Detection of novel brominated flame retardants (NBFRs) in the urban soils of Melbourne, Australia Academic research paper on "Environmental engineering"

Emerging Contaminants xxx (2017) 1—9

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Emerging Contaminants

Detection of novel brominated flame retardants (NBFRs) in the urban soils of Melbourne, Australia

Thomas J. McGrath a, Paul D. Morrison a'b, Andrew S. Ball a, Bradley O. Clarke a' *

a School of Science, Centre for Environmental Sustainability and Remediation, RMIT University, GPO Box 2476, Melbourne, Victoria 3001, Australia b Australian Centre for Research on Separation Science (ACROSS), School of Science, RMIT University, GPO Box 2476, Melbourne, Victoria 3001, Australia

ARTICLE INFO

ABSTRACT

Article history: Received 12 October 2016 Received in revised form 11 January 2017 Accepted 11 January 2017 Available online xxx

Keywords:

Novel brominated flame retardants (NBFRs) Persistent organic pollutants (POPs) Land contamination Soil

A range of brominated flame retardants (BFRs) have been incorporated into polymeric materials like plastics, electronic equipment, foams and textiles to prevent fires. The most common of these, poly-brominated diphenyl ethers (PBDEs), have been subject to legislated bans and voluntary withdrawal by manufacturers in North America, Europe and Australia over the past decade due to long-range atmospheric transport, persistence in the environment, and toxicity. Evidence has shown that replacement novel brominated flame retardants (NBFRs) are released to the environment by the same mechanisms as PBDEs and share similar hazardous properties. The objective of the current research was to characterize soil contamination by NBFRs in the urban soils of Melbourne, Australia. A variety of industrial and non-industrial land-uses were investigated with the secondary objective of determining likely point sources of pollution. Six NBFRs; pentabromotoluene (PBT), pentabromoethylbenzene (PBEB), hexabromobenzene (HBB), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE) and decabromodiphenyl ethane (DBDPE) were measured in 30 soil samples using selective pressurized liquid extraction (S-PLE) and gas chromatography coupled to triple quadrupole mass spec-trometry (GC-MS/MS). NBFRs were detected in 24/30 soil samples with S5NBFR concentrations ranging from nd-385 ng/g dw. HBB was the most frequently detected compound (14/30), while the highest concentrations were observed for DBDPE, followed by BTBPE. Electronic waste recycling and polymer manufacturing appear to be key contributors to NBFR soil contamination in the city of Melbourne. A significant positive correlation between S8PBDEs and S5NBFR soil concentrations was observed at waste disposal sites to suggest that both BFR classes are present in Melbourne's waste streams, while no association was determined among manufacturing sites. This research provides the first account of NBFRs in Australian soils and indicates that these emerging contaminants possess a similar potential to contaminate Melbourne soils as PBDEs.

Copyright © 2017, KeAi Communications Co., Ltd. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://

creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

A range of brominated flame retardants (BFRs) have been incorporated into plastics, electronic equipment, foams and textiles to prevent fires [1,2]. The most common of these, polybrominated diphenyl ethers (PBDEs), have come under a great deal of scientific and regulatory scrutiny due to long-range atmospheric transport, persistence in the environment and evidence of bioaccumulation in humans and wildlife [3,4]. Toxicological reports have described a

* Corresponding author. E-mail address: bradley.clarke@rmit.edu.au (B.O. Clarke). Peer review under responsibility of KeAi Communications Co., Ltd.

range of adverse effects in humans and animals exposed to PBDEs, including endocrine disruption and neurodevelopmental toxicity [5,6]. In light of environmental and health hazards, PBDEs have been subject to legislated bans and voluntary withdrawal by manufacturers in North America [7,8], Europe [9,10] and Australia

[11] over the past decade. Commercial PBDE formulations Penta-BDE and Octa-BDE were listed as United Nations Persistent Organic Pollutants (POPs) under the Stockholm Convention of 2009

[12], while registration of the remaining product, Deca-BDE, has been officially proposed [13]. Restriction and regulation of PBDEs, however, has driven a rise in manufacture and use of replacement products, known as "novel" brominated flame retardants (NBFRs). Many of the compounds described as "novel" have been in

http://dx.doi.org/10.1016/j.emcon.2017.01.002

2405-6650/Copyright © 2017, KeAi Communications Co., Ltd. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

2 T.J. McGrath et al. / Emerging Contaminants xxx (2017) 1—9

production for decades, but have only been recognized as significant environmental contaminants recently, since replacing PBDEs in a range of products. Most NBFRs have comparable vapour pressures and log I<ow values to PBDEs and are, likewise, not chemically bound within polymers [2]. Consequently, research has shown that NBFRs are likely to be released to the environment by the same mechanisms as PBDEs and share a similar fate as persistent pollutants in air, soil and sediments [14—17]. Industries involved in the manufacture or disposal of flame retarded goods are expected to be key emission sources [18—21]. Many NBFRs also exhibit analogous bioaccumulation potential and toxicity to PBDEs [22]. Experimental evidence has identified hazards of NBFRs to include endocrine disruption of the thyroid and reproductive systems [22], neurotoxicity and genotoxicity [2,23,24].

To date, as many as 75 NBFRs have been manufactured. A subset of these are considered to be priority contaminants due to high production volume, prevalence in the environment and bioaccumulation potential (Table 1) [4,22,25]. Among the most widely utilized of the NBFRs is decabromodiphenylethane (DBDPE), which is marketed as a direct replacement for Deca-BDE commercial mixtures in a range of plastics, resins, rubbers, adhesives and textiles [1,2]. 1,2-bis(2,4,6-tribromophenoxy) ethane (BTBPE) constitutes the main replacement for octa-BDE mixtures, used mostly in hard plastics while 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB) is used in conjunction with other flame retardants in soft polymer materials like polyurethane foams as replacements for

Penta-BDE [2,26]. Pentabromotoluene (PBT), pentabromoe-thylbenzene (PBEB) and hexabromobenzene (HBB) are each used in a wide range of materials such as hard plastics, flexible foams and textiles to meet flammability standards [25].

Although primary production of NBFRs has not taken place in Australia to date, these compounds may be imported in their raw form for incorporation into secondary materials by local manufacturers. Australia's peak chemical regulation body, the National Industrial Chemicals Notification and Assessment Scheme (NIC-NAS) maintains the Australian Inventory of Chemical Substances (A1CS), in which chemicals approved for manufacture or import are listed. BTBPE, PBEB and PBT are currently included in the inventory while BTBPE is the only NBFR to have been reviewed as part of a Priority Existing Chemical (PEC) assessment [27]. The 2001 assessment estimated the import of BTBPE during the years 1998—1999 to be 17 metric t/y, though this number has not been updated in recent years. No domestic import estimates are currently available for any of the other NBFRs analysed in this study. Flame-retarded precursor materials imported to Australia may also contain NBFRs not documented by the A1CS [27].

The NBFRs described above have been detected in atmospheric samples from Europe [16], USA [28], Asia [29] and Africa [30] at concentrations similar to and exceeding those of PBDEs. As with PBDEs, evidence suggests that most NBFRs undergo net atmospheric deposition to land [31—33]. NBFR soil levels have rarely been studied, although contamination has been reported in the

Table 1

Novel brominated flame retardants (NBFRs) of emerging environmental concern.

Compound

Abbreviation3

Vapour pressure (Pa) (25 °C)

Octanol-water coefficient (log Kow)

Chemical structure

Pentabromotoluene

Pentabromoethylbenzene

Hexabromobenzene

2-Ethylhexyl-2,3,4,5-tetrabromobenzoate

1,2-Bis(2,4,6-tribromophenoxy)ethane

Decabromodiphenylethane

EH-TBB

1.22E-03c

3.2E-04c

7.5E-04b 1.14E-04c

6.33E-08 -4.58E-06d

3.88E-10c

6.0E-15c

5.87 ± 0.62c

6.40 ± 0.62c

5.85 ± 0.67c

8.72—8.75d

7.88 ± 0.86c

a Organobromine flame retardant abbreviation standard proposed by Bergman et al. [68]. b Tittlemier et al. [69], experimental results. c Covaci et al. [25], from SciFinder Database calculation. d Kuramochi et al. [65], calculation.

T.J. McGrath et al. / Emerging Contaminants xxx (2017) 1—9

soils of China [29,34,35], Sweden [16], England [36] and Indonesia [37].

The current study aims to characterize soil contamination by six NBFRs (PBT, PBEB, HBB, EH-TBB, BTBPE and DBDPE) in the urban soils of Melbourne, Australia. A variety of industrial and non-industrial land-uses were investigated with the secondary objective of determining likely point-sources of pollution. To the authors knowledge, this research is the first investigation of NBFRs in any matrix in the Australian environment, and aims to broaden our understanding of the contamination potential of these emerging pollutants.

2. Methods and materials

2.Í. Standards

Individual standard solutions of pentabromotoluene (PBT), pentabromoethylbenzene (PBEB), hexabromobenzene (HBB), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), decabromodiphenylethane (DBDPE), 3,4,4'-tribromodiphenyl ether (BDE-37) and 3,3',4,4'-tet-rabromodiphenyl ether (BDE-77) were purchased from AccuS-tandard Inc. (New Haven, CT, USA). Isotopically labeled 2,2',4,4'-tetrabromo[13C12]diphenyl ether (13C-BDE-47), 2,2',4,4',5-pentabromo[13C12]diphenyl ether (13C-BDE-99), 2,2',4,4',5,5'-hex-abromo[13C12]diphenyl ether (13C-BDE-153) and decabromo[13C12] diphenyl ether (13C-BDE-209) were obtained from Wellington Laboratories (Guelf, ONT, Canada). Concentration and isotopic purity data are included in Table S1.

2.2. Soil sampling

A total of 30 soil samples were collected from an area spanning approximately 40 km x 120 km across the Greater Melbourne region, Australia, between March and June 2014 (Fig. 1). Sample sites were categorized by land-use as manufacturing industries (n = 18), waste disposal facilities (n = 6) or non-industrial sites (n = 6). Manufacturing sites includes principal production of polymeric materials as well as industries involved in consequent manipulation of plastics and foams through processes such as molding, extrusion or cutting. Waste disposal sites comprise waste incineration (n = 2), electronic waste recycling (n = 2) and domestic dumpsites (n = 2), while non-industrial samples were collected from residential (n = 2), urban parkland (n = 2) and background (n = 2) locations. A brief description of each sampling site is provided in Table S2. All sampling of industrial sites was conducted at external property boundaries due to site access limitations. Care was taken to retrieve samples from as close to suspected pollution source activity as possible, which generally represented a distance no greater than 10 m. At all sites, a single surface soil sample was collected from approximately 1 m2 to a depth of 0—10 cm using a stainless steel hand trowel. The hand trowel was cleaned with detergent and then rinsed with deionized water followed by a 1:1 mixture of hexane/acetone between each sample. Samples were transported to the laboratory in amber glass jars at <4 °C and stored at -20 °C until analysis.

2.3. NBFR extraction

The method used for selective pressurized liquid extraction (S-PLE) of target compounds from soil has been described in detail previously [38]. Briefly, 33 mL Accelerated Solvent Extraction (ASE) cells contained, from bottom to top, a cellulose filter, 3 g of activated Florisil, 6 g of acid silica (10% w/w), 3 g of Na2SO4, a second cellulose filter, 2 g of activated copper, and 3 g of soil sample dispersed in 1 g

Hydromatrix and 2 g Na2SO4. Surrogate internal standards 13C-BDE-47,13C-BDE-99,13C-BDE-153 (5 ng) and 13C-BDE-209 (100 ng) were spiked into each soil sample prior to extraction. The extraction program entailed 5 min heating time, 5 min static time, 60% flush volume and 2 min nitrogen purge. A total of 3 cycles was performed on each sample at 100 °C and 1500 psi (~10.34 MPa) using a 1:1 mixture of n-hexane and dichloromethane. Extracts were evaporated to dryness under a gentle nitrogen stream and reconstituted to 100 mL with iso-octane:toluene (80:20 v/v) in amber glass vials with 250 mL inserts. Aliquots of 5 ng of each BDE-37, BDE-77 and 13C-BDE-138 were spiked into final extracts to be used as recovery internal standards for determination of surrogate standard recovery.

2.4. Instrumental analysis

1nstrumental parameters used for analysis have been detailed by McGrath et al. [38]. Briefly, NBFR analysis was performed using an Agilent 7000C gas chromatograph (DB-5MS column; 15 m x 0.180 mm internal diameter, 0.18 mm film thickness) coupled to a triple quadrupole mass spectrometer (GC-MS/MS) operated in electron ionization (E1) mode. Helium was used as the carrier gas while the temperature of the transfer line, ion source and quadrupoles were 325 °C, 280 °C and 150 °C, respectively. GC-MS/MS acquisition parameters are listed in Table S3. Target compounds were monitored according to retention time and two ion transitions and quantified using Agilent MassHunter analysis software (v. B.06.00).

2.5. Quantitation and QA/QC

Analytes were considered detected when the signal to noise ratio (S/N) in the quantitative ion transition exceeded three and the GC retention time was within ±5% of those in standards. Analytes were only quantified when the S/N ratio exceeded 10 in the quantitation transition, three in the qualitative transition and the ratio between the two monitored transitions was within ±20% of those measured in calibration standards. Method detection limits (MDLs) and method quantification limits (MQLs) were defined as the analyte concentration in soil corresponding to the lowest calibration point to meet analytical detection and quantitation criteria, respectively (Table S4). Analytes were quantified by isotope dilution according to the closest eluting surrogate standard (Table S4) using a five-point calibration containing all target analytes and internal standards. Linear regression lines fit the calibration curves with R2 > 0.999 for PBT, PBEB, HBB and EH-TBB while BTBPE had R2 > 0.994. QA/QC spiking tests revealed that internal standard quantification of DBDPE using 13C-BDE-209 resulted in an over-estimation of DBDPE concentrations. DBDPE was, therefore, quantified in all soil and QA/QC samples by external calibration according to peak area response. Calibration curves produced by this method were best fit by a quadratic regression model, which achieved R2 > 0.999. QA/QC measures showed this protocol to be acceptably accurate and precise, as detailed below. 13C-BDE-209 was retained in the method as an indicator of DBDPE extraction efficiency. The concentration of HBB exceeded the upper calibration range (1000 ng/mL) in one of the soil sample extracts (Sample 24). 1n this instance, the extract was diluted in surrogate internal standard at the initial spike concentration, reanalyzed and then quantified by the same protocol as original extracts.

A set of three method QA/QCs consisting of a method blank, LCS and matrix spike were analysed with every eight soil samples. Each QA/QC sample underwent the same preparation, extraction and analysis processes as the soil samples. HBB was detected in each method blank (n = 4) at trace levels, while no other compounds

T.J. McGrath et al. / Emerging Contaminants xxx (2017) 1—9

Fig. 1. Map of soil sample locations showing 1) Australia, 2) the State of Victoria and, 3) the City of Melbourne. WI = waste incinerator, ER = electronics waste recycling and DD = domestic dumpsite.

were detected in any blanks. The MDL and MQL for HBB were set to meet 95% and 99% confidence intervals, respectively, above the mean concentration detected in blanks. Blank corrections were, therefore, not performed. Field blanks (n = 3) showed that no introduction of contamination occurred via the sampling methods.

Matrix spikes and LCSs were spiked with 10 ng of PBT, PBEB and HBB, 20 ng of EH-TBB and BTBPE, and 200 ng of DBDPE in order to assess accuracy and precision of the method. Mean ± %RSD recoveries of PBT, PBEB, HBB, EH-TBB, BTBPE and DBDPE were 102 ± 6%, 101 ± 5%, 104 ± 2%, 75 ± 22%, 135 ± 15% and 81 ± 22%, respectively, in the LCSs, and 85 ± 4%, 96 ± 10%, 90 ± 8%, 82± 27%, 131 ± 12% and 86± 11%, respectively, in the matrix spikes. The current method provided excellent accuracy and precision for PBT, PBEB and HBB while quantitation of EH-TBB, BTBPE and DBDPE was subject to greater variability, reflecting the well documented analytical challenges associated with these compounds [25,38]. Surrogate performance of 13C-BDE-47, 13C-BDE-99, 13C-BDE-153 and 13C-BDE-209 met the limits described by USEPA Method 1614 for PBDE quantitation [39] with mean ± %RSD recoveries of 104 ± 9%, 95 ± 14%, 99 ± 14% and 107 ± 32%, respectively.

2.6. Statistical analysis

Statistical analyses were performed in Microsoft Excel and Minitab 17. Mean, median and standard deviation have been calculated only where a minimum of three values are available. All concentrations reported to be below <MQL were assigned a value of half the MQL in statistical calculations, while results which were <MDL, reported as not detected (nd), were assigned a value of zero. Pearson correlation analyses were performed using a 95% confidence interval and only included sites where both PBDEs and

NBFRs were detected. 3. Results and discussion

NBFR concentrations in soil samples are shown Fig. 2 and summarized in Table 2. PBT, HBB, EH-TBB, BTBPE and DBDPE were each detected in Melbourne soils with a summed total range of nd-385 ng/g dw. Overall, 24 of the 30 soil samples contained at least one of the NBFRs, while HBB was the most frequently detected compound (14 samples), followed by BTBPE (13 samples), and DBDPE (9 samples). PBT was detected in seven samples, albeit at very low levels, and EH-TBB was detected in only one sample. PBEB was not identified in any of the samples analysed. As such, S5NBFR refers to the sum of PBT, HBB, EH-TBB, BTBPE and DBDPE concentrations. Individual sample concentrations are reported in Table S5.

3.1. Manufacturing sites

NBFRs were detected in 16 of the 18 manufacturing soil samples with a mean S5NBFR concentration of 36.0 ng/g dw and range of nd-385 ng/g dw. DBDPE was detected in six samples and contributed some of the highest concentrations to overall contamination levels. This reflects the fact that international estimates of production and demand for DBDPE make it likely to be the most commercially prevalent of the NBFRs measured in this study [2,40,41]. DBDPE has been produced as a flame retardant since the 1990's [42] and is among the most broadly applied of the NBFRs, used in materials like plastics, polyesters, nitrile rubbers, adhesives and textiles [1,2,26]. The presence of DBDPE in the soils of manufacturing areas in the city of Melbourne appears to reflect its uptake as a replacement flame retardant for the banned Deca-BDE

T.J. McGrath et al. / Emerging Contaminants xxx (2017) 1—9

Fig. 2. Concentrations of NBFRs in soil samples (ng/g dw). WI = waste incinerator, ER = electronic waste recycling, DD = domestic dumpsite, R = residential, UP = urban parkland and B = background.

commercial products. The greatest concentration recorded in manufacturing soils, and indeed all soils, occurred at Site 14, where DBDPE measured 384 ng/g dw. The industry at Site 14 specializes in flexible insulation foams for hot and cold water piping and offers a number of products formulated to meet stringent fire safety standards regarding construction of commercial and multi-residential buildings. DBDPE has been determined in such piping insulation materials by Kierkegaard et al. [42] with an estimated concentration of 4.8 mg/g. A measurement of 59.9 ng/g dw DBDPE in the soil of Site 17, where architectural panels are fabricated, may further indicate that DBDPE is being utilized to meet building flammability standards in construction materials manufactured in Melbourne.

There are few studies investigating the environmental release of DBDPE specifically from manufacturing industries. Soil samples (n = 81) from two large-scale BFR-manufacturing plants in Shandong Province, China, measured mean concentrations of 1200 ng/g dw (range 12-9000 ng/g dw) and 810 ng/g dw (range nd-4600), respectively [43]. As was observed in the present study, Li, et al. [43] reported DBDPE concentrations to generally be three to four orders of magnitude greater than those of PBT, PBEB and HBB. Li et al. [43] also observed that the concentrations of NBFRs in soils decreased exponentially within 3—5 km from the manufacturing source, more notably for DBDPE than the monoaromatic NBFRs. In a separate study, Li, et al. [44] determined the total air concentrations of DBDPE at manufacturing sites to be 85—96% particulate-associated while PBT, PBEB and HBB were present mostly in gaseous phase. A number of studies have described preferential atmospheric deposition of particulate-bound organohalogen contaminants [45—47]. To some extent, elevated DBDPE levels in soil may have been enhanced by the propensity for particles to deposit closer to point-sources, while gas-phase contaminants are transported further before deposition, thus becoming diluted within the air column.

BTBPE levels in manufacturing soils were generally lower than those of DBDPE, with a mean concentration of 6.86 ng/g dw and range of nd-63.8 ng/g dw. BTBPE was, however detected in a number of samples where DBDPE was not present, including substantial measurements of 45.9 ng/g dw and 63.8 ng/g dw at Sites 3 and 13, respectively. Both of these locations comprise large-scale manufacturers that produced a wide range of raw engineering polymers. BTBPE is mostly utilized in materials like acrylonitrile butadiene styrene (ABS), high impact polystyrene (HIPS) and resins [1,2,26], each of which are produced at these sites. These findings suggest the application of BTBPE in Melbourne manufacturing of hard plastics to replace the banned Penta- and Octa-BDE formulations. Data regarding present day demand for BTBPE is not available, though high rates of use in Japan and the USA through the 1980's and 1990's have been described [28,48,49].

Soil samples measured from a transect through the Chinese city and industrial centre of Harbin contained BTBPE levels no higher than 0.0336 ng/g dw [50]. No BTBPE was detected in any soil samples from similar transects through the cities of Stockholm, Sweden [16] and Birmingham, England [36], respectively. Although BTBPE was analysed in matched atmospheric samples from both Birmingham and Stockholm, it was only detected in Stockholm, with a detection frequency of 33% and maximum concentration of 0.26 pg/m3 [16]. A number of studies, however, have recorded BTBPE in atmospheric samples which reveal population centres to be general emission sources [30,51].

HBB was detected at eight manufacturing sites with a mean concentration of 0.12 ng/g dw and range of nd-1.37 ng/g dw, while PBT was detected at <MQL at just three sites. HBB and PBT are each additive flame retardants with a range of material applications such as plastics, textiles and polyurethane foams [1,25]. Like DBDPE, HBB was detected at all three sites associated with building material fabrication (Sites 7, 14 and 17) to infer that it too is employed in

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Table 2

Summary of NBFR concentrations in soil (ng/g dw) by land-use category.

Compound Manufacture Waste disposal Non-industrial Total

(n = 18) (n = 6) (n = 6) (n = 30)

PBT Mean <MQL 0.03 <MQL <MQL

Median nd 0.01 nd nd

Min nd nd nd nd

Max <MQL 0.10 <MQL 0.10

Det 3 2 2 7

HBB Mean 0.12 17.2 <MQL 3.52

Median nd 0.25 nd nd

Min nd nd nd nd

Max 1.37 90.9 <MQL 90.9

Det 8 5 1 14

EH-TBB Mean — 0.30 — <MQL

Median nd nd nd nd

Min nd nd nd nd

Max nd 1.79 nd 1.79

Det 0 1 0 1

BTBPE Mean 6.86 3.35 — 4.79

Median <MQL 0.71 nd nd

Min nd nd nd nd

Max 63.8 11.4 nd 63.8

Det 10 3 0 13

DBDPE Mean 29.0 62.7 — 30.0

Median nd 4.17 nd nd

Min nd nd nd nd

Max 384 295 nd 384

Det 6 3 0 9

S5NBFRs Mean 36.0 83.6 <MQL 38.3

Median 1.56 44.3 nd 0.88

Min nd 0.34 nd nd

Max 385 320 0.04 385

Det 16 6 2 24

Measurements of <MQL have been assigned a value of half MQL and non-detects have been assigned a value of zero in statistical calculations. Mean concentrations have not been calculated for land-use categories in which detection frequency was zero. S5NBFRs refers to the summed concentration of PBT, HBB, EH-TBB, BTBPE and DBDPE. PBEB was not detected in any samples.

construction materials. Japanese production of HBB was estimated to be 350 t/y throughout 1994-2001 [49] while the Chinese Shou Guang Longfa Chemical Company reportedly manufactured 600 t/y of each HBB and PBT in 2011 [25]. PBT production was estimated to be between 1000 and 5000 t/y in 1997 by WHO [1] but was classified as "low volume" in the EU during 2010 [25]. There is currently no information available regarding volumes HBB in Europe or of either flame retardant in the USA.

Experimental evidence has shown that pelletized flame retarded oligomer stocks designed for use in thermoplastic polyesters and nylon manufacture released PBT at a rate of 2480 ± 500 ng/g per hour at room temperature [19]. Emission rates increased up to 42,400 ± 4700 ng/g per hour at temperatures of 100 °C for PBT and 120 ± 10 ng/g per hour at 50 °C for HBB. This evidence indicates a high potential for environmental release of these compounds during compounding of thermoset plastics, and also during storage at ambient temperatures.

The concentrations of HBB measured in soils around two BFR-manufacturing plants in Shangdong Province, China were of a similar order to the levels in the present study, with mean levels of 0.89 ng/g dw (range; nd-17 ng/g dw) and 0.31 ng/g dw (range; nd-2.0 ng/g dw), respectively [43]. Mean PBT soil concentrations at the two Chinese locations were somewhat higher than in Melbourne's soils, however, measuring 4.9 ng/g dw (range; nd-190 ng/g dw) and 1.3 ng/g dw (range; nd-8.6 ng/g dw), respectively. Concentrations of HBB (mean; 3.4 ng/g dw, range; <reporting level-720 ng/g dw) in the soils of the Pearl River Delta, China, were somewhat higher than those of the present study, and were observed to correlate with

population density and level of urbanization [52]. The concentrations of HBB and PBT reported by Newton et al. [16] in the soils of Stockholm, Sweden, were similarly low to those of manufacturing sites in the present study, ranging <0.00079-6.1 ng/g organic matter (om) and <0.0085-0.018 ng/g om, respectively.

EH-TBB and PBEB were not detected in any of the manufacturing soils.

3.2. Waste disposal sites

NBFRs were detected in the soils of all six of the waste disposal sites. The S5NBFR mean concentration at waste disposal sites, 83.6 ng/g dw (range; 0.34-320 ng/g dw) was the highest of the land-use categories. Electronic waste recycling facilities appear to be substantial contributors to NBFR soil contamination with Site 22, in particular, recording a S5NBFR concentration of 320 ng/g dw. Site 22 was the only soil sample to contain five NBFRs, and was the only location where EH-TBB was detected amongst the 30 samples. Australia was estimated to have produced approximately 410,000 t of electronic waste per year in 2005 [53]. Input wastes at electronic waste recycling plants typically contain a high proportion (~80%) of flame retarded goods [54]. DBDPE and BTBPE have been identified as constituents in a variety of raw plastic materials and electrical and electronics equipment at concentrations typically in the mg/g to mg/g concentration ranges [55-57]. HBB, PBT and PBEB have also been shown to be present in the raw brominated oligomers used to produce polybutylene terephthalate, a thermoplastic common in electronics devices [19]. The role of electronic waste recycling as a

T.J. McGrath et al. / Emerging Contaminants xxx (2017) 1—9

major source of PBDEs to the environment has been well established [58—61]. High concentrations of NBFRs have also been recorded in dust and air of e-waste recycling facilities [14,62]. Tian et al. [21] measured the atmospheric deposition of DBDPE in an electronic waste recycling area in the Pearl River Delta region of China to be 9780 ng/m2 per year, while BTBPE, HBB, PBT and PBEB were each found to have considerably lower rates of deposition flux. Soil sampled from close to an e-waste recycling area in Northern China (n = 5) contained similar concentrations of DBDPE to the levels to those of the current study, ranging 0.03—173 ng/g [35]. Another Chinese study investigating NBFR transfer from e-waste recycling activities to nearby farmland soils in Guangdong Province (n = 4), however, determined only low levels of BTBPE (0.07—6.19 ng/g dw) and DBDPE (<2.50—4.56 ng/g dw) [29].

Interestingly, HBB was the most prevalent NBFR at domestic dumpsites by a substantial margin. The measurement of 90.9 ng/g dw at Site 24 was significantly higher than all other measurements of HBB across the study sites, which may indicate that a specific point-source exists at this location. Although HBB has not been studied at similar land-uses previously, BTBPE was identified on municipal dumpsites in Surabaya City, Indonesia ranging 0.027—0.15 ng/g dw [37].

Only low levels of HBB and DBDPE were detected in soils near waste incinerators. It is possible that very high temperatures involved in waste incineration degrade NBFRs such that emission of parent structures are minimal [63]. On the other hand, experiments by Liu et al. [64] observed that certain pyrolysis techniques may retain brominated compounds, including DBDPE, in the char residue for solid disposal or reclamation.

In general, the relative abundances of NBFRs measured at waste disposal sites in Melbourne show a broad similarity to compound compositions in waste from other studies [14,21,37,62]. This may provide evidence that the replacement NBFRs present in Australian consumer goods are similar to those being utilized internationally. However, there are few studies for comparison to draw strong conclusions.

3.3. Non-industrial sites

No NBFRs were measured at quantifiable levels in any of the non-industrial sampling sites. HBB and PBT were both detected in one of the background samples while PBT was also identified in one residential sample. The low detection of NBFRs in soils among non-industrial sites supports the conclusion that manufacturing and waste disposal processes are responsible for the contamination observed in proximity to these industries. Further research is required to determine whether the low levels of NBFRs detected in Melbourne's non-industrial soils are due to atmospheric transport from industrial emissions or specific onsite sources such as outdoor furniture or building materials. Monoaromatic NBFRs like HBB, PBT and PBEB are likely to have a higher potential for atmospheric transport than other NBFRs due to lower molecular weights and higher vapour pressures [25], with software calculations predicting HBB to be transported 7—8 times further than BTBPE, for example [65]. HBB and PBT have each been detected at low levels in urban background soils from Stockholm, Sweden [16], while HBB measured a range of nd-0.34 ng/g dw in forest soils of China [34]. Heavier NBFRs such as DBDPE and BTBPE were, however, also measured in forest soils by Zheng et al. [34] and have been detected at low levels in rural soils of Indonesia [37]. This may indicate that transfer of NBFRs to background soils in Melbourne is a potential consequence of ongoing or increased industrial use of these compounds.

3.4. Correlations with PBDEs

As part of a previous study [61], eight PBDE congeners (BDEs -28, -47, -99, -100, -153, -154, -183 and -209) were analysed in all 30 samples of the current study to assess the implications of the Australian National Environment Protection Councils (NEPC) soil contamination guidelines [66]. The NEPC's Assessment of Site Contamination Measure of 1999 was amended in 2013 to introduce a health investigation level (HIL) for all 208 lower PBDE congeners (excluding BDE-209) in soil. PBDEs were detected in 29 of the 30 soil samples with S8PBDEs measuring higher than S5NBFR levels in all but three samples. The S7PBDE concentrations (excluding BDE-209), which represent the NEPC regulated congeners analysed by McGrath et al. [61], exceeded those of S5NBFR at all of the non-industrial sites, but only around half of the industrial locations. This indicates that the potential for NBFRs to contaminate the soils of industrial sites within the city of Melbourne could be comparable to the impact represented by PBDE congeners deemed to be a health risk by Australia's NEPC [66].

Many of the NBFRs discussed in the current study are being marketed and implemented as direct replacements for the commercial Penta-BDE, Octa-BDE and Deca-BDE products represented by these PBDE congeners. Given the analogous physicochemical properties of NBFRs to the PBDEs they replace, similar potential for environmental contamination might be expected. Correlation analysis was also performed between concentrations of S8PBDEs and S5NBFR in soil to evaluate potential shared sources (Fig. 3). No association was determined between S8PBDEs and S5NBFR concentrations in the soils of manufacturing sites (R2 = 0.011, p = 0.676), while a significant positive correlation was observed at waste disposal sites (R2 = 0.934, p = 0.002). It could be rationalized that although individual manufacturing facilities in Melbourne may have been a source of both PBDEs and NBFRs over time, a switch from the former products to the latter replacements might mean that emissions of the two classes did not occur concurrently. Indeed Stapleton etal. [7] found the detection rate ofPenta-BDE in couches purchased in the USA before and after PBDE bans were 39% and 2%, respectively. Detection of the FM550 flame retardant product (of which EH-TBB is a constituent) rose from 5% to 18% over the same period. Conversely, as NBFRs have become more common in consumer goods throughout the previous decade, feedstocks to waste processing industries are likely to contain a mixture of older products predominated by PBDE-infused materials and newer items containing NBFRs. Post-processing e-waste samples (n = 2) were found to contain similar proportions of BTBPE to the commercial PBDE components by Ballesteros-Gómez et al. [55] while samples from a scrap metal reclamation plant, which uses shredding and pyrolysis techniques, identified BTBPE, HBB and PBEB in conjunction with PBDEs in waste residues [67].

4. Conclusion

Soil contamination by six NBFRs has been assessed for the first time at a variety of manufacturing, waste disposal and non-industrial sites in the city of Melbourne, Australia. DBDPE, BTBPE, EH-TBB, HBB and PBT were each detected in at least one soil sample while PBEB was not present at any sites. Electronics recycling facilities and polymer manufacturing industries appeared to be the greatest potential sources of NBFRs to Melbourne's soil, while minimal impacts were observed at non-industrial sites. Although few sources are available for comparison, the concentrations of most NBFRs in this study were lower than those of highly industrialized areas in China, but broadly resembled those in Sweden, the UK and Indonesia. A significant positive correlation between S8PBDEs and S5NBFR soil concentrations was observed at waste

T.J. McGrath et al. / Emerging Contaminants xxx (2017) 1—9

Fig. 3. Correlations between concentrations (ng/g dw) of S8PBDEs and S5NBFRs in manufacturing soils (R2 = 0.011, p = 0.676) and waste disposal soils (R2 = 0.934, p = 0.002). Compounds detected at <MQL have been assigned a value of half MQL. Two manufacturing soil samples where S5NBFRs were not detected have been omitted.

disposal sites to indicate that waste streams in the City of Melbourne are likely to contain a mixture of the legacy and replacement BFRs. A lack of association between PBDEs and NBFR among manufacturing sites, however, suggests that the two BFR classes are not being used simultaneously in Melbourne's manufacturing industries. This research provides the first account of NBFRs in Australian soils and indicates that these emerging contaminants possess a similar potential to contaminate Melbourne soils as PBDEs.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.emcon.2017.01.002.

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