Article Cite This: Environ. Sci. Technol. XXXX, XXX, XXX−XXX
pubs.acs.org/est
Tri(2,4-di‑t‑butylphenyl) Phosphate: A Previously Unrecognized, Abundant, Ubiquitous Pollutant in the Built and Natural Environment Marta Venier,†,* William A. Stubbings,† Jiehong Guo,† Kevin Romanak,† Linh V Nguyen,‡ Liisa Jantunen,§,∥ Lisa Melymuk,⊥ Victoria Arrandale,#,△ Miriam L. Diamond,∥,‡,# and Ronald A. Hites† †
School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana 47405, United States Department of Physical and Environmental Science, University of Toronto Scarborough, Toronto, Ontario M1C 1A4, Canada § Air Quality Processes Research Section, Environment and Climate Change Canada, Toronto, Ontario M3H 5T4, Canada ∥ Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S 3B1, Canada ⊥ Research Centre for Toxic Compounds in the Environment (RECETOX), Masaryk University, Kamenice 753/5, pavilion A29, 62500 Brno, Czech Republic # Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario M5G 1X3, Canada △ Occupational Cancer Research Centre, Cancer Care Ontario, Toronto, Ontario M5G 2L3, Canada
Environ. Sci. Technol. Downloaded from pubs.acs.org by RMIT UNIV on 10/31/18. For personal use only.
‡
S Supporting Information *
ABSTRACT: Using high-resolution mass spectrometry, we identified tri(2,4-di-t-butylphenyl) phosphate (TDTBPP) in e-waste dust. This is a previously unsuspected pollutant that had not been reported before in the environment. To assess its abundance in the environment, we measured its concentration in e-waste dust, house dust, sediment from the Chicago Ship and Sanitary Canal, Indiana Harbor water filters, and filters from high-volume air samplers deployed in Chicago, IL. To provide a context for interpreting these quantitative results, we also measured the concentrations of triphenyl phosphate (TPhP), a structurally similar compound, in these samples. Median concentrations of TDTBPP and TPhP were 14 400 and 41 500 ng/g, respectively, in e-waste dust and 4900 and 2100 ng/g, respectively, in house dust. TDTBPP was detected in sediment, water, and air with median concentrations of 527 ng/g, 3700 pg/L, and 149 pg/m3, respectively. TDTBPP concentrations were generally higher or comparable to those of TPhP in all media analyzed, except for the e-waste dust. Exposure from dust ingestion and dermal absorption in the e-waste recycling facility and in homes was calculated. TDTBPP exposure was 571 ng/kg bw/day in the ewaste recycling facility (pro-rated for an 8-h shift), and 536 ng/kg bw and 7550 ng/kg bw/day for adults and toddlers, respectively, in residential environments.
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INTRODUCTION
Information on the production, use, and applications of these chemicals is not public; thus, new environmental pollutants are often discovered in the environment or in consumer products by chemists using nontargeted screening methods.1,2 Once the identifications are known, data on the compound’s presence in the natural and built environments begins to appear in the scientific literature, which in turn triggers studies to assess the compound’s toxicity. For example, in 2008, Stapleton et al.3 identified two previously undetected
Many common, commercial chemicals have been used for decades, but they have escaped the attention of environmental chemists. In the 1970s, when the U.S. Toxic Substances Control Act (TSCA) was passed, over 85 000 chemicals were “grandfathered in”. This meant that they were not subject to regulatory scrutiny and, unless they were going to be used for new purposes, no further information on them was required. Because of this regulatory approach, a large number of consumer products contain chemicals about which we have little knowledge concerning their chemical properties, environmental fates, or toxicities. Eventually, many of these chemicals leak into the environment and, in some cases, are bioaccumulated throughout the food web. © XXXX American Chemical Society
Received: May 31, 2018 Revised: September 24, 2018 Accepted: October 6, 2018
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DOI: 10.1021/acs.est.8b02939 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Environmental Science & Technology flame retardants, 2-ethylhexyl tetrabromobenzoate and bis(2ethylhexyl) tetrabromophthalate in house dust samples from the greater Boston, MA, area. These compounds are the brominated components of FireMaster 550, a commercial mixture presumed to be used as a replacement for polybrominated diphenyl ethers. Over the next 10 years, numerous studies were published reporting on the presence of these two alternative flame retardants in the environment and in humans, as well as on their biological effects. These and other flame retardants are widely used in plastics, casings, wires, and printed circuit boards used in electrical and electronic equipment, where they are applied at weight percent levels.4,5 Most of these products are recycled as e-waste, which turns out to be a good media in which to look for previously unidentified pollutants. In fact, during the analysis of dust from an e-waste dismantling facility in Ontario, Canada, we previously identified 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5triazine (TTBP-TAZ); this was the first report of TTBP-TAZ in the North American environment.6 Here, we present the identification of a high molecular weight compound, tri(2,4-dit-butylphenyl) phosphate (TDTBPP), which we found in this e-waste dust for the first time, and we demonstrate that it is relatively abundant both in the natural and in the built environment. In particular, we report its concentrations in ambient air, water, and sediment from southwestern Lake Michigan and in e-waste and residential dust from Ontario, Canada. We also speculate on its sources relative to its production and use, and we provide some information on human exposure to TDTBPP from dust ingestion and dermal absorption.
treatment, and analysis can be found elsewhere7 and only a brief description is given here. After sampling, dust samples were transferred to precleaned vials and stored at −20 °C until chemical analysis. Before extraction, the dust samples were passed through a 500 μm sieve. About 100 mg of sieved dust was spiked with surrogate standards (d12-TCEP and MTPP), sonicated in 30 mL of a 1:1 (v/v) mixture of hexane and acetone, vortexed for 1 min, ultrasonicated for 5 min more, and centrifuged for 15 min; the supernatant was then decanted into a pear-shaped flask. The procedure was repeated two additional times, and the extracts were combined. Extracts were fractionated on a 3.5% (by weight) water deactivated silica gel column using 25 mL of hexane, 25 mL of 1:1 (v:v) hexane in dichloromethane, and 25 mL of 3:7 (v:v) dichloromethane in acetone as eluting solvents. Each fraction was then concentrated to 1 mL and spiked with known amounts of the internal standards. The analytes eluted in the second and third fractions. The Canadian residential dust samples (N = 20) were collected from 20 houses in Ontario, Canada in 2015. Dust was collected using a small vacuum cleaner (Omega HEPA Abatement, Atrix International, Burnsville, MN) with a polyester vacuum bag (25 μm pore size, 155 mm long, 73/ 38 mm o.d., Allied Filter Fabrics Pty Ltd., Australia). This bag was precleaned using accelerated solvent extraction with hexane at 90 °C for 4 cycles. The bag was attached to the front end of a cleaned vacuum hose (rinsed with isopropanol). The dust was sieved through a 150 μm sieve for 5 min. Precleaned anhydrous Na2SO4 was mixed with 0.100 g of the dust and with 3 mL of dichloromethane, spiked with surrogate standards (d12-TCEP and MTPP), vortexed for about 5 s, sonicated for 15 min, and centrifuged for 5 min at 2500 rpm for better separation. The extraction and separation procedure was repeated twice more. Extracts were combined and concentrated to about 0.2 mL; then, they were cleaned on a Florisil column (500 mg Florisil) on a Visiprep SPE vacuum manifold system (Supelco, St. Louis, MO). The Florisil columns had been cleaned and conditioned with 8 mL of methanol followed by 4 mL of hexane. After the samples had been loaded onto the columns, they were eluted with 10 mL of ethyl acetate followed by 3 mL of methanol. The eluent was concentrated, solvent exchanged to about 0.5 mL of isooctane, and spiked with the internal standards. The analytes eluted in the first fraction. The following outdoor samples were also analyzed: Atmospheric particles were collected on glass fiber filters in 2015 (N = 20) from an urban site in Chicago, IL, using a highvolume air sampler deployed as part of the Integrated Atmospheric Deposition Network (IADN).8 Surface sediment samples were collected in 2013 (N = 20) by a Ponar grab from the Chicago Ship and Sanitary Canal (CSSC).9 Particle phase water samples from the Indiana Harbor and Ship Canal (IHSC) were collected in 2015 (N = 9). Details on sample collection and analysis procedures for air, sediment, and water are reported elsewhere. The analytical details, such as surrogate and internal standards and instrument parameters, were the same as reported previously.10−12 Instrumental Analyses. TDTBPP, TDTBPPO, and TPhP were analyzed simultaneously at Indiana University in all samples. These compounds were quantitated on an Agilent 6890 series gas chromatograph (GC) coupled to an Agilent 5973 mass spectrometer (MS) operating in the electron impact (EI) mode using a RTX-OP-Pesticides-2 (30 m, 250 μm i.d.,
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MATERIAL AND METHODS Chemicals. Tri(2,4-di-t-butylphenyl) phosphate (TDTBPP, CAS no. 95906-11-9, 98% purity) was purchased from Santa Cruz Biotechnology (Dallas, TX). A related compound, tri(2,4-di-t-butylphenyl) phosphite (TDTBPPO, CAS no. 31570-04-4, 98% purity), was purchased from SigmaAldrich (St. Louis, MO). Triphenyl phosphate (TPhP, CAS no. 115-86-6; purity > 98%), perdeuterated tri(2-chloroethyl) phosphate (d12-TCEP, purity > 98%), and 13C18-triphenyl phosphate (MTPP, purity > 98%) were purchased from Wellington Laboratories (Guelph, ON, Canada). The internal standards, d10-anthracene, d12-dibenz[a]anthracene, and d12perylene, were obtained from Chem Service (West Chester, PA), and d10-fluoranthene was from Sigma-Aldrich. Silica gel (100−200 mesh, 75−150 μm, grade 644) and granular anhydrous sodium sulfate (Na2SO4) were purchased from Fisher Scientific (Pittsburgh, PA). Before use, Na2SO4 was heated at 500 °C for at least 8 h, and silica gel was heated at 300 °C for at least 12 h. All these sorbents were then cooled in a desiccator. Silica gel was deactivated with 3.5% water (by weight) 1 day before use. All solvents were HPLC or Optima grade. Sampling and Sample Treatment. The e-waste dust samples were collected from an e-waste dismantling facility in Ontario, Canada, in May, June, and September of 2016. Dust from the floor (N = 7), from the top of work benches where the dismantling took place (N = 8), and from the sorting bins (N = 9) was collected using a small vacuum cleaner (Sanitaire Professional, Peoria, IL) fitted with a precleaned polyester sock (25 μm pore size, 155 mm long, 73/38 mm o.d., Allied Filter Fabrics Pty Ltd., Australia) inserted at the end of the hose attachment. A detailed description of sample collection, B
DOI: 10.1021/acs.est.8b02939 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Environmental Science & Technology 0.25 μm film thickness) column (Restek Corporation, Bellefonte, CA). One microliter of the sample was injected in the pulsed splitless mode at 285 °C. The GC-MS interface was kept at 285 °C. Temperatures of the ion source and quadrupole region were set at 230 and 150 °C, respectively. High-purity helium (99.999%; Indiana Oxygen Co., Indianapolis, IN) was used as the carrier gas. The GC oven temperature was held at 50 °C for 3 min, increased to 100 °C at 20 °C/min, increased to 170 °C at 10 °C/min, held for 3 min, increased to 230 °C at 12 °C/min, held for 4 min, increased to 260 °C at 5 °C/min, increased to 300 °C at 10 °C/min, and held for 14 min. Compounds were quantitated by monitoring the following ions: TDTBPP (m/z 647), TDTBPPO (m/z 441 and 442), d12-TCEP (m/z 261 and 263), TPhP (m/z 326 and 325), 13C18-TPhP (m/z 343 and 344), d10-anthracene (m/z 188 and 189), d12-dibenz[a]anthracene (m/z 240 and 236), d10-fluoranthene (m/z 212), and d12-perylene (m/z 264). Full scan mass spectra were obtained on an Agilent 6890 series GC coupled to an Agilent 5973 MS operating in the (EI) mode. A Restek RTX-OP-Pesticides-2 (30 m, 250 μm i.d., 0.25 μm film thickness) column was used, and the mass spectrometer was scanned from m/z 50 to m/z 800. The oven temperature was held at 50 °C for 3 min, increased to 270 °C at 20 °C/min, increased to 300 °C at 5 °C/min, and held at 300 °C for 15 min. The temperatures of the ion source and quadrupole region were set at 230 and 150 °C, respectively. Two μL of the sample was injected in the pulsed splitless mode at 285 °C. The GC/MS transfer line was maintained at 300 °C. High purity helium (99.999%; Indiana Oxygen, Indianapolis, IN) was used as the carrier gas The TDTBPP standard and one e-waste dust sample were also analyzed on a MAT-95 XL magnetic sector highresolution mass spectrometer (Thermo Electron Corporation, Waltham, MA) in the electron impact mode (70 V electron energy). This instrument was operated at a mass resolution of 18 000. Aliquots of the sample were deposited onto a tungsten filament of the desorption chemical ionization probe and allowed to dry. The probe was inserted into the mass spectrometer, and the sample was held at 50 °C for 1 min, ramped to 500 °C over 14 min, and held at 500 °C for 2 min. No chromatographic separation was used. The spectra were internally calibrated with ions from super high boiling perfluorokerosene (TCI America, Portland, OR). Quality Control. Field blanks (N = 2 for e-waste dust, house dust, and air samples) and procedural blanks were processed and analyzed along with samples. Field blanks were precleaned polyester socks (for dust) or filters (for air), which had been exposed by unsealing the aluminum foil wrap during sample retrievals. Field blanks were not available for the sediment samples from the Chicago Ship and Sanitary Canal or for the samples from the Indiana Harbor water filters. In these cases, procedural blanks were analyzed instead. These procedural blanks consisted of combusted diatomaceous earth for sediments and of empty Soxhlet extractors for the water samples. All procedural blanks were treated the same as the field samples. Table S1 gives the field blank results. If the mass (in ng) of TDTBPP or TPhP in the samples was less than two times the mass in the average field or procedural blank for each specific matrix, two times the mass in the average blank was subtracted from the sample mass. TDTBPP was not detected in any of the procedural blanks. The average recoveries of the surrogate standards were within the U.S.
EPA acceptable range of 50−150%. Matrix spike experiments were conducted for TDTBPP using two methods: one employed Soxhlet extraction and was representative of the air, water, and sediment samples; the other employed sonication extraction and was representative of the dust samples. Recoveries were 129 ± 4% for the Soxhlet method (N = 3) and 99 ± 6% for the sonication method (N = 3). Details of these experiments are given in Table S2. Data Analysis. Individual concentrations are reported in Table S3. Descriptive statistical analyses were done with Microsoft Excel 2016. One-way analyses of variance (ANOVA) for the comparison of logarithmically transformed chemical concentrations were done in Minitab 17 (State College, PA). Results were considered statistically significant at the 95% confidence interval (P < 0.05).
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RESULTS AND DISCUSSION Structure Identification. Because of the relatively high abundance of many compounds, e-waste dust is a particularly rich media in which to search for untargeted pollutants. Thus, we screened a few of our samples using electron impact high resolution mass spectrometry (EI-MS) and noticed two ion clusters at m/z 647.4260 and 662.4536 (see Figure 1, top).
Figure 1. High-resolution and low-resolution electron impact mass spectra of a dust sample from an e-waste facility in Ontario, Canada, and of authentic TDTBPP from Santa Cruz Biotechnology. The m/z value for the most abundant ion in each cluster is labeled along with our structural assignments. The high-resolution data cover only the mass range 600−680. The structural assignment of the ion at m/z 316 is tentative.
The nominal molecular weight of this unknown compound was apparently 662, and the isotopic spacings and patterns of both of these ions clearly indicated the absence of chlorine or bromine. The difference between m/z 662 and 647 indicated that the molecule had at least one easily lost methyl group. The trick in converting an exact mass to an elemental composition is limiting the possible elements used in the calculation. In this case, the absence of halogens was clear. In addition, because samples from this facility had high levels of organophosphate esters, we hypothesized that this compound was also a phosphate ester. This suggested a limit for the elemental composition of C10−50H10−100O4P. Note that the “O4P” restricts the results to phosphate esters or their equivalent. An online calculation tool13 indicated that the elemental composition of m/z 662 was C42H63O4P (expected = 662.446, error = 11 ppm) and that m/z 647 was C41H60O4P (expected = 647.423, error = 5 ppm). In addition, the expected isotopic patterns of these two compositions agreed with those of the C
DOI: 10.1021/acs.est.8b02939 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Figure 2. Structure, CAS registry number, elemental composition, and nominal molecular weight of TDTBPP, TPhP, and TDTBPPO.
Table 1. Number of Samples (n), Detection Frequency (df), Median, Minimum (min), and Maximum (max) Concentration in Ontario E-waste Dust (E-waste Dust, ng/g), Ontario House Dust (House Dust, ng/g), Sediment from the Chicago Ship and Sanitary Canal (Sediment, ng/g), Indiana Harbor Water Filters (Water, pg/L), and Atmospheric Particles from Chicago (Chicago Air, pg/m3) for TDTBPP and TPHP e-waste dust (ng/g) n df median min max
house dust (ng/g)
sediment (ng/g)
Chicago air (pg/m3)
water (pg/L)
TDTBPP
TPHP
TDTBPP
TPHP
TDTBPP
TPHP
TDTBPP
TPHP
TDTBPP
TPHP
24 100% 14 400 5700 40 300
24 100% 41 500 17 000 176 000
20 100% 4900 3200 37 200
20 100% 2100 374 45 000
20 100% 527 52 1200
18 90% 34.5 nd 438
9 100% 3700 1100 19 600
8 89% 89.5 nd 614
18 95% 149 nd 3400
19 100% 67.8 34.7 221
Figure 3. Box and whisker plots of concentrations of TDTBPP (red boxes) and TPHP (blue boxes) in (from left to right) Ontario e-waste dust, Ontario house dust, sediment from the Chicago Ship and Sanitary Canal, particles from water in the Indiana Harbor Canal, and atmospheric particles from Chicago. The concentration scales are the same for all plots, but note the different concentration units for each panel. Shown are the medians (black line inside the box), the 25th and 75th percentiles (top and bottom of the box), the 10th and 90th percentiles (whiskers), and the outliers (circles). Boxes not sharing a letter are significantly different at a 5% level in an ANOVA analysis using the Tukey’s test.
we abbreviate here as TDTBPP; see Figure 2 for its structure. SciFinder led to a paper14 that included the low resolution mass spectrum of this compound, and the ratio of m/z 662 to 647 in this published spectrum was a good match to our unknown. We purchased a standard of TDTBPP from Santa Cruz Biotechnology to confirm our hypothesis. Using low-resolution gas chromatographic mass spectrometry, we compared the GC and MS data of the authentic TDTBPP standard to the data from a typical e-waste dust sample. The gas chromatographic retention time and peak shape of authentic material exactly matched those of the compound in the e-waste dust sample, and the low resolution
unknown mass spectral data. The difference between these compositions corresponds to the loss of CH3, as anticipated. The hydrocarbon part of this composition, C42H63, is exactly divisible by 3, suggesting that the three ester groups are all C14H21. Thus, a partial structure of this compound was (C14H21O)3PO. But an elemental composition is not an identification. To identify this molecule, we searched the SciFinder database for all molecules with the elemental composition C42H63O4P. Eleven molecules were retrieved and sorted based on the total number of papers citing each particular structure. The most highly cited compound (with 218 citations) was tri(2,4-di-t-butylphenyl) phosphate, which D
DOI: 10.1021/acs.est.8b02939 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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median concentration of TPhP was 67.8 pg/m3. The atmospheric concentrations of TDTBPP and TPhP were statistically indistinguishable from each other (Figure 3). Taken as a whole, these data show that the concentrations of TDTBPP are similar to or higher than those of TPhP in the indoor dust samples and in the sediment, water, and atmospheric samples. Levels of TDTBPP in the environment are relatively high and cannot be dismissed. Additionally, we suggest that, despite being geographically limited, these results can be considered to be representative of northeastern North America. Production and Use. Very little information is available on the uses or applications of TDTBPP. Conversely, information abounds for tri(2,4-di t-butylphenyl) phosphite (TDTBPPO), the structure of which is given in Figure 2. This compound is known by numerous trade names including Irgafos 168, Hostanox PAR 24, Alcanox 240, and Ultranox 668, and it is widely used as an antioxidant for polyolefins, polyesters, acrylonitrile butadiene styrenes, polycarbonate fibers, polyester resins, engineering thermoplastics, and polyvinyl chloride.16 Its main purpose is to protect the plastic in which it is embedded from degradation during the extrusion process at high temperatures, during sterilization (when it is used in food packaging), and during the shelf life of the material.17 Most of the information on TDTBPP that is available online and in the peer-reviewed literature is related to the degradation of TDTBPPO to TDTBPP and the migration of TDTBPP from the plastic. TDTBPP and 2,4-di-t-butylphenol are TDTBPPO’s main degradation products. In fact, Simoneit et al.,14 who detected TDTBPP in various plastic products (i.e., plastic bags, roadside litter, and landfill garbage) at significant levels, prepared the standard for TDTBPP by oxidizing TDTBPPO with hydrogen peroxide. Yang et al.18 also showed that TDTBPP was the major degradation product of Irgafos 168 after extrusion, storage, and sunlight exposure. In other studies, TDTBPP was detected during a survey of chemical substances in children’s products, including baby carriers, air mattresses,19 and plastic baby bottles.20 TDTBPP was added to Canada’s Domestic Substance List in 2007. Both TDTBPP and TDTBPPO are listed in the U.S. EPA’s Toxic Substances Control Act (TSCA) inventory as compounds “active” in U.S. commerce.21 A premanufacture notice, or PMN, for TDTBPP was recorded on 15 January 2010 on the U.S. EPA Web site. The 2015 Chemical Data Reporting (CDR) national aggregate database showed annual production volumes in the range of 5000−25 000 tonnes for TDTBPPO, but there were no data for TDTBPP.22 We could find no information on the direct use of TDTBPP in commercial applications. Instead, other compounds with related structures were found: The first was tetra(2,4-di-tbutylphenyl)-4,4′-biphenyldiphosphonite (CAS no. 38613-773), which is the product of the reaction of phosphorus trichloride, biphenyl, and 2,4-di-t-butylphenol. It is sold under the trade names Irgafos P-EPQ, Irganox P-EPQ, or Hostanox P-EPQ, depending on manufacturer (Addivant, BASF, or Clariant). It is possible that TDTBPP is formed during the synthesis of this larger molecule. The second related compound is 2,4-di-t-butylphenol (CAS 96-76-4). This is a chemical that several companies report on the TSCA inventory (Addivant, BASF, ICL). This phenol is a reagent used in the production of various commercial antioxidant mixtures, and
electron impact mass spectrum of the authentic TDTBPP matched that from the dust sample (see Figure 1, middle and bottom). In addition, the ions in the high resolution data at m/ z 316.210 and 316.710 (perhaps, representing [M−2CH3]+2; expected = 316.200, error = 32 ppm; expected = 316.701, error = 28 ppm) were present at the same abundance in the low resolution mass spectra of authentic TDTBPP and in that of the e-waste dust sample. We consider this a confirmed identification. We then asked if this was a common environmental contaminant and measured its concentrations in various environmental media. E-waste Samples. After we identified this compound in one specific e-waste dust sample (not included here), we measured its concentrations in 24 e-waste dust samples. TDTBPP was detected in all these samples at a median concentration of 14 400 ng/g (range = 5700−40 300 ng/g); see Table 1 and Figure 3. To provide a context for interpreting these results, we also measured the concentrations of TPhP in these samples. We selected TPhP because it is a well-known and widely measured organophosphate pollutant, and its structure is similar to that of TDTBPP (see Figure 2). The median concentration of TPhP in the same e-waste samples was 41 500 ng/g (range = 17 000−176 000 ng/g) (see Table 1 and Figure 3). An ANOVA of these data showed that the concentrations of TPhP was significantly higher than those of TDTBPP. Levels of TPhP measured here were within the range reported for an e-waste dismantling facility in Guiyu, China (range = 370−330 000 ng/g).15 The median concentration of TPhP in the Ontario e-waste dust was about 3-fold higher than that of TDTBPP. These results suggest that TDTBPP and TPhP are both used in electrical and electronic products, but TPhP may be used in higher quantities or in more applications. Residential Dust. TDTBPP was detected in all 20 house dust samples at concentrations ranging from 3200 to 37 200 ng/g (see Table 1 and Figure 3). The median TDTBPP concentration was 4900 ng/g, which is about one-third its median concentration in the e-waste dust. The median TPhP concentration in the same residential dust samples was 2100 ng/g, which is roughly 20 times lower than its concentration in the e-waste dust. Differences in the grid size of the sieve between the e-waste dust and the residential dust experiments are not likely to have a significant impact on the measured concentration. The concentration of TPhP in house dust was similar to what we previously reported for house dust samples from 2013 in Toronto, Ontario, where the median was 2350 ng/g.7 The concentrations of TDTBPP in house dust samples reported here were significantly higher than those of TPhP, which is the opposite of what we observed for the e-waste samples. Outdoor Environment. TDTBPP was detected in all 20 of the sediment samples from the Chicago Ship and Sanitary Canal with a median concentration of 527 ng/g and a range of 52−1200 ng/g. The median concentration of TPhP in these sediment samples was significantly lower than that of TDTBPP at 34.5 ng/g; see Figure 3. TDTBPP was also detected in all of the aquatic suspended particle samples collected in 2015 from the Indiana Harbor with a median concentration of 3700 pg/L. In the same samples, the median concentration of TPhP was 89.5 pg/L, which was significantly lower than that of TDTBPP. The median concentration of TDTBPP in the particulate air samples from Chicago from 2015, was 149 pg/m3, and it was detected in 95% of the samples. In the same samples, the E
DOI: 10.1021/acs.est.8b02939 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Environmental Science & Technology
In residential environments, assuming a 22 h exposure, the TDTBPP exposure estimate for adults was 536 ng/kg bw/day, when using the median dust concentration, and 2170 ng/kg bw/day, when using the 95th percentile for dust concentration. We assumed that most people spend the majority of their time indoors somewhere (i.e., home, office, or work) and to account for sections of the population that work outside or spend significant amount of time outside, we pro-rated residential exposure to 22 h. TDTBPP exposure estimate for toddlers was 7550 ng/kg bw/day, when using the median dust concentration, and 30 610 ng/kg bw/day, when using the 95th percentile for dust concentration. The estimates for TDTBPP were higher than those for TPhP when using the median but lower when using the 95th percentile. Toddlers are expected to be exposed to significantly higher levels of TDTBPP than adults, as was previously shown for organophosphate esters25−27 and for brominated flame retardants based on biomonitoring results.28 These results should be interpreted cautiously since they rely on several assumptions, as described above. No systematic toxicity assessments are available for TDTBPP. Yang et al.18 reported that TDTBPP is classified as a Cramer III substance on the Cramer toxicity scale. According to the Cramer Rules Manual, “Class III substances are those that permit no strong initial presumption of safety or may even suggest significant toxicity or have reactive functional groups.”29 On the basis of this decision tree approach, TDTBPP’s maximum recommended value for human exposure is 90 μg/person/day. Degradation products of other antioxidants were shown to have detrimental effects on cell growth in single-use bioprocess containers and bags.17 The lack of information on the toxicity of TDTBPP, the elevated concentrations measured in the built and natural environment, and the relatively high exposure estimates, especially for toddlers, indicate that further investigation of this compound and the related TDTBPPO is warranted. In particular, reference doses based on solid toxicological end points are needed.
TDTBPP could be a byproduct of these other production processes. Retrieving commercial information on TDTBPP is complicated because companies protect information in the TSCA inventory under the Commercial Business Information (CBI) blanket, de facto hiding useful data on production, import, export, or production volumes. Also, chemical companies are bought by larger groups, merge, or change names, making it difficult to track their products historically. For example, Chemtura, one of the three largest manufacturers of organophosphate esters, was acquired by SK Capital, a New Yorkbased private equity firm focusing on specialty materials, chemicals, and healthcare, and its products are now marketed under the new name of Addivant. With the little information available, we speculate that TDTBPP might be present in some commercial formulations as either a flame retardant or as a plasticizer and that it can also form after oxidation of the phosphite, TDTBPPO. Given the apparent ease of oxidation of this compound, we conducted matrix spike experiments with TDTBPPO. We observed almost complete oxidation of TDTBPPO to TDTBPP (see Table S2). Thus, this oxidation occurs during sample processing, most likely in the gas chromatographic injection port, which is held at 285 °C. Using GC/MS, we screened a subset of samples taken from each matrix and confirmed the absence of TDTBPPO in these samples. It is possible that TDTBPPO could be present as such in the environment but that we would not detect it, given that our analytical method almost quantitatively converts it to TDTBPP. Our high resolution mass spectral data were obtained under less thermally stressful conditions (a direct probe inlet to a high vacuum system); thus, we re-examined these data looking for the presence of TDTBPPO as indicated by ions at m/z 646.451 (M+) and m/z 441.292 (M−C14H21O+). None of these mass spectra contained these ions, indicating that TDTBPPO was not present in this e-waste dust sample. It is also possible that TDTBPPO is quickly and completely converted to TDTBPP in the environment. More experiments are needed on ambient environmental samples using low temperature methods to determine the lifetime of TDTBPPO in the environment. Incidentally, TDTBPP may also be an impurity in another structurally related compound, tri-(4-tbutylphenyl) phosphate (T4tBPP), which was recently detected in several commercial flame retardant mixtures.23 Exposure Assessment. Exposure of workers from dust ingestion and dermal absorption in the e-waste dismantling facility and of residents in homes was calculated for TDTBPP (and TPhP, which is included for reference). Details on the assumptions and method used for this calculation have been previously published24 and a brief description is provided in the Supporting Information. Parameters used in the exposure assessment calculations are reported in Table S4. Table S5 presents the estimates for exposure of both adults and toddlers (children aged 18 months to 3 years). For the workers in the e-waste dismantling facility, total exposure to TDTBPP over an 8-h work shift was 571 ng/kg bw/day, when using the median dust concentration, and 1260 ng/kg bw/day, when using the 95th percentile for dust concentration. The contribution from dust ingestion was
