Polycyclic aromatic hydrocarbon (PAH) deposition to and processing in a small rural lake, Cumbria, UK.

PAH concentrations were determined in a dated sediment core collected from Esthwaite Water (EW), a seasonally anoxic lake in the English Lake District. The most dramatic variations are associated with increased PAH fluxes from 1900 and a sub-surface maximum (29 mg m−2 year−1) in the late 1960s to early 1970s, followed by a fivefold decrease in fluxes to the sediment-water interface. This trend is believed to reflect enhanced fossil fuel burning, followed by general improvements in combustion technologies, shifts in the fuels used for domestic space heating and the implementation of various emission controls on releases from certain known PAH sources. When the relative contributions from individual compounds to the ∑PAH were plotted as vertical profiles, coherent time trends emerged. Perylene dominated the pre-1900 sedimentary PAH composition, contributing >75% to the ∑PAH mixture. The perylene profile provides good evidence for both natural and anthropogenic sources to EW. The ratios of annual sediment trap fluxes to surficial sediment accumulation rates are substantially greater than one for the low molecular weight compounds, suggesting release at or near the sediment water interface and subsequent recycling of these compounds. Recycling was found to increase with increasing solubility and decreasing log Kow