First assessment on trace elements in sediment cores from Namibian coast and pollution sources evaluation

Baseline trace element concentrations in marine sediment from the West African coast

Baseline studies play a crucial role as tools for environmental reconstructions and assessments, and guide future actions aimed at the restoration and preservation of marine ecosystems. Major and trace elements (TE) were determined in five sediment cores collected in the Angolan and Namibian coastal waters. Predominantly homogeneous vertical profiles indicate that natural sources control levels of TE in sediments. Enrichment Factors (EF) and the Geo Accumulation Index corroborate this hypothesis. Nevertheless, among potentially toxic elements, Cr was found in high concentrations in sediment (up to 640 mg kg-1), surpassing sediment benchmarks in almost all samples. This is likely ascribable to naturally occurring minerals rather than anthropogenic inputs, based on our current knowledge. In the cores near the Namibian coast, shale-normalized rare earth elements (REE) were slightly enriched in heavy rare earth elements (HREE), while in Angola the pattern was enriched in the light REE (LREE). The Pb isotopic composition of sediment was found to resemble that measured in uncontaminated sediments from Namibia (average 206Pb/204Pb = 18.98, 208Pb/204Pb = 39.3) and are indicative of carbon-rich minerals from the region, further underscoring the natural sources of Pb.

Sediment pollution: An assessment of anthropogenic and geogenic trace element contributions along the central Algerian coast

Sediment cores from the central Algerian coast were collected to investigate the distribution, sources and risk of trace metals. The local geochemical background of metals was defined from the core S collected in an uncontaminated area of the coast. The anthropogenic inputs in Algiers Bay elevated Ag, Cd, Pb and Zn concentrations as their maximum were 3.1, 3, 2.1 and 1.8 times the background values, respectively. Meanwhile, increased contents of Arsenic (up to 21.1 mg/kg) were detected in all sites. Correlations and PCA suggest that lithogenic sources controlled metal deposition, while most sediment arsenic was agriculture-derived. Organic matter acted as a sink or source for some trace metals. According to EFs, the study area showed slight to moderate enrichment with respect to Ag, As, Pb, Cd, Zn and Cu, whereas they remained uncontaminated with Cr, V, Co and Ni. This study provides a needed baseline for future environmental investigations.

Inferring pollution records in sediment cores from transitional environments of Marquelia coast, Guerrero, Mexico

The vertical distribution pattern and concentrations of elements (Fe, Al, Ca, Mg, Mn, Cr, Cu, Ni, Co, Pb, Zn, and As) in the estuarine and lagoon region of Marquelia coast, Guerrero, Mexico, were studied to comprehend the origin and pollutant phases of geochemical elements. Henceforth, two sediment core samples [C1 (127 cm) and C2 (110 cm)] were collected to assess the pollution status using geochemical indices, namely anthropogenic factor (AF), enrichment factor (EF), and geoaccumulation index (I_geo). Additionally, the elemental concentrations were compared with the sediment quality guidelines (SQGs) to examine the potential risks to biota. Among the two depositional environments, the sediments of lagoon Apozahualco exhibited higher concentrations of elements. The granulometry characteristics of sediment grains also attested that the concentration and mobilization of metals are largely governed by the fine-grained fractions. Major elemental concentration and grain size changes were identified at several depths (30-40, 60-70, and 90-100 cm) revealing the internal hydrodynamic condition. The overall assessment of geochemical indices revealed that the sediments were unpolluted to moderately polluted. The anthropogenic factor indicated that the upper portion of the sediments were affected by anthropogenic influences. The comparison of trace element concentration with SQGs denoted that Cr, Ni, and As could pose potential adverse effect to the organisms that live in and near the sedimentary environment. Factor analysis revealed the origin and behaviour of the studied elements during transportation and deposition processes in both the ecosystems (i.e. estuary and lagoon). The results of this study provided an in-depth understanding of variations in elemental concentration and pollution status of sediment profile in coastal transitional environments that would aid in sustainable management.

Seasonal variation and mobility of trace metals in the beach sediments of NW Borneo

Miri city has a dynamic coastal environment, mainly influenced by intensive sedimentation from the Baram River and excessive trace metal loading by the Miri River, which are significant environmental concerns. As the mobility, bioavailability, and toxicity of the trace metals in the sediments are largely controlled by their particulate speciation, the modified BCR sequential extraction protocol was applied to determine the particulate speciation of trace metals in the coastal sediments of Miri, to unravel the seasonal geochemical processes responsible for known observations, and to identify possible sources of these trace metals. The granulometric analysis results showed that littoral currents aided by the monsoonal winds have influenced the grain size distribution of the sediments, enabling us to divide the study area into north-east and south-west segments where the geochemical composition are distinct. The Cu (>84%) and Zn (82%) concentrations are predominantly associated with the exchangeable fraction, which is readily bioavailable. Pb and Cd are dominant in non-residual fractions and other metals viz., Fe, Mn, Co, Ni, and Cr are dominant in the residual fraction. Using Pearson's correlation and factor analysis, the major mechanisms controlling the chemistry of the sediments are identified as association of Cu and Zn with fine fraction sediments, sulphide oxidation in the SW segment of the study area, atmospheric fallout of Pb and Cd in the river basins, precipitation of dissolved Fe and Mn supplied from the rivers and remobilization of Mn from the coastal sediments. Based on various pollution indices, it is inferred that the coastal sediments of NW Borneo are contaminated with Cu and Zn, and are largely bioavailable, which can be a threat to the local aquatic organisms, coral reefs, and coastal mangroves.

Pollution and ecological risk assessment, and source identification of heavy metals in sediment from the Beibu Gulf, South China Sea

The Beibu Gulf is an important passageway between China and the Association of Southeast Asian Nations, where there has been an increase in pollution of heavy metals (HMs). High concentrations of Pb, Cr, Cd, Cu, Zn, As, and Hg in surface sediment were found in Qinzhou Bay, Fangchenggang, and other coastal areas. Stochastic geo-accumulation analyses identified the pollution to be "uncontaminated"; however, it had an 18% probability of deterioration. The Cd, Hg, and As pollution were relatively serious. Principal component analysis, positive matrix factor model, and mercury isotopes demonstrated that the HMs could mainly be attributed to industrial sources including petrochemical, coal-fired, metal and metalloid processing, leather tanning, and human activities: anthropogenic sources accounted for approximately 70% of all the contaminations. This study demonstrates the contribution of terrigenous input to HMs even at a low level and provides basic data for the coordinated development of land and marine resources.

Exploring the impacts of heavy metals on spatial variations of sediment-associated bacterial communities

One of the fundamental objectives in modern ecology is to decipher how bacterial communities in natural environment respond to anthropogenic activities. In recent times consequences of marine pollution, especially with heavy metals (HMs) have received increasing attention. However, insights into the response of bacterial communities to HMs in coastal sediments of India remain scarce. Here, we analyzed HMs content in three areas, along the southern coastal region of India. Based on the calculated pollution indices viz., enrichment factor (EF), contamination factor (CF), geo-accumulation index (Igeo) and sediment quality guidelines (SQGs), the studied areas were classified as uncontaminated, moderately contaminated and significantly contaminated. To explore the response of bacterial community to HMs, sediment-associated microbiota was investigated using high-throughput 16S rRNA gene amplicon sequencing. The obtained metataxonomic results revealed that bacterial diversity and community composition varied considerably in significantly contaminated area than moderately contaminated and uncontaminated areas. Proportion of bacterial classes was higher for Gammaproteobacteria, Betaproteobacteria and Actinobacteria, but lower for Alphaproteobacteria and Flavobacteriia in significantly contaminated area. Also, samples of significantly contaminated area were dominated by well-documented metal-resistant bacterial genera such as Ralstonia and Arthrobacter. Canonical correspondence analysis (CCA) showed that spatial variability of bacterial community composition was strongly correlated with HMs content such as Chromium, Cadmium and Nickel. Further analysis using PICRUSt programme indicated that the predictive functional profile also varied considerably in significantly contaminated area. By linking HMs with bacterial compositional variations, the present study highlights the likely influence of HMs in shaping sedimentary microbiota of coastal regions.

Trace elements contamination assessment in marine sediments from different regions of the Caribbean Sea

Trace elements (TEs), rare earth elements (REEs), and methylmercury (MeHg) concentrations as well as mercury (Hg) and lead (Pb) isotope compositions in sediment samples collected from strategic locations along the Caribbean Sea were determined. The analyzed sediment samples were collected at different core depths from localities in Colombia, Cuba, Haiti, and the Dominican Republic. The evaluation of pollution assessment indices i.e. enrichment factors and geoaccumulation index revealed significant enrichment of several priority substances, such as Pb, Cd and Hg, in most of the sampling sites. Hg was found in extremely high concentrations (up to 22 ± 3 mg kg^-1) in bottom samples of Colombian core, which led the authors to further investigate this area with respect to the source for Hg contamination. The analysis of Hg isotope ratios in Colombian sediments and the Pb isotope ratios in all studied cores, helped in the identification of likely pollution sources and represents a critically important record of anthropogenic influence in the region. Finally, the REEs patterns determined in all samples, also provide a needed baseline for these contaminants in the Caribbean region.