The spatial distribution of heavy metal pollution of canal sediments (
City of Delft, The Netherlands) was investigated in the framework of a
mass balance study, Heavy metal pollution in the accumulated dredged
sediments showed marked spatial and vertical variations, In the sedime
nt top layer of 10 to 15 cm thickness, copper levels varied from 45 to
281 mg Cu/kg, lead from 218 to 562 mg Pb/kg and zinc from 216 to 1400
mg Zn/kg. Values ill the sediment bottom layer of 10 to 15 cm thickne
ss were 20 to 50% higher, indicating a diminishing pollution load over
the past years, Significant statistical correlations were found betwe
en the Cu, Pb and Zn contents, pointing at (a) common source(s) of pol
lution for these metals. Particle size analysis showed substantially e
nhanced levels of heavy metals in the fraction smaller than 106 mu m.
Results of preliminary mass balance calculations indicate that the qua
lity of the surface water used for flushing the city canal system has
a predominant effect on the inner-city sediment accumulation and pollu
tion rates. Copyright (C) 1996 IAWQ.