Simultaneous determination of benzothiazoles, benzotriazoles, and benzotriazole UV absorbers by solid-phase extraction-gas chromatography-mass spectrometry

Benzotriazoles (BTRs), benzothiazoles (BTHs), and benzotriazole ultraviolet absorbers (BUVs) are common products in plastic rubber and personal care products. Due to their toxicity and bioaccumulation, they have been identified as emerging contaminants (ECs) in the environment. Solid-phase microextraction (SPME) and solid-phase extraction (SPE) combined with gas chromatography-mass spectrometry (GC–MS) were used for the enrichment and detection of the contaminants in seawater and sediment, respectively. The conditions of SPE and SPME were optimized in terms of material, temperature, time, pH, ionic strength, extraction solvent, and elution solvent. Although SPME requires a small sample volume, it is not reliable for the extraction efficiency and reproducibility of BTHs, BTRs, and BUVs in seawater. However, the precision of SPE-GC–MS for the determination of BTHs, BTRs, and BUVs was around 10%, with recoveries of 67.40–102.3% and 77.35–101.8% in seawater and sediment, respectively. The limits of detection of 14 contaminants in seawater and sediment were 0.03–0.47 ng/L and 0.01–0.58 ng/g, respectively. Secondly, BTHs, BTRs, and BUVs were detected with low ecological risk when SPE-GC–MS was applied to the analysis of seawater and sediment samples from the Yangtze estuary and its adjacent areas. The SPE-GC–MS was highly precise with lower detection limits relative to previous studies and thus was able to meet the requirements for the detection of BTHs, BTRs, and BUVs in seawater and sediments.


Introduction
ECs are not new chemicals, but rather unregulated pollutants that are widely present in the human living environment and are potentially deadly to our health. Fate, occurrence, and potential adverse effects of EC S are receiving increased attention due to heavy production and use (Bhatt et al. 2022). Benzotriazole (BTR), benzothiazole (BTH), and their derivatives (BTRs, BTHs) are emerging pollutants with specific chemical structures that are widely used in industrial applications and organic corrosion inhibitors (OCI). OCIs are high-yield chemicals applied in plastics, rubbers, colorants, and coatings to improve the performance of products (Kim et al. 2022). BTR can form metal complexes to delay the corrosion of metal surfaces and be used as aircraft deicer and anti-icer fluid (ADAF). BTR is also widely used in OCI, such as hydraulic fluids and dishwasher detergents. BTR was mutagenic in bacterial cell systems (Salmonella, E. coli) and was classified as a suspected human carcinogen. The United States produced at least 9000 tons of BTRs, and the output of various countries has also increased significantly in recent years (Cancilla et al. 1998;Liu et al. 2017). BTHs are widely used as corrosion inhibitors, antifogging agents, and rubber vulcanization accelerators to improve the service life of the rubber. BTHs were potentially toxic to luminescent bacteria, plants, and aquatic animals. BTHs are also used as high-production volume chemicals as corrosion inhibitors, herbicides, algaecides, fungicides (for the paper and pulp industries), bactericides (for the wood and leather industries), and photosensitizers. In the United States, BTH production is controlled at less than 4500 kg per year. The United States Environmental Protection Agency has listed BTH as an emerging pollutant for many years (Iadaresta et al. 2018;Liao et al. 2018). UV-absorbing compounds are widely used in personal care products and industrial products such as textiles, plastic products, coatings, adhesives, and rubbers (Pacheco-Juarez et al. 2019;Xue et al. 2022). Benzotriazole ultraviolet absorbers (BUVs), which absorb the full spectrum of UV, are common additives in polymers such as polypropylene (PP) and polyvinyl chloride (PVC) and are also additives in some sunscreen products. BUVs have been shown to have toxic and endocrine-disrupting effects on different marine organisms (Montesdeoca-Esponda et al. 2018). The Chinese national standard GB 7916-1987 "Hygiene standard for Cosmetics" has stipulated the types and limits of ultraviolet absorbers allowed to be used in cosmetics. From 2004 to 2008, Japan produced and imported an average of about 600 tons of UV stabilizers per year (Nakata et al. 2009).
Since the ocean often acts as a sink for contaminants of terrestrial origin, in addition to the large material input from rivers and the atmosphere at the surface, the same complex material exchange occurs at the bottom sediment-water interface (Hung et al. 2020;, thus requiring more stringent pretreatment of seawater and sediment. Solid-phase extraction (SPE) and solid-phase microextraction (SPME) are effective methods for extracting organic pollutants in the environment. SPME was more often used to enrich substances with lower boiling points. The SPME advantages included low sample consumption and less use of organic solvents. However, for low-volatile organic compounds, there are long extraction times and unstable reproducibility (Mendes et al. 2018). SPE was a one-step extraction and preconcentration method, increasingly used in environmental analysis to extract organic compounds from water and solid samples, even for samples requiring larger volumes (Caldas et al. 2013). Different SPE cartridges such as C 18 and HLB have been widely used to extract organic compounds from water samples. The present study aimed to establish an accurate and versatile method for the simultaneous measurements of BTRs, BTHs, and BUVs in the marine environment by SPE-GC-MS and to detect the main types and concentration levels. The developed method had the advantages of less use of organic solvents, simple operation, high recovery and precision. Moreover, the method was successfully applied to detect BTRs, BTHs, and BUVs in seawater and sediments of the Yangtze River Estuary and its adjacent areas.

Instruments
The target compounds were detected by Agilent 7890 gas chromatograph equipped with an Agilent 5975 C mass selective detector and a DB-5 MS column (30 m × 0.25 mm inner diameter, 0.25 µm film thickness) (Agilent Technologies, Avondale, PA, USA). Helium (purity 99.999%) was used as carrier gas at a flow rate of 1.50 mL min −1 . The sediment samples were freeze-dried by an FD-1-50 vacuum freeze dryer (Beijing Boyikang Laboratory Instruments Co., Ltd, China). The centrifugal treatment of the extract was performed by SC-3610 Low-speed centrifuge (Kedachuangxin Co., Ltd, China). The purge concentration of the sample was carried out under 24 Position N-EVAP nitrogen evaporators (Organomation, USA). The extraction of target substances in seawater was first carried out by solid-phase microextraction instrument and solid-phase microextraction probes (Qingdao Zhenzheng Analytical Instruments Co., Ltd, China).

Sampling and sample preparation
Samples of seawater and surface sediments were collected from 11 stations located in the Yangtze River estuary and its adjacent areas (Fig. 1). Details of the station are shown in Table S1. The collection and preservation of seawater and sediment samples followed a previously article . Surface sediment was collected using a box-type mud picker, and the 0-2 cm surface of sediment was taken in a glass jar. Sediment samples were frozen at − 20 °C for 24 h, then freeze-dried for 48 h, ground with a mortar, and homogenized by sieving through a 100mesh (0.150 mm) standard sieve. Seawater was collected into a 1-L brown glass sample bottle previously washed with concentrated H 2 SO 4 and deionized water. After the seawater sample was filtered by filter membrane (Whatman GF/F, 0.7 µm), 1% methanol was added to prevent compound adsorption on the bottle wall, and stored in cold storage at − 4 °C.

Sediments
Approximately 5.0 g of dry sediment was collected in a 50 mL glass tube, and 30.0 mL of extract solution was added, with the choice of dichloromethane/ethyl acetate (1:1, V/V), acetone/hexane (1:1, V/V), dichloromethane/hexane (1:1, V/V) for the extract solution. After a certain time (15, 20, 25, 30, 35, 40 min) of oscillation to reach equilibrium, the suspension was centrifuged continuously at 4000 rpm for 8 min and the upper layer was transferred to a 100 mL pearshaped flask. The procedure was performed twice, and the upper solutions were mixed. The solution was concentrated to about 2-3 mL by rotary evaporator at 40 °C, and 5 mL of isooctane was added.
Different SPE cartridges were used for the pretreatment of sediment solution after spin evaporation. The SPE method for sediment was evaluated by testing three commonly used SPE cartridges (CNWBOND Si 6 mL 500 mg, CNW polysery HLB 6 mL 500 mg, and Florisil PR 6 mL 500 mg). The service conditions of the SPE cartridges were as follows: CNWBOND Si cartridges were conditioned with 5 mL of n-octane, the supernatant was transferred to the column at Fig. 1 Distribution of sampling stations in the Yangtze River Estuary and its adjacent areas a flow rate of 5 mL min −1 , and finally, extracts were eluted with 10 mL of ethyl acetate. CNW poly-sery HLB cartridges were conditioned with 5 mL of methanol and 5 mL of Milli-Q water, the supernatant was transferred to the column at a flow rate of 5 mL min −1 , and finally, extracts were eluted with 10 mL of ethyl acetate. Florisil PR cartridges were conditioned with 5 mL of methanol and 5 mL of n-hexane, the supernatant was transferred to the column, the flow rate was set as 5 mL min −1 , and finally, extracts were eluted with 10 mL of ethyl acetate. The three SPE-treated enrichments and the untreated solution were concentrated under a gentle stream of nitrogen gas. Extracts were reconstituted with 950 µL of methanol and 50 µL of internal standard solution. The solution was filtered through a 0.22 µm nylon filter into a 2 mL amber glass vial for instrumental analysis.

Seawater
Firstly, SPME was used to enrich the seawater samples. Three probes with different coatings were selected: polydimethylsiloxane (PDMS), polydimethylsiloxane/divinylbenzene (PDMS/DVB), and activated carbon/polydimethylsiloxane/divinylbenzene (ACAR/PDMS/DVB). Seawater samples (50 ml) were taken in a glass bottle, and a coated probe was inserted into the seawater and sealed with a Teflon rubber spacer for extraction. The conditions such as temperature, pH, and extraction time of seawater were optimized under the effect of magnetic stirring. SPME method for seawater samples was evaluated by testing three SPE probes (PDMS, PDMS/DVB, and ACAR/PDMS/DVB), five extraction times (25 min, 30 min, 40 min, 50 min, and 60 min), six extraction temperatures (20 °C, 30 °C, 40 °C, 50 °C, 60 °C, and 80 °C) and two pH values (2 and 6). Optimization of sample ionic strength conditions was not performed due to the high salt content in seawater. When the sorption equilibrium was reached, the thermal resolution was performed on GC-MS. The extraction conditions of SPME were determined by comparing the peak area ratios between the target and 1 µL of the mixed standard (10 mg/L).
Next, seawater samples (1 L) were pretreated using two SPE columns cartridges (C18 6 mL 500 mg, HLB 6 mL 500 mg) with 13 mm diameter. The HLB cartridges were conditioned with 6 mL of dichloromethane, 6 mL of methanol, and 6 mL of Milli-Q water, then the fractions were discarded. The seawater sample was passed through the cartridge at a rate of 5-10 mL min −1 , and salts were washed off with 12 ml Milli-Q water and dried under a low vacuum. Finally, the SPE cartridge was eluted with 6 mL of methanol and 6 mL of dichloromethane under gravity. For the C 18 SPE cartridges, activation was performed with 5 ml of dichloromethane, 5 ml of methanol, and 5 ml of Milli-Q water. The seawater sample was passed through the SPE cartridge at a rate of 5-10 mL min −1 , the salts were washed off with 12 ml Milli-Q water, dried under low vacuum, and eluted with 5 mL of methanol and 5 mL of ethyl acetate. The eluted solution was dried under a gentle stream of nitrogen. The extracts were reconstituted in 950 µL of methanol and 50 µL of internal standard solution. The solution was filtered through a 0.22 µm nylon filter into a 2 mL amber glass vial for instrumental analysis.

GC-MS
GC-MS working conditions refer to previous research (Vimalkumar et al. 2018). Sample injection (1.0 µL) was performed using an autosampler in the split-less mode. The analytical separation was performed with a DB-5MS column (30 m × 0.25 mm, 0.25 µm thickness). The temperature of the injection port was 280 °C. The GC oven temperature was programmed from 120 °C (held for 3 min) to 260 °C (held 1 min) at 6 °C min −1 and finally increased to 320 °C (held for 5 min) at 8 °C min −1 , for a total run time of 40 min. The EI working voltage was set to 70 eV, and the quadrupole temperature and ion source temperature were 150 °C and 230 °C, respectively. The solvent delay was set for 4 min. The scanning mass range (m/z) was 50-500 u. The SIM mode was used for ion quantitative analysis. The standard spectra were obtained under GC-MS analysis conditions (Fig. 2).

Ecological risk assessment
In this paper, the method of risk quotient (RQ) was adopted to appraise the latent eco-environment risk of BTRs, BTHs, and BUVs. The calculation method of RQ followed Equation, which was defined by the European technical guidance document on risk assessment.
where MEC was the concentration of BTRs, BTHs, and BUVs in seawater and sediment environments; PNEC water was predicted no effect concentration obtained from US.EPA NORMAN; Kd was the sediment-water partition coefficient calculated by formula; Koc was the organic carbon-water partition coefficient obtained by EPI.Suit (Table 1); f oc was organic carbon content in sediments, we chose 0.003 to represent the content of organic carbon in the sediments of the study area (Ji et al. 2022). RQ was used to characterize the risk degree of the ecological environment. The high RQ value indicated a higher biological risk in the water According to the risk ranking criteria, the RQs were classified into 4 risk levels, i.e., RQ < 0.01, minimal risk; 0.01 < RQ < 0.1, low risk; 0.1 < RQ < 1, medium risk; and RQ > 1, high risk (Olisah et al. 2022).

Blank experiments
The reagents, instruments, and dust in the air during the experiment may contaminate the determination results, so it was necessary to conduct a blank experiment to improve the accuracy of the method (Pajewska-Szmyt et al. 2019). Twenty milliliters of chromatographic grade isooctane, methanol, and dichloromethane were taken and purged to 1.5 mL with high-purity nitrogen. After GC-MS analysis, no target components were detected. A blank sample (methanol) was added after every 10 samples and the blank value was subtracted from the final result. The sediment samples were treated at 450 °C and then extracted for determination. For seawater samples, the solid-phase extraction cartridge was eluted directly and then measured. Blank experiments for seawater and sediment were repeated 6 times each. The results showed that UV-328 was found in seawater and sediment samples tested at concentrations of 1.02 ng/g and 1.26 ng/g, respectively. All results were subtracted from the blank values.
After evaporation with a rotary evaporator, the results were compared. The results showed that the extraction efficiency of dichloromethane/ethyl acetate (1:1, V/V) was higher than the other two mixed extractants. Therefore, dichloromethane-ethyl acetate (1:1, V/V) was selected as the extractant for the sediments. In addition, we found that the recovery of the target reached a maximum after two solvent extractions. There was no clear difference in extraction efficiency with an increasing number of extractions and with increasing extraction solvent. Therefore, we chose to use an extraction solution volume of 25 mL and a cyclic extraction number of two times in the treatment of sediments.

Extraction methods
For sediment samples, SPE cartridges with three different materials were used for treatment. It was found that some contaminants (5-Cl-BTR, 2-OH-BTH, UV-326, UV-234) could not be detected in the three SPE cartridges under the same conditions, although the extraction efficiency of the CNWBOND Si cartridge was higher than that of the other two cartridges. However, the direct determination using the solution without SPE treatment showed a higher recovery, and all substances were detected, which was significantly better than the SPE. This suggests that some of the targets were lost when solid phase extraction was performed. This may be attributed to the fact that the target was run off with the solvent and was not adsorbed in the SPE cartridge when the extraction was performed. Other organic pollutants also had the phenomenon of target loss when SPE was used (Hennion 1999;Wang et al. 2018). Therefore, we did not use SPE for the sediment treatment. For seawater samples, BTRs, BTHs, and BUVs in seawater were first pretreated by SPME. The most important step of SPME is the selection of a suitable probe coating. By comparing the extraction results of the three SPME probes, the PDMS/DVB probe was clearly more effective than the other probes. The extraction conditions of temperature, pH, time, and stirring speed were determined by comparing the ratio of peak area between the target and 1 µL mixed standard material (10 mg/L). We found that the extraction efficiency was highest when the volume of seawater was 50 mL, the extraction time was 50 min, the extraction temperature was 50 °C, the pH value was set to 6, and the stirring speed was set to 800 rpm. Three samples of natural seawater were taken from the same location, 10 µL of mixed standard solution (1 mg/L) was added, measured in parallel under the above optimal extraction conditions, and the recoveries were calculated. The results showed that the recoveries of the target substances were not higher than 60%, but the reproducibility was extremely poor (Fig. 3). BTRs, BTHs, and BUVs have low volatility and require probes to be inserted into seawater samples for SPME operations. After optimizing the conditions of temperature, time, and pH, the highest recovery was obtained for UV-329 (38.9%) and the lowest for BTR (10.3%), while the recoveries of BUVs were higher than those of BTRs and BTHs. The recoveries of BTRs, BTHs, and BUVs were related to not only their concentrations in seawater but also their octanol-water partition coefficients (K ow ). The higher the K ow of BUVs than BTRs and BTHs, the easier it is to be adsorbed from seawater to the probes, and thus the better the extraction effect. Meanwhile, the low thermal stability of commercially available SPME probes can lead to low recovery. The development of composite coatings with specific adsorption properties is needed for the specific structures of emerging contaminants (da Silva Sousa et al. 2021;Jalili et al. 2020). Therefore, SPME is not suitable for the enrichment of BTRs, BTRs, and BUVs in seawater. Secondly, the extraction results of the two solid phase extraction columns (C18 6 mL 500 mg, HLB 6 mL 500 mg) also differed significantly, with the HLB column showing significantly better extraction results than the C18 column (Fig. 4). The hydrophilic-esterophilic HLB can retain acidic, basic, and neutral compounds of various polarities (from polar to non-polar), and especially has good enrichment for polar compounds, which is consistent with the results of extracting organic contaminants in other studies (Chafi and Ballesteros 2022;Zhang et al. 2019). Therefore, we used HLB solid phase extraction column to extract BTRs, BTHs, and BUVs from seawater.

Extraction time
Six sediment samples were taken from the same site and extracted for 15, 20, 25, 30, 35, and 40 min after adding dichloromethane/ethyl acetate (1:1, V/V). The extracts were centrifuged, rotary evaporated and concentrated by purging with nitrogen. The results showed that the peak area values of the 14 contaminants increased with time and reached the highest value at 35 min, when the extraction efficiency of the target substances reached saturation (Fig. 5). The longer extraction time did not improve the extraction efficiency, so we chose 35 min for the extraction time.

pH and salinity
To investigate the effect of salinity on the efficiency of SPE extraction of BTRs, BTHs, and BUVs from seawater, 10 µl of the standard mixture (1 mg/L) was added to natural seawater, artificial seawater, and distilled water (1 L), respectively. Then, the enrichment extraction was performed with HLB cartridges, respectively. The salinities of natural seawater, artificial seawater, and distilled water are 33, 30, and 0. If the salts contained in seawater are not treated prior to SPE elution, these salts can prevent contact between the elution solvent and the target in the cartridge, affecting the final elution effect (Burdette and Frossard 2021). In previous studies, the salt was washed with 30 ml of purified water or 0.1% triethylamine (Burdette and Frossard 2021;Kemmei et al. 2012). We finally found that there was little variability in the recovery of BTRs, BTHs, and BUVs in the three different water bodies, indicating that 12 ml of Milli-Q water can rinse off the salts from both natural and artificial seawater, thus not affecting the SPE elution process.
In general, the pH value of seawater samples affects the state of contaminants in seawater and the adsorption performance of SPE cartridges on contaminants, so it is necessary to optimize the pH value of seawater (Mirzaei et al. 2022). Therefore, seawater samples with different pH values were designed to explore the influence on the results. The pH of seawater was basically around 8.0, while the pH of seawater at the same station was adjusted to 2.0, 3.0, and 6.0 with hydrochloric acid (0.25 mol/L). Then the seawater samples were passed through the HLB cartridge and measured by GC-MS. The extraction efficiency of HLB cartridges for BTHs, BTRs, and BUVs in seawater at different pH values was evaluated based on the peak area values of the targets (Fig. 6). The peak area values of 14 contaminants treated and detected by SPE-GC-MS in seawater under different pH conditions did not vary significantly, indicating that pH is not the main factor affecting the enrichment of BTRs, BTHs, and BUVs by SPE.

Elution conditions
In the solid phase extraction process, the elution ability of different elution solvents for the target compounds varies greatly, and the choice of elution solvent is an important factor affecting the final results. According to the similar phase dissolution principle, the eluent should elute the target with similar polarity or structure from the SPE cartridges. An accurate amount of 1 L of filtered seawater spiked with 1 µL of the mixed standard solution (10 mg/L) was treated with HLB cartridges under the same conditions. The elution was carried out by gravity using the same volumes of isooctane, ethyl acetate, and dichloromethane/methanol (1:1, V/V) solutions, respectively. The final results were determined on GC-MS and the spiked recoveries were calculated. The results showed that the components to be measured were detected in all eluents except isooctane. The recovery of dichloromethane/methanol (1:1, V/V) was significantly higher than ethyl acetate (Fig. 7). Therefore, dichloromethane/methanol (1:1, V/V) was used as the eluent for HLB cartridges.

Method performance evaluation
The methodology showed excellent linear dynamic ranges (0.1-10.00 ng/mL) for the fourteen contaminants studied with correlation coefficients higher than 0.9906 ( Table 2). The precision and recovery of the method were determined under the optimized conditions. The limits of detection and limits of quantification (LODs and LOQs, respectively) were calculated based on the S/N of each peak of the substance, assuming minimum detectable S/N levels of 3 and 10, respectively. Considering that the concentrations of some components in the actual samples may be below detection levels, the relative standard deviation (RSD) of the samples was used to determine the precision of the method. The spiked recovery of each substance is calculated as: where X i and Xo are the concentration of each analyte in the spiked and blank samples, respectively. Xss is the concentration of each analyte in the standard solutions.

Recovery(%) =
Xi − Xo Xss × 100 Fig. 7 Effect of the elution solvents on analyte recoveries (n = 3) Six pretreated natural seawater samples from the same station were collected. Then two different concentrations of BTRs, BTHs, and BUVs standard solutions were quantitatively added to the seawater samples and extracted by SPE. The parallel spiked recoveries, a relative standard deviation, and the spiked recoveries at a spiked concentration of 0.100 µg/L were calculated. The results showed that the recoveries of the 14 targets ranged from 67.40 to 102.3%, and the RSD values ranged from 1.21 to 12.5% and 0.64 to 9.77% for the two different standard solutions (0.100 µg/L and 0.500 µg/L) (Table 3). Moreover, the recovery of BTR was remained low in other studies. The recoveries were 70-73% in the detection of BTR in fish . In water quality testing in the Netherlands, the recovery of BTR was 38-81% (van Leerdam et al. 2009). These indicate that BTR in the solution will be redissolved, resulting in low recovery.
Six dried sediment samples were weighed and quantitatively added to two different concentrations of BTRs, BTHs, and BUVs standard solutions, extracted, and determined as above. The relative standard deviations of the parallel spiked recoveries and the spiked recoveries at 100 ng/L spiked concentrations were calculated. The recovery of BTRs, BTHs, and BUVs was 77.35-101.8% (Table 4). When the spiked concentration was 100 ng/L and 500 ng/L, the RSD values ranged from 0.78 to 8.90% and 0.14 to 8.98%, respectively. In addition, the limits of quantification and limits of detection in the seawater and sediment were 0.12-1.57 ng/L, 0.03-0.47 ng/L and 0.02-1.90 ng/g, 0.01-0.58 ng/g, respectively.

A comparison to previous methods
We did a comparison of the current methods for the determination of BTRs, BTHs, and BUVs in various environmental matrices (Table 5). Compared with the previous methods, especially applied to the detection in marine environments, the present method (SPE-GC-MS) has lower LOD and LOQ for BTHs, BTRs, and BUVs in both seawater, wastewater, and sludge, with guaranteed recovery and higher precision. Secondly, we achieved the first simultaneous detection of BTRs, BTHs, and BUVs in seawater and sediment, which provides ideas for the detection of other ECs in the marine environment.

Sample analysis
Sediment and seawater samples were processed and measured according to the SPE-GC-MS method. The concentrations in surface seawater from the Yangtze estuary and its adjacent area ranged from not detected (ND) to 10.73 ng/L (Fig. 8a). Although UV-320 has been banned, it can still be detected in the marine environment. The highest values in seawater were found at station C1 and the lowest values were     found at station A7-1. Salinity is an important environmental parameter for assessing the occurrence of organic contaminants. Organic contaminants may hydrolyze in slightly alkaline media, reducing their occurrence in the environment, while an increase in salinity may lead to more rapid degradation of compounds, thus altering their persistence in the water system. Apart from salinity, seawater temperature, dissolved oxygen, microorganisms, pH, and the half-life of target compounds may influence the occurrence of organic contaminants in aquatic systems. Most of these factors lead to the formation of degradation products, which reduce the occurrence of parent compounds (Malhat et al. 2018;Kumar et al. 2019;Olisah et al. 2022). The Changjiang diluted water (CDW) will spread outward along the salinity gradient to form a plume into the Yellow Sea and East China Sea, and the increase in salinity may be responsible for the accelerated degradation of BTRs, BTHs, and BUVs, resulting in lower detection concentrations than LOD. The distribution trend showed an overall decreasing trend from the river to ocean, indicating that land runoff has an important influence Fig. 9 Composition of contaminants in seawater (a) and sediment (b) at different stations on the distribution of BTRs, BTHs, and BUVs in the marine environment, which is similar to the distribution of other organic pollutants (Olisah et al. 2021;. In this study, contaminant concentrations in sediments ranged from nd to 12.26 ng/g (Fig. 8b), which is much lower than concentrations in Pearl River Basin (Han et al. 2020;Hu et al. 2021) and Songhua River sludge (Zhang et al. 2011). Secondly, the concentrations in sediment were significantly higher than those in seawater, which may be due to their hydrophobicity leading to the adsorption on particles and precipitation into the sediment (Ya et al. 2014). The main species in seawater and sediment were BTR, UV-P, UV-PS, UV-329, and UV-328 (Fig. 9). The high detection rates of BTHs, BTRs, and BUVs indicate that they are widely present in the Yangtze estuary and its adjacent areas (Table S2 and S3).

Ecological risk assessment
Since BTR, UV-P, UV-PS, UV-329, and UV-328 were the main contaminants, we selected these five substances for ecological risk assessment of seawater and sediment at the collection stations (Fig. 10). The RQ values in both sediment and seawater were lower than the results of the survey in the Pearl River Basin (Hu et al. 2021). The RQ values of UV-PS, UV-328, and UV-329 were greater than 0.01 in seawater and sediment at only some stations, and the RQ values of BTR and UV-P were less than 0.01, suggesting a limited adverse impact on surface and benthic organisms. In general, the calculation of RQ values indicated that BTHs, BTRs, and BUVs were less threatening to the ecosystem in the collection area, but due to their high lipophilicity, these organic pollutants may still enter the food chain and pose a threat to aquatic organisms at higher trophic levels.

Conclusion
In light of the complexity of the marine environment, pretreatment comparisons of SPME and SPE were performed. SPE extraction conditions were optimized to establish an SPE-GC-MS to determine BTRs, BTHs, and BUVs in seawater and sediment samples of the Yangtze River estuary and its adjacent areas. The method was successfully used for the determination of 14 kinds of emerging contaminants in seawater and sediments in the Yangtze River estuary and its adjacent areas with concentrations in the range of nd-10.73 ng/L and nd-12.26 ng/g. The main species were UV-P, UV-PS, UV-329, and UV-328. The result demonstrates the ubiquitous presence of BTRs, BTHs, and BUVs in the environment of the Yangtze River estuary and its adjacent areas. The preliminary ecological risk assessment indicated that the ecological risk of BTRs, BTHs, and BUVs was low in the collected station areas. Overall, the used SPE-GC-MS method showed high recovery and precision, reduces operational complexity, improves the efficiency of analysis of BTRs, BTHs, and BUVs in the marine environment, and facilitates ecological risk assessment.
Acknowledgements Data and samples were collected onboard from the R/V "Zheyuke 2" and "Runjiang 1" implementing the open research cruise NORC2021-03 supported by NSFC Shiptime Sharing Project (no. 42049903).

Fig. 10
Risk assessment of 5 contaminants in seawater and sediment