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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.

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 (R 2  = 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., (Copyright © 2018 Elsevier B.V. All rights reserved.)

This study investigated the uptake and accumulation of polycyclic aromatic hydrocarbons (PAHs) in two mangrove species, Avicennia marina and Rhizophora mucronata. We tested the hypothesis that A. marina would absorb and accumulate more PAHs than R. mucronata. One-year old seedlings of both species were subjected to Bunker Fuel Oil 180 for 3 weeks, and the concentration of PAHs was analyzed by gas chromatography-mass spectrometry (GC/MS). The concentration of PAHs was significantly higher in A. marina than in R. mucronata. The major portion of the PAH pool was in roots (96% in A. marina, 98% in R. mucronata) compared to leaves. The dominant PAHs in roots of both species possessed two to three rings and included phenanthrene, anthracene, fluorene, and acenaphthene. In shoots, PAHs in A. marina included phenanthrene, chrysene, anthracene, acenaphthene, benzo[k+b]fluoranthene, pyrene, benzo[a] anthracene, and benzo[a] pyrene, while those in R. mucronata included phenanthrene, naphthalene, fluoranthene, fluorene, and acenaphthene. Phenanthrene was the dominant PAH in roots and shoots of both species. The greater susceptibility of A. marina appears to be due to its greater root length and specific root length, which permit more exposure to oil than R. mucronata. Other contributory factors include root anatomical characteristics such as larger air spaces, lower suberization of root epidermal cells, lower concentrations of polyphenols, tannins, lignin, and a less efficient antioxidative system. This study provides novel information on differences in the uptake and accumulation of PAHs in two contrasting mangrove species.

Wastewater often contains mixed toxic pollutants, and the contribution of plant uptake in constructed wetland treatment systems is affected by environmental conditions, particularly tidal flushing. In this study, the uptake of wastewater-borne pollutants, including a mixture of polycyclic aromatic hydrocarbons (PAHs) and polybrominated diphenyl ethers (PBDEs) congeners, by two mangrove plant species, namely Excoecaria agallocha L. and Kandelia obovata Sheue, Liu & Yong, under different tidal flushing regimes was investigated. Results showed that Fe plaque formed on root surfaces could immobilize wastewater-borne PAHs and PBDEs. At the end of 8-month wastewater treatment, most of the pollutants removed by plants ended up in Fe plaque, with 0.12-20.83% of total PAHs and 0.78-24.76% of total PBDEs added to the microcosm retained in Fe plaque. On the contrary, the percentages of PAHs and PBDEs taken up by plant tissues were relatively small, ranging from not detected to 0.09% and from 0.01 to 2.00%, respectively. More uptake of Fe plaque-immobilized PAHs and PBDEs was found in K. obovata than in E. agallocha, leading to more plant damages in the former species due to its weaker root outer layers. While E. agallocha with stronger root protective outer layer was able to uptake more PAHs and PBDEs from wastewater but immobilize in Fe plaque than that of K. obovata. In both plant species, tidal flushing regimes significantly affected the immobilization of PAHs and PBDEs in Fe plaque, and more frequent tidal flushing led to higher percentages of immobilization. This is the first study demonstrating that E. agallocha was a more suitable mangrove plant species to remove wastewater-borne PAHs and PBDEs than K. obovata, and the significance of tidal flushing on performance of constructed mangrove wetlands., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Metal pollution has been widely reported in mangrove wetlands; however, the mechanisms involved in metal detoxification by mangroves are still poorly understood. This study aimed to investigate the possible function of root lignification/suberization on Pb uptake and tolerance in mangroves. Two mangroves, Acanthus ilicifolius and Rhizophora stylosa with different root lignification/suberization were selected as plant materials; the former exhibits a thin exodermis and low lignification/suberization, while the latter possesses a thick exodermis and high lignification/suberization. A pot trial with addition of Pb was conducted to investigate the differences in Pb uptake and tolerance between the two mangroves. The experiment of rhizobox was designed to explore Pb dynamics and availabilities in the rhizosphere soils, besides, the ability of Pb uptake by the excised roots and X-ray analysis for Pb distribution within roots were also detected. The results revealed that R. stylosa exhibited relatively higher Pb tolerance together with less Pb accumulations when compared to A. ilicifolius. For both species, lower proportion of exchangeable and Carbonate Pb and higher higher Fe-Mn oxides Pb were observed in the rhizosphere zone when compared to the respective non-rhizosphere zone. The results from metal uptake by the excised roots and X-ray analysis clearly showed that the thick lignified/suberized exodermis of R. stylosa could more efficiently delay Pb entering into the roots, leading to less Pb accumulation. In summary, the present study proposes a barrier property of the lignified/suberized exodermis in dealing with the stresses of Pb.

Contaminant concentrations are reported for surface water, sediment, flora and fauna collected during 2010-2011 from the mangrove fringe along eastern Tampa Bay, Florida. Concentrations of trace metals, chlorinated pesticides, atrazine, total polycyclic aromatic hydrocarbons, and polychlorinated biphenyls were species-, chemical- and location-specific. Contaminants in sediments did not exceed proposed individual sediment quality guidelines. Most sediment quality assessment quotients were less than one indicating the likelihood of no inhibitory effect based on chemical measurements alone. Faunal species typically contained more contaminants than plant species; seagrass usually contained more chemicals than mangroves. Bioconcentration factors for marine angiosperms were usually less than 10 and ranged between 1 and 31. Mercury concentrations (ppm) in blue crabs and fish did not exceed the U.S. Environmental Protection Agency fish tissue criterion of 0.3 and the U.S. Food and Drug Administration action level of 1.0. In contrast, total mercury concentrations in faunal species often exceeded guideline values for wildlife consumers of aquatic biota., (Published by Elsevier Ltd.)

This work evaluated the roles of the low-molecular-weight organic acids (LMWOAs) from root exudates and the dehydrogenase activity in the rhizosphere sediments of three mangrove plant species on the removal of mixed PAHs. The results showed that the concentrations of LMWOAs and dehydrogenase activity changed species-specifically with the levels of PAH contamination. In all plant species, the concentration of citric acid was the highest, followed by succinic acid. For these acids, succinic acid was positively related to the removal of all the PAHs except Chr. Positive correlations were also found between the removal percentages of 4-and 5-ring PAHs and all LMWOAs, except citric acid. LMWOAs enhanced dehydrogenase activity, which positively related to PAH removal percentages. These findings suggested that LMWOAs and dehydrogenase activity promoted the removal of PAHs. Among three mangrove plants, Bruguiera gymnorrhiza, the plant with the highest root biomass, dehydrogenase activity and concentrations of LMWOAs, was most efficient in removing PAHs., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Polybrominated diphenyl ethers (PBDEs) are toxic and ubiquitous environmental contaminants, but their fate in aquatic environments is not clear. A mangrove microcosm study was employed to investigate the fate of two abundant congeners, BDE-47 and BDE-209, in contaminated sediment. After seven months, more than 90% of the spiked BDE-47 in the mangrove sediment was removed with the formation of lower brominated PBDEs, including BDE-28, -17, -15, -8, -7/4, suggesting that microbial debromination was the main contributor. Debromination of BDE-209 was also observed in the sediment but its dissipation rate was significantly lower than BDE-47. All these congeners were taken up, translocated and accumulated into the tissues of two typical mangrove plants, Kandelia obovata and Avicennia marina. PBDEs, even at very high contamination levels, in the sediment (5000ngg(-1)) and the debrominated congeners did not pose any adverse effect on the dry weight, augmentation and root/shoot ratio of either mangrove species. This is the first study to reveal that anaerobic microbial debromination and uptake by mangrove plants are the key processes controlling the fate of PBDEs in mangrove sediment., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The high consumption of crabs (Ucides cordatus) stimulated interest in the present study on the northern coast of Brazil, which encompasses a preserved area of mangrove forest. The objective was to describe and quantify the transfer of metals from the muddy sediments to the leaves of the Rhizophora mangle, and thence the crabs and humans. The samples were collected along two transects, while samples of hair were obtained from local habitants. The pH, interstitial salinity, Eh (mV) were measured, the granulometry and mineralogical and multi-element chemical analyses were run, and the organic material determined. The sediments are silty-clayey, composed of quartz, kaolinite, iron oxides, and illite, as well as smaller portions of smectite, pyrite, halite, and high levels of SiO2 (56.5 %), Al2O3 (18.5 %), and Fe2O3 (7 %). The elements Zn, Sr, As, and Zr are concentrated in the leaves, while the bioaccumulation of Zn, Se, Sr, and As was recorded in the crabs, of which, Se is the most concentrated in the tissue of the muscles and the hepatopancreas. The concentrations of nutrient and toxic elements were similar in all age groups (hair samples), with only Hg presenting an increasing concentration between infants and adults. The highest rates of transfer were recorded for the elements Zn and Se in the crabs and Hg in leaves and hair. The accumulation of metals in the leaves and crabs reflects the chemical composition of the sediments and low rates of sediment-vegetation-crab transfer, with the exception of Hg, which accumulated in the hair.

Bruguiera gymnorhiza, an evergreen mangrove tree, is tolerant of bisphenol A (BPA) and has potential BPA removal capability. BPA is highly toxic to plants at high concentrations, wherein they exhibit damaged symptoms such as chlorosis, necrosis, and wilting. The LD50 of BPA toxicity for this plant was statistically estimated to be 39.97 mg L(-1). B. gymnorhiza can reduce COD from 15408 +/- 246 to 49 +/- 30 mg L(-1) by (approximately 99% reduction of the initial value) and can reduce content to levels below the industrial effluent standard of Thailand (<120 mg L(-1)) within 48 days. This plant can completely remove BPA from the solution within 51 days of treatment. Polysaccharides and organic acids were found in the solution and were caused by plant response to the toxicity of BPA. In addition, B. gymnorrhiza can also reduce total dissolved solids (TDS) and salinity in real wastewater. Therefore, B. gymnorrhiza has potential for removal of BPA and TDS in contaminated in wastewater.

The crab Ucides cordatus and the red mangrove Rhizophora mangle are endemic mangrove species and potential bio-accumulators of metals. This study quantified the accumulation of six metals (Cd, Cr, Cu, Hg, Mn and Pb) in different organs (claw muscle, hepatopancreas and gills) of U. cordatus, as well as in different maturation stages of the leaves (buds, green mature, and pre-abscission senescent) of R. mangle. Samples were collected from mangrove areas in Cubatão, state of São Paulo, a heavily polluted region in Brazil. Data for metal contents in leaves were evaluated by one-way ANOVA; while for crabs a factorial ANOVA was used to investigate the effect of different tissues, animal size and the interactions between them. Means were compared by Tukey test at five percent, and the association between the metal concentrations in each crab organ, depending on the size, was evaluated by Pearson's linear correlation coefficient (r). Concentrations of Pb and Hg were undetectable for the different leaf stages and crab tissues, while Cd concentrations were undetectable in the leaf stages. In general, the highest accumulation of metals in R. mangle leaves occurred in pre-abscission senescent and green mature leaves, except for Cu, which was found in the highest concentrations in buds and green mature leaves. For the crab, Cd, Cu, Cr and Mn were present in concentrations above the detection limit, with the highest accumulation in the hepatopancreas, followed by the gills. Cu was accumulated mostly in the gills. Patterns of bioaccumulation between the crab and the mangrove tree differed for each metal, probably due to the specific requirements of each organism for essential metals. However, there was a close and direct relationship between metal accumulation in the mangrove trees and in the crabs feeding on them. Tissues of R. mangle leaves and U. cordatus proved effective for monitoring metals, acting as important bioindicators of mangrove areas contaminated by various metals., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The scientific literature for fate and effects of non-nutrient contaminant concentrations is skewed for reports describing sediment contamination and bioaccumulation for trace metals. Concentrations for at least 22 trace metals have been reported in mangrove sediments. Some concentrations exceed sediment quality guidelines suggesting adverse effects. Bioaccumulation results are available for at least 11 trace metals, 12 mangrove tissues, 33 mangrove species and 53 species of mangrove-habitat biota. Results are specific to species, tissues, life stage, and season and accumulated concentrations and bioconcentration factors are usually low. Toxicity tests have been conducted with 12 mangrove species and 8 species of mangrove-related fauna. As many as 39 effect parameters, most sublethal, have been monitored during the usual 3 to 6 month test durations. Generalizations and extrapolations for toxicity between species and chemicals are restricted by data scarcity and lack of experimental consistency. This hinders chemical risk assessments and validation of effects-based criteria., (Published by Elsevier Ltd.)

The influence of different environmental stresses, including salinity (5-35‰), tidal cycle (6/6, 12/12 and 24/24 h of high/low tidal regimes) and nutrient addition (1-6 times background nitrogen and phosphorus content) on Bruguiera gymnorrhiza and Aegiceras corniculatum grown in sediment contaminated with spent lubricating oil (7.5 L m(-2)) were investigated. The oil-treated 1-year-old mangrove seedlings subject to low (5‰) and high (35‰) salinity had significantly more reduction in growth, more release of superoxide radical (O2·-) and higher activity of superoxide dismutase (SOD) than those subject to moderate salinity (15‰). Extended flooding (24/24 h of high/low tidal regime) enhanced O2·- release and malondialdehyde (MDA) content in both oil-treated species but had little negative effects on biomass production (P>0.05) except the stem of A. corniculatum (P=0.012). The addition of nutrients had no beneficial or even posed harmful effects on the growth and cellular responses of the oil-treated seedlings., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Iron (Fe) plaque formed on mangrove root increased with wastewater discharge, but the extent was species-specific. For Bruguiera gymnorrhiza, Fe plaque concentration was 0.80 mg g(-1) root d.wt at Day 0 and increased to 4.59, 6.84 and 7.52 mg g(-1) at Day 75 in the fresh water control (FW), synthetic wastewater with pollutant concentrations five times of municipal sewage (5SW) and double of 5SW (10SW) treatments, respectively; the respective increases in Excoecaria agallocha were from 0.70 to 2.37, 10.73 and 13.21 mg g(-1). For Acanthus ilicifolius, similar increase was found in 5SW, but all of the plants were dead in 10SW at Day 75. The concentrations of heavy metals and phosphorus immobilized were positively correlated with the amounts of Fe plaque formed, but the regression coefficients varied among species. The performance of mangrove plants in wastewater treatments was related to the Fe plaque formed and its immobilized wastewater-borne pollutants., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

The temporal responses of peroxidase (POD), superoxide dismutase (SOD), total polyphenols (TP), extractable condensed tannins (ECT) to different levels of lead (Pb) or manganese (Mn) stress, as well as the metal accumulation, in seedlings of Kandelia obovata were investigated. Both stress time and stress intensity had significant effects with significant accumulation of Pb and Mn in roots at Day 1. Pb and Mn showed no significant effects on root or leaf TP and ECT at Day 1. Prolonged exposure to metals caused significant drops of root TP and ECT but increased in leaves at Days 7 and 49. POD activities decreased in both roots and leaves at Day 1, while POD and SOD both increased under moderate levels of Pb and Mn at Day 7. The present study showed that antioxidative enzyme activities were more sensitive indicators to Pb or Mn stresses than phenolic compounds., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

In this study, we investigated the microbial degradation of the phthalate esters (PAEs) dibutyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP), and change in microbial communities in mangrove sediment collected from 5 sampling sites along the Tanshui River in Taiwan. Aerobic degradation half-lives (t(1/2)) of DBP and DEHP ranged from 1.6 to 2.9 d and 5.0 to 8.3d, respectively. The addition of yeast extract (5mg/L), hydrogen peroxide (1mg/L), brij 35 (91 μM), humic acid (0.5 g/L), cellulose (0.96 mg/L), and sodium chloride (1%) enhanced PAE aerobic degradation. Sediment samples were separated into fractions with various particle size ranges from 0.1-0.45 to 500-2000 μm. Sediment fractions with smaller particle sizes demonstrated higher PAE biodegradation rates. Of the microorganism strains isolated from the mangrove sediment, strains J2, J4, and J8 (all identified as Bacillus sp.) expressed the best biodegrading ability. Our results showed that Bacillus sp. was the dominant bacteria in the process of PAE aerobic degradation in the mangrove sediments., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Effects of wastewater discharge on radial oxygen loss (ROL), formation of iron (Fe) plaque on root surface, and their correlations in Bruguiera gymnorrhiza (L.) Poir and Excoecaria agallocha L. were investigated. ROL along a lateral root increased more rapidly in control than that in strong wastewater (with pollutant concentrations ten times of that in municipal sewage, 10NW) treatment, but less Fe plaque was formed in control for both plants. For B. gymnorrhiza receiving 10NW, Fe plaque formation was more at basal and mature zones than at root tip, while opposite trend was shown in E. agallocha. At day 0, the correlation between ROL and Fe plaque was insignificant, but negative and positive correlations were found in 10NW and control, respectively, at day 105, suggesting that more ROL was induced leading to more Fe plaque. However, excess Fe plaque also served as a 'barrier' to prevent excessive ROL in 10NW plants., (Copyright (c) 2009 Elsevier Ltd. All rights reserved.)

A greenhouse experiment was conducted to study the partitioning and removal of Cd and Mn from wastewater using constructed mangrove (Kandelia candel) wetland treatment system. Three different strengths of artificial wastewater passed through the system in fixed quantities. Artificial seawater was used as a control. Three different compositions were natural wastewater concentration (C1), medium wastewater concentration (C5) and concentrated wastewater concentrations (C10). C1 had the characteristics and strength similar to natural municipal wastewater while C5 and C10 contained five and ten times of the nutrients and heavy metals in C1, respectively. Results showed that the major portion of the Cd and Mn entering the simulated wastewater treatment system entered the sediment pool where approximately 88% to 95% of the Cd, and between 63% and 89% of Mn, was retained. The amount of added Cd and Mn in the wastewater found in plants were between 0.16% to 1.1%, and 1.7% to 13.9%, respectively. Within the total plant pool, roots accounted for between 30% and 39% of Cd, and from 0.65% to 7.3% of Mn; leaves contained between 19.9% to 30.5% of Cd, and from 7.8% to 41.0% of Mn; litterfall contained 12.3% to 20.6% of Cd, and from 15.2% to 70.3% of Mn, respectively. The averaged accumulative coefficients concentration in plant tissues/concentration in sediment in plant for Cd and Mn were 1.22 to 2.40 and 0.02 to 0.08, respectively. Assimilated Cd and Mn were stored in non-activity plant zones such as cell wall, supplimentary cells of the lenticel, stone cells, cell gaps in root and stem, etc. Kandelia candel seedlings had a relative high toxicity resistance to the two heavy metals.