Seasonal assessment of trace element contamination in intertidal sediments of the meso-macrotidal Hooghly (Ganges) River Estuary with a note on mercury speciation

An appraisal of trace element concentration and environmental risk of sediments: a baseline study of sediments from Arasalar River Estuary, Tamil Nadu, India

A total of 21 surface sediment samples collected from Arasalar River are subjected to sediment texture (sand-silt-clay ratio), trace elements, organic matter, and CaCO3 studies to understand the accumulation dynamics of sediments. To assess the impact of metal pollution in estuarine sediments, the essential parameters should be done by checking the sediment characteristics, spatial distribution of heavy metal sources, sediment dynamics, and geochemical analysis. To evaluate the contamination level of metal pollution, a basic standard reference is required to decipher the values ranging from natural to anthropogenic contribution. From this research analysis, it is observed that the study area predominantly comprises silty sand and sand silty nature. The calcium carbonate content in the sediment is found to be proportional to the presence of shell fragments, whereas the organic matter (OM) is derived from riverine and coastal input which acts as a primary source. The obtained results confessed the average contents (mg/g) for the following selected eight elements in the order of Fe (35249-49068) > Mn (286-519) > Ni (107-279) > Cu (78.30-155.70) > Cr (50-99) > Zn (38.70-91.90) > Pb (39.90-62.40), and Co (12.6-29.1) by using an atomic absorption spectrophotometer (AAS) are utilized for this analysis. Multivariate analysis of heavy metals affirms geogenic sources (weathering of parent rocks) for Fe, Mn, Cr, Co, and Zn, whereas Cu, Ni, and Pb originated from anthropogenic activities (urban and industrial activities). The pollution load index, sediment pollution index, Igeo index, and PERI are categorized as under polluted, low to moderate polluted, and low potential environmental risk variety. Constant inspection and guidance are needed to prevent effluences from various agriculture and industrial activities in the nearby regions. The findings from this research may support and help the government to follow the suitable remediation on the better management of river and coastal areas.

Distribution patterns, risk assessment and potential sources of heavy metals in sediment in the Qiongzhou Strait, China

Risk assessment and pollutant source analysis are crucial tools for the management and protection of coastal ecosystems. The distribution patterns, risk assessment, and potential sources of heavy metals (Cd, Cr, Fe, Ni, Cu, Zn, As, Hg, and Pb) in surface sediment were analyzed in the Qiongzhou Strait, China, in summer and autumn of 2022. Heavy metals in autumn showed higher ecological risk than that in summer. Seasonal shifts in ocean currents may result in variations in heavy metal accumulation and dispersion. Cd and Hg were the priority heavy metals found, and according to the Positive Matrix Factorization results, the study area contains five sources of pollution, with natural sources, shipping-related activities, and industrial activities being the primary contributors. This study indicated that pollutants from adjacent areas should be considered for managing the environmental quality of Qiongzhou Strait.

Exploring seasonal, spatial and pathways of marine litter pollution along the Southeastern Black Sea Cost of Türkiye

Spatial and temporal variations in marine litter density and composition along the Southeastern Black Sea Coast were investigated. A total of 156,371 litter items weighing 327,258.3 kg were collected. The highest frequency of litter material by number was 15,869 ± 103.88 items/m2 16 and 74.466 ± 7.23 by weight. The highest litter concentrations (77,768 items; 81,737.1 kg) were observed in autumn, mainly comprising single-use items, with plastic being the most abundant (54.05 %), followed by metal (15.69 %), and paper (10.45 %). The subcategories of plastic litter items bags, caps/lids, cigarette lighters, cosmetic packages, gloves, and plastics pieces were found to be the most abundant litter in number. According to Principal Component Analysis (PCA) and Kruskal-Wallis statistical tests (p < 0.005), significant differences in marine litter were identified among the stations and seasons. These findings offer insights for modeling studies, advocating restrictions on single-use products, and enacting legal regulations for local governance.

Heavy Metal Distribution in Surface Sediments of the Coastal Pearl Bay, South China Sea

Six heavy metals (As, Cu, Cd, Zn, Cr, and Pb) in surface sediments (0–5 cm) from the twenty selected sites of the coastal Pearl Bay (South China Sea) were analyzed to assess the distribution pattern and potential ecological risk. Overall concentrations (mg/kg, dw) in the sediment samples were: As (10.88 ± 6.50), Cu (24.16 ± 18.63), Cd (0.55 ± 0.78), Zn (48.53 ± 30.06), Cr (35.78 ± 28.66), Pb (31.28 ± 18.50). Results showed that the overall mean values of Cd concentrations exceeded the standard of China Marine Sediment Quality, caused by significantly high levels of Cd contents in five sites (S8, S11, S13, S16, and S17) at the offshore area of Pearl Bay. Generally, the metal concentrations showed a decreasing trend from the offshore area to the inner bay. Various index values such as the geo-accumulation index (Igeo), the ecological risk index (Eri), and the contamination factor (CF) demonstrated that the coastal Pearl Bay was not polluted by the examined metals except for Cd, which might cause contamination and ecological risk in the region. Principal component analysis (PCA) results indicated that Cu, Zn, and Cr might originate from natural sources inland, and Pb and As might come from the gasoline and diesel fuel from engine boats. It is recommended that further research should focus on detecting the acute source and transferring mechanisms of the toxic metal Cd.

Role of sulfur biogeochemical cycle in mercury methylation in estuarine sediments: A review

Estuaries are sinks for mercury, in which the most toxic mercury form, neurotoxic methylmercury (MeHg), is produced by mercury methylators and accumulates in estuarine sediments. In the same area, the microbial sulfur cycle is triggered by sulfate-reducing bacteria (SRB), which is considered as the main mercury methylator. In this review, we analyzed the sulfur and mercury speciation in sediments from 70 estuaries globally. Abundant mercury and sulfur species were found in the global estuarine sediments. Up to 727 μg THg/g dw and 880 ng MeHg/g dw were found in estuarine sediments, showing the serious risk of mercury to aquatic ecological systems. Significant correlations between sulfur and MeHg concentrations were discovered. Especially, the porewater sulfate concentration positively correlated to MeHg production. The sulfur cycle affects MeHg formation via activating mercury methylator activities and limiting mercury bioavailability, leading to promote or inhibit MeHg formation at different sulfur speciation concentrations. These results suggest that sulfur biogeochemical cycle plays an important role in mercury methylation in estuarine sediments, and the effect of the sulfur cycle on mercury methylation deserves to be further explored in future research.

Spatial distribution of trace elements in surface sediments of Hooghly (Ganges) river estuary in West Bengal, India

The spatial distribution of trace elements in surface sediments of the Hooghly estuary was studied over the monsoons in 2014-2017. As, Cd, Ni, Pb and U were two- to sixteen-fold the crust means with increasing levels toward the estuary, with Ni peak during the post-monsoon. Pearson's correlation matrix, cluster analysis, enrichment factors and pollution index revealed the anthropic source and association of trace elements with Fe, Mn and Al and of Pb with U. Geoaccumulation index revealed for Ni an extremely contaminated situation at the estuary water during monsoon and for Cd a heavily contaminated situation at freshwater location. The potential contamination index was >6; thus, sediments were very severely contaminated by As, Cd and Ni with worst situation for As and Cd at fresh and brackish water and during post-monsoon. The overall ecological risk was severe, 300≤RI<600 at all sites and seasons, especially after the monsoon, at fluvial and brackish locations.

Distribution, source and risk assessment of heavy metals in the seawater, sediments, and organisms of the Daya Bay, China

Cu, Pb, Zn, Cd, Cr, Hg and As in seawater, sediment and organisms of the Daya Bay, Guangdong province, China were measured to acquire the comprehensive understanding on distribution, sources and risk assessment of heavy metals (HMs) in the marine ecosystem. The concentrations were relatively ideal, and the Pb was the major pollutant in the seawater and sediment. The contents of HMs were highest in spring; the concentrations near the sewage outlet and shore were noticeable. Submarine pipeline sewage, atmospheric deposition and runoff were the main sources of HMs in coastal waters. Studied HMs were preferentially retained by liquid phase; Cd, Cu and Zn were the most accumulated elements in the organisms from the surrounding environment. Cd in shellfish deserved particular attention, but the health risks including non-carcinogenic and carcinogenic risks of all elements were within acceptable limits. The potential health risks of Pb have been confirmed by molecular docking.

Assessment of the surface water quality improvement during pandemic lockdown in ecologically stressed Hooghly River(Ganges) Estuary, West Bengal, India

The countrywide COVID-19 pandemic lockdown accomplished what aggressive plans could not do throughout the long-term cleaning of the Ganga River. Here, we illustrated Hooghly River surface water quality [physico-chemical parameters, biological parameters, dissolved heavy metals] improvement by analyzing eight sampling station before and during the lockdown. Because of shutdown of industrial units and individuals staying at home, a complete decrease in industrial wastes, contaminants, and self-purging of the stream improved significantly water quality by about 40% to 50%. Among dissolved heavy metals, the concentrations of Cd (50%), Pb (53%), demonstrated noteworthy variations during the lockdown. Diminishing trends were also observed for TDS (62%), and BOD (52%), with significant reduction in the total coliform (63%), faecal coliform (61%), notably. Principal component analysis and paired t-test signify the alteration of water quality. The study concludes that the aquatic ecosystem can be revived if wastewater, and anthropogenic activities are properly managed by environmental surveillance.

Trace element bioaccumulation in the seagrass Cymodocea nodosa from a polluted coastal lagoon: Biomonitoring implications

This is the first investigation of the potential for using Cymodocea nodosa to biomonitor trace element (TE) contamination in Marchica lagoon (Morocco), a Mediterranean pollution hotspot. We measured concentrations of seven TEs in seagrass tissues (leaf-rhizome-root) and sediments. Single and multi-element indices confirmed that sediments near illegal discharges were heavily polluted and we predicted risks of frequent adverse biological effects in these areas. Four of the TEs increased concentrations in C. nodosa leaf and root along sediment pollution gradient. Leaves and roots were both good indicators of Cu and Cd contamination in sediment, whereas leaves were the best indicator of Zn and roots for Pb. This seagrass was not a bioindicator of Al, Cr and Ni contamination. These results show the bioaccumulation patterns of TEs in C. nodosa, and can be used to design biomonitoring programs.

Health Risk and Geochemical Assessment of Trace Elements in Surface Sediment along the Hooghly (Ganges) River Estuary (India)

This study investigated sediment spatial and seasonal distribution of trace elements (TEs) (n = 16) and human health effects along the Hooghly River Estuary (India). The index of geo-accumulation (Igeo), enrichment factor (EF), hazard quotient (HQ), modified hazard quotient (mHQ) and toxic risk unit (TRI) were calculated to estimate sediment pollution level, while hazard index (HI) and lifetime cancer risk (LCR) were used to assess TEs enrichment vs. human health. The concentrations (µg/g dry weight) of TEs were: Cd (0.01–1.58), Cr (41.98–105.49), Cu (16.41–51.09), Ni (28.37–63.90), Fe (22075–47919), Mn (423–630), Co (11.43–23.11), Zn (48.82–105.81), V (63.92–138.92), Pb (25.01–43.27) and Ti (0.18–3.50); As (2.92–16.26), B (59.34–98.78), Si (11.52–98.78); Be (1.71–4.81), Ba (95.23–293.72). From Igeo and EF, Cd was the major contaminant, while Ni presented moderate/high contamination (HQ and TRI). Children were more exposed to carcinogenic and non-carcinogenic risks compared to adults. For non-carcinogenic substances, no significant risk was found to both children and adults (HIs < 1). The LCR for Cr (3.924 × 10−4 for children) and As (1.379 × 10−4 for children) was higher than the threshold limit value (TLV, 10−4 and 10−6) indicating significant carcinogenic risks to be managed.

Determination and comparison of selected heavy metal concentrations in seawater and sediment samples in the coastal area of Suva, Fiji

The coastal area of Suva, Fiji is exposed to high degree of metals input from different sources such as land-based industrial activities like metal fabrication and construction, paint manufacturing, petroleum storage and garment manufacturing, food processing and fish cannery as well as activities of bottling plants. It is therefore essential to have continuous monitoring and environmental management for the coastal area. Thus, to assess the degree of contamination of metals, selected metals (Cd, Zn, Pb, Cu and Ni) concentrations were analysed in seawater and sediment samples collected from ten sites in the coastal area of Suva, Fiji. The concentration of these metals in the samples was analysed using flame atomic absorption spectrometer (FAAS). The concentrations of the metal in seawater were in the range: 0.23-0.80 mg/L, 0.08-1.45 mg/L, 0.15-0.25 mg/L, 0.88-1.77 mg/L and 0.88-10.29 mg/L for Ni, Zn, Cd, Pb and Cu, respectively. The corresponding concentrations of metal in the sediment samples in dry weight (dw) basis for Ni, Zn, Cd, Pb and Cu were in the range: 17.24-28.74 mg/kg, 18.55-68.78 mg/kg, 5.49-9.16 mg/kg, 116.96-233.92 mg/kg and 78.43-490.18 mg/kg, respectively. The quality of the seawater was evaluated with respect to WHO established guidelines while the quality of the sediments evaluated using internationally accepted Sediment Quality Guidelines (SQGs). The contamination of the sediments was also assessed in terms of geo-accumulation index (I_geo), contamination factor (C_f) as well as pollution load index (PLI). Zn complied with the guidelines in all ten sites, Cu in eight sites was within the guidelines while Ni complied with the guideline in six sites. However, the levels of contamination recorded for Cd and Pb in all ten sites did not comply with the guidelines.

Assessment of mining activity on arsenic contamination in surface water and sediments in southwestern area of Santurbán paramo, Colombia

The current emphasis of developing countries on policies that favor the intensification of mining exploitation as the main source of incomes, has generated negative consequences for ecosystems and rural communities, mainly due to the release of highly toxic elements into the environment. This study was carried out to evaluate the effect of the Vetas-California gold mining district on As distribution in stream sediments and surface water samples from Suratá River, located in the southwestern area of Santurbán paramo, Colombia. With this aim, samples distributed along the high Suratá River basin in areas near and far from mining areas were selected. Samples were chemically characterized. The As mobility, enrichment and sources were evaluated using sequential and single extractions, enrichment factor (EF), geoaccumulation index (I_geo), and hierarchical cluster analysis (HCA). The results highlight high As content (reaching up to 484 mg/kg) in stream sediment sampled near the gold mining district. For both sediment and water, the relative As content along the Suratá River exceeded the background content by 220 and 64.9 times, respectively. From the single-stage extractions performed, the reducible fractions found in As(NaOH) and As(HCl) were higher in all cases, meaning a high level of mobility and lixiviation of the As content in water samples by changes in pH and redox potentials. The correlations estimated using Spearman coefficients show that most of the bioavailable fraction of As(Exch) is related to main sediment constituents such as S, Fe₂O₃, SiO₂, and Al₂O₃ and the relative As content. Calculation of the enrichment factor (EF) confirms high enrichments around active sites of gold mining such as the municipalities of Vetas, California and Matanza with EF values of 285, 204, and 133, respectively. In addition, the I_geo values suggest moderate to strong As pollution due to the high I_geo found at the major mining effect points. The findings from this study are valuable for providing effective management options for risk prevention and control of the persistent As accumulation in Santurbán paramo.

Assessment of potentially toxic pollutants and urban livability in a typical resource-based city, China

Toxic pollutants are affecting the environment on a global scale. To quantify the extent of the elemental pollution in Peixian, a typical Chinese city, we collected 332 soil samples from agricultural, residential, woodland, and hydrological environments. Using multivariate statistical and geostatistical analyses, the results indicate that contaminants including chromium (Cr), zinc (Zn), copper (Cu), lead (Pb), cadmium (Cd), and arsenic (As) may share common sources such as commercial activities, coal mining activities, water transportation, power generation, and livestock manure. The presence of mercury (Hg) in the southern part of the study area, however, is almost entirely attributed to nearby mining activities. The value of contamination index was the highest in hydrological environments. Health exposure risk assessments of the elements were also investigated. With the exception of Pb, the potentially toxic elements in the study area do not pose a severe non-carcinogenic health risk. At the levels observed in our study, however, Pb may pose a non-carcinogenic risk to children. Based on these results, the area's livability is assessed. The urban livability analysis shows that the livability level is higher in the western part of the study area than it is in the eastern part.

Elemental composition of aquaculture fish from West Bengal, India: nutrition versus food safety

Aquaculture production continues to grow in West Bengal, where on average people consume 8.2 kg capita^-1 of fish each year, and an extensive mosaic of aquaculture ponds has developed along the River Hugli as clay pits are repurposed. The adjacent brickworks and industry (especially tanneries) are a source of environmental pollution, with potential for bioaccumulation of potentially harmful elements (PHEs) in fish farmed in these ponds. Fish from aquaculture present an opportunity to meet food sufficiency in West Bengal; however, an investigation to assess their effectiveness for micronutrient supply balanced against food safety is required. Five ponds close to industrial brick manufacture (urban) and three from rural areas were assessed for the degree of pollution within their pond sediments and waters. Fish were also sampled from each location including a subset from the market in Kolkata to determine the concentrations of PHEs in their fish muscle tissue. Dietary intake and PHE loading were calculated for four fish species to evaluate their nutrient content with respect to recommended daily intakes for adults, e.g. calcium (Ca), potassium (K), magnesium (Mg), iron (Fe), zinc (Zn) and selenium (Se), and to establish whether the provisional maximum tolerable intakes (PMTIs) are exceeded for PHEs, e.g. aluminium (Al), arsenic (As), mercury (Hg), chromium (Cr), tin (Sn), copper (Cu) and lead (Pb). Preliminary results suggest that aquaculture is making an important contribution to nutrition, with fish being a good source of Se. However, in contrast to small wild-caught fish, aquaculture fish in the present study were poor sources of Fe, Ca and Zn. The fish also made substantial contributions (> 10%) to the PMTI of Hg and As. Therefore, there is an urgent need for ongoing monitoring and an expanded sampling programme, as well as research into approaches which might improve the nutritional quality of the farmed fish.

Dry and wet seasonal variation of total mercury, inorganic mercury, and methylmercury formation in estuary and harbor sediments

This study analyzed the seasonal variations and the spatial distributions of total mercury (THg), inorganic divalent mercury (IHg), and methylmercury (MeHg) in sediments of river mouth (RM), main channel (MC), and entrance (E) of the Port of Kaohsiung, Taiwan. The THg, IHg, and MeHg concentrations were, respectively, 198-9130, 2.6-3164, and <0.3-42.6 μg/kg in the wet season and 362-2264, 11.0-790, and 3.3-65.6 μg/kg in the dry season. As for seasonal variations, the concentrations of THg and IHg for RM sediment were higher in the wet season than in the dry season, whereas for MC and E was converse. Generally, MeHg in sediment was higher in the dry season than in the wet season. THg and IHg were mainly transported from the river, whereas MeHg was generated by onsite microbes transforming the local available IHg. Results indicated that the formation of MeHg in sediment may be mainly influenced by the concentration of IHg and seasonal variations.

Trace metals contamination in different compartments of the Sundarbans mangrove: A review

This review study aimed to decipher distribution of trace metals (Al, As, Cd, Cr, Cu, Hg, Pb, Ni, Mn, V, and Zn) in different compartments and human health risk in the Sundarbans mangrove ecosystems. The literature suggested relatively higher contamination of soils and sediments than fish, crustaceans, and water. Cd, Fe, Ni, and Pb are most likely to accumulate in roots of mangrove trees, while Al, As, Co, Cr, Cu, Mn, and Zn tend to accumulate in the leaves. According to human health risk studies, fish consumption is the main route of trace metals exposure to human. Majority of the studies conducted in the Indian Sundarbans; whereas, in Bangladesh part, there is an evident lack of such kind of studies. Finally, this review highlights the foremost data and research gaps, which will help to refine the risk of trace metals and scarcity of researches in the Sundarbans mangrove ecosystem.

Baseline study of heavy metal contamination in the Sangu River estuary, Chattogram, Bangladesh

Sediment samples were collected from twelve selected sites of the Sangu River estuary and seven metals (As, Cr, Cu, Cd, Pb, Ni, Zn) were analyzed with Inductively Coupled Plasma-mass Spectrometry (ICP-MS) to assess the contamination degree of heavy metals in the Sangu River estuary and to represent it as a reference site. This study revealed the descending order of studied metals (mg/kg) observed in sediment as Zn (88.97 ± 58.97) > Ni (32.75 ± 16.09) > Cu (29.2 ± 10.78) > Cr (25.14 ± 5.20) > Pb (19.57 ± 7.01) > As (2.58 ± 2.55). Cadmium was observed below the detection level. Various indices like geo-accumulation index (I_geo), contamination factor (CF), pollution load index (PLI) suggested that the Sangu River estuary is not contaminated by studied metals excepting Pb. PCA and correlation matrix analysis indicates that Pb and Zn may have anthropogenic sources and As, Ni, Zn, Cu, Cr may come from natural sources.

Pollution evaluation of total and acid-leachable trace elements in surface sediments of Hooghly River Estuary and Sundarban Mangrove Wetland (India)

The present work investigated the spatial distribution and ecological risk assessment of total and mild acid-leachable trace elements in surface sediments (top 0-10 cm; grain size ≤ 63 μm) along the Hooghly (Ganges) River Estuary and Sundarban Mangrove Wetland, India. The trace elements, analyzed by ICPMS, showed wide range of variations with the following descending order (mean values expressed in milligrams per kilogram): Fe (25,050 ± 4918) > Al (16,992 ± 4172) > Mn (517 ± 102) > Zn (53 ± 18) > Cu (33 ± 11) > Cr (29 ± 7) > Ni (27 ± 6) > Pb (14 ± 3) > As (5 ± 1) > Se (0.37 ± 0.10) > Cd (0.17 ± 0.13) > Ag (0.16 ± 0.19) > Hg (0.05 ± 0.10). In the acid-leachable fraction, Cd (92%) is dominated followed by Pb (81%), Mn (77%), Cu (70%), and Se (58%) indicating their high mobility, imposing negative impact on the adjacent benthos. The sediment pollution indices (both enrichment factor and contamination factor) suggested severe pollution by Ag at the sampling site Sajnekhali, a wildlife sanctuary in Sundarban. The mean probable effect level quotient indicated that surface sediments in the vicinity of the studied region have 21% probability of toxicity to biota. The result of multivariate analyses affirms lithogenic sources (e.g., weathering parent rocks, dry deposition) for As, Pb, Cr, Cu, and Ni, whereas Cd and Hg originated from anthropogenic activities (such as urban and industrial activities). Both human-induced stresses and natural processes controlled trace element accumulation and distribution in the estuarine system, and remedial measures are required to mitigate the potential impacts of these hazardous trace elements.