Characterization of Individual Isopropylated and tert-Butylated

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Characterization of Individual Isopropylated and Tert-butylated Triarylphosphate (ITP & TBPP) Isomers in Several Commercial Flame Retardant Mixtures and House Dust Standard Reference Material SRM 2585 Allison Phillips, Stephanie Hammel, Alex Konstantinov, and Heather M Stapleton Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b04179 • Publication Date (Web): 27 Oct 2017 Downloaded from http://pubs.acs.org on October 27, 2017

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Environmental Science & Technology

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Characterization of Individual Isopropylated and Tert-butylated

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Triarylphosphate (ITP & TBPP) Isomers in Several Commercial

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Flame Retardant Mixtures and House Dust Standard Reference

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Material SRM 2585

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Allison L. Phillips†, Stephanie C. Hammel†, Alex Konstantinov‡, and Heather M. Stapleton†*

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†

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‡

Nicholas School of the Environment, Duke University, Durham, NC, USA

Wellington Laboratories, Inc., Guelph, Ontario, Canada

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*

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[email protected]; Address: 9 Circuit Drive, Box 90328, Durham, NC 27708-0328

Corresponding Author: Heather M. Stapleton; Phone: (919) 613-8717; Email:

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ACS Paragon Plus Environment

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Abstract

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Since the phase-out of pentaBDE in the early 2000s, replacement flame retardant mixtures

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including Firemaster® 550 (FM 550), Firemaster® 600 (FM 600), and organophosphate aryl

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ester technical mixtures, have been increasingly used to treat polyurethane foam in residential

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upholstered furniture. These mixtures contain isomers of isopropylated and tert-butylated

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triarylphosphate esters (ITPs and TBPPs), which have similar or greater neuro- and

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developmental toxicity compared to BDE 47 in high throughput assays. Additionally, human

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exposure to ITPs and TBPPs has been demonstrated to be widespread in several recent studies;

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however, the relative composition of these mixtures has remained largely uncharacterized. Using

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available authentic standards, the present study quantified the contribution of individual ITP and

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TBPP isomers in 4 commercial flame retardant mixtures: FM 550, FM 600, an ITP mixture, and

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a TBPP mixture. Findings suggest similarities between FM 550 and the ITP mixture, with 2-

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isopropylphenyl diphenyl phosphate (2IPPDPP), 2,4-diisopropylphenyl diphenyl phosphate

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(24DIPPDPP), and bis(2-isopropylphenyl) phenyl phosphate (B2IPPPP) being the most

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prevalent ITP isomers in both mixtures. FM 600 differed from FM 550 in that it contained TBPP

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isomers instead of ITP isomers. These analytes were also detected and quantified in a house dust

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Standard Reference Material, SRM 2585, demonstrating their environmental relevance.

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Introduction

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In the early to mid- 2000s, the use of polybrominated diphenyl ethers (PBDEs) was globally

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phased-out due to concerns about their persistence, bioaccumulation and potential toxicity

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(PBT). One PBDE commercial mixture, PentaBDE, was primarily used in furniture as a flame

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retardant to meet residential flammability standards; however, new flame retardant chemicals

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and mixtures have since entered the market. Recent studies by our group demonstrate that many

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of these new flame retardant mixtures contain alkylated organophosphate aryl esters, and in

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particular, several types of isopropyl- and tert-butyl-triphenyl phosphates (ITP and TBPP,

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respectively; Figure 1).1,2 In addition to being used as flame retardants, both ITPs and TBPPs are

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used in hydraulic fluids and as plasticizers in a variety of materials.3,4 In our previous research,

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we identified ITPs in a common commercial flame retardant mixture, Firemaster® 550 (FM

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550), a mixture of organophosphate and brominated flame retardants, and an ITP mixture.5

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Similarly, we identified TBPPs in Firemaster® 600 (FM 600) and in a mixture with TPHP that

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we refer to as the TBPP mixture.2 Despite their documented neuro- and developmental toxicity,

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there is currently very little information regarding human exposure to ITPs and TBPPs and

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limited documentation of the presence of these isomers in environmental samples.6,7 This

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pressing lack of data has been recognized by the U.S. Environmental Protection Agency (EPA),

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which recently prioritized ITPs as one of five Fast-Tracked PBT Chemicals for further

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assessment under the 2016 amendment to the Toxic Substances Control Act (TSCA).8 Previous

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research conducted by our laboratory has demonstrated that exposure to ITP chemicals is very

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common in the US population, and that exposure ranges considerably among individuals, likely

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based on differential exposure to flame retardant and plasticizer-treated consumer products. For

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instance, Hammel et al. detected ITPs on silicone wristbands worn by human participants with


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100% frequency (n=40).9 Furthermore, out of 5 organophosphate flame retardant (PFR)

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metabolites measured in urine in this study, mono-isopropylphenyl phenyl phosphate (mono-

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ipPPP), a confirmed metabolite of ITPs, had the highest geometric mean concentration (2.6

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ng/mL). Another recent study detected mono-ipPPP in 98% of all tested urine samples (n=48),

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and found that on average, levels of urinary mono-ipPPP were 1.2 times higher in children than

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in their mothers.10 Other recent studies have used commercial flame retardant mixtures

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containing ITPs and TBPPs to assess toxicological endpoints, and yet the composition of these

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mixtures has not been well described. For example, FM 550 has been shown to be endocrine

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disrupting and potentially obesogenic in rats, and exposure in fathead minnows resulted in

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significant DNA damage.11,12 The ITP and TBPP commercial mixtures have been found to

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disrupt C. elegans larval development, zebrafish embryonic development, and zebrafish behavior

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at concentrations in the low µM range.6,13 The TBPP mixture has also been shown to elevate

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estradiol serum levels, alter reproductive cycles, and elicit cholesteryl lipidosis in adrenocortical

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and ovarian interstitial cells of exposed female rats.14 However, because there have been no

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studies that identify the composition and ITP/TBPP isomer profile of these commercial mixtures,

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it is difficult to attribute toxicological findings to a specific component(s) of the mixture. Such

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information will give context to toxicological studies using these mixtures, and give direction to

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future exposure studies. Moreover, there is considerable confusion in the flame retardant

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literature regarding the naming and acronyms associated with these compounds, and these

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mixtures also have a myriad of technical/brand names associated with them from multiple

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manufacturers (Table I). For the purposes of this study and to avoid future confusion, individual

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ITP and TBPP isomer acronyms are used according to their practical abbreviations (PRABs).15

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Individual standards for these isomers have become available in the past year, and the present


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study attempts to alleviate confusion regarding these compounds. Here we characterize the ITP

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and TBPP isomer profiles present in FM 550 and FM 600, and two other types of

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organophosphate commercial mixtures that are currently available on the market.

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Experimental

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Materials

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Individual, authentic standards of 2-isopropylphenyl diphenyl phosphate (2IPPDPP), 3-

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isopropylphenyl diphenyl phosphate (3IPPDPP), 4-isopropylphenyl diphenyl phosphate

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(4IPPDPP), 2,4-diisopropylphenyl diphenyl phosphate (24DIPPDPP), bis(2-isopropylphenyl)

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phenyl phosphate (B2IPPPP), bis(3-isopropylphenyl) phenyl phosphate (B3IPPPP), bis(4-

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isopropylphenyl) phenyl phosphate (B4IPPPP), bis(2,4-diisopropylphenyl) phenyl phosphate

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(B24DIPPPP), tris(3-isopropylphenyl) phosphate (T3IPPP), tris(4-isopropylphenyl) phosphate

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(T4IPPP), 4-tert-butylphenyl diphenyl phosphate (4tBPDPP), bis(2-tert-butylphenyl) phenyl

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phosphate (B2tBPPP), bis(4-tert-butylphenyl) phenyl phosphate (B4tBPPP), 13C-TPHP,

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d15TPHP,

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Laboratories (Guelph, Ontario, Canada). TPHP (99% pure) and tris(4-tert-butylphenyl)

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phosphate (T4tBPP) were purchased from Sigma-Aldrich (St. Louis, Missouri). HPLC grade

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isooctane was purchased from Honeywell Burdick & Jackson (Muskegon, Michigan). FM 550

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was provided by Chemtura (lot #77000DI8P), the commercial mixture containing only ITPs was

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purchased from Jinan Great Chemical Industry Co. (no lot information provided by

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manufacturer), and the TBPP mixture was produced by Ubichem and obtained from the National

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Toxicology Program (lot #M062011NS) for research purposes as part of a materials transfer

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agreement. The commercial FM 600 mixture itself was not available for analysis; for this reason,

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C-EH-TBB, and 13C-BEH-TEBP were purchased from or provided by Wellington


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a block of FM 600-treated polyurethane foam was obtained from a North Carolina foam

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manufacturer for analysis.

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Commercial Mixture Preparation

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Each flame retardant mixture preparation was weighed using a Mettler Toledo A21 Comparator

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microbalance and dissolved in isooctane to make three low (~1 µg/ml) and three high (~5 µg/ml)

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concentration solutions. FM 600-treated foam was weighed (100 mg) and extracted in triplicate

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using dichloromethane according to previously published methods.16 For the analysis here, the

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concentration of FM 600 in the foam was assumed to be 4% by weight, similar to measurements

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made previously in polyurethane foam.16 Prior to analysis, each solution was spiked with the

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appropriate internal standards.

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SRM 2585 Analysis

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Approximately 300 mg of SRM 2585 (National Institute of Standards & Technology,

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Gaithersburg, MD) was spiked with 13C-TPHP and extracted three times in DCM with

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sonication. SRM extracts (n=4) were cleaned using Supelclean™ ENVI-Florisil® SPE cartridges

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(6 mL; 1.0g; Supelco, Bellefonte, Pennsylvania) using previously published methods.17 ITP and

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TBPP isomers were eluted using 10 mL of ethyl acetate. Eluents were concentrated under

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nitrogen and solvent-exchanged to hexane prior to analysis.

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Component Quantification

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EH-TBB and BEH-TEBP were quantified with previously described GC/ENCI-MS methods

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using 13C-EH-TBB and 13C-BEH-TEBP as internal standards.5 TPHP and individual ITP and


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TBPP isomers were quantified with previously described GC/EI-MS methods using 13C-TPHP as

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an internal standard.16 Briefly, quantification of TPHP, ITP, and TBPP isomers was performed

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using an Agilent (Wilmington, DE) gas chromatograph (model 7890A) mass spectrometer

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(model 5975C) operating in electron impact (EI) mode. Pressurized temperature vaporization

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(PTV) injection was employed in the inlet and a 0.25 mm (I.D.) x 30 m fused silica capillary

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column coated with 5% phenyl methylpolysiloxane (J&W Scientific, 0.25 µm film thickness)

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was used in the GC to resolve the analytes. Helium was used as the carrier gas in the GC with a

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constant flow rate of 1.3 mL/min. The inlet was set to a temperature of 80˚C for 0.3 minutes and

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then ramped to 300˚C at a rate of 600˚C/min to efficiently transfer samples to the head of the GC

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column. The GC oven was held at 80˚C for 2 minutes, then ramped to 250˚C at 20˚C/min, then

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ramped to 260˚C at 1.5˚C/min, then ramped to 300˚C at 25˚C/min and held at 300˚C for 20

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minutes. The transfer line temperature was held at 300˚C, and the ion source was maintained at

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200˚C. Table II outlines the m/z ions and retention times used for quantification of ITP and

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TBPP isomers.

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QA/QC

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Laboratory blanks were included in both the commercial mixture preparation (n=3) and the SRM

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2585 analysis (n=6). All samples were blank corrected using the average blank level, and method

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detection limits (MDLs) were calculated using 3 times the standard deviation of the average lab

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blanks, and were normalized to the amount of dust extracted for the SRM 2585 analysis. MDLs

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are reported in Table S-1 for each isomer. Linear calibration curves were constructed using a five

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point calibration for the quantification of each isomer, with r2 values ranging from 0.9985 to

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0.9999. To evaluate the recoveries of ITP and TBPP isomers in house dust, a matrix spike


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experiment was performed using a low and high dose of isomers. Samples of SRM 2585 were

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spiked with either a low dose (50 ng) or a high dose (500 ng) of all ITP and TBPP isomers, and

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extracted, in triplicate, according to the methods detailed above. 13C TPHP was added prior to

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GC/MS analysis to quantify recovery of each analyte. Recoveries ranged from 72.4 ±1.0% to

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109.9 ± 10.7% (see Table S-2) for the various isomers.

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Results & Discussion

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Firemaster® 550 and ITP Mixture

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The percent composition of each ITP isomer present in the FM 550 and ITP mixture,

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respectively, is shown in Table III and is presented on a percent w/w basis. The FM 550 mixture

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consisted of approximately 44% of the brominated components, with the remaining mass

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comprised of TPHP and the ITPs. Like the FM 550 mixture, the ITP mixture consisted of very

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similar ITP isomers, particularly TPHP, 2IPPDPP, and B2IPPPP, which were the dominant

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compounds in the mixture. Notably, the contribution of the individual organophosphate

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components in the ITP mixture is roughly twice that of their contribution in FM 550, suggesting

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a common ITP formulation and/or synthesis (Figure 2). T4IPPP was not detected in either of the

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mixtures. Our analyses accounted for 97.8 ± 1.5% of FM 550 and 97.0 ± 5.3% of the ITP

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mixture.

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Firemaster® 600 and TBPP Mixture

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The percent composition of each TBPP isomer present in the FM 600 and TBPP mixture is

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shown in Table IV and is presented on a percent w/w basis. In the case of the FM 600 analysis,

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we used foam as a standard which could be a limitation affecting the accuracy of our characterization.


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We assumed that the foam was treated with 4% FM 600 by weight.

Using that assumption, the

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foam treated with FM 600 contained approximately 40% of the brominated compounds, with the

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remaining mass being comprised of TPHP and TBPP isomers. The organophosphate

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formulation of FM 600 was dominated by B4tBPPP and T4tBPP isomers, with relatively little

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TPHP or 4tBPDPP present in the mixture. In contrast, the TBPP mixture was comprised of

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higher percentages of TPHP and 4tBPDPP (Figure 3). In total, we could account for 95.3 ±

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5.2% of the FM 660 mixture and 79.5 ± 1.1% of the TBPP mixture. 2tBPDPP and B2tBPPP

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were not detected in either FM 600 or the TBPP mixture, but chromatographic peaks for

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3tBPDPP and B3tBPPP were observed for both mixtures (Figure S1). These peaks were

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presumed to be the meta-isomers based on their mass spectra (m/z = 382 for 3tBPDPP and m/z =

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438 for B3tBPPP), retention times between ortho- and para-substituted isomers, and lack of

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matching with the ortho- and para-substituted isomers. Standards of meta-TBPP isomers are not

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commercially available so quantification of 3tBPDPP and B3tBPPP was not possible.

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Concentrations in SRM 2585

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Levels of ITP and TBPP isomers in house dust standard reference material 2585 are shown in

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Table V. Deuterated TPHP was used as a recovery standard and percent recovery of 13C-TPHP

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was 95.7 ± 6.2%. Measured concentrations of TPHP were 1002.13 ± 52.88 ng/g, similar to those

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reported previously.17,18 2IPPDPP, 4IPPDPP, 4tBPDPP, and B4BPDPP were the most prevalent

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ITP and TBPP isomers in SRM 2585, all of which had concentrations >200 ng/g. In contrast,

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T3IPPP, T4IPPP, 2tBPDPP, and B2tBPPP were not detected in SRM 2585 above MDL levels

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(0.67, 1.07, 0.61, and 0.98 ng/g respectively.) While individual isomer levels are lower than that

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of other organophosphate flame retardants, ΣITP and ΣTBPP levels (1098.28 and 762.09 ng/g,


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respectively) approach, and in some cases, exceed levels that have been reported for TPHP,

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TCEP, and TCPP previously.18,19 These concentrations suggest the potential for chronic human

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exposure to ITP and TBPP isomers via inadvertent dust ingestion and hand-to-mouth contact. In

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addition, the fact that SRM 2585 was prepared from dust collected in 1993 and 1994 suggests

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ITP and TBPP use has been ongoing before PentaBDE was phased out. Interestingly, it has been

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reported that the ITP isomers were originally developed as tricresyl phosphate replacements due

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to the erratic supply and increasing cost of cresols in the 1970s. Similarly, TBPP isomers were

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introduced in the 1970s for use in hydraulic applications.4 However, to the authors’ knowledge,

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this is the first demonstration of their presence in SRM 2585.

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Implications

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There is growing evidence that the organophosphate components in these mixtures may elicit

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adverse health effects and human exposure to them has been demonstrated to be widespread in

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recent years.9,20–22 A recent epidemiological study found a signfiicnat association between the

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urinary metabolite of ITPs and decreases in successful pregnancy outcomes.23 Identification of

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the predominant ITP and TBPP isomers in commonly used commercial flame retardant mixtures

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will aid in hazard characterization and the ongoing, prioritized, risk assessment of these

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compounds by the U.S. EPA. With the exception of FM 600, all of these mixtures contain ≥ 20%

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TPHP, a compound with known toxicological activity.24–26 Interestingly, FM 600 has very low

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TPHP content, potentially due to distillation or other treatment following isomerization. The four

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mixtures in this study are complex, containing many different components, each with potentially

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unique health hazards and physicochemical properties. These findings should be taken into

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account when designing and interpreting toxicological studies. Furthermore, it should be


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recognized that there are many different manufacturers of these mixtures, and mixture

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formulations may differ among manufacturers and across lots. It is possible that the minor

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components of the ITP mixture (

Characterization of Individual Isopropylated and tert-Butylated

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