Introduction

Phthalic acid esters (PAEs) are organic chemicals that are mainly used as plasticizers for the manufacture and processing of plastic products, especially to impart flexibility to polyvinyl chloride resins (Kimber and Dearman 2010). PAE is widely used as an additive in various industrial and commercial products, such as building materials, electronic and medical devices and pediatric articles, food packaging, children’s toys, personal care products, home furnishings (Berman et al. 2011; Wang et al. 2012a; Cai et al. 2008; Bello et al. 2014).

The global production of plastic has exceeded 150 million tons. The annual production of plastic reached 8 million tons in 2011, in which Europe’s consumption of PAEs accounts for approximately 1 million tons (Net et al. 2015a). The polymerization of phthalates does not entail a chemical bond (i.e., only a physical bond) to a polymer matrix, indicating that PAEs can be easily and directly released into the environment during manufacture, use, and disposal (Net et al. 2015b). PAEs were detected in different kinds of environmental media, including indoor and outdoor air, surface water, seawater, soil, sediment, animals and plants, and humans (Kong et al. 2012, Pei et al. 2013, Li et al. 2015, Liu et al. 2010, Wang et al. 2012, Yang et al. 2014, Amir et al. 2005, Cheng et al. 2013, Guven and Coban 2013).

People are in contact with PAEs, consumption of contaminated food and drinking water, or dermal contact (Heudorf et al. 2007; Wang et al. 2012b), Studies have shown that PAEs exist in body tissues and excretions, including human urine, blood, and breast milk (Fernández et al. 2012; Hines et al. 2011). Epidemiology and toxicology studies have demonstrated that certain PAEs, such as di-2-ethylhexyl phthalate (DEHP), di-n-butyl phthalate (DnBP), butyl benzyl phthalate (BBP), and diethyl phthalate (DEP), are endocrine-disrupting compounds. The possible harm of PAEs to humans includes problems on fertility (impact of endocrine disruption), neonatal development, and carcinogenic properties. Howdeshell et al. reported that the effects of PAEs, when mixed with other anti-androgen drugs, accumulate in the male reproductive organ and may affect human reproductive development (Howdeshell et al. 2008). Many countries have consequently raised their concern on the use and emission of PAEs, and some of them have even restricted PAEs to a certain extent. Dimethyl phthalate (DMP), DEP, dibutyl phthalate (DBP), BBP, DEHP, and di-n-octyl phthalate (DNOP) are listed as priority pollutants by the United States Environmental Protection Agency (U.S. EPA). The European Community has defined the environmental quality standard for DEHP concentration to be less than 1.3 ng mL−1 in surface waters (Sazan et al. 2008).

Lanzhou, abbreviated as “Lan,” is an important industrial base and an integrated transportation hub in the capital of Gansu Province, an important transportation hub in northwestern China, and one of the important central cities in the western region. The length of the Lanzhou section of the Yellow River is 152 km, starting from the Bapan Gorge in the west, to the Dongwu Gorge in the Yuzhong County in the east, and exiting to Wujinxia in the Suizhong County in the north. Li et al. (2012) focused on the occurrence and distribution of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls, organochlorine pesticides, and phthalate esters (PAEs) in drinking water samples obtained from the Yellow River. The total concentrations of 31 semi-volatile organic compounds (SVOCs) were in the range of 0.92–266.16 ng/L in March and 24.82–643.93 ng/L in August. PAEs occupied 79.17–100.00% of the total concentration of SVOCs obtained from the tributaries of Yangtze River in March. Then, we investigated the distribution of PAHs in this region. The total PAH concentrations were in the range of 548–2598 ng/L in water, 1502–11,562 ng/g in suspended particulate matter, and 181–1583 ng/g in sediments. Most research on persistent organic pollutants in China has concentrated on the Pearl River, the Yangtze River, and the lower reaches of the Yellow River. By contrast, the studies about the upper reaches of the Yellow River and other watersheds are rare. This study analyzes the PAEs in the water samples of the Lanzhou section of the Yellow River. Our findings offer important reference value for the living and industrial water in Lanzhou City. This paper revealed the PAES in the upper reaches of the Yellow River which are rarely studied, and studied their distribution in different seasons and media, which will help people to understand the source and destination of pollutants, and provide data support for research at home and abroad.

Materials and methods

Standards and reagents

DMP, DEP, diisopropyl phthalate (DIPrP), diallyl phthalate (DAP), di-n-propyl phthalate (DPrP), diisobutyl phthalate (DIBP), DBP, bis(2-methoxyethyl) phthalate (DMEP), diisohexyl phthalate (DMPP), di-2-ethoxyethyl phthalate (DEEP), diamyl phthalate, di-n-hexyl phthalate (DPXP), BBP, bis(2-butoxyethyl) phthalate (DBEP), dicyclohexyl phthalate (DCHP), DEHP, 1,2-diphenyl ester, di-n-octyl phthalate (DNOP), dibenzyl phthalate, dinonyl phthalate (DNP), diisodecyl phthalate, and an internal standard solution (benzyl benzoate) in hexane were purchased from Tokyo Chemical Industry Co. Ltd. (Tokyo, Japan). The basic physical and chemical information, including notations, molecular weight, structural formula, density, Vp, and logKoa, is listed in Table 1. All of the HPLC-grade solvent methylene dichloride, formic acid, and acetonitrile were purchased from Fisher Scientific (Ottawa, ON, Canada).

Table 1 Physicochemical properties of phthalates
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Sample collection

The Lanzhou section of the Yellow River has a temperate continental climate, with high rainfall incidence in autumn and summer and low rainfall in spring and winter, indicating distinct dry and wet periods. Paired water and sediment samples were collected from the Lanzhou section of the Yellow River from August 2016 to March 2017. The distribution of the 12 sampling sites is shown in Fig. 1. The latitude and longitude information of the sampling sites (Table 2) was expressed in SI. Surface water samples (0–50 cm) were collected and stored in 1 L glass bottles, while 50 g surface sediments (0–10 cm) were concurrently collected and stored in stainless steel jars. All sampling tools and vessels were preconditioned consecutively with Milli-Q water, methanol, and methylene dichloride to remove the contaminant residues. The samples were transported to the laboratory and water-stored at 4 °C, while the sediment was kept at − 20 °C before analysis.

Fig. 1
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Location of each sampling point

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Table 2 Longitude and latitude coordinates of each sampling point
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Sample pretreatment and instrument analysis

Water and sediment samples were extracted and purified as follows. Briefly, 500 mL of the water samples spiked with the internal standard were passed through 0.45 um glass fiber filters to remove particulates and suspended matter. Subsequently, the water sample bottles were washed with 100 mL dichloromethane (DCM) and transferred into a separator funnel and shaken continuously for 3 min. The separator funnel was held for 5 min to enable the organic phase to form at the bottom. This extraction process was repeated two more times. Then, the extract was dehydrated over anhydrous sodium sulfate, and the dehydrated organic phase was concentrated to 1 mL with a nitrogen blower. Freeze dry and grind the sediment sample to a size less than 100 mesh. The sediment sample (1 g) was extracted by 10 ml acetone / DCM shaking, in triplicate. Then, the sample was blown to 1 ml by nitrogen to the GC-MS for analysis. A known amount of internal standard (DnBP-d4 and DEHP-d4) is added to the extract prior to instrumental analysis.

Gas chromatography–mass spectrometry, followed by the methods in previous studies (Zhang et al. 2015), was used to identify and quantify the targets. A DB-5MS capillary column (60 m (length) × 0.25 mm (i.d.) × 0.25 μm (film thickness)) was used for the separation of target compounds under a constant flow rate of 2.0 mL/min by helium as the carrier gas. The oven temperature was maintained at 80 °C for 1.0 min, increased at 10 °C/min to 180 °C (held for 1 min), and further increased at 3 °C/min to 300 °C (held for 5 min). The injector, quadrupole, and ion source temperatures were maintained at 280 °C, 150 °C, and 250 °C, respectively. Qualitative and quantitative ionic values were expressed in SI.

Quality assurance and quality control

Deionized water and diatomite sediment blank samples(n = 3) were extracted similar to the real samples, except DEHP (15–102 ng/mL), no other contaminant was detected in blank sample. This scenario may mean that the containers and the samples were not contaminated during storage and transportation. Limits of detection (LODs) were calculated as a signal-to-noise ratio of 10. The LODs of the targets (n = 3) were in the range of 0.05–0.74 ng/L and 0.008–0.26 ng/g for the water samples and the sediment samples, respectively. The recoveries of the target compound were in the range of 70–140%. The obtained information was expressed in SI. An external standard method was performed to examine the quality of the compound. The results indicate a significant linear relationship in the concentration range of 10–2000 ng/mL.

Human health risk assessment

DMP, DEP, DnBP, and DOP were recognized as non-carcinogenic compounds with respect to human health, while BBP and DEHP were identified to present a cancer risk (Wang et al. 2018). Drinking and bathing are the most common approach through water by humans. Thus, this study used the health assessment model established by U.S. EPA and Hamibin et al. (Hamidin et al. 2008), to calculate the six priority PAEs in the water samples of the Lanzhou section of the Yellow River. The equation for the non-carcinogenic compound risk index (HI) is

$$ \mathrm{HI}=\mathrm{E}/\mathrm{RfD}, $$
(1.1)

where RfD (mg/(Kg day)) is the maximum acceptable concentration of pollutants per day in humans. The RfD values of DMP, DBP, DEP, were 10.0, 0.1, 0.8 respectively. E is the average daily dose of contaminants (mg/(Kg day)) through drinking water or skin contact. Drinking water exposure levels (E1) and skin exposure levels (E2) were calculated using Eqs. 1.2 and 1.3.

$$ \mathrm{E}1=\mathrm{CC}\times \mathrm{RM}\times \left(\mathrm{C}\times \mathrm{IRw}\times \mathrm{E}\mathrm{F}\times \mathrm{E}\mathrm{D}\right)/\mathrm{BW}/\mathrm{AT} $$
(1.2)
$$ \mathrm{E}2=\mathrm{CC}\times \mathrm{RM}\times \left(6\uptau \times \mathrm{TE}/\uppi \right)0.5\left(\mathrm{C}\times \mathrm{k}\times \mathrm{Asb}\times \mathrm{FE}\times \mathrm{E}\mathrm{D}\right)/500/\mathrm{BW}/\mathrm{AT}/\mathrm{f} $$
(1.3)

CC is the conversion coefficient, and the value is set to 0.1. RM is the PAEs’ residual rate factor after treatment in the water plant, and the value is set to 0.1. C is the concentrations of PAEs were detected in mg/L. IRw is the daily drinking water volume of the human body (2 L). EF is exposure frequency (365 days/year). ED is exposure delay (30 years, as recommended by the U.S. EPA). BW represents weight, and the average value is set to 70 kg. AT is the average lifetime exposure of humans (70 years·365 days/year). k is a skin adsorption parameter, and the value is set to 0.001 cm/h. τ is the lag time of the PAE contaminants, and a value of 1 h is assumed. TE is the average bathing time of people (0.546 h), Asb is the surface area of the human body (16,600 cm2), FE is bathing frequency (0.3 times/d), and f is intestinal absorption rate with a value set to 1. The formulas for carcinogenic risk (R) assessment are given by Eqs. 1.4.

$$ \mathrm{R}=\mathrm{SF}\times \mathrm{E}\ \left(\mathrm{R}<0.01\right) $$
(1.4)
SF:

is the slope factor, and the value is 0.014 mg/(Kg day).

Results and discussion

After pretreatment and on-machine analysis, the concentrations, concentration ranges, median values, and detection rates of the PAE compounds in the water samples for the dry and wet periods of the Yellow River in Lanzhou were calculated (Table 3). The sum of average concentrations for each PAE among all sampling sites in the water samples of the Yellow River for the dry period was 3236.0 ng/L, and the concentration ranged between n.d. and 5585.9 ng/L. PAEs were detected in all the sampling points. In particular, DMP, DEP, DIBP, DEHP, and DBP were found in all sampling points, but DIPrP, DPrP, DMEP, DMPP, DEEP, DPXP, DCHP, and DNP were non-existent. Different types of compounds were also detected in varying frequencies. Among the six phthalates preferentially controlled by the U.S. EPA, only DMP, DEP, DBP, and DEHP were detected in all sampling sites. DNOP was detected in four sampling sites only, while BBP was detected in one sampling site only. The average concentrations were 645.2 for DMP, 455.7 for DEP, 483.2 for DEP, 795.2 for DBP, 4.8 for BBP, and 2.0 ng/L for DNOP. The sum of average concentrations for each PAE among all sampling sites in the water samples for the wet period of the Yellow River in Lanzhou was 2300.0 ng/L, and the concentration ranged between n.d. and 6039.9 ng/L. PAEs were detected in all sampling sites, and all samples of DMP, DEP, DIBP, DBP, and DEHP were present. Four of the six PAEs prioritized and controlled by the U.S. EPA were detected. DNOP was detected in seven sampling points, while BPP is detected in four sampling points only. The average concentrations were 344.4 ng/L for DMP, 310.8 ng/L for DEP, 77.89 ng/L for DBP, 0.8 ng/L for BBP, 430.6 ng/L for DEHP, and 4.8 ng/L for DNOP.

Table 3 Concentration of Phthalates in Water Samples of Lanzhou Section of the Yellow River
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The concentration distribution, concentration range, median value, and detection rate of the PAE compounds in the sediments of the Yellow River for the dry and wet seasons are shown in Table 4. The sum of average concentrations for each PAE among all sampling sites in the sediments of the Yellow River for the dry period was 4238.9 ng/g, and the concentration ranged between n.d. and 9897.6 ng/g. PAEs were detected in all sampling points. In terms of individual compounds, DMP, DEP, DIPrP, DAP, DIBP, DBP, DMPP, DBEP, DEHP, and DNOP existed in all sampling points. The six PAEs (DMP, DEP, DBP, BBP, DEHP, and DNOP) prioritized and controlled by the U.S. EPA were detected in all sampling points, and their average concentrations were 141.8, 301.8, 589.9, 15.0, 2570.1, and 5.8 ng/g, respectively. The sum of average concentrations for each PAE among all sampling sites in the sediments of the Yellow River for the wet season was 3959.9 ng/g, and the concentration range was between n.d. and 8175.5 ng/g. PAEs were detected in all sampling points, and all six PAEs controlled by the U.S. EPA are detected. The average concentrations were 84.0 ng/g for DMP, 204.2 ng/g for DEP, 810.2 ng/g for DBP, 15.0 ng/g for BBP, 1451.7 ng/g for DEHP, and 14.9 ng/g for DNOP.

Table 4 Phthalates in sediments from the Lanzhou section of the Yellow River
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Temporal and spatial distribution of PAEs in the Lanzhou section of the Yellow River

The temporal and spatial distribution of PAEs in the Lanzhou section of the Yellow River is shown in Fig. 2. From the perspective of space, the PAEs in this river section have increased and then decreased from upstream to downstream in general. S1 is located in the upper reaches of the Lanzhou section of the Yellow River, and it is not contaminated by organic matter. S2 and S3 are located in the Xigu District of Lanzhou. Large-scale chemical companies, such as Lanzhou Petrochemical Company, Lanzhou Xigu Sanli Fine Chemical Plant, and Lanzhou Petrochemical Synthetic Rubber Plant, operate in this region. The pollutants in the wastewater produced by these enterprises are the main sources of water pollution in the Lanzhou section of the Yellow River. S4–S8 are located in the middle part of the Lanzhou section of the Yellow River. This area is a gathering place for people’s livelihood and business. Human production and activities generate a large amount of domestic wastewater, although the garbage is treated by a sewage treatment plant, organic pollutants in water cannot be traced and treated effectively. Plastic product companies, such as Lanzhou Plastics Six Factory and Lanzhou Hengtong Plastics Factory, operate in this area. Ninety percent of the PAEs are used as plasticizers by industry players to improve the flexibility and processability of polymers in China. (Teil et al. 2006). S9–S12 are located in the lower reaches of the Lanzhou section of the Yellow River. As the rivers flow, pollutants are continuously diluted and absorbed into suspended matter and mud. Thus, the concentrations of PAEs in these waters are reduced.

Fig. 2
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Time and spatial distribution of PAEs in the water samples from the Yellow River in Lanzhou

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From the viewpoint of time, the concentration of PAEs in the water samples collected from the Yellow River for the dry season was higher than that for the wet season. This finding can be attributed to precipitation in Lanzhou, which is mainly concentrated in autumn and summer, and a large amount of precipitation flows into the river, thus diluting the concentration of pollutants in the water. During the wet period, the temperature of the Yellow River in Lanzhou is relatively high, and this phenomenon promotes the volatilization of PAEs from the water environment to the atmosphere. During the dry season, the low temperature of the Yellow River limits the growth and activity of microorganisms, indicating that the degradation of pollutants in water by these microorganisms is not conducive. The difference in PAE concentrations in the water environment for the two different sampling periods can be explained on the basis of the above explanations.

The distribution of PAEs in the sediments of the sampling sites for the low and dry periods in the Lanzhou section of the Yellow River is shown in Fig. 3. From a spatial viewpoint, the distribution of PAEs in the sediment samples is nearly the same as that in the aqueous phase. From the time viewpoint, the concentration of PAEs for the dry season is not that different from the dry season, and this similarity may be due to the accumulation of organic matter in the sediments for many years and the small sampling time interval, resulting in negligible changes in PAE concentrations.

Fig. 3
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Time and spatial distribution of PAEs in the water sediments from the Yellow River in Lanzhou

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The compositions of PAEs in the aqueous phase of the Yellow River for the dry and wet periods are shown in Table 5. In the water samples for the dry season, the preferentially regulated six PAE compounds of the U.S. EPA accounted for 15.67% (DMP), 13.51% (DEP), 33.86% (DBP), 0.03% (BBP), 18.72% (DEHP), and 0.21% (DNOP). As for the water samples for the wet season, the six compounds accounted for 19.94% (DMP), 14.08% (DEP), 24.57% (DBP), 0.01% (BBP), 25.61% (DEHP), and 0.06% (DNOP).

Table 5 Composition and concentration (average concentrations between all sampling points) of PAEs in the water phase of the Yellow River during the dry and wet periods in Lanzhou
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The compositions of PAEs in the sediments of the Yellow River for the dry and wet periods are shown in Table 6. In the sediment samples for the dry season, the prioritized and regulated six PAEs of the U.S. EPA accounted for 3.3% (DMP), 7.1% (DEP), 13.9% (DBP), 0.4% (BBP), 60.6% (DEHP), and 0.4% (DNOP). As for the corresponding wet period, the six compounds accounted for 2.12% (DMP), 5.16% (DEP), 18.8% (DBP), 0.01% (BBP), 36.66% (DEHP), and 0.38% (DNOP). The composition analyses showed that the sum of DMP, DEP, DBP, and DEHP accounted for more than 80% of the entire six PAEs prioritized by the U.S. EPA. DMP, DEP, DBP, and DEHP accounted for more than 60% and 85% of the sediment samples for the wet period and the dry season, respectively. Therefore, these four compounds are the main components of the PAEs in the Lanzhou section of the Yellow River, and they entail large amounts of production and emissions. Moreover, DIBP is as excessive as the above four compounds. Our results are consistent with those of previous studies, in which DEHP, DIBP, and DBP are the main components of PAE distribution in water and sediment samples and are also consistent with the reports of DEHP, DIBP and DBP(Vethaak et al. 2005, Fan et al. 2008, Mackintosh et al. 2006,Vitali et al. 1997).

Table 6 Composition and concentration (average concentrations between all sampling points) of PAEs in the sediment of the Yellow River during the dry and wet periods in Lanzhou
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The distributions of water samples and sediment components were compared. The proportions of DMP and DEP are relatively high in the water samples, while DEHP content is relatively high in the sediments. These findings can be explained by the small molecular weights of DMP and DMP and thus can be easily dissolved in the aqueous phase. In addition, DEHP has a relatively high molecular weight and hence can be easily adsorbed in the sediments (Staples et al. 1997). As can be seen from Tables 5 and 6, PAEs in sediment has a higher detection frequency than that in water. This finding was determined on the basis of the physicochemical properties of the PAE compounds. The log Koa value is relatively large of PAEs, such as DEHP, which proportion in sediment is larger than that in water. Conversely, less hydrophobic substances, such as DEP, DMP, account for more in water than in sediment. PAEs have a low polarity and can easily be changed into suspended matter and thus can adsorbed from the aqueous phase to the particulate phase in the sediments (Li et al. 2017a).

Comparison of phthalate esters in the Lanzhou section of the Yellow River with other areas

The total concentration of the sediments in the Lanzhou section of the Yellow River and the compounds with higher detected concentrations compared with those in the other areas are shown in Table 7 (Li et al. 2017b, Adeogun et al. 2015, Li et al. 2016a, Li et al., 2016d, Adeogun et al. 2015, Hermann Frommea, et al. 2002, Huang et al. 2008). The phthalates in the Lanzhou section of the Yellow River are in the intermediate levels for both dry and wet seasons, and several compounds are also in the same level as most of the areas listed in the table. The results of the comparison show that PAEs are extensively produced and used in the Lanzhou area. The concentration in this river section is not as high as those in the other areas, but it cannot be ignored. Despite the occurrence, the research on PAEs in the Lanzhou section of the Yellow River is rare. The other data obtained in this work are discussed below.

Table 7 Comparison of phthalates in the Yellow River section of Lanzhou with other areas
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Dong Jiyuan evaluated the health risks of PAEs in the Lanzhou section of the Yellow River in 2005. The concentration of the PAEs on the monitoring section (Xishuiqiao, Xigu Dachuan Township) was 2.52 μg/L. The concentration value of the drinking water source (Chaimen Village Suspension Bridge) was 37.59 μg/L. Guo Hongdong studied four PAEs in the Lanzhou section of the Yellow River in 2007. The total concentration of PAEs in the sediment samples in the summer ranged from 5.041 to 41.305 μg/L, and the total concentration of PAEs in the winter ranged from 8.016 to 29.882 μg/L. The PAE concentrations were as high as 4.357 mg/kg, and the lowest values was 1.127 mg/kg. Compared with the above studies, the concentration of PAEs in this experiment is relatively low. We can presume that the period between the “Eleventh Five-Year” and the “Twelfth Five-Year Plan” was a period of relatively high treatment of pollutants in the Lanzhou section of the Yellow River. The regulations implemented for the discharge and treatment of pollutants during that time have become strict, and water quality has improved. However, efforts should also focus on rectifying the Lanzhou section of the Yellow River and improve the water quality of the river.

Risk assessment of phthalate esters in the Lanzhou section of the Yellow River

Among the six priority PAEs, DBP, DEP, and DMP are classified as D (non-human carcinogens), BBP is classified as C (a probable carcinogen), and DEHP is classified as B (human carcinogen) (Matsumoto et al. 2008). According to the literature, the R value acceptable for chemical contaminants should be less than 10−6; as for HI, the values should be less than 1(Brandes et al. 1991). The calculation results are shown in Tables 8 and 9. The risk assessment indexes of the phthalates in the Lanzhou section of the Yellow River are all lower than the reference value, indicating that the PAEs in the Lanzhou section of the Yellow River are not carcinogenic risks and health risk to local residents. However, PAEs can accumulate in organisms and humans, and they are not easily degraded; thus, attention should be paid to the production and use of PAEs. Strengthening the monitoring and treatment of PAEs in organic compounds in sewage treatment plants and water plants is also necessary to reduce the environmental impacts. Overall, PAEs may still cause harm to creatures.

Table 8 Risk assessment of PAEs in the dry period of Lanzhou section of the Yellow River
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Table 9 Carcinogenic risk assessment of PAEs in the wet period of Lanzhou section of the Yellow River
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Conclusion

The concentration, chemical composition, and distribution of PAEs in the Lanzhou section of the Yellow River were systematically investigated. The average PAE concentration of the water samples for the dry and wet periods of the Yellow River in Lanzhou was3236.0 ng/L and 2300.0 ng/L, respectively. The average concentrations of PAEs in the sediments were 4238.9 ng/g for the dry season and 3959.9 ng/g for the wet period. PAEs were detected in all the sampling sites. The six PAEs (DMP, DEP, DBP, DEHP, DNOP, and BBP) controlled by the U.S. EPA were detected. The concentrations of four priority PAEs (DMP, DEP, DBP, and DEHP) were high in all samples. The proportion of low-molecular-weight PAEs was high in the aqueous phase, and the proportion of high-molecular-weight PAEs was high in the sediments. The concentration of PAEs in the water samples for the dry season is higher than that for the wet season, and the results for the sediment components were somewhat similar. The PAEs of the Yellow River in Lanzhou have high concentrations in the upstream and middle reaches and low concentrations in the downstream. In addition, the health risks of the six PAEs were also evaluated. The findings indicate that PAEs in the Lanzhou section of the Yellow River are not carcinogenic nor pose any health risk.