Application of the peat archive as tool in environmental chemistry
Ombrotrophic peat bogs are natural archives of atmospheric deposition of pollutants. Therefore, peat profiles can be used to study the chronology of environmental contamination with harmful pollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and per- and polyfluorinated alkylated substances (PFAS). These mostly carcinogenic organic compounds are ubiquitously present in the environment. To derive historical deposition rates from the peat archive the pollutants have to be persistent and immobile, and an accurate dating technique is needed to calculate the age of the analyzed peat. To test these requirements and the accuracy of peat archives twelve peat profiles were sampled in four bogs in Ontario, Canada, as well as surface peat in one bog. To make sure sampling sites were not influenced by local roads, we analyzed the concentration decrease in the air from the roads into the bogs. Aerobic or anaerobic degradation of PCBs and PAHs did not occur over a 3-year period in incubation experiments. The heterogeneity of concentrations within a bog was determined in surface samples and by sampling three peat cores per bog. Concentrations varied up to 70 % indicating a high heterogeneity. A vertical sampling resolution of 5 cm lead to imprecision in the dating of sampled peat segments. Temporal deposition trends inferred from peat cores are generally in agreement with trends derived from a sediment core sampled close by, but rates are higher to the sediment for PAHs but similar for PCBs. Indication for mobility of PAHs was minor but has been observed in peat for PCBs and PFAS. To predict the environmental behavior of pollutants, e.g. the atmospheric travel distance of pollutants, computer models can be used. To evaluate the results of these models experimentally derived travel distances of PAHs were determined using the peat bog archives along a transect originating at a large mining area. The comparison of the modeled and experimentally derived travel distances indicate that the computer models give realistic results for most PAHs. We conclude that peat cores are suitable archives for inferring atmospheric deposition trends for PAHs, but not for PCBs and PFAS. Due to the relatively low temporal resolution short-term events might not be discovered. The analysis of more than one core per site is suggested to provide realistic reconstructed deposition trends and inventories.
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