CONCENTRATIONS AND DEPOSITION FLUXES OF POLYNUCLEAR AROMATIC-HYDROCARBONS AND HEAVY-METALS IN THE DATED SEDIMENTS OF A RURAL ENGLISH LAKE

Deposition fluxes have been estimated from concentrations of 12 polynu clear aromatic hydrocarbons (PAHs) and six heavy metals measured in se diment cores from Esthwaite Water, a rural English lake. Atmospheric d eposition is a major source of PAHs and heavy metals (Cd, Cu, Pb, and Zn) to the lake, so trends in the core may indicate the long-term reco rd of changes in the atmospheric loading of these pollutants. The core s were dated radiometrically and pollutant trends studied since about 1820. PAH fluxes began to increase from stable background levels aroun d the turn of the century (4.1 mug SIGMAPAH per gram dry weight, 287 n g SIGMAPAH per centimeter squared per year), rising to maximum inputs between 1950 and 1970 (42.0 mug/g, 2,954 ng/cm2 per year). The deposit ion flux of PAHs has decreased steadily since then and is now less tha n half the maximum (18.0 mug/g, 1,238 ng/cm2 per year). In recent sedi ments (1900-1970), the relative proportions of individual PAHs making up the SIGMAPAH burden have remained virtually unchanged, with fluoran thene, pyrene, and benzo[ghi]perylene the most abundant compounds. How ever, perylene, a biogenically produced PAH, dominates the mixture in the sediments older than 1890. Cadmium, Cu, Ni, Pb, and Zn concentrati ons in the Esthwaite sediments broadly follow the same temporal trends as the PAHs, with varying peak inputs between 1925 and 1975. Concentr ations in the modern (surface) sediments are now lower than in recent decades, with SIGMAPAH, Cd, and Pb showing the greatest reduction. How ever, fluxes of these contaminants to surface sediments are still grea ter than those deposited before 1840.