Pollution assessment of the canal sediments in the city of Delft (the Netherlands)

Pollution sources for the deposited sediment material in the canals of Delf t (the Netherlands) were investigated by detailed monitoring at 51 stations during the period 1991-1996, both in the inner city and the outskirts of t he city. The sediment samples were all analysed for (heavy) metals, PAHs, P CBs, pesticides and mineral oil According to the pollution classes used in the Netherlands, cn. 95% of all inner city stations in Delft were in the hi ghly polluted classes 3 and 4, necessitating sediment dredging followed by disposal under strict conditions. In contrast, only 33% of the sediment sam ples in the Delft outer city fell into these pollution classes. Factor anal ysis showed that the inner and outer city sediments cold be divided into tw o different clusters, each with their own characteristics. The chemical com ponents mainly responsible for the sediment pollution were Cu, Zn, DDT, PAH s and Pb. For the latter two parameters, this points to traffic-reslated po llution lands whereas the main sources of copper and zinc are probably rela ted to the corrosion of metal structures. Mass balance calculations for the Delft inner city canal system show that, of the accumulated heavy metals, around 65% of Zn and Pb and even 85% of Cu originate from outside the Delft inner city, viz. via open inlets with the main Rijn-Schie canal. In view o f the decreasing contents in the sediment top layer, it is anticipated that , with the various pollution abatement measures bring taken, a gradual impr ovement of the Delft canal sediment quality will take place. (C) 2000 Publi shed by Elsevier Science Ltd. All rights reserved.