The plastic containers that were used for the migration analysis were divided into two groups: five new containers (Group I) and five containers that had already been used for a prolonged period of time (Group II) of approximately one year. The presence of BBP was not observed in any of the containers that were evaluated. The results that were obtained for DBP are presented below.
3.3.2. GROUP II: Containers that Were Used for Prolonged Periods of Time
The concentrations of DBP that migrated into the food simulant under different exposure conditions are shown in
Figure 4a‒e.
The results observed for the DBP concentrations in the Group I containers ranged from <LOQ to 2.0 µg/L, while the DBP concentrations in Group II containers ranged from <LOQ to 7.5 µg/L. The total of all measurements of DBP concentrations that were obtained in the two groups were compared by ANOVA. The results showed that there was a difference in the average concentration of the two groups, with the average DBP concentration found in Group II containers being larger than that found in Group I containers. Therefore, it can be concluded that the release of phthalates from plastic containers increases with continued use of the containers.
All containers were exposed to the same heating conditions; however, it is known that microwave irradiation often leads to non-homogeneous heating, which also depends on the shape and size of the containers. To evaluate the heating the simulant temperature was measured immediately after heating. A thermometer was placed into the sample, which was shaken to allow for measurement of the mean temperature. The temperatures obtained for the Group I Group II containers are presented in
Figure 5 and
Figure 6, respectively.
Figure 3.
Concentrations of DBP that migrated into Group I food simulant (a) container A, (b) Container B, (c) Container C, (d) Container D, and (e) Container E.
Figure 3.
Concentrations of DBP that migrated into Group I food simulant (a) container A, (b) Container B, (c) Container C, (d) Container D, and (e) Container E.
Figure 4.
Migrated DBP concentrations in the Group II food simulant containers (a) container F, (b) Container G, (c) Container H, (d) Container I, and (e) Container J.
Figure 4.
Migrated DBP concentrations in the Group II food simulant containers (a) container F, (b) Container G, (c) Container H, (d) Container I, and (e) Container J.
Figure 5.
Temperatures of simulants measured for times and powers studied for Group I containers (a) Container A, (b) Container B, (c) Container C, (d) Container D, and (e) Container E.
Figure 5.
Temperatures of simulants measured for times and powers studied for Group I containers (a) Container A, (b) Container B, (c) Container C, (d) Container D, and (e) Container E.
Figure 6.
Temperatures of simulants measured for times and powers studied for Group II containers (a) container F, (b) Container G, (c) Container H, (d) Container I, and (e) Container J.
Figure 6.
Temperatures of simulants measured for times and powers studied for Group II containers (a) container F, (b) Container G, (c) Container H, (d) Container I, and (e) Container J.
An examination of
Figure 3 and
Figure 4 shows that, in new containers the increase in heating time influences the increase in temperature; however, there is not a correlation between these factors and the migration of phthalates. Therefore, the DBP concentrations in the Group I containers were independent of the heating duration or the power conditions that were used for the containers that were evaluated. The variation in the concentration of DBP in the simulant was random. The highest concentration of DBP (2.0 µg/kg) was observed in container D. However, this values is less than the specific migration limit (SML) for DBP, which is 0.3 mg/kg.
In Group II, different amounts of DBP were observed in the samples. Through the comparison between the migration of phthalate (
Figure 4) and the temperature obtained in each migration assay (
Figure 6), it was observed that the migration of phthalate in the containers that had already been used for a prolonged period of time depended on the temperature achieved during heating and the exposure time of the container to this temperature. The temperature reached depended on the time of exposure to the microwaves, volume and shape of the container and power used. In general, it was observed that, using 750 W and 350 W powers, the temperature increased abruptly with increasing of time. When heating at the 210 W power level, the temperature began high and increased slightly with heating time.
Container J had the smallest volume, 300 mL, and consequently a large temperature variation was observed in the interval from 1 to 3 min at the 700 W power level. Heating at this power for 3 min resulted in a final temperature of 90 °C. This temperature remained constant for the longest time; thus the simulant remained in contact with the container at a high temperature for a longer time which resulted in an increased migration of phthalates to the simulant. At the 350 W power level the temperature variation occurred more gradually and there was an increase in the migration of DBP with the increase in temperature. However, the variation in the concentration of DBP in the sample was lower. At 210 W power, a small variation of temperature was observed for different exposure times, and thus there was not a linear relationship between exposure time and phthalates migrations.
Containers G and I had large volumes of 1,000 mL and 1,200 mL, respectively. Lower temperatures were obtained when compared to other containers heated at the same power. Consequently, a small variation in the concentration of DBP was observed. Containers F and H have the same volume, 600 mL, but different dimensions. In general, it was observed that an increase in temperature caused an increase in the migration of phthalates into the simulant.
The obtained results suggest that the increase in temperature is the main cause of phthalate migration. Theoretically, containers used in microwaves are inert; however, studies have shown that the migration of various chemical substances may occur during microwave heating. A study by Nerin
et al. demonstrated that the release of compounds from plastic containers is temperature-dependent. According Nerin, the temperature increase leads to an increase in the decomposition of additives and breakdown of polymer chains which causes the release of chemicals from the hot plastic surface [
31]. Other studies indicate that phthalates may be released during microwave heating. Phthalates are not commonly used as plasticizers in PP. However a study by Jen and Liu determined an average concentration DBP of 32 µg/L in PP soup bowls when they were heated for 10 minutes in a microwave oven at a power of 500 W [
28]. A study by Gonzales-Castro
et al. determined a DBP concentration of 0.001 µg/L in aqueous solutions that were heated in the microwave oven [
20]. In these two studies, the analysis conditions, such as the heating duration and temperature, were not varied. The results of other studies in which where phthalates were monitored in different types of food are shown in
Table 4.
When evaluating the concentration of phthalates, it is essential to consider the characteristics of the food. Phthalates are lipophilic and are found in higher concentrations in fatty foods, such as olive and other oils [
15,
32]. In this work, DBP concentrations that were similar to the concentrations reported in the analysis of hydrophilic food samples were obtained [
17,
20].
The plastic containers that are used in microwave ovens are usually made of polypropylene, where the use of plasticizers is not essential and its addition should not be intentional. Therefore, phthalate migration tests are often not required for PP packaging. However, Shen reported the presence of phthalates at concentrations of 1.44 mg/kg for DBP, 0.10 mg/kg for BBP, and 8.72 mg/kg for DEHP in plastic containers that were being used in microwave ovens [
33]. These results demonstrate that PP containers can contain plasticizers. A possible source of DBP contamination is the use of the TiCl
4/dibutylphthalate/Mg(OEt)
2 catalyst in the manufacturing of polypropylene. During the polymer manufacturing process, the catalyst may undergo degradation and release this phthalate into the polymer material [
34]. Another possible source of contamination could arise from the contact Group II containers with food contaminated with phthalates. Frequent contact with contaminated food could cause contamination of containers over prolonged use. Several studies have shown that many foods are contaminated with phthalates (
Table 4). This hypothesis has been raised, because higher concentrations of phthalates have been found in containers with long-term use when compared to new containers. Although the concentrations of DBP in Group II containers were larger than Group I containers, it was observed that the concentration of DBP was much smaller than 0.3 mg/kg in all containers, which is the legal specific migration limit. The legislation control for regulating phthalates in various routes of exposure is not established for all compounds in this class because more studies are needed for many phthalates. In drinking water, the US EPA stipulates a maximum contamination level (MCL) of 6.0 µg/L for DEHP [
35]. However, the MCL has not been estimated for other phthalates. In this work, the maximum concentration of DBP found in the water samples that were heated in a microwave oven was 7.5 µg/L. If the value set by the US EPA for DEHP was extended to the entire class of phthalates, the value found in this study would exceed the MCL. Legislation for food is less strict for the migration of phthalates used in plastic packaging. The Brazilian Institution ANVISA, which has reference guidelines from the Food and Drug Administration and documents from the European Union, established a specific migration limit of 0.3 mg of DBP per kilogram of simulant that is in contact with food packaging [
36]. The SML of BBP is 30.0 mg/kg. Hence, following the Brazilian legislation from ANVISA, the concentrations that were found in this work would be within the allowed amount. With regards to health effects, many types of foods can be contaminated by phthalates during the manufacturing process, resulting in even higher concentrations of phthalates in foods. Thus, there is a great need for further studies to evaluate food contamination by phthalates.
Table 4.
Phthalate concentrations that have been reported in the literature.
Table 4.
Phthalate concentrations that have been reported in the literature.
Compounds | Concentration (µg/kg) | Samples | Method of Extraction | Instrumental | LOD | LOQ | Reference |
---|
DBP | 7.30 to 50.3 | Commercial whole milk | SPE (C18) | GC/MS | 0.09 | | [37] |
BBP | 1.11 to 2.93 | 0.12 | — |
DEHP | 15.1 to 27.2 | 0.06 | |
DBP | <LOD to 490 | Olive oil | Gel permeation chromatography | GC-MS/MS | | | [15] |
BBP | <LOD to 1,750 | | |
DEHP | <LOD to 4,700 | — | — |
DEHP | 22.8 to 270.3 | Cereals and legumes, Meat based, fish based, dairy, vegetables, condiments, fresh fruit, bread | LLE | GC-FID | — | — | [38] |
DBP | 10.2 to 142.8 |
DBP | <LOD to 244 (µg/L) | Wines | SPE | GC/MS | 18 (µg/L) | 29 (µg/L) | [16] |
BBP | <LOD to 269 (µg/L) | 18 (µg/L) | 29 (µg/L) |
DEHP | <LOD to 276 (µg/L) | 15 (µg/L) | 24 (µg/L) |
DBP | 4.07 to 9.79 | Cow milk | HS-SPME | GC/MS | 0.02 a 072 | | [17] |
BBP | <LOD | 0.23 a 4.7 | — |
DEHP | 8.40 to 282.90 | 0.31 a 3.3 | |
DBP | 0.001 to 0.003 | Water (food simulant) | LLE | GC/MS, HPLC/UV-VIS and HPLC fluorescence | 2.0 ×10−3 | 5.0 ×10−3 | [20] |
DBP | 32 and 24 (µg/L) | Water released from disposable PP soup bowl and PVDC wrap film | Hollow fiber microdialysis enrichment system | HPLC/UV | 0.4 (µg/L) | — | [28] |
DEHP | 77 to 1643 | Commercial vegetable Oils | Direct injection of thediluted oil | GC/MS | 10 | 40 | [32] |
DBP | 22 to 360 | 10 | 40 |
DBP | <LOD to 175 | Olive oil | SPME | GC/MS/MS | 30 | — | [29] |
BBP | 87 to 211 | 30 |
DEHP | 198 a 840 | 30 |
DBP | <LOD to 9,840 | Plastic containers | Sonication-assisted extraction | GC/MS | 10 | — | [33] |
BBP | <LOD to 9,980 |
DEHP | <LOD to 1.76 × 106 |
DBP | <LOD | Bottled mineral water | AALLME | GC-FID | 0.37 (µg/L) | — | [39] |
DEHP | 0.26 to 0.32 (µg/L) | 0.75 (µg/L) |
DBP | 0.32 to 0.51 (µg/L) | Bottled mineral water | LPME | GC/MS | 0.005 (µg/L) | — | [40] |
BBP | <LOD |
DEHP | 0.57 to 0.65 (µg/L) | 0.01 (µg/L) |
0.02 (µg/L) |
DBP | <LOD | Bottled mineral water | DLLME | GC/MS | 0.005 (µg/L) | — | [41] |
BBP | <LOD | 0.002 (µg/L) |
DEHP | <LOD | 0.005 (µg/L) |
DBP | 0.2 to 7.5 | Water (food simulant) | SPME | GC/MS | 0.08 (µg/L) | 0.2 (µg/L) | This study |
BBP | <LOD | 0.31 (µg/L) | 0.5 (µg/L) |