Reconstruction of the Deposition of Polycyclic Aromatic Hydrocarbons (PAH) in Peatlands of Eastern Canada
Annekatrin Dreyer (01/2004)
Support: Christian Blodau, Michael Radke
Peat cores of 15 ombrotrophic bogs were dated with 210Pb in 5 cm intervals for the period of 1850-2000 because ombrotrophic bogs form an almost ideal archive of compounds deposited from the atmosphere. Samples of these and two additional peatlands were analysed for PAH as indicator substances for diffuse environmental pollution with organic contaminants. A method was optimised for the analysis of the 16 EPA-PAH, benzo[e]pyrene (BeP) and perylene (Pery). Concerning the extraction, accelerated solvent extraction (ASE) with hexane/acetone 2:1 (v:v) yielded the best results. Purification with 3 g aluminium oxide (15% deactivated) upon 5 g silica (0% deactivated) eluted with 35 mL hexane and 30 mL hexane/dichloromethane 3:1 (v:v) proved to be a successful procedure for the clean-up of peat samples. Samples were measured using a GC-MS/MS. 170 samples of Canadian peat cores were analysed with this method. The EPA-PAH concentrations of most recent samples ranged from 85 to 400 µg kg-1 dry weight (dw). Highest EPA-PAH concentrations of about 2850 µg kg-1 dw were reached in the 1950ies. EPA-PAH concentrations of the oldest analysed sections were in the range of 75 to 650 µg kg-1 dw. Corresponding EPA-PAH deposition rates of the oldest sections were between 5 and 200 µg m-2 yr-1. Maximum EPA-PAH deposition rates reached up to 1450 µg m-2 yr-1. PAH deposition rates of recent sections ranged between 55 and about 700 µg m-2 yr-1. BeP, analysed for the purpose of source identification, was found in almost all samples. Pery as biologically formed PAH could not be identified in any sample. Highest PAH depositions were found in the densely populated and industrialised regions in the centre of the analysed transect. Lowest PAH depositions were found at northern sites and in Nova Scotia. Generally, phenanthrene (Phen), benzo[b+k]fluoranthene (Bb+kF), fluoranthene and pyrene were the predominant PAH. Phen was the most abundant PAH in peripheral regions whereas the central region of the transect was dominated by Bb+kF and showed elevated proportions of indeno[1,2,3-c,d]pyrene and benzo[g,h,i]perylene. Three different types of long-term PAH deposition were found: bogs showing two distinct maxima, one single maximum or no distinct maximum. Temporal trends of PAH deposition rates coincided with some major steps of the industrial development in Canada. PAH deposition rates in Canadian peatlands were lower and peaked generally later than those of Europe. Besides the overall PAH deposition rates and the PAH composition, the spatial distribution of bogs according to the long-term PAH depositions also stressed the special situation of the central area along the St. Lawrence River. Identification of potential PAH sources in eastern Canada point at coal combustion and vehicle exhausts. Vehicle exhausts were found to be an important PAH contributor in the central region of the analysed transect.