A simulation study on the temperature-dependent release of endocrine-disrupting chemicals from polypropylene and polystyrene containers

Abstract

Due to the ubiquity of plastic packaging, this study evaluated the release of endocrine-disrupting chemicals (EDCs) into liquid foods at various temperatures. Solid-phase extraction (SPE) and gas chromatography-mass spectrometry (GC/MS) methods were used to identify EDCs, including phthalates (BBP, DEHP, DBP), bisphenol A (BPA), and nonylphenol (NP) from cups and containers made of polypropylene (PP) and general-purpose polystyrene (GPPS). The distilled water in PP and GPPS contained no EDCs at 4–10 °C. DEHP, DBP, BBP, BPA, and NP were found in water contained in PP cups and containers at higher temperatures (40–100 °C), with DEHP released the most at 100 °C (1242.5 ± 53.0 ng/L and 1615.3 ± 68.9 ng/L) for water contained in cups and containers, respectively. No BPA, DBP, or BBP was found in the contents of GPPS cups or containers at any temperature. The average EDCs released from PP cups and containers at every storage temperature was significantly higher (P < 0.001) than GPPS. These findings highlight the importance of temperatures and material composition in plastic packaging for food safety. Consumers should be careful when using plastic cups and containers, especially at higher temperatures, as EDC release can pose health risks.

Introduction

Plastics are widely used in food and drink storage because of their durability, lightness, and cost-efficiency^1,2. However, the inevitable human exposure to these materials and their constituents has raised concerns about migrating endocrine-disrupting chemicals (EDCs) from plastic packaging to consumer products^3,4. EDCs are exogenous substances or mixtures that alter the functions of the endocrine system, potentially causing adverse health effects in organisms, their offspring, or populations. These chemicals can bind to hormone receptors, including estrogen receptors, and mimic or interfere with the actions of natural hormones^3,5,6.

Polymers used in packaging applications may release EDCs under certain conditions, particularly in response to temperature variations^7,8. Among EDCs, phthalates⁹ bisphenol A (BPA)^10,11 and nonylphenol (NP)^10,12 have received significant attention due to their widespread use and potential toxicity. These chemicals are commonly incorporated into plastic materials as plasticizers, stabilizers, or additives, leading to their unintentional migration into food and beverages stored in plastic containers. These chemicals can desorb from polymer matrices and subsequently enter food, beverages, and, ultimately, the human body, where they may disrupt normal endocrine function. This chemical migration process represents a complex phenomenon influenced by multiple factors, and temperature can be a key factor^7,8,10,13,14. Increased temperatures accelerate chemical reactions, consequently increasing the solubility of chemical compounds present in the walls of plastic containers into the packaged contents. This aligns with the general principle that higher temperatures typically enhance the solubility of substances and the degradation processes of polymer compounds^7,8,13.

Phthalates are a group of chemicals commonly used in the plastics industry as plasticizers to enhance the flexibility and durability of plastics. These compounds have been linked to various health issues, including endocrine disruption, reproductive toxicity, and developmental problems in children¹⁵. Phthalates are not tightly bound to the plastic matrix, allowing them to migrate into water or food in contact with the plastic container over time¹⁶. The five most commonly used phthalates in the plastics industry are di-(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), di-isononyl phthalate (DINP), di-isodecyl phthalate (DIDP), and benzyl butyl phthalate (BBP)¹⁷. BBP, DEHP, and DBP are classified as EDCs, posing potential risks to human health¹⁸. BPA is a well-known industrial chemical used to make epoxy resins and polycarbonate plastics, and it is found in products like water bottles, disposable containers, and can liners^11,19. It has also been recognized for its endocrine-disrupting aspects that may alter hormonal balance and have adverse health effects^20–22. BPA molecules are released into food or beverages in polycarbonate containers when the bonds holding BPA molecules in polycarbonate plastic break down over time, especially when the plastic is heated or exposed to acidic or alkaline substances²³. This substance is a xenoestrogen with weak estrogenic activity that can disrupt wildlife’s and humans’ endocrine systems, raising the risk of breast and testicular cancer²⁴. NP is another alkylphenol (AP) added to plastics as an additive and is recognized as another EDC^10,25.

The migration of these compounds into food packaging content can be influenced by factors such as the chemical composition of the plastic, the nature of the food or beverage in contact with it, and storage conditions^1,2,7,8,14. For example, it has been found that the rate of BPA migration from bottles to water increases rapidly at temperatures above 80 °C²⁶ Another study reported that with an increase in temperature, the migration of BPA and NP from disposable cups and mineral water bottles into water significantly increases¹⁰.

Among the materials commonly used in the production of disposable containers, cups and containers made of polypropylene (PP) and general-purpose polystyrene (GPPS) play a significant role in everyday life, each with its own advantages and applications due to its unique properties. Due to its flexibility and high resistance, PP is an ideal option for producing reusable containers in various applications. In contrast, GPPS is more commonly used for packaging and disposable products due to its transparency and suitable strength.

In Iran, disposable cups and containers made of PP and GPPS are widely used in the food industry, as well as in traditional applications, due to their low price and availability. Also, these products are widely used in food preparation and distribution centers, beverage shops, and various ceremonies for serving hot and cold drinks.

Therefore, given the widespread use of PP and GPPS in food packaging and the potential implications of their key additives, including phthalates, BPA, and NP, for human health, it is crucial to understand the extent of their release in these packaging containers. This study investigates the release of key phthalates (BBP, DEHP, and DBP), BPA, and NP from PP and GPPS cups and containers into beverages and food liquids under various temperature conditions. Understanding the aspects examined in this study is essential for developing safer food packaging materials and ensuring consumer health protection in a global context.

Materials and methods

Reagents and standards

The analytical-grade solvents and standards (> 99% purity) of BBP, DEHP, DBP, BPA, and NP (Sigma-Aldrich, St. Louis, USA) were used. Stock solutions (250 mg/L in acetonitrile) were stored at − 18 °C, and working solutions were freshly prepared by dilution.

Study approach and sample preparation

In the initial phase, the study aimed to assess the impact of varying temperature conditions on disposable cups made of PP and GPPS concerning the release of phthalate, BPA, and NP. Two popular brands of disposable cups in Iran, PP and GPPS, were selected for hot and cold drinks. These cups were filled with distilled water at different temperatures (4, 10, 40, 60, 80, and 100 °C). Samples were collected for analysis after approximately 2 h. While this time frame can represent a realistic scenario for the typical use of these cups, it was considered a sufficient period for the liquid within the cups to reach thermal equilibrium with the surrounding environment. Additionally, it likely provides an adequate contact period to assess the initial migration of target compounds from the plastic materials. This phase involved analyzing 12 samples (2 types of cups × 6 temperature conditions) with two repetitions to determine the presence of the specified compounds.

In the subsequent phase, the study examined how different temperature conditions affect the release of the mentioned pollutants from disposable containers made of PP and GPPS designed for liquid foods like soup and stew. The temperature and experimental conditions mirrored those of the disposable cup investigation. Similarly, 12 samples were analyzed with two repetitions to evaluate the presence of the desired compounds in this study stage.

Samples extraction and analysis

The target analytes were extracted from water samples using vacuum-assisted solid-phase extraction (SPE), based on Massahi et al.¹³ with a slight modification. C18 bonded-phase silica cartridges (Supelco, Bellefonte, PA, USA) were used as the SPE sorbent. The cartridges were conditioned with 10 mL of methanol for 10–15 min, followed by 10 mL of deionized water. For sample analysis, 100 mL of water was passed through C18 cartridges at 10 mL/min using a vacuum system. After percolation, the cartridges were dried under vacuum for 10–15 min. The target analytes were eluted with 3 mL of methanol, and the extracts were evaporated to dryness under high-purity nitrogen (99.9999%). The residues were reconstituted in 0.5 mL methanol in a 1.5 mL vial. Samples were analyzed using GC/MS (GC 7890 A and MS 5975 C, Agilent Technologies). The injector was set at 290 °C. The oven program began at 50 °C (held for 1 min), increased to 310 °C at 15 °C/min, and was held for 4 min. The inlet operated in 20% split mode (20:1 split ratio), with helium (99.999%) as the carrier gas at a 1 mL/min flow rate. The electron impact (EI) source was operated at 230 °C, while the interface temperature was kept at 280 °C. The detector voltage was set to 0.2 kV above the tuning voltage. The scan mode used was monitoring mode. The selected ion monitoring (SIM) mode was implemented for quantitative analysis, utilizing one quantitative ion and two qualitative ions for each target compound.

Figure 1 shows the chromatogram of the standard solution at a concentration of 100 µg/L for all analytes (A), a water sample in a PP container at 10 °C (B), and a water sample in a PP container at 60 °C (C). The retention times of BPA, NP, DBP, BBP, and DEHP were 6.88, 14.32, 16.65, 21.19, and 28.44 min, respectively.

Fig. 1.

Chromatograms of the standard solution for all analytes (A), a water sample in a PP container at 10 °C (B), and a water sample in a PP container at 60 °C (C). The retention times of BPA, NP, DBP, BBP, and DEHP were 6.88, 14.32, 16.65, 21.19, and 28.44 min, respectively.

Method validation

Method validation was conducted using the U.S. FDA guidelines for the industry²⁷. Table 1 summarizes the relevant validation parameters and confirms the method’s high reproducibility, sensitivity, and suitability for quantifying DEHP, BBP, DBP, NP, and BPA in different drinks.

Table 1.

Performance of GC/MS method for determination of considered compounds in drink.

Analytes	Spiked level (ng/L)	Recovery (± RSD %)	LOD (ng/L)	LOQ (ng/L)	R 2	RE (y = mx + c)
DEHP	50	95.5 ± 4.6	45	140	0.998	y = 1.35x + 1.02
	100	98.3 ± 5.2
DBP	50	99.5 ± 5.4	40	120	0.997	y = 1.42x + 1.09
	100	101.6 ± 3.8
BBP	50	97.5 ± 2.9	45	130	0.996	y = 1.37x + 1.01
	100	101.2 ± 5.5
NP	50	99.3 ± 5.2	50	145	0.995	y = 1.35x + 0.98
	100	102.4 ± 4.1
BPA	50	101.5 ± 2.8	40	130	0.999	y = 1.38x + 0.89
	100	100.5 ± 3.5

LOD: Limit of detection, LOQ: Limit of quantification, RSD: Relative standard deviation, DEHP: Di(2-ethylhexyl) phthalate, DBP: Dibutyl phthalate, BBP: Benzyl butyl phthalate, NP: Nonylphenols, BPA: Bisphenol A, R²: correlation coefficient, RE: Regression equation, represents the relationship between the concentration of the analyte (x) and the detector response (y), where “m” is the slope and “c” is the y-intercept.

Statistical analysis

All statistical analyses were performed using SPSS Version 21. One-way analysis of variance (ANOVA) assessed differences among multiple groups, while comparisons between two groups were evaluated using independent t-tests, with significance set at α = 0.05.

Results and discussion

Effect of different temperatures on the release of various EDCs

Table 2 shows the results of the effects of different temperature conditions (ranging from 4 °C to 100 °C) on the migration of selected EDCs (including DEHP, DBP, BBP, NP, and BPA) from disposable cups constructed from PP and GPPS. A critical initial observation derived from the data is the absence (not detected-ND) of detectable levels for all investigated EDCs in the liquid simulants (distilled water) held within both PP and GPPS cups when maintained at lower temperatures (4 °C and 10 °C). This indicates that under refrigerated or cool temperature conditions, the migration of these specific phthalates, NP, and BPA from either PP or GPPS cup materials remains below the analytical method’s detection limit. This absence of detectable EDCs at lower temperatures is consistent with the understanding that both the diffusion and mass transfer processes of some of the toxicants contained in the polymeric materials are significantly reduced at low temperatures²⁸. Essentially, the energy required for the EDC molecules to overcome intermolecular forces and migrate from the polymer matrix into the liquid simulant is insufficient at these temperatures^16,29,30. The increased movement of molecules at higher temperatures facilitates their migration within the plastic and through the interface into the food simulant³¹.

Table 2.

The effect of different temperatures on the release of various EDCs (ng/L) from disposable cups.

Compounds	Type of cups	Temperature conditions												P
		4 °C		10 °C		40 °C		60 °C		80 °C		100 °C
		C	P	C	P	C	P	C	P	C	P	C	P
DEHP	PP	ND	1	ND	1	555.0 ± 17.0	P < 0.001	845.5 ± 6.4	P < 0.001	937.0 ± 22.6	P < 0.001	1242.5 ± 53.0	P < 0.001	P < 0.001
	GPPS	ND		ND		437.0 ± 8.5		683.5 ± 7.8		838.5 ± 9.2		959.0 ± 2.8		P < 0.001
DBP	PP	ND	1	ND	1	341.5 ± 14.8	P < 0.001	525.0 ± 12.7	P < 0.001	741.0 ± 17.0	P < 0.001	923.0 ± 17.0	P < 0.001	P < 0.001
	GPPS	ND		ND		ND		ND		ND		ND		1
BBP	PP	ND	1	ND	1	335.0 ± 19.8	P < 0.001	522.0 ± 26.9	P < 0.001	713.0 ± 25.5	P < 0.001	940.5 ± 19.1	P < 0.001	P < 0.001
	GPPS	ND		ND		ND		ND		ND		ND		1
NP	PP	ND	1	ND	1	260.5 ± 36.1	P < 0.001	465.0 ± 9.9	P < 0.001	741.0 ± 17.0	P < 0.001	945.5 ± 14.8	P < 0.001	P < 0.001
	GPPS	ND		ND		178.0 ± 24.0		378.0 ± 27.6		543.5 ± 27.6		773.0 ± 24.0		P < 0.001
BPA	PP	ND	1	ND	1	145.5 ± 14.8	P < 0.001	256.5 ± 9.2	P < 0.001	357.5 ± 17.7	P < 0.001	637.5 ± 23.3	P < 0.001	P < 0.001
	GPPS	ND		ND		ND		ND		ND		ND		1

DEHP: Di(2-ethylhexyl) phthalate, DBP: Dibutyl phthalate, BBP: Benzyl butyl phthalate, NP: Nonylphenols, BPA: Bisphenol A, PP: Polypropylene, GPPS: General-Purpose Polystyrene, ND: Not detected, P: P-Value, C: Concentration.

However, a statistically significant shift in the EDC release profiles occurs as temperatures rise beyond these initial cold conditions. For PP cups, the analysis showed the presence of all five target EDCs (DEHP, DBP, BBP, NP, and BPA) at temperatures of 40 °C, 60 °C, 80 °C, and 100 °C. The concentration of each compound detected showed a positive relationship with the rising temperature. For example, the concentration of DEHP released from PP cups systematically increased from 555.0 ± 17.0 ng/L at 40 °C to 845.5 ± 6.4 ng/L at 60 °C, further rising to 937.0 ± 22.6 ng/L at 80 °C, and culminating in the highest observed concentration of 1242.5 ± 53.0 ng/L at 100 °C. Similar temperature-dependent increases were observed for DBP (341.5 ± 14.8 ng/L at 40 °C to 923.0 ± 17.0 ng/L at 100 °C), BBP (335.0 ± 19.8 ng/L at 40 °C to 940.5 ± 19.1 ng/L at 100 °C), NP (260.5 ± 36.1 ng/L at 40 °C to 945.5 ± 14.8 ng/L at 100 °C), and BPA (145.5 ± 14.8 ng/L at 40 °C to 637.5 ± 23.3 ng/L at 100 °C). The statistical analysis confirms this trend, with P-values consistently below 0.001, indicating a highly significant effect of temperature on the release of these compounds from PP cups across the 40–100 °C range compared to the baseline negligible release at 4 °C and 10 °C. The increased release of contaminants from disposable containers at higher temperatures can be attributed to increased diffusion and solubility of contaminants, structural changes, and potential degradation of polymeric materials^8,13,28,32. A study in Brazil showed that the DBP levels in the examined food samples were reported between < 0.08 and 7.5 µg/L. The study found that increasing heating time and repeated use of plastic containers led to higher concentrations of phthalates in food³³. These findings highlight the potential of thermal conditions to influence the migration of EDCs from common plastics into food simulants in contact with food, and they are consistent with the results of previous studies^8,34. A study showed that after three months of exposing the samples to the open air, the concentration of DEHP had decreased. This finding suggests that environmental factors such as temperature and sunlight may contribute to the degradation of phthalates over time³⁵.

In contrast, the release profile from GPPS cups presented a different pattern for several analytes. While DEHP and NP were detected in GPPS cups at temperatures from 40 °C upwards, exhibiting a similar, albeit generally less pronounced, temperature-dependent increase (DEHP: 437.0 ± 8.5 ng/L at 40 °C to 959.0 ± 2.8 ng/L at 100 °C; NP: 178.0 ± 24.0 ng/L at 40 °C to 773.0 ± 24.0 ng/L at 100 °C), the other targeted compounds (including DBP, BBP, and BPA) remained ND across the entire temperature spectrum, including the highest temperature of 100 °C. This absence suggests that these specific phthalates and BPA are not present as additives or residual monomers in the GPPS material or that their migration potential under these conditions is substantially lower than PP. The observed differences in the release rates of the target compounds between the two cup types at the same temperatures suggest that the specific polymeric composition also plays a role in the contaminant release characteristics³⁶. The detection of only DEHP and NP leaching from GPPS suggests a distinct formulation or manufacturing process compared to PP.

Comparison between polypropylene (PP) and general-purpose polystyrene (GPPS)

Comparative analysis between the two materials at each elevated temperature point (40 °C, 60 °C, 80 °C, 100 °C) consistently revealed significantly higher concentrations of total measured EDCs migrating from PP cups compared to GPPS cups (P < 0.001 for the overall comparison at each temperature). Even for the compounds detected in both materials (DEHP and NP), the concentrations released from PP cups were generally higher than those from GPPS cups at equivalent temperatures. However, this difference narrowed for DEHP at 100 °C. These findings underscore a substantially greater propensity for the investigated EDCs to leach from PP cups, particularly under elevated temperatures typical for hot beverages. DEHP consistently emerged as the most abundant phthalate released from both materials at higher temperatures, reaching peak levels at 100 °C. According to previous reports, long-chain DEHP shows weak interaction with the polymer structure and is readily translocated under the influence of heat³⁷. Different PP and GPPS polymer compounds may exhibit varying degrees of structural changes, leading to differences in pollutant emission profiles³⁶. Therefore, the results showed that PP cups and containers release more pollutants than GPPS cups and containers, potentially due to differences in the polymer structure, additive composition, and production processes. Additionally, high temperatures can cause structural changes in polymeric materials, such as increased chain mobility, which facilitates the release of trapped contaminants. The type of plastic, its physical state, and the solubility of the plasticizer in water also significantly affect the release rate of additives into the ingredients within it^38,39.

Table 3 extends the investigation to disposable containers typically intended for various types of liquid foods such as soups or stews, again comparing PP and GPPS materials across the identical temperature range (4 °C to 100 °C) and for the same set of EDCs (DEHP, DBP, BBP, NP, BPA). The results shown in Table 3 largely reflect the fundamental trends observed for the disposable cups, which are detailed in Table 2, reinforcing the conclusions regarding material type and temperature dependence but providing specific quantitative data relevant to container usage scenarios. Consistent with the cup findings, negligible migration of any target EDC was observed at the lower temperatures of 4 °C and 10 °C, with all measurements reported as ND for both PP and GPPS containers under these conditions.

Table 3.

The effect of different temperatures on the release of various EDCs (ng/L) from disposable containers.

Compounds	Type of container	Temperature conditions												P
		4 °C		10 °C		40 °C		60 °C		80 °C		100 °C
		C	P	C	P	C	P	C	P	C	P	C	P
DEHP	PP	ND	1	ND	1	721.5 ± 22.1	0.043	1099.2 ± 8.3	0.254	1218.1 ± 29.4	0.321	1615.3 ± 68.9	0.023	P < 0.001
	GPPS	ND		ND		552.5 ± 24.0		844.0 ± 14.1		1043.0 ± 31.1		1163.0 ± 17.0		P < 0.001
DBP	PP	ND	1	ND	1	444.0 ± 19.3	P < 0.001	682.5 ± 16.5	P < 0.001	963.3 ± 22.1	P < 0.001	1199.9 ± 22.1	P < 0.001	P < 0.001
	GPPS	ND		ND		ND		ND		ND		ND		1
BBP	PP	ND	1	ND	1	431.5 ± 14.8	P < 0.001	658.5 ± 27.6	P < 0.001	967.0 ± 19.8	P < 0.001	1170.5 ± 57.3	P < 0.001	P < 0.001
	GPPS	ND		ND		ND		ND		ND		ND		1
NP	PP	ND	1	ND	1	338.7 ± 46.9	0.045	604.5 ± 12.9	0.046	963.3 ± 22.1	0.048	1229.2 ± 19.3	0.035	P < 0.001
	GPPS	ND		ND		231.4 ± 29.4		486.2 ± 35.9		712.0 ± 28.2		1004.9 ± 31.3		P < 0.001
BPA	PP	ND	1	ND	1	189.2 ± 19.3	P < 0.001	335.5 ± 12.0	P < 0.001	464.8 ± 23.0	P < 0.001	828.8 ± 30.3	P < 0.001	P < 0.001
	GPPS	ND		ND		ND		ND		ND		ND		1

DEHP: Di(2-ethylhexyl) phthalate, DBP: Dibutyl phthalate, BBP: Benzyl butyl phthalate, NP: Nonylphenols, BPA: Bisphenol A, PP: Polypropylene, GPPS: General-Purpose Polystyrene, ND: Not detected, P: P-Value, C: Concentration.

As the temperature was increased from 40 °C to 100 °C, the PP containers demonstrated a significant release of all five monitored EDCs. The concentrations again showed a strong positive relationship with temperature, validated by highly significant P-values (< 0.001) indicating the temperature effect. For PP containers, DEHP release increased from 721.5 ± 22.1 ng/L at 40 °C to a maximum of 1615.3 ± 68.9 ng/L at 100 °C. Similarly, DBP increased from 444.0 ± 19.3 ng/L (40 °C) to 1199.9 ± 22.1 ng/L (100 °C), BBP from 431.5 ± 14.8 ng/L (40 °C) to 1170.5 ± 57.3 ng/L (100 °C), NP from 338.7 ± 46.9 ng/L (40 °C) to 1229.2 ± 19.3 ng/L (100 °C), and BPA from 189.2 ± 19.3 ng/L (40 °C) to 828.8 ± 30.3 ng/L (100 °C). The magnitude of the release, particularly for DEHP, appeared somewhat higher in PP containers compared to PP cups at the maximum temperature (1615.3 ± 68.9 ng/L vs. 1242.5 ± 53.0 ng/L). The similar trends observed in the container study further support the conclusion that temperature significantly influences the release of EDCs from PP materials. The higher levels detected in containers than in cups may be due to larger surface area or differences in manufacturing processes^8,13,36.

The GPPS containers exhibited a distinctively different release profile considering the cup results. Again, DBP, BBP, and BPA were consistently ND across the investigated temperature range (4 °C to 100 °C). DEHP and NP, however, were detected migrating from GPPS containers at temperatures of 40 °C and above. The release of DEHP from GPPS containers increased from 552.5 ± 24.0 ng/L at 40 °C to 1163.0 ± 17.0 ng/L at 100 °C, and NP release increased from 231.4 ± 29.4 ng/L at 40 °C to 1004.9 ± 31.3 ng/L at 100 °C. While these represent substantial concentrations, especially at 100 °C, the pattern of absent DBP, BBP, and BPA release from GPPS remained consistent between cups and containers. The consistency of GPPS results between cups and containers reinforces the conclusion that these specific EDCs are either not present in the GPPS material or have very low migration rates under these conditions.

The comparative analysis between the two container materials at higher temperatures (40 °C to 100 °C) further confirmed the findings from the cup study. The release of detectable EDCs (DEHP and NP from GPPS and all five from PP) was significantly greater from PP containers than GPPS containers. For example, at 100 °C, the DEHP concentration from PP containers (1615.3 ± 68.9 ng/L) was higher than from GPPS containers (1163.0 ± 17.0 ng/L), and similar disparities existed for NP and, by definition, for DBP, BBP, and BPA which were only present in PP contents. The statistical significance (e.g., P = 0.023 for DEHP comparison at 100 °C, P = 0.035 for NP at 100 °C, and P < 0.001 for the others due to ND in GPPS) confirms the differential leaching behavior. Among the compounds leached from PP containers at 100 °C, DEHP exhibited the highest concentration, followed by NP, DBP, and BBP. BPA showed the lowest concentration among the detected compounds, although its release was still significant. These results align with previous studies demonstrating the migration of BPA and NP from disposable cups and mineral water bottles with increasing temperature¹⁰. The study of PET bottles in Egypt revealed that after two months of storage, the concentration of DEHP increases significantly with rising temperatures⁴⁰. The study conducted by Jeddi et al.⁴¹ revealed that higher storage temperatures and longer storage times increase phthalate migration from the bottle wall into the water⁴¹. Moreover, a study by Nam et al.²⁶ found that BPA migration from new polycarbonate baby bottles into the water contained within at 40 °C and 95 °C was 0.03 µg/L and 13.0 µg/L, respectively. After six months of use, these values increased to 18.0 µg/L and 47.18 µg/L at the same two temperatures, respectively. The study found that BPA migration from the bottle to the water increases rapidly at temperatures above 80 °C and that the BPA migration rate increases with each bottle use²⁶.

The results of both Tables 2 and 3 consistently demonstrate that temperature is a critical factor governing the migration of the studied EDCs from both PP and GPPS food contact items. Minimal release occurs at low temperatures (≤ 10 °C), but leaching significantly increases at elevated temperatures (≥ 40 °C), peaking at 100 °C. Furthermore, the data unequivocally highlights a material-dependent difference, with PP cups and containers consistently releasing a broader range and significantly higher overall quantities of the targeted EDCs compared to their GPPS counterparts under identical, especially high-temperature, conditions. The absence (ND) of detectable DBP, BBP, and BPA from GPPS materials under any examined condition is a notable distinction between the two polymer types studied.

This study exclusively used distilled water (4, 10, 40, 60, 80, and 100 °C) as the contents of cups and containers made of PP and GPPS to investigate the migration levels of various EDC compounds. Therefore, it should be noted that in real-world conditions, the type of food and beverage compositions, the pH status of the mixture, and food and beverage additives are also contributing parameters and may play a decisive role in the migration levels of chemical substances. On the other hand, the duration of contact between plastic materials and their contents can influence reactions and alter the process and extent of EDC leaching into food or beverages^13,16,19.

European Commission Directive No. 10/2011 sets specific migration limits (SML) of 1.5 mg/kg (1,500,000 ng/kg) for DEHP, 30 mg/kg (30,000,000 ng/kg) for BBP and 0.05 mg/kg (50000 ng/kg) for BPA^42,43. Similarly, the USFDA has defined SMLs of 0.3 mg/kg (300,000 ng/kg) for DBP and 30 mg/kg (30,000,000 ng/kg) for BBP in food-contact materials³³. The findings of this study indicate that the concentrations of these targeted EDCs are lower than the established regulatory thresholds. However, consumers should be cautious about using disposable plastic cups and containers, especially at higher temperatures, as the release of contaminants can pose potential health risks⁴⁴. Further research is needed to fully understand contaminant release mechanisms and long-term consequences of different disposable cups and container materials. It is recommended to use disposable containers and cups at low temperatures to minimize the release of contaminants. If possible, use alternative materials instead of disposable plastic cups and containers.

Conclusions

This study concludes that temperature significantly affects the release of DEHP, DBP, BBP, BPA, and NP from disposable cups and containers made of PP and GPPS to the contents inside them. The findings showed that at lower temperatures of 4 °C and 10 °C, none of the target compounds were detected in the liquid inside the PP and GPPS cups and containers. However, there was a significant increase in the release of these EDCs from 40 °C to 100 °C (P < 0.001). PP cups and containers exhibited significantly higher compound release levels at higher temperatures than GPPS (P < 0.001). DEHP showed the highest release rate at 100 °C (1242.5 ± 53.0 ng/L in PP cups and 1615.3 ± 68.9 ng/L in PP containers). In GPPS cups and containers, BPA, DBP, and BBP were not detected at any temperature. The increase in EDC release at higher temperatures can be attributed to changes in the structure of the plastic materials, increased diffusion, and solubility. Although the levels of target EDCs in this study are lower than some regulations, the findings suggest that consumers should be more cautious about using disposable plastic cups and containers, particularly when temperatures are high, as increased release of contaminants may pose health risks over time. Further research is warranted to fully comprehend the long-term effects of pollutant release from various materials in disposable cups and containers and to develop safer alternatives that prioritize consumer health and environmental sustainability.

Author contributions

Tooraj Massahi, Abdullah Khalid Omer, Hamed Soleimani, and Masoud Moradi: investigation, writing original draft, writing, review and editing, formal analysis. Amir Kiani, Nazir Fattahi, and Borhan Mansouri: writing, review and editing, visualization, validation. Kiomars Sharafi: conceptualization, writing, review and editing, visualization, validation, project administration. All authors reviewed the results and approved the final version of the manuscript.

Data availability

All data generated or analyzed during this study are included in this published article.

Declarations

Competing interests

The authors declare no competing interests.

Ethics approval

Ethical approval was not required for this study as it does not involve human or animal participants. This study does not involve experiments on live vertebrates, higher invertebrates, or human subjects. Therefore, ethical approval and informed consent are not applicable to this manuscript.