Macroalgal morphology mediates microplastic accumulation on thallus and in sediments

The accumulation process of microplastics (MPs) is a key to understanding their fate in the environment. However, there is limited information about the short-term accumulation of MPs on macrophytes. The ability of macrophyte to attenuate wave and reduce current velocity is potentially facilitating MPs deposition. We hypothesize that the macroalgae retain MPs with their morphologies (filamentous and non-filamentous) being one of the factors to govern retention. Our hypothesis was tested by field observation during the dry season in Hong Kong when the macroalgae communities were the most diverse. MPs per biomass, surface area, or interstitial volume were used to represent the abundances on macroalgae. We found that filamentous algae retained a 2.35 times higher number of MPs when compared with non-filamentous algae if unit per biomass was considered. Other units, however, showed insignificant differences in MPs abundances between algal morphologies. Fibre was the most dominant shape of MPs with no significant difference in their abundances between filamentous and non-filamentous algae, suggesting fibres were retained regardless of the algal morphologies. To further evaluate the potential accumulation in the environment, sediment samples were also collected under the algal mat and immediate vicinity (~50 cm) of the algal mat. We found that sediment collected under the vegetated area contained significantly higher MPs. This was 3.39 times higher than the unvegetated area. Sediment collected under/near filamentous algae retained much higher abundances of MPs than those of non-filamentous algae. Provided that the observed retention of MPs on macroalgae, we speculate macrophyte system is one of the short-term MPs accumulation hotspots where the temporal increase of MPs depends on the seasonality of macrophyte in a given region.

Do distribution and expansion of exotic invasive Asteraceae plants relate to leaf construction cost in a man-made wetland?

Exotic species especially Asteraceae plants severely invade wetlands in Shenzhen Bay, an important part of the coast wetland in Guangdong-Hong Kong-Macau Bay Area, China. However, the reasons causing their expansion are unclear. The leaf traits and expansion indices of six invasive Asteraceae plants from the Overseas Chinese Town (OCT) wetland were studied and the results showed that nearly 45% of the total plant species (31 out of 69 species) in the OCT wetland, belonging to 15 families and 27 genera, were exotic invasive species. The expansion indices of six Asteraceae species negatively correlated with their leaf construction cost based on mass (CCM), caloric values and carbon concentration, but their relations with ash content were positive. Multiple linear regression analysis revealed that CCM was the most important factor affecting the expansion of an exotic species, indicating CCM may be an important reason causing the expansion of exotic species in coastal wetlands.

Enhanced remediation of BDE-209 in contaminated mangrove sediment by planting and aquaculture effluent

Toxic and persistent flame retardant (BDE-209) and aquaculture effluent (AE) are ubiquitous in coastal environments, but how their co-existence influences their fate is not yet investigated. This study investigated AE effects on remediation and uptake of BDE-209 by Kandelia obovata (Ko) and Avicennia marina (Am), true and dominant mangrove species. After 12-months, a significant removal of BDE-209 was achieved in planted mangrove sediment and the removal was significantly enhanced by AE addition, possibly due to the enhancement of nitrogen (N) and phosphorous (P) content in sediment. Residual percentages of parent BDE-209 in Ko and Am planted sediments without AE were 61.4% and 70.9%, respectively, but decreased to 46.9% and 48.0% with AE addition after 12-months. A similar trend was found in unplanted sediment, with 86.5% and 65.3% of BDE-209 retained in sediments without and with AE addition, respectively. The results demonstrated that AE addition not only increased the debromination of BDE-209 in all treated sediments with the production of debrominated congeners (de-PBDEs) like di- to nona-BDEs in unplanted and planted sediments, but also enhanced the take up of BDE-209 in Ko root, and de-PBDEs in both Ko and Am, thus enhancing the phytoremediation of BDE-209 in contaminated sediments.

Physiological response and oxidative transformation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) by a Chlorella isolate

Polybrominated diphenyl ethers (PBDEs) are ubiquitous, toxic and persistent pollutants in environments. Microalgae frequent exposed to these pollutants may possess defense mechanisms against their toxicity and have the ability to metabolize them, thus are important in bioremediation. This study investigated the mechanism of a Chlorella isolate to degrade BDE-47, a common PBDE congener, and its subcellular responses to BDE-47 stress. Results showed that 86-98% of the spiked BDE-47 was removed by Chlorella via adsorption, uptake and metabolism. BDE-47 was metabolized through debromination, hydroxylation and methoxylation. The oxidative transformation to hydroxylated products was the initial and main metabolic process. BDE-47 induced the production of hydrogen peroxide (H₂O₂) in cell wall, plasma membrane and chloroplast of Chlorella, and such increase was regulated by nicotinamide adenine dinucleotide phosphate oxidase and H₂O₂-producing peroxidases (PODs). The activity of H₂O₂-consuming PODs and the content of glutathione were also significantly enhanced to detoxify the oxidative stress.

Changes of substrate microbial biomass and community composition in a constructed mangrove wetland for municipal wastewater treatment during 10-years operation

Constructed wetlands (CWs) have been used for wastewater treatment for decades, but research on microorganisms involved, especially long-term changes, is still limited. In this study, we evaluated changes in the substrate microbial community in a pilot-scale horizontal subsurface-flow constructed mangrove wetland during 10-years operation. In the 3rd year of operation, microbial biomass carbon and phospholipid fatty acids (PLFAs) reached peak values in two vegetated belts planted with Aegiceras corniculatum (Ac) and Kandelia obovata (Ko), respectively, then stabilized or declined in the 9th and 10th years of operation. PLFA profiles reflecting microbial community compositions varied significantly in the Ac belt during the operation period. Principal component (PCA) and redundancy analyses (RDA) revealed that microbial community compositions were significantly correlated with organic matter content, especially in the 9th and 10th years of operation, implying that the substrate microbial community in constructed mangrove wetland is sensitive to substrate characteristics and can be used as an indicator for long-term performance of CWs.

Barnacles as potential bioindicator of microplastic pollution in Hong Kong

Microplastic (MP) pollution is an emerging problem in the marine environment and the assessment of the presence and abundance of microplastics in wild organisms is essential for risk assessment. The occurrence of microplastics in four species of barnacles at 30 sites in Hong Kong waters was investigated. The median number of microplastics ranged between 0 and 8.63 particles g^-1 wet weight, or 0 and 1.9 particles individual^-1, with fibers being the most abundant type of microplastics. The chemical composition of 152 pieces out of 606 potential microplastics was analyzed using micro-Fourier Transform Infrared Spectroscopy (μ-FTIR). Fifty-two of them were synthetic polymers, 95 natural cotton fibers and five unknowns. Eight types of polymer were identified with cellophane being the most abundant (58%). Correlation analysis was conducted between the abundance of MPs in sediments obtained in our previous study and that in individual barnacle species in this study, and a positive correlation was established for the barnacle Amphibalanus amphitrite, highlighting the potential of using this species as a bioindicator of microplastics.

Is Laguncularia racemosa more invasive than Sonneratia apetala in northern Fujian, China in terms of leaf energetic cost?

Laguncularia racemosa and Sonneratia apetala are fast-growing exotic mangrove species in Southern China and widely used for afforestation. However, the invasiveness of the two exotic species is still unclear. We compared structural and physiological traits and energy-use related traits between L. racemosa and S. apetala, and with two natives (Kandelia obovata and Aegiceras corniculatum) in northern Fujian. Results showed that leaf construction cost based on mass (CCM) and caloric values of L. racemosa were significantly lower than S. apetala, and the two natives had highest CCM. Because lower CCM, L. racemosa grew faster with a taller height (4.83 m) and wider ground diameter circumference (40.03 cm) than S. apetala (4.43 m tall and 35.63 cm wide) and the two natives (2.42 m tall and 26.78 cm wide). These findings indicated that L. racemosa could be more invasive than S. apetala in mangrove forests in northern Fujian, China where it still grew well, which deserves more attention.

Effects of aquaculture effluents on fate of 2,2',4,4',5-pentabromodiphenyl ether (BDE-99) in contaminated mangrove sediment planted with Kandelia obovata

The problems of aquaculture effluent (AE) and polybrominated diphenyl ethers (PBDEs) are common in coastal areas. The fate of 2,2',4,4',5-pentabromodiphenyl ether (BDE-99), a dominant PBDE congener, in mangrove sediments and the effects of AE on it have never been reported. A 12-months microcosm study was conducted and more than 55% of the BDE-99 in contaminated sediment was removed at the end. The removal percentages depended on treatments, with the highest removal in the treatment planted with Kandelia obovata (Ko) and irrigated with AE (WP_AE), followed by Ko planted but without AE (WP), unplanted with AE (NP_AE) and unplanted without AE (NP). Hydroxylation of BDE-99 was observed in all treatments, with a preference in the para position bromine substitution, followed by meta position and the lowest was ortho bromine substitution. BDE-99 was also debrominated to lower brominated congeners like tri- and di-BDEs congeners. Different from parent BDE-99, ortho-substituted BDE-28 and -15 were more dominant than that of para-substituted BDE-17 and -7, suggesting that para-substituted congeners could further be debrominated. The AE addition enhanced root uptake of PBDEs in Ko. These findings suggested that the addition of AE and planting Ko could be an effective way to remedy BDE-99 in contaminated sediments.

Could mangrove plants tolerate and remove BDE-209 in contaminated sediments upon long-term exposure?

Polybrominated diphenyl ethers (PBDEs) such as BDE-209, the commonest congener, are known to be toxic. A 24-months study using mangrove mesocosms with mixed mangrove species, namely Avicennia marina (Am), Aegiceras corniculatum (Ac) and Kandelia obovata (Ko), or without any plant was conducted to examine toxicity, removal, translocation and uptake of BDE-209. At month 24, BDE-209 stimulated the production of root superoxide radical (O₂^-*), and leaf and root malondialdehyde (MDA) of Ko, enhanced leaf O₂^-* of Ac, but did not affect the production of O₂^-* and MDA in Am. These findings indicated that the tolerance to BDE-209 was species-specific, with Am being the most tolerant and Ko the most sensitive species. In leaf and root, BDE-209 stimulated peroxidase (POD) activity in both Ac and Ko, and superoxide dismutase (SOD) in Am. After 24-months, more than 60% and 40% of BDE-209 in contaminated sediments were removed in planted and unplanted groups, respectively, with more PBDEs in upper than bottom sediment layers. This study demonstrates that planting tolerant species such as Avicennia marina with high uptake could remedy PBDEs in contaminated sediments.

Growth and antioxidative response of two mangrove plants to interaction between aquaculture effluent and BDE-99

Mangroves are subject to contamination of polybrominated diphenyl ethers (PBDEs) due to waste and wastewater disposal, and aquaculture effluent (AE) from nearby aquaculture activities. However, the response of mangrove plants to these two stresses and their interaction has seldom been reported. A six-month microcosm study, planted with either Kandelia obovata (Ko) or Avicennia marina (Am), the two most dominant species in South China mangrove swamps, was conducted to investigate the effects of BDE-99, and the interactions of BDE-99 (one of the most abundant PBDE congeners) and AE on growth and physiological responses of these plants. In addition to mixed stressors, both stressors were also applied individually. Results showed that Avicennia was more tolerant to BDE-99 contamination than Kandelia, as reflected by the reduced biomass, but increased superoxide radical (O₂^-⁎) release and malondialdehyde (MDA) content in Kandelia. Addition of AE alleviated toxicity of BDE-99 in Kandelia by promoting biomass but lowering oxidative stress and MDA production. The hormesis model also demonstrated that the interaction between BDE-99 and AE on leaf and root MDA and O₂^-⁎ content in both Kandelia and Avicennia were mostly antagonistic. Activities of catalase (CAT), superoxide dismutase (SOD) and peroxidase (POD) in both leaf and root of Kandelia were reduced by BDE-99. On the contrary, BDE-99 significantly enhanced the three enzyme activities in Avicennia root at month 3. Addition of AE also significantly enhanced root CAT, POD and SOD activities, and leaf SOD in both plant species to remove excess ROS produced under BDE-99 exposure. These results indicated that the tolerance of mangrove plants to oxidative stresses depended on antioxidative enzymes that were inducible.

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

The present study compared accumulation of heavy metals in a mangrove swamp dominated by Kandelia obovata with that by Sonneratia apetala in Pearl River Estuary, China. The results showed that the concentrations of heavy metals at all sediment depths in the S. apetala site were significantly higher than that in K. obovata. The geo-accumulation index and potential ecological risk index also showed that S. apetala sediment had a higher contamination of heavy metals, especially Cd. S. apetala significantly altered the biogeochemical cycles of Cd, lead (Pb), nickel (Ni) and chromium (Cr). In S. apetala sediment, TOC played an important role in sequestering heavy metals as reflected by its positive correlations with Zn and Pb. This study demonstrated the importance of plant species in altering soil quality and heavy metal accumulation, and S. apetala is more efficiently working as a pollution barrier than K. obovata.

Effects of root morphology and anatomy on cadmium uptake and translocation in rice (Oryza sativa L.)

A clear description of the certain mechanisms of cadmium (Cd) uptake and translocation in rice (Oryza sativa L.) may help to reduce Cd accumulation in rice grain. Hydroponic experiments were carried out to determine the effects of cultivation conditions (aerated and stagnant) on the uptake, translocation and subcellular distribution of Cd in relation to the morphology and anatomy of roots in two rice genotypes with different Cd accumulations in grains. Marked differences in morphology and anatomy were observed between these two genotypes under different cultivation conditions. Genotypes with low Cd accumulation in grains tended to develop fewer root tips per root surface area, larger root porosity and more mature apoplastic barriers. The stagnant cultivation condition decreased the number of root tips per root surface area but increased root porosity and accelerated apoplastic barrier formation in root tissues. Correlative Cd uptake studies revealed that rice plants with fewer number of root tips per root surface area reduced root Cd uptake ability, while mature apoplastic barriers increased root Cd retention in cell walls and the symplast. Thus, the fewer number of root tips per root surface area and the earlier formation of mature apoplastic barriers led to lower Cd uptake and translocation. The results indicated that the morphology and anatomy of roots could play important roles in Cd uptake and translocation in rice, and could be influenced by both genotype and cultivation conditions. The present results would be useful in screening and planting rice plants with low Cd accumulation.

Does ammonium nitrogen affect accumulation, subcellular distribution and chemical forms of cadmium in Kandelia obovata?

Heavy metals and nutrients are commonly found in mangrove sediments, but the effect of nutrients on heavy metals in mangrove plants is not clear. A study quantifying the effects of ammonium nitrogen (NH₄⁺-N) on the accumulation, subcellular distribution and chemical forms of cadmium (Cd) in Kandelia obovata seedlings were conducted. The experiment consisted of four levels of NH₄⁺-N (0, 10, 50 and 100 mg L^-1) in each of which consisted of four Cd levels (0, 1, 5 and 10 mg L^-1). The results showed that NH₄⁺-N magnified the Cd toxicity due to reduced plant biomass, especially with 10 mg L^-1 Cd and 100 mg L^-1 NH₄⁺-N supply. NH₄⁺-N, especially at 100 mg L^-1, enhanced the concentration and accumulation of Cd in root but its role on Cd translocation from root to stem and leaf was limited, probably due to low translocation factor. At subcellular level, Cd mainly accumulated in root cell wall but its fractionation depended on Cd levels. Under the stress of 1 and 5 mg L^-1 Cd, 50 mg L^-1 NH₄⁺-N supply improved transfer of Cd from root cell wall into cell, and increased pectate and protein integrated forms of intracellular Cd to alleviate Cd toxicity. Under the stress of 10 mg L^-1 Cd, NH₄⁺-N supply promoted the deposition of Cd on root cell wall to restrain its transfer to root cell, which was verified by the reduced levels of pectate and protein integrated forms of Cd in root cell. Thus, NH₄⁺-N supply improved immobilization of Cd in roots and alleviated Cd toxicity through integration with pectate and protein as well as cell wall combinations in root of K. obovata.

Diversity and Dynamics of Microbial Community Structure in Different Mangrove, Marine and Freshwater Sediments During Anaerobic Debromination of PBDEs

Little is known about the diversity and succession of indigenous microbial community during debromination of polybrominated diphenyl ethers (PBDEs). This study examined the diversity and dynamics of microbial community structure in eight saline (mangrove and marine) and freshwater sediment microcosms exhibiting different debrominating capabilities for hexa-BDE 153, a common congener in sediments, using terminal restriction fragment length polymorphism (T-RFLP) and clone library analyses. The results showed that microbial community structure greatly differed between the saline and freshwater microcosms, likely leading to distinct variations in their debrominating capabilities and pathways. Higher relative abundances of Chloroflexi and Deltaproteobacteria succeed by Alphaproteobacteria and Betaproteobacteria were detected in the two mangrove microcosms with the fastest debrominating capabilities mainly via para pathway, respectively; the dominance of Alphaproteobacteria resulted in less accumulation of tetra-BDEs and more complete debromination of lower brominated congeners (from di- to tetra-BDEs). Meanwhile, the shifts in both microbial community structure and PBDE profiles were relatively small in the less efficient freshwater microcosms, with relatively more ortho and meta brominated products of BDE-153 resulted. Coincidently, one of the freshwater microcosms showed sudden increases of Chloroflexi and Deltaproteobacteria by the end of incubation, which synchronized with the increase in the removal rate of BDE-153. The significant relationship between microbial community structure and PBDEs was confirmed by redundancy analysis (18.7% of total variance explained, P = 0.002). However, the relative abundance of the well-known dechlorinator Dehalococcoides showed no clear correlation with the debrominating capability across different microcosms. These findings shed light in the significance of microbial community network in different saline environments on enhancement of PBDE intrinsic debromination.

Glutathione-Ascorbate Cycle Is an Early Warning Indicator of Toxicity of BDE-47 in Mangroves

Mangroves are often exposed to contamination by polybrominated diphenyl ethers (PBDEs) from wastewater discharges and solid waste dumping. As one of the most prevalent and toxic PBDE congeners in the environment, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and its oxidative stress deserves more attention. In plants, the glutathione-ascorbate (GSH-AsA) cycle plays an important role in the defensive processes against oxidative stress. However, the importance of this cycle in mangroves to defend against PBDE toxicity has not been reported. We conducted a study to evaluate the effects of BDE-47 on GSH-AsA cycle-related antioxidants in a mangrove species, namely Sheue, H.Y. Liu & J. Yong. An 8-wk hydroponic culture experiment was conducted with 1-yr-old seedlings of exposed to five levels of BDE-47 contamination. At the two high BDE-47 levels (5 and 10 mg L), seedling growth, expressed as dry biomass of leaves and roots, was suppressed from Weeks 4 to 8. Parameters in the GSH-AsA cycle in roots and leaves changed significantly within the first week after exposure, indicating that they were more sensitive indicators to BDE-47 toxicity than growth. The suppression of seedling growth, expressed as final biomass production, at the end of the 8-wk experiment was positively correlated to the antioxidative responses in the first week, confirming the indicative roles of these antioxidants. This is the first study to demonstrate that GSH-AsA cycle-related antioxidants in mangrove plants are sensitive indicators of BDE-47 toxicity. These antioxidants, in particular, ascorbate and glutathione peroxidase, could provide early warning of the toxicity of PBDEs.

The uptake of mixed PAHs and PBDEs in wastewater by mangrove plants under different tidal flushing regimes

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.

Antioxidative response of Kandelia obovata, a true mangrove species, to polybrominated diphenyl ethers (BDE-99 and BDE-209) during germination and early growth

A 3-months microcosm experiment with mangrove sediment spiked with PBDEs and planted with propagules of Kandelia obovata was conducted to investigate PBDE toxicity and antioxidative responses of the germinated seedlings. BDE-99 suppressed germination rate, leaves formation and growth of mangrove seedlings. The leaves and roots of BDE-99 treated seedlings had significantly higher superoxide (O₂^-) release, malondialdehyde (MDA) and total polyphenol (TP) content, and peroxidase (POD) activity than the control. BDE-209 increased activities of all three antioxidative enzymes, catalase (CAT), POD and superoxide dismutase (SOD) in roots, but in leaves, only CAT activity was stimulated. The MDA content of BDE-209 treated seedlings was less than the control. PBDEs were found in plant tissues of the treated seedlings. These results indicated that even though PBDEs were taken up in tissues, K. obovata, due to its antioxidative defense enzymes, could tolerate PBDEs and could be used for the bioremediation of PBDE-contaminated environments.

Temporal variations in physiological responses of Kandelia obovata seedlings exposed to multiple heavy metals

A study was conducted to quantify temporal variations in physiological responses of Kandelia obovata under multiple heavy metal stress. The results showed that plant growth was not significantly affected by multiple heavy metal stress during the 120-days experiment. At the start, levels of net photosynthetic rate (P_n), stomatal conductance (G_s) and transpiration rate (T_r) showed effects of "low-promotion, high-inhibition", but P_n and G_s reduced with increasing heavy metal stress at the end. Temporary lipid oxidation was shown by high levels of malondialdehyde (MDA) under high heavy metal stress at the start but was unaffected at the end of the experiment. MDA negatively correlated with biomass and photosynthetic parameters and acted as a sensitive indicator. Proline also shared similar trend and indicated its temporary role in osmotic adjustment. Negative correlations between osmotic adjustment matter and photosynthetic parameters further confirmed the significant role of osmotic adjustment under heavy metal stress.

Removal of decabromodiphenyl ether (BDE-209) using a combined system involving TiO2 photocatalysis and wetland plants

There is a rising concern about the capability of sewage treatment works in treating emerging chemicals, such as polybrominated diphenyl ethers (PBDEs). A combined photocatalysis (TiO₂ and visible light) and constructed wetland system (planted with Oryza sativa (rice cultivar: Hefengzhan) and Phragmites australis (common reed)) was designed to study PBDEs removal efficiencies. After the pre-treatment in TiO₂ suspension, the artificially BDE-209 spiked sewage (78.2 and 782nmol/L) was discharged into the sub-surface flow constructed wetland tanks planted with rice and common reed, respectively. The treated sewage, soil, plant roots, shoots, rice grains and hulls were collected and analyzed for PBDEs by GC-MS. The removals of BDE-209 in the combined systems (93.6±2.19% (78.2nmol/L) and 92.1±1.11% (782nmol/L)) were significantly higher than those in the photocatalytic systems (56.3±5.78% (78.2nmol/L) and 54.7±9.47% (782nmol/L)), which could be explained by the enhanced biodegradability of PBDEs in photocatalysis, led to its better dissipation by rice plants. Therefore, this combined system might help to degrade BDE-209 in the wastewater effluent, reducing its potential entry into aquatic food chains.

Uptake and transport mechanisms of decabromodiphenyl ether (BDE-209) by rice (Oryza sativa)

The extensive industrial use of brominated flame retardants has aroused rapidly growing public concerns about their ubiquity in the environment. The feasibility of uptake and translocation of decabromodiphenyl ether (BDE-209) by three rice cultivars, namely Fengmeizhan, Hefengzhan and Guangyinzhan, and the uptake mechanisms of BDE-209 into rice roots, were investigated by employing a partition-limited model. Uptake of BDE-209 by the rice cultivars (Fengmeizhan, Hefengzhan and Guangyinzhan) was examined by a 60-day cultivation in sterilized BDE-209 spiked sand, followed by Soxhlet extraction and gas chromatography-mass spectrometry (GC-MS) analysis. A partition-limited model was applied for estimating and describing the approach of the uptake of BDE-209 by rice in sand. The average quasi-equilibrium factor (αpt) of BDE-209 in root uptake in sand was 0.112×10(-3) for three rice cultivars in the present study (<1), implying a non-equilibrium movement of molecules and a dominated passive transport uptake. According to the results of sorption analysis of dead and fresh roots, apoplastic pathway likely dominated the transport of BDE-209 into roots cells.

Effects of salinity on anatomical features and physiology of a semi-mangrove plant Myoporum bontioides

The effect of different concentrations of NaCl, 0, 100, 200, 300 and 400 mM, on the anatomical features and physiology of Myoporum bontioides was investigated. The photosynthetic rates (Pn) were significantly reduced by salt stress, with the lowest values at 400 mM NaCl. The content of malondialdehyde (MDA), proline and soluble sugar, as well as the activities of peroxidase (POD) and catalase (CAT) increased at the beginning, but became similar to the control as the experiment proceeded. The NaCl effect on superoxide dismutase (SOD) was different from the other parameters, with a significant reduction at 400 mM NaCl at Day 7. Salt glands were found in both upper and lower epidermis, and the ratios of the thickness of palisade to spongy mesophyll tissues increased with NaCl concentrations. The medullary ray was clearly damaged by NaCl at levels of 200 and 300 mM. These results demonstrated that M. bontioides could adapt to a relatively low salinity, and was not a halophilous species.

Effect of a polybrominated diphenyl ether congener (BDE-47) on growth and antioxidative enzymes of two mangrove plant species, Kandelia obovata and Avicennia marina, in South China

The effects of BDE-47 on the growth and antioxidative responses of the seedlings of Kandelia obovata (Ko) and Avicennia marina (Am) were compared in an 8-week hydroponic culture spiked with different levels of BDE-47, 0.1, 1, 5 and 10 mg l(-1). The two highest BDE-47 levels significantly suppressed the growth and increased the activities of three antioxidative enzymes, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), of Ko in week 1. However, SOD and POD activities at high levels of BDE-47 became lower than the control in week 8. On the contrary, growth of Am was not affected at all contamination levels, and the activities of three enzymes were enhanced by BDE-47 in weeks 1 and 4, but such stimulatory effect became insignificant in week 8. Avicennia was more tolerant to BDE-47 toxicity than Kandelia, as its antioxidative enzymes could better counter-balance the oxidative stress caused by BDE-47.

Structure and function of soil microbial community in artificially planted Sonneratia apetala and S. caseolaris forests at different stand ages in Shenzhen Bay, China

The present study examined the relationships between soil characteristics, microbial community structure and function in the forests artificially planted with exotic Sonneratia apetala at stand ages of 1-, 2-, 7-, 10- and 14-years and Sonneratia caseolaris of 1-, 4-, 7-, 10- and 14-years in Futian National Nature Reserve, Shenzhen Bay, China. The 7-years old forests of both Sonneratia species reached peak growth and had the highest content of nitrogen and phosphorus, enzymatic activities, including dehydrogenase, cellulase, phosphatase, urease and ß-glucosidase, except arylsulphatase which increased continuously with stand ages. The microbial community structure reflected by phospholipid fatty acid (PLFA) profiles also reached the maximum value in the 7-years old forests and soil bacterial PLFAs in both forests were significantly higher than fungal PLFAs. The canonical correlation analysis revealed that differences in microbial structural variables were significantly correlated to the differences in their functional variables, and the highest correlation was found between the soil enzymatic activities and the content of carbon and nitrogen.

Cr(III) removal by a microalgal isolate, Chlorella miniata: effects of nitrate, chloride and sulfate

In the present study, nitrate, chloride and sulfate anion systems were used to investigate the presence of anions on the removal of Cr(III) by Chlorella miniata. Kinetic studies suggested that the equilibrium time of Cr(III) biosorption was not affected by the presence of different sodium salts, even at the concentration of 1.0 M, and all reached equilibrium after 24 h. Equilibrium experiments showed that the effects of different anions on Cr(III) biosorption varied, and the inhibitory order was SO4 (2-) > Cl(-) > NO3 (-). Langmuir isotherm indicated that the maximum sorption capacity of C. miniata increased with the increase of pH under different anion systems. The strongest inhibition effect of the sulfate system was attributed to the formation of Cr(OH)SO4 aq. and the decrease of Cr(OH)(2+) and Cr(3+) in solution, while the difference of inhibitory effect in the other two anion systems could be accounted by the formation of the inner-sphere surface complex in the nitrate system and the outer-sphere surface complex in the chloride system. The present study suggested that the presence of anions greatly affected the removal of Cr(III) on C. miniata and thereby their transport in the environment.

Root exudates of wetland plants influenced by nutrient status and types of plant cultivation

The present study investigated the amounts of root exudates and composition of organic acids released from two wetland plants (Typha latifolia and Vetiver zizanioides) under two nutrient treatments: low level (0.786 mM N and 0.032 mM P) and high level (7.86 mM N and 0.32 mM P) and two types of plant cultivation: monoculture and co-culture of the two plants. Low nutrient treatment significantly (p < 0.05) increased the root exudates of T. latifolia during the initial growth period (1-21 d) and those of V. zizanioides and the co-culture during the whole growth period. The concentrations of dissolved organic carbon in the root exudates of the co-culture in the low nutrient treatment were 3.23-7.91 times of those in the high nutrient treatment during the medium growth period (7-28 d). The compositions of organic acids varied between the two plant species and between the two nutrient treatments. The pattern of organic acids was also different between the co-culture and the monoculture. Oxalic acid was by far the major organic acid exuded from the two wetland plants. The present study on root exudates suggests that co-culture of wetland plant species would be more useful in the reclamation of waste water than a monoculture system.

Characterizing the optimal operation of photocatalytic degradation of BDE-209 by nano-sized TiO2

Brominated flame retardants have been widely used in industry. There is a rapid growing public concern for their availabilities in the environment. Advanced oxidation process (AOP) is a promising and efficient technology which may be used to remove emerging chemicals such as brominated flame retardants. This study aims at investigating optimal operational conditions for the removal of BDE-209 using nano-scaled titanium(IV) oxide. The residual PBDE congeners after photocatalytical degradation of BDE-209 by TiO2 were analysed by gas chromatography-mass spectrometry (GC-MS). It was found that the degradability of BDE-209 by TiO2 was attributed to its photocatalytic activity but not the small size of the particles. The half-life of removing BDE-209 by TiO2 was 3.05 days under visible light. Tetra- and penta-BDEs were the major degraded products of BDE-209. Optimum conditions for photocatalytical degradation of BDE-209 was found to be at pH 12 (93% +/- 1%), 5, 10, 20 mg/L (93.0% +/- 1.70%, 91.6% +/- 3.21%, 91.9% +/- 0.952%, respectively), respectively of humic acid and in the form of anatase/rutile TiO2 (82% +/- 3%). Hence, the efficiency of removing BDE-209 can be maximized while being cost effective at the said operating conditions.

Removal and biodegradation of nonylphenol by immobilized Chlorella vulgaris

The removal and biodegradation of nonylphenol (NP) by alginate-immobilized cells of Chlorella vulgaris were compared with their respective free cultures. The effects of four cell densities of 10(4) per algal bead were investigated, as were the four algal bead concentrations, with regard to the removal and biodegradation of NP. Although immobilization significantly decreased the growth rate and NP's biodegradation efficiency of C. vulgaris, NP removal over a short period was enhanced. The NP removal mechanism by immobilized cells was similar to that by free cells, including adsorption onto alginate matrix and algal cells, absorption within cells and cellular biodegradation. The optimal cell density and bead concentration for the removal and biodegradation of NP was 50-100×10(4) cells algal bead(-1) and 2-4 beads ml(-1) of wastewater, respectively. These results demonstrated that immobilized C. vulgaris cells under optimal biomass and photoautotrophic conditions are effective in removing NP from contaminated water.

Formation of iron plaque on mangrove roots receiving wastewater and its role in immobilization of wastewater-borne pollutants

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.

Modeling sorption and biodegradation of phenanthrene in mangrove sediment slurry

A mathematical model, combining both sorption and biodegradation process, was developed to predict the biodegradation of phenanthrene by Sphingomonas sp. in different sediment slurries. The model includes two sorption parameters, α (the partition coefficient) and 1/K (the diffusion resistance); a kinetic parameter k (the first order rate constant); and a sediment parameter, A(V) (the specific sediment surface area in unit volume of slurry). These parameters were evaluated and verified in three types of sediment slurry systems (namely sandy clay loam Ho Chung sediment with fastest degradation, sandy Kei Ling Ha sediment with medium degradation, and clay Mai Po sediment with slowest degradation) at different initial phenanthrene concentrations. High R(2) values, ranging from 0.935 to 0.969, were obtained. Based on this integrated sorption-biodegradation model, the phenanthrene biodegradation in any sediment slurry could be predicted as long as the parameters of the specific sediment surface area in unit volume of slurry, total organic carbon and clay content were measured.

Effects of environmental stresses on the responses of mangrove plants to spent lubricating oil

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.

Microbial community dynamics and biodegradation of polycyclic aromatic hydrocarbons in polluted marine sediments in Hong Kong

Dynamics of microbial community and biodegradation of polycyclic aromatic hydrocarbons (PAHs) in polluted marine sediments, artificially spiked with a mixture of PAHs (fluorene, phenanthrene, fluoranthene and pyrene), were examined for a period of 60 days. Microbial communities were characterised by bacterial counts, ester-linked fatty acid methyl ester (EL-FAME) analysis and denaturing gradient gel electrophoresis (DGGE). A noted reduction in species diversity occurred only in the high PAH level treatment at onset. Both EL-FAME and DGGE demonstrated a marked shift in microbial community, in all the PAH level treatments, afterwards, with increases in the number of fatty acid degraders, the relative abundance of fatty acid biomarkers for gram-negative bacteria and a decrease in species diversity. The shift was also accompanied by the significant decrease in PAH concentrations. By the end of the experiment, diversity indices, based on both approaches, recovered when PAH concentrations declined to their background levels, except in the high PAH level treatment.

Temporal changes of polyphenols and enzyme activities in seedlings of Kandelia obovata under lead and manganese stresses

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.

Responses of bioaugmented ryegrass to PAH soil contamination

The physiological and biochemical responses of ryegrass (Lolium multiflorum) to PAH induced stress in soils contaminated with phenanthrene and pyene were investigated, in the presence of PAH-degrading bacteria (Acinetobacteria junii) or arbuscular mycorrhizal fungi (AM fungi, Glomus mossae). The parameters monitored included chlorophyll content, chlorophyll a/b ratio, soluble-carbohydrate content, soluble-protein, malondialdehyde and electrolyte leakage, and superoxide dismutase (SOD) and peroxidase (POD) activities. Ryegrass showed good resistance and acclimation to PAH stress in soil, however, PAH contamination resulted in adverse effects such as damage of photosynthetic function and acceleration of shoot senescence. At PAH level of 100 mg kg(-1), chlorophyll contents were 14% lower than control (no PAH). Activities of SOD and POD were more sensitive indicators of PAH stress as compared to other parameters. However, all parameters showed trends based on either the bioaugmentation of the plants or PAH treatment level. It was concluded that the inoculation of AMF and PAH-degrading bacteria, especially the former, have a positive effect on alleviation of PAH toxicity to ryegrass plants. Furthermore, the inoculation of AMF increased the shoot and biomass of ryegrass by 11-19% and 18-78%, respectively. Bioaugmented ryegrass plants show promise as a host plants in the phytoremediation of PAH contaminated soils.

Removal and biodegradation of nonylphenol by different Chlorella species

All four Chlorella species, including one commercially available species, Chlorella vulgaris and three local isolates, Chlorella sp. (1 uoai), Chlorella sp. (2f5aia) and Chlorellaminiata (WW1), had a rapid and high ability to remove nonylphenol (NP). Among these species, C. vulgaris had the highest NP removal (nearly all NP was removed from the medium) and degradation abilities (more than 80% of NP was degraded) after 168 h, followed by WW1 and 1 uoai; 2f5aia had the lowest NP degradation ability. The NP removal by C. vulgaris was less affected by growth conditions, but its biodegradation efficiency was significantly increased by temperature and light intensity, suggesting that the biodegradation ability was positively related to photosynthetic and metabolic activities. These results indicated that C. vulgaris was the most suitable species for effective removal and biodegradation of NP, especially under 25 °C with light illumination and initial biomass between 0.5 and 1.0 mg chlorophyll l(-1).

Growth, photosynthesis and antioxidant responses of two microalgal species, Chlorella vulgaris and Selenastrum capricornutum, to nonylphenol stress

The effect of nonylphenol (NP) on growth, photochemistry and biochemistry of two green microalgae, Chlorella vulgaris and Selenanstrum capricornutum, and their ability to degrade NP were compared. The 96 h EC50 of C. vulgaris and S. capricornutum were greater than 4.0 and 1.0 mg L(-1) NP, respectively, suggesting that the former species was more tolerant to NP. Both microalgae acclimated to NP stress through down-regulating their photosynthetic activities, including antenna size (chlorophyll a content), maximal photochemistry (Fv/Fm) and the light absorbed by PSII (ABS/CS0), but the dissipation of energy from reaction centres (DI0/RC) increased with the increase of NP concentrations. In C. vulgaris, the changes of these parameters were more significant than in S. capricornutum and recovered completely after a 96 h exposure. The antioxidant responses, such as GSH content, CAT and POD activities in C. vulgaris increased with the increase of NP concentrations after a 24h exposure, but these changes disappeared with exposure time and recovered to the control levels after 96 h. In S. capricornutum, although GSH content, CAT and POD activities also increased when exposed to low- to moderate-NP concentrations, these values were significantly reduced at a high concentration (4 mg L(-1)) even after a 96 h exposure, indicating its antioxidant responses were significantly delayed. It is clear that the more NP-tolerant species, C. vulgaris, acclimated better with a faster recovery of its photosynthetic activity from the NP-induced damage, and exhibited more efficient and rapid responses to NP-induced oxidative stress. C. vulgaris also had a higher NP degradation ability than S. capricornutum.

Dose and accumulative effects of spent lubricating oil on four common mangrove plants in South China

The growth of four mangrove species seedlings, namely Bruguiera gymnorrhiza, Kandelia obovata, Aegiceras corniculatum and Acanthus ilicifolius in sediments contaminated by spent lubricating oil, even at the lowest oil dose (2.5 L m(-2)), showed different degrees of sub-lethal damages. All the seedlings of K. obovata and A. corniculatum were killed at 10 L m(-2) oil, while the lethal oil dose was 15 L m(-2) for A. ilicifolius seedlings. B. gymnorrhiza was the most tolerant species to oil pollution, which could survive under the highest oil dose treatment (15 L m(-2)). Biochemical responses including superoxide radical (O(2)(-)) release, superoxide dismutase (SOD) activity and malonyldialdehyde (MDA) content in both leaves and roots of the oil-treated seedlings were increased significantly with oil dose, and presented a positive relationship with leaf and root biomass.

Effect of wastewater discharge on root anatomy and radial oxygen loss (ROL) patterns of three mangrove species in southern China

The effects of wastewater discharge on radial oxygen loss (ROL) and root anatomy varied among mangrove species. ROL of Bruguiera gymnorrhiza (L) increased from 22.44 ng cm(-2) min(-1) in the control (just fresh water) to 31.09 ng cm(-2) min(-1) when received normal wastewater (NW) and to 44.22 ng cm(-2) min(-1) when treated with strong wastewater (10NW). However, discharge of both NW and 10NW caused 28% decreases of ROL in the root tip of Excoecaria agallocha L., and the decreases in Acanthus ilicifolius L were even more significant, with 45% when treated by 10NW The changes of ROL were related to the root anatomy. Among three species, A. ilicifolius had the highest proportional cross-sectional area of aerenchyma air spaces, suggesting that the internal oxygen transfer to root tip was the fastest. However, the area of aerenchyma air spaces in the root tip of 10NW treated A. ilicifolius was significantly reduced while area of epidermis and hypodermis (E + H) increased leading to less oxygen supply to root tip. Compared to B. gymnorrhiza and E. agallocha, the (E + H) layer of A. ilicifolius was the thinnest, and the cells without suberized walls were loosely packed in all three treatments. These results suggested that the root anatomy and ROL of B. gymnorrhiza was least affected by wastewater discharge, followed by E. agallocha, and A. ilicifolius was the most susceptible species thus was not suitable for treating strong wastewater.

Cellular responses, biodegradation and bioaccumulation of endocrine disrupting chemicals in marine diatom Navicula incerta

The cellular responses, biodegradation and bioaccumulation of four endocrine disrupting chemicals, including nonylphenols (NPs), bisphenol A (BPA), 17alpha-ethynylestradiol (EE2), and estradiol (E2), in the marine diatom Navicula incerta, were investigated through the 96-h exposure test. The 50% effective concentration (EC(50)) values in the algal growth inhibition test for NPs, BPA, EE2 and E2 were 0.20mgL(-1), 3.73mgL(-1), 3.21mgL(-1) and >10mgL(-1), respectively. With the increase of test concentrations, the cellular contents of polysaccharides and protein were reduced but the lipid content was increased, while the levels of chlorophyll a and total chlorophyll c were not affected by target EDCs. The activities of superoxidase dismutase and glutathione-S-transferase were stimulated by EDCs. The activities of peroxide dismutase were inhibited by NPs, BPA, and EE2, but were enhanced by E2. The bioaccumulation and biodegradation of target EDCs were inhibited with the increasing exposure concentrations. Nevertheless, the toxic and inhibitory effects of these EDCs on the diatom at their environmental relevant concentrations were relatively low. At the environmental relevant concentration (0.001mgL(-1)), 20.69% of NPs, 37.78% of BPA, 31.26% of EE2 and 52.26% of E2 were removed from the seawater in 96h via biodegradation, and the respective 96-h bioconcentration factor (BCF) values were 2077, 261, 470, and 39. These results showed that among the four target EDCs, NPs would be most problematic as reflecting by their low biodegradation and high BCF in the diatom, suggesting that the NPs would accumulate within the algal cell and pose threats to organisms at higher tropic levels, especially the larvae feeding on the diatom.

Summer fluxes of atmospheric greenhouse gases N2O, CH4 and CO2 from mangrove soil in South China

The atmospheric fluxes of N(2)O, CH(4) and CO(2) from the soil in four mangrove swamps in Shenzhen and Hong Kong, South China were investigated in the summer of 2008. The fluxes ranged from 0.14 to 23.83 micromol m(-2)h(-1), 11.9 to 5168.6 micromol m(-2)h(-1) and 0.69 to 20.56 mmol m(-2)h(-1) for N(2)O, CH(4) and CO(2), respectively. Futian mangrove swamp in Shenzhen had the highest greenhouse gas fluxes, followed by Mai Po mangrove in Hong Kong. Sha Kong Tsuen and Yung Shue O mangroves in Hong Kong had similar, low fluxes. The differences in both N(2)O and CH(4) fluxes among different tidal positions, the landward, seaward and bare mudflat, in each swamp were insignificant. The N(2)O and CO(2) fluxes were positively correlated with the soil organic carbon, total nitrogen, total phosphate, total iron and NH(4)(+)-N contents, as well as the soil porosity. However, only soil NH(4)(+)-N concentration had significant effects on CH(4) fluxes.

The role of radial oxygen loss and root anatomy on zinc uptake and tolerance in mangrove seedlings

Root anatomy, radial oxygen loss (ROL) and zinc (Zn) uptake and tolerance in mangrove plants were investigated using seedlings of Aegiceras corniculatum, Bruguiera gymnorrhiza and Rhizophora stylosa. The results revealed that B. gymnorrhiza, which possessed the 'tightest barrier' in ROL spatial patterns among the three species studied, took up the least Zn and showed the highest Zn tolerance. Furthermore, zinc significantly decreased the ROL of all three plants by inhibition of root permeability, which included an obvious thickening of outer cortex and significant increases of lignification in cell walls. The results of SEM X-ray microanalysis further confirmed that such an inducible, low permeability of roots was likely an adaptive strategy to metal stress by direct prevention of excessive Zn entering into the root. The present study proposes new evidence of structural adaptive strategy on metal tolerance by mangrove seedlings.

Using orthogonal design to determine optimal conditions for biodegradation of phenanthrene in mangrove sediment slurry

In the present paper, the effects of four factors, each at three levels, on biodegradation of phenanthrene, a 3-ring PAH, in contaminated mangrove sediment slurry were investigated using the orthogonal experimental design. The factors and levels were (i) sediment types (clay loam, clayey and sandy); (ii) different inoculums (Sphingomonas sp., a mixture of Sphingomonas sp. and Mycobacterium sp., and without inoculum); (iii) presence of other PAHs (fluorene, pyrene, and none); and (iv) different salinities (5, 15 and 25 ppt). Variance analysis based on the percentages of Phe biodegradation showed that the presence of other PAHs had little effect on phenanthrene biodegradation. The kinetics of phenanthrene biodegradation in all experiments was best fitted by the first order rate model. The highest first order rate constant, k value was 0.1172 h(-1) with 97% Phe degradation; while the lowest k value was 0.0004 and phenanthrene was not degraded throughout the 7-d experiment. The p values of k for the four factors followed the same trend as that for the biodegradation percentage. Difference analysis revealed that optimal phenanthrene biodegradation would take place in clay loam sediment slurry at low salinity (5 to 15 ppt) with the inoculation of both Sphingomonas sp. and Mycobacterium sp.

Effects of wastewater discharge on formation of Fe plaque on root surface and radial oxygen loss of mangrove roots

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.

Analysis and occurrence of typical endocrine-disrupting chemicals in three sewage treatment plants

Seven typical endocrine-disrupting chemicals (EDCs), including bisphenol A (BPA), 4-tert-octylphenol (OP), estrone (E1), estradiol (E2), 17α-estradiol (17α-E2), estriol (E3) and 17α-ethinylestradiol (EE2) in wastewater, were simultaneously determined with gas chromatography-mass spectrometry (GC-MS). Samples, including influents, effluents and wastewater of different unit processes, were taken seasonally from three different sewage treatment plants. The result showed that BPA and EE2 were the two main types of EDCs in all the samples. The average concentration of BPA were in the range of 268.1-2,588.5 ng l⁻¹ in influents and 34.0-3,099.6 ng l⁻¹ in effluents, while EE2 ranging from 133.1 to 403.2 ng l⁻¹ and from 35.3 to 269.1 ng l⁻¹, respectively. Seasonal change of EDCs levels in effluents was obvious between wet season and dry season. Besides, BPA and E3 could be effectively removed by the biological treatment processes (oxidation ditch and A²/O) with the unit removal of 64-91% and 63-100% for each compound, while other five EDCs had moderate or low removal rates. The study also proved that physical treatment processes, including screening, primary sedimentation and pure aeration, had no or little effect on EDCs removal.

Mixed heavy metals tolerance and radial oxygen loss in mangrove seedlings

The effects of a mixture of heavy metals (Pb, Zn and Cu) on growth, radial oxygen loss (ROL) and the spatial pattern of ROL were investigated in mangrove seedlings of three species: Aegiceras corniculatum, Avicennia marina and Bruguiera gymnorrhiza. Heavy metals inhibited the growth of seedlings and led to decreased ROL and changes in the "tight" barrier spatial pattern of ROL. There was a significant positive correlation between the amount of ROL from the roots of seedlings and metal tolerance. The species with the highest ROL amount, B. gymnorrhiza, were also the most tolerant to heavy metals. The "tight" barrier spatial ROL pattern was also related to metal tolerance in the seedlings. Therefore, we conclude that both ROL amount and "tight" barrier spatial ROL pattern in the roots of the mangrove seedlings play an important role in resistance to heavy metal toxicity.

Static and dynamic sorption of phenanthrene in mangrove sediment slurry

The static and dynamic sorption of phenanthrene (Phe) in three types of mangrove sediment slurries (sandy, silty and muddy) were described by three models, namely linear model, Freundlich adsorption isotherm model and Langmuir adsorption isotherm model. The Freundlich adsorption isotherm was the best model to describe the static sorption behavior of Phe in mangrove sediment slurry with the regression coefficients ranging from 0.96 to 0.99. In static sorption, the sorption capacity and sorption intensity were reduced with the inoculation of Sphingomonas, a PAH-degrading bacterial isolate, suggesting that the inoculum even though inactive and/or dead would enhance bioavailability of Phe. On the other hand, the static sorption of Phe was significantly enhanced at high salinity (20ppt) while no difference was found at low salinities ranging from 5 to 15ppt. During the dynamic sorption process, i.e. with biodegradation by indigenous microorganisms and the inoculation of Sphingomonas, linear regression was the most suitable model to describe Phe sorption behavior. The partition coefficient alpha was the highest in silty sediment, followed by sandy sediment and the muddy sediment had the lowest value. These results indicated that the sorption behavior of Phe changed from non-linear to linear when biodegradation took place and the silty mangrove sediment slurry had the highest sorption affinity.

Effects of humic acid on solubility and biodegradation of polycyclic aromatic hydrocarbons in liquid media and mangrove sediment slurries

The effects of humic acid (HA) on the solubility and biodegradability of mixed polycyclic aromatic hydrocarbons (PAHs) (phenanthrene (PHE), pyrene (PYR), and benzo[a]pyrene (BAP)) in liquid media and mangrove sediment slurries were investigated. The addition of HA to the liquid media (0-1.6%, w/v) significantly enhanced the solubility of all mixed three PAHs and the biodegradation of PHE and PYR (but not BAP) by MP-PYR1, a PYR-degrading bacterium isolated from mangrove sediment. Amendment with 0.2% HA to the sediment slurries exhibited little enhancement in either PAH solubility or degradation. Although amendment with 1.6% HA increased the aqueous phase PAHs in the sediment slurries, it did not have any significant enhancement effect on biodegradation. Natural attenuation of PHE in sediment was evident, with 91% degraded after 7 d. The highest biodegradation of PHE and PYR was found in the sediment slurries inoculated with MP-PYR1, and the degradation efficiency was even higher than that in the liquid media (99% vs. 85% for PHE and 97% vs. 63% for PYR). The degradation capacity of MP-PYR1 for both PHE and PYR was comparable when it was inoculated to the sterile and non-sterile sediment slurries, implying that the inoculum was able to compete with the indigenous microorganisms. The reason why BAP was not degraded in either liquid media or mangrove sediment slurries was more likely due to the lack of degraders than its low solubility. These results suggested that the success of PAH degradation did not rely solely on the amounts of soluble PAHs which could be enhanced by the HA amendment; the presence of a suitable degrader was also important.

Toxicity of bisphenol A and its bioaccumulation and removal by a marine microalga Stephanodiscus hantzschii

The toxicity of bisphenol A (BPA) to Stephanodiscus hantzschii, a diatom isolated from tidal water of Futian Mangrove Nature Reserve, China, and the bioaccumulation and removal capability of the marine microalga to BPA were investigated in the present study. Toxicity experiments showed that the 96-h EC50 of BPA was 8.65+/-0.26 mg/L, and the cell number and chlorophyll a content of S. hantzschii decreased significantly with increases in BPA at concentrations higher than 3.00 mg/L. S. hantzschii had high removal capability at low BPA concentrations as BPA was bioaccumulated and biodegraded by cells. After 16-day treatment, 88%, 99%, 92%, 61%, 48%, 28% and 26% of BPA were removed by the diatom in the media supplemented with 0.01, 0.10, 1.00, 3.00, 5.00, 7.00 and 9.00 mg/L BPA, respectively. The present study demonstrated that S. hantzschii was a tolerant isolate that could be used to remove BPA from contaminated waters.

Effects of anion species and concentration on the removal of Cr(VI) by a microalgal isolate, Chlorella miniata

The presence of nitrate, chloride and sulfate anions on the removal of Cr(VI) by Chlorella miniata was investigated. Results of kinetic studies indicated that the equilibrium time in each anion system increased with increases of the initial salt concentration, and the inhibitory order was NO(3)(-)>Cl(-)>SO(4)(2-) for Cr(VI) removal and was SO(4)(2-)>Cl(-) approximately NO(3)(-) for the biosorption of the bioreduced Cr(III). The inhibitory effect caused by different anions was attributed to biosorption mechanism and metal speciation. Since both biosorption and bioreduction were involved in Cr(VI) removal, the presence of anions could compete with Cr(VI) for the adsorption sites, and the affinity of anions to the algal biomass followed the order of NO(3)(-)>Cl(-)>SO(4)(2-), which was consistent with their inhibitory order on Cr(VI) removal. Speciation results also indicated that the formation of CrO(3)SO(4)(2-) in the sulfate system made it easier to be adsorbed on the biomass than HCrO(4)(-). The biosorption-bioreduction model further suggested that the bioreduction rate constant k decreased with increases of anion concentrations ranging from 0 to 0.5M, and followed the order of SO(4)(2-)>Cl(-)>NO(3)(-). The biosorption constant b also decreased with anion concentrations in the range of 0-0.2M, suggesting that this parameter was more sensitive to anion effects than the k values. The higher b values in the sulfate than in the nitrate and chloride systems indicated that Cr(VI) in the sulfate system was more easily adsorbed on the algal biomass. These findings demonstrated that the presence of anions significantly affected the removal of Cr(VI) by C. miniata. Since chloride, nitrate and sulfate ions are commonly found in industrial wastewater, it may be necessary to eliminate these ions prior to chromium removal.

Feasibility of using microalgal biomass cultured in domestic wastewater for the removal of chromium pollutants

The feasibility of obtaining and using the biomass of a microalga, Chlorella miniata, from domestic wastewater (DW) cultures for the removal of chromium(III) [Cr(III)] and chromium(VI) [Cr(VI)] was compared with that from commercial Bristol medium (BM). Results showed that Chlorella miniata cultured in DW under 16-8 hours light-dark cycle [DW(16-8)] had similar growth to that in BM [BM(16-8)], but these two biomass had different biochemical compositions, and the former one had lower carbohydrate and higher protein content. When cultured in domestic wastewater, a higher biomass was obtained under continuous illumination [DW(24-0)], and the cells had higher carbohydrate and lower protein concentrations than that of DW(16-8). The spectra of the Fourier transform infrared spectrometer revealed that the functional groups on the surface of the three kinds of biomass--DW(16-8), DW(24-0), and BM(16-8)--were comparable, except an additional peak at 1731 cm(-1) was found in the biomass cultured in domestic wastewater, which was probably the result of bacterial contamination. Although biochemical differences were found among the three kinds of microalgal biomass, similar biosorption performances to chromium pollutants were recorded, with approximately 75% Cr(III) and 100% Cr(VI) removed at equilibrium in Cr(III) and Cr(VI) experiments, respectively, when dead biomass was used as a biosorbent. Therefore, it is possible to culture Chlorella miniata in domestic wastewater and use the biomass for the removal of chromium pollutants.