Metallic contents (Cd, Cu, Pb, Zn) of suspended solids (SS) were measu
red in two sites (Suresnes and Chatou) in the river Seine, downstream
Paris, during three summer periods. These two sites, which are respect
ively located downstream and upstream two of the most important combin
ed sewer overflows (CSO's) of the Parisian sewer system (Clichy and La
Briche), allow us to assess these CSO immediate impacts. Samples were
collected using sediment traps, weekly during dry weather and daily d
uring the week following the major CSO's events. The heavy metal conce
ntrations, relatively large but stable during summer periods, were sho
wn to further increase downstream Paris after main rain discharges occ
urred. Metal concentrations measured within the Seine SS during rain e
vents, allowed us to establish that the observable immediate impact of
Clichy overflows is only 5% of what it could be. The general principl
e demonstrated through this work is that most SS originating from CSO'
s rapidly settle once they reach the river. These polluted particles g
reatly contribute to the SS chronic pollution downstream Paris during
dry weather, through a slow resuspension mechanism of the deposited se
diments.