Critical geochemical insight into Alexandria coast with special reference to diagnostic ratios (TOC/TN & Sr/Ca) and heavy metals ecotoxicological hazards

Abstract

The current study was designed to gain deep insight into the geochemical nature as well as to assess the marine sediment quality of the Alexandria coast along the Mediterranean Sea. The geochemical analysis revealed that calcium carbonate is the predominant form of carbonate in most of the stations compared to magnesium form. Furthermore, total phosphorus has a concentration range of 0.10–0.28% relating to different environmental conditions. The TOC/TN ratio <10 (ten stations) suggesting a predominant marine origin, and the ratio exceeded 10 at five stations reflecting a mixture of terrestrial and marine materials. The Sr/Ca ratio is firstly examined along the Alexandria coast for describing the diagenetic effects of calcite recrystallization. The higher Sr/Ca ratio which was identified at four stations (>8.8 mmol mol−1) may coincide with sea level regressions. The studied elements in sediments showed the distribution pattern: Ca>Al>K>Fe>Mg>Ba>Sr>Mn>B>Zn>Pb>Cr>Cu>Ni. The environmental hazards associated with metals were assessed by different approaches. According to sediment quality guidelines (SQGs): none of the studied heavy metals exceeded the probable effect level (PEL) except Cr at Rashid station. The enrichment factor of lead (EFPb) > 10 in 87% of the sites, revealing an anthropogenic input of lead. Based on the ecological contamination index (ECI), all sites except Rashid were classified as uncontaminated. The principal component analysis was applied to understand the sources and pathways of the studied parameters.