Environmental Research

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Environmental Research

journal homepage:www.elsevier.com/locate/envres

Resin-based dental sealants as a source of human exposure to bisphenol analogues, bisphenol A diglycidyl ether, and its derivatives

Jingchuan Xue

^a,1

, Pranav Kannan

^a,1

, Taha A. Kumosani

^b

, Abdulrahman L. Al-Malki

^c

, Kurunthachalam Kannan

^a,b,⁎

aWadsworth Center, New York State Department of Health, and Department of Environmental Health Sciences, School of Public Health, State University of New York at Albany, Empire State Plaza, P.O. Box 509, Albany, NY 12201-0509, USA

bBiochemistry Department, Faculty of Science, and Production of Bioproducts for Industrial Applications Research Group and Experimental Biochemistry Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah, Saudi Arabia

cBiochemistry Department, Faculty of Science, Bioactive Natural Products Research Group, and Experimental Biochemistry Unit, King Fahd Medical Research Center, King Abdulaziz University, Jeddah, Saudi Arabia

A R T I C L E I N F O

Keywords:

BPA BPF Bisphenols BADGE Dental sealants Exposure assessment

A B S T R A C T

Although studies have examined leaching of bisphenol A (BPA) from dental sealants into saliva, occurrence of BPA, bisphenol A diglycidyl ether (BADGE), and their derivatives in dental sealants themselves has not been investigated. In this study, concentrations of eight bisphenol analogues (BPs), BADGE and its derivatives (BADGEs), including BADGE‧H₂O, BADGE‧HCl, BADGE‧2H₂O, BADGE‧2HCl, and BADGE‧H₂O‧HCl, were determined in 70 dental sealants collected from the U.S. market. Of the 70 dental sealants analyzed, 65 contained at least one of the target chemicals measured. BADGE‧2H2O was the most abundant compound, found at concentrations of up to 1780 µg/g. The geometric mean (GM) concentration of total BADGEs was 47.8 µg/g, which was two to three orders of magnitude higher than that of total BPs (GM: 539 ng/g). BPA was found in 46% of the sealants and BADGEs was found in 87% of the sealants analyzed. Majority of the dental sealants analyzed in this study were manufactured in the United States and Korea; no significant differences were observed in the concentrations of BPs and BADGEs between the two countries. An exposure assessment was made based on the concentrations of BPs and BADGEs measured in sealants and their application rates in dentistry. The worst-case exposure scenario with the highest measured concentration of total BPs and BADGEs and application on 8 teeth at 8 mg each yielded an estimated daily intake (EDI) of 1670 and 5850 ng/kg·bw/day for adults and children, respectively. Although the EDI is below the specific migration limit set by the European Food Safety Authority, dental sealants are a source of exposure to BPs and BADGEs, especially in children.

1. Introduction

Resin-based dental sealants, also known as pit andfissure sealants, are widely used in dentistry for the prevention of tooth decay. Pit and fissure sealants are applied to teeth that are vulnerable to decay by placing them within certain areas to create a smooth surface that is easy to clean. The effectiveness of these sealants in preventing and arresting the progression of dental caries has been demonstrated (Ahovuo- Saloranta et al., 2008; Gooch et al., 2009;Griffin et al., 2008). The use of dental sealants is more common among children due to their sub- stantial risk for tooth decay. Over the last two decades, the use of pit andfissure sealants among children has steadily increased, following stimulation through federal programs, including those by the Centers

for Disease Control and Prevention (CDC) and the Maternal and Child Health Bureau of the United States (Dye et al., 2007). From 1988–1994 to 1999–2004, the percentage of adolescents in the United States between 12 and 19 years of age who had at least oneﬁlling on permanent teeth increased from 18% to 38% (Dye et al., 2007).

The sealant and composite resinﬁllings are polymerized prior to use. A study showed, however, that these polymers are not chemically stable and can be released into the oral environment (Moharamzadeh et al., 2007). Incomplete polymerization of dental sealants and sec- ondary decomposition of these composites under the inﬂuence of physical and chemical agents in the oral environment can contribute to human exposure to chemicals present in dental sealants (Leprince et al., 2012; Finer and Santerre, 2003;Malkiewicz et al., 2015; Olea et al.,

https://doi.org/10.1016/j.envres.2017.12.011

Received 20 November 2017; Received in revised form 12 December 2017; Accepted 13 December 2017

⁎Correspondence to: Wadsworth Center, Empire State Plaza, P.O. Box 509, Albany, NY 12201-0509, USA.

1Equally contributed.

E-mail address:[email protected](K. Kannan).

T

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1996). Bisphenol A diglycidyl ether (BADGE)-based epoxy resins are widely used in the manufacture of dental resins (Fleisch et al., 2010).

Bisphenol A (BPA) is used in the production of BADGE and is present in dental sealants as impurities due to the incomplete polymerization.

Nevertheless, studies about the occurrence of BPA and other bisphenol analogues (collectively referred to as BPs in this study), BADGE and its derivatives (collectively referred to as BADGEs in this study) in resin- based dental sealants and composites are very limited.

As an emerging class of endocrine-disrupting chemicals, BPs and BADGEs have been reported as reproductive and developmental tox- icants (Hyoung et al., 2007; Richter et al., 2007; Kang et al., 2008). BPs, including BPA, BPF, and BPS, elicit estrogenic activities in in vitro bioassays (EHHI, 2008). Exposure to BADGE and its derivatives, BAD- GE‧H2O and BADGE‧2H2O, has been associated with reproductive failure in Spanish sows (Nerin et al., 2014). Although BADGE was classified as a Group 3 carcinogen (i.e., not classifiable as to its carci- nogenicity in humans) by the International Agency for Research on Cancer (1999), a variety of in vitro assays have suggested genotoxic effects of this chemical (IARC, 1999;Suarez et al., 2000;Sueiro et al., 2001, 2006). Human exposure to BPA has been linked to endocrine disorders and obesity (Lang et al., 2008;EHHI, 2008). Thus, exposure of humans to BPs and BADGE is a matter of concern, and the assessment of sources of human exposures is important to the development of stra- tegies to mitigate exposures. The objective of this study was to provide baseline information on the concentrations of BPs and BADGEs in dental sealants currently marketed in the United States. Exposure of adults and children to BPs and BADGEs through dental sealant application has also been assessed.

2. Materials and methods 2.1. Standards and reagents

Information regarding analytical standards and reagents used in this study is provided in theSupporting Information.

2.2. Sample collection and preparation

All dental sealants (n= 70) analyzed in this study were purchased from online vendors and distributors from June to August 2015, and these products originated from the United States, Korea, Japan, the Netherlands, Liechtenstein, and Greece. The dental sealants represented 15 manufacturers/distributors and 19 popular brands available in the U.S. market. Various shades of sealants (e.g., opaque, clear, ultra-clear, natural, oﬀ-white) and types of cure (e.g., light, self-cure) were in- cluded. Detailed information of the dental sealant samples is shown in Table S1.

The method for the extraction of BPs and BADGEs from the dental sealants was similar to that described elsewhere, with some modiﬁca- tions (Wang et al., 2016). Brieﬂy, 100–200 mg of resin were accurately weighed and transferred into a 15-mL PP tube. Six milliliters of methanol were added, and samples were shaken in an oscillator shaker at 100 strokes per minute for 60 min. The mixture was then centrifuged at 5000 rpm for 5 min, and the supernatants were passed through an ENVI-Carb solid phase extraction (SPE) cartridge (Sigma-Aldrich, St.

Louis, MO, USA), which was preconditioned with 6 mL of methanol.

Analytes were eluted with 3 × 2 mL of methanol. Both elutes were combined and concentrated to 5 mL under a gentle nitrogen stream. An aliquot of the extract was vortex mixed and transferred into a glass vial for high-performance liquid chromatography-tandem mass spectro- metry (HPLC-MS/MS) analysis. All procedural blanks and samples were spiked with 100 ng of¹³C-BPA andd6-BADGE, as internal standards, prior to extraction.

2.3. Instrumental analysis

Instrumental analyses of BPs and BADGEs have been described in detail elsewhere (Xue et al., 2016, 2017). Briefly, chromatographic separation of BPs was carried out using a Shimadzu Prominence Mod- ular HPLC system (Shimadzu Corporation, Kyoto, Japan), consisting of a system controller, a binary pump, and an auto sampler. Identification and quantification of BPs were performed with an Applied Biosystems API 3200 electrospray triple quadruple mass spectrometer (ESI-MS/MS;

AB SCIEX, Framingham, MA, USA). Further details of instrumental methods are provided in theSupporting Information.

Chromatographic separation of BADGEs was carried out using an Agilent 1100 Series HPLC system (Agilent Technologies Inc., Santa Clara, CA, USA). Identiﬁcation and quantiﬁcation of the target chemicals were performed with an Applied Biosystems API 2000 electrospray triple quadrupole mass spectrometer (ESI-MS/MS; Applied Biosystems, Foster City, CA, USA). Further details of the instrumental analysis of BADGEs are provided in theSupporting Information.

2.4. Quality assurance/quality control

Quantiﬁcation was performed by an isotope-dilution method based on the responses of ¹³C-BPA (for BPs) and d6-BADGE (for BADGEs).

Instrument calibration standards were injected at concentrations that ranged from 0.1 to 1000 ng/mL. For BADGE·2H2O and BADGE·HCl·H2O, that were found at elevated concentrations in dental sealants, the highest concentration used for instrumental calibration was 10,000 ng/mL. Both linear and polynomial curves were applied in the calculation of concentrations. The regression coefficients (r) were≥ 0.99 for all calibration curves. The consistency and appearance of the dental sealant matrix varied, depending on the brand, and, therefore, the method limits of quantification (MLOQs) were determined based on the minimum concentration of analytes in sample extracts that provided a signal-to-noise ratio (S/N)≥10. The MLOQs of BPF, BPA, BPB, BPS, BPZ, BPAP, BPAF, and BPP were 21.9, 175, 21.9, 8.77, 21.9, 13.2, 4.39, and 132 ng/g, respectively, and those of BADGE·2H2O, BADGE·H2O, BADGE, BADGE·HCl·H2O, BADGE·HCl, and BADGE·2HCl were 1.31, 2.19, 0.44, 0.44, 0.44, and 0.88 µg/g, respectively. For the calculation of the MLOQ, an average weight (114 mg) of dental sealants used for extraction was applied. BPA and BADGE·2H2O were found in procedural blanks at respective concentrations of 15.8 and 5.33 ng/mL, and these values were subtracted from the measured concentrations in samples. Five samples were selected randomly for pre-extraction matrix spike (MS) by fortification of 100 ng of target analytes and by passing them through the analytical procedure. Post-extraction matrix matches (MM) of thefive samples were followed for the calculation of relative recoveries, which ranged from 84% to 105% and 73% to 84% for BPs and BADGEs, respectively.

2.5. Data analysis

Data were acquired by Analyst software version 1.4.1 (Applied Biosystems, Foster City, CA, USA). Statistical analyses were performed with statistics software package R v.3.1.0 and Microsoft Excel 2007. For the calculation of geometric mean (GM) and arithmetic mean, we substituted values below the MLOQ with a value equal to half the MLOQ. A Shapiro-Wilk test and quantile-quantile (Q-Q) plot were used to determine the normality of the data. To examine the relationship between chemicals, Spearman (when data did not follow a normal distribution after logarithmic transformation) or Pearson (when data followed a normal distribution after logarithmic transformation) correlation analyses was used. Only those samples with detectable concentrations of the target analytes were used in performing correlation analysis. To assess the diﬀerence between means, Student'st-test (when data followed a normal distribution after logarithmic transformation) or Mann-Whitney U test (when data did not follow a normal

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Table1 Concentrations(ng/g)ofbisphenolanalogues(BPs)indentalsealantscollectedfromtheU.S.marketofvariousgeographicalregion(theU.S.,Korea,Liechtenstein,theNetherlands,JapanandGreece).a No.BPFBPABPBBPSBPZBPAPBPAFBPP∑(BPs) U.S. #1423.2;23.7208;504n.d.bn.d.n.d.n.d.n.d.n.d.328;624 #22n.d.305;12,700n.d.n.d.n.d.n.d.33.4n.d.413;12,900 #33216979,500(982,000±82,900)n.d.n.d.n.d.n.d.n.d.n.d.979,700(982,000±83,000) #46n.d.113n.d.n.d.n.d.n.d.n.d.n.d.220 #51n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d. #6265.960588n.d.15.512.8;89.5199;209n.d.398;1140 #73n.d.609n.d.n.d.n.d.n.d.n.d.n.d.717 #83541230n.d.n.d.5654.711470.3;180200;1700 #94n.d.372n.d.n.d.n.d.n.d.n.d.n.d.480 #101626.7(49.7±70.6)151(214±215)38.3;65.7n.d.n.d.12.5(21.2±23.3)5.6(48.5±106)67356(426±279) #111n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d. #122n.d.181;5090n.d.n.d.n.d.n.d.n.d.n.d.289;5200 #134n.d.378n.d.n.d.n.d.n.d.n.d.n.d.485 ∑5116.9(29.6±50.7)284(58,300±234,000)12.1(14.1±13.6)n.d.n.d.8.96(13.9±19.0)4.00(27.4±72.6)67.2(68.1±15.9)556(58,500±234,000) Korea #1227.9159n.d.n.d.n.d.n.d.n.d.n.d.283 #24n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d. #34n.d.376(1750±3190)n.d.n.d.n.d.n.d.249an.d.677(1920±3150) ∑10n.d.166(760±2030)n.d.n.d.n.d.n.d.n.d.n.d.333(894±2020) Liechtenstein(n=2) #11n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d. #21n.d.435n.d.n.d.n.d.n.d.n.d.n.d.543 TheNetherlands(n=2) #11n.d.7920n.d.n.d.n.d.n.d.n.d.n.d.8030 #21n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d.n.d. Japan(n=1) #11374n.d.57.821.529.669.788.881.2811 Greece(n=4) #1422981(1080±575)n.d.n.d.n.d.n.d.n.d.n.d.1100(1190±580) Allsamples 7016.2(30.1±60.5)283(42,800±201,000)12.1(13.9±12.8)n.d.11.4(11.9±5.81)8.52(12.8±17.9)3.83(25.3±68.8)67.0(67.7±13.7)539(42,900±201,000) aWhentherewerelessthan3detects,eachindividualvaluewasgiven;whenthereweremorethan3detects,including3,bothgeometricmean(GM)andarithmeticmean(±standarddeviation)(mean±SD)weregiven. bn.d.:notdetected.

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distribution after logarithmic transformation) was used. Statistical sig- niﬁcance was set atp< 0.05.

3. Results and discussion 3.1. BPs in dental sealants

Among the eight bisphenol (BPs) analogues measured, BPA was the most abundant compound found at a detection rate (DR) of 46%, at concentrations that ranged from below MLOQ to 1070 µg/g (GM:

283 ng/g) (Table 1). Studies have reported exposure to BPA following the placement of dental sealants in individuals (Han et al., 2012;

Joskow et al., 2006), although the actual measurements of concentrations of BPA in dental sealants themselves were not conducted prior to this study. Unpolymerized BPA based monomers can leach into saliva, followed by systemic absorption into the blood stream (Downs et al., 2010). To the best of our knowledge, this is theﬁrst study of the occurrence of BPA in resin-based dental sealants currently sold in the U.S.

market.

BPF was the second most abundant BPs found in dental sealants at a DR of 24% and at a concentration range of below MLOQ to 374 ng/g (GM: 16.2 ng/g) (Table 1). Other BPs were less frequently detected, with DRs that ranged from 1.4% (BPS) to 14% (BPAF) (Table 1). The GM concentration of total BPs in dental sealants was 539 ng/g, with a concentration range of < MLOQ-1070 µg/g. BPA accounted for most of the total BPs measured in dental sealants (Table 1).

3.2. BADGEs in dental sealants

Of the 70 resin-based dental sealants analyzed, 61 samples (87%)

contained at least one of theﬁve BADGEs measured (Table 2). Total BADGE concentrations ranged from < MLOQ to 1820 (GM: 47.8) µg/g (Table 2), which were two to three orders of magnitude higher than those of BPs. The most abundant BADGE found was BADGE·2H2O, at a GM concentration of 13.7 µg/g (range: < MLOQ to 1780) (Table 2).

The highest BADGE·2H2O concentration of 1780 µg/g was found in a dental sealant that was made in Liechtenstein (Table 2). BAD- GE·HCl·H2O and BADGE·2HCl were the second and third most abundant BADGEs, detected in 42 (60%) and 36 (51.4%) of the samples, respectively, at a respective GM concentration of 2.76 and 1.94 µg/g (Table 2). Both BADGE and BADGE·HCl were found in 9 samples (12.9%) at concentrations that ranged from < MLOQ to 10.9 (GM:

0.29) and < MLOQ to 21.7 µg/g (0.35), respectively (Table 2).

Few studies have investigated the release of BADGEs from resin- based dental sealants into saliva. One study used distilled water, satu- rated solution of NaHCO3, and 1 M NaOH as simulants for saliva to investigate the eﬀect of pH on the leaching of chemicals from dental sealants (Pulgar et al., 2000). The maximum amount of BADGE released (6.1 µg/mg) at a pH of 7 was found in polymerized Delton, a com- mercial brand available in the Spanish market in 2000 (Pulgar et al., 2000). In our study, the maximum concentrations of BADGE and total BADGEs found were 10.9 µg/g and 1820 µg/g, respectively (Table 2).

Correlations among the concentrations of derivatives of BADGE measured in dental sealants were examined (Fig. S1). Signiﬁcant negative correlations between the concentrations of BADGE and all other derivatives (except for BADGE·H2O, for whichp= 0.09) were observed.

This may suggest that all BADGE derivatives originated from the parent compound, BADGE (Fig. S1), and that an increase in the concentration of one derivative resulted in the reduction in concentration of another BADGE derivative. A signiﬁcant negative correlation between ln

Table 2

Concentrations (µg/g) of bisphenol A diglycidyl ether and its derivatives (BADGEs) in dental sealants collected from the U.S. market of various geographical region (the U.S., Korea, Liechtenstein, the Netherlands, Japan and Greece).^a

No. BADGE·2H2O BADGE·H2O BADGE BADGE·HCl·H2O BADGE·HCl BADGE·2HCl ∑(BADGEs)

U.S.

#1 4 656 (686 ± 227) n.d.^b n.d. 23.7 (24.5 ± 7.27) n.d. n.d. 681 (712 ± 234)

#2 2 8.30; 11.5 4.28; 5.53 10.9; 9.17 1.80; 1.76 1.00 n.d. 26.7; 28.6

#3 3 27.7 (27.9 ± 4.35) n.d. n.d. 6.17 (6.17 ± 0.09) n.d. n.d. 35.9 (36.1 ± 4.28)

#4 6 538 (580 ± 237) n.d. n.d. 17.6 (17.7 ± 1.80) n.d. 1.02 (1.09 ± 0.33) 560 (600 ± 239)

#5 1 243 n.d. n.d. 14.1 n.d. 1.68 261

#6 2 n.d. n.d. n.d. n.d. n.d. 6.56; 14.35 8.97; 16.8

#7 3 n.d. n.d. n.d. n.d. n.d. n.d. n.d.

#8 3 n.d. n.d. n.d. n.d. n.d. n.d. n.d.

#9 4 438 (447 ± 101) n.d. n.d. 19.7 (20.0 ± 3.82) n.d. 1.25; 2.00 461 (469 ± 102)

#10 16 n.d. n.d. n.d. n.d. n.d. 13.0 (13.5 ± 3.67) 15.5 (15.9 ± 3.67)

#11 1 134 n.d. n.d. 9.44 n.d. 1.27 146

#12 2 10.9; 14.2 n.d. n.d. 3.17; 3.93 n.d. n.d. 16.0; 20.1

#13 4 194 (201 ± 54.2) 8.28 (8.30 ± 0.74) 1.77 (1.77 ± 0.11) 41.9 (42.1 ± 3.64) 8.44 (8.46 ± 0.67) 4.66 (4.68 ± 0.54) 261 (266 ± 56.8)

∑ 51 12.5 (183 ± 272) 1.36 (1.81 ± 2.06) 0.30 (0.73 ± 1.96) 1.96 (10.0 ± 13.1) 0.30 (0.88 ± 2.24) 2.10 (5.43 ± 6.29) 50.2 (202 ± 278) Korea

#1 2 n.d. n.d. n.d. n.d. n.d. n.d. n.d.

#2 4 16.7 (16.7 ± 0.93) n.d. n.d. 2.73 (2.73 ± 0.19) n.d. n.d. 21.4 (21.4 ± 1.09)

#3 4 74.4 (78.2 ± 25.0) 6.86 (6.95 ± 1.27) 0.45 (0.49 ± 0.22) 392 (417 ± 145) 16.6 (17.1 ± 4.49) 110 (116 ± 40.1) 601 (636 ± 213)

∑ 10 15.9 (38.1 ± 37.9) 2.28 (3.44 ± 3.11) 0.29 (0.33 ± 0.19) 12.0 (168 ± 230) 1.24 (6.97 ± 9.09) 3.99 (46.8 ± 64.2) 54.3 (264 ± 344) Liechtenstein (n = 2)

#1 1 6.29 n.d. n.d. 2.46 n.d. n.d. 10.7

#2 1 1780 n.d. n.d. 35.2 n.d. 3.67 1820

The Netherlands (n = 2)

#1 1 40.2 n.d. n.d. 7.74 n.d. n.d. 49.9

#2 1 n.d. n.d. n.d. n.d. n.d. n.d. n.d.

Japan (n = 1)

#1 1 1.45 n.d. n.d. n.d. n.d. n.d. 3.64

Greece (n = 4)

#1 4 31.1 (32.3 ± 10.6) n.d. n.d. 8.15 (8.21 ± 1.13) n.d. n.d. 41.5 (42.5 ± 11.0)

All samples

70 13.7 (167 ± 311) 1.43 (2.77 ± 2.19) 0.29 (0.60 ± 1.68) 2.76 (32.4 ± 101) 0.35 (1.66 ± 4.38) 1.94 (10.8 ± 28.1) 47.8 (214 ± 337)

aWhen there were less than 3 detects, each individual value was given; when there were more than 3 detects, including 3, both geometric mean (GM) and arithmetic mean ( ± standard deviation) (mean ± SD) were given.

bn.d.: not detected.

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(BADGE·2H2O) and ln(BADGE·2HCl) may suggest competitive forma- tion of these derivatives from BADGE (Fig. S1). Nevertheless, the ex- istence of signiﬁcant positive correlations between ln(BADGE·2H2O) and ln(BADGE·HCl·H2O), ln(BADGE·2HCl) and ln(BADGE·HCl·H2O), ln (BADGE·HCl) and ln(BADGE·2HCl), ln(BADGE·HCl) and ln(BAD- GE·HCl·H2O), ln(BADGE·H2O) and ln(BADGE·2H2O) suggests similar sources of origin and/or the presence of one or more of the derivatives as impurities in BADGE-based resins (Fig. S1). Associations between ln (BADGE·2H2O) and ln(BPA) as well as ln(Total BADGEs) and ln(BPA) also were examined, and a negative relationship was found, although this was not statistically signiﬁcant (p> 0.05) (Fig. S2).

3.3. Variations in BPs and BADGEs concentrations in dental sealants Signiﬁcant diﬀerences in the concentrations of BPs and BADGEs between various brands of dental sealants were observed. The highest GM concentrations of total BPs (980 µg/g) and total BADGEs (1820 µg/

g) were found in a brand from the U.S. and Liechtenstein, respectively (Tables 1 and 2). Several brands of dental sealants, however, did not contain any BPs or BADGEs (e.g., Brands 5, 7, and 8 from the U.S. and Brands 1 and 2 from Korea) (Tables 1 and 2). Significant differences in BP and BADGEs concentrations also were observed in different brands of dental sealants from a single manufacturer. For instance, Brands 2 and 3 from Korea were two assorted brands of dental sealants made by the same manufacturer. Although no BPs were found in Brand 2, samples of Brand 3 contained BPA at a GM concentration of 376 ng/g (Table 1). Further, the GM concentration of total BADGEs in Brand 2 was approximately 30 times lower than that found in Brand 3 (Table 2).

No signiﬁcant diﬀerence was observed in the concentrations of BPs and BADGEs in dental sealants made in the U.S. and Korea.

The forms of BADGEs found in dental sealants varied, depending on the brand. For example, all BADGE derivatives were found in Brand 13 made in the U.S. (Table 2). BADGE·2H2O and BADGE·HCl·H2O were found in most of the brands, whereas, in some brands (e.g., Brands 6 and 10 from the U.S.), only BADGE·2HCl was detected (Table 2). This diﬀerence in the proﬁles of BADGEs between dental sealants may be related to the composition or formulation of resins used in these products.

3.4. Release and exposure of BPs and BADGEs from dental sealants

The migration and human exposure to BPs and BADGEs from dental sealants were investigated based on the assumption that one quadrant of teeth (i.e., 8 teeth) was sealed at 8 mg of sealant for each tooth and that the body weight of adults and children was 70 and 20 kg, respectively (Gruninger et al., 2015; Wang et al., 2016; U.S.EPA, 2011). When eight teeth were sealed, the mean and maximum amounts of total BPs and BADGEs released into the buccal cavity were 16.5 and 117 µg, respectively (Table 3). It should be noted that this estimation was based on the concentrations of BPs and BADGEs extracted in methanol. Thus, the extraction of BPs and BADGEs from sealants by saliva is expected to be lower than that calculated. Nevertheless, the results of this study provide evidence that dental sealants can be a source of exposure to BPs and BADGEs, especially in children.

The body weight adjusted exposure doses of total BPs and BADGEs through dental sealant application are shown inTable 4. The highest estimated daily intake (EDI) of total BPs and BADGEs for adults through dental sealants was 209, 833, and 1670 ng/kg·bw/day when one, four, and eight teeth, respectively, were sealed (Table 4). To estimate the total BPs and BADGEs exposure in children, following dental sealant application, we assumed that the sealants were applied to eight primary molars and premolars during a single oﬃce visit (Gruninger et al., 2015). The highest EDI of total BPs and BADGEs in children through dental sealants was 5.85 µg/kg·bw/day, which was higher than that calculated for adults (Table 4). Because dental sealants are commonly used on children, exposure of this age group to BPs and BADGEs is a

Table 3

Amount (µg) of total BPs and BADGEs released after 1 tooth, 4 and 8 teeth sealed, respectively, following dental sealant application (^*: mean;^**: maximum).

1 tooth sealed 4 teeth sealed 8 teeth sealed U.S.

#1 5.70^*/7.48^** 22.8/29.9 45.6/59.9

#2 0.27/0.32 1.10/1.27 2.20/2.53

#3 8.15/8.86 32.6/35.4 65.2/70.9

#4 4.80/7.26 19.2/29.0 38.4/58.0

#5 2.09 8.35 16.7

#6 0.11/0.14 0.44/0.57 0.87/1.15

#7 0.03/0.03 0.10/0.11 0.21/0.23

#8 0.03/0.04 0.11/0.15 0.23/0.29

#9 3.76/4.61 15.0/18.4 30.1/36.8

#10 0.13/0.18 0.52/0.71 1.05/1.42

#11 1.17 4.67 9.35

#12 0.17/0.20 0.67/0.81 1.33/1.62

#13 2.13/2.46 8.53/9.86 17.1/19.7

T 2.08/8.86 8.33/35.4 16.7/70.9

Korea

#1 0.03/0.03 0.10/0.10 0.20/0.20

#2 0.17/0.18 0.69/0.73 1.38/1.46

#3 5.11/6.33 20.4/25.3 40.8/50.6

T 2.12/6.33 8.47/25.3 16.9/50.6

Liechtenstein

#1 0.09 0.35 0.70

#2 14.6 58.3 117

The Netherlands

#1 0.46 1.85 3.71

#2 0.02 0.10 0.20

Japan

#1 0.04 0.14 0.29

Greece

#1 0.35/0.48 1.40/1.91 2.79/3.82

T 2.06/14.6 8.23/58.3 16.5/117

Table 4

Estimated daily intake (EDI) of total BPs and BADGEs (ng/kg·bw /day) for adults and children after dental sealant placement (^*: mean;^**: maximum).

Adults Children

1 tooth sealed 4 teeth sealed 8 teeth sealed 8 teeth sealed U.S.

#1 81.4^*/107^** 326/427 651/856 2280/2940

#2 3.86/4.57 15.7/18.1 31.4/36.1 110/127

#3 116/127 466/506 931/1010 3260/3545

#4 68.6/104 274/414 549/829 1920/2900

#5 29.9 119 239 835

#6 1.57/2.00 6.29/8.14 12.4/16.4 43.5/57.5

#7 0.43/0.43 1.43/1.57 3.00/3.29 10.5/11.5

#8 0.43/0.57 1.57/2.14 3.29/4.14 11.5/14.5

#9 53.7/65.9 214/263 430/526 1505/1840

#10 1.86/2.57 7.43/10.1 15.0/20.3 52.5/71

#11 16.7 66.7 134 467.5

#12 2.43/2.86 9.57/11.6 19.0/23.1 66.5/81

#13 30.4/35.1 122/141 244/281 855/985

T 29.7/127 119/506 239/1010 835/3545

Korea

#1 0.43/0.43 1.43/1.43 2.86/2.86 10.0/10.0

#2 2.43/2.57 9.86/10.4 19.7/20.9 69/73

#3 73.0/90.4 291/361 583/723 2040/2530

T 30.3/90.4 121/361 241/723 845/2530

Liechtenstein

#1 1.29 5.00 10.0 35

#2 209 833 1670 5850

The Netherlands

#1 6.57 26.4 45.60 185.5

#2 0.29 1.43 2.86 10.0

Japan

#1 0.57 2.00 4.14 14.5

Greece

#1 5.00/6.86 20.0/27.3 39.9/54.6 139.5/191

T 29.4/209 118/833 236/1670 825/5850

(6)

concern. The calculated exposure dose for BPs and BADGEs was higher than that reported for butylated hydroxytoluene (BHT), which are antioxidants measured in the same set of dental sealants (Wang et al., 2016).

To protect migration of chemicals into foods, the European Food Safety Authority (EFSA) has specified a tolerable daily intake (TDI) or specific migration limit (SML) for BPA (TDI: 4 µg/kg·bw/day) and BADGEs (SML: 10 mg/kg·bw/day) (EFSA, 2004, 2015). Although the EDIs for total BPs and BADGEs in dental sealants were below the re- commended limit set by the EFSA, other exposure sources also should be considered when assessing the overall human health risks, as these chemicals have been reported to occur in food, air, and indoor dust (Xue et al., 2016; Summerfield et al., 1998; Wang et al., 2012).

4. Conclusions

Dental sealants are a source of exposure to BPs and BADGEs. This is theﬁrst study to report the occurrence of BPs and BADGEs in dental sealants currently available in the U.S. market. The measurable concentrations of BPs and BADGEs [GM (total BPs): 539 ng/g; GM (total BADGEs): 47.8 µg/g] found in dental sealants suggest the widespread use of these chemicals in these products. The concentrations of BADGEs in dental sealants were two to three orders of magnitude higher than those of BPs. Leaching of BPs and BADGEs into saliva can be a pathway of exposure to these chemicals by humans. The concentrations of BPs and BADGEs in dental sealants varied, depending on the formulation.

Further studies are needed to establish the permissible levels of BPs and BADGEs in sealants.

Acknowledgements

We thank Mr. Karl Brosch for help with sample collection. This project was funded by the Deanship of Scientiﬁc Research (DSR) at King Abdulaziz University, Jeddah, Saudi Arabia, under grant no. (2-141-36- HiCi). The authors, therefore, acknowledge with thanks DSR for tech- nical andﬁnancial support.

Competingﬁnancial interest declaration The authors report no conﬂicts of interest.

Appendix A. Supplementary material

Supplementary data associated with this article can be found in the online version athttp://dx.doi.org/10.1016/j.envres.2017.12.011.

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