Determination of organophosphate ester flame retardants in indoor dust and their potential health exposure risk

Cite this paper: Vietnam J. Chem., 2020, 58(6), 723-730 Article DOI: 10.1002/vjch.202000039 723 Wiley Online Library © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH Determination of organophosphate ester flame retardants in indoor dust and their potential health exposure risk Trinh Thu Ha 1 , Nguyen Duc Cuong 2 , Le Thi Huyen 3 , Le Truong Giang 1* 1 Institute of Chemistry, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi 10000, Viet Nam 2 Key Laboratory Research on Dioxin, Center for Research and Technology Transfer, 18 Hoang Quoc Viet, Cau Giay, Hanoi 10000, Viet Nam 3 Department of Energy and Environmental, Faculty of Environmental engineering, National University of Civil Engineering, 55 Giai Phong, Hai Ba Trung, Hanoi 10000, Viet Nam Submitted March 19, 2020; Accepted August 18, 2020 Abstract This study was conducted to determine organophosphate ester compounds in indoor dust in Hanoi - a populated city in Vietnam. In the study, the concentration and distribution of fifteen organophosphate esters (OPEs) were analyzed in indoor dust specimen. In general, the recorded total concentrations of OPEs in dust ranged from 2.7 to 14.1 g/g and the average quantities varied from 0.2 to 1.0 g/g. Particular, 100 % of survey samples were detected signals of OPEs, indeed, tris-(2-chloroisopropyl) phosphate (TCPP) and tris(2-butoxyethyl)phosphate (TBEP) were two of the OPE substances, which their content accounted for the most in 15 analyzed compounds. OPE emission sources in indoor dust could be from locally used wide variety of consumer products and building materials in Hanoi houses. Moreover, tri-m- cresyl phosphate (TMCP) was practically observed in survey dust samples, and thus effects of traffic activities on OPEs contamination were not significant. Estimating human exposure to OPEs through directly absorbing foods was implemented and illustrated that this absorption route did not substantially affected adult and children health. Keywords. Organophosphate ester flame retardant, dust, Hanoi, human health risk assessment. 1. INTRODUCTION Organophosphate ester (OPE), whichis a group of chemicals possessing basic structure of ester phosphatehosphate, has been intensively used in daily life. [1] Such compounds are usually added to commercial materials or possibly used as additives to adjust physical properties of materials that manufacturers orient. [2] While OPE compounds are not halogenized and utilized as plasticers, stabilizers, flotation frontiers as well as wetting agents, they are primarily applied for fireproof materials because of abilities to constrain or slow down ignition process of materials. [3,4] Most OPE substances are appended to materials by physical methods and not formed any chemical bonds to material substrates, and thus these compounds readily dispersed into the environment through evaporation, physical abrasion and dilution. [1,5] This leads to gradually popular existence of the OPE compounds in the environment, foods, outdoor and indoor air, dust, etc. [6-8] Because of this, human health are easily influenced bysuch compounds through gastrointestinal exposure (food), respiration (air, dust) as well as skin exposure (air, personal health care products). [9,10] Studies related to toxicity of OPE substances on animals and human proved that such compounds easily have adverse impacts on human health. [11,12] Particularly, numerous research studies demonstrated that OPEs were contributing factor bringing about cancer in human, genetic changes, cardiac toxicity, dermatitis and reproductive dysfunction. [2,13-15] In vitro and in vivo investigations were conducted and manifested that when being absorbed into living organisms, OPE compounds were easily decomposed into metabolites through several processes such as O- dealkylation, hydroxylation, carboxylation, and oxidative dehalogenation (only for ClOPEs) forming major by-products like diester phosphatesand hyfrolated (OHOPE).[16] Because high water solubility, these compounds were excreted from the body through metabolism. [17] Diester phosphates were often detected in biological studies associated with Vietnam Journal of Chemistry Le Truong Giang et al. © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 724 human as well as objects used to assess OPE exposure in occupational workers and the general population. [18-20] Indoor dust has been subject to frequent research studies and a pivotal contacting source of OPE in house. In comparison with exposure through dietary and inhalation, absorbing indoor dust was considered as a major exposure process of OPE for human because 1) houses, where people work and live, are equipped with furniture and a variety of electric/electrical appliances containing halogenated OPE compounds; and 2) FR is possibly emitted from devices through evaporation or abrasion during use. [21] Organophosphate flame retardants (OPFR) and replacement brominated flame retardants (RBFR) are ubiquitous in indoor dust during the polybrominated diphenyl ether (PBDE) phase-out, and recent investigations reported significantly high concentrations of OPE compounds in indoor dust. [22,23] Two novel OPE groups owning structures similar to TPHP, triarylphosphate and stearyl phosphate (ITP and TBTPP) were detected in 100 % of indoor dust in Guangzhou (China) and Carbondale (USA). Although levels of ΣITP and ΣTBTPP are often ten times higher than that of TPHP in one dust sample, the widespread presence of these isomers in dust at two locations conceivably propound their extensive applications in household products. [23] In this study, we developed a method to determine 15 OPE compounds presenting in dust samples by using gas chromatography coupled with mass spectrometry detector. The OPE substances including tris-(2-chloroisopropyl) phosphate (TCPP) (mixture of 3 isomers); triethyl phosphate (TEP); tributylphosphate (TBP); tris(2- chloroethyl)phosphate (TCEP); triphenylphosphate (TPP); tris(2,3-dichloropropyl)phosphate (TDCPP); tris(2-butoxyethyl)phosphate (TBEP); 2-Ethylhexyl diphenyl phosphate (EHDPP), tris(2-ethylhexyl) phosphate (TEHP); tri-o-cresyl phosphate (TOCP) ; tri-m-cresyl phosphate (TMCP); tri-p-cresyl phosphate (TPCP); dibutyl phenyl phosphate (DBPP) were analyzed in 10dust samples (n = 10) in Hanoi, Vietnam. The primary purposes of this study comprise 1) analyzing concentration as well as assessing existence of these compounds in n = 10 dust indoor samples collected in a number of areas (consisting of houses, hair salons and 2) estimating risks of OPE exposure through inhaling dust containing OPE. 2. MATERIALS AND METHODS 2.1. Apparatus and chemical Fifteen OPE standards include tris(2- chloroisopropyl) phosphate (TCPP) (mixture of 3 isomers); triethyl phosphate (TEP); tributylphosphate (TBP); tris(2- chloroethyl)phosphate (TCEP); triphenylphosphate (TPP); tris(2,3-dichloropropyl)phosphate (TDCPP); tris(2-butoxyethyl)phosphate (TBEP); 2-ethylhexyl diphenyl phosphate (EHDPP), tris(2-ethylhexyl) phosphate (TEHP); tri-o-cresyl phosphate (TOCP); tri-m-cresyl phosphate (TMCP) and tri-p-cresyl phosphate (TPCP) were obtained from Sigma- Aldrich (St Louis, MO, USA). Isotope compounds were obtained from Cambridge Isotope Laboratories, Inc (Tewksbury, MA, USA), including the internal standards: tris(2-chloroethyl)phosphate- D12 and triethyl phosphate-D15 surrogate. Solvents used during analysis were all of analytical grade: acetone, n-hexane, dichloromethane (DCM), ethyl acetate (EtOAc) and methanol (MeOH) were purchased from Fisher chemical (Pittsburgh, PA, USA). 2.2. Experimental condition In this study, GC-MS/MS provided fromThermo Scientific (Waltham, MA, USA) was used to quantify OPE consisting of a Trace 1310 gas chromatographand TSQ 9000 mass spectrometer (Thermo, Waltham, MA, USA). A TG-5MS (30 m  0.25 mm, 0.25 m) gas chromatography column was used to separate OPEs (Thermo, MA, USA). Temperature protocol was established as follows: the initial temperature was 70 C and kept in 1 min, and then the temperature was increased linearly 15 C/min to 280 C, and subsequently the temperature was increased linearly 5 C/min to 300 C and the last temperature was kept in 2 mins. Helium and argon gas were utilized as carrier and collision gas, with the rate of 1.2 mL/min and 1 mL/min, respectively. The injection volume was 1 L, with splitless mode. The GC was interfaced by a heated transfer liner (300 C) to the mass spectrometer in electron ionization mode with an electron energy of 70 eV. 2.3. Sample collection Indoor dust samples were collected in one room after setting up a dust sampling device installed complete sampling parameters. The dust sampling method, in this study, was manipulated based on the research study of Van den Eeden et al. [24] Such samples were primarily handled in numerous sites such as floor of other rooms, bedroom and surfaces Vietnam Journal of Chemistry Determination oforganophosphate ester flame © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 725 of furniture decorations. After being collected, the samples were folded with aluminum paper and concealed by plastic bags. Before analysis, these samples were sieve by a sieve 250 m and stored at 20 C. The dust specimens were collected in a variety of districts in Hanoi comprising Long Bien (2 samples), Cau Giay (3 samples), Thanh Xuan (2 samples) and Ha Dong District (3 samples). 2.4. Sample preparation A procedure of extracting and cleaning dust samples was carried out based on the study of Van den Eede et al. with a few suitable adjustments. [25] A sample after being preliminarily treated was prepared according to the following process: Approximately 1 g of the sample was transferred into a 50 mL centrifuged tube. After that, 20 mL organic solvent mixture including dichloromethane:n- hexane:acetone with the volume ratio 3:1:1 (v/v/v) was added to the sample. The tube was shaken in 3 mins. Then, the sample was stabilized in darkness for 15 mins for equilibrium. Next, the sample was sonicated at 40 o C and the frequency of 50 kHz for 5 mins and vortexed for 1 min at the rate of 240 rpm. Subsequently, the sample was centrifuged at the rate of 3000 rpm for 10 mins. The above solution in the tube was transferred to another glass tube and the procedure was repeated 3 times. The obtained extract was concentrated by flowing N2 and taken to 1 mL with n-hexane. The extract was loaded through a solid phase extraction cartridge ENVI-Florisil respectively activated with 8 mL MeOH and 3 mL n-hexane, and 3 mL n-hexane was used as the cleaning solvent. After being cleaned, 10 mL EtOAcwas utilized as the elution solvent. The eluted extract was evaporated to dryness with N2 gas and re-dissolved with 0.2 mL n-hexane. 100 ng internal standard was added to the sample before analyzing by GC-MS/MS. 2.5. Method validation A standard addition was carried out at a concentration of 1 g/kg in 3 blank samples (NaCl) to determine limit of detection as well as repeatability of the method. To achieve median reproducibility additional spiking at 5 and 10 of duplicate samples in three series was included. The recovery is calculated through standard addition method with the concentration of 10 μg/kg (n = 6). The LOD was calculated as three times of the standard deviation on the calculated amount in each of the spiked samples 2.6. Health risk assessment In this study, we rudimentarily assessed risks of OPE exposure to human health via indoor dust ingestion and estimated human daily absorbed OPE concentration with the help of the previously studied equation, [24,26] which did not take into account of other exposure routes such as inhalation, food intake as well as dermal permeation. [21] The equation was used to estimate as follows: Exposure dose (ng/body weight/d) = C  Ddust  IR/Body weight In this equation, C (ng/kg) is measurable concentration of an individual OPE in one indoor dust sample, Ddust is the daily amount of dust and IR is the rate of dust absorption. We assume that the quantity of OPE is 100 % absorbed by ingestion, and mean dust ingestion rates of 20 and 50 mg/day and the high dust ingestion rates of 50 and 200 mg/day were used for adults and children, respectively. [24] The average weight of the selected adults and children in this calculation was 63 and 13.8 kg. [27] The hazard index values, the ratio of daily intake of OPEs to its corresponding reference dose, were calculated based on the estimates exposure dose. [25] 3. RESULTS AND DISCUSSION 3.1. Method validation Limit of detection (LOD) and limit of quantification (LOQ) of 15 OPE compounds varied from 0.01 to 0.05 g/L and 0.03 to 0.15 g/L, respectively. The method attained high reproducibility and repeatability because the relative standard deviations (RSDr) and relative standard deviation (RSDR) value ranged from 5 to 20 %, the LOD should be lower than 0.3 μg/L. 3.2. OPE concentration in indoor dust sample The appearance and distribution of OPE compounds in collected dust samples in this study are demonstrated in figure 1. From figure 1, 100 % of the dust samples collected in this study detected OPE compounds, which concentrations varied from 0.011 g/g to 7.250 g/g. Therein, the substances such as TCEP, TCPP1, TCPP2, TPP, EHDP and TOCP were detected in all of the samples, amounting to 100 % of the samples. In general, the content distribution of OPE analytes was relatively uneven and concentrated in a few typical OPEs. Particularly, TCPP3, TBEP and TCPP2 were OPEs detected in comparatively high quantities. The mean, Vietnam Journal of Chemistry Le Truong Giang et al. © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 726 medium and the highest values of TCPP3 were 2.689 g/g, 2.442 g/g and 7.250 g/g, those of TBEP were 2.456 g/g, 2.912 g/g and 4.201 g/g and those of TCPP2 were 0.718 g/g, 0.717 g/g and 1.780 g/g. TCPP1, TDCPP and TPP were 3 OPEs containing relatively high concentrations, which the means were 0.495 g/g, 0.287 g/g and 0.418 g/g, respectively. Depending on different substituents in the structure, all over the world, more than 10 OPEs are being used and discovered in the environment. In this study, only TCPP was not completely recorded in the survey dust samples. The average concentration of TBEP in this study was 2.456 g/g, which was 6 times higher than other studies observing TBEP in indoor dust samples in Guangzhou, Saudi Arabia and Germany. In contrast, numerous studies have manifested that TBEP content in indoor dust samples was significantly high in Beijing (8.554 g/g), Kuwait (10.685 g/g), Norway (12.8 g/g), Sweden (5.7 g/g) and USA (11.0 g/g).[26,28,29] For this reason, the quantity of TBEP noticed in this study were low compared to other locations in the world. Likewise, the average TCPP content in this study was 2.689 times lower than that in the study of Zeng et al. (5.474 g/g) recorded in Wuhan City. [30] Figure 1: OPEs content in indoor dust in Hanoi As mentioned above, OPEs are discovered everywhere in indoor dust around the world because their consumption has been increasing when PBDEs has gradually eliminated. This increasing leads to serious concerns related to indoor environmental pollution owning to negatively potential effects of OPEs on human health. Although the contents of OPEs were detected in this study were lower than those in other investigations around the world, the study illustrated a comprehensive perspective of the contamination of OPEs containing in indoor dust as well as provided important documents associated with evaluating risks to human health. 3.3. Composition profile of OPs in indoor dust Figure 2a describes the distribution of OPEs presenting in dust samples in different survey locations. By collecting the samples from different areas in Hanoi such as Long Bien (N1, N2), Cau Giay (N3, N4, N5), Thanh Xuan (N6, N7) and Ha Dong District (N8, N9, N10), OPE contamination in indoor dust was initially revealed. A similarity among survey locations was that TBEP and TCPP were the two types of OPEs accounting for high proportion of OPE pollution in indoor dust, which ranged from 27.0 % to 62.3 % and from 24.6 % to 63.9 %, respectively. Particularly, N3 was the location recording the highest TBEP concentration and N10 was the site noticing the highest TCPP content. The appearances of high concentration of TBEP and TCPP in indoor dust samples result from furniture items containing these substance. Specifically, TBEP are often used in wax materials coating floor surfaces as well as in the compositions of rubber buttons. [31] Meanswhile, TCPP is an Vietnam Journal of Chemistry Determination oforganophosphate ester flame © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 727 N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 0 20 40 60 80 100 D is tr ib u ti o n ( % ) Sample TPCP TMCP TOCP TEHP EHDP TBEP TPP TDCPP DBPP TCPP3 TCPP2 TCPP1 TCEP TBP N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 0 2 4 6 8 10 12 14 16 18 20 C o n ce n tr a ti o n (  g /g ) TPCP TMCP TOCP TEHP EHDP TBEP TPP TDCPP DBPP TCPP3 TCPP2 TCPP1 TCEP TBP TEP Sample indispendable component in PU paint coating used for wooden stuff. [1] In relation to N3 area, the sampling location in living room had wooden floor polished with wax. Regarding N10 site, there were numerous wooden furniture items coated with PU paint such as warbrobe, chair, altar, etc. Moreover, these two sampling areas have been pushed into use recently, and thus the furniture has been still adequately new. By constrast, the other areas had significantly lower and TCPP concentrations because these locations has been used for years as well as equipped with more modern ventilation systems than N3 and N10 areas. Conversely, TMCP, DBPP and TPCP compounds were virtually not detected in all of the survey places. The particularly notice OPEs such as TEP and TCEP lowly distributed in the samples. TEP are usually used in unsaturated polyester resins, cellulose acetate, PVC, numerous kinds of synthetic rubber while TCEP is often applied in flexible and rigid polyurethane foams. [32,33] The distribution ratio of TEP among the samples ranged from 0 to 6.7 % and that of TCEP varied from 0.5-6.2 %.TEP and TCEP accounting for low proportion were possibly explained by the fact that the survey areas were mainly decorated with wooden ornaments as well as PE plastic items. [33] The distribution of EHDP and that of TEHP amounted to low proportions among the research samples (< 10 %). From figure 2b, the concentrations of OPEs collected in Hanoi were considerably different. The location recording the highest and lowest total content of OPEs were N8 (14.4 g/g) and N7 (2.7 g/g). The total concentration of OPEs at the survey sites ranged from 6 to 8 g/g. The high content of OPEs in indoor dust samples were recorded at the locations possessing similar peculiarities such as small ceiling are