Diffusive Exchange of Gaseous Polycyclic Aromatic Hydrocarbons and Polychlorinated Biphenyls Across the Air−Water Interface of the Chesapeake Bay (original) (raw)
Related papers
Patterns of Mass Sedimentation and of Deposition of Sediment Contaminated by PCBs in Green Bay
Journal of Great Lakes Research, 1996
Almost one thousand sediment samples were collected from many sediment depths at sixty-four sampling stations in Green Bay as part of the Green Bay Mass Balance Study. The samples were analyzed for and PCB congeners. Mass sedimentation rates and mixed depths were calculated from radionuclide profiles constructed for each sampling station. Most of the mass sedimentation in Green Bay occurs in the southern bay. Maximum sedimentation rates reach levels above 150 mglcm 2 /yr. Three distinct sedimentation zones exist. The main sedimentation zone, located between the Peshtigo River and Sturgeon Bay, receives sediment from throughout the southern bay. South of this zone, the Oconto River helps to create a second smaller zone of sedimentation. The Fox River supports a much larger zone which is focused at its southern end, located along the eastern shore of Green Bay about 35 Km from the mouth of the Fox River. Maximum depth-averaged sediment PCB concentrations are about 1500 ng/g dry. By combining sedimentation data and measured sediment PCB concentrations, it was possible to calculate the mass of PCBs in Green Bay sediment. Green Bay contains about 8500 Kg of PCBs, and PCB-contaminated sediment is not uniformly distributed over the bay. 1nstead, the most contaminated sediments, as well as the greatest mass of sediment-bound PCBs, are located in the Fox River deposition zone. Sediment from the other three major rivers entering the bay dilutes the contaminated Fox River sediment. Highly contaminated sediment is found only in the Fox River deposition zone. About 50% of the total mass of PCBs in Green Bay sediments is found within 10 Km of this zone, in an area equal to about 3% of the total area of the bay. Despite this fact, eliminating PCBs from Green Bay would require the removal of large amounts of sediments.
Polychlorinated biphenyls in Narragansett Bay surface sediments
Chemosphere, 2004
Polychlorinated biphenyls (PCBs) were evaluated in 41 surface sediments collected from Narragansett Bay, RI in 1997-1998. Highest concentrations of total PCBs (1760 ng/g) were in rivers at the head of the bay and the values decreased southward toward the mouth of the bay, with elevated concentrations in some of the coves. The PCB levels in $43% of the samples exceeded the effects range median (ERM) guideline [Environ. Manage. 19 (1995) 81] indicating possible adverse biological effects at these stations. Principal component analysis (PCA) of the surface sediment PCBs separated the Taunton River samples from the rest of the samples. This result suggests that this river has a different PCB composition and sources than the other areas investigated. It also showed that this river has a limited influence on other bay stations as the adjacent samples downstream did not have the same chemical signature. Congener ratios derived from the PCA were useful in distinguishing stations that had different sources of PCBs than the bulk of the bay sediments. Although Aroclor 1268 and 1270 accounted for <1% of all PCB production, their major components, CB206 and CB209, account for 3-6% of the CBs in most bay samples. This may reflect more local use of these Aroclor mixtures and/or be indicative of their relative stability, compared to less chlorinated mixtures. Using linear alkyl benzenes (LABs) as a marker for sewage derived PCBs suggested that up to 95% of the PCBs at the most contaminated sites in the Seekonk, Providence, and Taunton Rivers were sewage derived. This analysis also showed that there is a high background level (167 ng/g) of PCBs in the Seekonk and Providence River, while the Taunton River had a relatively low background level (23.7 ng/g). At the furthest stations south in the Providence River, the sewage derived PCBs only accounted for 23% of the total which suggests that PCB associated with sewage particles are rapidly deposited and are therefore not the most significant source of these compounds to the lower reaches of Narragansett Bay.
Dynamic Air−Water Exchange of Polychlorinated Biphenyls in the New York−New Jersey Harbor Estuary
Environmental Science & Technology, 2001
Simultaneous measurements of polychlorinated biphenyls (PCBs) in the air and water over Raritan Bay and New York Harbor were taken in July 1998, allowing the first determinations of air-water exchange fluxes for this heavily impacted system. Average gas-phase concentrations of ∑PCBs were 1.0 ng m -3 above Raritan Bay and 3.1 ng m -3 above New York Harbor. A similar gradient was observed for dissolved water concentrations (1.6 and 3.8 ng L -1 , respectively). Shallow slopes of log K OC vs log K OW plots indicated a colloidal contribution to the dissolved concentrations, and a three-phase partitioning model was therefore applied. PCBs associated with colloids ranged from 6% to 93% for trichloro-to nonachlorobiphenyls, respectively. Air-water gas exchange fluxes of ∑PCBs exhibited net volatilization for both Raritan Bay at +400 ng m -2 day -1 and New York Harbor at +2100 ng m -2 day -1 . The correction for the colloidal interactions decreased the volatilization flux of ∑PCBs by about 15%. Net air-water exchange fluxes of PCBs are expected to remain positive throughout the year due to the large waterair fugacity gradient and relatively constant seasonal water concentrations. The volatilization fluxes are approximately 40 times greater than atmospheric deposition of PCBs via both wet and dry particle deposition, suggesting that the estuary acts as a net source of PCBs to the atmosphere year-round.
Atmospheric Environment, 2001
Polychlorinated biphenyls (PCBs) and particulate organic/elemental carbon (OC/EC) differ as to sources, but are both elevated in major urban areas leading to loadings of proximate terrestrial and aquatic systems. Because of the dramatic difference in speciation, sources, and sinks of these compunds, gas+particulate phase PCBs and particulate OC/EC were measured in urban Baltimore, MD and over Chesapeake Bay at 4 and 12 h frequencies in July 1997. Gas phase P PCBs averaged 1180 pg m @3 for Baltimore and 550 pg m @3 for northern Chesapeake Bay. PCB homolog distributions in the gas phase differed between the land and over-water sites whereby the trichlorobiphenyls were higher in Baltimore compared to Chesapeake Bay. Autocorrelation analysis yielded a diurnal cycle for gas phase PCBs at Baltimore with the lowest concentrations observed during the day. Particulate organic and elemental carbon constituted 12.4% (17.4% organic matter) and 2.8% of total suspended particles (TSP) in Baltimore, and 15.0% (21.0% organic matter) and 5.3% over the Chesapeake Bay, respectively. Variability in PCB concentrations was not related to the variability in OC/EC concentrations. OC/EC ratios suggest that particulate organic carbon was mostly primary aerosol. Emissions of both classes of compounds into the Baltimore atmosphere and vicinity are major sources to the Bay.
Volatilization of polychlorinated biphenyls from Green Bay, Lake Michigan
Environmental Science & Technology, 1993
rn The volatilization of polychlorinated biphenyls (PCBs) from Green Bay was estimated as part of the Green Bay Mass Balance Study (U.S. EPA). The strategy employed was to simultaneously collect air and water samples above and below the air-water interface, analyze the atmospheric gas phase and the water column dissolved phase for 85 PCB congeners, and calculate the direction and magnitude of flux for each congener using Henry's law and meterological and hydrological parameters. Sampling covered the period of June through October 1989. Air-water transfer rates were calculated for the 14 individual days spanning the three cruises by using the stagnant two-film model. Calculated total PCB volatilization rates ranged from 13 to 1300 ng/m2.day. The most important factors affecting the magnitude of the flux are wind speed and water concentration. The range of fluxes calculated compares well with other estimates for the Grate Lakes. The results of this study support the hypothesis that volatilization is an important phenomenon controlling the fate of hydrophobic organic chemicals (HOCs) in aquatic systems. Department of Civil and Mineral Engineering. Gray Freshwater Biological Institute.
Reevaluation of Air−Water Exchange Fluxes of PCBs in Green Bay and Southern Lake Michigan
Environmental Science & Technology, 2003
Air-water exchange of persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) is an import process for the delivery of contaminants to water bodies, as well as for their removal, and is thus a pivotal parameter in the construction of mass balances in aquatic systems. Simultaneous measurements of PCB concentrations in the gas and dissolved phases conducted in Green Bay in 1989 and in southern Lake Michigan in 1994-1995 were used to estimate air-water exchange fluxes. In this work, improved Henry's law constants for PCBs and new mass-transfer rates across the air-water interface were used to update the previous calculations. The new model calculations suggest that the net volatilization flux of PCBs out of Green Bay ranges from +170 to +5300 ng m-2 day-1 , which is 2-20 times larger than previous estimates. The flux of PCBs in southern Lake Michigan exhibits net volatilization of +0.5 to +230 ng m-2 day-1 throughout the study period (May and July 1994, January 1995), whereas previous estimates reported that the net flux was seasonally absorptive. Thus, water-to-air fluxes are more important for the removal of PCBs from both Green Bay and Lake Michigan than previously recognized.
Atmospheric Environment, 2002
Polycyclic aromatic hydrocarbons (PAHs) were measured in the Baltimore and adjacent Chesapeake Bay in July 1997. Time series of 4-and 12-h samples were taken at two sites 15 km apart in order to evaluate the influence of a number of processes on the short-term variability of PAH in the Baltimore and northern Chesapeake Bay atmospheres. PAH concentrations were 2-3-fold higher in the Baltimore atmosphere than in the adjacent Chesapeake Bay atmosphere. For example, gas-phase phenanthrene and pyrene concentrations were 12.5 and 2.14 ng m À3 in the Baltimore site and 5.57 and 0.548 ng m À3 in the Chesapeake Bay, respectively. The influence of wind direction, wind speed and temperature was evaluated by multiple linear regressions which indicated that atmospheric gas-phase PAH concentrations over the Chesapeake Bay were significantly higher when the air mass was from the urban/industrial Baltimore area. Furthermore, the increase of gas-phase low-MW PAH concentrations with temperature and wind speed suggests that volatilization from the bay is an important source of pollutants to the atmosphere, at least when air masses are not influenced by the Baltimore urban and industrial area. Indeed, while on the long-term, the Chesapeake Bay is a receptor of atmospherically deposited PAHs, on the short-term and during appropriate meteorological conditions, the bay acts as a source of pollutants to the atmosphere. Aerosol-phase PAH concentrations and temporal trends showed a strong dependence on aerosol soot content due to the high affinity of PAHs to the graphitic structure of soot. These results confirm the important influence of urban areas as a source of pollution to adjacent aquatic environments and as a driving factor of the short-term variability, either directly by transport of urban-generated pollutants or by volatilization of previously deposited pollutants. Conversely, the complex diurnal trends of gas-phase PAHs at the Baltimore site suggests that degradation processes dominate the diurnal trends of PAHs in urban atmospheres. This conclusion is supported by estimated rate constants for PAH reaction with OH radicals which show good agreement with reported values within a factor of two. r
Fate of PCB Congeners in an Industrial Harbor of Lake Michigan †
Environmental Science & Technology, 2010
We have quantified the release of polychlorinated biphenyls (PCBs) from Indiana Harbor and Ship Canal (IHSC) to Lake Michigan and the atmosphere. Navigational dredging is planned for this system and there is concern that dredging will result in releases of PCBs. We have measured >158 PCBs in surficial sediment, water, suspended particles, and air. We predicted the release of PCBs from sediments to water and from water to air. To quantify the level of confidence in our calculations, we used a Monte Carlo simulation for each congener flux. We determined that 4±0.05 kg of ΣPCBs were released from the sediment to the water and 7±0.1 kg of ΣPCBs were volatilized from the water to the air annually. We measured input from the upstream regions of the canal system of 45.0 kg yr −1 and export to Lake Michigan of 43.9 kg yr −1 . The ΣPCBs mass balance accounts for nearly all the PCB inputs and losses to the navigational regions. The congener profiles in sediment, water, and air support our determination that the contaminated sediment is a major source of PCBs into the water and air above it. We have shown that the system is currently a significant source of PCBs to the air and to Lake Michigan, even under quiescent conditions.