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The purpose of this paper is to evaluate the historical pollution of the Hostivar Reservoir (largest reservoir in Prague) sediment by metals, polyaromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB) and identify the trends in pollution of aquatic environment.

Core samples, 140 cm long, recording the 45-year history of the reservoir, were separated to 5 cm width subsamples (approximately 1.5 years of sedimentation) and analyzed for metals (Cd, Pb, Cu, Zn, Cr, Ni, Al), PAH and PCB. Following methods were used: US EPA 3051 for metals, US EPA 505 and US EPA 8082 A for PCB, and ISO 18287:2006 for PAH.

Most of the contaminants had the highest concentration at the beginning of the existence of the reservoir, suggesting that the contamination results from construction activities. Significant decrease of Pb occurred in the second half of the 1990s. It was caused by termination of the addition of lead as a detonation suppressant to the gasoline. Most concentrations of PAHs, PCBs and metals, except copper do not present eco-toxicological risk.

The results show the volume of priority pollutants removed from the reservoir by sediment extraction, and point risk to the terrestrial environment due to application of the sediment in the construction of a noise protecting wall.

The paper presents unique data about historical contamination of the largest reservoir in Prague, the capital of Czech Republic. It shows how the watershed and the construction phase of the dam cause a pollution of the reservoir sediment and possible environmental risk for aquatic biota.