Health risks to metals in multimedia via ingestion pathway for children in a typical urban area of China

Chemosphere 226 (2019) 381e387

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Health risks to metals in multimedia via ingestion pathway for children in a typical urban area of China Beibei Wang a, b, Xiaoli Duan a, Weiying Feng b, Jia He b, Suzhen Cao a, *, Shasha Liu b, Di Shi b, Hongyang Wang b, Fengchang Wu b a b

University of Science & Technology Beijing, Beijing, 100083, China State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China

h i g h l i g h t s

g r a p h i c a l a b s t r a c t


5 metals in duplicated diet, water, and soil were analyzed for urban children.
Child-specific exposure factors were investigated.
Health risk associated with metals oral exposure was evaluated for local children.
Food ingestion was the largest contributor to the total expose dose.
Health risk posed by metals oral exposure was unacceptable for local children.

a r t i c l e i n f o

a b s t r a c t s

Article history: Received 30 November 2018 Received in revised form 1 March 2019 Accepted 25 March 2019 Available online 26 March 2019

With the rapid development of the industrialization and urbanization, the urban environment was heavily contaminated by metals. Therefore, studies on health risk assessment of exposure to metals for urban population is necessary and urgent, especially for children, who are more susceptible to environmental pollution due to their undeveloped immune system. Moreover, ingestion has been proved to be the most important pathway of human metals exposure. Therefore, typical metals, including Lead(Pb), Cadmium(Cd), Arsenic(As), Chromium(Cr), and Manganese(Mn), were analyzed in duplicated diet, drinking water, and soil in this study. The integrated risks of oral exposure to these metals for the local children were then evaluated on a field sampling and measured child-specific exposure factors basis. Results showed that the studied urban environments were polluted by metals to a certain degree. Food ingestion was the largest, which accounted for 66.7%e98.4%. Furthermore, soil ingestion was also a nonnegligible exposure route, which accounted for 29.7% for Pb. The combined oral non-carcinogenic and carcinogenic risks all exceeding the corresponding maximum acceptable levels. The non-carcinogenic risk was mainly attributed to the food ingestion of As and Cr, and the soil ingestion of As, while, the carcinogenic risk was mainly attributed to the food ingestion of As and Cr, and the soil ingestion of Cr. This study emphasizes attentions should be paid to children in urban areas due to the potential adverse health risk associated with metals via oral exposure pathway. © 2019 Elsevier Ltd. All rights reserved.

Handling Editor: A. Gies Keywords: Health risks Metals Oral exposure Children Urban

1. Introduction * Corresponding author. E-mail address: [email protected] (S. Cao). https://doi.org/10.1016/j.chemosphere.2019.03.158 0045-6535/© 2019 Elsevier Ltd. All rights reserved.

Epidemiological studies and toxicological experiments have

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revealed that metals exposure, like Cadmium(Cd), Lead(Pb), Arsenic(As) (since As is usually treated as metal in toxicology, As is classified as metal in this study), Manganese(Mn), and Chromium(Cr), could pose a serious threat to human health. For instance, human exposure to Cd could cause the failure of organ systems, damage of bone and cardiovascular system, renal toxicity, neurotoxicity, diabetes and cancer (Satarug et al., 2010); the health hazards caused by Pb include nerve, immune, blood and hematopoiesis, reproductive endocrine, digestive system and so on (ATSDR, 2010). Pb exposure has also been proved to be associated with increased blood pressure in adults and children (Farzan et al., 2018). Moreover, a majority of studies have evidenced that there is no safe threshold value for exposure to Pb, with negative effects on human health even at low exposure level (Haefliger et al., 2009); in addition to cancer, chronic As exposure would result in a wide range of adverse health effects, such as skin lesions, cardiovascular diseases, developmental toxicity, abnormal glucose metabolism, neurotoxicity, and immune toxicity (Lin et al., 1999; Jiang et al., 2001; Andrew et al., 2006; Sun et al., 2014); prolonged excessive exposure to Mn demonstrates a close relationship with central nervous system disorders (Bjorklund et al., 2017); moreover, chronic exposure to Cd can lead to adverse effects such as lung cancer, prostatic proliferative lesions, pulmonary adenocarcinomas, kidney dysfunction, and bone fractures (Wu et al., 2018). With the rapid development of the industrialization and urbanization, the urban environment was heavily contaminated by heavy metals (Li et al., 2011; Zhang et al., 2018a, 2018b). A majority of studies on health risk associated with metal or metalloid exposure have been conducted for people living near large-scale smelters, mine, and other industrial enterprises with heavy metal emission (Cao et al., 2014; Cai et al., 2015, 2019; Van et al., 2013), while few such studies have been conducted for general urban population (Cao et al., 2016). Additionally, children are more susceptible to environmental pollution than adult due to their undeveloped immune system. Therefore, study on health risk assessment of metals exposure for urban children is necessary and urgent. People can be exposed to metal(loid)s through the pathway of ingestion, inhalation and dermal contact, and ingestion has been proved to be the most important exposure route, which accounted for at least 80% of the total exposure dose (Cao et al., 2014, 2016; Ruby and Lowney, 2012). People could ingest metals via food, drinking water, and direct incidental ingestion of soil. Previous studies associated with oral metal(loid) exposure mainly focus on exposure through the singe route of soil (Jiang et al., 2017; Huang et al., 2018), drinking water (Zhang et al., 2018a, 2018b), and food (Li et al., 2011; Yu et al., 2017a, 2017b), but little was done on the accumulated risk (Jiang et al., 2015; Bacigalupo and Hale, 2012). It is important to identify the predominant exposure route. Additionally, previous dietary exposure studies mainly used the indirect method, multiplying daily food consumption by the pollutant concentration in raw food (Li et al., 2011; Yu et al., 2017a, 2017b), which could not account for the additional pollution of food from preparation and processing (Kurziusspencer et al., 2013; Cubadda et al., 2017). Therefore, the duplicated diet sample was considered to be the most accurate method for assessing dietary exposure. Moreover, the parameters of soil ingestion rate from the United States were generally used to evaluate the soil exposure for Chinese population. However, the exposure parameters of foreign population cannot be globally representative, due to differences in lifestyle and habits (Lin et al., 2017), so it is necessary to use the exposure factor of the relative population to carry out risk assessment. The major objectives of the current study were as follows: (1) to determine the concentrations of metals (As, Pb, Cr, Cd, and Mn) in food, drinking water, and soil in a typical urban area of China; (2) to

identify the exposure levels and the major exposure pathway of the metals for the local children; and (3) to evaluate the children's health risks posed by metals exposure through the ingestion pathway.

2. Materials and methods 2.1. Study areas and participants selection The studied city is a crucial heavy chemical industry base and integrated transportation hub of northwestern China. The problem of heavy metal pollution has been of concern for years (He, 2015). It has obvious semi-arid continental monsoon climate of the North Temperate Zone, with less precipitation, dry air, large temperature difference between day and night, and significant seasonal changes. A population sample of 60 children was randomly selected to participate in this study, including 30 children from the urban (the center of the city) and 30 from suburban areas (the place outside the city center). The children's ages ranged from 2 to 11 years old, with an average of 6.8 years. The children's average weight was 22.5 kg (10.0e57.0 kg), while the average height was 115.0 cm (75e165 cm). After obtaining the ethical permission from the ethics committee of the National Center for Disease Control, and consent forms being signed by participants' parents or guardians, the study was then conducted. 2.2 Sampling collection and processing. One-day duplicate diet sample, drinking water sample, and soil sample were collected to determine the accumulative exposure and risk levels to the target metals through ingestion pathway. All food samples within 24 h for each child, including breakfast, lunch, dinner, snacks, vitamin and medications, were completely collected using the ‘duplicate plate’ method. Each subject was provided with 4 Tupperware containers and 1 cooler with ice packs for the collection of meal samples. These samples were kept in cool before sent back to laboratory. Then, all the food samples were weighed and homogenized evenly with a stainless steel blade to form a composite sample for each subject. A subsample (1 g) was digested with concentrated nitric acid and hydrogen peroxide (HNO3-H2O2) using microwave heating (CEM-MARS, USA) for analyzing the metals concentration. Since children's drinking water source was tap water, a total of 20 samples were randomly collected from local families in 1 L acid washed polyethylene bottles to represent the concentration level of each study area. After adding two drops of 65% concentrated HNO3 into the water, the samples were stored at 20  C until analysis. Water samples were filtered using the filter membrane (Whatman No.1, F ¼ 0.45 mm) before analysis. Considering children spending most of their daily time in school, soil samples were collected from the kindergarten yard and schoolyard by scraping the surface layer of soil from a 10 cm by 10 cm area to a depth of 2 cm. In the laboratory, soil samples were air-dried, broken up lightly with a ceramic mortar and a rubber pestle, and sieved into <250 mm particle size fractions. A 0.5 g subsample was digested with concentrated HNO3-HF-HClO4 using microwave heating to analyze the metals concentration. All reagents and acids used were analytical grade.

2.2. Sampling analysis The concentration of As, Cr, Cd, Pb, and Mn were measured by high resolution inductively coupled plasma mass spectrometry (Agilent-7500a, Agilent Scientific Technology Ltd., USA) under the optimized conditions (Zhang et al., 2010).

B. Wang et al. / Chemosphere 226 (2019) 381e387

2.3. Quality control To assure the quality, each pretreatment batch included a reagent blank, a duplicate sample, and a spiked sample with representative standard reference material during the sample preparation. Duplicated sample and standard reference materials (10% of the samples) were also conducted in analysis program to determine and assess the precision and accuracy of the analysis process. The detection limits for As, Cr, Cd, Pb, and Mn were 0.2, 5, 20, 2 and 10 mg kg1, respectively. The reagent blank was subtracted from the sample results. The average recoveries of spiked samples ranged from 84% to 110%. The average coefficients of variation for repeated measurements ranged from 0.31% to 2.32%. The results were acceptable for metals analysis. Additionally, 2.5 Exposure calculation. According to the recommended exposure assessment models by the U.S. EPA (USEPA, 1989), the average daily dose (ADD) (mg kg1 day1) of a chemical via the ingestion exposure pathway can be estimated using the following equation.

ADD ¼

C  IR  EF  ED BW  AT

(1)

where C is the pollutant concentration in each environmental medium (food, drinking water, and soil) in mg kg1 or mg L1; IR is the ingestion rate of each environmental media in mg day1 or mL day1; EF is the exposure frequency in days year1; ED is the exposure duration in year; BW is the body weight in kg; AT is the average time in days. The children's water ingestion rate and body weight were obtained through the questionnaire during sampling. The ingestion rate of the consumed food was obtained by weighting the duplicate food. The soil ingestion rate was obtained from the literature by employing a tracer mass-balance method for the same children (Lin et al., 2017). All the exposure factors were present in Table 1. 2.4. Risk assessment 2.4.1. Non-carcinogenic risk For the non-carcinogenic effect, A Hazard Quotient (HQ) is estimated as the non-cancer risk during a lifetime and calculated by the following equation (USEPA, 1989).

HQ ¼

ADD RfD

(2)

where RfD is the estimated maximum permissible daily oral exposure level on humans that is likely to be without appreciable risk of deleterious effects in mg kg1 day1. It has been concluded that there is no adverse health effect when HQ < 1, and potential adverse health effect is likely to occur when HQ > 1. To assess the overall potential oral non-carcinogenic effects posed by more than one exposure pathway (e.g., i), the HQ calculated for each pathway is summed and expressed as a Hazard Index

383

(HIing). Moreover, a total Hazard Index (HIting) is used to assess the overall potential non-carcinogenic effects posed by multiple pollutants (e.g., j) by summing the HQ calculated for each pollutant.

HIing ¼

Xi

HIting ¼

1

HQ

Xi 1

(3)

HIing

(4)

2.4.2. Carcinogenic risk For the carcinogenic effects, the Incremental Lifetime Cancer Risk (ILCR) is estimated as the incremental probability of an individual developing cancer over a lifetime due to exposure to the potential carcinogen. The ILCR is determined by multiplying the ADD via ingestion pathway by the oral slope factor (SF) (USEPA, 1989).

ILCR ¼ ADD  SF

(5)

where SF is the estimate of an upper-bound probability of an individual developing cancer as a result of a lifetime oral exposure to a chemical in kg day mg1. Risk in the range of 106 - 104 has been judged to be acceptable. According to the classification group orders defined by the IARC (International Agency for Research on Cancer) (IRAC, 2011), Mn, Cr, Cd, Pb and As were regarded as non-cancer effect elements, while Cr and As were treated as having potential carcinogen effect. The SF and RfD are listed in Table S1 (USEPA, 1989; 2011b). 2.5. Statistical analysis The statistical analysis was conducted by SPSS 20.0. The contents of each metal were presented as medians and inter-quartile ranges. The correlation coefficients were calculated using the Spearman's method. Kruskal -Wallis test was used to compare the means when the distribution was not normally distributed. An alpha level of 0.05 was chosen to determine the significance. 3. Result and discussion 3.1. Contents of metals in environmental media The measured results of the metals content in various environmental media are presented in Table 2. As shown, the concentration of Cr in soil exceeded the corresponding regulatory values of environmental quality standard for development land (GB366002018), while the content of other metal were observed to be within the relevant thresholds. In contrast, the concentration of metals in soil were 1e3 times higher than the related natural background levels (Lu et al., 1987), indicating anthropogenic activities and industrial development causing a certain degree of pollution to the soil environment. Compared with the metal pollution levels associated with urban soil at a national scale comprehensively

Table 1 Summary of exposure factors developed for the investigated children. Exposure factors

Water ingestion rate (ml day1) Food ingestion rate (g day1) Soil ingestion rate(mg day1) Body weight(kg)

Total

Urban

Suburban

3~<12 years

3~<6 years

6~<12 years

3~<12 years

3~<6 years

6~<12 years

3~<12 years

3~<6 years

6~<12 years

1112.2 911.0 150 24.2

968.1 892.5 139 16.2

1256.3 929.5 161 32.3

1052.9 1019.3 123 27.7

882.0 1016.5 103 17.2

1235.9 1022.3 140 39.0

1167.7 809.7 173 20.9

1054.1 768.5 164 15.1

1274.1 848.3 182 26.4

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Table 2 Contents of the target metals in environmental media. Contaminant

Number

Value

Mn

Pb

Cr

Cd

As

Soil(mg kg1)

60

Duplicated diet(mg kg1)

60

Drinking water（mg L1）

20

Median P25 P75 Median P25 P75 Median P25 P75

603.6 570.7 626.0 0.344 0.294 0.436 0.58 0.10 0.32

38.1 23.6 71.6 0.009 0.007 0.010 0.36 0.29 0.42

64.3 60.1 68.2 0.022 0.017 0.028 3.23 3.18 3.35

0.3 0.2 0.5 0.002 0.002 0.003 0.02 0.01 0.04

11.8 10.1 12.8 0.047 0.035 0.061 0.98 0.72 1.15

evaluated by Zhang et al. (2018a, 2018b), the level of metals in soil in this study were around the national average. Furthermore, the content of metals in this study were lower than those previously found in a coking area (Cao et al., 2014), and an urban area with orerelated manufactures (Cao et al., 2014). Additionally, It was found that the Pb and Cd content in urban soil, of approximately 59.8 mg kg1 and 0.35 mg kg1, respectively, were significantly higher than the 25.2 mg kg1 and 0.22 mg kg1 in suburban soil by Kruskal -Wallis test (p < 0.05). As revealed by Yan et al. (2018), Pb and Cd were mainly controlled by traffic activities with high contamination levels found near traffic-intensive areas, so the discrepancy between urban and suburban areas could be partly attributed to the heaver traffic in urban areas. The metals content in duplicated diet in this study were all below the thresholds for metals in major food categories regulated by the national food quality standard (GB2762-2012). At present, little research has been done on levels of heavy metal in food in the studied areas. Li et al. (2011) and Yu et al. (2017a, 2017b) have reviewed the concentration of As and Cd in Chinese food based on the existing literature, which provides an opportunity to compare the result of this study with the national level. It is observed that the Cd and As concentrations in duplicated food samples in this study were in the range of those reported in different food types. Furthermore, it's worth noting that previous studies estimated daily metals intake levels based on metals levels in raw food, however, the preparation and cooking process could be important factors affecting the metals content in food (Cubadda et al., 2017), so it is more reasonable to use the concentration of metals in cooked food to reflect the actual exposure level. The Mn, Cr, Cd, Pb, and As concentrations of duplicated food samples for 2e11 years old children in this study were much lower than those observed for 5e8 years old children from an industrial city of Hunan province studied by Cao et al. (2016). The variance could be explained by the different environmental metals pollution situation and dietary patterns. No statistical difference in metals content was observed in duplicated diet sample between urban and suburban children. Most metals in food significantly correlated with one another in the concentration (Table S2), indicating the contamination metals in food having similar pollution sources. In addition, it is observed that the concentration of Mn and Cd in food of suburban children showed a significant correlation with those in soil (Spearman r ¼ 0.371, p < 0.05; Spearman r ¼ 0.383, p < 0.05, respectively), implying that Mn and Cd pollution in soil may be an important pollution source for those in food. This outcome may be attributable to that part of food suburban children consumed was locally grown. The content of metals in drinking water were all within the thresholds of the national drinking water quality standard (GB 5749-2006). The concentration of metals in drinking water in this study was also lower than those previously found in the coking area and an industrial city (Cao et al., 2014; 2016). Moreover, no significant difference in metals content was observed in drinking

water between urban and suburban children. 3.2. Daily exposure dose of metals Human oral exposure to metals mainly through the route of ingesting food, drinking water and unconsciously ingestion of soil. Based on the concentration of metal in soil, food and drinking water, combined with the actual child-specific intake parameters, the oral exposure dose via various routes were estimated. The contribution of each exposure route to children's oral average daily dose (ADD) is listed in Fig. 1. As shown in Fig. 1, food ingestion is the predominant route of oral exposure to metals, with the contribution of 88.8%, 66.7%, 72.8%, 98.8%, 98.4% for Mn, Pb, Cr, Cd, and As, respectively, to the total oral ADD. Moreover, soil ingestion is also an important exposure route for Pb, Cr, and Mn, which accounted for 29.7%, 16.3%, and 11.1% of the total oral ADD. Additionally, water intake is another non-negligible exposure route for Cr exposure, which accounted for 10.9% of the total oral ADD. 3.3. Risk characteristics 3.3.1. Non-cancer risk Base on the oral ADD and reference dose (RfD) of each pollutant, the non-carcinogenic risks of oral exposure to metals for local children via various routes were calculated and are listed in Table 3. The average combined HQ of these five metals was 8.29, indicating a potential non-carcinogenic risk for the local children. It is observed that food ingestion was the largest contributor for these five metals, with a contribution of 53.5%e96.2% to the total oral

Fig. 1. The contribution of exposure to each metal through ingesting food, drinking water, and soil to the total oral exposure dose for children.

B. Wang et al. / Chemosphere 226 (2019) 381e387

385

Table 3 Summary of the non-carcinogenic risk associated with metals oral exposure via ingesting food, soil, drinking water, and the total non-carcinogenic risk (Sum) for children at the 5th, median and 95th percentiles. Metal (loid)s

Mn Pb Cr Cd As Total

P5

Median

P95

Food

Soil

Water

Sum

Food

Soil

Water

Sum

Food

Soil

Water

Sum

0.030 0.065 0.070 0.025 1.785 1.985

0.012 0.075 0.059 0.001 0.108 0.255

0.000 0.007 0.028 0.001 0.082 0.117

0.043 0.163 0.206 0.029 2.028 2.479

0.110 0.250 0.305 0.100 6.725 7.480

0.029 0.182 0.143 0.002 0.263 0.619

0.000 0.013 0.055 0.002 0.166 0.236

0.138 0.467 0.499 0.104 7.130 8.292

0.225 0.600 0.750 0.210 18.255 20.155

0.057 0.359 0.283 0.003 0.520 1.222

0.000 0.023 0.097 0.004 0.292 0.416

0.281 0.905 1.066 0.214 18.932 21.526

risk, which was in accordance with the result reported by Cao et al. (2016). Soil ingestion was the second important exposure route for Mn, Pb, and Cr, which accounted for 21%e39% to the children's daily intake. Additionally, drinking water is another non-negligible route for Cr exposure, with 11% contribution. As shown in Table 3, the non-carcinogenic risk of children's exposure to metals was in the decreasing order of As > Cr > Pb > Mn > Cd. The HQ of As exposure was greater than 1 even at the 5th percentile, implying that daily As exposure via ingestion may pose potentially adverse health hazards to the local children. In addition to As, the non-carcinogenic risk associated with Cr oral exposure was 1.07 at the 95th percentile, which indicated that children with high intake of Cr might be at risk. It's worth noting that for Cr non-carcinogenic risk at the 95th percentile, the risk level from each exposure route was acceptable, but the accumulated risk was beyond the maximum acceptable levels, which emphasize the importance of aggregative exposure. Moreover, risk depends not only on the concentration of environment pollutant exposed, but also on the intake rate. It is observed that the levels of metals in food are not too high, but the risks are unacceptable, which revealed that slight environmental pollution could be harmful to human health because of high intake. There was statistical difference between urban and suburban children in non-carcinogenic risk resulting from a single or combined metal exposure via water ingestion and unconsciously soil intake pathway (p < 0.05). Since no significant urban-suburban difference was observed for most metals in the relative environmental media, the discrepancy mainly attributed to the difference in children's behavior patterns, like water consumption rate and soil ingestion rate. However, no significant urban-suburban difference was found in the accumulated non-carcinogenic risk via ingestion pathway (p > 0.05), which predominately because the ingestion of metals via food ingestion route, the non-cancer risk resulting from which has no statistical urban-suburban difference (p > 0.05), was the largest contributor to the total non-cancer risk, and it offset the risk discrepancy associated with the ingestion of water and soil. Due to the differences in behavior patterns of population and the pollution levels of contaminants, the contributions of exposure routes for people in different areas vary. For As exposure, the contribution rate from ingesting food, soil, and drinking water was estimated to account for 94.3%, 3.7%, and 2.3% to the total oral non-

carcinogenic risk in this study, respectively, which is comparable to the results of a previous study for children in a typical lead-acid battery plant by Cao et al. (2014). However, this result is quite different from that reported by Jiang et al. (2015) for people in a town of Jiangsu province, in which the risk of As exposure resulting from food consumption was estimated to account for 49.1% of the total intake risk of As via food, drinking water, soil ingestion and soil contact. Additionally, the non-carcinogenic risk of As exposure via soil ingestion was much higher than that through the food ingestion pathway in an industrial area of Volos, Greece (Antoniadisa et al., 2019). For Pb and Cr exposure, the contribution rate from the ingestion of food and drinking water, 53.5% and 61.2% in this study, were much lower than the results of 97.32% and 88.96% in Cao et al. (2014, 2016). The difference could be mainly explained by the lighter metals pollutant levels in food and the higher soil ingestion rate in this study, in comparison with the previous studies.

3.3.2. Cancer risk Base on the oral ADD and cancer slope factor (SF) of each pollutant, the carcinogenic risks of oral exposure to Cr and As for the local children via various routes were calculated and are listed in Table 4. The ILCR values for As, Cr, and the combined through ingestion exposure pathway were all higher than the maximum acceptable level (1.0  104), indicating that As and Cr could pose potential carcinogenic risk to the local children. The potential cancer risk resulting from As oral exposure was 3 times higher than that from Cr. Food consumption was the major contributor for As and Cr carcinogenic risk, with the ILCR values of 5.85  104 and 2.22  103, respectively, all exceeding the maximum acceptable level. In addition, Cr exposure through soil ingestion pathway could also pose potential carcinogenic risk, with the ILCR value higher than the maximum acceptable level, indicating that soil ingestion is also an important exposure source. Additionally, the potential carcinogenic risk from drinking water ingestion route could not be neglected, since although the carcinogenic risk of As or Cr exposure via drinking water ingestion was among the range of 104 to 106, which is regarded as an acceptable or inconsequential risk (USEPA, 2011b), the combined ILCR through this route was greater than the maximum acceptable level.

Table 4 Summary of the carcinogenic risk associated with metals oral exposure via ingesting food, soil, drinking water, and the total carcinogenic risk (Sum) for children at the 5th, median and 95th percentiles. Metals

Cr As Total

P5

Median

P95

Food

Soil

Water

Sum

Food

Soil

Water

Sum

Food

Soil

Water

Sum

1.30E-04 2.90E-04 6.25E-04

5.50E-05 3.50E-05 9.00E-05

4.00E-05 4.00E-05 8.00E-05

3.00E-04 4.50E-04 9.00E-04

5.85E-04 2.22E-03 2.81E-03

1.30E-04 7.00E-05 2.05E-04

9.00E-05 7.00E-05 1.60E-04

9.00E-04 2.35E-03 3.15E-03

1.83E-03 1.02E-02 1.15E-02

3.85E-04 2.15E-04 6.00E-04

1.45E-04 1.20E-04 2.60E-04

2.05E-03 1.04E-02 1.19E-02

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3.4. Uncertainty analysis Uncertainty is an important part of health risk assessment. The uncertainty in this study mainly include: firstly, the exposure concentration used in our study didn't take into account the bioaccessibility, which is considered to be a more accurate measure for assessment of health risk associated with oral ingestion exposure (Wragg and Cave, 2002), so the health risk assessments in this study could be somewhat overestimated; secondly, certain uncertainties might exist during the extrapolation from animal to human and high dose to low dose for the dose-response simulation. Thirdly, limited by the research method, which required a great amount of workload and participants' high degree of cooperation, the study group is small relative to children's age range, so there could be some uncertainty about the representativeness of the subject. However, exposure factors, especially the soil ingestion rate, are derived from the actual investigation and study. Moreover, duplicated-diet method was used to collect the actual food ingested to avoid the impact of food processing on pollutant concentration. These measures could reduce the uncertainty to a certain extent. 4. Conclusions Anthropogenic activities and industrial have brought a certain degree of pollution to the urban environment. Although the pollution level was lower in urban areas than that in environment around the industrial enterprises, it also posed health risks to children, which should be of concern. In the study area, elevated concentrations of metals were observed in the soil, while the concentration of metals in food and drinking water didn't exceed the corresponding national quality standards. However, children in urban areas were at risk of metals exposure, with the accumulated oral non-carcinogenic and carcinogenic risks all exceeding the corresponding maximum acceptable level. Food ingestion was the major source of risk, which accounted for over half of daily oral intake, and soil ingestion is another important exposure source. The non-carcinogenic risk mainly attributed to the food ingestion of As and Cr, and the soil ingestion of As, while the carcinogenic risk mainly attributed to the food ingestion of As and Cr, and the soil ingestion of Cr. Therefore, attentions should be paid to children in urban areas due to the potential adverse health risk associated with metals exposure. In addition, studies on exposure levels of metals in different types of food contribute to further identify the main risk source, then precise measure could be taken to reduce risk. Conflict of interest. Conflicts of interest The authors declare no conflict of interest. Acknowledgments This work was supported by the Special Fund for Public Welfare Industry of National Environmental Protection (201309044). We are indebted to everyone who helped with the sampling. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.chemosphere.2019.03.158. References Agency for Toxic Substances and Disease Registry, 2010. Case Studies in Environmental Medicine (CSEM)- Lead Toxicity.

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