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Fate and Ecological Effects of Decabromodiphenyl Ether in a Field Lysimeter Wenchao Du, Rong Ji, Yuanyuan Sun, Jianguo Zhu, Jichun Wu, and Hongyan Guo Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es400730p • Publication Date (Web): 30 Jul 2013 Downloaded from http://pubs.acs.org on August 3, 2013
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Environmental Science & Technology
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Fate and Ecological Effects of Decabromodiphenyl
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Ether in a Field Lysimeter
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Wenchao Du,† Rong Ji,† Yuanyuan Sun,*, ‡ Jianguo Zhu,§ Jichun Wu, ‡ and Hongyan Guo †
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†
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Nanjing University, Nanjing 210046, China
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‡
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Geochemisty, Ministry of Education, School of Earth Science and Engineering, Hydrosciences
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Department, Nanjing University, Nanjing 210093, China
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§
State Key Laboratory of Pollution Control and Resource Reuse, School of Environment,
State Key Laboratory of Pollution Control and Resource Reuse, Key Laboratory of Surficial
State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese
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Academy of Science, Nanjing 210008, China
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ABSTRACT Flame-retardant polybrominated diphenyl ethers (PBDEs) are environmental
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contaminants. Deca-BDE is increasingly used commercially, but little is known about the long-
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term fate and impact of its major component, decabromodiphenyl ether (BDE-209), on the soil
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environment. In this study, we investigated the fate and ecological effect of BDE-209 over 4
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years in outdoor lysimeters planted with a rice-wheat rotation. BDE-209 and six lower-
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brominated PBDEs (BDE-28, -47, -99, -153, -154, and -183) were detected in soil layers of the
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test lysimeter. We calculated an average BDE-209 migration rate of 1.54 mg·m−2·yr−1. In
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samples collected in May 2008, November 2008, November 2009, November 2010, and
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November 2011, 95.5%, 94.3%, 108.1%, 33.8% and 35.5% of the spiked BDE-209 were
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recovered, respectively. We predicted the major pathway for debromination of BDE-209 in soil
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to be: BDE-209BDE-183BDE-153/BDE-154BDE-99BDE-47BDE-28. In plants,
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BDE-209 and seven lower-brominated PBDEs (BDE-28, -47, -99, -100, -153, -154, and -183)
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were detected. BDE-100 was mainly derived from the debromination of BDE-154 in plants, but
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sources of other lower-brominated PBDEs were still difficult to determine. In soils containing
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BDE-209 for 4 years, soil urease activity increased, and soil protease activity slightly decreased.
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Our results provide important insights for understanding the behavior of BDE-209 in agricultural
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soils.
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INTRODUCTION
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Polybrominated diphenyl ethers (PBDEs) are used as flame retardants in a wide variety of
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products. PBDEs are now globally dispersed in the environment,1–3 with soil as a major sink.4,5
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Their persistence, bioaccumulation, and potential toxicity has raised concern.6 Accordingly, the
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production and use of commercial penta- and octa-BDE mixtures have been recently restricted.7
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However, deca-BDE is still legally used in electrical and electronic products.8 With the
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increasing production and use of deca-BDE, the environmental concentration of its major
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component, BDE-209, already the predominant PBDE congener in soils,9-11 may increase over
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time.
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BDE-209 is also a source of lower-brominated congeners in soil.12 BDE-209 and its lower-
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brominated derivatives can be retained in soils and subjected to many processes and reactions,
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including adsorption and desorption, degradation, uptake by plants, and leaching. If taken up
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by plants, these congeners translocate from roots to shoots and could accumulate in the food
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chain.13 At the same time, the preferential flow of particles and dissolvable organic matter could
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enhance transport of such organic pollutants to deeper soil layers, which could endanger
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groundwater quality.14 However, vertical transport of BDE-209 has not yet been investigated,
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which is necessary for an understanding of its overall environmental fate. Toxicological effects
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of BDE-209 on soil microbial activity have also been investigated, proving adverse impacts of
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BDE-209 on the structure and function of the soil microbial community and microbial
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processes.15,16 But these studies were carried out in laboratory for short period, and the long-term
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impact of BDE-209 on natural soil still needs further investigation.
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In the study presented here, we conducted a 4-year outdoor lysimeter experiment to investigate
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the long-term fate and ecological effect of BDE-209 in agricultural soils. We periodically
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determined the concentration and vertical transport of BDE-209 and its debrominated congeners
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in the soil column and their distribution in crops, which provided insights into the fate of BDE-
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209. We also evaluated the effects of BDE-209 on soil quality by assessing differences in soil
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enzymes related to C and N cycle in soil, including urease, protease, catalase and peroxidase,
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between control soil and soil spiked with BDE-209 and aged for 4 years.
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MATERIALS AND METHODS
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Experiment Site and Lysimeters. The study was carried out in the Changshu Agroecological
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Experimental Station of the Chinese Academy of Sciences (Changshu, Jiangsu, China)
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(31°32′45″N, 120°41′57″E). The research site has a humid subtropical monsoon climate. During
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the study period, the annual mean air temperature was about 15.5 °C, the annual mean
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precipitation was 1,038 mm, and the length of the annual non-frost period was approximately
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242 days. The field was previously used for agronomic management. The soil was classified as
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gleysols with a pH of 7.36. Sand, silt, and clay contents of the upper soil (0–15 cm) were 32.6,
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44.7, and 22.7%, respectively. Organic carbon content was 4.6% in the upper 0–15 cm layer,
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1.9–2.5% in the 15–40 cm layer, and 1.5% in the 40–70 cm layer.
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The lysimeters (100 cm in height and 80 cm in inner diameter) used were established in 2000.
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Details of their construction are provided in Supporting Information. Two lysimeters were used,
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the control lysimeter and the test lysimeter. On November 10, 2007, the plowed layer of soil (0–
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15 cm in depth, ~90 kg) was removed from the lysimeters, air-dried, and crushed. For the test
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lysimeter, the removed soil was mixed thoroughly with 2.1 g BDE-209 dissolved in 50 mL
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toluene to reach a concentration at ~20 mg/kg, added back to the lysimeter, and covered with
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non-spiked soil (5 kg) to establish a buffer layer in an effort to minimize evaporation and
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photolysis of BDE-209 in soil. The starting concentration was finally measured to be 23.3
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mg/kg in 0-15 cm layer of the test lysimeter. For the control lysimeter, the removed and crushed
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soil was mixed with 50 mL toluene without any PBDEs and added back as test lysimeter. Since
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the plowed layer was originally poorly structured, spiking presumably did not adversely alter its
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structure.
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Crop Cultivation and Sampling. Experiments were conducted from November 2007 to
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November 2011. Wheat and rice were planted in rotation: wheat sown in November and
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harvested in May; rice sown in June and harvested in October. Field management of the plants
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followed agricultural practices of local farmers.
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Soil cores (2 cm in diameter and 80 cm in depth, n=3) from test and control lysimeters were
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sampled after the wheat/rice harvest in May 2008, November 2008, November 2009, November
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2010, and November 2011. Soil cores were sampled using an earth-boring auger (2 cm in
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diameter). Samples were taken layer by layer, at 10-cm-deep intervals. Each soil layer sample
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was thoroughly mixed, and a small amount of soil was removed for determining PBDEs. Soil
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from each lysimeter remaining after sampling was mixed layer by layer. Holes in the lysimeter
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were then carefully restocked with mixed soil of the respective layer and compacted. Four years
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after spiking, in November 2011, surface soils (0–20 cm depth) of the control lysimeter and the
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test lysimeter were sampled, homogenized, air-dried, and ground to pass through a 2-mm sieve;
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the enzyme activities of these samples were assayed. At grain maturity, in May 2008, May 2009,
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November 2009, November 2010, and November 2011, wheat or rice plants were harvested and
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separated into four parts (leaves, stems, shells, and grains); the concentration of PBDEs in these
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samples were determined.
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Determination of PBDEs. Briefly, soil and plant samples were extracted using an accelerated
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solvent extractor (ASE-350, Dionex, Sunnyvale, CA, USA) with a mixture of acetone and n-
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hexane (1:1, v/v). The polychlorinated biphenyl PCB-209 was added as a surrogate standard to
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samples prior to extraction, and PCB-141 was added to final solutions as an internal standard.
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PBDEs were analyzed by gas chromatography with tandem mass spectrometry (GC-MS/MS
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7890A-7000B, Agilent, USA). A HP-5 15m×0.25mm×0.5µm column (Agilent, USA) was used
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for determination of BDE-209 and lower-brominated PBDEs (BDE-28, -47, -99, -100, -153, -
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154, and -183). Details of sample extraction and analysis are provided in Supporting
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Information.
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Quality Assurance and Quality Control. Quality control included regular analyses of
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procedural blanks, blind duplicate samples, and random injection of solvent blanks and
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standards. The limit of detection of the method, a signal of three times the noise level, ranged
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from 0.1 µg/kg for lower-brominated PBDE congeners and 1 µg/kg for BDE-209. For each
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batch of 12 samples, procedural blanks were consistently analyzed; PBDE levels in blanks were
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under the limit of detection. The recovery of the surrogate standard PCB-209 was 86–102%. The
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recoveries of PBDE congeners in spiked laboratory blank samples (PBDE congeners spiked into
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anhydrous sodium sulfate) were as follows: BDE-28, 88–92%; BDE-47, 80–95%; BDE-100, 76–
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92%; BDE-99, 87–93%; BDE-154, 75–91%; BDE-153, 78–84%; BDE-183, 67–69%; and BDE-
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209, 67–68%. The relative standard deviations were
