure (cm 2 ), AF the dermal adherence factor (mg/cm 2 /h), ABS the dermal adsorption fraction and PEF the particle emission factor (m 3 /kg). PEF is the particle emission factor (m 3 /kg) [8,44,67]. The detailed description about the values of exposure factors for children and adults applied to the above models (Equations (2)-(4)) in the present study are given in Table 1.

Concentration of PAH Compounds in Surface Street Dusts
The average concentrations of the individual and total PAH compounds in the surface street dusts collected from the different land use pattern of Jeddah and a rural area of Hada Al Sham are shown in Figure S1. For the street dust of Jeddah, the average concentrations of the individual PAH compounds in descending order were BbF > BGP > CRY > DBA > BaP > BaA > FLT > IND > PYR > PHE > ANT > ACE > FLU > NA > ACY ( Figure S1a). The concentration values ranged from 81.44 ng/g (ACY) to 410.00 ng/g (BbF). Figure S1b shows the average concentrations of different categories of PAH compounds based on aromatic ring number. PAHs with five aromatic rings represented the highest levels in surface street dust of Jeddah. The average concentrations were 1051.30 ng/g for five aromatic rings, 1040.20 ng/g for four aromatic rings, 643.74 ng/g for six aromatic rings, 502.32 ng/g for three aromatic rings and 83.28 ng/g for two aromatic rings. Meanwhile, PAH compounds with five aromatic rings showed the highest concentration (95.10 ng/g) followed by six aromatic rings (55.00 ng/g), four aromatic rings (53.60 ng/g), three aromatic rings (17.05 ng/g) and two aromatic rings (2.20 ng/g) in surface street dust of RUA. PAHs, respectively. This indicates that the PAH compounds in the street dust might be derived mainly from anthropogenic sources and they tend to accumulate in surface street dust particles that can be used as indicator of environmental pollution in urban areas [8,11,13,44].
The wide variations of PAHs concentrations in street dust of urban areas arise from the different characteristics of the sampling areas such as location, traffic density, and type of vehicle. The spatial variations of the individual and total PAHs concentrations in surface street dusts from different land use patterns of Jeddah are shown in Table 2. The individual and total PAHs concentration levels showed variation with different land use pattern. The highest concentrations of the individual PAH compounds in surface street dust were found in TRA, and the lowest levels in REA (Table 2). Moreover, the highest concentrations of total PAHs were found in TRA (4980 ng/g) followed by URA (4150 ng/g), MCRA (3320 ng/g), SUA (2490 ng/g) and REA (1660 ng/g) ( Table 2). The observed high values of the PAH compounds in the surface street dust in TRA indicate that the TRA areas may be a reservoir of PAH compounds arising from heavy traffics and human activities, since TRA in Jeddah cover major highway, parking areas, roundabout and crossroads with the highest traffic volumes. Anthropogenic activities contribute to PAHs accumulation in road dust [82]. Concerning road dusts from city centres, vehicle exhausts is the major source of pyrogenic PAHs [3,79,83]. Traffic exhausts, tire wear, resuspended soils dust, asphalt, and power plants are the main sources of PAH compounds in urban areas [84][85][86]. The minimum level of PAH compounds in the present study was found in REA. This might be due to its land use type and low anthropogenic activities [8]. Generally, the spatial variations of the concentrations of PAH compounds in different land use types might be attributed to the distinctive artificial activities in each land use type that emit PAH compounds deposited in the surface street dust.

Profile of PAH Compounds in Surface Street Dust
The relative contribution of the individual PAH compounds to the total PAHs concentrations in surface street dust of MCRA, REA, TRA, URA and SUA, were nearly similar. Generally, they increased with increasing molecular weight of PAH compounds. BbF, BGP, CRY, DBA and BaP showed relatively higher contribution, while NA, ACY, ACE and FLU were the least contributing. This similarity in contribution of the individual PAH compounds indicates that the study areas do share a common source of vehicle emission [11,87]. Figure 2 shows the relative contribution of each individual PAH compound and different categories of PAHs based on aromatic ring number to the total PAHs concentrations in street dusts collected from all areas of Jeddah city and rural area. PAH compounds with four and six aromatic rings were the dominant in the surface street dust of Jeddah. The contribution of high molecular weight (HMW)-PAHs (four to six aromatic rings) (82.40%) was higher than that of low molecular weight (LMW) ones (two to three aromatic rings) (17.60%). This indicates the tendency of HMW-PAHs to adhere to street dust [11]. Moreover, the high contribution of HMW-PAHs suggests that they mostly come from pyrogenic sources [88] such as petroleum fuels combustion [4] and vehicular emissions [75]. The PAHs speciation in gasoline vehicle soot is enriched by HMW PAHs [78].

Profile of PAH Compounds in Surface Street Dust
The relative contribution of the individual PAH compounds to the total PAHs concentrations in surface street dust of MCRA, REA, TRA, URA and SUA, were nearly similar. Generally, they increased with increasing molecular weight of PAH compounds. BbF, BGP, CRY, DBA and BaP showed relatively higher contribution, while NA, ACY, ACE and FLU were the least contributing. This similarity in contribution of the individual PAH compounds indicates that the study areas do share a common source of vehicle emission [11,87]. Figure 2 shows the relative contribution of each individual PAH compound and different categories of PAHs based on aromatic ring number to the total PAHs concentrations in street dusts collected from all areas of Jeddah city and rural area. PAH compounds with four and six aromatic rings were the dominant in the surface street dust of Jeddah. The contribution of high molecular weight (HMW)-PAHs (four to six aromatic rings) (82.40%) was higher than that of low molecular weight (LMW) ones (two to three aromatic rings) (17.60%). This indicates the tendency of HMW-PAHs to adhere to street dust [11]. Moreover, the high contribution of HMW-PAHs suggests that they mostly come from pyrogenic sources [88] such as petroleum fuels combustion [4] and vehicular emissions [75]. The PAHs speciation in gasoline vehicle soot is enriched by HMW PAHs [78].  In surface street dust of RUA, the relative contribution of the individual PAH compounds to the total PAHs concentrations indicated that BbF, CRY, BGP, DBA, INSD and BaP were the predominant (Figure 2a). Based on aromatic ring number of PAH compounds, PAHs with five aromatic rings were the dominant (42.60%), followed by six aromatic rings (24.70%), four aromatic rings (24.03%), three aromatic rings (7.60%) and two aromatic rings (0.99%) (Figure 2b). High contribution of HMW-PAHs to the total PAHs concentrations in RUA suggests that PAHs mostly come from pyrogenic sources, which means that the rural background area received PAHs from the surrounding areas and predominantly was related to the traffic emissions. RUA at Hada Al Sham is far from traffic density. Therefore, the measured concentrations of PAHs in this rural area might result from the diffusion and dispersion of PAHs produced from the traffic density in the surrounding areas. Lee et al. [89] reported that high carbon content and more PAHs adsorbed in the young aerosol are emitted by the automobile exhaust. They added that the PAHs shift from the particle phase to gas phase in order to reach thermodynamic equilibrium during the transportation process from traffic to rural atmosphere. In the present study, the contribution of LMW-PAHs to the total PAHs concentrations in surface street dust of Jeddah (17.64%) was higher than that found in surface street dust of RUA (8.59%). This indicates that the time required for the transportation of the PAHs allows significant decrease the LMW-PAHs concentrations in particulate phase, and consequently their contribution to the total PAHs concentrations in street dust of the RUA decreased.

Possible Sources of PAH Compounds in Surface Street Dust
To distinguish between both sources, LMW-PAHs/HMW-PAHs, ANT/(ANT + PHE), BaA/(BaA + CRY), FLU/(FLU+ PYR), IND/(IND + BGP), PHE/ANT and FLT/PYR concentration ratios are used. A LMW-PAHs/HMW-PAHs ratio > 1 indicates petrogenic source, while the ratio < 1 refers to pyrogenic sources [24]. An ANT/(ANT + PHE) ratio < 0.1 reflects a petroleum sources, while a ratio > 0.1 suggests a combustion source [62]. The ratios of PHE/ANT < 10 and FLT/PYR > 1.00 indicate that PAH compounds are emitted from pyrogenic source, while the ratios PHE/ANT > 15.00 and FLT/PYR < 1.00 suggest petrogenic origins of PAH compounds [90]. Similarly, Flu/(Flu + PYR) ratio < 0.4 indicates a petroleum source, ratios between 0.4 and 0.5 reveal a liquid fossil fuel combustion source, and a ratio > 0.5 characterizes biomass and coal combustion [62]. To identify the traffic sources, IND/BGP, BaA/CRY and BaP/BGP concentration ratios are used. The IND/BGP ratio for gasoline engines is about 0.40 and approaches 1.00 for diesel engine [91]. BaA/CRY concentration ratios range from 0.28 to 1.20 for gasoline engines and from 0.17 to 0.36 for diesel engines [25,92]. BaP/BGP concentration ratios higher than 0.60 also refer to the presence of traffic emissions [93]. IND/(IND + BGP) and BaA/(BaA + CRY) ratios are used to characterize the nature of potential PAH emission sources [62]. Ratios of IND/(IND + BGP) < 0.2 and BaA/(BaA + CRY < 0.2 indicate petroleum and petrogenic sources, respectively. BaA/(BaA + CRY) ratios between 0.2-0.35 and IND/(IND + BGP) ratios between 0.2-0.5 suggest that PAHs originate from petroleum combustion. To assess the presence of PAHs from fossil fuels inputs, ANT/ (ANT + PHE) concentration ratio is used [62]: ANT/ (ANT + PHE) concentration ratios < 0.1 suggest non-burned fossil fuel inputs, while the combustion sources may prevail if the ratios are > 0.1. Figure 3  PAHs concentrations in surface street dust can be influenced not only by local sources but also by long-distance transport sources. The ratio of a more reactive PAH to less reactive PAH can be used to give information about the photochemical degradation of PAH compounds and the aging of air mass [94,95]. BaA photodegradation is very fast and easier than its isomer CRY during their transportation [14,96], To estimate the distance of potential PAHs sources, BaA/CRY ratio is used as a diagnostic indicator to assess the origin of PAH compounds. A lower BaA/CRY ratio due to the photodegradation and oxidized degradation of most BaA means that the PAHs sources may be far away from the urban areas, whereas a higher ratio suggests that those PAHs might emit mostly from local sources [97]. away from the urban areas, whereas a higher ratio suggests that those PAHs might emit mostly from local sources [97]. Lohmann et al. [94] reported that a BaA/CRY ratio higher than 0.40 suggests that the PAHs pollution is freshly emitted and photochemical processing of the air mass is relatively lower, whereas a BaA/CRY ratio lower than 0.40 indicates that the major sources of PAHs are not local or the air masses are aged. In the present study, the mean concentration ratios of BaA/CRY were 0.75 in MCRA, 0.81 in REA, 0.71 in TRA, 0.72 in URA and 0.86 in SUA (Figure 3), which suggest that PAHs in street dusts of Jeddah come mainly from emission of local sources and the air masses are not aged. Liu et al. [4] reported that the BaA/CRY ratios of Shanghai road dust ranged from 0.6-1.4, which indicate that Shanghai might be close to its potential sources of dusts. On the other hand, the BaA/CRY ratio in the present study was 0.30 in RUA (Figure 3). This indicates that the sources of PAHs in RUA might not be local and transported from the surrounding urban areas. This result is in agreement with Mai et al. [97] who found that the BaA/CRY ratios in street dust ranged from 0.2-0.3 and suggested that Macao street dust might be transported from distant areas.
FLT, PYR, BaA, CRY, BbF, BaP, IND and BGP are eight combustion related non-alkylated PAH compounds (CPAHs). The ratio of the concentration of CPAHs to the total concentration of PAH compounds (CPAHs/total PAHs) is used to distinguish the possible emissions of PAHs from mobile versus stationary combustion sources. For mobile sources, the value of CPAHs/total PAHs ratio was found to be less than one [1]. In the present study, the average CPAHs/total PAHs concentration ratios at Jeddah (0.72) indicates that the mobile sources are the principal PAHs contributor to surface street dusts of Jeddah city.

Carcinogenic PAHs (CPAHs) Determination
The total concentration of CAPAHs in the surface street dusts of different land use pattern of Jeddah were 1918.7 ng/g (MCRA), 957.35 ng/g (REA), 2887.05 ng/g (TRA), 2405.88 ng/g (URA) and Lohmann et al. [94] reported that a BaA/CRY ratio higher than 0.40 suggests that the PAHs pollution is freshly emitted and photochemical processing of the air mass is relatively lower, whereas a BaA/CRY ratio lower than 0.40 indicates that the major sources of PAHs are not local or the air masses are aged. In the present study, the mean concentration ratios of BaA/CRY were 0.75 in MCRA, 0.81 in REA, 0.71 in TRA, 0.72 in URA and 0.86 in SUA (Figure 3), which suggest that PAHs in street dusts of Jeddah come mainly from emission of local sources and the air masses are not aged. Liu et al. [4] reported that the BaA/CRY ratios of Shanghai road dust ranged from 0.6-1.4, which indicate that Shanghai might be close to its potential sources of dusts. On the other hand, the BaA/CRY ratio in the present study was 0.30 in RUA (Figure 3). This indicates that the sources of PAHs in RUA might not be local and transported from the surrounding urban areas. This result is in agreement with Mai et al. [97] who found that the BaA/CRY ratios in street dust ranged from 0.2-0.3 and suggested that Macao street dust might be transported from distant areas.
FLT, PYR, BaA, CRY, BbF, BaP, IND and BGP are eight combustion related non-alkylated PAH compounds (CPAHs). The ratio of the concentration of CPAHs to the total concentration of PAH compounds (CPAHs/total PAHs) is used to distinguish the possible emissions of PAHs from mobile versus stationary combustion sources. For mobile sources, the value of CPAHs/total PAHs ratio was found to be less than one [1]. In the present study, the average CPAHs/total PAHs concentration ratios at Jeddah (0.72) indicates that the mobile sources are the principal PAHs contributor to surface street dusts of Jeddah city.

Carcinogenic Potency of PAHs Based on BaP equi
BaP is known to be the most potent carcinogenic PAH compound [98] and is used as a good index for whole PAH carcinogenicity [99]. It is also used as a marker for total PAHs exposure in the environment [100]. The levels of carcinogenic potency of each PAH compounds in the surface street dust were calculated and assessed on the basis of its BaP equi concentration using TEFs (Table 3). BaP equi concentrations of the individual PAH compounds in the surface street dust ranged from 0.07 ng BaP equi /g (NA) to 338.68 ng BaP equi /g for DBA in MCRA, 0.04 ng BaP equi /g (NA and ACY) to 169.29 ng BaP equi /g (DBA) in REA, 0.12 ng BaP equi /g (ACY) to 507.87 ng BaP equi /g (DBA) in TRA, 0.10 ng BaP equi /g (ACY) to 423.23 ng BaP equi /g (DBA) in URA, 0.06 ng BaP equi /g (NA and ACY) to 253.94 ng BaP equi /g (DBA) in SUA and 0.002 ng BaP equi /g (NA and FLU) to 30.40 ng BaP equi /g (DBA) in RUA (Table 3). In addition, the total carcinogenic potency (total PAHBaP equi ) for the total PAHs were 741, 369, 1119, 933, 552 and 67 ng BaP equi /g in street dust of MCRA, REA, TRA, URA, SUA and RUA, respectively. Carcinogenic 6 PAH compounds (BaA, CRY, BbF, BaP, DBA and IND) were the major contributors to total PAHBaP equi in street dust samples. Their contribution to the total PAHBaP equi decreased in the order of DBA > BaP > BbF > BaA >IND > CRY for MCRA, REA, TRA, URA, SUA, and DBA > BaP > BbF > IND >BaA > CRY for RUA. The average value of the total PAHBaP equi in street dust of Jeddah (742.7 ng BaP equi /g) was lower than that found in street side soil of Sanghai, China (892 ng BaP equi /g [101]), traffic soil of Delhi, India (1009 ng BaP equi /g [58]). Whereas total PAHBaP equi values in street dusts of Jeddah was higher than those found in street dust of Guwahati city (357.7 ng BaP equi /g [14]), Lanzhou, China (300 ng BaP equi /g [44]), street dust of Asansol city, India (661 ng BaP equi /g [8]).

Incremental Lifetime Cancer Risk (ILCR)
The estimated ILCR value (based on the values of TEF and CSF) was used to identify the potential cancer risks for human exposure to PAH pollution sources. Chen and Liao [31] and Jiang et al. [44] reported that the values of ILCR between 10 −6 and 10 −4 indicate potential risk, ILCR ≤ 10 −6 indicate virtual safety, and ILCR > 10 −4 indicate a potentially high risk. Based on the calculated ILCR values for the ingestion (ILC ingesion ), inhalation (ILCR inhalation ), dermal (ILCR dermal ) pathways and total cancer risk (∑ILCR ingestion + ILCR inhalation + ILCR dermal ) for children and adults exposed to PAHs in street dust (Tables S1 and S2) Results reveal that potential risk for both children and adults was found only for exposure to BaP and DBA in street dust in different land areas in Jeddah, since cancer risk (∑ILCRs) values were between 10 −6 and 10 −4 [31,44]. Similarly, the average ILCR ingestion , ILCR dermal and cancer risk values based on average total PAHBaP equi concentrations in Jeddah were found between 10 −6 and 10 −4 (Table 4), indicating a potential risk. Table 4 also shows that the ILCR dermal and ILCR ingestion values for children and adults are higher than that of ILCR inhalation , indicating that the inhalation pathway for PAHs exposure is of minor importance. This is confirmed by Jiang et al. [44], Soltani et al. [41], Keshavarzi et al. [67], Gope et al. [8] and Škrbić, et al. [43]. The cancer risk values of direct ingestion for children were higher than the corresponding risk values of ingestion for adults at the different study areas, indicating that the young children were the most sensitive subpopulation due to their hand-to-mouth activity [8,11,44].

Conclusions
The present study reports the status, source and health risk assessment of PAHs in the surface street dust from different land use patterns in Jeddah and a rural area at Hada Al Sham. The concentration of ∑PAHs in street dust indicates that PAH compounds might be derived mainly from anthropogenic sources and tend to accumulate in surface street dust particles. High PAHs levels were observed in traffic, urban and mixed commercial/residential areas and low levels in residential area. This was referred to the distinctive artificial activities in each land. High molecular weight-PAHs were dominant in the surface street dust. The main source of PAH compounds in the study areas is pyrogenic, mainly traffic emission. Moreover, PAHs in street dusts of Jeddah come mainly from emission of local sources and the air masses are not aged, whereas the sources of PAHs in Hada Al Sham might not be local but transported from the surrounding urban areas. Based on the calculated ILCR ing. , ILCR inh. , ILCR dermal and cancer risks for children and adults exposed to PAHs in street dust, the sequence of cancer risk of the different areas was TRA > URA > MCRA > SUA > REA > RUA. Moreover, the ILCR dermal and ILCR ingestion values for children and adults are higher than that of ILCR inhalation , indicating that the inhalation pathway for PAHs exposure is of minor importance. Potential risk for both children and adults was found only for exposure to BaP and DBA in street dust in different land areas in Jeddah. The average ILCR ingestion , ILCR dermal and cancer risk values based on average total PAHBaP equi concentrations for children and adults exposed to PAHs in street dust of different areas in Jeddah were found between 10 −6 and 10 −4 , indicating a potential risk.