The River Rhine as a source of micropollutants in the canal sediments of the city of Delft (The Netherlands)

This paper presents a statistical analysis of the pollution levels for heavy metals and organic micropollutants at 182 sediment stations in the city canals of Delft. High pollution levels were especially observed in the inner city canal sediments, probably related to the import of polluted river Rhine water. In contrast, the more-or-less isolated outer city sites were generally much less polluted. Regression analysis on the database generally showed highly significant correlations between individual heavy metal contents. The heavy metal contents were usually significantly correlated with polycyclic aromatic hydrocarbons (PAHs) as well. This points to one or more common sources for these micropollutants. Factor analysis and the K-means cluster analysis technique were applied on the above database; it showed a large cluster of stations, nearly all located in the outer city of Delft, characterized by relatively low heavy metal and organic micropollutants’ contents. Another cluster of 18 stations, mostly located in the inner city of Delft, possessed intermediate pollution levels, directly related with the supply of river Rhine water. Finally, the stations of a third cluster, situated in the inner city as well, were highly polluted, especially by local pollution sources. The above hypotheses were further supported by a more detailed statistical analysis for a number of inner city stations, together with 10-year river Rhine pollution data.