Sedimentary record of polycyclic aromatic and aliphatic hydrocarbons in the Windermere catchment

Abstract

Sediment profiles from two lakes (Windermere and Priest Pot, Cumbria, U.K.), in which the depositional chronology had been previously established by measurement of unsupported 210Pb, were analysed to determine present and past hydrocarbon levels. Chromatographic separation of sedimentary lipids gave two fractions containing aliphatic and aromatic hydrocarbons, respectively. Anthropogenic inputs to the sediments were assessed from the abundance of 17α(H),21β(H)-norhopane among aliphatic hydrocarbons and from the combined abundance of 10 polycyclic aromatic hydrocarbons. Sub-surface maxima in anthropogenic input occurred in the sediment column of both lakes. For identification of constituents by GC-MS, aliphatic compounds indicative of pollution were isolated by urea adduction; polycyclic aromatic hydrocarbons were isolated by solvent partition. Significant oil pollution in Windermere surficial sediments, probably owing to increasing motor boat use and road runoff, was recognised from the dominance of αβ-hopanes, including C 31–C 34 alkyl derivatives in which the C-22S:C-22R epimer abundance ratio was that of thermally mature geological oil-like sources. The flux of anthropogenic PAH to Windermere reached high levels ( c. 4000 ng cm −2 yr −1) early this century, probably due to local water-borne input; levels have decreased since the 1970s but remain ten times greater than before the industrial revolution.