DOI: https://doi.org/10.4316/fens.2025.012 134 Journal homepage: www.fia.usv.ro/fiajournal Journal of Faculty of Food Engineering, Ştefan cel Mare University of Suceava, Romania Volume XXIV, Issue 2 - 2025, pag. 134 - 142 REUSABLE KITCHEN – AND TABLEWARE MATERIAL STABILITY TESTING WITH REGARD TO SPECIFIC MIGRATION OF MELAMINE AND FORMALDEHYDE * Svetla PETROVA 1, *Valentina CHRISTOVA – BAGDASSARIAN 2 1Food Composition and Consumer Products, National Center of Public Health and Analyses, Sofia, Bulgaria, 2Food Composition and Consumer Products, National Center of Public Health and Analyses, Sofia, Bulgaria, *Corresponding author: s.chavdarova@ncpha.government.bg; v.hristova@ncpha.government.bg Received 27 March 2025, accepted 24 June 2025 Abstract: Reusable melamine and bamboo kitchen and tableware containing melamine-formaldehyde resin as a filler and binding agent are popular among consumers. It has been found that melamine and formaldehyde can migrate into food and have adverse effects on human health. European legislation sets two conditions that reusable items must meet - they must meet specific migration limits and material stability requirements. This work aimed to test the compliance of reusable kitchen and tableware containing melamine-formaldehyde resin in terms of material stability. The test was carried out on 10 items made of melamine and bamboo. A Standard HPLC–UV method for melamine and spectrophotometric method for formaldehyde were used. The results for melamine migration varied. In 40% of the samples, the material did not comply with the legislation. In one item, the specific migration limit (SML) was exceeded by 8 times. In certain products, material instability has been established. In 30% of the samples, melamine migration was below the LOD, and the material demonstrated stability. Formaldehyde migration results were below the SML in all but one sample, which exceeded the limit by more than four times. In 27% of the samples, an increase in formaldehyde migration was found during the second exposure. However, according to the calculated value of │Z│, the material is considered stable under the legislation. For 40% of the items, formaldehyde specific migration levels were below the LOD. Therefore, the material stability testing of reusable kitchenware and utensils demonstrated non-compliance with the requirements of the legislation in more than half of the melamine and bamboo items tested. This can lead to unpredictable migration from bamboo and melamine products during their repeated use and raises concerns about the health of consumers. Keywords: melamine, formaldehyde, food contact materials, compliance with legislation. 1. Introduction A wide variety of reusable plastic dishes and utensils are commonly used in modern kitchens. Among the most widely sold kitchen items are those made from melamine-formaldehyde resin, commonly referred to by consumers as melamine [1, 2]. This thermosetting plastic is produced through the catalytic polycondensation of melamine and formaldehyde (Fig. 1). It is inexpensive, durable, easily colored, and often marketed as dishwasher-safe and microwaveable. Melamine-formaldehyde resin is also used in the production of bamboo dishes and utensils as a bonding agent for bamboo flour [3, 4]. As a result of technological issues-such as incomplete polycondensation during polymer production, surface damage and scratching during molding, microwave use, heating, food acidity, and other factors-melamine and formaldehyde may migrate from such kitchenware into food. The literature reports a range of negative health effects associated with exposure to both monomers [5, 6, 7]. The IARC Monographs on the Evaluation of Carcinogenic Risks to Humans describe the harmful effects of each compound [8, 9]. Melamine primarily affects the kidneys and the male reproductive system [5, 6]. It is classified under Regulation (EC) No 1272/2008 (CLP) as a Category 2 carcinogen, toxic to reproduction, and as a substance with https://doi.org/10.4316/fens.2025.009 http://www.fia.usv.ro/fiajournal mailto:s.chavdarova@ncpha.government.bg Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XXIV, Issue 2 – 2025 Svetla PETROVA, Valentina CHRISTOVA–BAGDASSARIAN, Reusable kitchen – and tableware material stability testing with regard to specific migration of melamine and formaldehyde, Food and Environment Safety, Volume XXIV, Issue 2 – 2025, pag. 134-142 135 specific toxicity for certain organs and systems after repeated exposure [10]. The effects of formaldehyde primarily affect the central nervous system [8]. It is a mutagen and a proven human carcinogen, classified in Group 1 by the IARC. Formaldehyde is also an irritant to the mucous membranes, eyes, and skin [9, 11]. Both compounds- melamine and formaldehyde-are included in the list of authorized monomers in Regulation (EU) No 10/2011 on plastic materials and articles intended to come into contact with food, with specific migration limits of 2.5 mg/kg for melamine and 15 mg/kg for formaldehyde [12]. Most of the melamine and bamboo tableware and utensils available on the market are imported from China. In 2021, tests on children's bamboo utensils revealed that some items did not comply with the legal requirements regarding specific migration limits [9]. Fig.1. Preparation of melamine-formaldehyde resin [3] Some authors [2] have reported a wide variation in the specific migration results of the two monomers across consecutive tests on the same item. As a result, a change in legislation was introduced [13], requiring reusable items to be assessed against two indicators. First, the migration test results must be below the relevant specific migration limits (SMLs); second, the material must demonstrate stability. For stability compliance, migration values from three consecutive exposures of the same item must be evaluated. These results are compared to the requirement that each subsequent migration must not exceed the previous one. To determine whether there is a significant difference between the values obtained from two consecutive migration tests, the following formula (1) is used: |𝑍|= (𝑚𝑘−𝑚𝑘−1) √(𝑢𝑚𝑘 2 + 𝑢𝑚𝑘−1 2 ) , (1) where k = 1, 2, or 3 indicates the order of migration from the same item; and 𝑈𝑚𝑘 is the standard uncertainty of the migration measurement mk. When the value of ǀZ| > 2, the material is considered not to comply with the legislative requirements regarding material stability. The aim of this paper was to assess the compliance of reusable tableware and cutlery containing melamine-formaldehyde resin with regard to material stability. 2. Materials and methods 2.1. Description of the samples The study was conducted on 10 items (kitchenware sets, bamboo and melamine cups, plates, and bowls) made of melamine- formaldehyde resin and bamboo, as shown in Figures 1-10. According to the label, the items are dishwasher safe, intended for use at temperatures not exceeding 70 °C for no longer than 2 hours, and are manufactured in China. Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XXIV, Issue 2 – 2025 Svetla PETROVA, Valentina CHRISTOVA–BAGDASSARIAN, Reusable kitchen – and tableware material stability testing with regard to specific migration of melamine and formaldehyde, Food and Environment Safety, Volume XXIV, Issue 2 – 2025, pag. 134-142 136 Fig. 1 Bamboo kitchen utensils, set of 4 items, 30 cm, manufacturer 1 Fig. 2. Bamboo spoons, set of 2, manufacturer 2 Fig. 3. Bamboo bowls (450 mL) Fig. 4. Reusable melamine plates, d=20 cm Fig. 5. Reusable melamine plate, rectangular, 30 x 14 cm Fig. 6. Bamboo cups with blue plastic lid, 400 mL Fig. 7. White melamine bowl, d=10 cm Fig. 8. Bamboo children's cups, 200 mL Fig. 9. Plastic melamine cups, dotted, 200 mL Fig. 10. Melamine bowls, blue, 720 mL Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XXIV, Issue 2 – 2025 Svetla PETROVA, Valentina CHRISTOVA–BAGDASSARIAN, Reusable kitchen – and tableware material stability testing with regard to specific migration of melamine and formaldehyde, Food and Environment Safety, Volume XXIV, Issue 2 – 2025, pag. 134-142 137 2.2. Analytical instrumental methods Standardized instrumental methods, described in detail by [1], were used to test for the presence of the two monomers. A standardized reverse-phase liquid chromatography method with UV detection was used for the determination of melamine [14], while a standardized spectrophotometric method was applied for formaldehyde determination [15]. The methods were validated in accordance with ISO/IEC 17025:2017 General requirements for the competence of testing and calibration laboratories (Table 1). Table 1. Analytical Parameters of the Methods Used for Melamine and Formaldehyde Determination Parameter HPLC-UV method for melamine, λ =230 nm Spectrophotometric method for formaldehyde, λ=574 nm Limit of Detection (LOD), mg/kg 0.5 0.7 Limit of Quantification (LOQ), mg/kg 1.0 1.5 Working Range, mg/kg (1.00 ÷ 8.00) (1.5 ÷ 30.0) Expanded Uncertainty, mg/kg (0.07 ÷ 0.24) (0.87 ÷ 2.41) Correlation Coefficient R2 = 0.9997 R2 = 0.9987 Sample pre-treatment was performed according to the procedures described in the Guidelines of the European Reference Laboratory for Food Contact Materials and Articles (EURL-FCM) [16, 17]. The applied test conditions for repeated exposure were as follows: simulant B (3% acetic acid), for 2 hours at 70 °C. 3. Results and discussion Table 2 presents the results obtained for the specific migration of melamine from reusable melamine and bamboo tableware and kitchenware over three consecutive exposures using a food simulant—3% aqueous acetic acid. For three of the items (Item 3 – bamboo bowls, 450 mL; Item 5 – rectangular melamine plates; and Item 9 – dotted melamine cups), the results were below the detection limit of the method used (LOD = 0.5 mg/kg), indicating compliance with the legislation regarding specific melamine migration. By contrast, the melamine migration limit was exceeded in all three exposures for Items 1 and 2—bamboo kitchen utensils and bamboo spoons, respectively. In the first test, melamine migration from the bamboo kitchen utensils exceeded the specific migration limit (SML) by approximately 8.7 times, while the bamboo spoons exceeded it by nearly three times. Although the specific migration values for both items decreased progressively from the first (m1) to the third (m3) exposure (i.e., m1 > m2 > m3), the items are not considered compliant with the legislative requirements-neither in terms of the specific migration limit nor with respect to material stability [10]. For the bamboo cups with a blue plastic lid (Item 6), melamine migration during the second exposure (m2) was higher than during the first (m1), i.e., m2 > m1. Since |Z| = 2.86 > 2, the material was deemed unstable, and the article does not comply with the legislative requirements. For the melamine plates (Item 4), melamine migration during the first exposure exceeded the specific migration limit (SML) by nearly twice the permitted amount, although subsequent exposures were below the limit of detection (LOD). Since │Z│1-2 > 2, the item is considered non-compliant. In contrast, the results for the reusable bamboo cups (Item 8) and melamine bowls (Item 10) showed a decrease in migration from the first (m1) to the third (m3) exposure, i.e., m1 > m2 > m3. The migration Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XXIV, Issue 2 – 2025 Svetla PETROVA, Valentina CHRISTOVA–BAGDASSARIAN, Reusable kitchen – and tableware material stability testing with regard to specific migration of melamine and formaldehyde, Food and Environment Safety, Volume XXIV, Issue 2 – 2025, pag. 134-142 138 values were below the SML, indicating that these products comply with the legislative requirements for both stability and specific migration of melamine. For the white melamine bowls (Item 7), a migration value of (2.46 ± 0.45) mg/kg was recorded at the first exposure, which, including the expanded uncertainty, exceeds the specific migration limit (SML). Despite a decrease in migration during the subsequent two exposures, │Z│ = 3.00 > 2, indicating that the material is unstable and the article does not comply with the legislation in this regard. Table 2. Melamine migration in reusable melamine and bamboo table and kitchenware Item No. Melamine- formaldehyde resin and bamboo articles, SML1 = 2.5 mg/kg Exposure 1, m 1 Exposure 2, m 2 Exposure 3, m 3 ǀZǀ1-2, m 1 and m 2 ǀZǀ2-3, m 2 and m 3 1 Bamboo kitchen utensils, 30 cm (Fig. 1) 21.73 ± 1.92 9.30 ± 0.82 7.47 ± 0.66 5.95 1.74 2 Bamboo spoons, couple (Fig. 2) 7.85 ± 0.69 4.58 ± 0.40 4.43 ± 0.39 4.10 0.27 3 Bamboo bowls (450 mL) (Fig. 3) ˂ LOD2 ˂ LOD2 ˂ LOD2 N/A3 N/A3 4 Reusable melamine plates, d=20 cm (Fig. 4) 4.60 ± 0.41 ˂ LOD2 ˂ LOD2 11.22 N/A3 5 Reusable melamine plate, rectangular, 30 x 14 cm (Fig. 5) ˂ LOD2 ˂ LOD2 ˂ LOD2 N/A3 N/A3 6 Bamboo cups with blue plastic lids, 400 mL (Fig. 6) 1.98 ± 0.31 2.08 ± 0.34 0.84 ± 0.27 0.22 2.86 7 White melamine bowl, d=10 cm (Fig. 7) 2.46 ± 0.45 0.99 ± 0.18 1.00 ± 0.18 3.00 0.04 8 Bamboo children's cups, 200 mL (Fig. 8) 2.33 ± 0.42 1.99 ± 0.36 1.95 ± 0.35 0.61 0.08 9 Plastic melamine cups, dotted, 200 mL (Fig. 9) ˂ LOD2 ˂ LOD2 ˂ LOD2 N/A3 N/A3 10 Melamine bowls, blue, 720 mL (Fig. 10) 2.22 ± 0.41 2.02 ± 0.36 2.00 ± 0.35 0.37 0.04 1SML - The specific migration limit; 2LOD - Limit of detection of the method; 3N/A - "Not Applicable" for ǀZǀ, when the results are m₁), the calculated │Z│ = 1.46 < 2 indicates that the material is stable, and the item complies with the legislative requirements. For bamboo cups with blue plastic lids (Item 6), migration during the second Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XXIV, Issue 2 – 2025 Svetla PETROVA, Valentina CHRISTOVA–BAGDASSARIAN, Reusable kitchen – and tableware material stability testing with regard to specific migration of melamine and formaldehyde, Food and Environment Safety, Volume XXIV, Issue 2 – 2025, pag. 134-142 139 exposure (m2) was higher than during the first (m1), i.e., m2 > m1; however, since │Z│ = 0.81 < 2, the material is considered stable, and the item complies with legislative requirements. For melamine plates (Item 4), an increase in migration values was observed from the first to the third exposure, i.e., m1 < m2 < m3. Although the specific migration limit (SML) of 15 mg/kg was not exceeded, the material is considered unstable since │Z│ = 2.41 > 2, and therefore the article does not comply with legislative requirements. For white melamine bowls (Item 7), migration decreased from the first to the third exposure (m1 > m2 > m3), with │Z│ = 0.34, indicating compliance with legislative requirements. Similarly, for children's bamboo cups (Item 8), migration also decreased across exposures (m1 > m2> m3), with │Z│ = 0.34; therefore, the material is stable and complies with legislation regarding formaldehyde migration. Table 3. Formaldehyde migration in reusable melamine and bamboo tableware and kitchenware Item No. Melamine-formaldehyde resin and bamboo articles, SML1 = 15 mg/kg Exposure 1, m1 Exposure 2, m2 Exposure 3, m3 ǀZǀ, m1 and m2 ǀZǀ, m2 and m3 1 Bamboo kitchen utensils, 30 cm (Fig. 1) ˂ LOD2 ˂ LOD2 ˂ LOD2 N/A3 N/A3 2 Bamboo spoons, couple (Fig. 2) ˂ LOD2 ˂ LOD2 ˂ LOD2 N/A3 N/A3 3 Bamboo bowls (450 mL) (Fig. 3) 1.88 ± 0.26 2.54 ± 0.37 2.23 ± 0.33 1.46 0.42 4 Reusable melamine plates, d=20 cm (Fig. 4) 4.40 ± 0.64 3.00 ± 0.44 5.10 ± 0.75 1.80 2.41 5 Reusable melamine plate, rectangular, 30 x 14 cm (Fig. 5) ˂ LOD2 ˂ LOD2 ˂ LOD2 N/A3 N/A3 6 Bamboo cups with blue plastic lids, 400 mL (Fig. 6) 2.57 ± 0.37 3.04 ± 0.45 2.50 ± 0.37 0.81 0.93 7 White melamine bowl, d=10 cm (Fig. 7) 3.76 ±0.56 2.18 ± 0.32 2.03 ± 0.30 2.45 0.34 8 Bamboo children's cups, 200 mL (Fig. 8) 2.48 ± 0.36 2.31 ± 0.35 1.51 ± 0.23 0.34 1.91 9 Plastic melamine cups, dotted, 200 mL (Fig. 9) 66.49 ± 9.67 N/A3 N/A3 6.88 N/A3 10 Melamine bowls, blue, 720 mL (Fig. 10) ˂ LOD2 ˂ LOD2 ˂ LOD2 N/A3 N/A3 1SML - The specific migration limit; 2LOD - Limit of detection of the method; 3N/A - "Not Applicable" for ǀZǀ, when the results are m1; however, the calculated stability index |Z| = 0.5 < 2, indicating that the material is considered stable. Similarly, the average values for formaldehyde migration showed an increase from the first to the second exposure (m2 > m1), yet with a |Z| value of 1.37 < 2, the material again meets the stability criteria. Consequently, the tested item complies with the legislative requirements in terms of both migration limits and material stability. The items submitted for interlaboratory comparison testing demonstrated a wide variability in results, both regarding the specific migration of the two monomers and the material's stability. This variability highlights the importance of material homogeneity as a critical factor in determining whether a given article complies with legislative requirements. 5. Conclusions The test results for melamine-formaldehyde resin and bamboo products reveal significant variability in both melamine and formaldehyde migration, as well as in material stability. More than half of the tested items (specifically items 1, 2, 4, 6, 7, and 9) failed to comply with the legislative requirements for either or both parameters. These findings raise serious concerns regarding consumer safety. Therefore, melamine and bamboo products should not be widely marketed for repeated use in households. Clear labeling should be mandated to inform consumers that such items are not safe for use in dishwashers or under elevated temperatures, as supported by the evidence obtained in this study. 6. References [1]. PETROVA, S. P., CHRISTOVA– BAGDASSARIAN, V. Migration of melamine and formaldehyde from kids' bamboo dinner sets, Food and Environment Safety Journal, 20(2): 128-136, (2021) [2]. LUND K. H., PETERSEN J. H. Migration of formaldehyde and melamine monomers from kitchen- and tableware made of melamine plastic, Food Additives and Contaminants, 23 (09): 948-955, (2006) [3]. https://askfilo.com/chemistry-question- answers/the-polymer-melmac-is-obtained-by (accessed 24 April 2025) [4]. EBNER I., HABERER S., SANDER S., KAPPENSTEIN O., LUCH A., BRUHN T. Release of Melamine and Formaldehyde from Melamine- Formaldehyde Plastic Kitchenware, Molecules, 25, 3629, (2020); doi:10.3390/molecules25163629 [5]. HSIEH T. J., HSIEH P. C., TSAI Y. H., WU C. F., LIU C. C., LIN M. Y., WU M. T., Melamine induces human renal proximal tubular cell injury via transforming growth factor-β and oxidative stress, Toxicol Sci., 130(1): 17 – 32, (2012) https://askfilo.com/chemistry-question-answers/the-polymer-melmac-is-obtained-by https://askfilo.com/chemistry-question-answers/the-polymer-melmac-is-obtained-by Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University - Suceava Volume XXIV, Issue 2 – 2025 Svetla PETROVA, Valentina CHRISTOVA–BAGDASSARIAN, Reusable kitchen – and tableware material stability testing with regard to specific migration of melamine and formaldehyde, Food and Environment Safety, Volume XXIV, Issue 2 – 2025, pag. 134-142 142 [6]. YANG Y. et al., Acute low-dose melamine affects hippocampal synaptic plasticity and behavior in rats, Toxicol Lett, 214: 63 – 68, (2012) [7]. KALOYANOVA F., Hygienic Toxicology, 115 – 116, (1983) [8]. Some chemicals that cause tumours of the urinary tract in rodents, IARC Monographs on the evaluation of carcinogenic risks to humans, 2019, Vol. 119, Melamine, 115-160 [9]. Chemical Agents and Related Occupations IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, A review of human carcinogens, Vol. 100F, Formaldehyde, 401-435, (2012) [10]. Safety data sheet Safety data sheet acc. to Regulation (EC) No. 1907/2006 (REACH). Melamine ≥99 %, for biochemistry. Revision: 2024- 10-09 [11]. Safety data sheet Safety data sheet acc. to Regulation (EC) No. 1907/2006 (REACH). Formaldehyde solution ≥37 %, Revision: 2025-02- 20 [12]. Commission regulation (EU) № 10/2011 of 14 January 2011 on plastic materials and articles intended to come into contact with food (last amendment 20.01.2025) [13]. Commission regulation (EU) 2020/1245 of 2 September 2020 amending and correcting Regulation (EU) No 10/2011 on plastic materials and articles intended to come into contact with food [14]. DD CEN/TS 13130-27:2005. Materials and articles in contact with foodstuffs. Substances in plastics subject to restriction. Part 27: Determination of 2,4,6-triamino-1,3,5-triazine in simulants [15]. DD CEN/TS 13130-23:2005. Materials and articles in contact with foodstuffs. Substances in plastics subject to restriction. Part 23: Determination of formaldehyde and hexamethylenetetramine in food simulants [16]. EUR 23814 EN 2009, Guidelines on test conditions for articles in contact with foodstuffs. A CRL-NRL-FCM Publication, 1st Ed., (2009) [17]. EUR 23815 EN 2011, Technical guidelines on testing the migration of primary aromatic amines from polyamide kitchenware and of formaldehyde from melamine kitchenware, 1st Ed., (2011) [18] BRADLEY E. L., BOUGHTFLOWER V., SMITH T. L., SPECK D. R., CASTLE L., Survey of the migration of melamine and formaldehyde from melamine food contact articles available on the UK market, Food Additives and Contaminants, 22: 597- 606, (2005). [19]. BRATINOVA S.P., ROBOUCH P., BELDI G., SENALDI C., HOEKSTRA E., Determination of melamine and formaldehyde (FA) in food contact material migration solutions., Publications Office of the European Union, Luxembourg, (2024), doi:10.2760/42351, JRC137627 https://publications.jrc.ec.europa.eu/repository/hand le/JRC137627 https://publications.jrc.ec.europa.eu/repository/handle/JRC137627 https://publications.jrc.ec.europa.eu/repository/handle/JRC137627