Migration of metal elements from polylactic acid dinner plate into acidic food simulant and its safety evaluation

Food Packaging and Shelf Life 22 (2019) 100381

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Migration of metal elements from polylactic acid dinner plate into acidic food simulant and its safety evaluation ⁎

T

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Jin-Feng Hea, Xin-Guang Lva, , Qin-Bao Lina, , Zhong Lib, Jia Liaob, Cai-Yun Xub, Wen-Jun Zhongb a b

Key Laboratory of Product Packaging and Logistics, Packaging Engineering Institute, Jinan University, Zhuhai, 519070, China Chemical Analysis Laboratory of Gongbei Customs Technology Center, Zhuhai, 519000, China

A R T I C LE I N FO

A B S T R A C T

Keywords: Polylactic acid Dinner plate Metal elements Migration ICP-OES

The metal elements in polylactic acid (PLA) dinner plate were determined by inductively coupled plasma optical emission spectrometer (ICP-OES); migration of these metal elements from PLA dinner plate into 3% acetic acid food simulant at 40, 60 and 70 °C was investigated; three subsequent migration experiments under 40 °C for 10 days and 70 °C for 2 h to simulate migration under multiple-use conditions were conducted. The results revealed that the PLA dinner plate contains aluminum, barium, calcium, iron, magnesium, titanium and zinc. As expected, with the exposure time and temperature increases, the migration of metal elements increased; even after a long exposure time (40 °C for 10 days, 60 °C for 6 days, 70 °C for 6 days), the migration still continued. Migration of aluminum, barium, iron, and zinc was not exceed their specific migration limit (SML), while the estimated daily intake (EDI) of calcium and magnesium was not beyond their tolerable upper intake level (UL). The overall migration into acidic food simulant was not exceed overall migration limit (OML). For three subsequent migration experiments, the results revealed that the migration mainly occurred from the surface of PLA dinner plate when the exposure time is shorter, while the migration not only occurred from the surface but also from the interior of PLA dinner plate when the exposure time is long.

1. Introduction The extensive use of petroleum-based polymers has caused the environmental pollution (Madhavan Nampoothiri, Nair, & John, 2010; Saleem, Adil Riaz, & Gordon, 2018). A growing environmental awareness, safety challenges, demand for renewable materials, have driven the bio-based and biodegradable materials to gradually substitute the petroleum polymers (Farah, Anderson, & Langer, 2016; Narayan, 2006; Scarfato, Di Maio, & Incarnato, 2015; Souza & Fernando, 2016). One of the most important markets of the bio-based polymers is food packaging. Compared with other biodegradable materials, polylactic acid has received a special attention and been extensively researched (Aframehr et al., 2017) due to its high mechanical strength, good gas permeability, biocompatible, biodegradable under composting conditions and in soil (the degradation products are water and carbon dioxide), easy processability, energy-saving, low toxicity and suitable for food packaging (Farah et al., 2016; Phetwarotai & Aht-Ong, 2016; Scarfato et al., 2015). However, it also has many drawbacks, for example, poor thermal stability, poor barrier properties, low crystallinity, slow crystallization rate, brittleness (Fortunati et al., 2012; Henricks, Boyum, & Zheng, 2015; Shi & Dou, 2015).

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In order to improve its processing performance and other properties, various additives could be added in its manufacturing process, such as: plasticizers, antioxidants, nucleating agents, slip agents, compatibilizer, inorganic fillers, etc (Ashter, 2016). Polylactic acid has been known as a very safe packaging material (Scarfato et al., 2015), however, those additives might migrate into the packaged food and endanger consumer’s health. Except for those additives, which are also known as intentionally added substances (IAS), non-intentionally added substances (NIAS) might migrate into the packaged food as well. NIAS, which could be the result of reaction, degradation or impurity of raw materials, have gaining increasingly attention in recent years (Nerin, Alfaro, Aznar, & Domeno, 2013). Talc is commonly used as nucleating agent to improve PLA’s crystallization behavior and thus enhance its mechanical performance due to its low cost (Huang et al., 2016; Nanthananon, Seadan, Pivsa-Art, Hamada, & Suttiruengwong, 2018; Phetwarotai & Aht-Ong, 2016; Refaa, Boutaous, Xin, & Siginer, 2017). Its main content is hydrated magnesium silicate (Mg3[Si4O10](OH)2), however, it may contains significant and variable levels of other minerals as impurities as well, which would differ a lot depending on its origin. Hu et al. found the talc contains lead, cadmium, chromium, arsenic, antimony, copper, zinc,

Corresponding authors. E-mail addresses: [email protected] (X.-G. Lv), [email protected] (Q.-B. Lin).

https://doi.org/10.1016/j.fpsl.2019.100381 Received 13 March 2019; Received in revised form 8 August 2019; Accepted 8 August 2019 2214-2894/ © 2019 Elsevier Ltd. All rights reserved.

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plate was provided by a local company (Guangdong, China). The PLA plate has a thickness of 0.520 ± 0.005 mm, diameter of 11.5 ± 0.2 cm. Mean densities of PLA plates were 0.3049 ± 0.0027 g/ cm3.

manganese, nickel, molybdenum, cobalt, lithium and chromium, manganese, zinc, copper by ICP-MS and ICP-OES (Hu, Pang et al., 2011; Hu, Zeng et al., 2011); while, Zhang et al. found magnesium, calcium, aluminum, iron, lead, arsenic, mercury, chromium in talc by ICP-AES (Zhang, Xiao, Wei, Shi, & Qian, 2013). In other words, talc may contains many metal elements, some of which are heavy metals that are toxic or dangerous. High concentration of aluminum was reported to have adverse effects on the nervous system and can result in loss of memory, problems with balance and loss of coordination (Krewski et al., 2007); arsenic can cause formation of skin lesions, internal cancers, neurological problems, hypertension and cardiovascular disease and diabetes mellitus (Smith, Lingas, & Rahman, 2000). Calcium carbonate, as a well known inorganic filler, is widely added to polymers due to its low cost and ability to improve performance (Fukuda, Tsuji, & Ohnishi, 2002). However, Hao et al. found that calcium carbonate contains iron, maganese, lead, cadmiun, chromium, arsenic, mercury, barium, magnesium, copper (Hao et al., 2013). Therefore, specific attention should be paid to the content and migration of different metal elements in talc and calcium carbonate-containing PLA food contact material. Regarding the impurities of talc and calcium carbonate, the purpose of this study was to determine the content of metal elements present in talc and calcium carbonate-containing polylactic acid dinner plate and their migration into food simulant.

2.3. Determination of total content of metal elements in samples 2.3.1. Wet digestion The polylactic acid plate was cut into 5 mm × 5 mm pieces, and then weighed (0.2000 g) into an erlenmeyer flask. The sample was carbonized in an electronic universal electric furnace, and mixed acid (10 ml, HNO3:HClO4 = 4:1, v:v) were then added. The mixture was heated on the furnace to digest, when the erlenmeyer flask emitted a lot of white smoke and the solution became clear, the sample was completely digested. After cooling down to room temperature, the solution was diluted to 50 ml with ultrapure water. Finally, it was filtered with a millex filter (PTFE 0.22 μm), dilute, if necessary, to make the concentration falls in the linear range, and analyzed by ICP-OES. Unless otherwise specified, all measurements were carried out in triplicate.

2.3.2. Hydrofluoric acid digestion As for hydrofluoric acid digestion, the sample was put into a polytetrafluoroethylene (PTFE) bottle and digested with 10 ml of mixed acid on microcontroller digital electric heating plate at 185 °C. When the white smoke came out, 5 ml hydrofluoric acid was added and the lid was covered for further digestion.

2. Materials and methods 2.1. Instrumentation The polylactic acid plate were digested using a microcontroller digital electric heating plate (XMTD-701; Xuanyuan, Yancheng, China) and an electronic universal electric furnace (DK-98-Ⅱ; Taster, Tianjin, China). A temperature-controlled oven (GZX-9420MBE; Boxun, Shanghai, China) was used for the migration test. The determination of the metal elements in both, polylactic acid dinner plate and acidic food simulant, was carried out by ICP-OES (5100 ICP-OES; Agilent, USA). The ICP-OES was operated under the following conditions: RF power 1200 W, nebulizer flow 0.7 L/min, plasma gas flow 11.0 L/min, auxiliary gas flow 1 L/min, compensated gas flow 0 L/min, observation mode axial, observation height 8 mm, stable time 15 s, pump speed 12 r/min, repeat time twice, read time 5 s. Aqueous extracts were analyzed directly by ICP-OES.

2.4. Migration tests The specific migration tests were carried out. As indicated in a previous study by our group, silver showed higher migration in 3% acetic acid than in 50% ethanol (Su et al., 2015). 3% acetic acid was selected as food simulant in this study. The surface-food-ratio was 6 dm2 per kg food as suggested by the European Commission regulation (European Commission, 2011). Two pieces of PLA dinner plate (1 cm × 3 cm for each) (double-side, 12 cm2 in total) were then placed into a glass tube and 20 ml of 3% acetic acid at set temperature was then added. The migration tests were conducted in a temperaturecontrolled oven. The PLA dinner plate can be used to serve hot meal, thus the migration at 100 °C was the real situation, however, in order to harmonize the handling and make sure that laboratories came to the same result, 70 °C for 2 h is the better testing condition (European Commission, 2011). Considering that PLA is of increasingly interest to substitute petroleum-based food contact materials, safety relevant data under different exposure conditions could be interesting and useful, more migration conditions including 40 °C up to 10 days, 60 °C up to 6 days, and longer time for 70 °C were investigated as well, hoping to have a better comprehension of the migration behavior of different metal elements. Overall migration of PLA plate into 3% acetic acid under 70 °C for 2 h was investigated. The PLA plate was cut into pieces (3 cm × 3 cm), two of them (double-side, 36 cm2 in total) were placed into wide-mouth bottle, 60 ml food simulant was added to conduct migration test (S/V: 6 dm2/1 L). At the same time, blank experiments were prepared in the same manner but without any sample.

2.2. Reagents and samples Nitric acid (HNO3), perchloric acid (HClO4) and hydrofluoric acid (HF) of guaranteed grade were purchased from Guangzhou Chemical Reagent Factory (Guangzhou, China), acetic acid (CH3COOH) of analytical grade were purchased from Damao Chemical Reagent Factory (Tianjin, China). The solutions were prepared with ultrapure water which was obtained from water purification system (EPED-10TS; EPED, Nanjing, China). Stock solutions of 24 metal elements (aluminum, arsenic, boron, barium, beryllium, bismuth, cadmium, cobalt, chromium, copper, iron, gallium, lithium, magnesium, manganese, nickel, lead, antimony, tin, strontium, titanium, thallium, vanadium, zinc) of 100 mg/L, calcium and magnesium of 1000 mg/L, were obtained from National Nonferrous Metals and Electronic Materials Analysis and Testing Center (Beijing, China). Working solutions for the quantification of metal elements in digested solution and food simulant were obtained by diluting stock solutions (100 mg/L for 24 metal elements; 1000 mg/L for calcium and magnesium) with 5% nitric acid and 3% acetic acid, respectively. Concentrations used to establish calibration curves for 24 metal elements were 0.2, 0.4, 0.6, 0.8, 1.0 mg/L while that for calcium and magnesium were 2.0, 4.0, 6.0, 8.0, 10.0 mg/L. Stock solutions and working solutions were stored at 4 °C. Talc and calcium carbonate containing polylactic acid (PLA) dinner

2.5. Assessment of migration under multiple-used condition Providing that this PLA dinner plate can be used repeatedly, repeated exposures were also carried out. In this case, 3 subsequent migrations were conducted using another new portion of simulant each time, but the sample remained the same. The condition was 40 °C for 10 days, 70 °C for 2 h and 3% acetic acid was used as well. 2

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2.6. Method validation

Table 2 The recoveries and RSDs of the studied metal elements in the migration experiment (n = 3).

The validation procedure of the analytical method for determination of initial concentration of metal elements and the migration of metal elements into 3% acetic acid, includes linearity, LOD, LOQ, accuracy and precision. LOD and LOQ were determined as 3 and 10 times the SD of 11 blank measurements, respectively. Accuracy and precision were evaluated with recoveries and RSDs. The recoveries of the proposed method were verified by spiking the metal elements into 3% acetic acid at three concentration levels (0.2, 0.6, 1.0 mg/L for aluminum, barium, iron, titanium, zinc; 2.0, 6.0, 10.0 mg/L for calcium and magnesium). The spiked solutions were then treated in the same fashion as samples.

Elements name

spiked concentration (mg/L)

Recoveries (%)

RSD (%)

Aluminum

0.2 0.6 1.0 0.2 0.6 1.0 2.0 6.0 10.0 0.2 0.6 1.0 2.0 6.0 10.0 0.2 0.6 1.0 0.2 0.6 1.0

103.5 108.3 108.5 102.3 101.4 99.8 102.8 100.4 99.1 115.3 114.7 105.9 99.8 99.6 98.8 97. 7 100.2 101.4 115.6 104.3 102.3

8.8 6.3 2.3 1.3 0.6 1.2 3.5 1.3 0.9 9.9 2.7 3.4 0.4 0.7 0.1 0.3 0.9 0.8 4.1 1.8 3.4

Barium

Calcium

Iron

2.7. Estimated daily intake (EDI)

Magnesium

For those elements with no specific migration limit (SML) available, estimated daily intake (EDI) was used to evaluate their safety. The EDI can be calculated by the following Eq. (1) (Vera, Canellas, & Nerín, 2013):

EDI (mg /person /day ) = migration × 3kg × CF

Titanium

Zinc

(1)

where 3 kg represents food intake is 3 kg per person per day, CF is the fraction of daily diet expected to be in contact with a specific packaging material (0.05 for polyester).

recoveries of aluminum, barium, iron, titanium and zinc at low (0.2 mg/L), intermediate (0.6 mg/L) and high (1.0 mg/L) spiked concentration ranged from 97.7%˜115.6%, 100.2%˜114.7% and 99.8% ˜108.5%, respectively, while the recoveries of calcium and magnesium at low (2.0 mg/L), intermediate (6.0 mg/L) and high (10.0 mg/L) concentration were from 99.8%˜102.8%, 99.6%˜100.4% and 98.8% ˜99.1%, respectively, and all RSDs were less than 10%. Taken all of the above data together, the proposed methods were suitable for migration tests.

2.8. Compliance assessment For repeat use articles, migration test for compliance are often carried out three times, the result of the third exposure is used for the verification of compliance with the migration limit (European Commission, 2011). 3. Results and discussions

3.2. Initial concentration of metal elements in PLA dinner plate 3.1. Method validation In this study, two methods were compared for the determination of metal element content in the sample. Wet digestion is widely used for determination of metal elements content in different matrixes. Considering that the main contents of talc is hydrated magnesium silicate (Mg3[Si4O10](OH)2) which could react with hydrofluoric acid to form water-soluble magnesium salts (Zhang et al., 2013), hydrofluoric acid digestion was proposed to see the difference. Table 3 shows the initial concentration of each metal elements obtained by two digestion methods. Compared to wet digestion, hydrofluoric acid digestion resulted in much higher aluminum, barium, iron, magnesium, titanium and zinc concentration. This result illustrates wet digestion was

The LODs, LOQs, linear equation, correlation coefficient (r) and linear ranges of aluminum, barium, calcium, iron, magnesium, titanium, zinc are shown in Table 1. LODs for all metal elements ranged from 0.06˜3.99 μg/L in 5% HNO3, 0.23˜2.45 μg/L in 3% CH3COOH, respectively. And the correlation coefficient (r) for all metal elements were greater than 0.999. In the linear equation, y represents the signal intensity of metal elements, x represents the concentrations of metal elements (mg/L). The recoveries and RSD of aluminum, barium, calcium, iron, magnesium, titanium, zinc at three spiked levels are shown in Table 2. The Table 1 Linear equation, LOD and LOQ of studied metal elements. Elements name

Linear equation

Linear ranges (mg/L)

correlation coefficient (r)

LOD (μg/L)

LOQ (μg/L)

Aluminum

y = 24064.4x+365.36a y = 23704.8x+904.93b y = 1416134.4x+18805.86a y = 253834.6x+2484.86b y = 55974.9x+2813.26a y = 60742.4x+5591.45b y = 1762.3x+14.12a y = 10396.3x-79.26b y = 16424.4x+142.16a y = 17253.9x+238.17b y = 27714.4x+126.06a y = 2833.7x+24.88b y = 29339.5x+239.79a y = 16271.8x+238.17b

0.2–1.0 0.2–1.0 0.2–1.0 0.2–1.0 2.0–10.0 2.0–10.0 0.2–1.0 0.2–1.0 2.0–10.0 2.0–10.0 0.2–1.0 0.2–1.0 0.2–1.0 0.2–1.0

0.9990 0.9984 0.9997 0.9999 0.9998 0.9999 0.9998 0.9999 0.9999 0.9994 0.9999 0.9999 0.9992 0.9990

2.70 2.21 0.06 0.33 2.47 0.23 3.99 2.45 0.59 0.64 0.31 1.20 0.53 0.32

8.99 7.36 0.18 1.11 8.21 0.75 13.32 8.17 1.97 2.13 1.05 4.01 1.76 1.07

Barium Calcium Iron Magnesium Titanium Zinc

Note:

a

and

b

represent determination of the elements in 5% nitric acid (for initial concentration) and in 3% acetic acid (for migration), respectively. 3

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time and temperature increases, the migration of aluminum, barium, calcium, iron, magnesium and zinc increased because their solubility increased with temperature. In addition, James Lunt found that the hydrolytic degradation of PLA is primarily temperature- and humiditydependent. As a result, PLA polymers degrade rapidly under high humidity and high temperature (55˜70 °C); the time needed for PLA ester bond breaking was 132, 8.5 and 1.8 days under 30, 60, and 70 °C, respectively (Lunt, 1998). Mi-Yeong Jo et al. indicated that the molecular weight of PLA reduced from 164000 to 2300 after 10 days in 70 °C water, while that only reduced from 164000 to 121000 after 10 days in 50 °C water (Jo, Ryu, Ko, & Yoon, 2013). The migration also increased under the acidic environment and high temperature (Scarfato et al., 2015). So acidic environment could accelerate the cleavage of eater bond of PLA and thus increases the migration. Moreover, the glass transition temperature of PLA is about 60 °C (Farah et al., 2016). When the migration temperature is higher than this temperature, the migration increased significantly. On the contrary, when the migration temperature is lower than the glass transition temperature, the migration was much smaller (Fig. 1). Fig. 1 also shows, that the migration of barium, calcium and magnesium had no equilibrium trend even after long time exposure (10 days at 40 °C, 6 days at 60 °C and 6 days at 70 °C). Maria A. Busolo et al. (Busolo, Fernandez, Ocio, & Lagaron, 2010) also found the migration of silver from PLA increased in an exponential fashion after 6 days. They explained that the result could be due to plasticisation and/or partial acid hydrolysis of the material by 3% acetic acid, trigger the migration of the silver from the sample and accelerated hydrolysis of the ester linkages in the interior, these all facilitated the migration process.

Table 3 The initial concentration of the studied metal elements in PLA dinner plate by two digestion methods (n = 3). Elements

Wet digestion

Aluminum Barium Calcium Iron Magnesium Titanium Zinc

Hydrofluoric acid digestion

Initial concentration (mg/kg)

RSD(%)

Initial concentration (mg/kg)

RSD(%)

353.2 362.2 80618.2 208.2 4788.5 177.4 176.6

2.2 0.1 0.5 9.1 4.2 7.9 0.1

714.1 398.9 81409.1 565.1 26263.2 2318.8 195.3

2.7 0.4 0.6 0.1 0.3 0.9 1.7

insufficient for the determination of metal element contents from talccontaining PLA, and hydrofluoric acid digestion is suggested. As mentioned above, hydrofluoric acid can react with the main component of talc (hydrated magnesium silicate), hence those metal elements encased in talc can be better released.

3.3. Migration tests and safety assessment Fig. 1 displays the migration of metal elements to food simulant at 40, 60 and 70 °C. No migration of titanium was observed despite its initial concentration was quite high using hydrofluoric acid digestion. The phenomenon suggests that titanium element could be tightly enclosed in talc and it was not easy to migrate out. Fig. 1 shows that as the o

(A2)

40 oC Aluminum Iron

(A1) 0.2

40 C Caicium

200

Barium Zinc

o

(A3) 40 C Magnesium

5

0.1

Migration (mg/kg)

Migration (mg/kg)

Migration (mg/kg)

4

150

100

3

2

50

0.0

1

0 0

2

4

6

8

0

0

10

2

4

(B1)

800

o

60 C Aluminum Iron

Barium Zinc

0

18

0.3 0.2

500 400 300

0.1

100

0.0

0 3

4

5

6

10

12 10 8 6

2 0

0

1

2

3

4

5

6

0

1

2

Time (days) 2000

o

(C1) 70 C Aluminum Iron

1.6

8

4

Time (days) 1.8

6

14

200

2

4

60 oC Magnesium

(B3)

16

Migration (mg/kg)

0.4

1

2

Time (days)

600

0.5

0

(C2)

Barium Zinc

3

4

5

6

Time (days) 50

o

70 C Calcium

o

(C3) 70 C Magnesium

40

1.4 1.2 1.0 0.8 0.6

Migration (mg/kg)

1500

Migration (mg/kg)

Migration (mg/kg)

10

60 oC Calcium

(B2)

700

Migration (mg/kg)

Migration (mg/kg)

0.6

8

Time (days)

Time (days) 0.7

6

1000

500

0.4

30

20

10

0.2 0

0

0.0 0

1

2

3

4

Time (days)

5

6

0

1

2

3

4

5

6

0

1

2

Time (days)

Fig. 1. Migration of metal elements from polylactic acid plate into food simulant (n = 3). 4

3

Time (days)

4

5

6

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70 °C for 2 h was shown in Figs. 2 and 3, respectively. After the first cycle of migration test at 40 °C for 10 days, the migration of calcium and magnesium decreased dramatically (Fig. 2), and the migration of second and third cycle were almost the same, in addition, under the second and third cycle, the migration still doesn’t reach equilibrium and the slope of the second cycle and third cycle is almost the same. It suggested that the migration of calcium and magnesium in first cycle might mainly occurred on the surface of the plate, while in the second cycle and third cycle the migration mainly occurred in the internal of materials with the acid erosion of the PLA plate. As shown in Fig. 3, the migration of second cycle is higher than the third cycle, this result due to the exposure time is shorter, the structure of the material has not been damaged (von Goetz et al., 2013; Echegoyen & Nerín, 2013), so the migration is mainly occurred on the surface of PLA plate and decreased with the migrate times. James Lunt also indicated that PLA occurred the cleavage of the ester linkages by absorbed water after 1.8 days under 70 °C (Lunt, 1998).

Table 4 The Maximum migration amount of studied metal elements from PLA dinner plate into acidic food simulant under 40 °C, 60 °C,70 °C (n = 3) and their specific migration limit (SML).

Aluminum Barium Calcium Iron Magnesium Zinc

40 °C, 10 days

60 °C, 6 days

70 °C, 6 days

Mmax (mg/kg)

RSD (%)

Mmax (mg/kg)

RSD (%)

Mmax (mg/kg)

RSD (%)

Specific migration limits (mg/kg)

0.14 0.13 192.42 0.20 4.69 0.03

3.4 1.8 0.7 1.6 0.1 7.3

0.16 0.61 730.16 0.33 15.67 0.09

5.5 2.3 4.5 5.6 2.2 7.5

0.16 1.52 1752.81 0.41 43.25 0.27

5.4 8.1 5.4 4.4 4.6 4.3

1 1 – 48 – 5

Note: “Mmax” represent the maximum migration of each metal elements at 40 °C for 10 days, 60 °C for 6 days, 70 °C for 6 days. “-” represent that there is no SML for this element in European Commission regulation for plastic materials and articles intended to be in contact with food.

3.4. Compliance assessment

Furthermore, different metal elements were found to have distinct migration behaviors. Compared with other elements, calcium had much higher migration. This phenomenon can be explained by its high initial concentration as shown in Table 3 and the high solubility of calcium carbonate in acidic solutions. By the way, in Fig. 1(A1) and (C1), there is a data point declined deviant possibly caused by the experimental error. Table 4 shows the maximum migration of each metal element at 40 °C for 10 days, 60 °C for 6 days, 70 °C for 6 days and specific migration limit (SML) of the each elements (European Commission, 2016). The migration of aluminum, barium, iron, zinc did not exceed their SML under almost all conditions. However, under the condition of 6 days of 70 °C, the migration of barium was 1.52 mg/kg, which exceeded the 1 mg/kg. However, serving plates are not used for such a long time at such high temperature. There is no SML for calcium and magnesium, EDI is calculated to evaluate their safety. According to Eq. (1), the EDI of calcium were 28.86, 105.54, 262.92 (mg/person/day), and that of magnesium were 0.70, 2.35, 6.49 (mg/person/day) under 40 °C for 10 days, 60 °C for 6 days and 70 °C for 6 days, respectively. These values are lower than tolerable upper intake level (UL) in Chinese dietary reference intakes-Part 2: Macroelement (National Health Commission of China, 2018). For infants aged 0˜0.5, the UL about calcium and magnesium is 1000 mg/day and 20 mg/day, respectively. This means the studied PLA dinner plate is safe for consumers in terms of studied metal elements. As the migration of calcium and magnesium was much higher than that of other metal elements, further attention was paid to their migration. Regarding multiple-use, condition at 40 °C for 10 days and

The three sequential overall migration of PLA plate into 3% acetic acid under 70 °C for 2 h was 34.4 ± 1.3, 14.2 ± 0.6, 9.6 ± 0.7 mg/ dm2, respectively. The third overall migration did not exceed the overall migration limit (10 mg/dm2).However, this value is around the limit. The manufacturer should pay more attention on it and reduce the overall migration of the PLA plate. The first migration of metal elements was lower than its SML or UL and the second and third migration are all less than the first migration (Figs. 2 and 3), so, the third migration of metal elements also compliant with their SML. In summary, the overall migration of the studied PLA dinner plate and the specific migration of the metal elements are all compliant with the migration limit. 4. Conclusion Metal elements aluminum, barium, calcium, iron, magnesium, titanium and zinc were found in PLA dinner plate. The presence of aluminum, barium, iron, magnesium, titanium and zinc was thought to be the impurities of talc filler in the PLA plate. The migration of aluminum, barium, iron and zinc did not beyond the specific migration limit under the applied conditions, and the EDI of calcium and magnesium did not beyond the tolerable upper intake level. The overall migration of PLA plate did not exceed OML, but around OML. The migration occurred on the surface of PLA plate when the exposure time is short, while the migration not only occurred on the surface of materials but also the inside as the exposure time is long and the acid erosion is increased. In summary, considering overall migration and the migration of metal

Fig. 2. The migration of calcium (A) and magnesium (B) from polylactic acid plate into acidic food simulant under the multiple-use condition (n = 3). 5

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Fig. 3. The migration of calcium (A) and magnesium (B) from polylactic acid plate into acidic food simulant under the multiple-use condition (n = 3).

elements, the studied PLA plate can be used as food contact materials. In future, more attention need to be paid to other additives which could present in PLA plate and the degradation products of PLA.

plasma atomice emission spectrometric of acid-soluble metal elements chromium,manganese,zinc and copper in talcum powde. Metallurgical Analysis, 30(09), 7–10 Chinese with English abstract. Huang, A., Yu, P., Jing, X., Mi, H., Geng, L., Chen, B., ... Peng, X. (2016). The effect of talc on the mechanical, crystallization and foaming properties of poly(lactic acid). Journal of Macromolecular Science Part B- Physics, 55(9), 908–924. Jo, M. Y., Ryu, Y. J., Ko, J. H., & Yoon, J. S. (2013). Hydrolysis and thermal degradation of poly(L-lactide) in the presence of talc and modified talc. Journal of Applied Polymer Science, 129(3), 1019–1025. Krewski, D., Yokel, R. A., Nieboer, E., Borchelt, D., Cohen, J., Harry, J., ... Rondeau, V. (2007). Human health risk assessment for aluminium, aluminium oxide, and aluminium hydroxide. Journal of Toxicology and Environmental Health Part B, 10(Sup1), 1–269. Lunt, J. (1998). Large-scale production, properties and commercial applications of polylactic acid polymers. Polymer Degradation and Stability, 59(1), 145–152. Madhavan Nampoothiri, K., Nair, N. R., & John, R. P. (2010). An overview of the recent developments in polylactide (PLA) research. Bioresource Technology, 101(22), 8493–8501. Nanthananon, P., Seadan, M., Pivsa-Art, S., Hamada, H., & Suttiruengwong, S. (2018). Facile preparation and characterization of short-fiber and talc reinforced poly(lactic acid) hybrid composite with in situ reactive compatibilizers. Materials (Basel, Switzerland), 11(7), 1183. Narayan, R. (2006). Biobased & biodegradable polymer materials: Rationale, dationale, drivers,and, technology exemplars. ACS Symposium, 939, 282–283. National Health Commission of China (2018). WS/T 578.2-2018. Chinese dietary reference intakes-Part 2: Macroelement. Nerin, C., Alfaro, P., Aznar, M., & Domeno, C. (2013). The challenge of identifying nonintentionally added substances from food packaging materials: A review. Analytica Chimica Acta, 775, 14–24. Phetwarotai, W., & Aht-Ong, D. (2016). Isothermal crystallization behaviors and kinetics of nucleated polylactide/poly(butylene adipate-co-terephthalate) blend films with talc. Journal of Thermal Analysis and Calorimetry, 126(3), 1797–1808. Refaa, Z., Boutaous, M. H., Xin, S., & Siginer, D. A. (2017). Thermophysical analysis and modeling of the crystallization and melting behavior of PLA with talc. Journal of Thermal Analysis and Calorimetry, 128(2), 687–698. Saleem, J., Adil Riaz, M., & Gordon, M. (2018). Oil sorbents from plastic wastes and polymers: A review. Journal of Hazardous Materials, 341, 424–437. https://doi.org/ 10.1016/j.jhazmat.2017.07.072. Scarfato, P., Di Maio, L., & Incarnato, L. (2015). Recent advances and migration issues in biodegradable polymers from renewable sources for food packaging. Journal of Applied Polymer Science, 132(48), 42597. Shi, N., & Dou, Q. (2015). Non-isothermal cold crystallization kinetics of poly(lactic acid)/poly(butylene adipate-co-terephthalate)/treated calcium carbonate composites. Journal of Thermal Analysis and Calorimetry, 119(1), 635–642. Smith, A. H., Lingas, E. O., & Rahman, M. (2000). Contamination of drinking-water by arsenic in Bangladesh: A public health emergency. Bulletin of the World Health Organization, 78(9), 1093–1103. Souza, V. G. L., & Fernando, A. L. (2016). Nanoparticles in food packaging: Biodegradability and potential migration to food-a review. Food Packaging and Shelf Life, 8, 63–70. Su, Q., Lin, Q., Chen, C., Wu, Y., Wu, L., Chen, X., ... Wang, Z. (2015). Effect of antioxidants and light stabilisers on silver migration from nanosilver-polyethylene composite packaging films into food simulants. Food Additives & Contaminants Part A, Chemistry, Analysis, Control, Exposure & Risk Assessment, 32(9), 1561–1566. Vera, P., Canellas, E., & Nerín, C. (2013). Identification of non-volatile compounds and their migration from hot melt adhesives used in food packaging materials

Acknowledgements This work was supported by the National Key Research and Development Program of China [2018YFC1603204] and the Research Funding Program of General Administration of Quality Supervision, Inspection and Quarantine, China [2017IK133], and Zhuhai PremierDiscipline Enhancement Scheme, China. References Aframehr, W. M., Molki, B., Heidarian, P., Behzad, T., Sadeghi, M., & Bagheri, R. (2017). Effect of calcium carbonate nanoparticles on barrier properties and biodegradability of polylactic acid. Fibers and Polymers, 18(11), 2041–2048. Ashter, S. A. (2016). 6 additives and modifiers for biopolymers. Introduction to bioplastics engineering. Oxford: William Andrew Publishing153–178. Busolo, M. A., Fernandez, P., Ocio, M. J., & Lagaron, J. M. (2010). Novel silver-based nanoclay as an antimicrobial in polylactic acid food packaging coatings. Food Additives & Contaminants Part A, 27(11), 1617–1626. Echegoyen, Y., & Nerín, C. (2013). Nanoparticle release from nano-silver antimicrobial food containers. Food and Chemical Toxicology, 62, 16–22. European Commission (2011). Commission Regulation (EU) No 10/2011 on plastic materials and articles intended to come into contact with food. Official Journal of the European Communities. European Commission (2016). Commission Regulation (EU) 2016/1416 of 14 January 2011 on plastic materials and articles intended to come into contact with food. Official Journal of the European Communities. Farah, S., Anderson, D. G., & Langer, R. (2016). Physical and mechanical properties of PLA, and their functions in widespread applications–A comprehensive review. Advanced Drug Delivery Reviews, 107, 367–392. Fortunati, E., Peltzer, M., Armentano, I., Torre, L., Jiménez, A., & Kenny, J. M. (2012). Effects of modified cellulose nanocrystals on the barrier and migration properties of PLA nano-biocomposites. Carbohydrate Polymers, 90(2), 948–956. Fukuda, N., Tsuji, H., & Ohnishi, Y. (2002). Physical properties and enzymatic hydrolysis of poly(l-lactide)-CaCO3 composites. Polymer Degradation and Stability, 78(1), 119–127. Hao, Y., Sun, Y., Cheng, C., Fang, Q., Jiang, K., & Shi, L. (2013). Simultaneous determination of iron, manganese, lead, cadmium, chromium etc 10 kinds of metal elements in calcium carbonate by ICP-AES. Chemical Analysis and Meterage, 22(1), 34–36 Chinese with English abstract. Henricks, J., Boyum, M., & Zheng, W. (2015). Crystallization kinetics and structure evolution of a polylactic acid during melt and cold crystallization. Journal of Thermal Analysis and Calorimetry, 120(3), 1765–1774. Hu, X., Pang, Y., Zhao, J., Sheng, X., Ren, Y., Zhang, H., ... Wang, Y. (2011). Determination of multiple trace elements in taclum powder by inductively coupled plasma mass spectrometry after microwave. Metallurgical Analysis, (11), 29–33 Chinese with English abstract. Hu, X., Zeng, Z., Wang, C., Qiu, X., Mu, M., Fu, Y., ... Liu, X. (2011). Inductively coupled

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Food Packaging and Shelf Life 22 (2019) 100381

J.-F. He, et al.

Analysis, Control, Exposure & Risk Assessment, 30(3), 612–620. Zhang, P., Xiao, X., Wei, F., Shi, S., & Qian, Z. (2013). ICP-AES analytical studies on inorganic elements of Mineral Chinese Medicine Talci Pulvis from different hibitats. Chinese Journal of Pharmaceutical Analysis, (3), 428–434 Chinese with English abstract.

characterized by ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry. Analytical and Bioanalytical Chemistry, 405(14), 4747–4754. von Goetz, N., Fabricius, L., Glaus, R., Weitbrecht, V., Günther, D., & Hungerbühler, K. (2013). Migration of silver from commercial plastic food containers and implications for consumer exposure assessment. Food Additives & Contaminants Part A, Chemistry,

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