The present study was conducted to provide a comprehensive picture of marine sediment characterization in terms of geochemistry and the extent of pollution. A total of 99 surface coastal sediments were collected from coastal areas along with the Egyptian Mediterranean Sea. The samples were analyzed by neutron activation analysis (NAA) and the mass fractions in mg/kg of 39 trace elements were determined. The normalized mass fractions show significant amounts of Cl (26.4%), Sn (12%), Zr (7.3%), Hf (5.9%), Ti (4.7%), Cr (4.2%), Ca (3.4%), Si (3.1%), Sr (2.9%). The mass fractions of the rare earth elements REEs (La, Ce, Nd, Sm, Eu, Tb, Dy, Yb, and Lu) are almost double compared to literature data. Principal component analysis PCA and positive matrix factorization PMF were used to decipher the sources of pollutions. Sediment quality was quantified using different pollution indices such as enrichment factor (EF), modified pollution index (MPI), pollution load index (PLI) and the new approach to calculate total pollution index (TPI). The results of the study recognized four locations with significant pollution, namely the coastal area along Al Manzalah Lake, the Nile River estuaries at Ras Elbar and its western coastal area, at the outlet of Elbrullus Lake, and finally the Abu Qir Bay. The obtained result can serve as a geochemical background of the sediments of the study coastal area, which allows following the quality of marine sediments along with the Egyptian Mediterranean Sea.

Various in-situ capping materials have been studied to remediate contaminated sediments for sustaining a healthy ecosystem in a coastal area. We developed Granulated coal bottom ash and oyster shells (GBO) with different mixing ratios of OS. Pyrolyzed and grounded coal bottom ash and oyster shells were used to produce GBO, which the main chemical elements were analogous to cement. The nutrient-removal abilities of GBO were evaluated through long-term mesocosm experiments. It was found that GBO was an effective in-situ capping material for remediation of eutrophic coastal sediments, decreasing PO₄-P and SiO₂-Si concentrations in pore water by 88.4% and 56.5%, respectively. The most efficient mixing ratio of coal bottom ash and oyster shells was at a weight ratio of 1:1 for PO₄-P and SiO₂-Si removal.

The Egyptian beaches on the Red Sea and the Gulf of Aqaba in Sinai are a destination for international tourism throughout the year. Therefore, assessing the concentration levels of heavy metal pollutants and identifying the extent of their impact on human health is important. Single and integrated pollutants indices have been used to assess the risks of these elements. The results of single indices proved that the study area contain Fe and Zn came mostly from natural source while Cu, Pb, Cd and Hg originated from anthropogenic sources. However, the integrated pollutants indices revealed that this area is not polluted with heavy metals. On the other hand, the hazard index, and the carcinogenic risk over the lifetime coefficients proved that the beach sand of the study area is completely safe and does not have additional health risks to children or adults, where LCR < 10⁻⁶.

Seagrass carbon emission is mainly due to the land-use change; therefore, conservation will be an approach required for carbon offset. A method for estimating carbon offset from conservation activities has been developed. This study aims to evaluate the carbon-offset potential of the seagrass ecosystem by applying this method to five provinces in Indonesia. North Maluku has the widest seagrass area, but only 5% of this is the conserved area. Meanwhile, Jakarta has the highest percentage of its conserved seagrass within the area. Emission reduction at the year 2020 ranged 0.03–1.02 tC/year (with leakage) or 0.05–2.04 tC/year (without leakage). The percentage of emission reduction among the five provinces ranged from 0.75% to 11.3%. About 9.03 tC/year emission from seagrass ecosystems in Jakarta will decrease by up to 8.01 tC/year. Further assessment shows a positive correlation between the percentage of the conserved area and the percentage of emission reduction.

The first stranded macrodebris study on a national scale in Indonesia was conducted on 18 beaches from February 2018 to December 2019. The average weight and abundance of beach debris were higher between October and February (rainy season). The highest stranded macrodebris was located in Ambon, Manado, Takalar, and Padang. Plastic (46.38 %) was the most prevalent type of debris across all macrodebris categories, with single-use plastics such as plastic sachets, plastic bags, and plastic bottles being the dominant macroplastic debris (64.64 %). Based on CCI, HII, and BGI, 18 beaches are “moderately clean,” with few hazardous items observed, and “Good.” This anthropogenic macrodebris is thought to be more localized (55 %) than transboundary macrodebris. Litter control and environmental quality of this Indonesian coastal region should be improved through a proactive and flexible approach. Finally, extensive stranded beach debris monitoring is recommended to better understand the distribution of macrodebris in the region.

Among the main sources of atmospheric mercury emissions are thermoelectric plants that use coal to generate electricity. This heavy metal is transported by air from its origin to neighboring coastal areas, where it is deposited in the sediment record. This research evaluated the content and temporal distribution of Hg in the coastal sediments of Central Chile, Coronel Bay, industrialized zone with two operative thermoelectric plants, and Coliumo Bay, reference zone free of industry. To this end, sediment cores from the centers of the two bays were obtained. Laboratory results show that the greatest Hg contents were found in the surface strata of the Coronel Bay core, with concentrations up to an order of magnitude greater than those obtained in the same strata in Coliumo Bay. This increase in Hg concentration coincides with the beginning of industrial activity in Coronel, with greater concentrations observed from 2012 on, the year in which the industrial operation of two coal-fired thermoelectric plants on the bay began. Based on ²¹⁰Pb activity and the relationships between Hg content and organic matter, it was established that the main pathway of Hg to sediment is atmospheric deposition, while Coliumo presented inputs that reflect local non anthropogenic sources.

The oceanic acidification and coastal hypoxia have potential to enhance biological uptake of dissolved iron (Fe) by phytoplankton. In this study, the Fe uptake rate (FeUR) in Daya Bay was significantly negatively correlated with pH and dissolved oxygen (DO) (r = −0.81 and −0.73, respectively, p < 0.001). In addition, binary regression (FeUR = −1.45 × pH − 0.10 × DO + 13.64) also indicated that both pH and DO played key roles in FeUR variations. As pH and DO decreased, Fe uptake by phytoplankton was promoted, and the contribution of nano-phytoplankton to Fe uptake increased significantly, while that of pico-FeUR decreased. These will result in the phytoplankton community to be miniaturized and Fe requirement of phytoplankton goes higher, thereby leading changes of phytoplankton composition and coastal ecosystem. This study helps to understand how Fe could affect the coastal ecosystem under the increasing anthropogenic influences.

In this work, sediments collected from a 150-m deep litho-section of a coastal region and encompassing Quaternary, Tertiary and Cretaceous sedimentary formations were studied for arsenic distribution and other trace and redox sensitive elements. Arsenic concentration in the sediments is found to vary from <0.5 to 30 mg·kg⁻¹ and showed an increasing trend with the depth. The highest As content is observed at a depth of 129–131 m bgl belonging to Cretaceous formation. Though XRD studies do not indicate any arsenic mineral in sediments, positive correlations between As–Fe and S, as well as ESEM-EDS and TXRF studies confirm the presence of As sorbed to FeS mineral. The organic matter and As correlations suggest microbial mediated reduction process, which may pose future risk to water quality of this prolific coastal fresh water aquifer system. The elemental profiles infer that Cretaceous and Tertiary formations demonstrate inner shelf and marginal marine condition respectively.

Trace Metals (TMs: Pb, Zn, Cu, Cr, Cd, and Ni), major elements (Al and Fe) and radionuclides (²¹⁰Pb/¹³⁷Cs) investigations on EL-C01 sediment core provides new information on sedimentary regime and anthropogenic impacts during the last 175 years in the Po river prodelta area. The results allow to identify some TMs/Al peak in the upper part of the core, likely related to the major flood events of the Po river during the XXth century. Sediments deposited after the year 1900 exhibit a gradual increase of some TMs concentrations compared to pre-industrial era values. In particular, Pb, Zn, and Cu high contents are detected after the World War II and during the “Italian Economic Miracle” period. The decrease of heavy metal (Zn and Pb) contents from the second half of the 1980s is probably the effect of the Italian Law 319/76 and anti-pollution environmental policies concerning industrial and urban emitters.

Quantification of four toxic metals (As, Cr, Cd, and Pb) in water and sediments at the Sitakunda ship breaking area in Bangladesh was studied. Along with this, sediment quality and ecological risk were evaluated for the metal intrusion to the study area. A total sample number of 120 (water; n = 60 and sediment; n = 60) were analyzed for both winter and summer seasons using atomic absorption spectrophotometer (AAS). The trace metal concentration in both water and sediment showed decreasing trend as follows; Cr (mean-W: 0.118 mg/L; mean-S:121.87 mg/kg) > Pb (mean-W: 0.064 mg/L; mean-S: 65.31 mg/kg) > As (mean-W: 0.03 mg/L; mean-S: 32.53 mg/kg) > Cd (mean-W: 0.004 mg/L; mean-S: 4.81 mg/kg). However, in both segments, the concentrations of the toxic metals exceeded the recommended acceptable limits. As and Cd showed significant variation (water and sediment) between the seasons, while Pb and Cr had no seasonal impact. Metal pollution index (MPI) and contamination factor (CF) was evaluated and revealed that the study area exhibited the critical score of water quality (MPI > 100). The cumulative effect of the metal concentrations was high (CI > 3). The assessed mean geoaccumulaiton index (Igₑₒ) revealed that the study area was moderate to strongly polluted except for Cr. According to the contamination factor (CF), the sediment samples were moderate to highly contaminated by Cd, Pb, and As. Moreover, the explored range of pollution load index (PLI) in all sampling sites in the ship breaking region was from 1.75 to 3.10, suggesting that the sediment in the study area was highly polluted by heavy metals (PLI > 1). The risk index and the potential ecological risk index (PERI) suggested that the study area was at high risk due to metals pollution. Therefore, it is obligatory to maintain some crucial efforts for the betterment of the surrounding environment near the investigated sites.