Impact of rapid urbanisation and industrialisation on river sediment metal contamination

This study aimed at evidencing contaminant inputs from a rapidly growing population and the accompanying anthropogenic activities to river sedi- ments. The Fez metropolitan area and its impacts on the Sebou's sediments (the main Moroccan river) were chosen as a case study. The Fez agglomeration is surrounded by the river Fez, receiving the wastewaters of this developing city and then flowing into the Sebou. The sedimentcores fromthe Fezand Sebou Rivers were extractedand analysedfor major elements, butyltins and toxic metals. Normalised enrichment factors and geoaccumulation index were calculated. Toxicity risk was assessed by two sets of sediment quality guideline (SQG) indices. A moderate level of contamination by butyltins was observed, with monobutyltin being the dominant species across all sites and depths. The lowest level of metal pollution was identified in the Sebou's sediments in upstream of Fez city, whilst the Fez' sedi- ments were heavily polluted and exhibited bottom-up accumulation trends, which is a clear signature of recent inputs from the untreated wastewaters of Fez city. Con- sequently, the sediments of Fez and Sebou at the down- stream of the confluence were found to be potentially toxic, according to the SQG levels. This finding is concerned with aquatic organisms, as well as to the riverside population, which is certainly exposed to these pollutants through the daily use of water. This study suggests that although Morocco has adopted environ- mental regulations aiming at restricting pollutant dis- charges into the natural ecosystems, such regulations are neither well respected by the main polluters nor efficiently enforced by the authorities.