Scholarly article on topic 'Total lead content and its bioaccessibility in base materials of low-cost plastic toys bought on the Beijing market'

Total lead content and its bioaccessibility in base materials of low-cost plastic toys bought on the Beijing market Academic research paper on "Materials engineering"

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Academic research paper on topic "Total lead content and its bioaccessibility in base materials of low-cost plastic toys bought on the Beijing market"

J Mater Cycles Waste Manag DOI 10.1007/s10163-013-0223-9

ORIGINAL ARTICLE

Total lead content and its bioaccessibility in base materials of low-cost plastic toys bought on the Beijing market

Shaoguo Kang • Jianxin Zhu

Received: 26 June 2013/Accepted: 2 December 2013 © Springer Japan 2013

Abstract The neurological hazards of lead are well-known. Few studies have focused on lead content in plastic toys, especially in China. Therefore, this study aimed to determine total lead content in low-cost plastic toys bought in Beijing, based on the bioaccessibility (BA) of lead through an in vitro leaching method. A total of 27 of the 72 items (37.5 %) examined exceeded the American toy safety limit (100 mg/kg), but HCl extraction results showed that all the samples met the Chinese standard (\90 mg/kg). The BA of lead ranged from 0.80 to 8.86 %, with averages of 1.53 ± 0.74, 3.65 ± 1.28, 4.09 ± 1.83 and 2.62 ± 0.82 % for diluted HCl and three other leaching solutions, respectively. Our results indicated that the bioavailability risk of lead in plastic toys might be underestimated, as the HCl extraction was regulated under the standard procedures of toy safety testing. Total Pb content measurement combined with RIVM methods would be helpful in efforts to reduce children's exposure to toxic heavy metals.

Keywords Bioaccessibility • In vitro method • Lead • Plastic toys

Introduction

Recently, the exposure of children to heavy metals has been recognized as a major threat to their healthy development. Other than background exposure via air, water,

S. Kang • J. Zhu (&)

Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 18 Shuangqing Road, Haidian District, 100085 Beijing, China e-mail: zhujx@rcees.ac.cn

and soil [1], the frequent hand-to-mouth activity of children and dermal contact with contaminated toys or other children's products may increase their health risks [2]. Many studies show that children's toys and other children's products contain different kinds of metals. Maas et al. [3] detected high levels of Pb in metallic jewelry acquired from various nationwide retail stores located in California. Another study by Weidenhamer demonstrated that inexpensive jewelry purchased in the American market contained high levels of Cd [4]. Kawamura et al. [5] investigated the contents of eight harmful elements in baby toys sold in Japan, and confirmed findings of antimony, arsenic, barium, cadmium, chromium, lead, mercury, and selenium in their samples.

Children are highly sensitive to exposure to toxic substances due to many factors, including a higher metabolic rate and greater surface area-to-weight ratio than adults, immaturity of organ systems, and rapid growth and development of organs and tissues such as bone and brain [6]. Among those toxic heavy metals, lead (Pb) is well-known for its harm to almost every organ, particularly the nervous system. It was estimated that an adult would absorb 5-10 % of ingested lead [7], whereas a child can absorb up to 50 % of lead that enters the body [8]. In the past few years, hundreds of recalled incidents were reported because of chemical safety hazards, roughly 17.6 million toy units were recalled because of excessive lead levels [9], and about 6,970 Captain Cutlass Toy Pirate Pistols were recalled because of a violation of the federal lead paint standard [10] in the US. According to Guney and Zagury, there were three major factors that resulted in the metal contamination of children's products: the use of metals as stabilizers in plastics during manufacturing, the application of paint containing metal pigments to toys and jewelry, and the use of contaminated recycled plastics or metals in toy production [2].

Published online: 25 December 2013

a Springer

China is the largest toy manufacturing and exporting country—more than 70 % toys in the world are made in China. According to a report on toy industry development conducted by the China Toy & Juvenile Products Association, the accumulative total of Chinese toys exported was worth up to U$248.00 billion in 2011. Among these toys, plastic toys accounted for a large proportion. Recently, foreign toy safety standards are becoming increasingly stringent for the heavy metal contents. The US Consumer Product Safety Improvement Act (CPSIA) set 90 mg/kg as the maximum allowable lead amount in paint or any similar surface coatings as of August 2009, and 100 mg/kg for accessible parts in all children's products including toys manufactured after August 14, 2011 [11]. The heavy metal migration limits in EU Directive 2009/48/EC were much lower than that in Directive 88/378/EEC, i.e., the lead migration limit was 90 mg/kg in the old toy safety directive, but in the new one it was 13.5 and 3.4 mg/kg for category I and II, respectively. As the toy standards abroad grow stricter and stricter, some toys that cannot meet the requirements of foreign standards and thus cannot be exported abroad might enter into the domestic market. Compared with other countries, Chinese laws and regulations are not strict regarding the heavy metal contents in toys. The migration limits regulated in GB 6675-2003 [12] were the same as ISO 8124-3:1997(E) and EN 71-3:1995 [13]. Some of the toys with high lead content that were unqualified according to the international standards might therefore flow into the domestic, low-end market in China.

The production of toys using recycled waste plastics are another important source of heavy metals. Recycled plastics are much cheaper than virgin plastics. For example, for new PVC, the typical price is about 11,000 RMB/t, while the price is roughly 4,500 RMB/t for recycled PVC; for recycled ABS (acrylonitrile-butadiene- styrene), the price is 9,800 RMB/t, while the original costs 21,000 RMB/t. Therefore, it is possible that these contaminated recycled plastics were used to manufacture children's toys. According to the Chinese plastics recycling industry, in 2008 [14], China imported about 7,075 kt of waste plastics and the amount of domestic recycled plastics was up to 9,000 kt that year as well. Due to lack of supervision and outdated technology, these waste plastics might have been polluted by metals during the recycling process. What's worse, some waste plastics were recycled illegitimately, such as medical wastes, which were reported by China Central Television (CCTV). The possible hazards of plastic toys produced by recycled plastics were thus unclear.

In summary, according to the published papers [2, 3, 15-19], low-cost plastic toys were more likely to contain heavy metals (including Pb) compared to expensive plastic toys, considering that because recycled plastics are cheaper than the original plastics, low-cost plastic toys are probably

manufactured with recycled plastics. However, past studies have mainly paid attention to metal toys and coating or paint on the surface of toys. Furthermore, the target groups for low-cost plastic toys in Beijing were the children of the city's suburban areas, children at rural areas around Beijing, and peasant laborers' children in Beijing. When considering the high potential health risk of low-cost plastic toys in the Beijing market, there are few studies focused on their lead content and BA. Therefore, this paper focused on lead in the base materials of low-cost plastic toys in Beijing, through an in vitro investigation of the BA of lead in toys. We aimed at determining whether low-cost plastic toys purchased in Beijing were contaminated with potentially dangerous amounts of lead and as well as their migration characteristics in simulated body liquids.

Materials and methods

Plastic toy samples

A random sampling strategy was adopted following several earlier studies [20, 21]. A total of 59 low-cost, plastic toy samples in this study were randomly purchased from two large, wholesale toy markets that distribute their low-cost plastic toys to many small retailers in Beijing. Eight common colors (pink, red, yellow, green, white, orange, purple, and blue) were covered in the samples. Plastic materials including PVC, PE, and ABS were included. Both soft and hard plastic toys were considered. The price of these selected samples was below US$5 per toy. Then, 72 items were extracted from the 59 plastic toys as final samples, based on their colors and materials. All of the items were clearly designed for children and the general description of the 72 plastic toy items is presented in Table 1. Figure 1 shows some examples of the tested plastic toys.

We focused not on the coating materials, but instead the base material of the plastic toys in this study. All of the 72 toys were analyzed for their total Pb contents, and 20 of the samples with higher lead content (>100 mg/kg) were subjected to three leaching test methods to simulate their lead leaching potential and bioaccessbility in the mouth, gastric, and intestinal juices, respectively. Once brought into the laboratory, all items were placed in plastic bags to prevent cross-contamination by highly leaded items. The experimental and pretreatment methods were based on the test portion procedure set in the National Safety Technical Code for Toys (GB 6675-2003) [12]. In brief, if the sample is not of a color, a test portion is obtained from each color present in a mass >100 mg and crushed into pieces with handheld pliers to ensure that each piece in the uncompressed condition has no dimension >6 mm if the sample

Table 1 Summary of characteristics of the 72 tested samples and concentrations of Pb

Sample ID Name Color Place of origina Materials'3 Target groupsc Total lead (mg/kg)

1 Peashooter Pink Non-marked ABS Non-marked 366

2 Toy trumpet Red Non-marked Hard Non-marked 104

3 Plastic building block Blue Non-marked Soft Non-marked 317

4 Toy duck Yellow Non-marked PVC Non-marked 112

5 Spring bubbles Green Non-marked Hard Non-marked 306

6 Baby rattles White Guangdong, province ABS >3 months 84

7 Finger puzzle Green Guangdong, province ABS >6 months 16

8 Finger puzzle Orange Guangdong, province ABS >6 months LOD

9 Shrilling pig Purple Guangdong, province PVC >3 years 42

10 Toy fish Red Guangdong, province PVC >3 years 72

11 Toy fish Green Guangdong, province PVC >3 years 47

12 Plastic doll White Guangdong, province PVC >3 years 15

13 Plastic doll Blue Guangdong, province PVC >3 years 31

14 Finger puppet Yellow Zhejiang, province PVC >96 months LOD

15 Finger puppet Orange Zhejiang, province PVC >96 months LOD

16 Finger puppet Purple Zhejiang, province PVC >96 months 21

17 Finger puppet Green Zhejiang, province PVC >96 months 16

18 Smiley face finger puppet Blue Zhejiang, province PVC All age 14

19 Bath toys Red Zhejiang, province PVC All age 15

20 Bath toys Yellow Zhejiang, province PVC All age 15

21 Bath toys Green Zhejiang, province PVC All age LOD

22 Bath toys Blue Zhejiang, province PVC All age LOD

23 Bath toys White Zhejiang, province PVC All age LOD

24 Plastic coin bag toys Green Zhejiang, province Soft Non-marked 219

25 Soft spike ball Orange Zhejiang, province PVC Non-marked 21

26 Kids glass toys Purple Zhejiang, province ABS Non-marked 43

27 Peashooter Green Non-marked Hard Non-marked 105

28 Peashooter Blue Non-marked Hard Non-marked 48

29 Peashooter Red Non-marked Hard Non-marked 22

30 Plastic building block Blue Non-marked Soft Non-marked 311

31 Plastic building block Yellow Non-marked Soft Non-marked 177

32 Toy duck Yellow Non-marked Soft Non-marked 79

33 Toy duck Green Non-marked Soft Non-marked 75

34 Toy duck Blue Non-marked Soft Non-marked 90

35 Spring bubbles Green Non-marked Hard Non-marked 191

36 Spring bubbles Red Non-marked Hard Non-marked 101

37 Baby rattles Blue Non-marked Hard Non-marked 161

38 Baby rattles Purple Non-marked Hard Non-marked 244

39 Baby rattles Yellow Non-marked Hard Non-marked 147

40 Baby rattles Red Non-marked Hard Non-marked 89

41 Whistle Pink Non-marked Hard Non-marked 257

42 Whistle Green Non-marked Hard Non-marked 122

43 Whistle Blue Non-marked Hard Non-marked 179

44 Spinning top Yellow Non-marked Hard Non-marked 105

45 Spinning top Red Non-marked Hard Non-marked LOD

47 Angry birds Purple Non-marked Hard Non-marked 98

46 Angry birds Pink Non-marked Hard Non-marked 162

48 Angry birds Orange Non-marked Hard Non-marked 132

Table 1 continued

Sample ID Name Color Place of origina Materialsb Target groupsc Total lead (mg/kg)

49 Angry birds Yellow Non-marked Hard Non-marked 256

50 Toy ball Yellow Non-marked PVC Non-marked 55

51 Toy ball Green Non-marked PVC Non-marked 88

53 Water gun Yellow Non-marked Hard Non-marked 41

54 Summer beach toy Blue Non-marked Hard Non-marked 168

55 Crazy hand toy candy Green Non-marked Soft Non-marked 54

56 Dancing animals toy candy Yellow Non-marked Soft Non-marked 226

57 Toy cartoon cars Blue Non-marked Hard Non-marked 17

58 Building block Blue Non-marked PE Non-marked 52

59 Plastic model toy cars Orange Non-marked Hard Non-marked 201

60 Animal balloon toy Green Non-marked Soft Non-marked 105

61 Funny teeth Yellow Non-marked Hard Non-marked 205

62 Funny teeth Red Non-marked Hard Non-marked 64

63 Funny teeth Pink Non-marked Hard Non-marked 17

64 Funny teeth Green Non-marked Hard Non-marked 9

65 Funny teeth Blue Non-marked Hard Non-marked 18

66 Funny teeth Purple Non-marked Hard Non-marked 63

67 Plastic smiley doll Blue Non-marked Soft Non-marked 59

68 Plastic smiley doll Red Non-marked Soft Non-marked 70

69 Plastic smiley doll Yellow Non-marked Soft Non-marked 39

70 Balanced eagle toy Orange Non-marked Soft Non-marked 40

71 Balanced eagle toy Red Non-marked Soft Non-marked 55

72 Balanced eagle toy Pink Non-marked Soft Non-marked 137

LOD means the limit of detection of ICP-OES, the value is 10 mg/kg The bold words indicate that these samples were used in the vitro tests

a c "Non-marked" means that the place of origin or the target groups of a certain toy was not indicated in the instruction b If the materials of a toy were not indicated in the instruction, we only distinguish them as hard or soft

was the same color. The pliers were cleaned in between samples to prevent cross-contamination.

HNO3 digestion for total Pb

Total Pb was determined by digestion of duplicate 0.1-0.15-g samples in concentrated nitric acid (Guaranteed Reagent (GR), purchased from Sinopharm Chemical Reagent Co., Ltd) and perchloric acid (GR, purchased from Sinopharm Chemical Reagent Co., Ltd). All glassware used was washed with conc. nitric acid prior to analysis. After thoroughly digested, Pb concentrations were measured by ICP-OES (the Prodigy, Leeman).

HCl extraction

The diluted-HCl extractable Pb was regulated by the maximum acceptable Pb migration value from toy materials in Chinese toy safety standards. Thus, in our study, 20 toy items were used to determine the level of diluted-HCl leachable Pb to determine whether these selected samples complied with the national toy safety standards. We think this part will be helpful for future policy and management of safety standards. We also compared the bioavailability of the sample using different in vitro methods.

The diluted HCl extraction procedure was as follows: using a 25-mL erlenmeyer flask, we mixed 0.1 g prepared samples with 5 mL 0.07 mol/L aqueous HCl solution at 37 ± 2 °C. Then, we shook the mixture for 1 min and

adjusted the pH of the mixture to be between 1.0 and 1.5 with 2 mol/L aqueous HCl solution, protecting the mixture from light. Next, we agitated the mixture continuously at 37 ± 2 °C for 1 h and then allowed it to stand for 1 h at 37 ± 2 °C. At last, without delay, we efficiently separated the solid from the solution. Lead concentrations were measured by ICP-MS (Agilent 7500a).

RIVM method

RIVM is a commonly used in vitro method for BA assessment, which was developed by the Dutch National Institute for Public Health and the Environment (RIVM) [22-24]. The simulated solutions are shown in Table 2. Specifically, the procedure was as follows: we added 0.1 g toy materials and 10 mL simulated saliva into a 25-mL erlenmeyer flask, and adjusted the pH to 6.5 ± 0.05. After covering the flask, we put it into the shaker bath, keeping the temperature at 37 °C and adjusting the shaking speed to 180 r/min. After 30 min, 5-mL liquid samples were collected and saved in 4 °C, awaiting analysis. To simulate the stomach and small intestinal phase, 0.15 g toy matrices and 5 mL simulated saliva were added to a 25-mL flask. These were adjusted to the same conditions as the saliva step, maintained for 5 min, and then mixed with 10 mL simulated gastric juice, titrated to pH 1.2 ± 0.05 by HCl. Two hours later, 5-mL liquid samples were collected and saved in 4 °C, to await analysis. We then added 10 mL simulated duodenal juice into the previous flask and

Table 2 Constituents of the various synthetic juices of the in vitro digestion and the reaction parameters

Saliva Gastric juice Duodenal juice

Constituents 10 mL KCl 89.6 g/L 15.7 mL NaCl 175.3 g/L 40 mL NaCl 175.3 g/L

10 mL KSCN 20 g/L 3.0 mL NaH2PO4 88.8 g/L 40 mL NaHCO3 84.7 g/L

10 mL NaH2PO4 88.8 g/L 9.2 mL KCl 89.6 g/L 10 mL KH2PO4 8 g/L

10 mL Na2SO4 57 g/L 18 mL CaCl2 2H2O 22.2 g/L 6.3 mL KCl 89.6 g/L

1.7 mLNaCl 175.3 g/L 10 mL NH4Cl 30.6 g/L 10 mL MgCl2 5 g/L

1.8 mLNaOH 40 g/L 8.3 mL HCl 37 % g/g 180 iL l HCl 37 % g/g

8 mL urea 25 g/L 10 mL glucose 65 g/L 4 mL urea 25 g/L

Augmented to 500 mL 3.4 mL urea 25 g/L 9 mL CaCl2 2H2O 22.2 g/L

with ultrapure water 10 mL 33 g/L glucosamine hydrochloride 1 g BSA

1 g BSA, 1 g pepsin 3 g pancreatin

Augmented to 500 mL with Augmented to 500 mL with

ultrapure water ultrapure water

Liquid-to-solid ratio 100 100 100

Time 2h 1h 4h

Shaking speed 180 r/min

Temperature 37 °C

pH 7.8 ± 0.05 1.2 ± 0.05 7.0 ± 0.05

adjusted the pH to 7.8 ± 0.05. After shaking at 37 °C for 2 h, 5-mL liquid samples were collected for analysis. Just as with the PBET method, lead concentrations in the liquid samples were measured by ICP-MS (Agilent 7500a).

Quality control and quality assurance

The BA of lead was calculated by dividing the amount in the simulated human body liquids by the total amount in the toy materials [22]. Quality control and quality assurance were tested via a processing method blank, laboratory fortified blank, and laboratory fortified matrix. The average recovery of Pb from laboratory fortified blank was 97.3 ± 3.2 %. For the laboratory fortified matrix, the average recovery was 101.5 ± 2.7 %. The ICP-OES detection limit for Pb was 10 mg/kg and for ICP-MS it was 15 ig/kg.

Results and discussion

Total Pb

The Pb content of the 72 toys is shown in Table 1. It could be calculated that the mean of Pb contents in the tested items was 95 mg/kg, with a maximum of 360 mg/kg. We used the function of the Q-Q (Quantile-Quantile) plot in OriginPro 8.5 for testing whether our date follows a given distribution (Normal, Exponentia). Results were shown in Fig. 2. According to Fig. 2a, it was obvious that the date did not conform to normal distribution and we could find from Fig. 2b that nearly all the points lie close to the 45° straight line. It indicated that the data conform to exponential distribution with a scale parameter of 95.11 mg/kg. Thus, the regression equation is: y = 0.0105e-00105x; where, y is the expected exponential value and x is the determined total Pb content. Interval estimation revealed that a 95 % confidence interval for the mean of total Pb of the analyzed items is (76.4, 121.6). That means the total Pb content of some low-cost plastic toys was greater than the maximum limit of American standards (100 mg/kg). Thus, the sampled plastic toys carry the potential risk of Pb exposure to children.

Compared with other studies (Table 3), total lead content varied greatly. Weidenhamer studied the lead content in inexpensive seasonal and holiday products, and found lead contents of paint ranging from 0.13 to 15.53 % [19]. Yost and Weidenhamer studied the total lead in low-cost jewelry items purchased in Washington, and concluded that among the 64 components tested, 78 % of jewelry items contained a total lead content >0.06 %. Eight of them exceeded 90 % [15]. The research of Maas demonstrated that the average lead content in children and adult jewelry

-2 О Ф Œ X

-100 0 100 200 Total lead, mg/kg

° Expected Value — Reference Line

100 200 300 400 Total lead, mg/kg

Fig. 2 Normal and exponential Q-Q (Quantile-Quantile) plot of total lead contents

Table 3 Comparison of lead content in children's products conducted by different researchers

Sample Number of Average Sampling References

type samples country

Metal jewelry 139 44.0 % USA [18]

Metal jewelry 285 30.6 % USA [3]

Paints 95 3.0 % USA [19]

Plastic toys 88 112.5 mg/kg India [17]

Plastic toys 60 1.2 mg/kg USA [25]

Plastic toys 72 95.0 mg/kg China This study

products was 30.6 % [3]. Kumar and Pastore's study showed that the average content of lead in soft plastic toys in India was 112.51 mg/kg [17]; results were similar in our study. In 2010, the Center for Health, Environment, and Justice surveyed the lead content in the toys/children and infant products, collecting 60 random samples whose

analysis showed that 5 % (3/60) of the toys contained low levels of lead. The maximum was 51 mg/kg and the mean was 1.2 mg/kg [25]. According to the comparisons above, we may safely draw the conclusion that lead content in metal jewelry was greater than that in plastic base materials. This might be explained by the fact that leaded electronic wastes were used to manufacture metal jewelry [26, 27]. Therefore, plastic toys seemed to generally carry a lower Pb exposure risk to children comparing to metal toys. This opinion was also supported by the work of Guney and Zagury [21]. Another conclusion was that lead content in plastic toys sold in the US was much lower than that in China, highlighting the reentry into the Chinese market of toys that could not be exported to America because of the improvement of American toy safety standards.

Pb is mainly used as a stabilizer and coloring agent in polyvinyl chloride plastics (PVC) in order to eliminate free radicals and make the product more appealing during the plastic production. Generally, the typical use of Pb as a plastics stabilizer or a coloring agent results in elevated Pb (>600 mg/kg) in PVC as compared to non-PVC plastics [28]. When comparing the Pb contents of the low-cost plastic toys in Table 1, we can see that all the test samples contained Pb <600 mg/kg. Moreover, no clear correlations between total Pb and the raw material and color of the toys could be identified in our study. Therefore, the Pb in plastic toys is likely to be caused by contamination during their production, rather than due to the addition as a stabilizer or coloring agent, considering that more and more regulations have banned the use of lead-containing stabilizers in plastic production. The use of Pb-containing recycled plastics might be a major source of Pb contamination in those toys, since they were widely used in low-cost plastic products from their price advantage. The price of these recycled plastics is typically only half the price of the new plastics.

Diluted HCl-extractable Pb

Twenty toy samples with total lead content exceeding 100 mg/kg were used to determine whether the bioaccessible Pb content complied with the requirements of Chinese toy safety standards. The results are shown in Fig. 3. As seen in the figure, the bioaccessible Pb in diluted HCl (D-HCl) was much lower than the total lead content of the toys. According to the toy safety standards of China, lead migration limits in diluted HCl from plastic toy materials are 90 mg/kg. For our study, we did not find any of the items to exceed the lead thresholds of Chinese standards. That is, total Pb exceeded the thresholds of the CPSC [29], but the accessible Pb was lower than the allowed maximum limit of Chinese toy safety standards. In other words, these toys could be legally sold in the Chinese market, but could not be exported to the US; this also means that Chinese

children can be more easily exposed to high levels of lead. Further, it indicates that Chinese toy safety standards might be out of date, and thus China should update its toy safety standards as soon as possible in order to protect children from toxic chemicals. As seen in Fig. 3, we found that total Pb and diluted HCl-extractable Pb content levels in the sampled toys were not correlated. High total lead content did not equal high diluted HCl-extractable Pb content. Therefore, in order to protect children from exposure to Pb via plastic toys, more comprehensive toy safety standards are needed, and a measurement combining total Pb content with bioaccessible Pb content would be a good choice.

BA of Pb with RIVM method

The BA of lead was calculated by dividing the amount in the simulated human body liquids by the total amount in the toy materials [22]. The BA calculations were conducted with the RIVM methods introduced previously. Results are summarized as a box chart in Fig. 4. Our findings clearly showed that the BA of Pb in the samples ranged from 0.36 to 8.86 %. Specifically, the averages were 1.53 ± 0.74, 3.93 ± 2.34, 4.91 ± 3.12, and 2.62 ± 1.25 % for D-HCl, and the Dutch National Institute for Public Health and the Environment's mouth phase (RIVM-M), stomach phase (RIVM-S), and small intestinal phase (RIVM-SI), respectively. The highest BA values of lead were obtained with RIVM-S and the lowest were obtained with D-HCl. According to previous works, we knew that the pHs of D-HCl, RIVM-M, RIVM-S and RIVM-SI were 1.15, 6.5, 1.2, and 7.8, respectively. For each phase, we added different substances and placed them in a shaker bath for different times. Thus, we might conclude that the main differences in the results of BA with the three methods were attributed to the conditions of applied simulated body liquids and their components. Additionally, the various properties of the studied toys might have contributed to the different results.

Based on the data shown in Fig. 4, it was clear that the BA of lead in the D-HCl was the minimum among the four tested leaching solutions. This illustrated that the use of diluted HCl-Pb to siimulate a matrix based on the worst case of a child swallowing a toy might be irrational. To simulate the conditions of a child's stomach, not only do the pH conditions have to be taken into consideration, but also the components of the gastric juices need to be considered. Therefore, China needs to update its toy safety standards related to the migration of lead. Basing standards around the total Pb limits together with migration limits, determined via the RIVM method, might be a good choice.

Compared with other studies that focused on the BA of Pb (Table 4), it could be concluded that the BA of Pb-containing plastics was lower than Pb-containing in soils

Fig. 3 Diluted HCl-extractable Pb for 20 plastic toys tested, plotted against the total lead content of the items

CO CD о о

D-HCl RIVM-M RIVM-S

Leaching solution

RIVM-SI

Fig. 4 Bioaccessibility of Pb in different simulated body fluids. The box represents the 25-75th percentiles; the squares represent the means; circles represent the minimum and maximum

Table 4 Summary of lead bioaccessibility (%) using the RIVM method from different studies

Samples RIVM-M RIVM-S RIVM-SI References

Soils - 91.4 ± 2.6 66.2 ± 1.5 [30]

Chalks - 59.0 ± 8.0 3.3 ± 0.4 [32]

Soils - 70.9 ± 0.8 31.8 ± 2.5 [31]

Plastic toys 3.65 ± 1.28 4.09 ± 1.83 2.62 ± 0.82 This study

[30, 31] and chalks [32]. In other words, the Pb content in plastic toys was not as easily bioavailable. This might be due to the complex and strong polymer structure of the

plastics. It also could be found that the BA of Pb in RIVM-S was greater than that in RIVM-SI, no matter what the test material was. The reason might be that the pH of the RIVM-S was much lower than that of the RIM-SI. To summarize, the RIVM method could be most helpful in assessing the Pb bioaccessibility in the mouth, stomach, and small intestine phase when plastic toy matrices are ingested orally. Furthermore, to save time and cost, the RIVM-S test could be selected instead of both of the tests in future applications of RIVM.

Conclusions

Low-cost plastic toys were collected via random sampling between July 2012 and October 2012 in Beijing, China. Total Pb content of the 72 inexpensive, plastic toy items was determined and its BA was estimated using diluted HCl and RIVM methods. It was found that 27 of the 72 items exceeded 100 mg/kg Pb content, with a maximum as high as 366 mg/kg. The bioaccessibility of Pb determined through diluted HCl ranged from 0.36 to 2.78 %, with an average of 1.53 ± 0.74 %, while the values were 3.93 ± 2.34, 4.91 ± 3.12 and 2.62 ± 1.25 % for RIVM-M, RIVM-S and RIVM-SI, respectively. So, although the HCl extraction results show that all the samples meet the current Chinese standard, these results might underestimate the environmental and health risk of lead in plastics toys. The RIVM methods will be helpful in supplementing total Pb content measurement, in efforts to reduce children's expose to toxic heavy metals and to control the related health risk from plastic toys.

Acknowledgments This work was financially supported, in part, by the National Natural Science Foundation of China (20977105 and 50708110).

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