Sediment quality and ecological risk assessment in Mediterranean harbors of Occitanie, France: implications for sustainable dredged material management

The Mediterranean coastal region of Occitanie (France) hosts numerous harbors with economic and touristic activities requiring periodic dredging that may release potentially toxic elements and organic pollutants into the marine environment. Monitoring sediment quality using Sediment Quality Guidelines (SQGs) is essential to assess contamination risks. This study summarizes the geochemical and physical characteristics of sediments from ten harbors of the Occitanie region and evaluates associated ecological risks to inform management strategies. Results are based on measurements required by the French regulation and showed that studied harbors are mostly composed of fine-grained sediments rich in organic matter (32 % on average), those accumulate few contaminants, mainly copper (38-123 mg/kg), zinc (66-156 mg/kg), and lead (15-48 mg/kg), as well as organic pollutants including polycyclic aromatic hydrocarbons (0.23-2.1 mg/kg), and polychlorinated biphenyls (0.05-0.3 mg/kg). Statistical analysis revealed strong correlations between sediment grain size and contaminants distribution. Ecological risk assessment indicated varying but low contamination levels. Copper emerged as the main contaminant, exceeding the threshold effect concentration in 77 % of samples and the probable effect concentration in 5 %. The mean probable effect quotient index suggested moderate ecological risks, with a 33-58 % probability of adverse effects on benthic organisms, emphasizing the need for regular monitoring to prevent potential increases in contamination. Results underlined the interest of adaptive sediment management approach, integrating chemical analyses, bioaccumulation studies, and toxicity testing. While French regulatory thresholds provide disposal guidelines, further studies are needed to refine risk assessments and support sustainable remediation strategies.