Anomalous distribution of fluoride and phosphorus forms in surface sediments along eastern Egyptian Mediterranean Sea coast

The study focused on the distribution of fluoride, total phosphorus, and four phosphorus fractions in some sites along the Egyptian Mediterranean Sea coast. The geochemical parameters and textures of 30 surficial sediment samples from six sectors were determined. The sediment’s geochemical parameters (total carbonates (TCO 3 ) and total organic carbon (TOC), exchangeable and carbonate-associated phosphorus (P ex ), iron- and aluminum-associated phosphorus (P OH ), calcium-associated phosphate/apatite (P HCl ), residual phosphorus (P R ), total phosphorus (TP), calcium (Ca s ), magnesium (Mg s ), and fluoride (F s )) showed variable values. The rank of phosphorus fractions in the sediments P HCl > P R > P OH > P ex reflected that the eastern Egyptian coast was still uncontaminated. Generally, P ex levels gave a gradual increase in the offshore direction, while P OH values varied along the stations of each sector. Also, the presented data indicated that the apatite-P fraction was the main storage of the phosphate in the sediments with a contribution to TP ranging from 58 to 87 %. The highest and lowest average fluoride contents (0.49 ± 0.10 and 0.25 ± 0.31 mg/g) were determined in the Port Said and Damietta sectors, respectively. Interestingly, the variability of both phosphorus and fluoride levels in the investigated area seemed to be accompanied with the sediment’s character beside the proximity to potential effluent sources.