Research Evidence for Increased Gaseous PCB Fluxes to Lake Michigan from Chicago HUIXIANG ZHANG,† S T E V E N J . E I S E N R E I C H , * ,† T H O M A S R . F R A N Z , †,‡ JOEL E. BAKER,§ AND JOHN H. OFFENBERG§ Department of Environmental Sciences, Rutgers University, 14 College Farm Road, New Brunswick, New Jersey 08901, and Chesapeake Biological Laboratory, University of Maryland, Solomons, Maryland 20688
Urban-industrial areas exhibit atmospheric concentrations of organic contaminants that are often > 5-10× regional background. Increased emissions of PCBs into the urbanindustrial atmosphere leads to enhanced depositional fluxes to proximate waters. In this study, the increased airwater exchange inputs of PCB congeners into southern Lake Michigan driven by elevated atmospheric concentrations emanating from the Chicago, IL/Gary, IN air plume was studied. Intensive experiments were conducted in May and July 1994 and January 1995. The gaseous ΣPCB concentrations at the overlake site 15-km from Chicago ranged from 132 to 1120 pg/m3 with higher concentrations occurring in warm periods and when winds were from southerly and westerly quadrants. Dissolved phase ΣPCB concentrations ranged from 48 to 302 pg/L with concentrations in winter ∼2.5× higher than summer concentrations. Instantaneous net air-water exchange fluxes ranged from -32 (absorption) to + 59 ng/m2-d with absorptive flux highest in summer when winds were from the urban area and gas-phase concentrations were highest. Air and surface water temperatures and wind direction were the dominant factors influencing the magnitude and direction of air-water exchange fluxes. The modeled net air-water exchange flux of ΣPCB in the southern quarter of Lake Michigan was -18 ug/m2-yr (net absorption) in 1994, corresponding to 140 kg/yr net input.
mass balances, and as a potential mode of direct entry into the aquatic food chain (7-17). PCBs exhibited net volatilization on a whole-lake annual basis from Lake Superior and Lake Michigan in the early 1990s (11-13), while PAHs yielded net air-to-water transfer in Chesapeake Bay (17, 18) and Green Bay, Lake Michigan (7). Atmospheric deposition networks such as the Integrated Atmospheric Deposition Network (IADN) operating in the Great Lakes (14) and the Chesapeake Bay Atmospheric Deposition Study (CBADS) (19) were designed to capture the regional deposition signal and were focused in rural areas away from local sources. However, many urban/industrial centers are located near the Great Lakes and other coastal waters. Emissions of pollutants into the urban atmosphere are likely reflected in localized intense atmospheric deposition that is not observed in the regional signal. The southern basin of Lake Michigan is subject to contamination by urban and industrial air pollutants such as PCBs and PAHs, Hg, and trace metals (3, 5, 20-23) because of its proximity to industrialized and urbanized areas. Concentrations of PCBs and PAHs are significantly elevated in the Chicago atmosphere and over the lake 15-20 km offshore as compared to the regional signal (20). Higher concentrations are ultimately reflected in enhanced rain (24) and dry particle fluxes of PCBs and PAHs (6) to the coastal waters. The hypothesis of AEOLOS (Atmospheric Exchange Over Lakes and Oceans Study) was that emissions of hazardous air pollutants into the coastal urban atmosphere increased atmospheric depositional fluxes to proximate Great Waters, such as southern Lake Michigan off Chicago, IL/Gary, IN. This project grew out of Section 112m of the 1990 Clean Air Act Amendments that mandated an investigation of atmospheric depositional fluxes of contaminants and their source(s) and strengths to the Great Waters. The objective of this research was to determine the magnitude and direction of air-water exchange fluxes for PCBs in Lake Michigan as impacted by the Chicago air plume and to quantify the urban influence on annual and spatial inputs. The strategy of this research was to collect air and water samples simultaneously over the lake during seasonal intensive campaigns in order to calculate instantaneous fluxes within the southern basin. The measured air concentrations over the lake are correlated with meteorological conditions to estimate the annual cycle of atmospheric PCBs over the basin. Finally, the annual airwater exchange flux of PCBs in southern Lake Michigan is estimated.
Experimental Section Introduction Wet deposition via rain and snow (1, 2), dry particle deposition (3-6), and gaseous air-water exchange (7) are the three major atmospheric pathways for semivolatile organic chemical (SOC) input to aquatic systems such as the Great Lakes. Airwater exchange of polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and hexachlorocyclohexanes (HCHs) is now thought to be especially important in whole-system cycling of these compounds, in lake-wide * Corresponding author phone: (732)-932-9588; fax: (732)-9323562; e-mail:
[email protected]. † Rutgers University. ‡ Present address: Metropolitan Council Environmental Services, St. Paul, MN 55106. § University of Maryland. 10.1021/es981073+ CCC: $18.00 Published on Web 04/22/1999
1999 American Chemical Society
Sampling Strategy. The overall strategy was to simultaneously collect air and water samples from the EPA R/V Lake Guardian in southern Lake Michigan during intensive field campaigns in May and July 1994 and January 1995 while land-based air measurements were simultaneously made at Chicago, IL and South Haven, MI. Samples were collected in the southern lake basin at EPA monitoring sites 5, 1, and 0 (Table 1). Air Sampling. General Metal Works high volume air samplers were used to collect atmospheric gas and particulate-phase PCBs. Air was first passed through a glass fiber filter (GFF) (Whatman EP 2000, 20 × 25 cm) to collect particulate matter, followed by a polyurethane foam (PUF) adsorbent (0.05 g/cm3 density, 8 cm diameter × 10 cm height) to trap gaseous SOCs. Two Graseby GMW (Cleves, OH) HiVol organic samplers were modified for use onboard ship to VOL. 33, NO. 13, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Lake Michigan Sampling Sites and Sampling Information LM site 5 LM site 1 LM site 0 Chicago (IIT) South Haven MI
latitude
longitude
description
42°00′00′′ 41°46′00′′ 41°40′00′′ 47°50′04′′ 42°27′52′′
87°25′00′′ 87°20′00′′ 87°22′00′′ 87°39′29′′ 86°10′09′′
15 km NE Chicago 12 km SE Chicago 5 km from the shore 1.6 km W of the lake downwind site
study period
no. of samples
sampling site
May 17-19,1994 July 17-28, 1994 January 17-19, 1995
3, 12-h 18, 12-h 5, 12-h
site 5 site 5, 1, 0 site 5
separate the motor from the sampling head to minimize selfcontamination and interference with sampler operation and integrity. Air samples were taken every 12 h (0800-2000 h and 2000 to 0800 h corresponding to a day and night cycle, respectively) at calibrated flow rates of 0.5-0.8 m3/min at each site. The full sampling procedure can be found in Simcik et al. (20) and Zhang (25). Two air samplers were operated simultaneously aboard the ship on a yardarm deployed over the water. Two GFFs were sometimes positioned in-line to evaluate gaseous adsorption to the filter substrate or two PUF plugs were positioned in series to assess breakthrough of gas-phase PCBs. After sampling, PUF plugs were stored in sealed glass jars, while GFFs were placed in aluminum foil pouches. Meteorological data were collected aboard the ship at the overlake sampling sites throughout the sampling periods. The meteorological data collected at a 5 min frequency included air temperature, wind speed, wind direction, wave height, and atmospheric pressure. Water Sampling. Water samples were collected within the well-mixed surface layer (2-5 m) as determined by temperature profiles measured by casts with a Sea Bird 19 CTD every 12 h from aboard the EPA R/V Lake Guardian in the middle of the air sampling period (1600 and 0400 h). More than 500 L of lake water was first pumped from a depth of 5 m through a GFF (Schleicher and Schuell, No. 25, 293 mm) to collect particles, and ∼50 L of the filtrate was drawn (200 mL/min) through a glass column (2.5 × 30 cm) containing cleaned Amberlite XAD-2 resin to obtain the dissolved phase compounds. Details of the water sampling protocol are found in Offenberg et al. (26). Lake water was also analyzed for total suspended matter, particulate organic carbon (POC), and dissolved organic carbon (DOC). Analytical Procedure. Surrogate standards (10-25 ng) containing 3,5-dichlorobiphenyl (IUPAC no. 14), 2,3,5,6tetrachlorobiphenyl (IUPAC no. 65) and 2,3,4,4′,5,6-hexachlorobiphenyl (IUPAC no. 166) were added to PUF plugs in the field or soon after the samples were taken back to the laboratory. PCB surrogates (50 ng each) were similarly added to the XAD-2 resin prior to water sampling (26). The PUF plugs were extracted in a Soxhlet apparatus with 4:1 (v/v) mixture of petroleum ether and dichloromethane for 24 h. The extracts were concentrated in a Buchi rotavap apparatus where solvent was exchanged to hexane and subsampled for PCB analyses. The samples were then reduced to 1 mL under a gentle stream of purified N2. The PCB fraction was cleaned and on an alumina/silica column. Details of the procedure may be found in Simcik et al. (20) and Zhang (25). The internal standards used in this study were 2,3,5,6tetrachlorobiphenyl (IUPAC no. 30) and 2,2′,3,4,4′,5,6,6′octachlorobiphenyl (IUPAC no. 204). The final extract was concentrated to 0.1-0.2 mL under N2 and analyzed on a HP 5890 gas chromatograph (GC) equipped with a 63Ni electron capture detector (ECD), a HP autosampler, and a HP 3365 2130
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ChemStation on a 60 m 5% DB-5 capillary column (0.32 mm i.d.) with 0.25 µm film thickness (J & W Scientific). Details may be found in Simcik et al. (20). Concentrations of the individual PCB congeners were calculated using the internal standard method. The XAD-2 resin was extracted with 1:1 hexane:acetone and cleaned up on a silica and Florisil column, the extract reduced in volume, internal standards added, and the extract analyzed as above (see ref 26).
Quality Control and Quality Assurance Three types of PUF blanks were obtained in this study: laboratory blanks, field blanks, and 12-h field blanks. The laboratory blanks were clean PUFs left in the laboratory freezer. Field blanks were PUFs transported to the field and exposed to the field atmosphere. The PUF loaded in an inoperable air sampler for 12 h in the field was defined as a 12-h field blank. PCB mass in the field blanks was relatively higher in summer than in winter. The field blanks contributed
