Thermal paper receipts are widely used in various sectors and settings, such as event tickets, retail, banking, healthcare, and education, to provide customers with a record of their transactions. However, these receipts may pose a potential health and environmental hazard, as they often contain Bisphenol A (BPA), 2,2-bis(4-hydroxyphenyl) propane, a synthetic chemical substance. as shown in Figure 1 [38]. There are concerns when touching these thermal papers, as Bisphenol A may leach from the paper surface and enter the human body through dermal absorption, ingestion, or inhalation [1].

Figure 1. Bisphenol A, 2,2-bis(4-hydroxyphenyl) propane, Chemical Formula: C₁₅H₁₆O₂, M. Wt.: 228.29.

BPA is the most common color developer found in thermal paper, and it is easily released into the environment, which may cause dermal harms for those who are working in cashiers during their working hours [2]-[4]. BPA can be absorbed throughout the skin or enter the bloodstream of individuals touching their mouths after coming into contact with it [5]. More importantly, many individuals fail to recognize the potential risks associated with the transfer of substances from the thermal paper to their bodies. This concern is especially critical under conditions of humidity, sweating, or following the use of alcohol-based sanitizers.

There are four common chemicals (e. g., Lueco dyes, Developers, sanitizers, and stabilizers) that are used in the production of thermal paper. When they are combined, a clear and long-lasting image is created. The developers, such as Bisphenol A (BPA) and Bisphenol S (BPS), as well as sulfonylureas and zinc salts, are the essential components to produce the color [6]. When the dye is subjected to temperatures above its melting point within an acidic environment, the dye then becomes colored. When all of the aforementioned substances are mixed together under a heat source, the dye becomes dark. To ensure the chemical reaction is controlled and successful, sensitizers also have to be included, which are usually 3-methyl-phenoxy or 2-(benzyloxy) naphthalene, that melt around 100˚C. Sensitizers help improve the thermal reaction of the coating, facilitating dye and developer integration during melting, while stabilizers ensure smudge-free, durable prints [7].

It was reported that BPA is an endocrine disruptor that can interfere with the hormonal system and cause various adverse effects, such as reproductive dysfunction, metabolic disorders, neurodevelopmental impairment, and increased risk of cancer [8][9]. Studies in mice show BPA exposure can result in increased prostate weight, brain and reproductive development issues, disrupted testosterone and sperm production, and reduced semen quality with DNA damage [10]. Moreover, BPA can also contaminate the environment and affect wildlife and ecosystems, as thermal paper receipts are frequently discarded and not recycled properly [11]-[12]. Therefore, the use of this substance in baby and drinking bottles was prohibited in the European Union in 2011. (Directive, 2011/8/EU) [13].

Large quantities of BPA has been used in industry for manufacturing polycarbonate plastic, epoxy resin, dental materials as well as paper industry [14]. The production of BPA reached 8000 tons as market size volume by 2023 [15]. Forty-six percent of production is in Asia, followed by Europe (⁓28%), and America (26%) [10]. Globally, BPA is a key components of the production of polycarbonate plastics used for food packaging, epoxy resins, medical devices, printing, coatings, printer inks, and flame retardants raising concerns about human exposure [16].

Thermal papers that are coated with BPA have the potential to readily transfer BPA to human skin upon contact, hence, it cannot be negligible [3]. In literature, people involved in direct handling of thermal paper are exposed to BPA at levels approximately 50 to 3366 folds higher than those not in contact with it [17]-[19]. These studies are based on a constructed layout of exposure, which may lead to conflicting observations. In another study, voluntary employees (n = 32), who are in continuous contact with thermal papers receipts for at least 2 hours, showed higher levels of BPA [20]. There is an increasing concern about BPA in receipts, in terms of its harmanes and Extraction for both human and environment, respectively. In Europe, the tolerable daily intake (TDI) levels for BPA was established to avoid health risks, therefore, risk management should keep daily human exposure below these limits [21]. Recent studies have shown that the average total amount of BPA in urine in people regularly exposed to thermal paper was 2.5 times higher than in the control group. Therefore, to avoid exposure to BPA from receipts, the European Union has set a limit of <0.02 wt% (0.2 mg/g, 200 μg/g or ng/mg) for concentrations BPA in thermal paper and this restriction is in effect, since January 2020 [22]. Some EU Member States, such as Denmark, Belgium, Sweden, and France, have implemented additional national bans on the use of BPA in food contact materials and coatings. For instance, France banned BPA from all food packaging, causing a conflict with the plastic industry [23]. The Saudi Food and Drug Authority (SFDA) has implemented regulations and standards that worn against the exceeding limits of bisphenol A in the packaging of food and beverages, emphasizing the risks associated with elevated levels [24]. Many studies have shown that there is a variation in the amounts of BPA in the thermal papers, some of which are slightly higher than the permissible percentages. Semerjian et al. [22] reported detection of BPA in thermal papers receipt samples from various locations in Sharjah, United Arab Emirates, with most samples exceeding the EU limit of 200 ng/mg. The estimated daily intakes (EDI) ranged from 8.22 × 10⁻¹¹ to 8.12 × 10⁻⁴ μg∙kg⁻¹∙bw∙day⁻¹, and for the cashiers, the study showed that EDI was between 7.89 × 10⁻⁹ and 0.0681 μg/kg bw/day. Therefore, all calculated TDIs, (4 μg/kg body weight/day), are below the European Food Safety Authority’s, while the possible daily intake of Health Canada established the provisional tolerance of 25 ug/kg body weight/day according to various documents [16]. The first UAE study [22] on BPA in thermal paper receipts, highlights the importance of BPA limits set by the EU’s and emphasizing that policies, education, and awareness can reduce dermal BPA exposure in the general and occupational populations.

Various extraction methods have been employed in previous studies to detect and quantify Bisphenol A (BPA) in thermal papers [25]. Traditional solvent extraction methods, such as those using methanol and acetonitrile, have been commonly applied due to their effectiveness in dissolving BPA [5][26]. These organic solvents efficiently disrupt the thermal paper matrix, releasing the trapped BPA molecules.

Solid-liquid extraction procedures have been further optimized to enhance the efficiency of BPA recovery. Studies have explored solvents like distilled water and methanol, often at elevated temperatures or with sonication (ultrasound) to improve extraction efficiency [3][27]. For instance, Liao and Kannan (2011) employed a methanol-based extraction method at 35˚C for one hour to determine BPA concentrations in thermal paper receipts, demonstrating significant recovery rates exceeding 80% [3]. Similarly, research by Hormann et al. (2014) and Biedermann et al. (2010) utilized combinations of water and organic solvents, such as water-methanol mixtures, to improve BPA extraction from thermal paper [5][26]. These studies achieved reliable and reproducible results, highlighting the effectiveness of these optimized techniques.

Beyond traditional methods, innovative approaches like the use of artificial sweat solutions have been explored to simulate human exposure conditions more realistically [24]. Artificial perspiration, formulated to mimic both the acidic and alkaline pH of human sweat, has been used to evaluate BPA Extraction from thermal paper under conditions mimicking skin contact. These studies indicate that the pH and composition of artificial sweat can influence BPA extraction efficiency. For example, studies have shown that acidic sweat solutions may extract lower amounts of BPA compared to alkaline solutions, reflecting the potential impact of sweat pH on BPA Extraction from thermal paper [16][21]. This research provides valuable insights into potential exposure risks associated with the everyday handling of thermal paper receipts.

This study aims to establish the best method for extracting bisphenol A (BPA) from thermal papers like receipts and tickets, considering the potential risks associated with BPA exposure and the insufficient information regarding its concentration in thermal papers within Saudi Arabia. The research will evaluate six extraction techniques to determine which one maximizes BPA recovery from thermal paper receipts, thereby determining the most effective and dependable method for subsequent BPA research in the region. This study will use LC-MS/MS as a highly sensitive and precise method, to separate and measure BPA and other substances in present thermal paper.

Calibration curve was tested for seven levels. It was done by preparing standard solutions from the standard Bisphenol A (99% purity), LGC limited, Teddington, UK. The calibration was performed using standard solutions prepared in the same extraction medium used for sample analysis, ensuring matrix matching and minimizing matrix effects. The validity of the calibration for the other extraction media was confirmed through spike recovery experiments, which showed acceptable recovery values within ±10%, demonstrating that the calibration is suitable for all extraction media used in this study (Table 2).

Table 2. The validity of the calibration for the other extraction media.

A spike recovery experiment was conducted at a fortification level of 10 ppm in the extraction medium consisting of 70% methanol and 30% water. The mean concentration of the spiked sample was 210.447, while the unspiked sample showed a mean concentration of 200.430. The difference between the two means (10.017) closely matched the nominal spike level, resulting in a calculated recovery of 100.17%. This recovery value falls well within the internationally accepted accuracy range of 80% - 120%, demonstrating that the analytical method provides reliable quantification and performs accurately within this extraction matrix.

The linearity showed a correlation coefficient of a good linearity (R² = 0.998). The calibration curve, (Figure 2) was constructed and validated using concentration levels expressed in ppm, as this unit accurately reflects the working range of the analytical method and corresponds to the expected concentration levels in real samples. Although the raw instrument signals may appear numerically similar to ppb-scale values, the calibration standards themselves were prepared and verified on a ppm basis. Consequently, all calculations of mean response, standard deviation, %RSD, recovery, accuracy, and bias were performed relative to the true ppm concentrations.

Using ppm ensures full consistency with the method’s quantitative range, the LOD/LOQ values reported in the study, and the regulatory framework under which the method is intended to operate. The results in Table 3 demonstrate that the method provides excellent precision (%RSD 0.32% - 2.58%) and acceptable accuracy (97.24% - 103.12%) across the 20 - 200 ppm range. These findings confirm that expressing the calibration curve in ppm is scientifically justified and aligned with the analytical purpose of the method.

Three replicates of each sample were analyzed, and the BPA concentrations

Figure 2. Calibration curve of standard BPA solutions.

Table 3. Accuracy and precision of calibration curve (ppm Basis).

were evaluated as the mean of the three replicates. Validation parameters which characterize the analytical procedure are reported in Table 3.

The precision and accuracy for the BPA are summarized in Table 3. Samples of 20, 100, and 200 ppm of standard materials (BPA) with nine replicates were analyzed under the same conditions (30:70) distilled water and methanol.

The extraction process of BPA from unprinted thermal papers rolls was done according to previous reported methods [5][23][24][26]. The concentration of BPA in the eight thermal papers samples was detected using different solutions mixtures as illustrated in Figure 3.

The BPA concentrations was found to range from 2.24 to 434.4 mg∙L⁻¹ for the samples. The Technical Regulation for Paper and Cardboard by SASO, (SASO-2934), has reported that 200 mg∙L⁻¹ is the allowed limit of BPA in thermal papers [31]. In the solid-liquid extraction, we have noticed that the Extraction of BPA in the different mixtures varied according to each solvent’s property. Solid-liquid extraction by aqueous 70% methanol and alkaline sweat/methanol for each sample showed higher Extraction of the BPA, as extractable compound, in comparison to other solvents. This result is consistent with the reported data for BPA extraction from plastic products [32][33] BPA, in samples number 1, 4, 5, 6, and 8, was found above the allowed limit that set by SASO, compared to other samples, (2, 3, and 7) which is detected less than the permissible limit. The average concentration of BPA in each thermal paper sample after extraction with distilled

Figure 3. Concentration of BPA in the eight-samples of thermal papers.

water, distilled water/methanol, alkaline sweat/methanol, acidic sweat/methanol, alkaline sweat, and acidic sweat are 220.15, 11.7, 25.56, 307.1, 220.1, 145.6, 17.7, and 215.7 mg∙L⁻¹, respectively as illustrated in Figure 3.

For samples that subjected to extraction with solution containing methanol have showed significant higher extraction of BPA, which is consistent with reported data in literature [34][35]. Interestingly, the extraction of the BPA when using both basic sweat and acidic sweat without methanol is higher than that of distilled water. This is an alert since many people deal with receipts and tickets made of thermal papers, they may be exposed to the substance, especially in hot climates such as that of Riyadh region.

When comparing the Extraction of BPA into alkaline and acidic artificial sweats, the results showed almost similar concentration of the BPA for most of the thermal paper samples, with a slight increase noted for the samples that were treated with the alkaline artificial sweat, (Figure 4). These results are attributed to the chemical composition and pH values for the artificial sweats [36]. Still it falls into the risk for people health through dermal exposure. More investigations need to be carried out about transdermal exposure in terms of temperatures and humidity. Based on this Detection, samples 2, 3, and 7 showed the lowest concentration of BPA even after heating for a period of time. This is an interesting observation, it reveals that the BPA embedded in these thermal papers, is difficult to extract unlike in other thermal papers and hence may be safer to use in humid and hot climates.

In this study, eight samples of thermal paper rolls, from Saudi Arabia markets, were randomly collected and analyzed for determining the concentrations of Bisphenol A (BPA) in thermal paper receipts. The method involved solid-liquid extraction and analysis via liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results of our study provide important insights into the presence and variability of BPA in thermal paper receipts and its potential implications for human health and the environment. The method of analysis was validated and statistically analyzed, and it showed good linearity, trueness, and precision. Regardless of the extraction method. For BPA in thermal paper receipts set by the Saudi Standards, Metrology and Quality Organization (SASO) and the European Union (EU) BPA concentrations vary depending on the amount and type of BPA present in the paper coating, as well as the brand and source of thermal paper receipts. It is important to conduct further studies on a wide range of samples from different sources and applications of thermal paper, such as restaurants, banks, hospitals, schools, etc. This would help assess the prevalence and diversity of BPA in thermal paper receipts and estimate exposure and risks for different segments of the population, especially those most vulnerable to the effects of BPA. The results of this study will help raise awareness of the prevalence of BPA in thermal paper receipts in the Saudi Arabian market and aid in developing policies and strategies to mitigate the potential health and environmental risks associated with this synthetic chemical. Based on our analysis, we found that BPA concentrations in thermal paper receipts varied depending on the brand and source of the receipts. The levels of BPA detected in some samples exceeded the regulatory limits and guidelines set by the Saudi Standards, Metrology and Quality Organization (SASO) and the European Union (EU). This suggests that there may be a potential health risk associated with the use of thermal paper receipts in Saudi Arabia. Further research is needed to expand the scope of this study and investigate a wider range of thermal paper receipt samples from different sources and applications, such as restaurants, banks, hospitals, schools, etc. This would help provide a more comprehensive understanding of the prevalence and diversity of BPA in thermal paper receipts in Saudi Arabia and allow for a more accurate estimation of exposure and risks.

The authors thank manager and supervisors at the Chemical and Petroleum Materials Laboratory at SASO for their support and engorgement, and the instruments laboratory staff for experimental assistance on varying parts of the current study. The authors also extend their appreciation and thanks to the Department of Chemical technology at Riyadh College of Technology and the Department of Chemistry at Imam Mohammad Ibn Saud Islamic University (IMSIU) for their academic support of this study.

Conceptualization, S. S and A. M. A.; data curation, S. M. S., A. M. A., A. S. A, and M.A.A., and M. H. T.; formal analysis, A. G. A. and S. A.J.A.; investigation, A.G.A., S. M. S., A. M. A., A. S. A, and M.A.A., and M. H. T; methodology, S.M.S, A.M.A, A.G.A; project administration, A.G.A and S.M.S.; software; writing—original draft, A.G.A and S.M.S; validation, S. M. S., A. M. A., A. S. A, S.J.A.A and M.A.A., and M. H. T writing—review and editing, A.G.A and S.A.J.A. All authors have read and agreed to the published version of the manuscript.

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy and ethical reasons.