Contamination and ecological risk assessment of trace metals in surface sediments from coastal areas (El Jadida, Safi and Essaouira) along the Atlantic coast of Morocco

Abstract Concentrations of four heavy metals (Cd, Cr, Cu and Zn) in surface sediments were quantified seasonally to evaluate the metal contamination and to determine the possible environmental risks. This study was performed at three coastal areas in northwest Morocco. Samplings were conducted quarterly at six intertidal stations with two stations per area (north to south: S1 vs. S2; S3 vs. S4 and S5 vs. S6). The heavy metal concentrations were generally found greater in wet seasons for all sampling stations, and their mean values were arranged in the following decreasing order: Zn (28.35–136.10 μg g−1 dry weight) > Cr (6.50–130.90 μg g−1) > Cu (5.00–83.4 μg g−1) > Cd (0.02–5.95 μg g−1). As expected, the highest metal concentrations were recorded at stations exposed to the polluting point-source discharges from important industrial phosphate plans near El Jadida (S2: Jorf Lasfar) and Safi (S4: Jorf Lihoudi), which greatly exceeded the geochemical background values. Interestingly, all of the four heavy metals were significantly correlated with each other, implying the same source of contamination. This was mainly derived from industrial wastes generated by these huge phosphate industry plans. Meanwhile, results from HCA confirmed the correlations’ findings. This ecotoxicological evidence was primarily associated with untreated industrial discharges. Contamination Factor, Degree of Contamination, and modified Degree of Contamination indices confirmed that these two stations were the metal contamination hotspots, and the most affected locations in this region, especially for Cd. Moreover, Pollution Load Index and Geo-accumulation Index reflected a spatial distribution of pollution following the decreasing sequence S4 > S2 > S1 > S6 > S3 > S5. Based on the Potential Ecological Risk Index, Cd concentrations indicated a very high to moderate potential ecological risk at all sampling stations, except at one pristine station S5 (Bhibeh). Furthermore, the spatial distribution of Mean-ERM-Quotient showed a negligible ecological risk at Cap Beddouza (S3) and Bhibeh. Moreover, the mean values of Toxic Units (Σ TU) were found in the following decreasing order Cd > Cu > Cr > Zn, with a major contribution to the Σ TU for Cd (35.42%) and Cu (24.99%). Comparison of the current results with those found in other areas around the world revealed that the metal levels obtained hereby remained in general low, except for Cd, which appeared to be in greater concentrations. Based on the Sediment Quality Guidelines, Cd was likely to pose environmental risks while Zn appeared to present no environmental threat at all of the studied sites.