Spatial Distribution and Risk Assessment of Heavy Metals in Urban Road Dust From Shenyang, a Heavy Industrial City in Northeast China

: 124 road dust samples were collected from an urban area of Shenyang, a typical heavily 9 industrial city in Northeast China, to study the concentration, pollution level, source, spatial distribution, 10 and health risk of heavy metals. The average concentrations of Cd, Cr, Cu, Mn, Ni, Pb, and Zn were 11 1.802, 132.1, 60.33, 778.3, 54.80, 86.73, and 391.2 mg/kg, respectively. The levels of metal pollution 12 ranged from minimal to extremely high, with average levels in the ranked order: Mn < Ni < Cr < Cu < 13 Pb < Zn < Cd, indicating that the road dust was heavily polluted by Cd, Zn, and Pb. Source identification 14 results demonstrated that Cr, Mn, and Ni had mixed sources including industrial emissions and 15 weathering of soil, pavements, and building materials, while Cu, Pb, and Zn mainly originated from 16 traffic and industrial activities, and Cd had a complex mixture of sources (with various anthropogenic 17 sources). Hotspots of heavy metal pollution levels were closely correlated with local anthropogenic 18 activities, such as industrial discharge, traffic-related exhaust emissions, and agricultural activities. Furthermore, health risk assessment revealed significant non-carcinogenic risks for children from 20 multiple metals, and the carcinogenic risk assessment identified significant risks for children from Cd, 21 with ingestion being the main exposure pathway for carcinogenic and non-carcinogenic risk for adults 22 and children. However, no health risk was observed due to dermal and inhalation exposure pathways. heavy in from The primary aims of the present study to investigate the heavy metals distribution in road dust from city; 2) to evaluate the heavy metal pollution level; 3) to identify potential of different 4) to assess the potential health risk and different The this study provide an important multidisciplinary assessment of heavy in the urban environment providing useful guidance for the improvement and development of management in this

studied in megacities, such as Beijing (Men et al. 2018b), Shanghai (Bi et al. 2018), Xi'an (Pan et al. 45 2017), and Nanjing (Liu et al. 2014). Urban road dust has also been found to be polluted with heavy 46 metals in many other smaller cities in China, such as Guangzhou (Cai et    with the surrounding environmental conditions. At each sampling site, four to eight sub-samples were 92 collected from both road and pavement edges at the main street intersection and mixed thoroughly to 93 obtain a representative bulk sample. For each sub-sample, 500-1000 g of dust was collected by slowly 94 sweeping dust using a plastic brush and dustpan, directly transferring the dust into plastic bags, which 95 were labeled and transported to the laboratory for analysis. Extraneous matter, such as cigarette butts, 96 small stones, plastic waste, metal scraps, and other impurities, was manually removed from the sampling 97 area prior to dust collection.

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After the dust samples were air-dried at ambient temperature in the laboratory, they were sieved 99 through a 53 μm nylon sieve. Previous studies have reported that human exposure to dust particles 100 smaller than 53 µm in diameter can occur easily via ingestion, inhalation, or dermal absorption (Gope et

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where, IngR indicates the dust ingestion rate (mg·day -1 ); EF is the exposure frequency (days·year -1 ); ED 136 is the exposure duration (years); BW refers to the average body weight (kg); AT indicates the averaging 137 time (days); and CF is the conversion factor (1×10 -6 kg·mg -1 ).
where, SA represents the surface area of skin in contact with the dust (cm 2 ); AF is the skin adherence 140 factor for dust (mg·(cm 2 ) -1 ); and ABS is the dermal absorption factor (chemical specific).

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The potential non-carcinogenic and carcinogenic risks for individual metals were calculated using 145 Eqs. (7), (8), and (9) (US.EPA, 1989), as follow: where, RfD indicates the reference dose (mg/(kg·d)); and SF is the slope factor (per (mg/(kg·d)). The           Igeo values were ranked in the decreasing order of Cd > Zn > Pb > Cu > Cr > Ni > Mn (Fig. 2a) Table S4. For non-carcinogenic effects, the health risks for children were higher than for adults. Children 340 are more susceptible to the effects of heavy metals, due to children's behavioral and physiological 341 characteristics, including hand-to-mouth activities and higher breathing rate per unit body weight (Liu et

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The HQ values for children were < 1 for all the assessed metals, which were ranked in the descending 345 order of Cr > Pb > Mn > Cu > Ni > Cd > Zn. Although the children's HQ value for Cr (0.68) was below 346 the safety threshold, if children are exposed to a sufficiently large dose over a long term period, it may cause neurological and developmental disorders. Therefore, exposure of Cr in urban dust in Shenyang 348 could pose a potential threat to children's health. The contribution from the ingestion pathway was the 349 highest (88.4% for children and 66.8% for adults), followed by dermal contact and inhalation, which is 350 consistent with the reported results of earlier studies (Chabukdhara and Nema, 2013;Tang et al., 2017).

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Due to the lack of corresponding RfD or SF values, only Cd, Cr, and Ni were evaluated in terms of 352 their carcinogenic risk. Cd exposure was evaluated for all three pathways, while Cr and Ni were only 353 evaluated for carcinogenic health risks via the inhalation pathway. CR values for multiple metal exposure 354 for adults and children were 2.17 × 10 -5 and 1.65 × 10 -4 , respectively (Table S4). The carcinogenic risk 355 for children was higher than the maximum tolerable value (1 × 10 -4 ), while the carcinogenic risk for 356 adults was within the acceptable range (1×10 -6 -1×10 -4 ). For adults and children, the CR values for Ni 357 were below the negligible risk level of 1×10 -6 , indicating no significant effect on health. The carcinogenic 358 risk levels for Cr for adults and children and Cd for adults were within the acceptable limits, while the 359 CR values for Cd for children were 1.59-fold higher than the CR threshold. The ingestion pathway 360 accounted for 93.1% and 96.4% of the total CR for adults and children, respectively, which was much 361 higher than the other two pathways, indicating that ingestion was the main CR exposure pathway for 362 both adults and children. Therefore, the non-carcinogenic and carcinogenic risks to children in the study 363 area were higher than the risk to adults, highlighting the need for more research attention in this field and