Dechlorane Plus and Other Flame Retardants in a Sediment Core

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Environ. Sci. Technol. 2007, 41, 6014-6019

Dechlorane Plus and Other Flame Retardants in a Sediment Core from Lake Ontario XINGHUA QIU,† CHRIS H. MARVIN,‡ AND R O N A L D A . H I T E S * ,† School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana 47405, Water Science and Technology Directorate, Environment Canada, Burlington, Ontario, L7R 4A6 Canada

Our previous research on atmospheric samples suggested that Lake Ontario might receive significant amounts of Dechlorane Plus (DP), a highly chlorinated flame retardant, from the atmosphere and from inputs from DP’s manufacturing facility in Niagara Falls, New York. To confirm this suspicion, a sediment core from the central basin of Lake Ontario was analyzed for the two isomers of DP, for polybrominated diphenyl ethers (PBDEs), and for 1,2-bis(2,4,6-tribromophenoxy)ethane (TBE). The results showed that the concentration of DP in sediment increased rapidly starting in the mid-1970s and reached its peak concentration (310 ng g-1 dry weight) in the mid-1990s. The peak flux and total inventory of DP were estimated to be 9.3 ng cm-2 yr-1 and 120 ng cm-2, respectively. These values suggest that the total burden of DP in Lake Ontario is ∼20 tons and that the maximum load rate was ∼2 tons per year. The highest concentrations of PBDEs and TBE were found in the surficial sediment, with average concentrations of 2.8, 14, and 6.7 ng g-1 d.w. for PBDE3-7 (tri- through heptaBDEs), BDE-209, and TBE, respectively. The surface fluxes were 0.08, 0.43, and 0.20 ng cm-2 yr-1, and the inventories were 0.87, 3.9, and 1.8 ng cm-2 for PBDE3-7, BDE-209, and TBE, respectively. The concentration of DP in Lake Ontario sediment exceeds that of the brominated flame retardants combined.

Introduction Over the past three decades, the market for flame retardants has grown rapidly because of regulations aimed at reducing death and injury from fires. As a result, the fraction of bromine used to produce brominated flame retardants (BFRs) has increased from 8% in 1975 to 38% in 2000, taken on a global basis (1). Although saving lives is a good thing, it turns out that some of these BFRs have become environmentally ubiquitous and are now facing governmental regulations. A class of widely used flame retardants, the polybrominated diphenyl ethers (PBDEs), has received much attention over the past 5-10 years because of their potential toxicity, environmental persistence, and bioaccumulation (1, 2). As a result, two PBDE products, penta- and octa-BDE, have been banned in Europe and in some U.S. states, and the major manufacturer of these two products in the U.S. stopped production at the end of 2004 (3). Although this is a welcome * Corresponding author e-mail: [email protected]. † Indiana University. ‡ Environment Canada. 6014

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development, it should be noted that there are more than 175 different types of flame retardants (1), and those taken off the market are likely to be replaced by nonregulated ones. Clearly, it is prudent to monitor the environment for the presence of unexpected flame retardants that may enter the marketplace as other, regulated compounds leave. An early chlorinated flame retardant, developed by Hooker Chemical (now a part of Occidental Chemical Corporation and known as OxyChem), was called Dechlorane (C10Cl12). This same compound was also marketed under the name Mirex as a pesticide. Dechlorane (or Mirex) was banned in the 1970s because of its environmental effects (4). However, another highly chlorinated flame retardant, Dechlorane Plus (DP, C18H12Cl12), was introduced as a substitute for Dechlorane. Although DP was introduced into the flame retardant market in the 1960s, it did not receive much attention until recently, when it was found in air and sediment from the Great Lakes (5). Higher concentrations of DP were found in sediment from Lake Erie, as compared to Lake Michigan, an observation that suggested that the manufacturing plant, located in Niagara Falls, New York, might be an important source of DP to the Great Lakes (5). If this suggestion were true, Lake Ontario, which is downstream from DP’s production facility, would be even more highly contaminated with DP because of transport of DP emitted by the plant into the air or because of DP emitted by the plant into wastewater. We addressed this question by the analysis of a sediment core from Lake Ontario. Sediment is an important sink and reservoir of persistent pollutants, and emission histories are preserved as a function of depth in sediment, especially in lake sediment. Thus, the concentrations of pollutants in sediment cores indicate the chronology of that pollutant’s input into the environment. In this paper, we report concentrations of DP and other BFRs in a sediment core, as a function of depth, from the central basin of Lake Ontario.

Experiment Section Sampling Collection and Dating. The samples were taken from station 403 in Lake Ontario (43°,35′,32′′ N, 78°,13′,53′′ W) (Figure 1) in July 2004. Subcores were taken by inserting a tube (6.67 cm i.d.) into the sediment box, and each subcore was extruded and cut into 1 cm intervals. Two subcores were used for analysis (for one subcore, 0-15 cm was analyzed and for the other, 0-9 cm was analyzed). Samples were stored below -20 °C before analysis. Another core, which was collected at the same location in July 2006, was used for determining the sedimentation rate by measuring the specific activities of 210Pb using the polonium distillation procedure (6). In brief, ground and homogenized samples were treated with HCl to remove the carbonate materials and then spiked with a known amount of 209Po. The polonium was distilled in a tube furnace at 700 °C for 2 h and condensed on a wet glass wool plug outside the furnace. After cooling, the damp glass wool was digested in concentrated HNO3 under reflux. The residue was then filtered, and the filtrate was boiled down and digested with two HCl treatments to remove any remaining traces of HNO3. The polonium was then plated from the remaining solution onto a finely polished silver disk. The disk was counted in an alpha spectrometer (Tennelec TC256, Aptec). 210Po, which is the granddaughter of 210Pb, was identified by its 5.305 MeV R particle. The 210Po counts were compared to the 209Po counts to determine the activity of 210Po in the sediment samples. 10.1021/es070810b CCC: $37.00

 2007 American Chemical Society Published on Web 08/02/2007

FIGURE 1. The sampling site (ON 403) in Lake Ontario. Other sampling sites (ER 15, ER 1098, and ER 1085) used in previous work are also shown (5, 11). The star indicates the location of OxyChem’s manufacturing plant in Niagara Falls, NY. Organic Chemicals. DP was obtained from OxyChem (Dallas, TX). 1,2-Bis(2,4,6-tribromophenoxy)ethane (TBE) was purchased from Wellington Laboratories (Guelph, ON). All the PBDE congeners, including BDE-28, -47, -49, -99, -100, -116, -153, -154, -181, -183, -196, -197, -198, -201, -203, -204, -206, -207, -208, and -209, were purchased from AccuStandard (New Haven, CT). 2,2′,4,4′,5,5′-Hexabromobiphenyl (BB-153) was purchased from Ultra Scientific (North Kingstown, RI). DP from OxyChem was calibrated with separated standards of syn- and anti-DP from Wellington Laboratories (50 µg mL-1 in toluene, purity >98%). BDE-209 from AccuStandard, which was used as the quantitation standard in this research, was certified with standard samples from both the National Institute of Standards and Technology (NIST) and Wellington Laboratories, and the differences were 5:1. (c) The isotopic ratios for selected ion pairs were within (15% of the theoretical values. The recovery of surrogate standards (mean ( standard deviation) was 96 ( 12%, 88 ( 11%, and 88 ( 13% for BDE-77, BDE-166, and 13C12-BDE-209, respectively. The recoveries for the matrix spiked sample were 102 ( 15%, 97 ( 2%, 101 ( 2%, 87 ( 13%, and 96 ( 1% for DP, BDE-47, BDE-99, BDE-209, and TBE, respectively, which were the most abundant target compounds in the samples. One procedural blank was also run with each batch of samples. DP, BDE-209, and TBE were undetected in the blank samples. For BDE-47, -99, and -100, the blank values were ∼6% of each concentration for those compounds detected in the surficial sediment, and ∼100% of each concentration for those compounds detected in the deepest layers. In this paper, concentrations have not been blank or recovery-corrected. The concentrations reported here are the average concentrations for each of the top nine sections taken pairwise for the two subcores; otherwise, the concentrations from sections from the deepest subcore are reported. The duplicate measurements had an average percent difference of (35% for the top five sections and about twice that for the next four sections.

Results and Discussion Sedimentation Rate. The 210Pb activity profile of the sediment core was used to determine the sedimentation rate. Data were analyzed using the constant rate of supply (CRS) model, which gave a mass sedimentation rate of 0.043 ( 0.005 g cm-2 yr-1. This sedimentation rate agrees with that observed at station 40 in Lake Ontario (43°,35′,00′′ N, 78°,00′,00′′ W), which was reported to be 0.037 g cm-2 yr-1 using the CRS model (8). The sediment focusing factor indicates the horizontal movement of sediment particles to the sampling site due to turbulence and mixing, which may cause the settled sediment particles to redistribute. The focusing factor was calculated as the ratio of the accumulated 210Pb activity (unsupported 210Pb inventory) to that expected from regional atmosphere input, which has been reported to be 15.5 pCi cm-2 or 34.4 dpm cm-2 for the Great Lakes Region (9, 10). Our calculated sediment focusing factor was 1.44. Flame Retardants. High concentrations of DP were detected in the sediment core from Lake Ontario, with the maximum concentration of 310 ng g-1 dry weight (d.w.) at the 2-3 cm depth, which corresponds to a deposition year of 1994. In addition to DP, other target brominated compounds, including TBE, BDE-28, -47, -49, -99, -100, -116, -153, -154, -181, -183, -196, -197, -198, -201, -203, -204, -206, -207, -208, and -209, were detected in most sediment layers, with the highest concentrations in the surficial sediment. After converting the depth in the core to deposition year using the above sedimentation rate, we determined the temporal trends of the main target compounds (see Figure 2). Note the concentration scales in the four panels in Figure 2 are different and that the concentration of DP far exceeds that of the BFRs, including BDE-209 and TBE. The concentration of octa- and nona-BDE (including BDE-196, -197, -198, -201, -203, -204, -206, -207, and -208) was 1.7 ng g-1 d.w. in the surficial layer. Another target compound, BB-153, 6016

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FIGURE 2. Concentrations of DP (sum of syn and anti isomers) and other brominated flame retardants in a sediment core from Lake Ontario as a function of year of deposition. was detected in some core segments, with an average concentration of 0.15 ng g-1 d.w. in the surficial sediment. The inventory (in ng cm-2) of each target compound represents the total integrated mass of this compound per unit area from onset to the present. We estimate this sediment inventory using

Inventory )

1 FF

∑CFd

i i i

(1)

where Ci is the concentration in sediment segment i (in ng g-1 d.w.), Fi is the in situ density of this segment (in dry g per wet cm3), di is the thickness of each increment, which was 1 cm in this research, and FF is the focusing factor. The burden (in tons) is the inventory times the area of the lake. The flux (in ng cm-2yr-1) into the sediment segment i was calculated using

Fluxi )

CiR FF

(2)

where R is the sedimentation rate (0.043 g cm-2 yr-1 in this research). The load rate (in kg/yr) is the flux times the area of the lake. The surficial and maximum concentrations and fluxes, the annual load rates, the total inventories, and the total burdens in Lake Ontario of DP, BDE-209, PBDE3-7 (trithrough hepta-BDEs, including BDE-28, -47, -49, -99, -100, -116, -153, -154, -181, and -183), and TBE are given in Table 1 as the average values for the two subcores. Dechlorane Plus. In the mid-1960s, Hooker Chemical introduced Dechlorane Plus as a substitute for Dechlorane. DP is a highly chlorinated flame retardant, which is incorporated in industrial polymers used for coating electrical wires and cables, connectors used in computers, and plastic roofing material. Although it has been in use for decades, DP has only recently been detected in the environment (5, 11, 12). For example, Hoh et al. reported that significant concentrations of DP were observed at some sampling sites in the Great Lakes region, and these concentrations may have been related to a potential point source; namely, the DP manufacturing plant in Niagara Falls, NY (5). DP had previously been detected in sediment cores from Lakes Erie and Michigan (5, 11). In the eastern basin of Lake Erie (site ER 15, see Figure 1), DP’s maximum concentration was 40 ng g-1 d.w. (5), but this concentration decreased to 20 ng g-1 d.w. in the central basin of Lake Erie (ER 1098), 2.5 ng g-1 d.w. in the western basin of Lake Erie (ER 1085) (11), and around 5 ng g-1 d.w. in Lake Michigan (5). All of these concentrations were several orders of magnitude higher than

TABLE 1. Concentration, Flux, Load Rate, Inventory, and Burden of DP, PBDE3-7, BDE-209, and TBE in the Sediment from Lake Ontarioa g-1

surficial concn (ng d.w.) maximum concn (ng g-1 d.w.) -2 surface flux (ng cm yr-1) maximum flux (ng cm-2 yr-1) surface load rate (kg yr-1) maximum load rate (kg yr-1) inventory (ng cm-2) burden (tons) a

DP syn

DP anti

DP syn + anti

PBDE3-7

BDE-209

TBE

35 53 1.1 1.6 200 300 22 4.3

115 260 3.4 7.7 650 1450 98 19

150 310 4.5 9.3 850 1750 120 23

2.8 2.8 0.08 0.08 16 16 0.87 0.16

14 14 0.43 0.43 81 81 3.9 0.74

6.7 6.7 0.20 0.20 38 38 1.8 0.34

Area: 18960 km2.

those detected in the sediment from Lake Winnipeg (0.03 ng g-1 d.w.) (12), which is a remote lake at least 1400 km away from Lake Erie. These observations suggested that atmospheric transport and deposition could be a source of DP to the Great Lakes. Lake Ontario is downstream from the Niagara River, which passes by DP’s manufacturing plant. In fact, significant concentrations of DP (up to 89 ng g-1 d.w.) were measured in suspended sediment collected from the Niagara River where it enters Lake Ontario (11). This suggested that Lake Ontario could be receiving significant amounts of DP from this facility. In this research, the concentration of DP was 150 ng g-1 d.w. in the surficial sediment from Lake Ontario, and it was twice as high (310 ng g-1 d.w.) at the 2-3 cm (1994) depth. These concentrations were similar to those in surficial sediment samples collected from the central basin of Lake Ontario in 1998 (210 ng g-1 d.w.) (12). All DP concentrations in Lake Ontario sediment were far higher than those measured in Lakes Erie and Michigan. We suspect that the source of DP in Lake Ontario is different from that in Lakes Erie and Michigan. For example, the DP concentrations in Lake Erie sediment increased from west to east, which suggested atmospheric transport and deposition from a source at the eastern end of Lake Erie. On the other hand, DP’s source into Lake Ontario could include direct or indirect dumping into the Niagara River in addition to atmospheric deposition. Proportioning the extent of these two mechanisms is not yet possible. Clearly, DP’s manufacturing plant in Niagara Falls, NY might be a significant source of DP to Lake Ontario. According to the U.S. EPA Inventory Update Rule, the annual production of DP in the U.S. was 450-4500 tons after 1986 (13), and because there is only one manufacturing plant, all of this DP was produced in Niagara Falls, NY. DP was detected in all segments of the sediment core; however, in the deepest layers, the concentrations were much lower than in the surface layers (see Figure 2). This “background” level in the deepest layers might come from the downward migration of the pollutant after burial; from sampling and analytical artifacts, such as sediment smearing during core extrusion; or both. Nevertheless, there was certainly a large increase of DP concentrations after the mid1970s. This “beginning date” in Lake Ontario sediment was close to that in Lakes Erie and Michigan (5). In general, DP began to appear in sediment in the Great Lakes in about 1975. The sediment inventory of DP was 120 ng cm-2. On the basis of this inventory and assuming that the sediment profile of DP was the same all over Lake Ontario (14), we estimate the burden of DP in Lake Ontario to be 23 tons (see Table 1). Both the inventory and the estimated burden were twice as high as those in Lake Erie (5). The surficial sediment flux of DP in Lake Ontario is 4.5 ng cm-2 year-1 and 9.3 ng cm-2 year-1 at the 2-3 cm (1994) depth. With these flux data, we

FIGURE 3. Temporal trend of the fraction of the anti isomer relative to the total concentration of the two DP isomers. Only data from core segments dating after 1975 (with a total DP concentration of >10 ng g-1 d.w.) are shown. The red dotted line indicates the isomeric composition of the commercial DP product. estimate the historical highest input rate of DP into the sediment of Lake Ontario was 1800 kg per year around 1994 and 850 kg per year now. A high concentration and burden of DP in the sediment of Lake Ontario is perhaps not surprising given that Dechlorane, which was banned in 1970s, was more concentrated in Lake Ontario than in the other four Great Lakes because of inputs from the Niagara and Oswego Rivers (15). From 1950 to 1990, a total of ∼2700 kg of Dechlorane had entered Lake Ontario, but only ∼550 kg (∼20%) had been removed, mainly by transport through the St. Lawrence River (15). Although at present there are no accurate physicochemical property data available for DP, the estimated value of Kow is 109.3 (5). This is several orders of magnitude higher than that of Dechlorane (106.89) (16), suggesting that much less than 20% of the DP will be removed from the lake through the St. Lawrence River and that most of the DP that has entered Lake Ontario is still there in the sediment. Technical DP has two conformational isomers: syn (Ushaped) and anti (chair shaped). The fractional abundance (fanti) of the anti isomer (defined as the concentration of the anti isomer divided by the sum of the concentrations of syn and anti isomers) is 0.75 in the technical product as measured in our laboratory. Incidentally, although there are three industrial formulations of the technical DP product, they differ only in the particle size and not in composition (17). The temporal trend in fanti for the Lake Ontario core studied here is shown in Figure 3, which indicates that the surficial value of fanti is (on average) 0.76, a value close to that of the technical product. The value of fanti increases in the deeper layers, and around 1980, it was >0.90. This increased fanti VOL. 41, NO. 17, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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is similar to previous measurements indicating that BDE209 first appeared at core depths corresponding to 1979 in Lake Erie (7) and at core depths corresponding to 1978 in Drammenfjord, Norway (21). These so-called “advent” dates also coincide with the increasing production of commercial deca-BDE beginning in the late 1970s (22).

FIGURE 4. Concentrations of flame retardants in surficial sediment from Lake Ontario. Note the logarithmic scale. value with the passage of time may suggest that the anti isomer is more environmentally persistent than the syn isomer in sediment, which agrees with a suggestion by Tomy et al. (12). In this research, although only two subcores from one station (ON 403) were studied, because this sampling station was located in the central basin of Lake Ontario (Figure 1), it should be representative of the entire lake. Nevertheless, it would be useful to take more sediment cores from Lake Ontario, ranging over the length of the lake, to more fully determine the spatial distribution of DP in this important ecosystem. Moreover, because the sedimentation rate was relatively low in Lake Ontario, thinner core segments would give better time-resolved information on the historical input of DP to Lake Ontario. PBDEs. PBDEs are brominated flame retardants that are widely used in a variety of consumer and commercial products, such as textiles, polyurethane foam, and thermoplastics. There were three kinds of commercial PBDE: penta-, octa-, and deca-BDE. In this research PBDE3-7 refers to those PBDEs with three through seven bromines, including BDE28, -47, -49, -99, -100, -116, -153, -154, -181, and -183, congeners which mainly come from the penta- and octaBDE products. Figure 4 shows the concentrations of the major PBDE congeners in the surficial sediments. Notice that DP is 10 times more concentrated than BDE-209; in fact, DP is 5 times more concentrated than all of the BFRs combined at this site. The concentration of PBDE3-7 found in the surficial sediment from Lake Ontario was 2.8 ng g-1 d.w. (Figure 2 and Table 1). This concentration is similar to previous measurements in Great Lakes’ sediment; namely, 1.4, 3.0, 1.5, 1.9, and 5.6 ng g-1 d.w. in sediment from Lakes Superior, Michigan, Huron, Erie, and Ontario, respectively (7, 8, 18, 19). The congeners represented by PBDE3-7 are the less brominated ones, and they are likely to move greater distances through the atmosphere (relative to the more highly brominated congeners) because of their relatively higher vapor pressures and resistance to photodegradation (20). The similar concentrations of PBDE3-7 in the five Great Lakes suggests that (unlike DP) there is no strong point source for these compounds around the Great Lakes and that atmospheric transport and deposition are the most significant mechanism by which these congeners enter the lakes. BDE-209 is the main congener in the commercial decaBDE product, which (unlike the penta- and octa- products) is still being produced in Arkansas. Our data show that the concentrations of BDE-209 in sediment from Lake Ontario increased rapidly starting in the early 1980s. This observation 6018

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BDE-209 is the dominant PBDE congener in most sediment samples, no matter whether they are from a river, an estuary, a lake, or a sea. This ubiquity might be due to the high production of deca-BDE (24 500 tons were produced in the U.S. in 2001, 23) and due to BDE-209’s high Kow value (24), which forces BDE-209 to partition to sinking sediment particles. In our core, the highest BDE-209 concentration (14 ng g-1 d.w.) was found in the surficial sediment. This concentration was much higher than those of the other BFRs (Figure 4); however, our BDE-209 concentration was much lower than those observed by others. For example, Song et al. reported that the maximum concentration of BDE-209 was 240 ng g-1 d.w. in the surficial sediment from a nearby station in Lake Ontario (8). Even in the sediment from the same lake, the concentrations of PBDEs, including BDE-209, varied (25); however, the more than 1 order of magnitude concentration difference between this work and that of Song et al. was unexpected. The cause of this difference is not yet known. One cause might be in the calibration standards: In one instance in our laboratory, an incorrectly labeled calibration standard gave BDE-209 concentrations that were five times too high (26). Another possible cause might be related to recovery corrections: The recovery of the surrogate standard, 13C-BDE209, was ∼40% in the research of Song et al. (8), and their concentrations were recovery-corrected. In our laboratory, the recovery of 13C-BDE-209 was 88%, and no recovery corrections were made. The analysis of a duplicate core collected at site ON 403 by another laboratory also gave a concentration of ∼15 ng g-1 d.w. of BDE-209 in the surficial sediment (27). TBE. 1,2-Bis(2,4,6-tribromophenoxy)ethane (trade name FF-680) is a flame retardant produced by Great Lakes Chemical. TBE is mainly used in the production of plastic materials that require high manufacturing temperatures. It was first observed in the environment in 1977 (28), but it did not receive much attention until recently (29, 30). Hoh et al. reported concentrations of TBE in air (particle phase) that maximized near its manufacturing plant in El Dorado, Arkansas (30). This observation suggested that (unlike DP) atmospheric transport and deposition could be an important source of TBE to the Great Lakes, including to Lake Ontario. Our measurements of TBE in the sediment core from Lake Ontario showed increased levels starting after the early 1980s (Figure 2), and the maximum concentration was 6.7 ng g-1 d.w. in the surficial sediment. This concentration was similar to that observed in sediment from Lake Michigan (7.2 ng g-1 d.w.) (30). Both of these concentrations are much lower than those observed in sediment near the manufacturing plant site in Arkansas in 1977, which was as high as 470 ng g-1 (28). The surficial sediment concentration of TBE from Lake Ontario was about one-half of that of BDE-209 and more than twice that of PBDE3-7 (Table 1 and Figure 4). These sediment TBE concentrations suggest that its production could be comparable to that of PBDEs in recent years; in fact, in North America, 450-4500 tons of TBE were produced in 1998 (13), as compared to 33 000 tons of the penta-, octa-, and deca-BDE products produced in 2001 (23). If TBE is now being used to replace the discontinued octa-BDE product (3), it is likely that the TBE concentrations in sediment from the Great Lakes will increase in the future.

Acknowledgments This work is supported by the Great Lakes National Program Office of the U.S. Environmental Protection Agency (Grant No. GL995656, Melissa Hulting, Project Officer). We also thank Fan Yang at Environment Canada, Burlington, for the 210Pb measurements and sediment dating.

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Received for review April 5, 2007. Revised manuscript received June 19, 2007. Accepted June 29, 2007. ES070810B

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