Fate of Brominated Flame Retardants and Organochlorine Pesticides

Article pubs.acs.org/est

Fate of Brominated Flame Retardants and Organochlorine Pesticides in Urban Soil: Volatility and Degradation Fiona Wong,*,†,‡,# Perihan Kurt-Karakus,§,∥ and Terry F. Bidleman†,⊥ †

Centre for Atmospheric Research Experiments, Science and Technology Branch, Environment Canada, 6248 Eighth Line, Egbert, L0L 1N0, Ontario, Canada ‡ Department of Physical and Environmental Sciences, University of Toronto Scarborough, 1256 Military Trail, Toronto, M1C 1A4, Ontario, Canada § Aquatic Ecosystem Protection Research, Science and Technology Branch, Environment Canada, 867 Lakeshore Road, Burlington, L7R 4A6, Ontario, Canada ∥ Faculty of Engineering, Department of Environmental Engineering, Bahcesehir University, Ciragan Cad. Osmanpasa Mektebi Sok. No: 4-6, 34353, Besiktas, Istanbul, Turkey ⊥ Department of Chemistry, Umeå University SE-901 87 Umeå, Sweden S Supporting Information *

ABSTRACT: As the uses of polybrominated diphenyl ethers (BDEs) are being phased out in many countries, soils could become a secondary emission source to the atmosphere. It is also anticipated that the demand for alternative brominated flame retardants (BFRs) will grow, but little is known about their environmental fate in soils. In this study, the volatility and degradation of BFRs and organochlorine pesticides (OCPs) in soil was investigated. A low organic carbon (5.6%) urban soil was spiked with a suite of BFRs and OCPs, followed by incubation under laboratory condition for 360 days. These included BDE- 17, -28, -47, -99; α- and β-1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), β-1,2,5,6-tetrabromocyclooctane (TBCO), and 2,3-dibromopropyl-2,4,6-tribromophenyl ether (DPTE), OCPs: α-hexachlorocyclohexane (α-HCH) and 13C6-α-HCH, trans-chlordane (TC), and 13 C10-TC. The volatility of spiked chemicals was investigated using a fugacity meter to measure the soil-air partition coefficient (KSA). KSA of some spiked BFRs and OCPs increased from Day 10 to 60 or 90 and leveled off afterward. This suggests that the volatility of BFRs and OCPs decreases over time as the chemicals become more strongly bound to the soil. Degradation of alternative BFRs (α- and β-TBECH, β-TBCO, DPTE), BDE-17, and αHCH (13C-labeled and nonlabeled) was evident in soils over 360 days, but no degradation was observed for the BDE-28, -47, -99, and TC (13C-labeled and nonlabeled). A method to separate the enantiomers of α-TBECH and β-TBCO was developed and their degradation, along with α-HCH (13C-labeled and nonlabeled) was enantioselective. This is the first study which reports the enantioselective degradation of chiral BFRs in soils. Discrepancies between the enantiomer fraction (EF) of chemicals extracted from the soil by dichloromethane (DCM) and air were found. It is suggested that DCM removes both the sequestered and loosely bound fractions of chemicals in soil, whereas air accesses only the loosely bound fraction, and these two pools are subject to different degrees of enantioselective degradation. This calls for caution when interpreting EFs obtained from DCM extraction of soil with EFs in ambient air.

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air exchange4 and evidence of fractionation of the lighter BDE (e.g., BDE-47) have been observed in background soils collected along a latitudinal transect through United Kingdom to Norway.5 High BDE levels in soils which have been received multiple applications of sewage sludge6,7 could be primary and secondary emission sources to the atmosphere, especially for

INTRODUCTION Polybrominated diphenyl ethers (BDEs) have been widely used in consumer products as brominated flame retardants (BFRs). BDEs are persistent, bioaccumulative, and can undergo longrange transport. Their occurrences in the environment have been widely reported.1 As the commercial formulations of the penta- and octabromodiphenyl ethers were added to the Stockholm Convention in 2009, the uses of BDEs are being phased out in many countries2,3 and the application for nonBDE BFRs (also referred to as alternative BFRs) will grow. A modeling study has suggested that BDEs can undergo surface © 2012 American Chemical Society

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was sieved with 2 mm mesh. A portion of the soil (200 g) was spiked with known amounts of chemicals in 15 mL acetone, dried for two hours (h) under a fume hood, and mixed with the remaining soil for 30 min. The chemicals spiked into soils included BDE-17,- 28, -47, -99 (200−400 ng g−1); alternative BFRs: α- and β-TBECH (each at 165 ng g−1), β-TBCO (160 ng g−1), DPTE (390 ng g−1), and OCPs: α-HCH (25 ng g−1), 13 C6-α-HCH (20 ng g−1), TC (20 ng g−1) and 13C10-TC (15 ng −1 g ). The spiked soil was divided into six portions of 200 g and stored in sealed glass jars. The soils were aged in the laboratory under room temperature and darkness. These nonsterilized soils are referred as experimental soils hereafter. A set of control soils was similarly prepared by sterilizing six 200 g portions of soil in glass jars using γ-irradiation (40 kGy) at the Department of Chemical Engineering and Applied Chemistry, University of Toronto, followed by spiking with the same suite of chemicals. The controls were aged in the laboratory, as for the experimental soils. The volatility (fugacity) and degradation of the chemicals in the experimental and control soils were monitored at days 10, 30, 60, 90, 180, and 360 after spiking. The experimental soils were aerated by briefly stirring the soils every 7−10 days. Measurement of Chemical Volatility from Soil. The volatility of a chemical from soil was described by the dimensionless soil-air partition coefficient, KSA=CSOIL·ρSOIL/ CAIR, where CSOIL (ng kg−1) and CAIR (ng m−3) are concentrations and ρSOIL is the dry solid soil density of 2650 kg m−3. CAIR was measured by placing the soils into a fugacity meter.21,26,27 Air was first passed through a water reservoir to achieve 100% relative humidity before it entered the soil column, where soil-air exchange occurred. The effluent air was passed through an adsorbent trap which contained C18-silica based sorbent (3 g) to capture the volatilized chemical. The C18 resin was rinsed with 10 mL acetone three times and 10 mL DCM before use. It was then dried by purging with nitrogen for 20 min. After a sample was collected, a surrogate recovery solution containing 26 ng 2H6-γ-HCH, 10 ng each of 13C10heptachlor exo-epoxide (13C10-HEPX), 13C12−PCB, -77, and -126, and 1 ng 13C12−PCB-118 was added to the C18 resin, then the C18 resin was eluted with 40 mL 50:50 hexane:DCM. The extract was blown down under a gentle stream of nitrogen and solvent exchanged to 200 μL isooctane for quantitative analysis. To ensure that measurements were performed under steadystate conditions in the fugacity meter, the flow rate was varied from 0.264 to 0.699 L min−1 and stable air concentrations were maintained (Supporting Information Table SI-1). The flow rate subsequently used was ∼0.67 L min−1 and ∼0.95 m3 of air was sampled for each event. Measurement of Chemical Degradation in Soil. CSOIL was determined by Soxhlet extracting 1 g of soil with 200 mL DCM which was blown down to 1 mL and solvent exchanged to isooctane, followed by cleanup on a column of 3 g neutral alumina (0.063−0.30 mm grain size, 6% water deactivated), eluted with 35 mL 20% DCM in hexane. The eluate was concentrated to 1 mL and solvent exchanged to isooctane. Prior to extraction, the soil was spiked with the same suite of recovery chemicals as for the air and mixed with granular anhydrous sodium sulfate to remove water. The soil moisture contents of the experimental and control soils in the jars were stable throughout the incubation period at 12 ± 0.4% and 12 ± 3% respectively. Microbial Parameters. Microbial activities were monitored and expressed in terms of colony forming units (CFUs)

the lower molecular weight BDEs and alternative BFRs of similar or higher volatility. Initial studies on alternative BFRs suggested that they may behave like BDEs and they have been reported in various environmental media. 1,8 α- and β-1,2-dibromo-4-(1,2dibromoethyl)cyclohexane (α- and β-TBECH) is found in arctic beluga,9 and eggs of herring gulls from the Great Lakes.10 2,3-dibromopropyl-2,4,6-tribromophenyl ether (DPTE) is found in the arctic atmosphere and seawater11−13 and also in blubber and brains of seals from the Barents Sea.14 In Canada, β-1,2,5,6-tetrabromocyclooctane (TBCO) is on the Canadian Environmental Protection Act nondomestic substance list, with import volume of 10 000 kg/y.15 Though not quantifiable, TBCO was identified in herring gulls from the Great Lakes.10 Little is known about the environmental fate and behavior of alternative BFRs in soils, although Nyholm et al.16,17 have investigated their degradation in soils and uptake by earthworms. After a chemical enters the soil it may relocate into the micropores of the soil matrix or become irreversibly bound to the soil, where it is less accessible for microbial processes or uptake by organisms.18−20 Similarly, the volatility of a chemical may be reduced the longer it stays in the soil, a phenomenon which has largely been ignored in soil emission models, which assume that the availability of a chemical for soil-air exchange does not vary over time. However, if only a fraction of the chemical is available for emission to the atmosphere, this could lead to over prediction in such models. Our previous laboratory and field investigations have shown that aging of spiked organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in a high-organic carbon muck soil led to a decrease in volatility of the residues21 and a decrease in extractability by the mild reagent aqueous hydroxypropyl-β-cyclodextrin (HPCD).21,22 Extractability by HPCD has been shown by others to correlate with bioaccessibility for microbial degradation23 and earthworm uptake.24 Furthermore, when we followed the enantioselective degradation of 13C6-α-hexachlorocyclohexane (HCH) in soil up to 700 days (d), we found that the (+) enantiomer was preferentially degraded leading to nonracemic residues. Surprisingly, we found that the enantiomer proportions in the dichloromethane (DCM) extract of the soil, were different from those obtained using HPCD and air, both of which yielded 13C6-α-HCH residues with the same enantiomer proportion.21 This difference occurred only for aged residues in unsterilized soil; 13C6-α-HCH in sterilized soil was not degraded over time and residues were racemic regardless of whether the soil was extracted with DCM, HPCD or air. This work is an extension of our previous study21 and was carried out with the aim of investigating the effect of aging on the volatility and degradation of BFRs and OCPs in soil over a one-year period. Chemicals selected were α-HCH, transchlordane (TC), BDE-17, -28, -47, -99; α- and β-TBECH, βTBCO, and DPTE. Except for the BDEs, all other chemical are chiral and their enantioselective degradation was examined as an indication of microbial processing. The enantiomer proportions in residues accessed by DCM vs air were also analyzed.

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MATERIALS AND METHODS Experimental Design. An urban soil with low organic carbon content of 5.6%25 from High Park, Toronto, Ontario, Canada was used in this study. Approximately 2 kg of the soil 2669

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Figure 1. Soil-air partition coefficients (log KSA) of BFRs and OCPs over 360 days of aging of nonsterile experimental (top) and sterile control, CON (bottom) soils. Vertical bars indicate standard deviations of triplicate measurements.

cyclodextrin in BGB 1, 15 m × 0.25 mm i.d., 0.18 μm film thickness, BGB Analytik AG, Switzerland). GC oven temperature program was: 80 °C for 1 min, ramped to 135 at 5 °C min−1 and held for 30 min, to 220 at 10 °C min−1 and held for 10 min. Inlet and MSD conditions followed the alternative BFRs method. Enantiomers of TC and 13C10-TC were separated using a BGB-172 column (BGB, 20% tertbutyldimethylsilylated β-cyclodextrin in OV-1701, 30 m × 0.25 mm i.d., 0.25 μm film thickness, BGB Analytik AG, Switzerland). Instrument operating conditions are reported in Kurt-Karakus et al.28 Results of enantiomer separations were expressed as enantiomer fraction (EF), EF = (+)/ [(+) + (−)] for αHCH, 13C6-α-HCH, TC, and 13C10-TC. Since correspondence between optical signs and chromatographic elution is not known for the alternative BFRs, EFs were calculated according to elution order, E1/(E1+E2) for α-TBECH and β-TBCO. Resolution of enantiomers was unsuccessful for β-TBECH and DPTE. Quality Control. A fugacity meter test with no soil was run as air blank (n = 13). Granular anhydrous sodium sulfate (1 g) was extracted as soil blanks (n = 15). Blanks were extracted and cleaned up in the same manner as samples. No target analytes were found in the air or soil blanks, but low levels of BDE-47 and -99 were found. The mean air blank values for BDE-47 = 0.15 ± 0.15 ng m−3 and BDE-99 = 0.06 ± 0.07 ng m−3. For soil, the mean blank value for BDE-47 = 4.7 ± 3 ng g−1, and BDE99 = 4.3 ± 3.7 ng g−1. All data were first screened by the limit of detection (LOD), which is 3 × SD of the blanks, and then blank corrected. BDE-47 measured in air was significantly higher than the air blanks, with p-value EFSOIL, while in others EFAIR < EFSOIL. In all of these studies, the soil extractions were done with DCM. Results have shown gradual increase in KSA over time for the spiked BFRs and OCPs, indicating formation of sequestered or bound residues and reduced volatility. The alternative BFRs were degraded more rapidly than the BDEs, which showed no declines over the 360 day period. Microbial processes were implicated by the enantioselective degradation of α-HCH (13Clabeled and nonlabeled), α-TBECH and β-TBCO. This is the first study which reports the enantioselective degradation of chiral BFRs in soils. The study also shows that care must be taken when interpreting EFs obtained from DCM extracts of soil alongside EFs in matched air samples during soil−air exchange studies. In such instances, use of a milder solvent such as HPCD may be used as an indication of the fraction of chemical in soil that is exchangeable with air.

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soils. This material is available free of charge via the Iinternet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Phone: 46 (0)8 674 7741; e-mail: [email protected], [email protected]. Present Address #

Department of Applied Environmental Science (ITM) Stockholm University, SE-106 91 Stockholm, Sweden

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ACKNOWLEDGMENTS We acknowledge funding from the Chemicals Management Plan of Environment Canada and Health Canada, and support of FW under the Research Affiliate Program through Environment Canada. Thanks to Georg Hottinger, BGB Analytik AG, for guidance in chromatography of the chiral BFRs. FW is grateful to Liisa Jantunen and Tom Harner of Environment Canada. We are grateful for comments of an anonymous reviewer, which improved the interpretation of the soil-air EF results.

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ASSOCIATED CONTENT

S Supporting Information *

Air concentration of BFRs and OCPs as function of flow rate; KSA measurements, soil concentration, and enantiomer fractions of BFRs and OCPs in experimental and control 2673

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