First assessment of domestic and industrial effluents impact on intertidal zone of Safi coastline (west of Morocco): physicochemical characteristics and metallic trace contamination

This study aimed to evaluate the effects of urban and industrial effluents on the intertidal seawater and sediments quality of Safi coastline (western Morocco). This is a pioneer work carried out in the transition zone between seawater and wastewater. In addition, it sheds light on the destructive consequences of the aforementioned effluents on the biocenosis specific to this biotope. For this purpose, four sampling campaigns covering five critical stations were selected. We considered the seaside area as a reference station. All the indicators of the environmental health and metallic contamination used for this monitoring were measured at low tide: the mixing waters' physicochemical parameters (temperature, pH, conductivity, salinity, and turbidity), the levels of four metallic trace elements (copper, zinc, lead, and cadmium) in both water and superficial marine sediments, the pollution indices that reflect the level of biotope healthiness, as well as the pollution load parameters (BOD5 and COD). The results indicated a great variability of physicochemical parameters measured at the seawater-wastewater mixing zone, with no significant difference observed between the reference station SO and the investigated stations S1, S2, S3 and S4. However, these last three stations revealed a much lower environmental quality. Furthermore, the effluents were found to be loaded with lead, cadmium and, to a lesser extent, copper. In fact, the pollution indices had confirmed that the analyzed seawater as well as the surficial sediments were heavily polluted with trace elements. The statistical analysis of wastewater revealed four distinct groups; (i) domestic; (ii) food industry; (iii) domestic-industry; and (iv) phosphate industry. These effluents are generally biodegradable except for station S5. This study provides a solid baseline for a future sustainable monitoring program to rehabilitate Safi coastline and safeguard its biocenosis.