Polychlorinated biphenyl and polycyclic aromatic hydrocarbon deposition to and exchange at the air-water interface of Esthwaite water, a small lake in Cumbria, UK

Atmospheric concentrations and deposition fluxes of several polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were measured concurrently over a 1-year period at a shore-based site at Esthwaite Water, to estimate their loadings from the atmosphere to the lake water surface. The PAH deposition fluxes (mu g m(-2) month(-1)) to conventional upturned Frisbees varied from 0.19 (anthracene) to 7.8 (phenanthrene), with a Sigma PAH deposition of 33.5. Phenanthrene, fluoranthene and pyrene contributed > 50% of the Sigma PAH deposited. The deposition fluxes of PCBs ranged from 0.03 (octa-PCBs) to 0.38 (tri-PCBs) mu g m(-2) month(-1) with a Sigma PCB Aux estimated at 0.87 mu g m(-2) month(-1). The coefficients of variation of deposition varied from 75% (octa-PCBs) to 120% (tri-PCBs) and from 90 to 150% for individual PAHs. Temporal variability in fluxes to the collector was large, suggesting highly variable atmospheric concentrations and scavenging processes. Atmospheric PAH concentrations were negatively correlated with temperature over the sampling period, suggesting that the source function-rather than temperature-dependent, air-surface equilibrium partitioning-primarily controlled air concentrations. Deposition fluxes of PAHs correlated well with rainfall between January and September, suggesting that particle washout was the main factor controlling deposition over this period. The controlling factor for deposition between October and December was related to the increased source function of the compounds to the atmosphere. Regression analysis of the data for PAHs with greater than or equal to 4 rings gave a strong positive correlation between the deposition flux and atmospheric concentrations, suggesting that the transfer of compounds occurred with a similar efficiency. Simultaneous air and water sampling over an annual cycle was used to calculate fugacity quotients for individual PAHs and PCBs. These calculations showed that PCBs were outgassing from the lake water throughout the year (i.e. volatilisation > deposition) whilst PAH transfers varied seasonally with net deposition in winter months when there is no ice cover, and net volatilisation at all other times. (C) 1998 Elsevier Science Ltd. All rights reserved.