Polycyclic aromatic hydrocarbons in the Chinese diet: contamination characteristics, indicator screening, and health risk assessment

Abstract Polycyclic aromatics hydrocarbons (PAHs) are ubiquitous in foods and environment and possess carcinogenic and mutagenic potential. Foods are the main source of exposure to PAHs in the general population. In this study, we determined the concentrations of 16 European Union priority PAHs in 1,564 foodstuffs acquired from nine provinces and commonly consumed by the Chinese population. The most predominant PAH was chrysene (16.7%), followed by benz[a]anthracene (12.4%) and benzo[b]fluoranthene (11.7%). Edible vegetable oils (17.89 μg/kg) and fruits (1.97 μg/kg) had the highest and lowest concentrations of total PAHs, respectively. Suitable indicators of PAH contamination in foods were assessed based on the occurrence of other PAHs in samples negative for benzo[a]pyrene and the correlation for the PAHs and their combinations. According to our results, PAH4 was a suitable indicator, better than PAH8 and benzo[a]pyrene alone. PAH exposure in the Chinese population was estimated by combining contamination data with national individual food consumption data, based on the middle bound approach. The overall average dietary exposures for BaP and PAH4 were 3.08 and 17.61 ng/kg bw/day, respectively. The major contributors to the total dietary exposure of PAHs were cereals (39%), edible vegetable oils (28%), and vegetables (20%). We used the margin of exposure (MOE) approach to assess health risk for consumers. MOEs of the mean estimated dietary exposures were >10,000, indicating a low concern for the health of the general population and of consumers of smoked, grilled, or barbecued foods. For high consumers and children, the MOEs were <10,000, indicating potential concerns.


Introduction
Polycyclic aromatic hydrocarbons (PAHs) are important food and environmental contaminants (EFSA 2008;Chen et al. 2018), primarily generated by the incomplete combustion or pyrolysis of organic substances (EFSA 2008;Veyrand et al. 2013;Zelinkova and Wenzl 2015). For nonsmokers, consumption of food has been generally recognized as the major route exposure to PAHs (Polachova et al. 2020).
Exposure to PAHs is a major concern for human health, due to their carcinogenicity, genotoxicity and teratogenicity (Culp et al. 1998;Kim et al. 2013;IARC 2021), as well as their potential damage to the immune system and the circulatory system (Huang et al. 2019;Fern andez et al. 2021).
The occurrence and health risk of PAHs have been evaluated by several international organizations, e.g. International Agency for Research on Cancer (IARC 2010), the Scientific Committee on Food (SCF 2002), the Joint FAO/WHO Expert Committee on Food Additives (JECFA 2006), and the European Food Safety Authority (EFSA 2008 [a]pyrene to ensure more efficient risk management. In China, GB2762-2017 sets maximum limits of benzo[a]pyrene in four food categories, including paddy and wheat (5 lg/kg), smoked or baked meats (5 lg/kg), smoked or baked aquatic products (5 lg/kg), and fats or oils(10 lg/kg) (NHC 2017). However, maximum limits of PAH4 have not been included.
EFSA also concluded that the toxic equivalency factor (TEF) approach in the risk characterization of the PAH mixtures in food is not scientifically valid. Therefore, risk characterization was conducted by calculating margins of exposure (MOE), based on the bench mark dose lower confidence limit for a 10% increase in the number of tumor-bearing animals compared to control animals (BMDL 10 ) of 0.34 mg/kg bw/day for PAH4 (EFSA 2008).
Several domestic studies have focused on the exposure to PAHs from different food categories, such as edible oils (Shi et al. 2016), grilled and fried meats (Jiang et al. 2018), aquatic products ) and vegetables (Jia et al. 2018), research gaps still remain in the total dietary exposure and risk assessment of PAHs for Chinese general population.
In the present study, the occurrence data collected during a National Food safety risk monitoring program for 16 EU priority PAHs (the 16 compounds are presented in Subsection 2.2.) and their distribution in the Chinese diet were presented, together with corresponding food consumption data of the Chinese population. We calculated the dietary intake of PAHs and performed the risk assessment using the MOE approach. Meanwhile, we evaluated suitable indicators of PAH contamination in foods by calculating the concentrations of other PAHs in the absence of benzo[a]pyrene and the correlation for the individual PAHs and their combinations. To the best of our knowledge, this is the first report to investigate total dietary exposure and risk assessment of PAHs in the Chinese general population.

Food sampling and food consumption data
Samples of foodstuffs in this study originated from a targeted sampling project carried out in March 2016-June 2017. We purchased 1,564 food samples (76 frying oil samples were not for dietary exposure assessment) from markets in nine provinces, located in Northern, Eastern, Southern and Central China ( Figure 1).
We carried out the food sampling based on the National food safety risk monitoring project, taking into account the most-consumed products in China and also some less-consumed foodstuffs that could potentially contain high concentrations of PAHs, such as smoked or grilled or barbecued (SGB) meats and aquatic products. Samples of foodstuffs included: cereals, vegetables, fruits, raw meats, raw aquatic products, SGB meats, SGB aquatic products, edible vegetable oils and frying oils (Table 1).
We obtained the food consumption data from the database of the fifth Chinese total diet study. The foodstuffs consisted of 8 food categories and 47 subcategories for 23,647 individuals. All food consumption data were collected in three consecutive days using a 24-h recall dietary questionnaires, except for the data for edible vegetable oils, which were collected using a three-day weighing method.

Analytical procedure
We analyzed PAHs in nine provincial-level laboratories, all of which received the National Analytical Quality Certification. The selection of analytical methods is based on personnel capability and instruments available in the laboratories. Food samples were prepared and analyzed based on the following two methods: 108 edible vegetable oil samples and 76 frying oil samples were analyzed by method b, while other samples were analyzed by method a. a. 16 EU priority PAHs were extracted and detected according to the reference method GB5009.265-2016 and the methods reported by (Cai et al. 2020;Wu et al. 2020) with some modifications. Briefly, we spiked 5 g food sample with isotope-labeled internal standards (deuterated PAHs) and homogenized the sample in a mixture of 20 g anhydrous sodium sulfate and 20 mL cyclohexane/ethyl acetate (50/50, v/v) in a 50 mL centrifuge tube. The sealed tube was vortexed for 1 min, sonicated for 15 min and finally centrifuged at 10,000 rpm for 3 min. The supernatant was concentrated to dryness at 45 C using a rotary evaporator. The residue was subjected to a saponification step. For the saponification step, the sample was mixed with 1.5 mol/L potassium hydroxide ethanol solution (5 mL), and placed in a 70 C water bath for 3 min. After cooling, we added 5 mL n-hexane and 4 mL ultrapure water. The sealed tube was vortexed for 2 min and centrifuged at 10,000 r/min for 2 min. Finally, the upper n-hexane phase was subjected to further purification through solid-phase extraction. Anhydrous sodium sulfate (1 g) was added to the solid-phase extraction (SPE) column for EU priority PAHs, and the column was conditioned with methylene chloride (3 mL) and nhexane (3 mL). Then the sample was loaded. The cartridge was washed with a n-hexane (5 mL) and target compounds were eluted using 5 mL of dichloromethane/ethyl acetate (50/50, v/v) as mobile phase. The cleaned and concentrated extracts (in acetone-isooctane, 50/50, v/v) were analyzed by GC-MS. The GC separation was performed using a DB-EUPAH capillary column (20 m length, 0.18 mm i.d., 0.14 mm film thickness). The oven temperature was programmed as follows: 80 C (2 min); 10 C min À 1 to 250 C (2 min); 8 C min À 1 to 315 C (5 min); and 20 C min À 1 to 320 C (8 min). Helium (purity ! 99.999%) was used as the carrier gas at a flow rate of 0.7 mL min À 1. The sample (1 lL) was injected into the splitless inlet in splitless mode at 280 C. The mass spectrometer was equipped with an electron ionization ion source (EI) operating at 70 eV electron impact energy. All experiments were carried out in the positive ion mode. The quadrupole, source, and auxiliary temperatures were 150, 230, and 280 C, respectively, and the solvent delay time was 18 min. PAHs were detected by selective ion mode (SIM). b. 16 EU priority PAHs (except BjFA and CPP, which were undetectable in this method) were extracted and detected according to a standard operating procedure established by Jiangsu Center for Disease Control. Additionally, we used the method reported by (Jiang et al. 2015) with some modifications.
Briefly, 0.5 g oil sample was extracted in 10 mL cyclohexane/ethyl acetate (50/50, v/v). The mixture was vortexed for 30 s, sonicated for 15 min and finally centrifuged at 8000 rpm for 5 min. The extracts were purified by gel permeation chromatography. The purification was conducted in fast GPC purification column: 300 mm Â 20 mm, filled with Bio Beads S-X3 (25 g); detection wavelength: 254 nm; mobile phase: ethyl acetate/cyclohexane (50/50, v/v); and flow rate: 5 mL min À1 . We injected 5 mL solution into GPC column through a sample ring. The 16-43 min fraction was collected, concentrated near dryness, and dissolved with 1 mL acetonitrile for HPLC-FLD determination. The chromatographic column for HPLC was PAH C 18 reversed bonded stationary phase column (250 mm length, 4.6 mm i.d., 5 mm particle size); mobile phase: acetonitrile and water. The sample injection volume was 20 lL. PAHs were separated at a flow of 1.2 ml min À1 , and the column temperature was 35 C. Fluorescence detection of PAHs was performed at different excitation and emission wavelengths. The 16 EU priority PAHs (except BjFA and CPP) were quantified using an external standard method, with a 15 EU priority PAHs mixed standard solution and a BcFL standard solution as external standards.
Internal quality controls and statistical analysis The two described methods have been validated, and performances have been found fit-for-purpose: In method a, the limits of detection (LODs) and limits of quantification (LOQs) for oil samples were 0.7 and 2.0 lg/kg, respectively. The LODs and LOQs for other foods were 0.3 and 1.0 lg/kg, respectively. In method b, LODs and LOQs were 0.3 and 1.0 lg/kg, respectively (16 EU priority PAHs except BjFA and CPP).
Recoveries were between 70 and 130% for method a, and between 60 and 130% for method b. The National Key Laboratory of Food Safety Risk Monitoring for Organic Pollutants in Jiangsu Center for Disease Control, which successfully passed the detection capability verification of FAPAS with PAHs in palm oil in 2015 (round number was 0662, z-scores were À1.1, À0.8, 0.6, 0.0, 2.0, 1.8, À0.5 for BaA, CHR, BbFA, BaP, IP, BghiP, PAH4, respectively.), was responsible for the Standard Operation Procedure (SOP), comparison of the two methodologies and quality control among laboratories. Before analysis of samples, all laboratories participated in the unified methodology and experimental technology training and passed the unified certification of quality control sample.
A quality control sample and a blank sample were systematically analyzed within each batch, and performances were checked to ensure a better quality for analysis. The deviation rate of assigned PAH values in the quality control sample performed by nine laboratories ranged from À25 to 43%.
For each PAH congener under the analytical limits we assigned the value one-half of the LOD (ND ¼ 1/2 LOD), according to WHO Global Environmental Monitoring System/Food (GEMS/ Food) 2nd meeting on 'Credibility Evaluation of Low Level Contaminants in Food' (WHO 1995). Oil samples analyzed by method b were not monitored for BjFA and CPP; the missing values were assigned to zero.
We evaluated the data using SPSS 19.0. The bivariate correlation test was applied to PAH concentrations. We assessed the statistical significance of correlations using the Spearman test. A probability lower than 0.05 (p<0.05) was considered significant. Ordinary statistical methods were used to calculate the mean, median, and 95th percentile (P95) of PAH concentrations.

Assessment of human dietary exposure
The dietary exposure to PAHs was estimated by combining the occurrence data on PAH concentrations and individual consumption data of the corresponding food categories, using the following formula.
where EXPj is the total dietary exposure of subject j to BaP, PAH2, PAH4 or PAH8 in ng/kg bw/d; Fi is the consumption amount of food i by subject j in g/day; Ci is the mean concentration of BaP, PAH2, PAH4 or PAH8 in food i in lg/kg; BWj is the individual body weight of subject j in kg; and n is the total number of food items in the diet of the subject j. Mean and 95th percentiles of exposure, the latter representing the exposure for high consumers, were calculated for the general population, and for each age and gender group.
We targeted the general population over 6 years of age, due to the lack of consumption data of people below this age. The population was divided into five groups, based on the energy intake and consumption patterns: children (6-12 years old), male adolescents (13-17 years old), female adolescents (13-17 years old), male adults (>18 years old), and female adults (>18 years old).
To evaluate the risk of exposure to PAHs, we calculated MOEs for population by dividing EFSA's BMDL 10 values (0.07, 0.17, 0.34, and 0.49 mg/kg bw/day for BaP, PAH2, PAH4 and PAH8, respectively) by the mean or the high levels estimates of dietary exposure to BaP, PAH2, PAH4 and PAH8. When MOE were >10,000, the estimated dietary intakes of PAHs were of low concern for human health; under this value there could be a potential concern for human health (EFSA 2008 Percentage of contribution of different food groups was calculated as the rate of exposure through the food group consumption in the total mean PAHs dietary exposure.

Results
Occurrence and patterns of PAHs in food PAH concentrations in the 1,564 food samples acquired from nine provinces in China are summarized in Tables 1 and 2. Out of the 1,564 samples, 722 (46.2%) were negative for PAHs. For individual PAHs, the proportion of results > LODs were very specific to the compound: from 41.05% for chrysene to 0.26% for dibenzo[a,h]pyrene.
Total PAH16 concentrations had an apparently positive skewness distribution and ranged from ND to 269.97 lg/kg, with an average of 6.19 lg/kg and a median of 2.40 lg/kg. In term of food groups, the current highest level of mean total PAH16 concentration was detected in edible vegetable oils (17.89 lg/kg), followed by SGB meats (17.32 lg/kg), SGB aquatic products (16.26 lg/kg) and frying oils (9.36 lg/kg). The other five food categories had the lowest mean total PAH16 concentrations (1.0-3.0 lg/kg).
The most abundant PAH was chrysene, with a mean value of 1.07 lg/kg, followed by benz[a]anthracene (mean value 0.80 lg/kg) and benzo[b]fluoranthene (mean value 0.75 lg/kg), and the lowest levels were dibenzo[a,h]pyrene (mean value 0.12 lg/kg) and dibenzo [a,i] The detection rates of individual PAHs across food categories are shown in Figure 2. PAH individuals were detected at high rates in the processed food products (SGB aquatic products, frying oils, SGB meat, and edible vegetables oils), and much lower rates in the fresh foods (raw aquatic products, raw meat, cereals, fruits, and vegetables). The differences of detection rates between the processed food products and the fresh foods were statistically significant (p<0.05).
PAH patterns varied among different food categories ( Figure 3). Chrysene predominated in SGB meats, SGB aquatic products, edible vege- Chrysene was predominant in cereals, vegetables, and fruits. However, unlike other food groups, benz[a]anthracene was the most abundant contributor in raw meat and raw aquatic products. In the aforementioned five food groups, PAH4 contributed about $30-40% to total PAH16. These differences could be explained by the different origins of the PAHs in different food species. We used the data on benzo[a]pyrene, PAH2, PAH4, and PAH8 in the eight food groups (Table S1) to calculate exposure and estimate MOEs based on BMDL 10 .

Suitable indicators screening
According to EFSA, the TEF approach is not scientifically valid in the risk characterization of PAH mixtures in foods (EFSA 2008). Therefore, we used individual PAHs as surrogate for PAH contamination. Suitable indicators were assessed based on the occurrence of other PAHs in samples with benzo[a]pyrene results < LOD, and   The situation for individual PAHs and for the group of eight PAHs not included in PAH8 (PAH16-PAH8) is illustrated in Table 3. Of samples in the absence of benzo[a]pyrene, chrysene (22.36%) was the most common PAH, followed by benz[a]anthracene (17.28%). In samples with PAH2 results < LOD, the proportion of sample numbers > LOD for other individual PAHs was below 5% except benz[a]anthracene still at 10.96%. Furthermore, in samples negative for PAH4, the proportion of sample numbers > LOD was below 3% for all other individual PAHs. Compared to samples negative for PAH4, the proportion of samples > LOD for PAH16-PAH8 (the sum of eight PAHs other than PAH8) slightly decreased from 7.96 to 7.81% for samples negative for PAH8.
To further assess the relationship between the different PAHs, we generated a correlation matrix covering 16 priority PAHs and their combinations ( Figure S1). Correlation coefficients (Spearman's rho) ranged from 0.716 and 0.986, explaining the high correlation between the individual PAHs and their combinations.
Results in Table 3 and Figure S1 indicated PAH8 is only slightly better than PAH4; PAH4 gave a sufficient accuracy that is not much improved by using the PAH8 combination. Considering cost-effectiveness of test, PAH4 is better than PAH8 as an indicator of PAH contamination in foods.

Human exposure assessment
Food consumption data for the general population of China are summarized in Table S2.
The daily intakes of benzo[a]pyrene, PAH2, PAH4, and PAH8 for the Chinese general population and the corresponding MOE values are shown in Table 4.
The overall average dietary exposures for benzo[a]pyrene and for PAH4 in the general population were 3.08 and 17.61 ng/kg.bw.day, respectively. The dietary exposures to benzo[a]pyrene and PAH4 for high consumers were 5.51 and 31.59 ng/kg.bw.day, respectively.  According to EFSA (EFSA 2008), MOE values <10,000 indicate a potential concern for human health. The MOEs in this study indicated a low concern for human health at the mean estimated dietary exposures. The MOE of exposure to PAH8 for high consumers was <10,000, indicating potential health hazards.
Concerning different age groups, we observed a decreasing tendency in the PAH intakes with increasing age, with the highest daily intakes found in children (6-12 years old) (Table S3). With respect to gender, females ingested slightly more PAHs than males, for both adolescents and adults (Table S3). The MOEs for high consumers of children and adolescents were 10,000, which indicates a potential concern for their health and a possible need for risk management (Table S3).
The contributions of food groups to the mean PAH4 exposure were calculated (Figure 4.) The main contributors to PAH4 exposure for the Chinese general population were cereals (39%), edible vegetable oils (28%), and vegetables (20%). The significantly high dietary intake amounts of cereals (375.8 g/day) and vegetables (286.9 g/day), and the high PAH concentrations in edible vegetable oils were probably the reasons for the results.
Among the cereals, rice (48%) and wheat (49%) contributed evenly to PAH exposure. Among the edible vegetable oils, rapeseed oil (46%) was the greatest contributor, followed by peanut oil (22%) and soybean oil (12%). SGB foods were not major contributors (1.02% for SGB meats and 0.05% for SGB aquatic products) due to the low consumption of these products (1.15 g/day for SGB meat and 0.05 g/day for SGB aquatic products).
SGB foods consumers, accounting for 2.70% of the total Chinese population, consumed 42.78 g/d SGB meats and 2.0 g/d SGB aquatic products on average. For SGB foods high consumers, the consumption of SGB meats and SGB aquatic products were 116.67 and 20.5 g/d, respectively. The mean and high dietary exposures to PAH4 for SGB food consumers were 23.64 and 46.71 ng/kg bw/d, respectively, and the corresponding MOEs were 14,380 and 7279. The exposure to PAH4 might cause potential health effects for SGB foods high consumers.

Discussion
In foods and the environment, PAHs exist as complex mixtures consisting of hundreds of compounds. Several studies have focused on the 16 PAHs selected by the U.S. Environmental Protection Agency (EPA) in 1976 (Keith 2015). However, the 16 EPA PAHs may be too limited when describing the toxic potential of total PAHs (Andersson and Achten 2015). The eight PAHs of PAH8, which are among the 16 EPA PAHs, have carcinogenic and mutagenicity/genotoxicity effects, and were of concern to the European Union. The European Union proposed a new list of 16 priority PAHs, including some heavier and more toxic PAHs, such as 5-methylchrysene and benzo(c)fluorene (EFSA 2008). Consequently, we evaluated the 16 EU priority PAHs in the Chinese diet.
We detected higher concentrations of PAHs in processed foods (e.g. edible vegetable oils, SGB meats, SGB aquatic products, and frying oils) and lower concentrations of PAHs in fresh foods (cereals, vegetables, fruits, raw meats, and raw aquatic products). Processed foods had five to seven times higher total PAH16 concentrations than fresh foods. Individual PAHs were detected at higher rates in the processed food products than in the fresh foods. PAH4 comprised more than 50% to the sum of total concentration of PAHs in the processed foods, but <35% in the fresh foods. The proportion of CPP was higher in the processed foods than in the fresh foods ( Figure S2). This difference might be related to the origin of PAHs (processing contamination vs environmental). For example, PAHs in cereals, vegetables, and fruits may originate from the atmosphere, particle deposition, soil, and irrigation water (Bansal and Kim 2015;Alegbeleye et al. 2017). Livestock, poultry, seafood and fish can be exposed to PAHs through the air, water, and sediments, as well as an accumulation of PAHs in the food chain, resulting in PAH contamination in raw meats and raw aquatic products (Sun et al. 2016;Tongo et al. 2017;Okoye et al. 2021).
Besides environmental sources, SGB foods, edible vegetable oils, and frying oils become contaminated during industrial food processing and certain domestic cooking practices. Smoking, baking, frying, or grilling are major factors for PAHs in processed foods (Rozentale et al. 2018;Gholizadah et al. 2021;Zhang et al. 2021). Direct smoking of meats or fish products resulted in higher PAH concentrations compared to indirect smoking methods. Additionally, hot smoking resulted in higher PAH levels than cold smoking (Zelinkova and Wenzl 2015). Cheng et al. 2019 reported that PAH concentrations markedly increased in vegetables and animal-based foods after grilling.
Edible vegetable oils are easily contaminated by PAHs due to their lipophilic property. Vegetable oils are mainly contaminated through environmental pollution of the raw oilseeds, also by pollution from direct smoke-drying, solvent extraction and mineral oils in oil manufacturing process, if precautionary measures are not taken (Zelinkova and Wenzl 2015;Shi et al. 2016).
Total PAH concentrations should not be compared among different studies on account of combinations of different individual PAH. Considering that benzo[a]pyrene and PAH4 can be used as indicators of PAH contamination in foods, we compared levels of benzo[a]pyrene and PAH4 in Chinese foods with concentrations in foods from other countries or regions (Table 5).
In our study, benzo[a]pyrene and PAH4 concentrations were higher than those reported in France (Veyrand et al. 2013), Sweden (Abramsson-Zetterberg et al. 2014), and Spain (Martorell et al. 2010). However, PAH concentrations in raw meats were similar to the results reported in those countries and in Korea (Kim Hwang and Shin 2014). Benzo[a]pyrene concentrations were lower in our study than those reported in Pakistan (Aamir et al. 2021), and considerably lower than those reported in India (Singh and Agarwal 2018). The lower PAH concentrations in food from European countries may be a result of improved food production processes, established maximum limits of PAHs in foods (European Commission 2011) and lower environmental pollution (Abramsson-Zetterberg et al. 2014).
PAH4 concentrations in raw meats were lower in our study than in Egypt (Darwish et al. 2019). However, benzo[a]pyrene showed the opposite trend. Concerning SGB foods, (Rozentale et al. 2018) reported comparatively higher PAH concentrations in smoked meat products from the Baltic states (Latvia, Lithuania, and Estonia). PAH concentrations in smoked fish from Japan were 7 to 13 times higher than those in smoked meats (Tsutsumi et al. 2020), whereas we obtained similar PAH concentrations in SGB meats and SGB aquatic products. Sahin et al. (2020) reported equivalent results to ours. The edible vegetable oils in our study had lower PAH concentrations than those reported by another domestic study (Shi et al. 2016).
Concerning the contamination profile of PAHs, similar findings were also observed by Veyrand et al. (2013), who reported that the most predominant PAHs in foods consumed in France were chrysene (25.7%), benzo[b]fluoranthene (15.0%), and benz[a]anthracene (9.0%). Similarly, benzo[a]pyrene contributed $4.5% of the total PAHs. The relative proportions of PAHs in our study were also in agreement with the report by EFSA, in which chrysene comprised more than a quarter of the total PAHs, followed by benzo[b]fluoranthene, benz[a]anthracene, cyclopenta[cd]pyrene and benzo[a]pyrene at 13, 12, 9, and 8%, respectively (EFSA 2008).
The indicator screening results in our study were in accordance with EFSA's findings. According to EFSA, the correlation coefficient between PAH2 and PAH4 or PAH8 was 0.92 and between PAH4 and PAH8 was 0.99. Among the samples negative for PAH4, 14 and 6% identified concentrations > LOD for at least one other PAH for samples tested for all 15 PAHs or all PAH8, respectively. Overall, EFSA concluded that PAH4 and PAH8 are better indicators of the occurrence of PAHs than PAH2, and that the PAH4 combination seems to give a sufficient accuracy that is not much improved by the PAH8 combination (EFSA 2008).
PAH dietary exposure levels vary among populations from different countries. For comparison of daily intakes, data from some international studies concerning dietary exposure to PAHs are summarized in Table S4. Veyrand et al. (2013) estimated the daily intakes of BaP and PAH4 for French adults at 0.191 and 1.48 ng/kg bw/day, respectively. The exposure levels were $ 12 to 16 times lower in French adults than in Chinese adults. In Swedish population, the mean intakes of BaP and PAH4 were 0.71 and 3.94 ng/kg bw/day, respectively (Abramsson-Zetterberg et al. 2014), which were much lower than those in the Chinese population. Catalonia, Spain reported lower exposure levels than our study, which were estimated at 1.09 ng/kg bw/day for BaP and 5.86 ng/kg bw/day for PAH4 (Martorell et al. 2010).
Considering the daily dietary exposure through different food categories, the whole population in China ingested approximately 15 times more PAHs through cereals than the Swedish population (Abramsson-Zetterberg et al. 2014). Equivalent results were reported for meats and meat products (Abramsson-Zetterberg et al. 2014). In contrast, dietary exposure to PAHs through raw and SGB meats were lower in China than in the United States (Pouzou et al. 2018) and Croatia (Bogdanovi c et al. 2019). Meanwhile, daily intakes of PAHs through SGB meats were lower in our study than in Egypt (Darwish et al. 2019), the Baltic states (Rozentale et al. 2018), and Shandong province (Jiang et al. 2018).
The calculated PAH intakes varied among different populations, probably due to the diverse PAH concentrations in different foods, the differences in dietary habits, and the selection of foods for the exposure calculation (Abramsson-Zetterberg et al. 2014). Veyrand et al. (2013) calculated the MOEs for mean exposures to PAH4 at 150,000 for children and 230,000 for adults, and concluded that exposure to PAHs through foods was not a major health problem for French consumers.
Some other evaluations of dietary exposure using the MOE approach indicated a negligible risk to human health for consumers in Croatia (Bogdanovi c et al. 2019), Turkey (Sahin et al. 2020), Korea (Kim Hwang and Shin 2014) and Denmark (Duedahl-Olesen et al. 2020). In contrast, Tsutsumi et al. (2020) reported a MOE of 8,629 based on the mean intakes of PAH4 for Japanese consumers through smoked fish and dried bonito flakes. The characterization of health risk in terms of the consumers' age indicated a potential risk in the middle-age (39-50 years) group from the Baltic states, with a MOE value of 8,486 for PAH4 (Rozentale et al. 2018).
The decreasing tendency in the PAH intakes with increasing age might be related to the different food intake amounts per body weight in different age groups. Our findings are in accordance with the results reported by Veyrand et al. (2013) and Ekhator et al. (2018).
Some studies have reported that dietary exposure to PAHs was higher in males than in females (Xia et al. 2010;Aamir et al. 2021), which was contrary to our result. Different dietary exposure between two genders is probably due to a higher food consumption in males, different physiological characteristics and dietary patterns between the two genders. However, the dietary intakes in these two studies were expressed in ng/day. When their results are converted to ng/kg bw/day, the dietary exposure of males is comparable with that of females.
In our study, the contributions of different food groups were similar to those observed in the UK (FSA 2002), Netherlands (De Vos et al. 1990), and Catalonia (Martorell et al. 2010), where cereals were the largest contributor to B(a)P intake. Singh and Agarwal (2018) concluded that major PAHs linked with cancer risk originated from consumption of cereal-based products. According to EFSA, cereals and cereal-based products are the main sources of PAHs, mainly due to the high amounts consumed (EFSA 2008;Zelinkova and Wenzl 2015). Among all food categories, the greatest contributions to the total PAHs exposure of the Pakistani population were from wheat and milk, at 43% and 34%, respectively (Aamir et al. 2021). The differences of food contributions to PAHs exposure may be related to diverse dietary habits.

Study limitations
There were a few limitations in this study. Firstly, dietary exposure could be overestimated, as sampling was not random but targeted. Secondly, some samples were not analyzed for BjFA and CPP, because LC-FLD cannot sensitively detect PAHs with weak or no fluorescence (BjFA and CPP). The amount of PAH16 might be underestimated. Thirdly, as approximately half of the samples (46.2%) were negative for PAHs, lowering LODs might provide a better picture on distribution of PAHs in different food groups and dietary exposure assessment.

Conclusions
In summary, we estimated the contamination levels of 16 EU priority PAHs in the Chinese diet. Edible vegetable oils and SGB foods were the most contaminated samples. PAHs with the highest proportion of results > LOD and the highest average concentrations were chrysene, benzo(a)anthracene, benzo(b)fluoranthene and benzo(a)pyrene (PAH4). Chrysene was the most important contributor to the total PAHs. According to our screening results, PAH4 is a suitable indicator of PAH contamination in foods, better than benzo(a)pyrene, PAH2, or PAH8. The exposures to PAHs through the diet of the Chinese general population and SGB food consumers were also calculated. The greatest contributors to the total dietary exposure of PAHs were cereals, edible vegetable oils and vegetables. The MOE approach was used to assess the health risk for consumers. The mean estimated dietary exposures were of low concern for the health of the general population and SGB food consumers. Nevertheless, for high consumers and children, the MOEs indicate a potential concern, which might require further risk management.
To the best of our knowledge, this is the first study that evaluates the health risk of PAHs for the Chinese general population through the total diet. The human health risk of PAHs needs to be further evaluated. It is important to reduce dietary PAH exposure by implementing reasonable and effective risk management strategies to reduce PAH concentrations in foods.

Disclosure statement
No potential conflict of interest was reported by the author(s).