Environ. Sci. Technol. 2008, 42, 9058–9064
Atmospheric Deposition of PBDEs to the Great Lakes Featuring a Monte Carlo Analysis of Errors MARTA VENIER AND RONALD A. HITES* School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana 47405
Received March 31, 2008. Revised manuscript received September 23, 2008. Accepted September 24, 2008.
The first estimates of atmospheric deposition of polychlorinated diphenyl ethers (PBDEs) into the Great Lakes are presented. Precipitation samples were collected monthly from 2005 to 2006 at five sites located in the Great Lakes region. Volume weighted mean concentrations of total PBDEs in precipitation ranged from 94 ( 19 ng L-1 at the urban site of Chicago to 0.65 ( 0.14 ng L-1 for the rural site of Sturgeon Point. Using gas and particle phase concentrations previously obtained in our laboratory and concentrations in precipitation measured in this study, the total annual net mass transfer rates to each lake and their relative errors were calculated using Monte Carlo analysis. The highest net mass transfer rates for BDE-47, and total PBDEs were measured for Lake Michigan (150 ( 40 and 310 ( 79 kg y-1, respectively) while the highest net mass transfer rate for BDE-209 was measured for Lake Erie (79 ( 56 kg y-1). We found good agreement between atmospheric and sediment net mass transfer rates for Lake Superior, but we found a significant imbalance of BDE-209 for the other two lakes and of BDE-47 for Lake Michigan. These findings suggest that Chicago might be a preferential source of BDE-47 to Lake Michigan and that Cleveland might be a preferential source of BDE-209 to Lake Erie.
Introduction With a water volume of ∼23 000 km3 and a surface area of 244 000 km2, the five North American Great Lakes contain, collectively, ∼20% of the world’s fresh surface water. Given their large surface areas, the input from atmospheric deposition plays a significant role in bringing pollutants to the lakes. The long residence times of these lakes (from 200 years for Superior to 3 years for Erie) (1) suggest that the impact of persistent pollutants will clear only slowly from the lakes. Moreover, approximately 35 million people live in this region (2). Some are distributed in sparsely populated regions, and some live in several big metropolitan and industrial areas (i.e., Milwaukee, Chicago, Detroit, Cleveland, and Toronto). All of these features make this system vulnerable to the input of pollutants, which can result from numerous anthropogenic activities. For many ubiquitous and persistent anthropogenic pollutants, the atmosphere is the main transport route from their sources to the Great Lakes (3). On the basis of their physical and chemical properties, pollutants can be transported on local, regional, and continental scales, and they can be removed from the atmosphere by dry particle * Corresponding author e-mail:
[email protected]. 9058
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deposition, gaseous air deposition, wet deposition, and atmospheric transformations. Although the atmospheric deposition of several persistent organic pollutants, such as PCBs and pesticides, to the Great Lakes has been studied in some detail (4), data on the atmospheric deposition of polybrominated diphenyl ethers (PBDEs) are lacking (5). To calculate PBDE’s net mass transfer rates, both air (gas and particle phase) and precipitation concentrations are required, and to date, no such data set is available. This study addresses this need. The objectives of this study were as follows: (a) to assess PBDE levels in precipitation in the Great Lakes basin in 2005 and 2006; (b) to evaluate the atmospheric deposition of PBDEs to lakes Michigan, Superior, and Erie; (c) to determine the influence of atmospheric deposition on the total net mass transfer rate of PBDEs to the lakes; and (d) to explain the observed net mass transfer rates, considering the possible sources of variability (i.e., deposition velocities and urban influences) and alternative inputs to the lakes. Thus, the annual net mass transfer rates to each lake were calculated using measured concentrations in the gas and particle phases obtained previously in our laboratory (6) and concentrations in precipitation measured in this study. The total net mass transfer rates (kg y-1) to each lake and their relative errors were calculated using a Monte Carlo analysis.
Experimental Section Sampling Methods. Samples were collected at the Integrated Atmospheric Deposition Network (IADN) sites; details are given at the IADN Web site (http://www.mscsmc.ec.gc.ca/iadn/index_e.html). The IADN network includes two urban sites, one in Chicago, IL (41.8344 °N, -87.6247 °W) and one in Cleveland, OH (41.4921 °N, -81.6785 °W); two rural sites, one at Sleeping Bear Dunes, MI (44.7611 °N, -86.0586 °W) and one at Sturgeon Point, NY (42.6931 °N, -79.0550 °W); and one remote site at Eagle Harbor, MI (47.4631 °N, -88.1497 °W). MIC automated wet-only samplers (MIC Co., Thornhill, ON, Canada) were used to collect precipitation samples. Details of the sampling procedure can be found elsewhere (7), and only a brief summary is presented here. Precipitation is collected with a 46 × 46 cm stainless steel funnel connected to a 30-cm long by 1.5-cm i.d. glass column (ACE Glass, Vineland, NJ) packed with XAD-2 resin (20-60 mesh). The funnel is normally covered with a Teflon padded lid. An electronic sensor detects a precipitation event and signals the lid to open. The XAD resin, through which the precipitation flows, collects both particle and dissolved phase organic compounds. Precipitation samples were integrated over 30 days, and the precipitation volume is recorded to calculate concentrations. Materials. A PBDE standard mixture was purchased from Wellington Laboratories (Guelph, ON). This solution contained the following PBDE congeners: 1, 3, 7, 10, 15, 17, 28, 30, 47, 49, 66, 71, 77, 85, 99, 100, 119, 126, 138, 139, 140, 153, 154, 156, 169, 171, 181, 183, 184, 191, 196, 197, 201, and 203-209. Other compounds we included in this standard mixture were the following: 2,2′,4,4′,5,5′-hexabromobiphenyl (BB-153), 1,2-bis(2,4,6-tribromophenoxy)ethane (TBE), and decabromodiphenylethane (DBDPE). Dechlorane Plus (DP) from OxyChem, BDE-118 from AccuStandard (New Haven, CT), and 13C12-BDE-209 from Wellington Laboratories were individually added to the calibration standard. Analytical Methods. The XAD-2 resin and the glass wool plugs were removed from the sampling column and Soxhletextracted for 24 h using a 1:1 (v/v) mixture of hexane and 10.1021/es8008985 CCC: $40.75
2008 American Chemical Society
Published on Web 11/07/2008
acetone. The extract was concentrated by rotary evaporation to a volume of ∼2 mL. The polar water layer was separated and back-extracted with hexane, which was added to the original extract. The extracts were fractionated on a 3.5% (w/w) water-deactivated silica gel column using hexane and a 1:1 (v/v) mixture of hexane and dichloromethane. The extracts were further concentrated by N2 blow down to ∼1 mL, spiked with the internal standard (BDE-118) for quantitation, and further concentrated to ∼100 µL. Both fractions were analyzed for PBDEs on an Agilent 6890 series gas chromatograph coupled to an Agilent 5973 mass spectrometer (GC/MS) using helium as the carrier gas. The 2 µL injections were made in the pulse splitless mode, with a purge time of 2.0 min. The injection port was held at 285 °C. An RxiTM, 15-m long × 0.25-mm i.d., 0.25-µm phase thickness, fused silica GC column (Restek Corporation, Bellefonte, CA) was used for determination of all the analytes. The GC oven temperature program was: isothermal at 100 °C for 2 min, 25 °C/min to 250 °C, 3 °C/min to 270 °C, 25 °C/min to 325 °C, and held at 325 °C for 11 min. The GC to MS transfer line was held at 280 °C. The samples were analyzed for the following PBDE congeners: 7, 10, 15, 17, 28, 47, 66, 85, 99, 100, 119, 126, 138, 139, 140, 153, 154 + BB-153, 156 + 169, 180, 183, 184, 191, 197, 201, and 203-209. TBE, DP, and DBDPE were also included in this analytical method. The mass spectrometer was operated in the electron capture negative ionization (ECNI) mode using methane as the reagent gas and an ion source temperature of 200 °C. Selected ion monitoring of the two bromide ions at m/z 79 and 81 was used to detect the less brominated PBDEs (from BDE-10 to BDE-180, plus TBE, BDE-205 and DBDPE). The ions at m/z 719.5 and 721.5 were used to quantitate BDE201, m/z 408.8 and 410.8 for BDE-197, m/z 561.7 and 563.7 for BDE-203, m/z 486.8 and 488.8 for BDE-204 and BDE-206 to BDE-209, and m/z 494.6 and 496.6 for 13C12-BDE-209. The ions at m/z 651.8 and 653.8 were used to detect the two conformers of DP. All compounds were quantitated using the internal standard method with BDE-118 as the internal standard. Quality Control. Four quality control criteria were used to measure the amounts of the target compounds: (a) The GC retention times matched those of the standard compounds within ( 0.1 min. (b) The signal-to-noise ratio was greater than 3:1. (c) The isotopic ratio between the ion pairs was within ( 15% of the theoretical value. (d) The recovery of at least two out of three recovery standards (BDE-77, BDE166, and 13C12-BDE-209) was over 70%. Either a procedural blank or a spike recovery sample containing PBDEs was run with every batch of 6-8 samples. Field blanks were collected at every site seasonally. The PBDE levels in the blanks were low enough so that we did not correct the concentration measured in the samples. At the remote sites, the average mass in the field blanks, as a percentage of the average mass in the samples, was
