The coastal area south of Jeddah, Saudi Arabia, eastern
Red Sea, receives daily more than 100,000 m3 of domestic sewage.
The solid material of the dumped wastes was analyzed for its organic
carbon, Al, Fe, Mn, Cu, Zn and Cr contents and their mass emission
was calculated. To trace the impact on the coastal area, the same elements
were analyzed in sediments and suspended matter in the receiving
basin and along a coastal strip extending for about 10 km southward
the discharge point.
It was found that the impact of the effluent was limited to the area
in the proximity of the effluent discharge point where concentrations
in both sediments and suspended matter were several times higher
than in the other parts of the area. Away from the effluent, concentrations
were comparable to those measured in uncontaminated carbonate
sediments. In the dilution basin, the distribution of the elements
correlated with the dilution pattern of the effluent water. Normalization
to aluminium revealed however, that only Fe, Cu and Zn were enriched
in the sediments (EF 1.7, 6.3 and 6.8 respectively), while Mn
and Cr were depleted. This behaviour was attributed to the difference
in the oxidation-reduction kinetics of the redox sensitive elements (Fe,
Mn, Cr) and to interaction with the organic matter and formation of
insoluble sulphides (Cu and Zn). In the suspended matter all the elements
showed a positive deviation from linearity at intermediate salinity.
The excess was accounted for by the resuspension of bottom sediments
(Fe, Cu and Zn) and adsorption of mobilized elements (Mn).