Heavy metal and organic contaminants in mangrove ecosystems of China: a review

The influence of salinity on sodium lauryl sulfate toxicity in Mytilus galloprovincialis

The influence of salinity on the effects of sodium lauryl sulfate (SLS) was evaluated using the Mediterranean mussel Mytilus galloprovincialis, exposed for 28 days to SLS (control-0.0 and 4.0 mg/L) under three salinity levels (Control-30, 25 and 35). The effects were monitored using biomarkers related to metabolism and energy reserves, defence mechanisms (antioxidant and biotransformation enzymes) and cellular damage. The results revealed that non-contaminated mussels tended to maintain their metabolic capacity regardless of salinity, without activation of antioxidant defence strategies. On the contrary, although contaminated mussels presented decreased metabolic capacity at salinities 25 and 35, they were able to activate their antioxidant mechanisms, preventing cellular damage. Overall, the present findings indicate that SLS, especially under stressful salinity levels, might potentially jeopardize population survival and reproduction success since reduced metabolism and alterations on mussels' antioxidant mechanisms will impair their biochemical and, consequently, physiological performance.

Effects of heavy metals and organic matter fractions on the fungal communities in mangrove sediments from Techeng Isle, South China

Heavy metal pollution has become a serious environmental problem in mangrove ecosystems and has attracted more attention. Most of previous studies have mainly focused on the effects of heavy metals on bacterial communities in mangrove sediments. This study was the first to investigate the effects of heavy metals (e.g., As, Co, Cr, Cu, Mn, Ni, Pb, V and Zn) and organic matter fractions (including total organic carbon (TOC), total nitrogen (TN), and total sulfur (TS)) on the fungal communities in mangrove sediments from Techeng Isle, South China. The results of this study indicated that the average contents of Mn, Pb and V of 8.30-161.80 μg/g presented relatively higher pollution levels, while the concentrations of Zn, Cr, Cu and Ni of 0.80-21.93 μg/g were lower than those recorded in other mangrove ecosystems. Furthermore, the sediment fungal community structures responded differently to the nine heavy metals and three organic matter fractions. Heavy metals Cr, Pb and V displayed significant positive correlations with Eutypella (P < 0.05), whereas significant negative correlations with Cystobasidium, Lulworthia, Cladosporium, Lulwoana and Cephalotheca (P < 0.05). In addition, the effects of heavy metals and TS on many fungal genera were opposite to those of TOC and TN. Fungal genera that decreased with high TOC and TN contents may be increased with high heavy metal contents and TS, and vice versa, and the genera that increased with high TOC and TN contents may be decreased with high heavy metals and TS. Our results suggested that many heavy metals, such as Cr, Pb and V, were sensitive to several fungal genera in mangrove sediments, and heavy metals together with organic matter fractions may participate and shape the fungal communities in mangrove sediments.

From Mangrove to Fork: Metal Presence in the Guayas Estuary (Ecuador) and Commercial Mangrove Crabs

Mangrove wetlands provide essential ecosystem services such as coastal protection and fisheries. Metal pollution due to industrial and agricultural activities represents an issue of growing concern for the Guayas River Basin and related mangroves in Ecuador. Fisheries and the related human consumption of mangrove crabs are in need of scientific support. In order to protect human health and aid river management, we analyzed several elements in the Guayas Estuary. Zn, Cu, Ni, Cr, As, Pb, Cd, and Hg accumulation were assessed in different compartments of the commercial red mangrove crab Ucides occidentalis (hepatopancreas, carapax, and white meat) and the environment (sediment, leaves, and water), sampled at fifteen sites over five stations. Consistent spatial distribution of metals in the Guayas estuary was found. Nickel levels in the sediment warn for ecological caution. The presence of As in the crabs generated potential concerns on the consumers' health, and a maximum intake of eight crabs per month for adults is advised. The research outcomes are of global importance for at least nine Sustainable Development Goals (SDGs). The results presented can support raising awareness about the ongoing contamination of food and their related ecosystems and the corresponding consequences for environmental and human health worldwide.

Storage and recycling of major and trace element in mangroves

The role of mangroves in sequestering metal and nutrients in sediment has been described in the past, but knowledge gaps still exist on storage capacity and recycling fluxes of elements in plant biomass, notably concerning their magnitude in root uptake and loss by litterfall. This study addresses the storage and transport pathways of 16 elements, classified as macro-nutrients (Ca, Mg, Na, K), micro-nutrients (Fe, Mn, Ni, Co, Cu, Cr, Zn, Mo), and potential toxicants (Al, Cd, Sn, Pb) in the world's largest mangroves, the Sundarbans. Elemental concentrations in plant organs were generally lower than in the sediment. The stock of macro and micro-nutrients in plant biomass varied from 60 to 2717 and 0.003 to 37.7 Mg ha^-1 respectively, with highest values observed for Na and lowest for Cd. The Avicennia species exhibited the maximal accumulation of all elements. Translocation of major elements to different plant organs increased with increasing their concentrations in the sediment. Elemental loss via litterfall indicated that Sundarbans mangrove could act as a source, particularly of Mn, to the Bay of Bengal. Moreover, belowground uptake of the 16 elements showed 2-3 fold higher fluxes than their loss via litterfall. There was a significant retention of some trace elements (notably Mo, Cd, and Sn) in plant biomass, which might allow one to use these mangroves for phytoremediation and restoration purposes. We conclude that mangroves efficiently store and remobilize major and trace elements from the sediments by root uptake and recycle back to sediment surface via litterfall.

The Influence of Temperature Increase on the Toxicity of Mercury Remediated Seawater Using the Nanomaterial Graphene Oxide on the Mussel Mytilus galloprovincialis

Mercury (Hg) has been increasing in waters, sediments, soils and air, as a result of natural events and anthropogenic activities. In aquatic environments, especially marine systems (estuaries and lagoons), Hg is easily bioavailable and accumulated by aquatic wildlife, namely bivalves, due to their lifestyle characteristics (sedentary and filter-feeding behavior). In recent years, different approaches have been developed with the objective of removing metal(loid)s from the water, including the employment of nanomaterials. However, coastal systems and marine organisms are not exclusively challenged by pollutants but also by climate changes such as progressive temperature increment. Therefore, the present study aimed to (i) evaluate the toxicity of remediated seawater, previously contaminated by Hg (50 mg/L) and decontaminated by the use of graphene-based nanomaterials (graphene oxide (GO) functionalized with polyethyleneimine, 10 mg/L), towards the mussel Mytilus galloprovincialis; (ii) assess the influence of temperature on the toxicity of decontaminated seawater. For this, alterations observed in mussels’ metabolic capacity, oxidative and neurotoxic status, as well as histopathological injuries in gills and digestive tubules were measured. This study demonstrated that mussels exposed to Hg contaminated seawater presented higher impacts than organisms under remediated seawater. When comparing the impacts at 21 °C (present study) and 17 °C (previously published data), organisms exposed to remediated seawater at a higher temperature presented higher injuries than organisms at 17 °C. These results indicate that predicted warming conditions may negatively affect effective remediation processes, with the increasing of temperature being responsible for changes in organisms’ sensitivity to pollutants or increasing pollutants toxicity.

Uptake and concentration of heavy metals in dominant mangrove species from Hainan Island, South China

By investigating three dominant mangrove species, namely Aegiceras corniculatum, Kandelia candel, Ceriops tagal and their rhizosediment in Mangrove wetlands in Hainan Island, this research analyzed absorption, concentration and distribution of heavy metals (Cr, Cu, Zn, As, Cd and Pb) in mangroves. The results found that the concentration of specific heavy metal differs in the different mangrove organs (leaf, stem and root). The content of heavy metals concentrated greatly in roots, but less in leaves and stems. The study also revealed that concentration capacity was weak in all three mangrove species (BCF0.02-0.91), with their organ ranking BCF_root > BCF_stem > BCF_leaf. Among three mangrove species, the transfer factors of leaves and stems in Ceriops tagal were highest, indicating a great distribution capability for heavy metals, followed by Kandelia candel. Transfer factors in Aegiceras corniculatum were the weakest. This ranking was opposite to bioconcentration factors of roots. This study can further reflect bioavailability of heavy metals in sediments, which provides scientific evidence on ecosystem protection and management in mangrove wetlands.

Heavy metal pollution increases CH4 and decreases CO2 emissions due to soil microbial changes in a mangrove wetland: Microcosm experiment and field examination

Mangrove plays an important role in modulating global warming through substantial blue carbon storage relative to their greenhouse gas emission potential. The presence of heavy metals in mangrove wetlands can influence soil microbial communities with implications for decomposition of soil organic matter and emission of greenhouse gases. In this study, field monitoring and a microcosm experiment were conducted to examine the impacts of heavy metal pollution on soil microbial communities and greenhouse gas fluxes. The results show that heavy metal pollution decreased the richness and diversity of the overall soil microbial functional groups (heterotrophs and lithotrophs); however, it did not inhibit the activities of the methanogenic communities, possibly due to their stronger tolerance to heavy metal toxicity compared to the broader soil microbial communities. Consequently, the presence of heavy metals in the mangrove soils significantly increased the emission of CH₄ while the emission of CO₂ as a proxy of soil microbial respiration was decreased. The soil organic carbon content could also buffer the effect of heavy metal pollution and influence CO₂ emissions due to reduced toxicity to microbes. The findings have implications for understanding the complication of greenhouse gas emissions by heavy metal pollution in mangrove wetlands.

Halogenated flame retardants in surface sediments from fourteen estuaries, South China

A total of seventy surface sediments were collected from fourteen estuaries of South China to investigate the distribution of polybrominated diphenyl ethers (PBDEs), decabromodiphenyl ethane (DBDPE), 1,2-bis (2,4,6-tribromophenoxy) ethane (BTBPE) and dechlorane plus (DP). The concentrations of Σ₁₆PBDEs, DBDPE, BTBPE and DP in estuarine sediments ranged from 0.39 to 81.2, 0.18 to 49.9, not detected to 0.62, and 0.025 to 1.66 ng/g dry weight, respectively. Significant differences for levels of Σ₁₆PBDEs, DBDPE, BTBPE and DP were found among the sediments from fourteen estuaries. Sediments from the Pearl River Estuary had the highest concentrations of Σ₁₆PBDEs, DBDPE and DP. PBDEs and DBDPE were the main halogenated flame retardants in estuarine sediments. BDE 209 was predominant congener of PBDEs with an average contribution of 88.1% to the total PBDEs. 32.9% sediment samples from South China had f_anti values lower than 0.65, suggesting that stereoselective enrichment of syn-DP occurred in estuarine sediments.

Heavy metal pollution and ecological risk assessment in the Maowei sea mangrove, China

The level and ecological impact of heavy metal pollution in the Maowei Sea mangrove are poorly understood. This work first investigated the distribution and ecological risk of Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn in Maowei Sea mangrove sediments. The results showed that heavy metals were mainly concentrated in the top 10 cm of mangrove stands, declined up to 20 cm deep, and were constant afterwards. Exceptionally, Mn concentration increased significantly with depth in the mudflat. Multiple environmental risk indices indicated that the investigated area was broadly contaminated by heavy metals and that Cd was the dominant contributor to potential ecological risks. However, the biological toxicity posed by these metals was negligible. Multivariate analyses implied that Cd, Co, Cr, Cu, Ni, Pb, and Zn originated mainly from anthropogenic sources, whereas Mn was primarily from natural processes. These findings could provide insightful information for future management of this mangrove.

An integrated assessment of land-use change impact, seasonal variation of pollution indices and human health risk of selected toxic elements in sediments of River Atuwara, Nigeria

River sediments contain environmental fingerprints that provide useful ecological information. However, the geochemistry of River Atuwara sediments has received less attention over the years. One hundred and twenty-six sediments from 21 locations were collected over a two-season period from River Atuwara, and a detailed investigation of the land use and land cover (LULC) change between 1990 and 2019, analysis of selected toxic and potentially toxic metal(oid)s (TPTM) (Cu, As, Cd, Pb, Ni, Cr, Zn, Fe, Co and Al) using ICP-OES, pollution index assessment, potential source identification (using center log-transformation approach), potential ecological, and human health risk assessment were conducted. The results of the LULC change revealed that the built-up area increased by 95.58 km², at an average rate of 3.186 km²/year over the past 30 years. The mean concentration of metal(oid)s increased in the order of Cd < As < Cr < Pb < Co < Ni < Cu < Zn < Fe < Al, and Cd < As < Cr < Co < Pb < Ni < Cu < Zn < Fe < Al during the dry and wet seasons, respectively. Meanwhile, the statistical analysis of the data spectrum inferred possible contamination from lithological and anthropogenic sources. According to the pollution load index, 90.48% of the sediment samples are polluted by the metal(oid)s. Potential ecological risk assessment identified Ni, As, and Cd as problematic to the ecological community of River Atuwara. Regarding the metal-specific hazard quotient via ingestion route, the risks are in order of Co ≫ As ≫ Pb > Cr > Cd > Al > Ni > Cu > Zn > Fe for both seasons and the carcinogenic risk for children via ingestion route presented a value higher than the safe limits for As, Cd, Cr, and Ni during both seasons. This outcome highlights the need for prompt action towards the restoration of environmental quality for communities surrounding River Atuwara.

An overview on heavy metal resistant microorganisms for simultaneous treatment of multiple chemical pollutants at co-contaminated sites, and their multipurpose application

Anthropogenic imbalance of chemical pollutants in environment raises serious threat to all life forms. Contaminated sites often possess multiple heavy metals and other types of pollutants. Elimination of chemical pollutants at co-contaminated sites is imperative for the safe ecosystem functions, and simultaneous removal approach is an attractive scheme for their remediation. Different conventional techniques have been applied as concomitant treatment solution but fall short at various parameters. In parallel, use of microorganisms offers an innovative, cost effective and ecofriendly approach for simultaneous treatment of various chemical pollutants. However, microbiostasis due to harmful effects of heavy metals or other contaminants is a serious bottleneck facing remediation practices in co-contaminated sites. But certain microorganisms have unique mechanisms to resist heavy metals, and can act on different noxious wastes. Considering this significant, my review provides information on different heavy metal resistant microorganisms for bioremediation of different chemical pollutants, and other assistance. In this favour, the integrated approach of simultaneous treatment of multiple heavy metals and other environmental contaminants using different heavy metal resistant microorganisms is summarized. Further, the discussion also intends toward the use of heavy metal resistant microorganisms associated with industrial and environmental applications, and healthcare. PREFACE: Simultaneous treatment of multiple chemical pollutants using microorganisms is relatively a new approach. Therefore, this subject was not well received for review before. Also, multipurpose application of heavy metal microorganisms has certainly not considered for review. In this regard, this review attempts to gather information on recent progress on studies on different heavy metal resistant microorganisms for their potential of treatment of co-contaminated sites, and multipurpose application.

Evaluation of ecosystem health and potential human health hazards in the Hangzhou Bay and Qiantang Estuary region through multiple assessment approaches

Anthropogenic pollution has become a major issue governing ecosystem and human health risks. The Hangzhou Bay and Qiantang Estuary region are facing unusual perturbation due to rapid development along the embayment in recent decades. This study evaluated the organic and inorganic pollutants in water, sediment, and from the muscles of higher trophic organisms (fish, crustacean, shellfish) during four different seasons (in 2018-2019) along the Qiantang Estuary and Hangzhou Bay region to assess the ecosystem health and potential hazard status. Dissolved inorganic phosphate and nitrogen were the major pollutants in this area, which led to severe eutrophication throughout the study period. Eutrophication signals coincided well with the phytoplankton abundance, which revels the control of nutrient enrichment on the spatio-temporal distribution of phytoplankton. Food availability, along with salinity and temperature, drives the zooplankton population distribution. Heavy metals were not the issue of water quality as their concentrations meet the national and international baseline standards. However, in the sediments, Copper (Cu) and Arsenic (As) concentrations were higher than the baseline value. Towards the northwestern part of the Qiantang Estuary, the overall potential risk index of sediment with higher Cadmium (Cd) and Mercury (Hg) depicted delicate condition with moderate risk for the sediment contamination. The As concentration in fishes was close to the baseline standards limit irrespective of low As values within water and sediments. The higher concentrations of Zinc (Zn) and As in shellfish muscles, whereas other metals were within the limit of baseline standard in all the organisms. However, the hazard analysis (Targeted hazard quotient, THQ) values for the seafood consumption to human health indicates the potentially threatening consequences of shellfish and crustacean consumption on human health.

Distribution and risk of mercury in the sediments of mangroves along South China Coast

The importance of mangrove was widely reported. However, the potential risks of pollutants (e.g., Hg) accumulated in the mangroves are often ignored. Thus, the present study aimed to explore the distribution and risk of mercury (Hg) in the sediments of mangroves along South China Coast. Results showed that concentrations of total Hg ranged from 0.0815 to 0.6377 mg/kg, with an arithmetic mean value of 0.2503 mg/kg. The contamination index (P_i) showed mild pollution toxicity risks in NS, slight toxicity risks in DZG, QZ, SY, ND, GQ, TLG, and free pollutions in BMW, SJ, ZJK and BLHK. NS, DZG and SY scored the highest values of I_geo among the eleven mangrove regions studied, indicating moderate to heavy pollution inputs in these regions. As for the distribution of Hg in the sediments along tidal gradient, concentrations of Hg in the sediments sharply increased from seaward mudflat to landward mangrove, corresponding with the increases of TOC. In summary, the present data indicated that mangrove ecosystem is efficient in Hg reservoir. However, the potential ecological risks of Hg, especially in some mangrove regions easily affected by human activities, should be noted.

Neutral monosaccharides and their relationship to metal contamination in mangrove sediments

Mangrove sediments act as an important natural sink and a secondary source for trace metals. The main objective of this study was to investigate metal contamination and its relationship to mangrove-derived carbohydrates in mangrove sediments. Sixteen metals (Be, V, Cr, Co, Ni, Cu, Zn, Ga, As, Sr, Cd, Sn, Sb, Ba, Tl, and Pb）were analyzed in the surface sediments from four sites at different latitudes on the southeast coastline of China. The sedimentary organic matter was characterized by Rock-Eval pyrolysis, and the neutral sugars were examined by gas chromatograph mass spectrometry. Our results from the enrichment factors indicated that the mangrove sediments were no enriched by Ga, Sr, and Ba, minor enriched by Be, V, Cr, Co, Ni, Cu, Zn, As, Sn, Sb, Tl, and Pb, and moderate enriched by Cd. Litterfall was a major source of organic matter in the mangrove sediments, and the neutral sugars were mainly derived from this litterfall. Significant correlations were detected between the total organic carbon, pyrolytic parameters, neutral sugars, and enrichment factors of V, Cr, Co, Ni, Zn, and Cd, suggesting the input of neutral carbohydrates played an important role in enhancing the metal accumulation in the mangrove sediments. The mangrove litterfall itself was a major source of metals for the sediments, and the mangrove-derived organic matter enhanced the sediment's metal accumulation.

Effects of phenolic acids on free radical scavenging and heavy metal bioavailability in kandelia obovata under cadmium and zinc stress

Current mechanism studies in plant heavy metal tolerance do not consider the effects of different phenolic acids on the bioavailability of heavy metals and the comparison with antioxidant enzyme system in the hydroxyl radical scavenging capacity. In present study, by a set of pot culture experiments with adding cadmium (Cd) and zinc (Zn) to the sediments, the effects of different phenolic acids on the toxicity of Cd and Zn in Kandelia obovata and the dominant role in scavenging hydroxyl radicals were evaluated. The results showed that 100 mg kg^-1 Zn treatment promoted the growth of plant under high concentrations of Cd and Zn stress. Under the stress of Cd and Zn, the phenolic acids were mainly metabolized by phenylpropanoid and flavonoid pathways, supplemented by shikimate and monolignol pathways in K. obovata. Eleven phenolic acids with different abilities of scavenging free radicals were detected in the plant, including pyrogallic acid (Gal), coumaric acid (Cou), protocatechuic acid (Pro), chlorogenic acid (Chl), 4-hydroxy benzoic acid (Hyd), caffeic acid (Caf), vanillic acid (Van), ferulic acid (Fer), benzoic acid (Ben), and salicylic acid (Sal). By adding phenolic acids to the sediments, chlorogenic acid (Chl), pyrogallic acid (Gal), cinnamic acid (Cin), and coumaric acid (Cou) behave as more reactive in changing Cd or Zn into residual fractions than the others, and chlorogenic acid (Chl), pyrogallic acid (Gal), ferulic acid (Fer) and caffeic acid (Caf) have higher ability of scavenging hydroxyl radicals than the others. In summary, K. obovata tends to synthesize phenolic acids with strong scavenging ability of free radicals and changing the bioavailability of Cd and Zn under high concentration of Cd and Zn stress. Phenolic acids played a crucial role in the mitigative effect of heavy metal stress via scavenging free radicals and involving in the process of Cd and Zn uptake and tolerance. The results will provide important theoretical basis and method guidance for mangrove wetland conservation.

Organochlorine Pesticides in Sediment of Zhang River Estuary Mangrove National Natural Reserve: The Implication of Its Source Change in China’s Mangroves

Seventeen organochlorine pesticides (OCPs) were examined in surface sediments from Zhang River Estuary Mangrove National Natural Reserve, which is situated in the Fujian province in southeast China. The range of ∑OCPs concentration was 0.29–25.41 ng/g dry weight (average 4.53 ng/g), ∑HCHs was 0.008–0.906 ng/g dry weight (average 0.240 ng/g), and ∑DDTs was ND–4.743 (average 0.664 ng/g). The concentrations of the HCH isomers were observed in the following decreasing order: α-HCH > β-HCH > δ-HCH > γ-HCH, and that of the DDT isomers were as in the following order: p,p’-DDT > p,p’-DDE > p,p’-DDD. According to the analysis of the isomer ratios, γ-HCH (lindane) and endosulfan were rarely used recently around this mangrove forest. Instead, the ratios of (DDD+DDE)/DDT showed that DDTs were still illegally used. Compared with other mangroves in China, the residue level and ecological risk of the OCPs in surface sediment from ZREMNNR are both at a low level. Based on stepwise regression analysis, current fruit planting, as well as mariculture in developed areas and vegetable planting in developing areas, had a positive relation with DDT residues in mangrove sediment in China. Oppositely, HCH residues in mangrove sediment were derived from historical consumption, and generally the higher levels occurred in the developed areas. Through this study, we help to close the knowledge gap of OCPs in China’s mangroves and provide a possible management implication for sustainable development in the future.

Interactions of soil metals with glomalin-related soil protein as soil pollution bioindicators in mangrove wetland ecosystems

Through binding of mineral particles and elements, glomalin-related soil protein (GRSP) plays a critical role in sustaining terrestrial soil quality and contributes to the fate of elements from terrestrial to aquatic ecosystems. There is little knowledge, however, of the metal sequestration patterns of GRSP in both terrestrial and aquatic soils, and this limits progress in understanding how environmental conditions influence GRSP characteristics. Here, we employed microcosm experiments to determine the molecular composition of original GRSP derived from three arbuscular mycorrhizal fungi, Glomus intraradices, Glomus versiforme and Acaulospora laevis. To gain insight into the metal sequestration patterns of environmental GRSP, we investigated major subtropical and tropical mangrove wetlands in southern China. GRSP-bound metals were significantly and positively correlated with total metals, and the metal binding contributed to the metal sequestration of mangrove soils. Fourier-transform infrared spectroscopy results showed that original- and environmental GRSP fractions contained hydroxyl, carboxyl, amide and carbonyl functional groups, which enhanced metal binding. Environmental process had no effect on the type of functional groups of the GRSP, while it significantly changed the relative content of the functional groups. The infrared fingerprint analyses of original- and environmental GRSP revealed field-specific, however, no taxon-specific characteristics of GRSP. Biostatistical analysis of the GRSP molecular composition further revealed that the soil pollution sources regulated the ratios of functional group contents associated with hydrocarbons, proteins, polysaccharides and nucleic acids. By GRSP infrared fingerprints coupled with multivariate analyses, we developed a technique for source identification of heavy metal pollution, giving more reliable evidence about contributing sources.

Terrestrial-derived soil protein in coastal water: metal sequestration mechanism and ecological function

Terrestrial fungi, especially arbuscular mycorrhizal (AM) fungi, enhance heavy metal sequestration and promote ecosystem restoration. However, their ecological functions were historically overlooked in discussions regarding water quality. As an AM fungi-derived stable soil protein fraction, glomalin-related soil protein (GRSP) may provide insights into the ecological functions of AM fungi associated with water quality in coastal ecosystems. Here, we first assessed the metal-loading dynamics and ecological functions of GRSP transported into aquatic ecosystems, characterized the composition characteristics, and revealed the mechanisms underlying Cu and Cd sequestration. Combining in situ sampling and in vitro cultures, we found that the composition characteristics of GRSP were significantly affected by the element and mineral composition of sediments. In situ, GRSP-bound Cu and Cd contributed 18.91-22.03% of the total Cu and 2.27-6.37% of the total Cd. Functional group ligands and ion exchange were the principal mechanisms of Cu binding by GRSP, while Cd binding was dominated by functional group ligands. During the in vitro experiment, GRSP sequestered large amounts of Cu and Cd and formed stable complexes, while further dialysis only released 25.74 ± 3.85% and 33.53 ± 3.62% of GRSP-bound Cu and Cd, respectively.

Microplastic accumulation in fish from Zhanjiang mangrove wetland, South China

Microplastics (MPs) are widespread in marine and estuarine environments, but the contamination of MPs in mangrove wetlands is relatively unknown. Here, we quantify the presence of MPs in fish collected from Zhanjiang mangrove wetland, the largest mangrove in South China, which provide baseline data on MPs accumulation in fish in mangrove environment as the first evidence in China. MPs were found in 30 out of 32 fish species at an average abundance of 2.83 ± 1.84 items individual^-1, ranged from 0.6 to 8.0 items individual^-1 in each species. MPs were detected in gills, stomach and intestine, and not found in muscles and livers. Positive relationship was found between MPs abundance and body length or weight of mangrove fish. The dominant polymers identified by micro-FTIR were polyethylene, polyethylene terephthalate, polypropylene and cellophane. MPs consisted primarily of fibers and with the prominent size range of 0.02-1 mm. The body sizes, living habitats and feeding habits of fish are important factors affecting MPs accumulation in different fish species. This study revealed the wide presences of MPs in fish species within a mangrove wetland.

Systematic Assessment of Health Risk from Metals in Surface Sediment of the Xiangjiang River, China

The common empirical screening method is limited to a preliminary screen target from vast elements for human health risk assessments. Here, an element screening procedure was developed for assessing the human health risk of the elements in the sediment of the Xiangjiang River. Ninety-six surface sediment samples from eight sampling stations were collected and 27 elements of each sample were investigated. Thirteen of the 27 elements were screened for human health risk assessments through the three-run selections by calculating anthropogenic factors, building element maps, and the removal of unnecessary elements. Pb posed the greatest health risk and exhibited a potential noncarcinogenic risk for adults at the stations S4 and S5, although no visible noncarcinogenic and carcinogenic risk for adults and children in the Xiangjiang River. Our study also suggested that the chalcophile elements were associated with greater health risk, compared to the lithophile and siderophile ones.

Oxidative stress, metabolic and histopathological alterations in mussels exposed to remediated seawater by GO-PEI after contamination with mercury

The modern technology brought new engineering materials (e.g. nanostructured materials) with advantageous characteristics such as a high capacity to decontaminate water from pollutants (for example metal(loid)s). Among those innovative materials the synthesis of nanostructured materials (NSMs) based on graphene as graphene oxide (GO) functionalized with polyethyleneimine (GO-PEI) had a great success due to their metal removal capacity from water. However, research dedicated to environmental risks related to the application of these materials is still non-existent. To evaluate the impacts of such potential stressors, benthic species can be a good model as they are affected by several environmental constraints. Particularly, the mussel Mytilus galloprovincialis has been identified by several authors as a bioindicator that responds quickly to environmental disturbances, with a wide spatial distribution and economic relevance. Thus, the present study aimed to evaluate the impacts caused in M. galloprovincialis by seawater previously contaminated by Hg and decontaminated using GO-PEI. For this, histopathological and biochemical alterations were examined. This study demonstrated that mussels exposed to the contaminant (Hg), the decontaminant (GO-PEI) and the combination of both (Hg + GO-PEI) presented an increment of histopathological, oxidative stress and metabolic alterations if compared to organisms under remediated seawater and control conditions The present findings highlight the possibility to remediate seawater with nanoparticles for environmental safety purposes.

Trace metals in aquatic environments of a mangrove ecosystem in Nansha, Guangzhou, South China: pollution status, sources, and ecological risk assessment

Mangrove forests are widely located along coastlines. They have been identified to be inimitable and dynamic ecosystems. This study investigated the trace metals in mangrove water and surface sediments of Nansha, Guangzhou, China. Zn (148.42 ± 247.47 μg L^-1) was the most abundant metal in waters, followed by As (82.34 ± 118.95 μg L^-1), Pb (22.96 ± 120.50 μg L^-1), and Ni (19.42 ± 47.84 μg L^-1). In sediments, the most abundant metal was Fe (27.04 ± 1.91 g kg^-1), followed by Mn (1049.04 ± 364.11 mg kg^-1), Zn (566.33 ± 244.37 mg kg^-1), and Cr (106.9 ± 28.51 mg kg^-1). Higher contents of trace metals were detected in vicinity areas of the river mouth. The results of pollution indexes, including contamination factor, enrichment factor, and geo-accumulation index, indicated the pollution of Cd, Cu, Pb, and Zn in sediments. The Spearman correlation and cluster analysis were used to evaluate the metal sources. In water, the significant correlations among Zn and water chemical parameters (Na, Mg, K, Ca, conductivity, pH, and Cl) might indicate the natural source of Zn from the seawater. Water sampling sites in estuaries and coastal areas were clustered separately, which might indicate the influences of upstream water and the seawater, respectively. In sediments, the significant relationships among Cd, Pb, and Zn concentrations were likely to imply the emissions from industries and exploitation of the Pb-Zn mine. The occurrence of Cr and Cu in sediments can be attributed to the spills of lubricants or oil. Cd in sediments could cause serious ecological risk.

Contamination and ecological risk of polybrominated diphenyl ethers (PBDEs) in surface sediments of mangrove wetlands: A nationwide study in China

Mangroves act as sinks for terrigenous pollutants to alleviate their influence on offshore marine ecosystem. The nationwide study of PBDEs contamination in mangrove wetlands of China has not been explored, and their risk for human health lack quantitative analysis. In this study, sediment samples were collected in six mangrove wetlands along coastal area of South China to evaluate the levels, congener distributions and ecological risks of eight PBDEs, including BDE-28, -47, -99, -100, -153, -154, -183, and -209. Levels of ∑PBDEs (the sum of seven PBDEs except BDE-209) and BDE-209 were 0.13-2.18 ng g^-1 and 1.44-120.28 ng g^-1, respectively. In particular, mean level of BDE-209 was highest in Futian, followed by Yunxiao, Fangchenggang, Zhanjiang, Dongzhaigang, and Dongfang. As dominant PBDE congener, BDE-209 accounted for 63.6%-99.1% of the total PBDEs, suggesting the major sources of commercial deca-BDE mixtures. Among seven PBDE congeners except BDE-209, slightly different percentages of PBDE congeners were detected, with BDE-154, -47, and -100 being predominant congeners. Positive relationship was observed for total organic matter (TOM) with BDE-209, with no such relationships found for particle size compositions (clay, silt and sand). As for sediment-dwelling organism, the ecological risks from tri-, tera-, and hexa-BDE congeners could be negligible, and those from penta- and deca-BDE congeners were low or moderate, indicating major ecological risk drivers of penta- and deca-BDE congeners in mangrove wetlands in China. The ecological risk of PBDEs in mangrove sediments for human health was thought to be consumption of fish which would bioaccumulate PBDEs from the contaminated sediment. As for human health, the levels of non-cancer risks of PBDEs were all lower than 1, and the cancer risk was far less than the threshold level (10^-6), demonstrating low risk for human health.

Bioaccumulation of Total Hydrocarbon and Heavy Metals in Body Parts of the West African Red Mangrove Crab (<i>Goniopsis pelii</i>) in the Niger Delta, Nigeria

This study is based on bioaccumulation of total hydrocarbon (THC) and heavy metals in body parts of the West African red mangrove crab (G. pelii), which inhabit polluted mangrove forests. Thirty crabs were captured in October, 2018 and sorted into male and female. Their lengths and widths were measured, and body parts dismembered and oven-dried at 70 ͦ C for 48 hours. Physicochemical analysis for Cadmium (Cd), Zinc (Zn), Lead (Pb) and THC was measured by spectrophotometric method using HACH DR 890 colorimeter (wavelength 420 nm) and microwave accelerated reaction system (MARS Xpress, North Carolina) respectively. There was no significant difference (P > 0.05) in THC and heavy metals in the body parts of crabs.  However, Zinc was highest in claw (993.4±91.3 mg/l) and body tissues (32.5±1.9 mg/l), Pb was highest in carapace (34.6±2.8 mg/l) and gill (151.9±21.6 mg/l) while THC was highest in intestine (39.5±2.9 mg/l) and gut (52.4±13.4 mg/l). The order of concentration is Zn>Pb>THC>Cd. Male crabs had slightly higher THC and heavy metal concentration than female crabs probably because of their large size. There is negative correlation between carapace area and THC concentration (R = -0.246), meaning THC decreases with increasing carapace size. Internal parts of crab had higher THC and heavy metal concentration than external parts. These results show that there is high bioaccumulation of THC and heavy metals in crab, which is above WHO/FAO standard. This implies that the crabs are unfit for human consumption. The smaller the crab the better it is for consumption in terms of bioaccumulation of pollutants.

Halogenated organic pollutants in sediments and organisms from mangrove wetlands of the Jiulong River Estuary, South China

Eighteen sediments and four biota species were collected from mangrove wetlands of the Jiulong River Estuary (JRE) in South China to investigate the distribution of dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), decabromodiphenyl ethane (DBDPE), dechlorane plus (DP) and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE). Concentrations of ΣDDTs, ΣPCBs, ΣPBDEs, DBDPE, DP, and BTBPE in mangrove sediments ranged from 21 to 84, 0.52-2.5, 9.0-66, 5.1-32, 0.05-0.14, and 0.03-0.25 ng/g dry weight, respectively. Levels of ΣDDTs, ΣPCBs, ΣPBDEs, DBDPE and DP in mangrove biota ranged from 950 to 30000, 56-400, 8.0-35, nd-20 and 0.44-3.1 ng/g lipid weight, respectively. DDTs were the predominant halogenated organic pollutants (HOPs) in mangrove sediments from the JRE, while PBDEs were the major HOPs in mangrove sediments from the Pearl River Estuary (PRE), suggesting that sediments in JRE and PRE had different sources of HOPs. The dominance of DDTs was found in both mangrove sediments and biota from the JRE, indicating that HOPs in JRE environment mainly come from agricultural sources. The biota-sediment accumulation factors for DDTs and PCBs were significantly higher than those of PBDEs, DBDPE and DP, suggesting high bioavailability of DDTs and PCBs in mangrove biota. Trophic magnification factors for DDTs, PCBs, PBDEs, and DP were 10.5, 3.00, 2.66 and 1.23, respectively, indicating their potential of biomagnification in mangrove food webs.

Contrasted resistance and resilience of two mangrove forests after exposure to long-term and short-term anthropic disturbances

Mangroves, coastal forests under the influence of tides, are known to be very resilient when they face natural disturbances such as storms or tsunami. While they provide several ecological services, they are threatened by many anthropic pressures. The aim of this study was to assess and to compare the stability of two mangrove fringes defined by contrasted set of natural constraints and exposed to pretreated domestic wastewaters discharges. The in situ experimental system set up in Mayotte Island (Indian Ocean) allowed us to determine both the short-term (2 years) and the long-term (9 years) resistance and the resilience. We focused on vegetation and crabs, an essential component of mangroves fauna. Wastewater discharges induced increases in tree coverage, leaves productivity and pigment content, and a decrease in crab diversity and density. Within 2 years after the release of the disturbance, several parameters reach back control values indicating fast resilience. Our results notably emphasized the high stability of the mangrove fringe dominated by Rhizophora mucronata trees, which was both more resistant and more resilient. This makes this fringe more suitable for application purposes, such as outfall for domestic wastewaters treatment plants.

Bioaccumulation and cycling of polybrominated diphenyl ethers (PBDEs) and dechlorane plus (DP) in three natural mangrove ecosystems of South China

Polybrominated diphenyl ethers (PBDEs) and dechlorane plus (DP) in mangrove sediments and tissues of nine species from three Mangrove Reserves of Hainan Island were studied. The average concentrations of PBDEs and DP in mangrove leaves, branches, roots and fruits were 1048, 498, 546 and 364 pg g^-1 dw, and 294, 181, 108 and 165 pg g^-1 dw, respectively. The elevated PBDEs and DP concentrations in mangrove leaves may be caused by atmospheric sedimentation. The predominant PBDE congeners in sediments were BDE-209 and those in mangrove tissues were BDE-28. The average f_anti (ratio of [anti-DP]/[DP]) of DP in sediments and tissues were 0.47 and 0.32, respectively. Sonneratia hainanensis, a fast growing mangrove plant, has a relatively high tolerance and absorptive capacity to PBDEs and DP in sediments, suggesting that it could be used as an effective plant for phytoremediation. The biota sediment accumulation factors (BSAFs) of PBDEs in mangrove branches were positively correlated with log K_OW (R² = 0.43, p < 0.05). The standing accumulation, annual absorption, annual net retention, annual return, and turnover period of PBDEs and DP in mangrove tissues of the ecosystems were estimated, and the results indicated that mangroves are playing an important role in retaining PBDEs and DP.

Mangrove Facies Drives Resistance and Resilience of Sediment Microbes Exposed to Anthropic Disturbance

Mangrove forests are coastal ecosystems continuously affected by various environmental stresses and organized along constraint gradients perpendicular to the coastline. The aim of this study was to evaluate the resistance and resilience of sediment microbial communities in contrasted vegetation facies, during and after exposure to an anthropic disturbance. Our hypothesis was that microbial communities should be the most stable in the facies where the consequences of the anthropic disturbance are the most similar to those of natural disturbances. To test this, we focused on communities involved in N-cycle. We used an in situ experimental system set up in Mayotte Island where 2 zones dominated by different mangrove trees are daily exposed since 2008 to pretreated domestic wastewater (PW) discharges. These freshwater and nutrients inputs should increase microbial activities and hence the anoxia of sediments. We monitored during 1 year the long-term impact of this disturbance, its short-term impact and the resilience of microbial communities on plots where PW discharges were interrupted. Microorganism densities were estimated by qPCR, the nitrification (NEA) and denitrification (DEA) enzyme activities were evaluated by potential activity measurements and pigment analyses were performed to assess the composition of microbial photosynthetic communities. At long-term PW discharges significantly modified the structure of phototrophic communities and increased the total density of bacteria, the density of denitrifying bacteria and DEA. Similar effects were observed at short-term, notably in the facies dominated by Ceriops tagal. The results showed a partial resilience of microbial communities. This resilience was faster in the facies dominated by Rhizophora mucronata, which is more subjected to tides and sediment anoxia. The higher stability of microbial communities in this facies confirms our hypothesis. Such information should be taken into account in mangrove utilization and conservation policies.

Polycyclic and organochlorine hydrocarbons in sediments of the northern South China Sea

We investigated the concentration distribution and composition of organic pollutants in sediments of the shelf and the deep northern South China Sea (NSCS). Concentrations of polycyclic aromatic hydrocarbons (Σ₁₅PAH; 10.69-66.45 ng g^-1), Dichlorodiphenyltrichloroethane (Σ₄DDT; 0-0.82 ng g^-1), and polychlorinated biphenyls (Σ₂₄PCB; 0-0.12 ng g^-1) are below established sediment quality guidelines, suggesting no environmental risk. Surprisingly, concentrations increase from the shelf to the deep NSCS, and are higher in the east of the study area. The organic pollutant composition indicates PAH mainly derived from pyrogenic sources, and mostly degraded DDT and PCB. However, in the deep NSCS, considerable contribution of petrogenic PAH, low chlorinated PCB and p,p'-DDT suggest more recent input from different sources compared to the shelf. From these results we infer that organic pollution in the NSCS does not originate from the Pearl River Estuary but from the NE SCS, SW of Taiwan.

Methane Emission from Mangrove Wetland Soils Is Marginal but Can Be Stimulated Significantly by Anthropogenic Activities

Mangrove wetland soils have been considered as important sources for atmospheric CH4, but the magnitude of CH4 efflux in mangrove wetlands and its relative contribution to climate warming compared to CO2 efflux remains controversial. In this study, we measured both CH4 and CO2 effluxes from mangrove soils during low or no tide periods at three tidal zones of two mangrove ecosystems in Southeastern China and collected CH4 efflux data from literature for 24 sites of mangrove wetlands worldwide. The CH4 efflux was highly variable among our field sites due to the heterogeneity of mangrove soil environments. On average, undisturbed mangrove sites have very low CH4 efflux rates (ranging from 0.65 to 14.18 μmol m−2 h−1; median 2.57 μmol m−2 h−1), often less than 10% of the global warming potentials (GWP) caused by the soil CO2 efflux from the same sites (ranging from 0.94 to 9.50 mmol m−2 h−1; median 3.67 mmol m−2 h−1), even after considering that CH4 has 28 times more GWP over CO2. Plant species, study site, tidal position, sampling time, and soil characteristics all had no significant effect on mangrove soil CH4 efflux. Combining our field measurement results and literature data, we demonstrated that the CH4 efflux from undisturbed mangrove soils was marginal in comparison with the CO2 efflux in most cases, but nutrient inputs from anthropogenic activities including nutrient run-off and aquaculture activities significantly increased CH4 efflux from mangrove soils. Therefore, CH4 efflux from mangrove wetlands is strongly influenced by anthropogenic activities, and future inventories of CH4 efflux from mangrove wetlands on a regional or global scale should consider this phenomenon.

Bioaccumulation and Cycling of Polycyclic Aromatic Hydrocarbons (PAHs) in Typical Mangrove Wetlands of Hainan Island, South China

Mangrove wetlands are important coastal ecosystems in tropical and subtropical regions, and mangrove sediments and tissues often are the pollutant sinks due to their high organic matter contents. Polycyclic aromatic hydrocarbons (PAHs) in the mangrove sediments and tissues of nine species from three typical mangrove wetlands of Hainan Island were studied. The average concentration of PAHs in all mangrove tissues was 403 ng g^-1 dw, with PAHs concentrations in leaf, branch, root, and fruit of 566, 335, 314, and 353 ng g^-1 dw, respectively. PAHs levels were much higher in leaf than in other mangrove tissues, which may be caused partly by atmospheric deposition of PAHs. The dominant individual PAH compounds in mangrove tissues were phenanthrene (41.3%), fluoranthene (14.7%), and pyrene (11.4%), while in sediments were naphthalene (73.4%), phenanthrene (3.9%), and pyrene (3.6%), respectively. The biota-sediment accumulation factors of PAH congeners in the mangrove wetlands showed different patterns, with the most predominant of phenanthrene. The cycling of PAHs in the mangrove wetlands of Hainan Island also were estimated, and the results showed that the standing accumulation, the annual absorption, the annual net retention, the annual return, and the turnover period in all mangrove tissues of the community were 2228 µg m^-2, 869 µg m^-2 a^-1, 206 µg m^-2 a^-1, 663 µg m^-2 a^-1, and 3.4 a, respectively. These results indicated that mangroves are playing an important role in retaining PAHs.

BaP-metals co-exposure induced tissue-specific antioxidant defense in marine mussels Mytilus coruscus

Both benzo(α)pyrene (BaP) and metals are frequently found in marine ecosystem and can cause detrimental effects in marine organism, especially the filter feeder-marine mussels. Although the biological responses in mussels have been well-studied upon the single metal or BaP exposure, the information about antioxidant defense, especially in different tissues of mussels, are still limited. Considering the variety of contaminants existing in the actual marine environment, single BaP (56 μg/L) and the co-exposure with Cu, Cd and Pb (50 μg/L, 50 μg/L and 3 mg/L respectively) were applied in a 6 days exposure followed by 6 days depuration experiment. The alterations of superoxide dismutase (SOD), catalase (CAT) activities and total antioxidant capacity (TAC) level were assessed in haemolymph, gills and digestive glands of marine mussels, Mytilus coruscus. An unparalleled change in antioxidant biomarkers was observed in all cells/tissues, with the SOD activity showing higher sensitivity to exposure. A tissue-specific response showing unique alteration in gill was investigated, indicating the different function of tissues during stress responses. Depressed antioxidant effects were induced by BaP-metals co-exposure, indicating the interaction may alter the intact properties of BaP. To our knowledge, this is the first research to explore the antioxidant defense induced by combined exposure of BaP-metals regarding to tissue-specific responses in marine mussels. The results and experimental model will provide valuable information and can be utilized in the investigation of stress response mechanisms, especially in relation to tissue functions in marine organism in the future.

Metals in mangrove ecosystems and associated biota: A global perspective

Mangrove forests prevalent along the intertidal regions of tropical and sub-tropical coastlines are inimitable and dynamic ecosystems. They protect and stabilize coastal areas from deleterious consequences of natural disasters such as hurricanes and tsunamis. Although there are reviews on ecological aspects, industrial uses of mangrove-associated microorganisms and occurrence of pollutants in a region-specific manner, there is no exclusive review detailing the incidence of metals in mangrove sediments and associated biota in these ecosystems on a global level. In this review, mangrove forests have been classified in a continent-wise manner. Most of the investigations detail the distribution of metals such as zinc, chromium, arsenic, copper, cobalt, manganese, nickel, lead and mercury although in some cases levels of vanadium, strontium, zirconium and uranium have also been studied. Seasonal, tidal, marine, riverine, and terrestrial components are seen to influence occurrence, speciation, bioavailability and fate of metals in these ecosystems. In most of the cases, associated plants and animals also accumulate metals to different extents and are of ecotoxicological relevance. Levels of metals vary in a region specific manner and there is disparity in the pollution status of different mangrove areas. Protecting these vulnerable ecosystems from metal pollutants is important from environmental safety point of view.

Limited impact of several years of pretreated wastewater discharge on fauna and vegetation in a mangrove ecosystem

It was hypothesized that mangroves, tropical wetlands, could be used for the finishing treatment of domestic wastewaters. Our aim was to determine if a nutrient-stressed mangrove could tolerate long-term discharges of pretreated wastewater (PW). Since 2008, in an in situ experimental system set up in Mayotte Island (Indian Ocean), domestic PW are discharged into two impacted areas (675 m²) dominated by different species of mangrove trees. Anthropogenic inputs during > 4.5 years led to an increase in vegetation growth associated with an increase in leaf pigment content, leaf surface and tree productivity. A marked increase in tree mortality was observed. There was no effect on crabs and meiofauna densities, but significant modifications of community structures. These effects may be directly linked to PW inputs, or indirectly to the modifications of the environment associated with higher tree growth. However, our results indicate that there was no major dysfunction the ecosystem.

Heavy metal pollution in immobile and mobile components of lentic ecosystems-a review

With growing population and urbanization, there is an increasing exploitation of natural resources, and this often results to environmental pollution. In this review, the levels of heavy metal in lentic compartments (water, sediment, fishes, and aquatic plants) over the past two decades (1997-2017) have been summarized to evaluate the current pollution status of this ecosystem. In all the compartments, the heavy metals dominated are zinc followed by iron. The major reason could be area mineralogy and lithogenic sources. Enormous quantity of metals like iron in estuarine sediment is a very natural incident due to the permanently reducing condition of organic substances. Contamination of cadmium, lead, and chromium was closely associated with anthropogenic origin. In addition, surrounding land use and atmospheric deposition could have been responsible for substantial pollution. The accumulation of heavy metals in fishes and aquatic plants is the result of time-dependent deposition in lentic ecosystems. Moreover, various potential risk assessment methods for heavy metals were discussed. This review concludes that natural phenomena dominate the accumulation of essential heavy metals in lentic ecosystems compared to anthropogenic sources. Amongst other recent reviews on heavy metals from other parts of the world, the present review is executed in such a way that it explains the presence of heavy metals not only in water environment, but also in the whole of the lentic system comprising sediment, fishes, and aquatic plants.

Biochar accelerates microbial reductive debromination of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in anaerobic mangrove sediments

A common congener of polybrominated diphenyl ethers, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), is a prevalent, persistent and toxic pollutant. It could be removed by reduction debromination by microorganisms but the rate is often slow. The study hypothesized that spent mushroom substrate derived biochar amendment could accelerate the microbial reductive debromination of BDE-47 in anaerobic mangrove sediment slurries and evaluated the mechanisms behind. At the end of 20-week experiment, percentages of residual BDE-47 in slurries amended with biochar were significantly lower but debromination products were higher than those without biochar. Such stimulatory effect on debromination was dosage-dependent, and debromination was coupled with iron (Fe) reduction. Biochar amendment significantly enhanced the Fe(II):Fe(III) ratio, Fe(III) reduction rate and the abundance of iron-reducing bacteria in genus Geobacter, thus promoting bacterial iron-reducing process. The abundances of dehalogenating bacteria in genera Dehalobacter, Dehalococcoides, Dehalogenimonas and Desulfitobacterium were also stimulated by biochar. Biochar as an electron shuttle might increase electron transfer from iron-reducing and dehalogenating bacteria to PBDEs for their reductive debromination. More, biochar shifted microbial community composition in sediment, particularly the enrichment of potential PBDE-degrading bacteria including organohalide-respiring and sulfate-reducing bacteria, which in turn facilitated the reductive debromination of BDE-47 in anaerobic mangrove sediment slurries.

Exogenous phosphorus enhances cadmium tolerance by affecting cell wall polysaccharides in two mangrove seedlings Avicennia marina (Forsk.) Vierh and Kandelia obovata (S., L.) Yong differing in cadmium accumulation

Phosphorous (P) is an essential element that mediates various stresses in plants. In this study, the effects of P on polysaccharides in the root cell walls of two hydroponically cultivated mangrove seedlings (A. marina and K. obovata) that differ in Cd accumulation ability were examined in the context of Cd stress. The results showed that A. marina exhibited a higher degree of tolerance to Cd than K. obovata. In both mangrove seedlings, pectin and hemicellulose 1 increased significantly with increasing P levels, the effects of which were greater in A. marina under Cd stress. In addition, cell wall pectin methylesterase (PME) activity was markedly increased in the presence of Cd and P compared with Cd alone. These effects were more pronounced in A. marina than in K. obovata. Taken together, the results of this study provide further insight into the mechanisms of P-mediated alleviation of Cd stress in mangrove seedlings.

Distribution and ecological risk assessment of heavy metals in surface sediments of a typical restored mangrove-aquaculture wetland in Shenzhen, China

The restoration of wetlands has attracted the attention in different countries. Restored coastal wetlands, especially urban wetlands, are sensitive to external pressures. Thus, it is necessary to evaluate the efficiency of the restoration of coastal wetlands, which benefits their management and functional maintenance. In this study, a restored mangrove-aquaculture system in Waterlands Resort at Shenzhen was selected for analysis. The distribution and ecological risk assessment of heavy metals in surface sediments were investigated. The results showed that restoration could effectively decrease the heavy metal concentrations in the sediment, while the restored mangrove posed a moderate ecological risk. Most of the heavy metal concentrations were higher during the dry season compared with the wet season. In addition, during the whole investigation, the sediment quality remained failed to achieve the marine sediment criteria required for aquaculture in China.

Spatial distribution, ecological and health risk assessment of heavy metals in marine surface sediments and coastal seawaters of fringing coral reefs of the Persian Gulf, Iran

Concentrations of 13 heavy metals (Al, Fe, Mn, Zn, Cu, Cr, Co, Ni, V, As, Cd, Hg, Pb) in 360 reef surface sediments (0-5 cm) and coastal seawater samples from ten coral Islands in the Persian Gulf were analyzed to determine their spatial distribution and potential ecological risks. Different sediment quality indices were applied to assess the surface sediment quality. The mean concentrations of metals in studied sediments followed the order: Al > Fe > Ni > V > Mn > Zn > Cu > Cr > Co > As > Cd > Pb > As. Average Cd and Hg exceeded coastal background levels at most sampling sites. With the exception of As, concentrations of heavy metals decreased progressively from the west to the east of the Persian Gulf. Based on the Enrichment Factor (EF) and Potential Ecological Risk Index (RI), concentrations of V, Ni, Hg and Cd indicated moderate contamination and is of some concern. The mean values of heavy metals Toxic Units (TUs) were calculated in the following order: Hg (0.75)> Cr (0.41)> Cd (0.27)> As (0.23)> Cu (0.12)> Zn (0.05)> Pb (0.009). Furthermore, the mean contributing ratios of six heavy metals to Toxic Risk Index (TRI) values were 79% for Hg, 11.48% for Cd, 6.16% for Cr, 3.27% for Cu, 0.07% for Zn and 0.01% for Pb. Calculated values of potential ecological risk factor, revealed that the risk of the heavy metals followed the order Cd > Pb > Ni > Cr > V > Cu > Zn. The results reflected that the level of heavy metals, especially Hg and Cd, are on rise due to emerging oil exploration, industrial development, and oil refineries along the entire Gulf. Fe, Mn, Cu, Zn, V and Ni concentrations in seawater were significantly higher (p < 0.05) than the other detected dissolved heavy metals in the sampling sites. A health risk assessment using the hazard quotient index (HQ) recommended by the USEPA suggests that there is no adverse health effect through dermal exposure, and there is no carcinogenic and non-carcinogenic harm to human health.

Influence of polycyclic aromatic hydrocarbons on nitrate reduction capability in mangrove sediments

In the present study, we investigated the influence of phenanthrene (PHE), a three-ring polycyclic aromatic hydrocarbon (PAH) compound, on nitrate (NO₃^-) reduction processes in mangrove sediments using microcosms. After 10days, nitrate/nitrite reductase activity and abundance of narG and nirS significantly decreased in the bulk sediment at both 10/50mgPHEkg^-1 contamination groups. In the rhizosphere, abundance of narG, nirS and nirK markedly declined at PHE treated sediments, while the drop in reductase activity at 10mgkg^-1 PHE treatment was insignificant. After 50days, apart from 10mgPhekg^-1 treated bulk sediment, abundance of denitrifiers and reductase activity in all PHE spiked sediment samples significantly dropped. Therefore, the influence of PAHs on NO₃^- reduction capability in mangrove sediments is dependent on spiked concentration, temporal scale of exposure and interaction with roots. Generally, PAHs play an inhibitor role, slowing NO₃^- turnover rates, which warrant attention from coastal managers.

Organophosphorus flame retardants in mangrove sediments from the Pearl River Estuary, South China

Forty-eight surface sediments were collected from three mangrove wetlands in the Pearl River Estuary (PRE) of South China to investigate the distribution of organophosphorus flame retardants (OPFRs) and the relationship between OPFRs and microbial community structure determined by phospholipid fatty acid. Concentrations of ΣOPFRs in mangrove sediments of the PRE ranged from 13.2 to 377.1 ng g^-1 dry weight. Levels of ΣOPFRs in mangrove sediments from Shenzhen and Guangzhou were significantly higher than those from Zhuhai, indicating that OPFRs were linked to industrialization and urbanization. Tris(chloropropyl)phosphate was the predominant profile of OPFRs in mangrove sediments from Shenzhen (38.9%) and Guangzhou (35.0%), while the composition profile of OPFRs in mangrove sediments from Zhuhai was dominated by tris(2-chloroethyl) phosphate (25.5%). The mass inventories of OPFRs in the mangrove sediments of Guangzhou, Zhuhai and Shenzhen were 439.5, 133.5 and 662.3 ng cm^-2, respectively. Redundancy analysis revealed that OPFRs induced a shift in the structure of mangrove sediment microbial community and the variations were significantly correlated with tris(1,3-dichloro-2-propyl)phosphate and tris(2-butoxyethyl) phosphate.

Phosphorus effects on radial oxygen loss, root porosity and iron plaque in two mangrove seedlings under cadmium stress

Phosphorus is an indispensable element for plants, but its role in alleviating the cadmium toxicity of mangrove seedlings is poorly documented. In this study, mangrove seedlings were grown in hydroponics and exposed to various Cd and P treatments. Data suggested that the inhibitory effect of Cd on the rate of radial oxygen loss and root porosity was alleviated by P. A. marina had a higher rate of ROL and POR, indicating that it had a stronger adaptability to anaerobic environment. K. obovata induced a higher Fe concentration in iron plaque under co-application of Cd and P, which may relate to higher biomass. Furthermore, P increased Cd concentration in iron plaque, implying that iron plaque can be an obstacle to prevent Cd entering into the plant, but most Cd was still distributed in its roots. These findings highlight a novel mechanism of Cd detoxification with P addition in mangrove seedlings.

Phosphorus mediation of cadmium stress in two mangrove seedlings Avicennia marina and Kandelia obovata differing in cadmium accumulation

Mangrove ecosystems are vulnerable to environmental threats. In order to elucidate the effect of phosphorus (P) on cadmium (Cd) tolerance and physiological responses in mangroves under Cd stress, a mangrove specie with salt exclusion Kandelia obovata and a specie with salt secretion Avicennia marina were compared in a hydroponic experiment. The results showed that most Cd was accumulated in mangrove roots and that P addition induced Cd immobilisation in them. Cd stress significantly increased malonaldehyde content, whereas P significantly decreased malonaldehyde in mangroves. Phosphorus positively regulated the photosynthetic pigment, proline content and synthesis of non-protein thiols, glutathione and phytochelatins in the leaves under Cd stress conditions. The results suggest different adaptive strategies adopted by two mangroves in a complex environment and A. marina showed a stronger Cd tolerance than K. obovata. The study provides a theoretical basis for P mediated detoxification of Cd in mangrove plants.

Source apportionment of polycyclic aromatic hydrocarbons and n-alkanes in the soil-sediment profile of Jianghan Oil Field, China

Surface soil in oil exploration area always contains high contents of polycyclic aromatic hydrocarbons (PAHs) and n-alkanes. To investigate the migration possibility of PAHs and n-alkanes from surface through aquitard and aquiclude to aquifer, the distribution, together with the source apportionment using several indicators, such as composition pattern, fluoranthene/(fluoranthene+pyrene) (Flt/(Flt+Pyr)), anthracene/(anthracene+phenanthrene) (Ant/(Ant+PA)), and the carbon preference index (CPI) of n-alkanes, in a 30-m-deep soil-sediment profile were studied. Results showed that there were considerable PAHs and n-alkanes not only in surface soil but also in aquitard, aquiclude, and aquifer sediments. The PAHs and n-alkanes in surface soil strongly suggested petroleum pollution. The high molecular weight PAHs and the n-alkanes with both long and short chains could not migrate into deep sediments as their sources in surface soil and deep sediment were different. Whereas the aquitard and aquiclude had significant input of low molecular weight PAHs (LMWPAHs) from petroleum sources, the LMWPAHs in confined aquifer suggested pyrogenic sources. Therefore, LMWPAHs migrated from surface to aquitard and aquiclude, but did not cause aquifer pollution in Jianghan Oil Field. However, the high mobility of LMWPAHs from surface to aquitard and aquiclude suggested that the long-term risk of groundwater pollution from oil exploration should be concerned.

Heavy metal contamination in sandy beach macrofauna communities from the Rio de Janeiro coast, Southeastern Brazil

We evaluated concentrations of eight heavy metals Cr, Zn, Pb, Ni, Cu, Cd, Co and V, in tissues of representative macrofauna species from 68 sandy beaches from the coast of Rio de Janeiro state. The links between contamination levels and community descriptors such as diversity, evenness, density and biomass, were also investigated. Metal concentrations from macrofaunal tissues were compared to maximum permissible limits for human ingestion stipulated by the Brazilian regulatory agency (ANVISA). Generalized linear models (GLM's) were used to investigate the variability in macrofauna density, richness, eveness and biomass in the seven different regions. A non-metric multidimensional scaling analysis (n-MDS) was used to investigate the spatial pattern of heavy metal concentrations along the seven regions of Rio de Janeiro coast. Variation partitioning was applied to evaluate the variance in the community assemblage explained by the environmental variables and the heavy metal concentrations. Our data suggested high spatial variation in the concentration of heavy metals in macrofauna species from the beaches of Rio de Janeiro. This result highlighted a diffuse source of contamination along the coast. Most of the metals concentrations were under the limits established by ANVISA. The variability in community descriptors was related to morphodynamic variables, but not with metal contamination values, indicating the lack of direct relationships at the community level. Concentration levels of eight heavy metals in macrofauna species from 68 sandy beaches on Rio de Janeiro coast (Brazil) were spatially correlated with anthropogenic activities such as industrialization and urbanization.

Occurrence, profiles, and ecological risks of polybrominated diphenyl ethers in mangrove sediments of Shantou, China

Surface sediments were collected from three mangrove wetlands (Yifeng Xi, Shuanghan, and Su'ai Wan) in Shantou coastal zone of South China to investigate spatial distributions of polybrominated diphenyl ethers (PBDEs). The results demonstrate that PBDEs were detected in all the samples, indicating their widespread occurrence in coastal sediments of the studied area. Σ₉PBDEs (defined as the sum of nine targeted PBDE congeners except BDE-209) and BDE-209 are in the range of 2.3 to 11.5 and 16.7 to 58.2 ng/g, respectively. BDE-209 is the dominant PBDE congener in all sediment samples. The sediment concentrations of ∑₉PBDEs and BDE-209 among the three wetlands decrease in the order of Su'ai Wan > Shuanghan > Yifeng Xi. The concentrations of ∑₉PBDEs are higher in mangrove sediments than in mudflats, but no obvious regularity can be found on the correlation between mangrove species and PBDE levels in sediments. The contents of total organic carbon are moderately correlated with BDE-209 concentrations in sediments but not with ∑₉PBDE concentrations. The samples collected from different locations show slightly different composition profiles except BDE-209, with BDE-100 and BDE-47 being the pre-dominated congeners. The mudflats exhibit higher abundances of tri- to hexa-substituted congeners than the mangrove sediments. Ecological risk assessment demonstrates that the surface sediments from Shantou may pose a potential ecological risk of exposure to sediment-dwelling organisms.

Combined effects of land reclamation, channel dredging upon the bioavailable concentration of polycyclic aromatic hydrocarbons (PAHs) in Victoria Harbour sediment, Hong Kong

The up-to-date concentration of polycyclic aromatic hydrocarbons (PAHs) in sediment materials of Victoria Harbour was investigated so as to evaluate the pollution potential associated with the reclamation projects in Hong Kong. A total of 100 sediment samples were collected at 20 locations. Except the control point in reservoir, the PAHs concentrations were detectable levels all sites (131-628.3ng/g, dw) and such values were higher than Dutch Target and Intervention Values (the New Dutch standard in 2016). The PAHs concentration indicating that construction waste and wastewater discharges were the main pollutant sources. Results of correlation in single cell gel electrophoresis assay (comet assay) studies also revealed that the PAHs concentration was highly correlated (<0.01) with DNA migration (i.e. the length of tail moment of fish cells) in 5mg/ml of PAHs. The above observation indicates that the PAHs present in the sediment may substantially effect the marine ecosystem. Although the dredged sediment can be a useful sea-filling material for land reclamation; however, the continuing leaching of PAHs and its impact on the aquatic environment need to be studied further.

Influence of introduced Sonneratia apetala on nutrients and heavy metals in intertidal sediments, South China

To investigate the influence of Sonneratia apetala on nutrients and heavy metals in intertidal sediments, sediment cores of S. apetala marsh and mudflat in Shenzhen Bay, China were analyzed. The results showed that S. apetala improved sediment nutrient properties due to increased total carbon (TC), total nitrogen (TN), and total sulfur (TS). The levels of heavy metals were higher in S. apetala site than in mudflat, including chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg). In S. apetala site, TC, TN, and TS were not positively correlated with Cr, Ni, As, Cd, and Pb, indicating their less important roles in trapping heavy metals. There were positive correlations among Ni, Cu, Zn, and Cd in both sites, suggesting similar anthropogenic source. Levels of As were higher than the probable effect level at both sites, indicating their toxicological importance. The geo-accumulation index and potential ecological risk index revealed higher metal contaminations in S. apetala site, especially for Cd, Hg, and As. Multivariate analysis implied that S. apetala alter the biogeochemical cycle of Cd and Cr to a certain extent. These findings indicate that S. apetala may improve soil nutrient properties and facilitate heavy metal accumulation in intertidal sediments.

Profiles and inventories of organic pollutants in sediments from the central Beibu Gulf and its coastal mangroves

Sediment cores from the central Beibu Gulf and its northern coastal mangroves were analyzed for polycyclic aromatic hydrocarbons (PAH), the organo-chlorine pesticides dichlorodiphenyltrichloroethane (DDT) and hexachlorobenzene (HCB), and polychlorinated biphenyls (PCB), to reconstruct the organic pollution history of developing south-west China. Reflecting regional development, in the gulf ∑PAH (38-74 ng g(-1)) decreased towards the surface after peak concentrations near 10 cm, while ∑DDT (ND - 0.5 ng g(-1)) increased due to fresh inputs, and HCB (ND - 0.04 ng g(-1)) occurred only in surface sediments. Profiles in mangrove sediments showed a continuing local scale increase in ∑PAH (29-438 ng g(-1)) as well as ∑DDT (0.2-41.0 ng g(-1)) and HCB (0.01-1.01 ng g(-1)) pollution, despite some variability. No trend was evident for ∑PCB (ND - 0.22 ng g(-1)), which was not detected in the central gulf. Calculated loads estimate that 2816 ng cm(-2) PAHs and 7 ng cm(-2) DDTs are stored in depositional areas of the Beibu Gulf. Mangrove sediments, threatened by land-use-change, contain 1400-4600 ng cm(-2) PAHs and 34-39 ng cm(-2) DDTs.