Metallic and organic pollutants associated with urban wastewater in the waters and sediments of a Maroccan river

The impact of wastewater on the Sebou river, one of the most important wate r resources in Morocco, is analyzed. A significant amount of wastewater is discharged every day in this aquatic system by the city of Fez. Heavy metal s and toxic elements (Cr, Zn, Fe, Co, As, La, Sr, Ag, Hg, Sb and Rb) were i dentified by neutron activation in the urban wastewater and in the waters a nd sediments of the river both upstream and downstream from their point of origin. Results show high contamination levels. The highest levels were for Cr and Zn, while Hg, Ag and As were found only at the downstream sites whe re there was also a large increase in organic loadings (COD, BOD, volatile organic matter), salinity and ammonium, orthophosphates, sulfate, sodium an d calcium, as well as a sharp drop in dissolved oxygen. Aside from the decl ine in water quality, there was a large decrease in the biotic index, from 8 upstream to 2 downstream. As a result of the water regime of this river a nd the climatic conditions in the region, heavy metals accumulating in the sediments could be remobilized and create the risk of large-scale contamina tion.