Occurrence and potential environmental risk assessment of alkylphenols and bisphenols in surface water collected in rivers flowing through Bac Ninh, Vietnam

Over the past two decades, there has been a significant surge in industrial production in Vietnam, necessitating the utilization of a large quantity of chemical substances and cutting-edge technology. A prime illustration of this phenomenon is the widespread use of plasticizers, which are additives incorporated into plastic manufacturing processes to enhance characteristics like flexibility, stability, and durability. These additives, such as bisphenol A (BPA) and alkylphenols (APs), are considered endocrine-disrupting chemicals (EDCs) (Salgueiro-González et al. 2017) that interfere with the biosynthesis, metabolism, or hormone system (Lu et al. 2013). Therefore, in Directive 2013/39/EU, 4-tert-octylphenol (4-t-OP), and 4-nonylphenol (4-NP) have been included in the list of 45 priority substances set in the new European water legislation (Kern 2014). However, these compounds are still found in the environment, especially in industrial wastewater (0.5–1.1 μg/L for NP, Japan), rivers (0.029–2.591 μg/L for NP, 0.011–0.35591 μg/L for OP, Hong Kong), and sediments (16.6–203.8 μg/L for NP, not detected (ND)–2.6 for OP, China) (Chokwe et al. 2017). According to the guidelines set by the European Food Safety Authority (50 μg/kg (body weight)/day for BPA) and the Danish Institute of Safety and Toxicology (5 μg/kg (body weight)/day for NP) and OP is unavailable (Ademollo et al. 2008). The levels of intake and concentrations of grains, livestock, and seafood play a crucial role in determining the overall risk associated with NP and BPA (Ademollo et al. 2008).

APs are a group of organic compounds obtained by the alkylation of phenols. Among them, 4-t-OP and 4-NP are the most used in industrial and household applications, with more than 80% of the total APs production used in applications for both industrial and commercial production of textiles, paper, food, or beverage packaging (Ying et al. 2002). Furthermore, APs are also the main degradation product of alkylphenol ethoxylates (APEO), one of the most widely used classes of surfactants as detergents, dispersants, emulsifiers, solubilizers, and foaming agents (Salgueiro-González et al. 2017). These compounds are less degraded in water and can be easily accumulated in biological tissues because of their lipophilicity (Selvaraj et al. 2014). Significantly, both 4-NP and 4-t-OP have been categorized as definitely endocrine disrupting, particularly in aquatic organisms. These chemical substances are capable of causing adverse effects on the reproductive system of aquatic organisms such as fish (Yusoff et al. 2017). They could affect the organism via binding receptors or hormone-binding proteins in the body by mimicking the effects of endogenous hormones (Beek 2000).

Furthermore, bisphenols (BPs) with two benzyl rings in the structure have many analogs, connected by a differently substituted bridging atom, mainly a carbon atom, with the exceptions of bisphenol P (BPP) and bisphenol S (BPS). BPA was used as a monomer to produce epoxy resins, phenolic resins, polycarbonate resins, polyester, and lacquer coatings for food cans (Salgueiro-González et al. 2012). BPA has received great attention due to its potential association with adverse health effects such as prostate cancer, breast cancer, obesity, and neurological and reproductive problems (Fu & Kawamura 2010). As a result, other compounds such as bisphenol B (BPB), BPS, bisphenol F (BPF), bisphenol AF (BPAF), bisphenol P (BPP), and bisphenol AP (BPAP), which were used to replace BPA in plastic production, have been also found in water and sediment, providing evidence for their widespread use (Gao et al. 2023). Recent studies indicate that these alternative compounds also show some negative effects on androgen receptor (AR) and estrogen receptor (ER) activity as well as synthetic steroid hormones, in the delayed hatching of zebrafish (Shi et al. 2015).

Various chromatography techniques have been employed to analyze APs and BPs on a global scale (Xie et al. 2006; Shao et al. 2007; Zhao et al. 2009; Yang et al. 2014). Gas chromatography (GC) is currently recognized as a suitable method for identifying diverse organic contaminants in different environmental matrices, as evidenced by the research studies of Duong et al. (2010) and the study of Česen et al. (2019). This technique usually requires an additional derivatization step, which is time-consuming, loss of analytes, and contamination from materials and the environment. Nowadays, liquid chromatography is considered a powerful technique for APs and BPs analysis (Shao et al. 2007; Jin & Zhu 2016; Liu et al. 2016; Salgueiro-González et al. 2017). Liquid chromatography combined with ultraviolet/fluorescence (UV/FLD) detectors is not recommended to quantify APs and BPs in the environmental sample due to the overlapping of analytes with similar properties, poor sensitivity of UV detector, or matrix effect to the emission of analytes with FLD detector (Zhao et al. 2009). Therefore, liquid chromatography coupled with mass spectrometry (LC-MS/MS) is currently the most powerful technique for analyzing APs and BPA in environmental matrices (Shao et al. 2007; Pérez-Palacios et al. 2012; Salgueiro-González et al. 2012). Effective sample preparation to remove possible interferences and pre-concentration of analytes are also mandatory to achieve the required levels. Techniques such as liquid phase extraction (LLE) (Xie et al. 2006), solid phase extraction (SPE) (Liu et al. 2016), ultrasonic extraction (USE) (Pérez-Palacios et al. 2012), and accelerated solvent extraction (ASE) (Shao et al. 2007) are usually applied to enrich these analytes in different matrices.

The objective of this study was to validate a simple LLE combined with an LC-MS/MS method to determine two APs and seven BPs in surface water (Supplementary Figure S1). This research aimed to gain knowledge of the occurrence and level of these compounds in the environment and environmental risk assessment. The results from this study will be valuable to help the corresponding management and conservation policies in this area, which locates a huge number of industrial enterprises.

High purity standards (purity >98%) for nine targeted compounds (4-NP, 4-t-OP, BPA, BPS, BPF, BPB, BPP, BPAP, and BPAF) and internal standards (4-NP-D₄, BPA-D₈, and BPS-D₈) were purchased from Cluzeau Info Labo (CIL, Sainte-Foy-La Grande, France). Organic solvents (acetonitrile, methanol, dichloromethane, and hexane) used for sample processing and LC-MS/MS analysis were purchased from Sigma-Aldrich (Singapore). Ultrapure water (18.2 MΩ cm⁻¹) was produced from the Smart 2 pure 12 UV water purification system (Thermo, England) and was used throughout this study. Ammonium acetate used for the mobile phase was purchased from Merck (Germany).

Bac Ninh Province is one of the pivotal economic regions within the Hong River Delta, beside Hanoi. With three large river systems flowing through, namely the Cau River, spanning 70 km and having an annual water volume of approximately 5 billion m³; the Thai Binh River, stretching 17 km and having an annual water volume of approximately 35.95 billion m³; and the Duong River, with a length of 42 km and an average total water volume of 31.6 billion m³. This river system has an estimated overall surface water flow of about 177.5 billion m³, with 176 billion m³ of water contained within the rivers. This abundant water supply plays an important role in the province's irrigation, drainage, and water management.

At the laboratory, the samples were filtered using a GF/F filter (Whatman, Ø 47 mm, pore size < 0.7 μm, pre-combusted at 450 °C for 6 h) with the help of a vacuum pump. The filtered samples were stored at 4 °C and analyzed within 48 h or stored at −80 °C for further analysis.

A 200 mL filtered sample was spiked with a solution of internal standards (15 μL each of 1 mg/L 4-NP-D₄, BPS-D_8, and BPA-D₈). This sample was then extracted by liquid–liquid extraction with 3 × 10 mL of dichloromethane, shaken vigorously for 10 min each time. Next step, the sample was allowed to stand until the aqueous phase and the organic phase completely separated. The organic phase was collected into a glass tube, evaporated under a gentle stream of nitrogen until dryness, and then reconstituted to 3 × 100 μL of H₂O/acetonitrile (ACN) (30/70, v/v). Finally, the solutions were filtered using a syringe with a 0.2 μm pore size and subjected to the LC-MS/MS system under optimal operating conditions.

Shimadzu Nexia (Shimadzu, Japan) was utilized for APs and BPs compound separation. The targeted compounds were separated by a reverse phase column (Waters BEH^® C18, 100 mm × 2.1 mm, 1.7 μm particle size) with a guard column (20 mm × 2.1 mm, 0.22 μm filter). The mobile phase consisted of 2 mM ammonium acetate buffer (pH 6.90) (channel A) and 2 mM ammonium acetate in acetonitrile (channel B). The gradient was started with 50% channel B and kept at this proportion for 0.5 min, then the percentage of channel B was linearly increased to 95% in 6 min and kept at this condition for 2 min before returning to the initial condition and waiting for the next injection. The total running time was 12 min. The column chamber was constantly kept at 40 °C and the injected volume was 20 μL. The separation was adopted from Loos et al. (2007), with slight adjustments made to the LC conditions (column, mobile phase) and MS conditions. The tandem mass spectrometer (Shimadzu 8050) equipped with an electrospray ionization (ESI) source was set up at −3 kV for capillary voltage. The temperatures of the ion source, nebulizer gas, drying gas flow, and heating gas flow were all optimized and maintained at 300 °C, 3 L min⁻¹, 10 L min⁻¹, and 10 L min⁻¹, respectively. The LC-MS/MS working conditions are detailed in Supplementary Table S1.

Target compounds were optimized to achieve the highest sensitivity via compound optimization function with flow injection experiments. Two transitions were selected and monitored using multiple reaction monitoring (MRM). All optimized parameters of the mass spectrometry, such as precursor ion, product ion, collision energy, and Q1 and Q3 bias for all analytes, are listed in Supplementary Table S2. The LC-MS LabSolution software (Shimadzu, Japan) was used for the acquisition and evaluation of data. Peak integration was based on the unit resolution for both precursor and product ions.

Recoveries were validated at three concentration levels (low, medium, and high). The MDL and MQL were determined using a signal-to-noise ratio of 3 and 10, respectively, and on a real sample matrix. If any compound was not detected in the real sample, the MDL and MQL were then calculated based on the spiked sample.

The environmental risk assessment was conducted using a risk quotient (RQ) methodology, as recommended by the European Commission's Risk Assessment Guidelines from 2004 (Janssen et al. 2004). RQ serves as a valuable tool for evaluating the potential ecological risks posed by contaminants in aquatic ecosystems (Hong et al. 2022).

During the investigation of the linear range, a calibration curve was established using seven different concentration levels ranging from 1 to 500 μg/L. The analyte concentrations were evaluated using corresponding internal standards 4-NP-D₄, BPA-D₈, and BPS-D₈, and each calibration point was fixed at the concentration of 50 μg/L. An eight-point calibration was prepared daily in ultrapure water and injected three times into the LC-MS/MS system under optimal conditions. The standard curve demonstrated the relationship between the peak area ratio and the concentration of analytes, and it was found to be a linear function. The peak area ratio was calculated by dividing the peak area of compounds by the peak area of the appropriate isotopic labeled internal standard. The results, as shown in Supplementary Table S3, indicate a rather strong correlation coefficient R², which falls within the range of 0.99 < R² < 1.

Supplementary Table S3 shows the results of calculating the instrument detection limit (IDL) and MDL. IDL values are computed by measuring the noise-to-signal ratio of the lowest/known concentration of linearity samples, whereas MDLs were estimated from actual or spiked samples and both were expressed as concentrations (ng/L) (Rao 2018). The analytes demonstrated good sensitivity to MDL in the region of 0.02–0.88 ng/L. The new method's sensitivity was equivalent to those in recent studies and adequate for the analysis of these APs and BPs in surface water (Loos et al. 2007; Yang et al. 2014).

To validate the method recovery (%), a mixed standard (APs, BPs, and their corresponding internal standard) was spiked into the ultrapure water. The extraction process was performed as mentioned above. Table 1 illustrates the recoveries for spiked analytes at different concentrations (5, 50, and 100 ng/L).

The recoveries for APs and BPs range from 50.4 to 110.5% with low relative standard deviations (RSDs) (<20%). The recovery in this study to the confidence intervals of AOAC standards was equivalent to those in recent studies for the analysis of these APs and BPs in surface water (Zheng et al. 2019). Besides, lower RSD (<20%) demonstrates good reproducibility and consistency (AOAC 2016). Therefore, the proposed method is accepted for the analysis of real water samples.

Interestingly, the distribution of these compounds' concentration follows an inverted ‘W’ shape (Figure 4), indicating complex influences on their occurrence (Wang et al. 2016). The total average concentrations of the Cau River (313.1 ng/L) and the Duong River (243.1 ng/L) are higher than that of the Thai Binh River (157.034 ng/L). Due to the primary sources of industrial activity (industrial production of textiles and paper, agriculture, metal, and plastic manufacturing) in the Bac Ninh province being located along the banks of the Duong River and the Cau River. On the banks of these rivers it was observed that there were many various residential areas, agricultural areas, discharge points, hospitals, factories, sewage plants, and craft villages.

Thuan Thanh District (TT) and Tien Du District (TD) have industrial areas located on both banks of the Duong River. The data indicates that the concentration of water pollution in Thuan Thanh is relatively lower than that in Tien Du. Specifically, the total average concentration in Thuan Thanh is recorded at 181.4 ng/L while that in Tien Du stands at 344.8 ng/L. The reason for this difference is Tien Du's strong industrial activities in producing consumer goods, garments, agricultural products, and food. These industries are sources of emissions that contribute to increased concentrations of AP and BP in water, harming the environment. On the other hand, in Thuan Thanh there are industries with high technology, clean production, and eco-friendliness, such as electronics, telecommunications, pharmaceuticals, supporting industries, new materials, and equipment manufacturing.

The progressive decrease in total average concentration from the Duong River's midstream to the Thai Binh River may be due to natural river mixing, pollution dispersion in the direction of water flow, and other causes (Bielski 2021). Other natural variables include (i) the high average temperature of the tropical monsoon climate of Vietnam can promote degradation of slowly biodegraded trace organics and (ii) high discharge of rivers may dilute these trace pollutants (Le Thi Minh et al. 2016).

The concentration of 4-NP in the samples was observed to be lower than the maximum allowable concentration (MAC) and the annual average (AA) in seawater samples and other surface waters. According to the Environmental Quality Standards (EQS) for these compounds, the AA for 4-NP in seawater samples and other surface waters is 300 ng/L, while the MAC is 2 μg/L (EU Commission 2022).

The dynamic fluctuations in 4-NP concentrations observed underscore the intricate nature of 4-NP emissions within these aquatic ecosystems. 4-NP in surface waters consistently reveals close correlations between its presence and anthropogenic activities (Gałązka & Jankiewicz 2022), particularly emphasizing the pivotal role of industrial/urban areas. Furthermore, the influence of stormwater discharge and runoff emerge as notable contributing factors to the widespread occurrence of 4-NP (Chokwe et al. 2017). 4-NP is highly toxic to aquatic life, causing reproductive effects on aquatic organisms at concentrations ranging from 0.13 mg/L to higher (Naylor 1996). Among all samples collected, no samples had 4-NP concentrations exceeding 0.13 mg/L, indicating that 4-NP has no significant influence on the ecological environment in these locations.

Furthermore, regarding 4-t-OP, which is approximately 25% more potent as an endocrine disruptor than 4-NP (Oketola & Fagbemigun 2013), concentrations of 4-t-OP were also detected in water samples from three different rivers, with concentrations ranging from 74.1 to 36.1 ng/L (Cau River), 482.0–39.8 ng/L (Duong River), and 76.3–48.0 ng/L (Thai Binh River). In the case of 4-t-OP, the MAC is not applicable as the AA (10 ng/L) is intended to protect against short-term pollution peaks in continuous discharges. However, the concentration of 4-t-OP obtained in the study for all samples was higher than the AA value. This suggests that the discharges of 4-t-OP into the aquatic environment of the Bac Ninh province may harm the environment and require more stringent regulations and monitoring.

Among these samples, 4-t-OP consistently exhibited higher concentrations than the others, with a maximum concentration of 482.0 ng/L observed at location R14 in the Duong River, where the textile industry is strongly developed. The concentrations of 4-t-OP at sites in Bac Ninh province in this study were higher than those in another study conducted in Vietnam (Le Thi Minh et al. 2016). This suggests continuous effluent discharge from both residential and industrial activities, especially the textile industry, is polluting these areas.

BPA, which has water solubility (120–300 mg/L) (Oketola & Fagbemigun 2013), was detected in low concentrations ranging from 1.0 to 30.2 ng/L in all samples. This may be attributed to the tendency of the compound to adsorb to river sediments (Oketola & Fagbemigun 2013). The presence of BPA on the surface, even in trace amounts, poses a significant threat to our environment. Its residues in natural ecosystems not only harm the environment but also disrupt metabolism (Gałązka & Jankiewicz 2022). Like 4-NP, BPA is present in the aquatic environment closely correlated with anthropogenic activity (Gałązka & Jankiewicz 2022). The BPs are the main ones used in the production of epoxy resins and polycarbonate plastics (Oketola & Fagbemigun 2013; Yan et al. 2017). A few samples from the Duong River have shown the signal of BPF but the concentrations were lower than MDL; therefore, the concentration of BPF was not reported. In contrast, BPS was detected in all samples (ranging from 27.8 to 234.3 ng/L), indicating that the majority of manufacturers are using BPS as a substitute for BPA. However, it is noteworthy that BP has not yet been legislated in water. BPA has been included in Annex II of the Directive 2008/105/EC as a future regulated substance in the ‘list of 33 priority substances’ (Salgueiro-González et al. 2012).

The confluence of the Duong River and the Cau River with the Thai Binh River has a higher possibility of increasing contaminant levels in the Thai Binh River. Comparing the results obtained in this study with previous research indicated that the concentrations of APs and BPs fall within the range of values found in waters assessed from other rivers, as shown in Table 2. Besides, BPA concentrations closely resembled those in a prior study in Long Xuyen, Vietnam, where there are agricultural, livestock, and industrial activities. The lower 4-NP levels observed in the current research and the higher 4-t-OP levels are likely a result of the strong influence of the textile industry in Bac Ninh province. The concentration analysis performed in this study revealed a significant rise in the concentration of BPS when compared to previous research findings in Long Xuyen. The difference in compound concentrations highlights the dynamic nature of pollutant dispersal in aquatic environments. Seasonal differences, as well as human activities in each place, may be causes for these variances.

Among the seven BP substances studied, only BPA and BPS were detected in 100% of the samples. According to the RQ assessment, BPA did not pose harm to aquatic organisms in the Duong and Thai Binh Rivers but presented a low-risk level in the Cau River. On the other hand, BPS resulted in a low risk for all three rivers. The risk assessment results for BPA and BPS are both lower compared to previous studies conducted in China (Yan et al. 2017). This also serves as a warning for the aquatic ecosystems in these regions.

This study investigated the validation of an analytical method, the occurrence, and potential ecological risks of APs and BPs in surface water collected from rivers flowing through Bac Ninh province in Vietnam. The analytical method used in this study, involving liquid–liquid extraction and LC-ESI-MS/MS analysis, proved effective for quantifying APs and BPs in surface water. The method validation demonstrated good linearity, sensitivity, and reliability. The results showed the widespread presence of 4-NP, 4-t-OP, BPA, BPS, and BPF in the water samples. The concentrations varied among rivers, with the Cau and Duong rivers indicating greater pollution levels than the Thai Binh River. According to the environmental risk assessment based on RQ values, 4-NP poses a medium risk in all three rivers, but 4-t-OP poses a high ecological danger in the Duong River. BPS is detected with low risk in three rivers, while BPA and BPF showed low to negligible risks in all rivers. In summary, this research contributes valuable information on the environmental occurrence and risks associated with APs and BPs in rivers of Bac Ninh province, providing a foundation for future studies and environmental management initiatives in the region.

This paper is a contribution to the LOTUS International Joint Laboratory (http://lotus.usth.edu.vn) and the French National Research Institute for Sustainability Development (IRD). The paper was supported from BEAM research team supported by USTH funding. The authors would like to send special thanks to the anonymous reviewer. Your valuable comments help us to improve a lot for our paper.

This research was funded by the Vietnam Academy of Science and Technology (VAST) (Project code: QTFR02.03/24-25).

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.