Environ. Sci. Technol. 2010, 44, 9189–9194
Accumulation of Polybrominated Diphenyl Ethers, Hexabromobenzene, and 1,2-Dibromo-4-(1,2-dibromoethyl)cyclohexane in Earthworm (Eisenia fetida). Effects of Soil Type and Aging JENNY RATTFELT NYHOLM, ROBERT KUMAH ASAMOAH, LEON VAN DER WAL, CONNY DANIELSSON, AND PATRIK L. ANDERSSON* Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden
Received July 11, 2010. Revised manuscript received October 7, 2010. Accepted October 11, 2010.
In the present study the accumulation potentials in earthworms (Eisenia fetida) of selected brominated flame retardants (BFRs) were investigated. The tested BFRs, including polybrominated diphenyl ethers (PBDEs), hexabromobenzene (HBB), and 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), were found to be bioavailable to Eisenia fetida, and they accumulated in the earthworms. To our knowledge, this is the first published study to address the bioaccumulation potential of TBECH in terrestrial biota. Aging the soil resulted in decreased accumulation of TBECH, HBB, and PBDEs with six or less bromine atoms. However, no effect of soil aging was seen for BDEs 183 or 209, possibly due to their low mobility in soil. The use of different soils (artificial OECD soil and two natural Swedish soils) also affected the degree of accumulation in the worms. The results indicate that use of the generally accepted standard OECD soil may overestimate accumulation of organic contaminants by earthworms, due to high bioavailability of the contaminants and/or weight loss of the worms in it. Further, the accumulation of selected PBDEs and HBB was compared to the accumulation of their chlorinated analogues. Brominated compounds accumulated to the same or a lesser extent than their chlorinated counterparts.
Introduction Brominated flame retardants (BFRs) are a varied group of brominated chemicals which are used to inhibit fire in various products and materials, e.g., electronic devices, cables, and plastic foam. Polybrominated diphenyl ethers (PBDEs) are BFRs that have been widely used for several decades and are now ubiquitous in the environment (1-3). In 1999 the global production volumes of three commercial mixtures pentaBDE, octa-BDE, and deca-BDE were 8500, 3825, and 54800 tons, respectively (1). However, the use of PBDEs in the European Union has been restricted since 2006, and the industry in the U.S. has voluntarily phased-out the pentaand octa-BDE mixtures. * Corresponding author phone: +46907865266; fax: +46907867655; e-mail:
[email protected]. 10.1021/es1023288
2010 American Chemical Society
Published on Web 10/28/2010
The BFR 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH) has been used as an additive flame retardant, and its use is currently not regulated. Technical TBECH contains two diastereomers, R- and β-TBECH, and the production volume in the U.S. was between 4 and 225 tons in 2002 (http:// www.epa.gov/oppt/iur/tools/data/2002-vol.htm). TBECH was recently identified in whales (Delphinapterus leucas) from the Canadian Arctic (4) and in eggs of herring gull (5) and has been shown to have the potential to cause endocrine disruption (6). Another brominated flame retardant is hexabromobenzene (HBB), which was recently found in sewage sludge, sediment, and air samples (7, 8) and in eggs of herring gull (5, 9). We found no information on current production volumes, but HBB was one of the most heavily used flame retardants in Japan in the 1980s (10), and the production volume in the United States was between 4 and 225 tons in 1998 (http://www.epa.gov/oppt/iur/tools/data/ 2002-vol.htm). Emissions of HBB from polymeric BFRs (11) and its formation during thermolysis of decabromodiphenyl ether (12) are other potential sources of HBB found in the environment. More information on persistence and bioaccumulation potential is needed to predict the environmental fate of most of the BFRs. However, since it is likely that soil will be a major sink for BFRs, as has been shown for PBDEs (13, 14), knowledge of the bioavailability of these compounds in soil and their bioaccumulation potential in terrestrial food webs is of particular importance. Earthworms consume large amounts of soil and their thin cuticle is in almost constant contact with soil or soil pore water. If an organic contaminant is bioavailable and bioaccumulates in earthworms, it will enter the terrestrial food chain, as earthworms are eaten by many organisms from higher trophic levels. Therefore, earthworms have become common model organisms for testing the toxicity and bioavailability of contaminants in soil. Several studies have shown that various organic compounds bioaccumulate in earthworms, but the accumulation of PBDEs has only been investigated in a few studies with earthworms (15, 16) and aquatic worms (17, 18). The accumulation of organic contaminants in earthworms is often described by equilibrium partitioning, i.e., partitioning of the contaminants between pore water and the lipids in the earthworm (19). However, several factors influence the availability of organic contaminants in soil, e.g. physicochemical properties of the contaminants, composition of the soil and “ageing”, i.e., the duration of contact between the soil and the contaminants (20). The aim of the present study was to evaluate the accumulation of PBDEs, HBB, and TBECH in earthworms exposed to treated soil in the laboratory and to compare bioaccumulation of these compounds from artificial OECD soil and two Swedish natural soils. The OECD soil was added as a reference soil to allow for comparisons between studies. Furthermore, the accumulation of selected PBDEs and HBB was compared with the accumulation of their chlorinated analogues. Finally, accumulation of BFRs was determined after aging of a spiked OECD soil for approximately two years.
Materials and Methods Earthworms, Soils, and Test Chemicals. Earthworms (Eisenia fetida) were bred indoors in a mixture of soil and horse manure. Artificial OECD soil was bought from Pelagia Environmental Consult AB and consisted of peat (10%), kaolin (20%), and sand (70%). An agricultural heavy clay soil was collected in Lanna, Sweden (Lanna soil, 47% clay, 6.2% VOL. 44, NO. 23, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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organic matter), and a forest soil was collected in Kloten, Sweden (Kloten soil, 39% organic matter). The Kloten soil is typical for coniferous forests (haplic podzol) with an organic rich mor layer. These natural soils are among 13 Nordic reference soils that represent the most common soil types in the Nordic countries (21). The chemical structures of the tested compounds are shown in the Supporting Information (Figure S1). The octanol-water partitioning coefficient (log Kow) and the water solubility (Sw) of the tested compounds were derived in EPI Suite and are available in Table S1, Supporting Information. The tested chemicals were obtained from Chemische Fabrik Kalk GmbH, Ko¨ln-Kalk, Germany (pentaBDE-mix: Bromkal 70-5), Bromine Co Ltd., Beer Sheva, Israel (octaBDE-mix: Octa LM), Sigma-Aldrich, Stockholm, Sweden (BDE 209, TBECH, HBB), AccuStandard, New Haven, CT, (hexachlorobenzene HCB), or synthesized in-house (the chlorodiphenyl ethers; CDEs 47, 99, and 153). Analytical standards of the bromodiphenyl ethers (BDEs 47 and 153) were obtained from AccuStandard, and BDE 99 was obtained from Cambridge Isotope Laboratories (Andover, MA). Labeled (13C) BDE 209, BDE 77, HBB, HCB, and PCB 47 were used as internal standards, and 13C-PCB 208 or 13C-PCB 80 was used as a recovery standard. The labeled compounds were purchased from Cambridge Isotope Laboratories. Sodium sulfate, Florisil, silica, sulfuric acid, and diethyl ether (SeccoSolv) were purchased from Merck, Germany. Hexane, acetone, and dichloromethane (glass distilled) were purchased from Fluka, Switzerland. Soil Treatments. After the natural soils were passed through a 5 mm sieve, a mixture containing each of the test chemicals in acetone or tetrahydrofuran was blended with 400 g portions of each soil to obtain the final concentrations described below. The chemicals were blended into the soil using a stainless steel spoon, and soil was vigorously mixed for several minutes following a procedure described by Reid et al. (22). For BDEs, commercial mixtures were used and the presented nominal concentrations are approximate and depend on the composition of these mixtures. Bromkal 70-5 have high content of BDEs 47, 99, and 100, and lower content of BDEs 153 and 154, while Octa LM consists mainly of BDE 183. The compounds added to soil are reported in the Supporting Information (Table S1); some of them were not analyzed and will not be discussed here, since they are considered not to have an effect on the study. The solvent of the test solution was left to evaporate from the soils at room temperature for at least 24 h, the soils were then wetted to 60% of their water-holding capacity (WHC), and portions of each soil (400 g) were left for seven days in glass beakers covered in aluminum foil to equilibrate in the dark and at room temperature. After this equilibration period, all soils were rewetted until 60% WHC before earthworms were introduced into the soil. Concentrations of BFRs in soils were determined at the beginning and end of each experiment (see below). During the experiments, deionized water was added every second day to compensate for evaporation losses and maintain 60% WHC of the soils. Exposure and Sampling. Three experiments were carried out to study the accumulation of the test compounds in earthworms exposed to laboratory-treated soil. In experiment I, uptake kinetics and accumulation of BFRs were studied in earthworms exposed to spiked OECD soil. In experiment II, the effect of aging on uptake and accumulation in earthworms was investigated in OECD soil two years after spiking with the test chemicals, while in experiment III the influence of different soil characteristics on uptake in earthworms was studied for OECD and two natural soils. In all experiments, sets of 10 worms were exposed to 400 g of soil in glass beakers spiked with BFRs. 9190
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In experiment I, OECD soil was spiked with BFRs at a low, medium, and high level treatment, with nominal concentrations of approximately 10 ng, 100 ng, and 10 µg of each contaminant/g soil (wet wt), respectively. In the low level treatment, worms were exposed for 28 days only. These experiments were performed in triplicate. In the medium level treatment, worms were exposed for 2, 5, 8, 10, 13, 21, and 35 days in single beakers, and six beakers were kept for 28 days. After the 28-day exposure period, three beakers were sampled and worms in the remaining beakers were transferred to nontreated OECD soil for depuration and collected 3, 7, and 14 days later. In the high level treatment, the worms were exposed for 2, 5, 8, 10, 13, 21, and 28 days, as single samples, with the exception of the 28-day exposure, which was performed in triplicate. Control exposures for a 28-day period were performed in triplicate, using nontreated OECD soil. For experiment II, the medium level-treated soil was stored in darkness and at room temperature for an aging period of two years after which sets of worms were exposed to the aged soil for 28 days in duplicate. In experiment III, artificial OECD soil and the natural soils from Lanna and Kloten were spiked at a nominal concentration of 100 ng/g wet weight, and worms were subsequently exposed for 28 days, with triplicate samples for each type of soil. After exposure, the worms were placed between two wet filter papers for 24 h to allow gut clearance and then weighed and stored frozen (-20 °C) until pretreatment and extraction. In a few cases only nine worms were found in the soil after the exposure period (Table S2, Supporting Information); however, this was not treatment related. Soil was collected before and after worm exposure and was analyzed for concentrations of test compounds, and dry matter content and loss of ignition were determined. The dry weight was determined by drying the soil at 105 °C for 20 h, and the loss on ignition was determined by heating preweighed soil samples for 2 h at 550 °C. The loss on ignition was assumed to be equal to the soil’s organic matter content, which was used to calculate biota to soil accumulation factors (see below). Chemical Analysis. The nine or ten worms tested in each beaker were pooled, mixed, and homogenized with sodium sulfate. 13C-Labeled internal standards were used throughout each test to compensate for possible losses. The resulting mixture was then placed in an open column and extracted with acetone:hexane (5:2; 60 mL) followed by hexane:diethyl ether (9:1; 60 mL) (experiment I) or extracted in a Soxhlet apparatus using 200 mL of hexane:acetone (experiments II and III). Lipid content was determined gravimetrically. Soil samples (1-5 g) obtained from each experiment were homogenized, mixed with sodium sulfate, and then extracted using 200 mL hexane:acetone (2:5) in a Soxhlet apparatus. Both soil and worm extracts were cleaned-up using gel permeation chromatography, Florisil gel and silica gel impregnated with sulfuric acid (experiment I). In experiments II and III, the Florisil step was skipped and the samples were further purified with liquid-liquid extraction. Concentrations of the test chemicals, except for BDE 209, in soil and worm extracts were measured by GC-MS (Agilent MSD 5975) in electron ionization (EI) mode, with a 15 m DB5-MS column (0.25 mm i.d. × 0.10 µm film thickness; J&W Scientific, Folsom, CA). The temperature program of the oven was set as follows: start at 90 °C (1 min) and then increase to 240 °C with 25 °C/min and further increase to 315 °C (3 min) at a rate of 5 °C/min. The m/z ratios of the fragments recorded were as follows: 264.9 and 266.9 for TBECH, 547.5 and 549.5 for HBB, 483.7 and 485.7 for BDE 47, 563.6, and 565.6 for BDE 99, 641.5, and 643.5 for BDE 153, 721.4, and 723.4 for BDE 183, 284, and 286 for HCB, 306 and 308 for CDE 47, 342, and 344 for CDE 99, and 376 and 378 for CDE 153. BDE 209
FIGURE 1. Concentrations in earthworms of hexabromobenzene (HBB), 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), and bromodiphenyl ether (BDE) 47, 99, 183, and 209 after exposure in spiked soil (highest concentration ∼10 µg/g) for up to 28 days. was analyzed in electron capture negative ionization (ECNI) mode, using methane as the carrier gas and monitoring the m/z ratios of the fragments 485 and 487. Data Analysis. The accumulation of BFRs in earthworms from soil can be described by first-order kinetics (18). Equation 1 was used to model the concentration of BFRs in the earthworms during the exposure: Cworm ) ks/keCsoil(1 - e-ket)
(1)
where Cworm represents the BFR concentration in the worms in ng g-1, Csoil represents the BFR concentration in soil, ks is the uptake rate in ng day-1g-1 worm, ke is the elimination rate constant in day-1, and t is the time in days. If concentrations during both uptake and elimination period were available, models were made by simultaneously fitting measured concentrations to eq 1 and the following equation: Cworm ) C0e-ket
(2)
where C0 is, in this case, the modeled concentration after 28 days of exposure. The models were used to evaluate if steadystate conditions were achieved within the test period. All calculations were performed on fresh weights, as these data were considered more reliable (very low lipid weights were recorded). Biota-soil accumulation factors (BSAFs) were calculated as the measured concentration in worms after 28 days of exposure (on a lipid weight basis) divided by the measured concentration in soil (on an organic matter basis). Quality Assurance. Laboratory blank samples were analyzed in parallel to the treated samples, to ensure that contamination during homogenization, cleanup, and instrumental analysis did not significantly influence the results. Unexposed earthworms (day zero samples), untreated soil, and control worms (exposed to untreated OECD soil for 28 days) were also analyzed, to determine whether the worms and soil contained any of the test compounds before exposure or spiking, and if there was any significant cross-contamination between beakers during the exposure period. Compensation for losses of BDEs 47, 99, 153, 183, and TBECH was based on the recovery of the internal standard 13C BDE 77, while the levels of BDE 209, HBB, the CDEs, and HCB were corrected based on the recoveries of 13C BDE 209, 13C HBB, 13C PCB 47, and 13C HCB, respectively. The average recoveries of the internal standards were 77, 57, 82, 87, and
96% for labeled BDE 77, BDE 209, HBB, PCB 47, and HCB, respectively. No significant decrease in measured concentrations (based on wet weight) of the test compounds was observed during the 28-day earthworm exposure period for all soils, with the exception of HBB which decreased to 45% of the initial concentration in Lanna soil (t-test, p < 0.05); see Supporting Information, Figure S2. The decrease in soil concentrations seems to be substance specific, since after two years aging of the OECD soil, the concentration of HBB was reduced by approximately 90%; however, no reductions in concentration were seen for the other BFRs. The measured concentrations in soil are reported in Supporting Information, Figure S2. The percentage dry weight and organic matter content significantly differed between the soils; the dry weights were 59%, 78%, and 35% (dry wt/wet wt) in OECD, Lanna, and Kloten soil, respectively, while their organic matter contents were 9.9, 6.2, and 39% (dry wt/dry wt), respectively.
Results and Discussion BFR Concentrations in Earthworms Exposed in OECD Soil (experiment I). The tested PBDEs, HBB, and TBECH were all bioavailable to Eisenia fetida and accumulated in the earthworms (Figure 1). The BFR concentrations in the worms increased during the exposure period, and the worms exposed to the highest concentration of BFRs also showed the highest concentrations. Although elimination data showed high variation, it was clear that the concentrations in earthworms decreased when they were transferred to clean soil (shown in Figure S3, Supporting Information). The data was fitted to eqs 1 and 2, and the modeled concentrations after 28 days showed that >90% of steady-state concentrations were reached for all BFRs in worms exposed to the medium level, and in worms exposed to high levels except for BDE 99 (86% of modeled steady-state level), BDE 153 (76%), and BDE 183 (83%). Thus, the exposure time (28 days) was considered sufficient for determination of BSAFs. One of the worm samples (ten pooled worms) after 28 days exposure to the medium level showed very high concentrations of the PBDEs and deviated from the other observations (having up to five times higher concentrations). We found no explanation for this, but excluded this sample from the modeling and BSAF calculations. Exposing worms to the contaminants at these three levels resulted in a similar pattern between levels of accumulation factors for PBDEs; i.e., BSAFs decreased with increasing degree of bromination (Figure 2 and Table S4, Supporting VOL. 44, NO. 23, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 2. BSAFs for 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), hexabromobenzene (HBB), and bromodiphenyl ethers (BDE) 47, 99, 153, 183, and 209 in earthworms exposed for 28 days to OECD soil spiked with BFRs in three different concentrations (white bars, lowest concentration; gray bars, medium concentration; dark gray bars, highest concentration). Error bars denote one standard deviation. BSAFs determined in a study by Sellstro¨m et al. (2005) are shown with black bars. Information), in accordance with findings reported by Sellstro¨m et al. (16). BSAFs were based on lipid weight in earthworms (found in Table S2, Supporting Information) and organic matter in soil. In this study we did not measure the organic carbon content; however, traditionally a conversion factor of 0.5 is used to convert total organic matter to total organic carbon. Notably, this factor varies depending on type of organic matter in soil. However, it can be used as a rule of thumb when comparing BSAFs on OM basis to BSAFs on OC basis. As can be seen in Figure 2, the mean BSAFs for BDEs 47, 99, 153, and 209 in low level spiked soil and medium level spiked OECD soil were higher than corresponding values reported for these compounds in earthworms from contaminated field soils (16). This might be explained by differences in characteristics of soil (other than amount of organic matter) affecting the degree of accumulation, and/ or aging of the BDEs in the reported field soils, or rather the lack of aging in the OECD soils in our study. The BSAF values calculated for worms exposed to high level spiked soil were lower for all compounds except TBECH. The exposure levels in low and medium level spiked soil might be considered most environmentally relevant. Zou et al. (23) found levels in soil up to 3.8 ng/g dry wt (sum of PBDEs); however, levels as high as 450 ng BDE 47/g dry wt have been measured in soil after application of sewage sludge, with corresponding concentrations in earthworms of 10 000 ng BDE 47/g lipid wt (16). In our study, the measured soil concentration of, for example, BDE 47 in the low level exposure experiments was 10 ng/g dry wt, and measured concentrations at medium and high level were approximately 10 and 1000 times higher, respectively. This means that the highest exposure level of BDE 47 in our study was approximately twenty times higher than soil concentrations found in environmental hotspots. HBB accumulated in earthworms, and the BSAFs for this compound were 6.1, 6.0, and 2.3 in low, medium, and high level exposure soil, respectively. We found no additional information on the fate and environmental concentrations of HBB in earthworms, but Belfroid et al. (24) exposed earthworms to HBB via spiked feed and reported uptake of HBB but no biomagnification. These results clearly differ from the current study, which probably is related to different exposure pathways. The calculated BSAFs for TBECH were 2.2, 3.3, and 6.1 in the low, medium, and high doses, respectively. Notably, TBECH was the only compound showing a higher BSAF in the high level treatment group, compared to the medium and low level treatments. To our knowledge, the current study is the first to examine the 9192
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FIGURE 3. BSAFs for 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), hexabromobenzene (HBB), and bromodiphenyl ethers (BDEs) 47, 99, 100, 153, 183, and 209 in earthworms exposed for 28 days in OECD soil (medium concentration, ∼100 ng/g) aged for seven days (dark gray bars) or for approximately two years (light gray bars). bioaccumulation potential of TBECH in terrestrial biota. The present study shows that the tested PBDEs, HBB, and TBECH were all bioavailable and accumulated in earthworms. These compounds can thus be transferred to higher trophic levels if earthworms are exposed in the environment. Effect of Soil Aging on Bioavailability (experiment II). The bioavailability of organic contaminants in soil, generally, decreases as the soil ages, i.e., the contaminants become gradually less available to biota by time (20, 25, 26). The reason that organic compounds can become unavailable to soil biota is that they move into sites and pores that are inaccessible even to microorganisms, or that sorption to soil organic matter prevents microbial biodegradation. Not taking aging into account in risk assessment processes could lead to overestimations of the risks associated with a contaminated soil. On the other hand, since aged contaminants can become inaccessible for microbial degradation, contaminants can remain in soil for extended periods of time. Our study indicates that the accumulation of TBECH, HBB, and BDEs 47, 99, 100 and 153 in earthworms after 28 days exposure decreased in soil aged for approximately two years as compared to accumulation after 28 days in nonaged OECD soil (Figure 3). The BSAFs decreased by 70, 49, 21, 33, 26 and 30% for TBECH, HBB, and BDEs 47, 99, 100 and 153, respectively. However, for BDEs 183 and 209 there were no observed decreases in BSAF after aging of the soil. These compounds seem to be less affected by aging as compared with the other tested compounds, possibly because the mobility in soil of BDE 183 and BDE 209 is very low. BFR Concentrations in Earthworms Exposed in Three Different Soils (experiment III). The concentrations in earthworms of all tested compounds except HCB were higher after exposure to the contaminants in OECD soil than in Lanna and Kloten soils. Calculated BSAFs also showed that the accumulation in earthworms was generally higher in OECD soil than Kloten and Lanna soils (Figure 4). The lower BSAF values in Kloten soil compared with OECD soil (significantly lower for all compounds except TBECH, t-test p < 0.05) might be due to variations in organic matter characteristics yielding different partitioning and sorption processes in the two soils. Recent studies indicate that organic contaminants have varying affinities for different types of organic matter, e.g., high affinity for black carbon (27). The lower BSAFs in Kloten soil may also partly be explained by growth dilution. The earthworms in Kloten soil gained weight during the exposure period (19-28%), while worms exposed to OECD and Lanna soils decreased in weight during the BFR exposure period (by 13-19% and 18-24%, respectively), probably due to the higher content of organic matter (more
FIGURE 4. BSAFs for 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), hexachlorobenzene (HCB), hexabromobenzene (HBB), chlorodiphenyl ethers (CDEs) 47, 99, and 153, and bromodiphenyl ether (BDEs) 47, 99, and 153 after 28 days exposure to artificial OECD soil (black bars), an agricultural clay-rich soil from Lanna, Sweden (gray bars), and a forest soil from Kloten, Sweden (light gray bars). The concentration of test compounds in soil is approximately 100 ng/g wet weight. feed) in Kloten soil. Weight loss/gain of the worms can be seen in Table S2, Supporting Information. The differences in BSAFs between OECD and Lanna soil (which were significant for CDEs and HCB, t-test p < 0.05) might also be explained by differences in the composition of organic matter (peat in OECD soil) or by additional sorption to clay minerals in Lanna soil. Luo et al. (28) demonstrated that, for instance, phenanthrene may sorb to clay minerals, especially when the content of organic carbon in soil is low. Thus, our results suggest that normalization to total organic matter content in soil is not sufficient to describe the differences in accumulation in earthworms exposed to different soils due to diverse chemical characteristics of organic matter and potential sorption to clay minerals. Note that the BSAFs were calculated based on levels in worms at day 28 and measured soil concentrations at day 0. No degradation in soil was observed for any compound except HBB in Lanna soil, which may yield an underestimation of the BSAF of that compound in Lanna soil. Small differences in BSAFs between the diphenyl ethers, depending on their bromine or chlorine substitution patterns, were observed. The largest differences were seen between BDE 153 and CDE 153 where significantly lower accumulation was observed for BDE 153. When we compared the BSAF values of BDEs 47, 99, and 153 with their chlorinated analogues, CDEs 47, 99 and 153, we observed a significant decrease of BSAF with increasing number of bromines (Pearson’s correlation test, p < 0.05). Contrary, higher numbers of chlorine atoms resulted in higher BSAF values for CDEs in Kloten soil (p < 0.05), which also seemed to be the trend for OECD soil (p ) 0.09) but not for Lanna soil. In the Lanna soil the BSAF values of the CDEs were around 6, independent of the number of chlorines. This general trend with decreasing accumulation with increased degree of halogenation for brominated compounds may be a result of higher affinity or sorption to organic matter and/or clay minerals in soil. High elimination and biotransformation of the higher brominated congeners is also a possible explanation for the observed trend. In a study of biomagnification in zebrafish, Andersson et al. (29) detected large differences in magnification between chlorinated and brominated diphenyl ethers, probably due to debromination. Andersson et al. found that the biomagnification factor was much higher for CDE 99 than for BDE 99, probably due to debromination of BDE 99 to BDE 47 and consequently much lower for CDE 47 than for BDE 47. Debromination has also been observed in other studies where fish have been exposed to PBDEs (30, 31) and HBB (32). No debromination products of HBB
in earthworms were detected in the present study; neither is the metabolic capacity of earthworms in general believed to be a strong factor in the transformation of contaminants. However, recent studies show that earthworms do have some metabolic capacity for PAHs (33) and insecticides (34), and in the present study metabolism of the BFRs cannot be ruled out, especially since the BSAFs were generally higher for chlorinated than for brominated analogues and the BSAFs decreased with increasing number of bromines. Using standardized soil to test the effects or accumulation of organic compounds has the advantage of allowing results from different studies to be readily compared. However, when interpreting the results (extrapolating to the environment), differences in the bioavailability of different compounds have to be considered. We found significantly different BSAFs for different concentrations of BFRs, when the soil was aged and when different soils were used. Higher accumulation potential was observed using the generally accepted standard OECD soil as compared to two natural soils. In contrast, Hofman et al. (35) recently found extractability and uptake of phenanthrene in enchytraeid worms (Enchytraeus albidus) to be several-fold lower in artificial soils than in natural soils. These contradictory results warrant further studies to explore the underlying processes in soil in relation to chemical properties. Amounts and composition of organic matter, as well as clay minerals in natural soils, and their roles in sorption and availability of organic contaminants need to be further studied.
Acknowledgments This study was financed by grants from the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (Formas) (21.0/2002-1377) and from the Swedish Research program New Strategy for Risk Management of Chemicals (NewS) funded by the Swedish Foundation for Strategic Environmental Research (MISTRA). We thank Emma Thelander for performing some of the analytical work.
Supporting Information Available Figure S1 shows the chemical structure of the tested BFRs and chlorinated analogues. Figure S2 shows the measured soil concentrations (a) before and after aging of soil in experiment II and (b) before and after exposure of worms in experiment III. Figure S3 shows the modeled uptake and elimination of the BFRs in worms exposed to the medium concentration in experiment II. Table S1 lists all the chemicals spiked to soil and their Kow partition coefficients and water solubility values. Table S2 shows the weight of worms before and after exposure and their lipid content. Table S3 shows bioaccumulation parameters derived in the modeling. Table S4 shows all BSAFs determined in experiments I-III. This material is available free of charge via the Internet at http:// pubs.acs.org.
Literature Cited (1) de Wit, C. A. An overview of brominated flame retardants in the environment. Chemosphere 2002, 46, 583–624. (2) Tanabe, S.; Ramu, K.; Isobe, T.; Takahashi, S. Brominated flame retardants in the environment of Asia-Pacific: an overview of spatial and temporal trends. J. Environ. Monitor. 2008, 10, 188– 197. (3) Law, R. J.; Herzke, D.; Harrad, S.; Morris, S.; Bersuder, P.; Allchin, C. R. Levels and trends of HBCD and BDEs in the European and Asian environments, with some information for other BFRs. Chemosphere 2008, 73, 223–241. (4) Tomy, G. T.; Pleskach, K.; Arsenault, G.; Potter, D.; McCrindle, R.; Marvin, C. H.; Sverko, E.; Tittlemier, S. Identification of the novel cycloaliphatic brominated flame retardant 1,2-dibromo4-(1,2-dibromoethyl)cyclohexane in Canadian Arctic Beluga (Delphinapterus leucas). Environ. Sci. Technol. 2008, 42, 543– 549. VOL. 44, NO. 23, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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(5) Gauthier, L. T.; Herbert, C. E.; Weseloh, D. V. C.; Letcher, R. J. Current-Use flame retardants in the eggs of herring gulls (Laurus argentatus) from the Laurentian Great Lakes. Environ. Sci. Technol. 2007, 41, 4561–4567. (6) Larsson, A.; Eriksson, L. A.; Andersson, P. L.; Ivarsson, P.; Olsson, P.-E. Identification of the brominated flame retardant 1,2dibromo-4-(1,2-dibromoethyl)cyclohexane as an androgen agonist. J. Med. Chem. 2006, 49, 7366–7372. (7) Kuch, B.; Schneider, C.; Metzger, J.; Weber, R. Hexabromobenzene and pentabromophenol in German sewage sludge Indication of significant commercial use. Organohalogen Compd. 2005, 67, 434–437. (8) Arp, H. P. H., Møskeland, T., Goss, K.-U., Andersson, P. L., Nyholm, J. R. Presence and partitioning properties of “reemerging” flame retardants pentabromotoluene, pentabromoethylbenzene and hexabromobenzene in Norwegian hotspots. J. Environ. Monitor., submitted. (9) Gauthier, L. T.; Potter, D.; Herbert, C. E.; Letcher, R. J. Temporal trends and spatial distribution of non-polybrominated diphenyl ether flame retardants in the eggs of colonial populations of Great Lakes herring gulls. Environ. Sci. Technol. 2009, 43, 312– 317. (10) Yamaguchi, Y.; Kawano, M.; Tatsukawa, R. Hexabromobenzene and its debrominated compounds in human adipose tissue of Japan. Chemosphere 1988, 17, 703–707. (11) Gouteux, B.; Alaee, M.; Mabury, S. A.; Pacepavicius, G.; Muir, D. C. G. Polymeric brominated flame retardants: Are they a relevant source of emerging brominated aromatic compounds in the environment. Environ. Sci. Technol. 2008, 42, 9039– 9044. (12) Buser, H. R. Polybrominated dibenzofurans and dibenzo-pdioxins: thermal reaction products of polybrominated diphenyl ether flame retardants. Environ. Sci. Technol. 1986, 20, 404– 408. (13) Palm, A.; Cousins, I. T.; Mackay, D.; Tysklind, M.; Metcalfe, C.; Alaee, M. Assessing the environmental fate of chemicals of emerging concern: a case study of the polybrominated diphenyl ethers. Environ. Pollut. 2002, 117, 195–213. (14) Gouin, T.; Harner, T. Modelling the fate of the polybrominated diphenyl ethers. Environ. Int. 2003, 29, 717–724. (15) Matscheko, N.; Tysklind, M.; de Wit, C.; Bergek, S.; Andersson, R.; Sellstro¨m, U. Application of sewage sludge to arable landsoil concentrations of polybrominated diphenyl ethers and polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls, and their accumulation in earthworms. Environ. Toxicol. Chem. 2002, 21, 2515–2525. (16) Sellstro¨m, U.; de Wit, C. A.; Lundgren, N.; Tysklind, M. Effect of sewage-sludge application on concentrations of higherbrominated diphenyl ethers in soils and earthworms. Environ. Sci. Technol. 2005, 39, 9064–9070. (17) Leppa¨nen, M. T.; Kukkonen, J. V. K. Toxicokinetics of sedimentassociated polybrominated diphenylethers (flame retardants) in benthic invertebrates (Lumbriculus variegatus, oligochaeta). Environ. Toxicol. Chem. 2004, 23, 166–172. (18) Ciparis, S.; Hale, R. C. Bioavailability of polybrominated diphenyl ether flame retardants in biosolids and spiked sediment to the aquatic oligochaete Lumbriculus variegatus. Environ. Toxicol. Chem. 2005, 24, 916–925. (19) Sijm, D.; Kraaij, R.; Belfroid, A. Bioavailability in soil or sediment: exposure of different organisms and approaches to study it. Environ. Pollut. 2000, 108, 113–119.
9194
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 23, 2010
(20) Alexander, M. Aging, bioavailability, and overestimation of risk from environmental pollutants. Environ. Sci. Technol. 2000, 34, 4259–4265. (21) Tiberg, E. Nordic Reference Soils. ISBN: 92-893-0194-5. Nordic Council of Ministers, Copenhagen, Denmark, 1998. (22) Reid, B. J.; Northcott, G. L.; Jones, C. K.; Semple, K. T. Evaluation of spiking procedures for the introduction of poor water soluble contaminants into soil. Environ. Sci. Technol. 1998, 32, 3224– 3227. (23) Zou, M. Y.; Ran, Y.; Gong, J.; Mai, B. X.; Zeng, E. Y. Polybrominated diphenyl ethers in watershed soils of the Pearl River Delta, China: Occurrence, inventory, and fate. Environ. Sci. Technol. 2007, 41, 8262–8267. (24) Belfroid, A.; Meiling, J.; Drenth, H.-J.; Hermens, J.; Seinen, W.; van Gestel, K. Dietary uptake of superlipophilic compounds by earthworms (Eisenia andrei). Ecotox. Environ. Safe. 1995, 31, 185–191. (25) Morrison, D. E.; Robertsson, B. K.; Alexander, M. Bioavailability to earthworms of aged DDT, DDE, DDD, and Dieldrin in soil. Environ. Sci. Technol. 2000, 34, 709–713. (26) Godskesen, B.; Holm, P. E.; Jacobsen, O. S.; Jacobsen, C. S. Aging of triazine amine in soils demonstrated through sorption, desorption, and bioavailability measurements. Environ. Toxicol. Chem. 2005, 24, 510–516. ¨ .; Bucheli, T. D.; Jonker, M. O.; (27) Cornelissen, G.; Gustafsson, O Koelmans, A. A.; van Noort, P. C. Extensive sorption of organic compounds to black carbon, coal, and kerogen in sediments and soils: Mechanisms and consequences for distribution, bioaccumulation, and biodegradation. Environ. Sci. Technol. 2005, 39, 6881–6895. (28) Luo, L.; Zhang, S.; Ma, Y. Evaluation of impacts of soil fractions on phenanthrene sorption. Chemosphere 2008, 72, 891–896. (29) Andersson, P. L.; Wågman, N.; Berg, H. A.; Olsson, P.-E.; Tysklind, M. Biomagnification of structurally matched polychlorinated and polybrominated diphenylethers (PCDE/PBDE) in zebrafish (Danio rerio). Organohalogen Compd. 1999, 43, 9–12. (30) Stapleton, H. M.; Letcher, R. J.; Baker, J. E. Debromination of polybrominated diphenyl ether congeners BDE 99 and BDE 183 in the intestinal tract of the common carp (Cyprinus carpio). Environ. Sci. Technol. 2004, 38, 1054–1061. (31) Tomy, G. T.; Palace, V. P.; Halldorson, T.; Braekevelt, E.; Danell, R.; Wautier, K.; Evans, B.; Brinkworth, L.; Fisk, A. T. Bioaccumulation, biotransformation, and biochemical effects of brominated diphenyl ethers in juvenile lake trout (Salvelinus namaycush). Environ. Sci. Technol. 2004, 38, 1496–1504. (32) Nyholm, J. R.; Norman, A.; Norrgren, L.; Haglund, P.; Andersson, P. L. Uptake and biotransformation of structurally diverse brominated flame retardants in zebrafish (Danio rerio) after dietary exposure. Environ. Toxicol. Chem. 2009, 28, 1035–1042. (33) Stroomberg, G. J.; Zappey, H.; Steen, R. J. C. A.; van Gestel, C. A. M.; Ariese, F.; Velthorst, N. H.; van Straalen, N. M. PAH biotransformation in terrestrial invertebrates - a new phase II metabolite in isopods and springtails. Comp. Biochem. Phys. C 2004, 138, 129–137. (34) Hartnik, T.; Styrishave, B. Impact of biotransformation and bioavailability on the toxicity of the insecticides R-Cypermethrin and chlorfenvinphos in earthworm. J. Agric. Food. Chem. 2008, 56, 11057–11064. (35) Hofman, J.; Rhodes, A.; Semple, K. T. Fate and behaviour of phenanthrene in the natural and artificial soils. Environ. Pollut. 2008, 152, 468–475.
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