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

Assessment of heavy metal contamination in the surface sediments, seawater and organisms of the Pearl River Estuary, South China Sea

Coastal heavy-metal contamination poses significant risks to marine ecosystems and human health, necessitating comprehensive research for effective mitigation strategies. This study assessed heavy-metal pollution in sediments, seawater, and organisms in the Pearl River Estuary (PRE), with a focus on Cd, Cu, Pb, Zn, As, Hg, and Cr. A notable reduction in heavy metal concentrations in surface sediments was observed in 2020 compared to 2017 and 2018, likely due to improved pollution management and COVID-19 pandemic restrictions. Spatial analysis revealed a positive correlation between elevated heavy-metal concentrations (Cu, Pb, Zn, Cd, and As) and areas with significant human activity. Source analysis indicated that anthropogenic activities accounted for 63 % of the heavy metals in sediments, originating from industrial effluents, metal processing, vehicular activities, and fossil fuel combustion. Cd presented a high ecological risk due to its significant enrichment in surface sediments. Organisms in the PRE were found to be relatively enriched with Hg and Cu, with average As concentrations slightly exceeding the Chinese food-health criterion. This study identified high-risk ecological zones and highlighted Cd as the primary pollutant in the PRE. The findings demonstrate the effectiveness of recent pollution control measures and emphasize the need for ongoing monitoring and mitigation to safeguard marine ecosystems and human health.

Ecological and health implications of heavy metal bioaccumulation in Thai Fauna: A systematic review

Heavy metals pose significant threats to ecosystems and human health due to their persistence and bioaccumulation. In Thailand, rapid industrialization, extensive agriculture, and urban development have exacerbated heavy metal pollution in both aquatic and terrestrial ecosystems. This systematic review, conducted according to PRISMA guidelines, evaluates study designs and methodologies to assess heavy metal bioaccumulation in Thai fauna, with a focus on ecological and health impacts. The review reveals that fish, particularly from families like Cyprinidae and Cichlidae, account for 42.11 % of studies, with species such as swamp eel, Henicorhynchus siamensis, Arius maculatus, Osteogeneiosus militaris, Puntioplites proctozystron, and Channa striata showing significant bioaccumulation. Molluscs (31.58 %), including Tegillarca granosa and Filopaludina martensi, serve as critical bioindicators of aquatic pollution due to their filter-feeding habits. Amphibians and crustaceans, like Fejervarya limnocharis and Fenneropenaeus merguiensis, also demonstrate vulnerability to heavy metal contamination. Key contamination hotspots include urban waterways in Bangkok, industrial discharges in Songkhla Lake, and mining sites in Loei Province, highlighting widespread environmental and health impacts. Despite extensive research, gaps remain, particularly concerning benthic scavengers and detritivores, which are vital for ecosystem functions. The review underscores the need for targeted monitoring and mitigation, including stricter regulations on industrial discharges, improved waste treatment, and better management of agricultural runoff. While metals like cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn) are well-studied, further research on less-examined metals and species-specific bioaccumulation patterns is crucial to enhancing environmental management, supporting biodiversity conservation, and improving ecosystem resilience in Thailand.

The molecular insights of cyanobacterial bioremediations of heavy metals: the current and the future challenges

In recent years, overexplorations of ore and the growth of industries are the prime factors in the release of heavy metals in environments. As a result, the food crops and water bodies are contaminated with metals which may have several adverse effects on the health of humans and other living species. These metals and metalloids, such as Zn, Cu, Mn, Ni, Cr, Pb, Cd, and As, upset the biochemical pathways of metabolite synthesis in living organisms and contribute to the etiology of different diseases. Microorganisms include bacteria, archaea, viruses, and many unicellular eukaryotes, which can span three domains of life-Archaea, Bacteria, and Eukarya-and some microorganisms, such as cyanobacteria, have shown high efficiency in the biosorption rate of heavy metals. Cyanobacteria are suitable for bioremediation as they can grow in adverse environments, have a less negative impact on the surrounding environment, and are relatively cheaper to manage. The structure of cyanobacteria has shown no extensive internal-bound membranes, so it can directly employ the physiological mechanisms to uptake heavy metals from contamination sites. Such biochemical makeups are suitable for managing and bioremediating heavy metal concentrations in polluted environments. This review aims to explore the potential of cyanobacteria in the bioremediation of heavy metals and metalloids in water bodies. Additionally, we have identified the prospects for enhancing bioremediation effectiveness.

Distribution, ecological risk, and sediment-influencing mechanisms of heavy metals in surface sediments along the intertidal gradient in typical mangroves in Hainan, China

The relative importance of each sediment physicochemical property to sediment heavy-metal (HM) contents has not yet been quantitatively evaluated. Differences in the HM contents of mangrove surface sediments among the high, middle, and low intertidal zones, and their quantitative relationships to sediment physicochemical properties, were investigated in Dongzhaigang and Qinglan Harbor reserves, Hainan, China. In both reserves, the Cu and Ni concentrations increased significantly from the low to high intertidal zones; the patterns of change in the Mn and Pb contents were opposite in the two reserves. The Cr concentration was significantly lower and the Pb concentration was significantly higher in the dry season than in the wet season. Ecological risks of HM were higher in Dongzhaigang than in Qinglan Harbor. Regression and redundancy (hierarchical partitioning) analyses showed that the sediment total sulfur, nitrogen and potassium contents and pH were key factors affecting the HM contents of mangrove surface sediments.

Examining temporal trends in heavy metal levels to analyze sediment pollution dynamics in the Saida urban watershed (N-W Algeria)

The study focuses on current pollution in the Saïda basin, a semi-arid region in north-western Algeria. By analyzing sediments, the study provides interesting results on urban pollution and its environmental impact. The research consists of two main phases, each addressing different aspects of pollution. In the first phase, different pollution indicators are used to analyze heavy metals and organic pollutants in urban drainage sediments. The results are compared with sediment quality guidelines, regulatory thresholds, and local and international references. Most of the metallic contaminants exceed the toxicity levels established by the continental crust and sediment quality guidelines, suggesting an anthropogenic origin. In addition, contamination indices show significant accumulation. In this context, the results highlight the importance of accumulation and transport processes in urban sediments. Hydrological parameters significantly influence heavy metal distribution mechanisms. Remarkable variations between copper (Cu) and lead (Pb) suggest a combined or singular source during transport. Conversely, chromium (Cr), nickel (Ni), and iron (Fe) are mainly derived from natural lithological sources. Cadmium (Cd) is associated with anthropogenic sources related to the agricultural use of phosphate fertilizers, whereas zinc (Zn) is mainly derived from physical corrosion processes. In the second phase, a combined descriptive and multivariate statistical analysis examines the mobility and distribution of heavy metals and their relationships with organic matter (OM) over time. Pronounced temporal variations in Cd, Zn, and Cu concentrations are attributed to human activities. Strong correlations exist between OM and cobalt (Co), Cu and Pb, confirming the ability of OM to adsorb these metals under specific geochemical conditions associated with waste disposal. Conversely, Zn, Cd, Cr, and Ni show weak or negative correlations with OM, suggesting diverse sources, including potential agricultural, industrial, and natural origins. The dendrogram confirms the existence of previously identified contaminant groups, suggesting common sources and potential co-occurrence patterns. This analysis highlights the role of the drainage network as a physico-chemical reactor in the mobilization of contaminants. It underlines the importance of sediment interactions in urban pollution processes. Finally, recommendations are proposed to ensure effective pollution control and remediation. PRACTITIONER POINTS: Useful information on pollution and its environmental impact is provided by the analysis of sediments in the urban basin of Saida (NW-Algeria). The results of this study indicate high levels of heavy metals in the sediments, in excess of toxicity limits, and evidence of anthropogenic sources. Temporal variations in metal concentrations indicate the influence of human activities. The study has made it possible to identify the sources, to understand the mobility and distribution, and to control the contamination by heavy metals in the urban sediments. Drainage system serves as a pathway for dispersing contaminants.

Controlling effects of terrestrial organic matter on metal contamination and toxicity risks in port sediments

The contents of metals, total carbon, total nitrogen (TN), total organic carbon (TOC), and stable isotope composition (δ13Corg and δ15N) of sediment organic matter (SOM) were investigated to explore the sources and spatial distribution of metals and SOM in the surface sediments (Kaohsiung Port, Taiwan). Results showed that TOC and metals in estuarine sediments are high, gradually decreasing toward the port entrances. The δ13Corg, δ15N, and TOC/TN ratios indicate that SOM comes mainly from terrestrial sources. This study proposes a befitting model between metal pollution and toxicity risk index and SOM sources in port sediments by combining stable isotope composition, correlation matrix, and multiple linear regression analysis. The model indicates that the degree of metal pollution and toxicity risk in sediments are mainly affected by TOCterr content and SOM source. The results help to understand the influence of organic matter sources in port sediments on metal concentration distribution.

Elemental composition and metal pollution in Egyptian Red Sea mangrove sediments: Characterization and origin

The present work was conducted to characterize the mangrove sediments along the Egyptian Red Sea in terms of elemental composition and to assess the extent of pollution and its sources. A total of 26 samples of mangrove sediments were collected from three different areas: Sharm El Madfea, Sowmaa Mangrove and Abu Fasi. The samples were analyzed using the inductively coupled plasma - mass spectrometry ICP-MS and atomic-emission spectrometry ICP-AES. Mass fractions of a total of 58 major and trace elements were determined in the mangrove samples. Univariate and multivariate statistical analyses were performed to determine the origin of trace and major elements in the mangrove sediments. The normalized values show that the elements above the background can be indicated in descending order as follows: P > Cd > Sr > Ca > U > Se > As > Sn > Cu > Sb > Pb > Mo > Ag. Several pollution indices were also calculated. Principal component analysis revealed three clusters of the studied sediment samples. The analysis of the ratio indicators shows that the origin of the sediments mostly falls near continental island arcs (CIA). The pollution indices show remarkable pollution levels and enriched elements. The data obtained can serve as baseline data for the sediments of the mangrove environment and can be used to study possible changes in the future.

Electrochemical and Colorimetric Nanosensors for Detection of Heavy Metal Ions: A Review

Human exposure to acute and chronic levels of heavy metal ions are linked with various health issues, including reduced children's intelligence quotients, developmental challenges, cancers, hypertension, immune system compromises, cytotoxicity, oxidative cellular damage, and neurological disorders, among other health challenges. The potential environmental HMI contaminations, the biomagnification of heavy metal ions along food chains, and the associated risk factors of heavy metal ions on public health safety are a global concern of top priority. Hence, developing low-cost analytical protocols capable of rapid, selective, sensitive, and accurate detection of heavy metal ions in environmental samples and consumable products is of global public health interest. Conventional flame atomic absorption spectroscopy, graphite furnace atomic absorption spectroscopy, atomic emission spectroscopy, inductively coupled plasma-optical emission spectroscopy, inductively coupled plasma-mass spectroscopy, X-ray diffractometry, and X-ray fluorescence have been well-developed for HMIs and trace element analysis with excellent but varying degrees of sensitivity, selectivity, and accuracy. In addition to high instrumental running and maintenance costs and specialized personnel training, these instruments are not portable, limiting their practicality for on-demand, in situ, field study, or point-of-need HMI detection. Increases in the use of electrochemical and colorimetric techniques for heavy metal ion detections arise because of portable instrumentation, high sensitivity and selectivity, cost-effectiveness, small size requirements, rapidity, and visual detection of colorimetric nanosensors that facilitate on-demand, in situ, and field heavy metal ion detections. This review highlights the new approach to low-cost, rapid, selective, sensitive, and accurate detection of heavy metal ions in ecosystems (soil, water, air) and consumable products. Specifically, the review highlights low-cost, portable, and recent advances in smartphone-operated screen-printed electrodes (SPEs), plastic chip SPES, and carbon fiber paper-based nanosensors for environmental heavy metal ion detection. In addition, the review highlights recent advances in colorimetric nanosensors for heavy metal ion detection requirements. The review provides the advantages of electrochemical and optical nanosensors over the conventional methods of HMI analyses. The review further provides in-depth coverage of the detection of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) ions in the ecosystem, with emphasis on environmental and biological samples. In addition, the review discusses the advantages and challenges of the current electrochemical and colorimetric nanosensors protocol for heavy metal ion detection. It provides insight into the future directions in the use of the electrochemical and colorimetric nanosensors protocol for heavy metal ion detection.

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.

Key factors influencing pollution of heavy metals and phenolic compounds in mangrove sediments, South China

Concentrations of heavy metals (HMs) and phenolic compounds with factors which potentially affected their spatial distribution were investigated in mangrove sediments, South China. Compared to Qi'ao, Futian sediments exhibited higher levels of Pb and nonylphenol (NP), but lower levels of Co and Ni. Seasonal variation showed higher concentrations of Pb, Cr, Co, NP and bisphenol A (BPA), while lower concentration of methylparaben (MP) in wet than dry season. Contaminant levels in sediments collected at different tidal heights showed insignificant variations, except for Zn and NP. MP was found negatively correlated with nearly all HMs and BPA, whereas the latter exhibited positive correlations with each other. Sedimentary total carbon, total nitrogen, C/N and N/P ratios were screened as the most influential factors affecting the distribution of these contaminants. Additionally, both salinity and total phosphate exhibited positive, while both pH and sedimentary particle size registered negative correlation, with one or more contaminants.

Bioremediation of PAEs-contaminated saline soil: The application of a marine bacterial strain isolated from mangrove sediment

Phthalic acid esters (PAEs) are known as the most widely used plasticizer as well as one of the ubiquitously distributed emerging pollutants. Biodegradation and bioremediation via application of PAEs-degrading microbes is promising. In this study, a novel marine microbe, Gordonia hongkongensis RL-LY01, was isolated from mangrove sediment showing high di-(2-ethylhexyl) phthalate (DEHP) degradation capacity. Strain RL-LY01 could degrade a wide range of PAEs and the degradation kinetics of DEHP followed the first-order decay model. Meanwhile, good environmental adaptability, preference to alkaline conditions and good tolerance to salinity and metal ions was shown. Further, metabolic pathway of DEHP in strain RL-LY01 was proposed, with di-ethyl phthalate, phthalic acid, benzoic acid and catechol as intermediates. Additionally, one known mono-alkyl phthalate hydrolase gene (mehpH) was identified. Finally, the excellent performance during bioremediation of artificial DEHP-contaminated saline soil and sediment indicated strain RL-LY01 employs great application potential for the bioremediation of PAE-contaminated environments.

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.