Effects of mangrove plant species on accumulation of heavy metals in sediment in a heavily polluted mangrove swamp in Pearl River Estuary, China

Regional pollution and diet drive organohalogen contaminant accumulation in mangrove-settled spiders (Nephila pilipes)

Mangrove-settled spiders play a crucial role in maintaining the ecological balance of mangrove wetlands, yet organohalogen contaminants (OHCs) pose a significant threat to these species. This study evaluated the dietary composition (including 15 insect species) and OHC accumulation in Nephila pilipes, a dominant spider species, across two mangrove habitats, using data from 80 OHCs and quantitative fatty acid signature analysis (QFASA). Dichlorodiphenyltrichloroethane (DDT) accounted for over 50 % of the total OHCs in both spiders and insects, followed by polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), alternative halogenated flame retardants (AHFRs), and hexachlorocyclohexane (HCHs). Biomagnification and trophic magnification patterns of OHCs were consistent across both mangroves, suggesting that spatial variability did not significantly influence overall biomagnification. Carnivorous insects exhibited lower proportions of tetra- and penta-BDEs compared to phytophagous insects but had significantly higher total OHC concentrations. The presence of carnivorous insects, such as the ditch jewel, in the spider diet was negatively correlated with phytophagous insects, such as the common emigrant and tobacco cutworm, suggesting potential niche exclusivity. Spiders from more polluted mangroves accumulated higher OHC concentrations, with carnivorous insects contributing 64.9 ± 3.90 % and 67.9 ± 5.79 % to the total OHC load in Zhuhai and Shenzhen, respectively. The regional differences in OHC concentrations were primarily attributed to higher background pollution levels in Shenzhen rather than dietary composition alone. This study highlights the influence of regional pollution on OHC accumulation in mangrove spiders and underscores the importance of region-specific dietary assessments for accurate pollutant bioaccumulation evaluations.

Eco-resilience of China's mangrove wetlands: The impact of heavy metal pollution and dynamics

Mangrove forests in China have significantly degraded over the past several decades primarily due to rapid economic growth and land reclamation for aquaculture and infrastructure development. Among various threats, heavy metal pollution, primarily from urbanization, agricultural runoff, and industrial runoff, poses a substantial risk to mangroves in China. It impairs their ecological functions, limiting biodiversity and reducing their natural ability to sequester carbon and detoxify coastal areas. Despite these challenges, the mangrove ecosystem's resilience in China has not been completely compromised. Natural adaptations and phytoremediation mechanisms, such as limiting metal uptake, excreting metal binding proteins, upregulating antioxidants, forming Fe plague, excreting metals through salt glands, and tolerance to specific metal concentrations, help mitigate heavy metal toxicity. However, these adaptive strategies are limited by the extent of pollutants and the speed at which these pollution factors arise. This review highlights a need to shift restoration efforts from expanding mangrove areas to enhancing ecosystem integrity, with a specific focus on reducing heavy metal pollution through phytoremediation. It also examines how heavy metal interactions at the sediment-water interface impact microbial communities and local fauna, contributing to climate change. Addressing these challenges is critical to improving mangrove conservation in China and ensuring the long-term health and resilience of these critical ecosystems for future generations.

How Does Mangrove Restoration or Reforestation Change Trace Metal Pollution in Mangrove Ecosystems? A Review of Current Knowledge

In recent years, mangrove restoration has gained significant attention due to its carbon storage capacity, role as a pollution sink, and ecological and economic benefits. Moreover, the United Nations Sustainable Development Goals' strategies include mangrove restoration. This review investigates the status of mangrove restoration research and the influence of restoration on trace metal accumulation, speciation, and associated risks in mangrove sediments. Our analysis reveals that research on mangrove restoration is increasing globally, with a notable surge in publications after 2017. However, fewer than 25 articles published between 2007 and 2024 address trace metals in restored mangroves, indicating limited focus from researchers on this topic. Research shows that mangrove restoration can quickly alter sediment properties, such as texture, salinity, and pH. As a result, restored sediments tend to accumulate higher organic carbon content than barren areas. Most studies also suggest that trace metal accumulation is higher in restored sites than in non-restored areas. However, metal speciation varies considerably between sites due to local environmental factors. Furthermore, many studies suggest that restoration may increase the risks posed by trace metals to aquatic biota. The challenges of mangrove restoration research include short study timeframes, low success rates, poorly defined targets, small-scale efforts, conflicts with local communities over resources and benefits, insufficient government funding, and a lack of historical data on community health and pollution status.

The inputs of autochthonous organic carbon driven by mangroves reduce metal mobility and bioavailability in intertidal regions

The significance of mangroves in carbon storage is widely acknowledged. However, the potential role of carbon enhancement driven by mangroves in mitigating the risk of metal exposure remains unclear. In this study, a natural mangrove reserve located in Futian was selected to investigate the potential role of autochthonous organic carbon on metal bioavailability. The presence of mangroves seemed to have little effect on the accumulations of Cu(II), Zn(II), Cr(VI/III), Pb(II), and Ni(II) in surface sediments. Metal mobility and bioavailability, however, were found to be directly influenced by the presence of mangroves. Compared with mudflat, mangrove sediments exhibited an obvious in the bioavailability of Cu(II), Zn(II), Cr(VI/III), Pb(II), and Ni(II) by 19-79 %, with the highest reduction occurring in the interior of mangroves dominated by K. obovata. Mangroves also significantly enhanced the accumulation of organic carbon in sediments, regardless of carbon components. Moreover, the results from random forest analysis further showed that autochthonous organic carbon was the most important carbon component that negatively related to metal bioavailability. In summary, this is the first study to provide a linkage between mangrove cover and increased autochthonous organic carbon input, which decreases metal bioavailability. The present data also suggest that mangroves are an efficient natural barrier to alleviate the risk of metal exposure in intertidal regions.

Assessment of heavy metals at mangrove ecosystem, applying multiple approaches using in-situ and remote sensing techniques, Red Sea, Egypt

Mangrove areas are considered the most retention zone for heavy metal pollution as it work as an edge that aggregates land and sea sediments. This study aims to examine if the heavy metals' existence in the mangrove sediment is related to contamination or natural resources. In addition, it gives an interpretation of the origin of these metals along the Egyptian Red Sea coast. Twenty-two samples of mangrove sediments were collected and then, analyzed for metals (Mn, Ni, Cu, Fe, Cd, Ag, and Pb) using inductively coupled plasma mass spectroscopy (ICP-MS). Integration between the in-situ data, contamination indices, and remote sensing and geographical information science (GIS), and multivariate statistical analysis techniques (PCA) were analyzed to assess and clarify the spatial origin of heavy metals in sediment at a regional scale. The average concentration of heavy metals from mangrove sediments were shown to be substantially lower than the referenced value, ranging from moderate to significant except the levels of Ag were very high. The heavy metals concentrations were expected to be naturally origin rather than anthropogenic and that be confirmed by mapping of Red Sea alteration zones spots. These alteration zones are parallel to mangrove sites and rich by several mineralization types including heavy metals that are carried by flooding to the coastline. Remote sensing and GIS techniques successfully contributed to interpreting the pattern of the origin of heavy metals and discharging systems that control the heavy metals concentration along the Red Sea coast.

Assessment of Heavy Metals at Mangrove Ecosystem, Applying Multiple Approaches using in-situ and Remote Sensing Techniques, Red Sea, Egypt.. [DOI: 10.21203/rs.3.rs-2581939/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Heavy metal pollution is one of the threats that impact on Mangrove ecosystem. This study aims to examine if the heavy metals in the mangrove sediment contamination status along the Red Sea coast, and give an interpretation of the origin of these metals. Twenty-two samples were collected and then, analyzed for metals (Mn, Ni, Cu, Fe, Cd, Ag, and Pb) using Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). Integration between the in-situ data, contamination indices, and remote sensing and geographical information science (GIS), and multivariate statistical analysis techniques (PCA) to assess and clarify the spatial origin of heavy metals in sediment at a regional scale. The average concentration is shown to be substantially lower than the referenced value. The heavy metals are naturally origin not anthropogenic origin and, ranging from moderate to significant except the levels of Ag were very high. According to Ag levels, should be exploited economically. Remote sensing and GIS technique successfully contributed to interpreting the pattern of the origin of heavy metals and discharging systems along the red sea coast.

Accumulation of nutrients and potentially toxic elements in plants and fishes in restored mangrove ecosystems in South China

Mangroves are highly dynamic ecosystems that offer important services such as maintaining biodiversity, filtering pollutants, and providing habitats for fishes. We investigated the uptake and accumulation of nutrients and potentially toxic elements in mangrove plants and fish to better understand the role of mangrove restoration in maintaining mangrove biota quality. In mangrove plants, the average bioconcentration factors of nutrients and potentially toxic elements were in the order P > Pb > Mn > Mg > Se > Zn > Hg > Cu > Cd > As > Co > Cr > Ni > Fe > V > Sb, where only P (all plant species) and Pb (Sonneratia apetala Buchanan-Hamilton) had a BCF > 1.0 in mangrove plants. In general, Sonneratia spp. had better performances than Kandelia candel (Linn.) Druce, Aegiceras corniculatum (Linn.) Blanco and Acanthus ilicifolius L. Sp. in terms of nutrient uptake and toxic metal(loid)s accumulation, and the best uptake capacity was found in S. apetala. Fast growth and easy adaptation make S. apetala suitable for a restored mangrove ecosystem, but continual management is needed to prevent its suppression of mangrove species diversity. The concentration of As, Cd, Hg, Cu, Cr and Pb in the mangrove sediment were 30-220% higher than the Chinese National Standard of Marine Sediment Quality Class I limits, suggesting that the sediments were unsuitable for aquaculture and nature reserves. Although a higher toxic metal(loid)s concentration in the sediment was found, the target hazard quotient (THQ) of this toxic metal(loid)s in 5 mangrove habitat fishes was <1.0, except THQ of Pb in Boleophthalmus pectinirostris Linnaeus was 1.17, and THQ of Cr in Bostrychus sinensis Lacépède was 1.12. The low THQ (less than 1.0) of mangrove habitat fishes suggested that the restored mangrove system could alleviate the bioaccumulation of toxic metal(loid)s in mangrove fish.

Potentially toxic elements in invasive fish species Prussian carp (Carassius gibelio) from different freshwater ecosystems and human exposure assessment

Concentrations of Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Sn, and Zn were detected in the muscle and gills of Prussian carp from three different freshwater ecosystems: isolated ponds and the South Morava River in Serbia, and Kopačko Lake in complex wetland ecosystem of the Kopački Rit Nature Reserve in Croatia. The main goals of the present research were to assess the concentrations of potentially toxic elements (PTEs) in the muscle and gills of Prussian carp (Carassius gibelio), to examine whether abiotic factors from three different freshwater ecosystems affect the accumulation of PTEs in fish tissues, and to estimate the human health risk resulting from fish consumption. There were only six concentrations of PTEs in the gill tissue (Cr, Hg, Mn, Pb, Sn, and Zn) that were not significantly different among the different freshwater ecosystems. In the muscles, the differences were much less visible. Kopačko Lake distinguished with the highest values of metal pollution index (MPI) for muscles (0.24) and isolated ponds with the highest values of MPI for gills (0.8). The redundancy analysis (RDA) showed that concentrations of Al, Mn, Zn, Cu, and Fe in the gill tissue were significantly correlated with the environmental variables. In contrast, the RDA based on element concentrations in the fish muscles indicated no significant relationship with the environment. Isolated ponds, with no inflow of freshwater, stand out as the most polluted, followed by Kopačko Lake with occasional floods. Flowing freshwater ecosystem South Morava River can be single out as at least polluted with PTEs. The target hazard quotients (THQ) and hazard index (HI) suggested there were no significant noncarcinogenic health risks. The target carcinogenic risk factor (TR) for As and Pb confirmed there were no cancer risks related to human fish consumption. Since the elevated concentrations of toxic Cd and As in Prussian carp were estimated, an early warning should be assumed, especially for fishing activities in these areas.

Role of phytomelatonin responsive to metal stresses: An omics perspective and future scenario

A pervasive melatonin (N-acetyl-5-methoxytryptamine) reveals a crucial role in stress tolerance and plant development. Melatonin (MT) is a unique molecule with multiple phenotypic expressions and numerous actions within the plants. It has been extensively studied in crop plants under different abiotic stresses such as drought, salinity, heat, cold, and heavy metals. Mainly, MT role is appraised as an antioxidant molecule that deals with oxidative stress by scavenging reactive oxygen species (ROS) and modulating stress related genes. It improves the contents of different antioxidant enzyme activities and thus, regulates the redox hemostasis in crop plants. In this comprehensive review, regulatory effects of melatonin in plants as melatonin biosynthesis, signaling pathway, modulation of stress related genes and physiological role of melatonin under different heavy metal stress have been reviewed in detail. Further, this review has discussed how MT regulates different genes/enzymes to mediate defense responses and overviewed the context of transcriptomics and phenomics followed by the metabolomics pathways in crop plants.

Depth-related dynamics of physicochemical characteristics and heavy metal accumulation in mangrove sediment and plant: Acanthus ilicifolius as a potential phytoextractor

The focus of this study was to determine the depth-wise variability of physicochemical properties (i.e., pH, TOC, TN, and EC), and heavy metals (i.e., Pb, Cu, Zn, As, and Cr) concentration, and the associated biological and ecological risks of the mangrove sediment. The accumulation of metal contents and the phytoremediation and phytoextraction were also investigated in a mangrove species, Acanthus ilicifolius. The mangrove sediment consists of a higher proportion of sand fraction (56.6-74.7%) followed by clay (10-28%) and silt (10.1-15. 7%) fractions. The concentrations (mg/kg) of Pb, Cu, Zn, As, and Cr were ranged from 22.05-34.3, 8.58-22.77, 85.07-114, 5.56-12.91, and 0.98-5.12 in all the sediment layers. The hierarchy of the mean metal concentration in sediment was Zn (102 mg/kg) > Pb (25.6 mg/kg) > Cu (14.8 mg/kg) > As (8.79 mg/kg) > Cr (2.74 mg/kg) respectively. The examined metal concentrations were below the respective average shale values (ASVs). The degree of environmental, ecological, and biological risks was minimal according to various pollution indices like geoaccumulation index (I_geo), contamination factor (CF), and pollution load index (PLI). According to sediment quality guidelines (SQGs), the adverse biological risk effect was not likely to occur. The result of the potential ecological risk index (PERI) demonstrated that the study area was in the low-risk condition as the corresponded RI value < 100. A combined influence of geogenic and anthropogenic factors was identified as the metal sources by multivariate analysis. The study found that the accumulation rate of the metal contents was higher in leaves than that of roots. The mean descending metal concentration values were Zn (107) > Pb (28. 7) > Cu (16.9) > As (11.2) > Cr (4.99) in leaves and Zn (104.32) > Pb (27.02) > Cu (15.29) > As (10.39) > Cr (3.80) in roots. The translocation and bioaccumulation factors of heavy metals suggested that the mangrove plant species, A. ilicifolius can be used for phytoremediation and phytoextraction since the bio-concentration factor and translocation factor > 1. The studied species exhibited the metal tolerance associated with two following strategies, metal exclusion, and metal accumulation. However, excess metal tolerance can impact the surrounding marine environment.

Assessment of water contamination by potentially toxic elements in mangrove lagoons of the Red Sea, Saudi Arabia

Mangrove (Avicennia marina) forests in the Red Sea cost have great concern from environmental, biological, economic, and social points of view. Therefore, assessing water contamination in this ecosystem is worth to be investigated. Consequently, here we aimed to examine the levels of salinity, acidity, and the total content of Fe, Mn, Cu, Zn, Cd, Cr, Ni, and Pb in water samples collected from the upper, middle, and lower part of three mangrove lagoons (i.e., Al-Shuaiba, Yanbu, and Jeddah), Red Sea, Saudi Arabia. The total metal content (µg L^-1) in water samples differed significantly among the studied areas and ranged from 286.2 to 4815.0 for Fe, 86.4-483.0 for Mn, 22.9-468.8 for Cu, 199.2-366.6 for Zn, 44.1-99.8 for Cd, 25.6-80.3 for Cr, 11.6-41.5 for Ni, and from 17.7 to 102.0 for Pb. The mean values of Cu, Zn, Cd, and Pb were higher than the WHO water quality standards for fisheries. Water samples in Yanbu were more contaminated and contained higher concentrations of all metals than Jeddah and Al-Shuaiba, due to the petrochemical industries in this industrial area. Our findings suggest that the high metal content in the water of these mangrove sites, particularly in Yanbu, should be considered due to the high potential environmental and human health risks in these ecosystems. These results may help for demonstrating effective approaches for the management of these lagoons. More studies will be carried out on the sediment and mangrove plants in this ecosystem.

Protecting water birds of wetlands: Using toxicological tests and ecological risk assessment, based on metal/loid (s) of water, sediment and biota samples

Water, sediment and biota (two fish and one shrimp species) samples were collected from rivers, ponds, mudflat and estuaries within the Mai Po Ramsar site in Hong Kong, China, to determine the concentrations of heavy metals/loid (HMs): cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb), zinc (Zn), and arsenic (As). The mutagenicity and toxicity of water and sediment samples were evaluated using Ames test and Microtox® bioassay, respectively. Ecological risk assessments on water birds were also conducted based on HM concentrations in biota, sediment and water samples. In general, results showed that downstream of Shan Pui River and Ng Tung River had relatively higher HM concentrations (e.g. Cu: 0.992-9.49 μg/L; As: 0.342-5.83 μg/L) when compared with estuaries (Cu: 0.400-3.69 μg/L; As: 0.220-0.931 μg/L) and ponds (Cu: 0.0402-2.41 μg/L; As: 0.0501-2.10 μg/L), except Hg and Cd. On the other hand, sediment samples collected from Ng Tung River showed mutagenicity on Salmonella typhimurium tester strain TA100, while the mudflat samples had mutagenicity on tester strain TA98 used in the Ames tests. Microtox® bioassay indicated that only sediment of Ng Tung River showed acute toxicity with a 15 min half maximal effective concentration (EC₅₀) value of 30.5%. Results of ecological risk assessments showed that grey heron (Ardea cinerea), which feeds on fish and shrimps at Shan Pui River and ponds were not at risk. However, common sandpiper (Actitis hypoleucos), which feeds at ponds were subjected to a potential health risk due to its behavior of seeking food from the sediments, especially this bird species has a small body size. This indicates juvenile birds of other species may also be affected. Remediation should be implemented to relief the potential risk of Cu and Pb, to these water birds in the Mai Po Ramsar site.

Copper and zinc differentially affect root glutathione accumulation and phytochelatin synthase gene expression of Rhizophora mucronata seedlings: Implications for mechanisms underlying trace metal tolerance

Mangroves are susceptible to contamination due to their proximity to shores and human activities. Exposure to excessive trace metals can disturb their physiological functions and may eventually lead to death. Rhizophora mucronata is a common species growing in the mangrove forests of Thailand. Previous studies have shown that seedlings of R. mucronata are tolerant of trace metal and that they accumulate a large metal content in their root tissue. However, knowledge of their tolerance mechanisms is still lacking. To elicit the role of metal detoxification and sequestration by phytochelatins (PC) in the roots of R. mucronata seedlings, the impacts of Cu and Zn exposure were assessed on 1) physiological characteristics 2) the concentration of glutathione (GSH), a precursor of PC and 3) the level of the transcripts encoding phytochelatin synthase (PCS), the key enzyme for PC biosynthesis. Seedlings of R. mucronata were exposed to Cu and Zn in a hydroponic experiment (200 mg Cu or Zn/L in 1/4× Hoagland solution containing 8‰ NaCl, single addition). We found that both trace metals were largely accumulated in the roots. Only Cu-treated seedlings showed a decrease in the photosynthetic efficiency, in line with observed toxicity symptoms (i.e. bent stems and slight wilting of leaves). Metal accumulation, however, did not induce oxidative stress in the roots as indicated by similar level of total reactive species and lipid peroxidation across treatments. The GSH content in the roots exposed to Cu was significantly reduced while no change was observed in Zn-exposed roots. Coordinated semi-quantitative PCR and RT-qPCR revealed pcs down-regulation in Cu-treated roots, whereas Zn-treated roots showed a down-regulation on day 1 and a subsequent recovery on day 5. Failure of detoxification and sequestration of excess Cu due to GSH limitation and down-regulation of pcs may lead to the phytotoxic effects observed in Cu-treated plants. Our results suggest that both GSH and PC play an important role in trace metal tolerance in R. mucronata seedlings.

Contamination evaluation and source identification of heavy metals in sediments near outlet of Shekou industrial district of Shenzhen City

Sediment samples in this study were taken from five typical sites near the outlet of Shekou industrial district of Shenzhen City, China. The concentrations of seven elements including Cr, Cu, Cd, Pb, Hg, Zn, and As were determined respectively by atomic absorption spectrometry or atomic fluorescence spectrometry. The pollution degrees of the seven elements were assessed with the contamination factor and potential ecological risk index respectively, and their different sources were identified using multivariate statistical methods. The calculated contamination factors of these elements indicated that the sediments were at least moderately polluted by all the surveyed elements except As. The values of potential ecological risk indexes obtained decreased as the following order: Cd > Hg > Cu > As > Pb > Zn > Cr, and suggested that Cd and Hg were respectively at high and considerable environmental health risks. In addition, multivariate statistical analyses indicated that Cd, Hg, Cu, and Zn were most likely from the waste of electroplating, metal, and battery industries at Shekou industrial district, while Pb and As originated from both natural processes and anthropogenic activities along the bank of Pear River such as coal transportation and combustion, glass manufacturing, and painting, and Cr came mostly from Cr-related industries especially leather tanning within Shenzhen City. This study provided useful reference information about heavy metal contamination in the sediments in the estuarine and coastal areas with rapid urbanization and industrialization, and should be very helpful for the local governments to make relevant policies and strategies of heavy metal contamination control and management in developing countries.

Spatial variation of soil properties impacted by aquaculture effluent in a small-scale mangrove

Small-scale mangroves serve ecological functions similar to large-scale mangroves regarding biological conservation, environmental purification, and supporting biogeochemical processes. The rising aquaculture neighboring mangroves results in their serving as an important sink for massive nutrients and pollutants from aquaculture effluent. We assessed how long-term aquaculture effluent discharge influenced the soil properties of a mangrove-tidal flat continuum using field survey and geostatistics. Common soil physical-chemical properties presented significant spatial variability. Continued aquaculture effluent discharge caused a significant cumulation of soil total organic carbon (SOC) (64.13 g·kg^-1), total nitrogen (TN) (2.44 g·kg^-1) and total phosphorus (TP) (1.12 g·kg^-1) in the mangrove soil, which were as 2-3 times as those on the mudflat. Most of the soil properties changed significantly with increasing distance from the effluent outlet along a tidal channel, and the maximum concentrations of SOC, TN and TP all occurred at 50 m away from the outlet. The results of principal component analysis indicated that aquaculture effluent significantly affected the spatial pattern of soil properties along the mangrove-tidal flat continuum. Continued aquaculture effluent input rendered extensive accumulation of SOC, TN and TP in the mangroves. The spatial heterogeneity of mangrove is the key driver to process the nutrient input spatially differently.

Spatial distribution and potential ecological risk assessment of some trace elements in sediments and grey mangrove (Avicennia marina) along the Arabian Gulf coast, Saudi Arabia

To assess trace element concentrations (Zn, Cu, Pb, Cr, Cd and Ni) in the mangrove swamps along the Saudi coast of the Arabian Gulf, thirteen samples of surface sediment and leaves of grey mangrove, Avicennia marina were collected and analyzed. The detected trace element contents (μg g-1) in surface sediments were in the following descending order according to their mean values; Cr (49.18) > Zn (48.48) > Cu (43.06) > Pb (26.61) > Ni (22.88) > Cd (3.21). The results showed that the average concentrations of Cd and Pb exceeded their world average concentration of shale. The geo-accumulation, potential ecological risk and toxicity response indices demonstrated that trace elements have posed a considerable ecological risk, especially Cd. The inter-relationships between physico-chemical characters and trace elements suggests that grained particles of mud represent a noteworthy character in the distribution of trace elements compared to organic materials. Moreover, the results revealed that Zn was clearly bioaccumulated in leaf tissues A. marina. Dredging, landfilling, sewage effluents and oil pollution can be the paramount sources of pollution in the area under investigation.