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 water resources in Morocco, is analyzed. A significant amount of wastewater is discharged every day in this aquatic system by the city of Fez. Heavy metals and toxic elements (Cr, Zn, Fe, Co, As, La, Sr, Ag, Hg, Sb and Rb) were identified by neutron activation in the urban wastewater and in the waters and 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 where there was also a large increase in organic loadings (COD, BOD, volatile organic matter), salinity and ammonium, orthophosphates, sulfate, sodium and calcium, as well as a sharp drop in dissolved oxygen. Aside from the decline 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 and the climatic conditions in the region, heavy metals accumulating in the sediments could be remobilized and create the risk of large-scale contamination.