Article pubs.acs.org/est
Benzotriazole, Benzothiazole, and Benzophenone Compounds in Indoor Dust from the United States and East Asian Countries Lei Wang,†,‡ Alexandros G. Asimakopoulos,† Hyo-Bang Moon,§ Haruhiko Nakata,∥ and Kurunthachalam Kannan†,* †
Wadsworth 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, New York 12210-0509, United States ‡ Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria/Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Nankai University, Tianjin 300071, China § Department of Marine Sciences and Convergence Technology, College of Science and Technology, Hanyang University, Ansan 426-791, South Korea ∥ Graduate School of Science & Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan S Supporting Information *
ABSTRACT: Organic corrosion inhibitors (OCIs), including ultraviolet light filters, are widely used in plastics, rubbers, colorants, and coatings to increase the performance of products. Derivatives of benzotriazole (BTR), benzothiazole (BTH), and benzophenone (BP) are high-production volume OCIs that have been detected in the environment and human tissues. However, knowledge of their occurrence in indoor environments, as well as human exposure to them, is still lacking. In this study, BTR, BTH, BP and their 12 derivatives were determined in indoor dust for the first time. All three groups of OCIs were found in all 158 indoor dust samples from the U.S. and three East Asian countries (China, Japan, and Korea). The geometric mean (GM) concentration of the sum of six BTRs (GM CΣBTRs) ranged from 20 to 90 ng/g among the four countries studied, with a maximum CΣBTRs of ∼2000 ng/g found in a dust sample from China. Tolyltriazole was the major derivative of BTR measured in dust. GM CΣBTHs in indoor dust from the four countries ranged from 600 to 2000 ng/g. 2-OH-BTH was the predominant BTH in dust from the U.S., Japan, and Korea. GM CΣBPs in dust ranged from 80 to 600 ng/g, with 2-OH-4-MeO-BP and 2,4-2OH-BP, contributing to the majority of ∑BP concentrations. Based on the concentrations of three types of OCIs in indoor dust, human exposure through dust ingestion was calculated. Daily intake of OCIs through dust ingestion was higher for people in the U.S., Japan, and Korea than in China; the residents in urban China are exposed to higher levels of OCIs via dust ingestion than are those in rural China.
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INTRODUCTION Corrosion inhibitors (including ultraviolet light filters, in this study) play important roles in the protection of materials from deterioration by reactions with its environment.1 In addition to inorganic compounds,2 such as chromate and nitrite, many organic compounds are used as corrosion inhibitors.3,4 Due to their favorable properties, such as light-absorbance, antisepsis, and cross-linkability, organic corrosion inhibitors (OCIs) are widely used in indoor environments, such as in coatings and paint for furniture, floors, walls, doors, and windows. For example, 1,2,3benzotriazole and its derivatives (BTRs) can retard the corrosion of metal surfaces by forming metal-BTR complexes.5 Benzothiazole and its derivatives (BTHs) are used in rubber products to accelerate the vulcanization of rubbers and to enhance mechanical strength and abrasion resistance.6 Some benzophenone derivatives (BPs),7 as well as some phenolic BTRs, are efficient UV light filters and are widely used in plastics and other polymeric materials. Some OCIs are high- production © 2013 American Chemical Society
volume chemicals. For example, at least 9000 tons of BTRs were produced in the U.S. in 1999, and a much greater production volume was expected in recent years.8 Production of benzothiazole (BTH) was reported to be in the range of 4.5−450 tons in 19939 and, of benzophenone (BP), was 136−1360 tons in 1983 in the U.S.10 Production capacity of BPs in China by ChangfengChem, the world’s largest manufacturer of this chemical, was reported to be 4000 tons per year.11 The acute toxicities of BTRs, BTHs, and BPs were reported to be low.12−14 However, various adverse effects from chronic exposure to these compounds have been reported.15 Mutagenicity and estrogenic potential of 1-H-BTR have been reported in bacteria and aquatic organisms.16,17 1-H-BTR and Received: Revised: Accepted: Published: 4752
December 6, 2012 March 28, 2013 April 1, 2013 April 1, 2013 dx.doi.org/10.1021/es305000d | Environ. Sci. Technol. 2013, 47, 4752−4759
Environmental Science & Technology
Article
tolyltriazole (TTR, a mixture of isomers of 4-methyl-1-H-BTR and 5-methyl-1-H-BTR) were phytotoxic.16,18 1-H-BTR has been classified as a suspected human carcinogen by the Dutch Expert Committee on Occupational Standards.16 BTHs were reported to be dermal sensitizers19 and respiratory tract irritants.20 Mutagenicity and carcinogenicity of BTHs were shown in microorganisms21 and in human epidemiological investigations.22,23 BTH was reported to occur in human thrombogenic coronary plaques.24 For BPs, carcinogenicity in mice25 and estrogenic and androgenic activity in human cell lines have been documented.26,27 Although the occurrence of BTRs, BTHs, and BPs in wastewater treatment plants (WWTPs) and aquatic environments was known for some time,28−30 knowledge of their exposure in humans is limited. Considering the wide range of applications of BTRs, BTHs, and BPs in consumer products and the potential for adverse health effects from exposure, it is important to examine the sources of these chemicals in indoor environments. Indoor dust is a relevant matrix used to monitor for contamination in the indoor environments; it also has been used to assess human exposure to many environmental chemicals.31 However, studies on the occurrence of BTHs and BPs in indoor dust are scant. Two studies have reported the occurrence of phenolic BTRs in indoor dust from Spain and the Philippines.32,33 In this study, we determined the concentrations of five BTRs (viz., 1-H-BTR, 1-OH-BTR, TTR, 5-Cl-BTR, and 5,6-dimethyl1-H-BTR [5,6-2Me-BTR]), five BTHs (i.e., BTH, 2-OH-BTH, 2-methylthio-BTH [2-MeS-BTH], 2-NH2-BTH, 2-thiocyanomethylthio-BTH [2-SCNMeS-BTH]), and four BPs (2-OH-4methoxy-BP (2-OH-4-MeO-BP), 2,4-2OH-BP, 22′-2OH-4MeO-BP, 22′44′-4OH-BP) and their degradation product, 4-OH-BP, in 158 indoor dust samples collected from the U.S., China, Japan, and Korea. The objectives of this study were (i) to examine the occurrence of BTRs, BTHs, and BPs in indoor dust; (ii) to elucidate the profiles and sources of OCIs in indoor dust from rural and urban homes; and (iii) to assess the magnitude of human exposure to BTRs, BTHs, and BPs through the ingestion of indoor dust.
Figure 1. Molecular structures of target analytes (BTR: benzotriazole; BTH: benzothiazole; BP: benzophenone).
analytes and internal standards were prepared at 1 mg/mL in methanol and stored at −20 °C. Sample Collection. In total, 158 indoor dust samples were collected from 14 cities in four countries, including Albany (U.S., 2006, n = 26, and 2010, n = 14), Beijing, Jinan, Guangzhou, Shanghai, Qiqihaer, and Urumchi (China, 2010, n = 55), Ansan and Anyang (Korea, 2012, n = 41), and Kumamoto, Nagasaki, Fukuoka, Saitama, and Saga (Japan, 2012, n = 22) between 2006 and 2012. Indoor dust samples from the U.S., Japan, and Korea were collected mainly from homes in urban locations using a vacuum cleaner, whereas samples from China were collected from urban homes (n = 38), offices (n = 12), and rural homes (n = 5) by sweeping the floor directly. All dust samples were sieved and homogenized by passage through a 2 mm sieve (U.S. Std. No. 10, Fisher Science Company, Suwanee, GA). Sample Preparation. Dust samples were extracted by a mixture of methanol/Milli-Q water and purified by solid phase extraction (SPE) cartridges, as described earlier.34 In brief, dust samples (50−100 mg) were accurately weighed and spiked with d4-1-H-BTR (10 ng) and 13C12-BP-3 (10 ng), and equilibrated at room temperature for 30 min. Then, a methanol/Milli-Q water mixture (5:3, v/v) was added, and the samples were shaken in an oscillator shaker (Eberbach Corp., Ann Arbor, MI) for 60 min. The mixture was centrifuged at 4500g for 5 min (Eppendorf Centrifuge 5804, Hamburg, Germany), and the supernatant was transferred into a glass tube. The samples were extracted twice with 5 + 3 mL of a methanol/Milli-Q
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MATERIALS AND METHODS Chemicals. Analytical standards of 1-H-BTR (99%), BTH (97%), and 2-OH-BTH (98%) were purchased from Alfa Aesar GmbH & Co KG (Karlsruhe, Germany). 5-Me-1H-BTR (98%), 5,6-2Me-1-H-BTR hydrate (99%) and 2-NH2-BTH (97%) were purchased from Acros Organics (Morris Plains, NJ). 2-SCNMeS-BTH (100%) was purchased from AccuStandard (New Haven, CT). 1-OH-BTR hydrate (≥98%), 2-Me-S-BTH (97%), 4-Me-1H-BTR (≥90%), 5-Cl-1-H-BTR (99%), 2-OH-4MeO-BP (98%), 2,4-2OH-BP(99%), 2,2′-2OH-4-MeO-BP (98%), 2,2′,4,4′-4OH-BP (97%), 4-OH-BP (98%), and d4-1-H-benzotriazole (D4-1-H-BTR; 100%) were purchased from Sigma-Aldrich (St. Louis, MO). 13C- labeled 2-hydroxy-4methoxybenzophenone (13C12-2-OH-4-MeO-BP) (99%) was purchased from Cambridge Isotope Laboratories (Andover, MA). The molecular structures and selected physicochemical properties of the target analytes are shown in Figure 1 and Supporting Information (SI) Table S1. Formic acid (98.2%) and methanol (HPLC grade) were purchased from Sigma-Aldrich and Mallinckrodt Baker (Phillipsburg, NJ), respectively. Milli-Q water was prepared using an ultrapure water system (Barnstead International, Dubuque, IA). The stock solutions of target 4753
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collected from China. However, the highest concentrations of ∑BTRs were found in some dust samples from China, with a maximum concentration of ∼2000 ng/g. The distribution of five BTRs in dust varied among the four countries studied (Figure 2). Dust samples from the U.S. contained TTR as the major derivative, with a detection rate (DR) of 92.5%, which accounted for 85% of ∑BTR concentrations (median concentration 26.8 ng/g). 5-Cl-BTR also was detected frequently in indoor dust from the U.S. (DR = 90%), with a median concentration of 4.58 ng/g, which accounted for 15% of ∑BTRs. Similar to that found for indoor dust from the U.S., TTR and 5-Cl-BTR were frequently found in dust samples from Japan and Korea, with median concentrations ranging from 10 to 40 ng/g. TTR accounted for ∼60% of ∑BTR concentrations for these two countries. Elevated levels of TTR, 100−1000 ng/g, were found in a few dust samples from Japan and Korea. A relatively high median concentration (15.8 ng/g) and detection rate (95.1%) of 1HBTR were found in dust from Korea, which accounted for 24% of ∑BTRs. 1H-BTR was the major BTR detected in dust from China, accounting for 43% of ∑BTR concentrations. Concentrations of TTR and 5-Cl-BTR in dust from China were lower than those found in the other three countries (p < 0.005, one-way ANOVA), with median concentrations of ∼5 and ∼1 ng/g, respectively. It should be noted that 1-OH-BTR was frequently detected (DR > 96%) in dust from China, with median concentrations higher than in the other three countries. Although 1-OH-BTR is used in industrial applications such as improving the yields in peptide syntheses using a racemization suppressor, or as a mediator in pulp bleaching to decrease the amount of bleaching chemicals,36 occurrence of notable concentrations of 1-OH-BTR in indoor dust from China suggests the need for further studies on the sources of this compound in indoor environments. Concentration and Distribution of BTHs. Remarkable concentrations of BTHs were found in indoor dust samples, especially those from Korea and the U.S., with a median C∑BTHs of 2000 and 1290 ng/g, respectively (Table 1). The median C∑BTHs in indoor dust from China and Japan were 857 and 605 ng/g, respectively. Among the five BTH derivatives analyzed, BTH is the largest production volume chemical and is used in the vulcanization of rubber. The concentrations of 2-OH-BTH were high in indoor dust from the U.S. and Korea, and this compound accounted for ∼95% of ∑BTH concentrations (Figure 2). The elevated proportion of 2-OH-BTH in ∑BTH concentration was thought to arise from the hydroxylation of BTH used in tires. As mentioned above, BTH and its derivatives are used in rubber to increase the mechanical strength of rubber by retarding abrasion. An earlier study reported the concentration of BTH in tire particles at 120−170 μg/g and a much lower concentration of BTH derivatives, including 2-OHBTH.13 A high concentration of BTH (0.3 μg/m3) also was reported in air from a waste incineration plant.37 2-OH-BTH has been identified as the primary oxidation product of BTH.38 Therefore, transformation of BTH to 2-OH-BTH is expected to occur during the incineration of rubber products, as a great proportion of scrap tires are incinerated for fuel in the U.S. and other countries. To provide further evidence of the formation of 2-OH-BTH from car tire rubber particles, we performed a laboratory test by heating a car tire at 200 °C for 60 min. The proportion of 2-OH-BTH increased during the heating of the rubber. The ratio of 2-OH-BTH/BTH in heated rubber (1:1.5) was 4-fold higher than that in nonheated rubber (1:6)
water mixture, and the combined extracts were concentrated to ∼4 mL under a gentle nitrogen stream and then diluted to 10 mL with Milli-Q water containing 0.2% formic acid (pH 2.5). The diluted extract was purified by passage through Oasis MCX cartridges (60 mg/3 cm3; Waters, Milford, MA), as follows: conditioning of cartridges with 5 mL of methanol and 5 mL of Milli-Q water, loading of sample extract (10 mL), cleaning of samples by passage of 15 mL of methanol/Milli-Q water (20:80, v/v) and 5 mL of Milli-Q water, drying of cartridges by a gentle nitrogen stream, and elution of target analytes with 5 mL of methanol. After concentration to 1 mL under a gentle nitrogen stream, the extract was analyzed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Chemical Analysis. Separation and detection of target analytes were accomplished with an Agilent 1100 Series HPLC (Agilent Technologies Inc., Santa Clara, CA), interfaced with an Applied Biosystems API 2000 electrospray triple quadrupole mass spectrometer (ESI-MS/MS; Applied Biosystems, Foster City, CA). Ten microliters of the extract were injected onto an analytical column (Betasil C18, 100 × 2.1 mm column; Thermo Electron Corporation, Waltham, MA), which was connected to a Javelin guard column (Betasil C18, 20 × 2.1 mm column; Thermo Electron Corporation). The mobile phase comprised 100% methanol (A) and 10% methanol in Milli-Q water that contained 2 mM of ammonium acetate (B). Two different gradient elutions at a flow rate of 200 μL/min were used for the analysis of BTRs/BTHs and BPs (SI Table S2). The MS/MS was operated in multiple reaction monitoring (MRM), and in positive and negative ion modes for BTRs/BTHs and BPs, respectively. The MS/MS parameters were optimized as described earlier28,35 and are shown in SI Table S3. Quality Assurance and Quality Control (QA/QC). Contamination arising from laboratory materials and solvents was evaluated by the analysis of procedural blanks. Recoveries of target analytes in spiked procedural blanks ranged from 47% to 95% (SI Table S4). Recoveries of all target analytes in spiked matrices, corrected for internal standard recoveries, ranged from 44% to 113% (SI Table S4). Quantification of BTRs, BTHs, and BPs was performed by an isotope-dilution method based on the responses of d4-1-H-BTR (for BTRs) and 13C12-2OH-4-MeO-BP (in the positive ion mode for BTHs and in the negative ion mode for BPs). The limits of quantification (LOQs) were 0.5 ng/g for all BTRs as well as BTH, 2-OHBTH, 2-NH2-BTH, and 2-OH-4-MeO-BP; 1.0 ng/g for 2-MeS-BTH, 2-SCNMeS-BTH, and 22′44′-4OH-BP; and 0.3 ng/g for 4-OH-BP, 2,4-2OH-BP, and 22′-2OH-4-MeO-BP. A calibration standard and methanol were injected after every 20 samples to check the drift in instrumental sensitivity and carry-over of target analytes between samples, respectively. Instrumental calibration was verified by the injection of 10 calibration standards (at concentrations ranging from 0.05 to 50 ng/mL), and the regression coefficients (R) of all calibration curves were ≥0.99.
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RESULTS AND DISCUSSION Concentration and Distribution of BTRs. BTRs were detected in all 158 indoor dust samples, and their concentrations and profiles varied among the four countries studied (Table 1). High median concentration of the sum of 5 BTRs in dust (median C∑BTRs) was found in samples from Korea, with a value of 87.1 ng/g, followed by those from the U.S. (Albany, NY) (36.2 ng/g) and Japan (33.7 ng/g). The lowest median C∑BTRs, 19.3 ng/g, was observed in samples 4754
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36.2 2.01−186
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a
DR: detection rate.
Korea (n = 41) median 15.8
