Environ. Sci. Technol. 2002, 36, 4741-4747
Atmospheric Concentrations and Fluxes of Organic Compounds in the Northern San Francisco Estuary PAM TSAI,* RAINER HOENICKE, AND DONALD YEE San Francisco Estuary Institute, 7770 Pardee Lane, Second Floor, Oakland, California 94621 HOLLY A. BAMFORD AND JOEL E. BAKER Chesapeake Biological Laboratory, University of Maryland, Center for Environmental Science, Solomons, Maryland 20688
A study was conducted to measure atmospheric concentrations of PAHs and PCBs and estimate their fluxes between air and water in the northern San Francisco Estuary. Ambient air samples were collected once every 12 days at a single sampling site in Concord, CA, from June to November 2000, using a modified high-volume air-sampling device equipped with glass fiber filters and polyurethane foam. Concentrations of total PAHs and PCBs ranged from 5.7 to 56 and 0.17 to 0.32 ng/m3, respectively. PAHs and PCBs in the ambient air were predominantly in the vapor phase (83-99%). Gaseous fluxes of PAHs in the estuary showed high seasonal variation, ranging from 110 ng‚m-2‚day-1 efflux in August to 1050 ng‚m-2‚day-1 influx in November. Gaseous PCBs showed consistent net volatilization (2.2-24 ng‚m-2‚day-1) for this period. Particle settling contributed estimated net deposition fluxes of 45960 ng‚m-2‚day-1 for PAHs and 0.39-2.1 ng‚m-2‚day-1 for PCBs. Combining these fluxes, PAHs were either deposited to or lost from the estuary via the atmosphere, depending on the month. In contrast, there consistently was net emission of PCBs from the estuary to the atmosphere.
Introduction Polychlorinated biphenyls (PCBs) impair at least one beneficial use of the San Francisco Estuary; fish caught from the estuary have shown high PCB concentrations (1), causing issuance of a fish consumption advisory by a state environmental agency. Polycyclic aromatic hydrocarbons (PAHs) are also contaminants of concern due to their potential toxicity to benthic organisms (2) at concentrations frequently found in sediments of the estuary. This study was therefore initiated and funded by participants in the Regional Monitoring Program for Trace Substances (RMP), a long-term environmental monitoring program in the region. The primary objectives of this study were as follows: (1) to determine concentrations of PAHs and PCBs, in both gaseous and particulate phases, in the ambient air; and (2) to estimate direct dry atmospheric deposition fluxes of PAHs and PCBs in the San Francisco Estuary to fill an important data gap in an ongoing pollutant mass budget evaluation. The region is densely urbanized, with a mix of residential, commercial, (primarily light) industrial, agricultural, and * Corresponding author, Current address: U.S. EPA Region IX, 75 Hawthorne St., San Francisco, CA 94105. Phone: (415) 947-4196. Fax: (415) 947-3583. E-mail:
[email protected]. 10.1021/es011470b CCC: $22.00 Published on Web 10/16/2002
2002 American Chemical Society
undeveloped (open space) land uses. There are many congested major highways surrounding the estuary, and several petroleum refineries are located in the North Bay region, near the sampling site. Given this mix of past and present land uses, the atmosphere may be one pathway by which organic contaminants may be introduced or redistributed within the region. Sources of PAHs. PAHs enter the environment primarily as a result of human activities. Vehicle traffic, coke manufacturing, aluminum production, and forest fires/wood burning are the major sources of PAH emissions in the United States (3). Sources of various particle-associated PAHs can be identified from isomer distributions. Ratios of nonalkylated to alkylated PAHs are typically 1-2 for pyrogenic mixtures formed at higher temperatures and 0.2-0.5 for petrogenic PAHs formed at lower temperatures (4). In a study analyzing gasoline and diesel exhaust samples collected in northern California, light-duty vehicles were a significant source of heavier (four- and five-ring) PAHs (HPAHs), whereas heavy-duty diesel engines were the dominant source of three-ring and lower molecular weight PAHs (LPAHs) (5). Older automobiles produced total PAHs in exhaust at over 25 times the rate of newer automobiles equipped with catalytic devices (6). New diesel trucks emitted PAHs at one-seventh the rate of older autos. In RMP water and sediment samples, HPAHs dominate, averaging over 80% in the particulate phase. Differences among LPAH-to-HPAH ratios of air, water, and sediment samples may result from differences in their contributing sources combined with environmental fate and transport processes. Sources of PCBs. Manufacturing of PCBs was banned in the United States in 1977 because of evidence that PCBs persisted, accumulated in the environment, and caused harmful effects (7). PCBs may still be in use in closed systems and other legacy equipment. Although no known PCB manufacturing or handling facilities were located in the San Francisco Bay area, their widespread use in a variety of consumer, industrial, and military applications in past decades resulted in environmental releases. They continue to cycle through the estuary through multiple pathways, including atmospheric transport. Like PAHs, the relative abundance of PCB congeners may represent the signature of their sources combined with environmental degradation and transport processes (8).
Experimental Section Sample Collection. The California Air Resources Board (CARB) and Bay Area Air Quality Management District (BAAQMD) monitor ambient air quality in the region. From June 5 to November 21, 2000, this study collected 24-h integrated air samples every 12 days from the BAAQMD monitoring station located in Concord, CA (Figure 1). Air was sampled by a modified Hi-Volume air sampler (model GPSHV1-313; Andersen Instruments Inc., Smyrna, GA) pulling air through a sampling unit. The unit consisted of a 25 cm × 20 cm, 40-µm nominal pore-size glass fiber filter held in a metal frame and a polyurethane foam plug (PUF; 8.5 cm × 10 cm) in a glass holder, arranged in series for sequentially extracting particulate and gaseous organic contaminants, respectively. The sampler flow rate was 0.35 m3/min to collect 500 m3 of air for the first five samples, which was later increased to 0.5 m3/min (800 m3). Washed glassware and glass fiber filters were wrapped in aluminum foil and baked at 450 °C. PUF plugs were soaked VOL. 36, NO. 22, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Air and water monitoring stations in the San Francisco region. in a detergent bath, rinsed with ultraclean (Nanaopure) water, and then Soxhlet extracted with chromatographic-grade petroleum ether for 24 h. Following extraction, PUFs were dried in a vacuum desiccator and stored in prebaked glass containers until assembly. Sampling units were prepared and preassembled at the Chesapeake Biological Laboratory (CBL) and shipped to the sampling site. Upon sample return to CBL, PUFs were removed from their glass sleeves with forceps, individually sealed in glass jars, and stored at -20 °C until analysis. Filters were folded individually in aluminum foil and stored frozen until analysis. Sample Extraction and Analysis. Filters were extracted with dichloromethane in Soxhlet flasks for 24 h. PUFs were extracted with petroleum ether for 24 h in Soxhlet flasks. Extracts were reduced to
