Ecological risk assessment of heavy metal contamination in mangrove forest sediment of Gulf of Khambhat region, West Coast of India

Tidal control of heavy metal loading in the nearshore of the northwestern Indian coast

Heavy metals accumulate in the marine food chain and their excessive amounts are hazardous to aquatic and human lives. The current study presents the role of ecosystem variables especially tides in deciding the presence of ten heavy metals (Fe, Zn, Cu, Co, Cr, Mn, Ni, V, Pb, and Cd) in seawater and copepods along the Indian west coast. The Indian northwestern coast is an industrial hub, where thousands of industries release enormous volumes of effluents, while the southwest coast has a far lower number of industries. Multiple surface seawater and zooplankton samples from eight selected marine outfall regions in the nearshore of the Indian west coast showed that Fe/Cd was generally the highest/lowest in seawater (av. 184 ± 12.40 μg L-1/ av. 0.01 ± 0.01 μg L-1) and copepods (av. 41,818 ± 2867 μg. g-1/ av. 0.2 ± 0.02 μg g-1). The heavy metals in seawater/copepods generally showed the order Fe/Fe > Zn/Zn > V/Mn > Cr/Cr > Pb/Cu > Ni/Ni > Cu/Pb > Mn/V > Co/Co > Cd/Cd. Contrary to expectations, despite being loaded with massive amounts of effluent from thousands of industries, most heavy metals in seawater on the northwestern Indian coast were not higher than on the southwestern coast. It is shown here that this feature is the result of the macro-tidal nature of the northwest Indian coast (av. 7 m tide), where tidal currents, sediment resuspension, and flushing are far more intense than in the southwest (av. 1 m tide), which reduce pollution levels. Yet, the marine pollution index and bioaccumulation factor of heavy metals in copepods was found highest along the northwestern Indian coast, which are important indicators to be considered when developing environmental management strategies for the area.

Phytoremediation efficacy of Sesuvium portulacastrum L. in mitigating industrial effluents and heavy metal contamination

Sesuvium portulacastrum L. is a halophytic plant species used for sand-dune fixation, desalination, and phytoremediation along coastal regions. This study investigates the potential of S. portulacastrum to remediate pollutants such as heavy metals found in industrial discharges. As a halophytic plant, S. portulacastrum demonstrates remarkable tolerance to high salinity and heavy metals, making it a promising candidate for environmental remediation. Over a 30-day experimental period, wastewater samples from the Tapi River and industrial sources were subjected to physicochemical characterization. Initial analyses revealed elevated concentrations of total suspended solids (TSS), total dissolved solids (TDS), total hardness (TH), chemical oxygen demand (COD), nitrates, chlorides, and heavy metals such as zinc, iron, and lead, indicating significant pollution levels. A specially designed bioreactor facilitated the treatment process, resulting in TSS removal rates of 86.30% in river water and 71.90% in the industrial inlet, while TDS removal reached 71.90% in the industrial inlet. The study also highlighted the plant's capacity for heavy metal bioaccumulation, achieving substantial reductions in chromium (60.12%), zinc (65.01%), iron (96.37%), manganese (69.82%), copper (44.83%), nickel (61.98%), cadmium (85.56%), and lead (67.35%). These findings underscore the potential of S. portulacastrum as an effective bioremediation agent for treating wastewater contaminated with heavy metals and organic pollutants, contributing to sustainable environmental management practices. Furthermore, this research highlights the potential of plant species in environmental remediation and provides a foundation for future studies to enhance phytoremediation techniques using natural plant-based solutions in polluted aquatic ecosystems. Furthermore, this research highlights the potential of plant species in environmental remediation and provides a foundation for future studies to enhance phytoremediation methods using natural plant-based solutions in polluted aquatic ecosystems.

Environmental risk assessment of the surface sediments based on trace elements analysis from the largest freshwater lake in the southern slope of the Himalaya, Nepal

Freshwater ecosystems, including high-altitude lakes, can be affected by trace metal pollution derived from a mix of natural sources and anthropogenic activities. These pollutants often collect in surface sediments, with notable concentrations in the deeper areas of lakes. To evaluate the environmental risk associated with metal contaminated sediment in Rara Lake, southern Himalaya, surface sediment samples were systematically collected in November 2018, with a subsequent specific emphasis on determinations of trace element concentrations. Subsequent analysis revealed nine elements exhibiting a descending mean concentrations order: iron (Fe) > manganese (Mn) > chromium (Cr) > rubidium (Rb) > nickel (Ni) > strontium (Sr) > cobalt (Co) > copper (Cu) > cadmium (Cd), of 7205.55 mg kg-1, 2290.34 mg kg-1, 176.29 mg kg-1, 153.78 mg kg-1, 51.86 mg kg-1, 44.61 mg kg-1, 38.89 mg kg-1, 29.11 mg kg-1, and 0.10 mg kg-1, respectively. Comparisons to sediment quality guidelines highlight that Mn, Cr, Cu, and Cd as significant threats to the aquatic ecosystem in Rara Lake. To assess the impact of metal pollution, enrichment factor (EF), geo-accumulation index (Igeo), pollution load index (PLI), and contamination factor (CF) were computed. All metals (except Cd) had Igeo value exceeding 5, displaying strong contamination. EF values for Mn, Cr, Co, and Ni metals were > 10, indicating severe effects of anthropogenic influences. CF and PLI values also indicated significant pollution for most of the investigated sites. Elevated trace element concentrations have the potential to adversely affect water, sediment, and aquatic life, also potentially impacting nutrient cycling and microbial activity. This study enhances our understanding of the metal compositions within Rara Lake sediments and provides a basis for more effective lake management and pollution control strategies. Urgent action by regional governing bodies is crucial to address the early stages of metals pollution, including identification and controlling of pollution sources, by appropriate regulations, optimizing industrial practices, and remediating existing pollution to prevent further contamination and protect the lake ecosystem.

Distribution, assessment, and causality analysis of soil heavy metals pollution in complex contaminated sites: a case study of a chemical plant

To effectively prevent and control pollution from heavy metals (HMs) in urban soils, it is essential to thoroughly understand the contamination status of contaminated sites. In this study, the contamination status and sources of six HMs (As, Cu, Cr, Ni, Pb, Cd) in the soil of a decommissioned chemical plant in southern China were comprehensively analyzed. The results indicated that the average concentration of HMs followed the sequence: Cr > Pb > Cu > Ni > As > Cd. Heavy metal accumulation in the upper soil layer was predominantly observed in industrial zones and low-lying areas, with notable variations in concentration along the vertical profile. Certain sections of the site exhibited severe HM contamination, particularly with Cu levels exceeding the background value by 46.77 times. Cd presented significant ecological risks in specific areas, with an average Ecological Index of 96.09. Carcinogenic and non-carcinogenic risks were identified at three and six sampling points, respectively, with sampling point S103 demonstrating both types of risks. The causes of HM contamination were primarily attributed to anthropogenic activities. Horizontal dispersion was mainly influenced by production operations and topographical features, while vertical distribution was predominantly affected by the permeability characteristics of the strata. The causality analysis incorporating production activities and topographical factors provides novel perspectives for understanding sources of contamination at contaminated sites. The study outcomes can offer guidance for the assessment and surveying of urban industrial pollution sites.

Heavy metals in afforested mangrove sediment from the world's largest delta: Distributional mapping, contamination status, risk assessment and source tracing

This study aims to assess seasonal and spatial variations, contamination status, ecological risks, and metal sources (Ni, Pb, Cr, Cu, Mn, and Zn) in human-afforested mangrove sediments in a deltaic region. Five sampling locations were sampled during dry and wet seasons. Heavy metal concentrations followed the order: Mn > Zn > Ni > Cr > Cu > Pb. Metal loads, except Cu and Pb, were higher during the dry season, aligning with national and international recommendations. Sediment quality guidelines, contamination factor, geoaccumulation index, enrichment factors, and pollution load index indicated uncontaminated sediment in both seasons. Potential ecological risk assessment showed low risk conditions in all sites. However, modified hazard quotient indicated moderate pollution risk from all metals except Pb. Analysis suggests anthropogenic sources, particularly evident near shipbreaking yards in Sitakunda. While initially uncontaminated, ongoing metal influx poses a potential risk to mangrove ecosystems.

Oxidative stress-induced DNA damage and DNA repair mechanisms in mangrove bacteria exposed to climatic and heavy metal stressors

Bacteria thriving in the mangrove ecosystem are major drivers of elemental cycles. Climate change and environmental stressors (heavy metals) influence the performance of these microorganisms, thereby affecting the biogeochemical cycle. The present study reports the genotoxic effect of climatic and heavy metal stressors on mangrove bacteria and their adaptation strategies. Comparative analysis between two bacterial strains, Bacillus stercoris GST-03 and Pseudomonas balearica DST-02 isolated from the Bhitarkanika mangrove ecosystem, Odisha, India, showed cellular injuries in response to various stressors as evident by declined growth, elevated levels of reactive oxygen species (ROS) and resulted DNA damage. B. stercoris GST-03 showed more tolerance towards acidic pH, whereas P. balearica DST-02 showed higher tolerance towards UV exposure and heavy metals (Lead and Cadmium). The adaptation strategies of the strains revealed a significant role of GST in ROS scavenging activity and the involvement of Nucleotide excision repair or SOS response pathways. However, irreparable DNA damage was observed at pH 9 and 200 ppm Cd in B. stercoris GST-03, and at pH 4, 1000 ppm of Pb and 200 ppm of Cd in P. balearica DST-02. The current findings provide a broad overview of bacterial response and adaptability concerning future climate and environmental changes.

Extreme rainstorm reshuffles the spatial distribution of heavy metals and pollution risk in sediments along the mangrove tidal flat

Mangroves as typical blue carbon ecosystems exhibit a high level of heavy metal accumulation capability. In this study, we investigated how extreme rainstorm effects the spatial variability and pollution risk of sediment heavy metals (i.e., Fe, Mn, Cr, Cu, Zn, Cd, Pb, As and Hg) at different compartments of a typical tidal flat, including the bare mudflat, mangrove zone, and tidal creek in Shenzhen Bay, China. The results showed that the extreme rainstorm can change the sediment particle size, which further regulated the spatial distribution, and source-sink pattern of heavy metals. Due to the strong rainstorm flushing, the concentrations of most heavy metals increased toward the sea and the comprehensive pollution level increased by 8.3 % after the extreme rainstorm. This study contributes to better understanding of how extreme rainstorm regulates heavy metal behavior in mangrove sediments to achieve sustainable development of mangroves under the pressures of extreme weather events.

Seawater intrusion decreases the metal toxicity but increases the ecological risk and degree of treatment for coastal groundwater: An Indian perspective

Contaminant vulnerability in the critical zones like groundwater (GW)-seawater (SW) continuum along the entire Gujarat coast was investigated for the first time through an extensive water monitoring survey. The prime focus of the study was to evaluate whether or not: i) seawater intrusion induced metal load translates to toxicity; ii) in the coastal groundwater, metal distribution follows the pattern of other geogenic and anthropogenic contaminants like NO₃- and F-; and iii) what future lies ahead pertaining to metal fate in association with saturation conditions of the coastal aquifers. The spatial distribution of contaminants depicts that the Gulf of Khambhat area is highly contaminated. Ecological risk assessment (ERA) indicates that the Gujarat coast is experiencing a high ecological risk compared to the southeast coast of India. Investigation results revealed that metals, pH, NO₃, and CO₃ are more vulnerable at the SW-GW mixing interface. An increase in pH is reflected in fewer ionic species of metals in the GW. Salinity ingress due to seawater intrusion (SWI) reduces the toxicities of all trace metals except Cu, attributed to the increase of Ca in GW, leading to dissociation of CuCO₃. Reactive species are dominant for Zn and Cd; and M-CO₃ ligands are dominant for Cu and Pb owing to the undersaturation of dolomite and calcite in the aquifer system. SWI tends to increase the metal load but the toxicity of metals varies with the density of industries, anthropogenic activities, changes in the mixing-induced saturation conditions, and intensive salt production across the coast. Multivariate analysis confirmed that the hydrogeochemical processes change due to GW-SW mixing and dictates over natural weathering. The ecological risk index (ERI) for the Arabian sea is experiencing moderate (300 ≥ ERI>150) to high ecological risk (ERI >600). Children population is likely to encounter a high health risk through ingestion and dermal exposure than adults. Overall, the study emphasizes the complexity of toxicity-related health impacts on coastal communities and suggests the dire need for frequent water monitoring along the coastal areas for quick realization of sustainable development goals.

Heavy metals distribution and ecological risk assessment including arsenic resistant PGPR in tidal mangrove ecosystem

Heavy metals (HM) are the major proximate drivers of pollution in the mangrove ecosystem. Therefore, ecological risk (ER) due to HM distribution/concentration in core-sediment of Puzi mangrove region (Taiwan) was examined with tidal influence (TI) along with indigenous rhizospheric bacteria (IRB). The HM concentration was observed higher at active-tidal-sediment compared to partially-active-sediment. Geo-accumulation index (I_geo) and contamination factor (CF) indicated the tidal-sediment was highly contaminated with arsenic (As) and moderately contaminated with Lead (Pb) and Zinc (Zn). However, the pollution loading index (PLI) and degree of contamination (C_d) exhibited 'no pollution' and 'low-moderate degree of contamination', in the studied region respectively. The isolated IRB (Priestia megaterium, Bacillus safenis, Bacillus aerius, Bacillus subtilis, Bacillus velenzenesis, Bacillus lichenoformis, Kocuria palustris, Enterobacter hormaechei, Pseudomonus fulva, and Paenibacillus favisporus; accession number OM979069-OM979078) exhibited the arsenic resistant behavior with plant-growth-promoting characters (IAA, NH₃, and P-solubilization), which can be used in mangrove reforestation and bioremediation of HM.

Geochemical Speciation, Risk Assessment, and Sources Identification of Heavy Metals in Mangrove Surface Sediments from the Nanliu River Estuary of the Beibu Gulf, China

To better understand heavy metal pollution and the potential ecological risk of mangrove sediments in the Nanliu River estuary, the speciation and distribution characteristics of heavy metals Fe, Mn, Zn, Co, Ni, Cd, Cr, Cu, and Pb in 13 surface sediments in the study area were determined and analyzed using a modified four-step BCR extraction method, and the ecological risk of heavy metals was assessed using the Geo-accumulation Index (Igeo), Potential Ecological Risk Index (RI), Risk Assessment Code (RAC), Pollution Load Index (PLI), Individual contamination factors (ICF) and Global contamination factor (GCF) methods, and source analyses were performed using correlation analysis and cluster analysis. The results showed that the heavy metal was in the order of Fe > Mn > Cu > Zn > Cr > Pb > Co > Ni > Cd. Except for Fe, Zn, Ni, Cr, Pb, and Co, the average heavy metal content of Mn, Cd, and Cu all exceeded the environmental background value; the Fe, Zn, Co, Ni, Cr, Cu, and Pd are mainly in the residual speciation, while Mn and Cd are mainly weak acid extraction and oxidation, respectively, both of which are predominantly in unstable speciation and are easily released into the environment. Mn and Cd pose a substantial ecological risk, while Cu and Pb present a moderate risk and require precaution. The source analysis results indicate that Fe, Mn, Zn, Ni, Cr, and Pb are most likely to originate from natural sources and the transportation industry, Co and Cu are likely to be mainly from ship manufacturing industrial activities, and Cd is likely to be mainly from agriculture and aquaculture. The GCF and PLI results show that places with high heavy metal enrichment and ecological risk are primarily located in areas with high industrial, agricultural, or human activity impacts.

Heavy Metal Contamination and Ecological Risk Assessments in Urban Mangrove Sediments in Zhanjiang Bay, South China

With the acceleration of industrialization and urbanization, increasing attention has been paid to the problem of heavy metal pollution in mangroves and its ecological restoration. Urban mangroves can be used to measure the impact of human activities on the urban ecological environment because mangroves are sensitive to human activities. However, studies on the evaluation of heavy metal elements in urban mangroves are still limited. Consequently, this study selected the urban mangroves in a central commercial area of Zhanjiang Bay as a case study to investigate the content and distribution of the heavy metals (Co, V, Cu, Pb, Ni, As, Cd, and Hg) in mangrove surface sediments. Risk levels and possible sources of heavy metals were evaluated based on multivariate statistical analysis methods and pollution indices. The results showed that the average concentrations of heavy metals for Co, V, Cu, Pb, Ni, As, Cd, and Hg were 2.91, 29.96, 18.24, 20.07, 7.86, 5.0, 0.20, and 0.09 mg/kg, respectively. Cd, Cu, and Hg were most prominent within the Zhanjiang Bay mangrove sediments, whereas other metals showed a low contamination factor of therm. Cd displayed a high potential ecological risk followed by Hg and Cu. The sampling site, the sewage outlet sampling site, exhibited the highest pollution degree followed by the surrounding area of the sewage outlet sampling site. Those polluted heavy metals could arise from anthropogenic sources, including domestic sewage and automobile exhaust emission. Correlation analysis between the heavy metals and physicochemical properties indicated that fine particles and organic matter play a key role in controlling heavy metal enrichment.