Biosorption of Mercury by Reed (<Emphasis Type="Italic">Phragmites australis</Emphasis>) as a Potential Clean Water Technology

Heavy metals are causing serious environmental and health problems worldwide, especially in places where mining is one of the major drivers of the country’s economy. Conventional technologies are considered expensive when providing the safe water; for this reason, new clean water technologies are needed. Biosorption has gained attention as a cost-effective system that uses biological materials to remove heavy metals from water; however, it can be noted that an efficient and proven biosorbent for several heavy metal has not been found. Reed (Phragmites australis) has demonstrated to be a potential biosorbent to remove several heavy metals because it is commonly found as heavy metal accumulator in wetlands. This study is focused on mercury (Hg) removal by using reed as biosorbent. Batch experiments were conducted and the microstructure of the biosorbent was analyzed by scanning electron microscope. The Langmuir isotherm and Freundlich isotherm model was applied for the data obtained. The pseudo-first-order and pseudo-second-order models were used to test adsorption kinetics data to investigate the mechanism of biosorption. A comparison with the performance of various adsorbents reported in literature was made. The results contribute to understand the use of Phragmites australis as potential biomass for biosorbent technology since it removed mercury (Hg) effectively in high concentrations. This study supports a variety of researches to achieve clean water technologies, and biosorption has proved to be a useful alternative to the conventional systems for the removal of heavy metal ions from aqueous solution.     

Occurrence of dark septate endophytes in Phragmites australis in the Baiyang Lake and their resistance to Cd stress

Heavy metal pollution poses a serious hazard to human health, and microbial remediation of heavy metals in soil has been widely studied. A group of ascomycetes classified as dark septate endophytes (DSEs) colonize plant roots and benefit host plants under abiotic stress conditions. In this study, Phragmites australis, a common remediation plant in the Baiyang Lake in North China, was investigated. Soils and roots of P. australis were collected in typical heavy metal-contaminated sites, and the species diversity and community structure of DSEs in P. australis roots were studied. In addition, DSE strains were isolated, cultured, and tested for their tolerance to Cd stress. The results showed that DSEs occurred extensively in P. australis roots, forming typical dark septate hyphae, with a total colonization rate of 19.7%-83.1%. Morphological and internal transcribed spacer sequencing analyses were used to identify 10 species within 9 genera of DSE fungi. Among these fungi, 6 strains with considerable resistance to Cd stress were identified. The biomasses of Poaceascoma helicoides, Alternaria doliconidium, and Acrocalymma vagum strains increased as the Cd levels increased. These results can not only help to understand plant-DSE interactions in wetland environments, but also provide a theoretical basis for making full use of DSE fungi to alleviate heavy metal contamination in soil.     

Salt marsh rhizosphere affects microbial biotransformation of the widespread halogenated contaminant tetrabromobisphenol-A (TBBPA)

Estuarine sediments are the repository for a wide range of contaminants. Anthropogenic impacts and variations in the belowground biomass of salt marsh plants potentially select for different sediment microbial communities with different functional capabilities, including the ability to biotransform anthropogenic contaminants. There are large differences in both root morphology and the amount of fine root biomass of Spartina alterniflora and Phragmites australis; Spartina is the species commonly used to replace Phragmites in northeastern US salt marsh restoration projects. Our study compared the effect of these two macrophyte species on sediment microbial communities responsible for the biotransformation of the halogenated flame retardant tetrabromobisphenol A (TBBPA). Sediments were obtained from contaminated and uncontaminated salt marsh field sites in New Jersey. Anaerobic methanogenic sediment microcosms were established and incubated for up to 130 days. TBBPA was reductively dehalogenated resulting in the transient formation of two intermediates, identified as tribromobisphenol A and dibromobisphenol A, and the formation and accumulation of bisphenol A (BPA) as the end product. Spartina sediments from both sites were found to dehalogenate TBBPA more rapidly than the Phragmites or unvegetated sediments, resulting in greater production of BPA. Microbial community diversity as measured by in situ sediment phospholipid fatty acid (PLFA) composition prior to TBBPA exposure, was found to be higher in the uncontaminated sediments; differences in microbial PLFA diversity were not seen in contaminated sediments associated with either the different plant species or unvegetated sediment. The results of this study demonstrate that these two plant species affected sediment microbial community function with respect to dehalogenation capabilities, even though the disturbed and undisturbed sediments varied in microbial community composition.     

Influence of Thermally Polluted Water on the Growth of Helophytes in the Vicinity of a Colliery Waste Tip

The impact of thermal pollution of leachate from a post-coal mine heap on three macrophyte species: Phragmites australis, Typha latifolia, and Scirpus sylvaticus was examined over the entire vegetation season. Hydrological measurements showed that the temperature of the leachate was ca 50?°C at the site of leachate inflow and decreased to ca 15?°C at the end of discharge canal. The annual temperature and conductivity of leachate from the two control sites, a polluted water stream in the vicinity of the waste tip and an unpolluted stream, differ significantly. However, only the temperature explained the differences in plant traits. In April, and in some cases in May, plants in the leachate were significantly higher than in those on the control sites in terms of biomass and plant height. Thermal pollution caused a phenological shift in all species and also caused Scirpus plants to die out more quickly. Temperature also affected the proportion flowering vs. vegetative individuals, e.g., none of Scirpus plants started to bloom.     

闽江口湿地沉积物各形态磷分布特征及风险评价

为探究湿地植被、理化性质等对沉积物磷的各赋存形态的影响,评价闽江口湿地污染程度和潜在环境风险。2017年在闽江河口湿地由陆向海选取4个采样点,用SMT法提取各形态磷,测定分析了闽江口湿地沉积物各形态磷变化规律并进行风险评价。结果表明:沉积物中有机磷含量为0.176～0.369mg/g,约占总磷的32.03%;而无机磷含量为0.308～0.666mg/g,占总磷66.49%;总磷含量为0.491～0.998mg/g,其污染指数为0.819～1.618,总体上为轻度污染。各形态磷在不同植被类型沉积物中含量分布不同,其中沉积物有机磷含量芦苇最高,扁穗莎草最低;无机磷中的钙磷含量则是互花米草最少,短叶茳芏和扁穗莎草明显高于其他植被类型;而铁铝磷含量是互花米草远高于其他植物;因总磷受无机磷影响较大,以致无机磷含量与总磷含量分布相似,均是扁穗莎草最高,芦苇最低。沉积物中钙磷与容重呈极显著负相关,与含水率呈极显著正相关,有机磷含量与有机质呈极显著正相关;总磷与含水率呈极显著正相关,与电导率呈显著负相关。以上现象可能由植被类型与生长阶段、理化性质、陆源物质、水文环境、凋落物、人类生产活动等多个因素的综合作用所导致。     

Heavy metals in the soil–plant system of the Don River estuarine region and the Taganrog Bay coast

Purpose

The aim of this work was to study the level and degree of mobility of heavy metals in the soil–plant system and to perform bioindication observations in the Don River estuarine region and the Russian sector of the Taganrog Bay coast.

Materials and methods

The objects of the study included samples of zonal soils (chernozem) and intrazonal soils (alluvial meadow and alluvial-stratified soils, Solonchak, sandy primitive soil) from monitoring stations of the Don river estuarine region and the Taganrog Bay coast, as well as their higher plants: Phragmites australis Cav., Typha angustifolia L., Carex riparia Curtis, Cichorium intybus L., Bolboschoenus maritimus L. Palla, and Rumex confertus Willd. The total concentrations of Mn, Ni, Cd, Cu, Zn, Pb, and Cr in the soils were determined by X-ray fluorescent scanning spectrometer. The concentration of heavy metal mobile forms exchangeable, complex compounds, and acid-soluble metal were extracted using the following reagents: 1 N NH₄Ac, pH 4.8; 1 % EDTA in NH₄Ac, pH 4.8; 1 N HCl, respectively. Heavy metals in plants were prepared for analysis by dry combustion at 450 °C. The heavy metal concentration in extracts from plants and soils was determined by AAS.

Results and discussion

The total contents of heavy metals in the soil may be described with a successively decreasing series: Mn?>?Cr?>?Zn?>?Ni?>?Cu?>?Pb?>?As?>?Cd. The total concentrations of As, Cd, and Zn in the soil exceed the maximum permissible concentrations levels. Contamination of alluvial soils in the estuarine zone with mobile Сu, Zn, Pb, and Cd has been revealed, which is confirmed by the high bioavailability of Cu and Zn and, to a lesser degree, Cd and Pb accumulating in the tissues of macrophytic plants. Data on the translocation of elements to plant organs have showed their predominant accumulation in the roots. Bioindication by the morphofunctional parameters of macrophytic plants (with a Typha L. species as an example) can be used for revealing the existence of impact zones with elevated contents of metals in aquatic ecosystems.

Conclusions

The results revealed that increased content of Zn, Pb, Cu, Ni, and As in soil have anthropogenic sources. The high content of Cr in the soils is related to the lithogenic factor and, hence, has a natural source.

     

The Bioaccumulation Performance of Reeds and Cattails in a Constructed Treatment Wetland for Removal of Heavy Metals in Landfill Leachate Treatment (Etueffont,France)

The aim of this study was to evaluate and compare the capacities of cattail (Typha latifolia L.) and reed (Phragmites australis L.) for heavy metal storage in the phytomass. Samples were studied in the fourth of the four interconnected natural lagooning basins of a constructed treatment wetland, developed as an integrated pilot system for the treatment of leachates in a domestic landfill site at Etueffont (Territoire de Belfort, France). The efficiency of the lagooning system was evaluated through physical and chemical parameter measurements over a period of three seasons. Anion/cation and heavy metal concentrations were sampled and analyzed in water flowing into and out of the lagooning basin. Simultaneously, reed and cattail biomass samples (roots/rhizomes, shoots) were collected at both inflow and outflow, and the biomass characteristics were determined. The average above-ground biomass of T. latifolia and P. australis varied, respectively, from 0.41 to 1.81 kg DW m⁻² in the fall, 0.31 to 1.34 kg DW m⁻² in winter, and 0.38 to 1.68 kg DW m⁻² in spring, with significant seasonal variations. The greatest mean concentrations of heavy metals were found in the below-ground plant parts of the two species during the spring season. The average standing stock of heavy metals was higher in the below-ground than in the above-ground phytomass, whatever the season. With the exception of nickel, heavy metal concentrations in the inflow were correlated to the plant content of both species.     

Accumulation and Distribution of Heavy Metals in Scirpus americanus and Typha latifolia from an Artificial Lagoon in San Luis Potosí, México

The concentrations of Pb, Cd, Cr, Mn and Fe were evaluated in leaves, stem and root of the Scirpus americanus and Typha latifolia aquatic macrophytes, which were collected from Tanque Tenorio, an artificial lagoon highly polluted by municipal and industrial wastewater. Some S. americanus and T. latifolia plants were collected from four different sites within Tanque Tenorio. The sites were chosen regarding their proximity with the main channel discharging wastewater into the lagoon. The results showed that S. americanus and T. latifolia have the ability to extract Pb, Cd, Cr, Mn and Fe from their water surroundings; on the whole, the roots presented higher concentrations of heavy metals than the stem and the leaves. The highest accumulation of heavy metals was observed in plants growing at the site near the channel entering the lagoon. S. americanus accumulated more Pb, Cr, Mn and Fe than T. latifolia; Cd concentrations were comparably the same in both species. This study provides information in relation to aquatic plants growing in polluted waters, which accumulate heavy metals. These findings are of interest pertaining to the removal processes for treating aquatic systems with heavy metal content.     

Impact of Seasonal Fluctuations on the Sediment-Mercury, its Accumulation and Partitioning in Halimione portulacoides and Juncus maritimus Collected from Ria de Aveiro Coastal Lagoon (Portugal)

The availability of metals to plants is a complex function of numerous environmental factors. Many of these factors are interrelated, and vary seasonally and temporally. The current study intended to understand the influence of seasonal fluctuations and the vegetation of salt marsh plants (SMPs; Halimione portulacoides, Juncus maritimus) on sediment??s mercury (Hg) and its pH and redox potential (Eh), as well as their cumulative effect on the plant??s Hg-accumulation and Hg-partitioning potential. The area selected for the study was Laranjo Basin at Ria de Aveiro lagoon (Portugal) where a known Hg gradient was existed due to chlor-alkali plant discharge. Three sampling sites (L1, L2 and L3) were selected along a transect defined by the distance from the main Hg source. Samples were also collected from the Hg-free site (R). Irrespective of the plant vegetation, Hg in sediments gradually increased with a decreasing distance towards Hg-point source. The sediment colonised by J. maritimus showed more Hg concentration compared with H. portulacoides irrespective of the season. As a whole, J. maritimus accumulated Hg more than H. portulacoides at all the sampling sites, whereas in root, stem and leaf, the concentration was ranked as: L1 > L2 > L3 in both the plant species and was differentially influenced by seasonal changes. Moreover, root of both plants exhibited highest Hg concentration compared with stem and leaf. In addition, the leaf of H. portulacoides exhibited more Hg than leaves of J. maritimus. Bioaccumulation and translocation factors and dry weight were differentially influenced by seasonal changes. Taking together the results, the physico-chemical properties of sediment especially the sediment-Eh seems to be influnced by the type of plant vegetation and seasonal changes which in turn may have influenced the chemistry of sediments; thus, it enfluences the bioavalability of Hg and the Hg-retention capacity of both salt marsh sediments (SMSs) and SMPs (bioaccumulation factor). Moreover, SMSs vegetated by J. maritimus exhibited a stronger capacity for the retention and phytostabilization of Hg belowground (in sediments and/or roots) than those dominated by H. portulacoides. Conversely, those SMSs extensively vegetated by H. portulacoides are expected to translocate more Hg to aboveground parts, acting as a potential source of this metal to the marsh ecosystem. Therefore, J. maritimus and H. portulacoides may be used repectively for phytostabilization (in rhizosediments) and phytoextraction (by accumulation in aboveground plant tissue for subsequent plant removal).     

Sediment toxicity and heavy metals in eleven lime reference lakes of Sweden

Sediments from an eutrophic reference lake (L. HjÄlmaren) and eleven oligotrophic Swedish lakes were analyzed for heavy metals (Cd, Cr, Cu, Hg, Ni, Pb, and Zn) and tested for whole sediment toxicity to Daphnia magna. Whole sediment toxicity, expressed as 48-hr EC50 on a wet weight basis in reconstituted dilution water, ranged from 2.8% (most toxic) to >32% (least toxic). Correlations between bulk sediment heavy metal concentrations and toxicity were significant (P≤0.05) for Hg, Pb, and Zn. However, a causal connection between the concentrations of these metals and toxicity was not supported by the results from metal-spiked sediment toxicity tests. In addition sediment toxicity was not affected by the addition of EDTA, which is a strong chelator known to reduce metal toxicity. After storage for several months test sediments either remained nontoxic, toxic, or increased in toxicity. These results illustrate some of the difficulties in the interpretation of bulk sediment chemistry data and the release of toxic chemicals from sediment samples, highlighting the effect of sediment storage on toxicity.     

Bioaccumulation of heavy metals in the lotus root of rural ponds in the middle reaches of the Yangtze River

Purpose

The subject of this study is the sediment and wild lotus plants in unmanaged ponds, near Yichang City, contaminated by heavy metals. The objective is to determine the extent and frequency of heavy metal accumulation by lotus root in the ponds of rural areas and its significance to food safety and human health.

Materials and methods

The study area is located in the middle reaches of Yangtze River. The 11 sampling sites selected (Z1–Z11) were unmanaged ponds, and the lotus root samples were from wild plants. The lotus root and soil samples were processed using wet digestion, according to the national standard method; we tested concentration of heavy metal (Pb, Cd, Cr, As, Cu, and Zn). Both a single-factor index and an integrated pollution index were used to assess the heavy metal pollution of soil and wild lotus root. Correlation was used to examine the relationship of lotus root concentration to sediment concentration for each heavy metal.

Results and discussion

Cadmium (Cd) and arsenic (As) in both soil and pond sediment exceeded standards. The maximum single pollution index (SPI) for Cd and As was 1.16 and 1.15, respectively. The maximum integrated pollution index (IPI) for heavy metals was 2.17 for soil and 2.10 for sediment (moderate pollution). The heavy metal content in some samples of lotus root exceeded the national food standard and pose a health risk. The significant correlations of heavy metal concentrations (Pb, Cd, and As) in pond sediment with those in the surrounding soil show that the ponds act as sinks for agricultural nonpoint source pollution (NPS). The heavy metal concentrations in the peel of the edible tuber were 1.3～9.0 times higher than those in the inner flesh.

Conclusions

While Cd, Pb, and As concentrations in the sediment did not violate soil standards, concentrations in the lotus root did violate food standards. This species could be proposed as a suitable heavy metal bioindicator for the early stages of pollution from agricultural NPS.

     

Distribution of Trace Metals in Channel Sediment: a Case Study in South Atlantic Coast of Spain

Recently, Sancti Petri channel on the southwestern (SW) part of Iberian Peninsula has been experiencing urban, industrial, and vehicular expansion. Until recently, there have been only few published reports documenting the pattern of metal accumulation in this estuarine sediment. In the present study, trace metals such as Cu, Zn, Ni, Mn, Pb, Co, Cd, As, and Hg concentrations were analyzed from 69 sediment samples collected from 23 sampling sites of the Santi Petri channel. The magnitude of trace metal accumulation found as the following trend: Mn > Zn > Cu > Pb > Ni > Co > As > Cd > Hg. Spatial distribution pattern demonstrated overall decreasing trend of trace metal from Cadiz Bay mouth to the open ocean mouth, clearly correlative to the presence of anthropogenic inputs. Results of the principle component analysis (PCA) revealed that sediment metal chemistry of Sancti Petri channel is mainly regulated by the concentrations of Pb, Cu, Zn, and Ni; possible sources of those were from vehicular-related emissions. Pollution load index (PLI) and geo-accumulation index (I _geo ) indicated overall low values. The study will stimulate improvement of our understanding regarding the pattern of accumulation of metals in the coastal sediments, and the recorded values of metals in the present study can be used as suitable reference for future studies.     

Accumulation and Distribution of Metals in Bolboschoenus maritimus (Cyperaceae), from a South African River

The Diep River is a major freshwater ecosystem in the Western Cape, South Africa. Although it is surrounded by many sources of metal pollution, the actual metal levels in this river system are unknown. Wetland plants are known to accumulate metals and may possibly be used as biomonitors of metal contamination in a river system. One such species, the sedge Bolboschoenus maritimus, is found in abundance along the banks of this river. The aim of this study was to investigate and monitor the degree of metal contamination in the water and sediments of the lower Diep River, as well as to study the seasonal accumulation and distribution of metals in B. maritimus, and the use thereof as biomonitor species. Two sampling sites were used: one site above the wetland section of the river, receiving runoff mainly from agricultural lands (site 1), and one site close to the river mouth (site 2), exposed to several possible pollution sources. Water, sediment, and plant (root, leaf and stem) samples were collected seasonally for 1 year and analyzed for Al, Zn, Cu, and Fe. There was greater bioaccumulation of metals by plants at site 2, due to greater bioavailability of metals. B. maritimus was shown to be a root accumulator of metals. Seasonal fluctuations in root, stem, and leaf metal concentrations did not follow seasonal sediment concentration patterns. However, using B. maritimus as test species did provide valuable additional information to sediment and water analyses. More extensive research is needed to conclude whether this species is an effective biomonitor in the lower Diep River environment.     

Hydrocarbons in Seawater and Water Extract of Jarzouna-Bizerte Coastal of Tunisia (Mediterranean Sea): Petroleum Origin Investigation Around Refinery Rejection Place

In this study, the occurrence of toxic heavy metals (As, Cd, Cr, Cu, Pb, and Zn) and relative bioaccumulation in biota samples were investigated in a freshwater ecosystem, the Basento river, one of the main aquatic systems in the south of Italy, which over the last years has been transformed into a sink of urban and industrial wastes. Therefore, the levels of arsenic, cadmium, chromium, copper, lead, and zinc were determined in water, sediments, and tissues of some macroinvertebrate—which are natural assessment endpoints for the evaluation of ecological risk in aquatic systems. Accumulation factors, as a ratio between the concentration of a given contaminant in biota and the one in an abiotic medium, were considered in order to estimate heavy metal contamination loads in biota. Statistical analysis was performed for a comparative evaluation of bioaccumulation among various macroinvertebrates, according to different feeding guilds. The Tukey honestly significantly different test showed significant differences in the bioaccumulation of As, Cd, and Cr among the considered biological receptors (collector–gatherer, predator, and filterer), suggesting that the biological uptake from immediate contact with the sediment or solid substratum (collector–gatherer), instead of the bioconcentration from water (filterer) or biomagnification along the biotic food webs (predators), is the more effective biological sequestering pathway for these metals. Biota–sediment accumulation factors, commonly used for the evaluation of sediment’s role in aquatic systems contamination, were determined for the considered metals. A linear correlation between the concentrations of As, Cd, Cr, and Zn in macroinvertebrates and those in the sediments suggested that the metal uptake data in macroinvertebrates can provide useful information for the estimation of heavy metal exposure risk or bioavailability when making assessments of sediment toxicity in freshwater ecosystems.     

Evaluation of Heavy Metal Pollution in the Arabian Gulf Using the Clam Meretrix meretrix Linnaeus, 1758

The present study is an attempt to assess the heavy metal contamination in the marine environment of the Arabian Gulf of Saudi Arabia. The concentrations of heavy metals in water and the soft tissues of the bivalve species Meretrix meretrix Linnaeus, 1758, from different stations along the Arabian Gulf coastline, were determined during the summer season of 2008. Bioaccumulation of some heavy metals (Cd, Pb, Cu, and Zn) in fresh parts of the clam (M. meretrix) was measured by an atomic absorption spectrophotometer. The average concentrations of heavy metals in the clam tissues were 0.224?C0.908, 0.294?C2.496, 3.528?C8.196, and 12.864?C24.56 mg/kg wet weight for Cd, Pb, Cu, and Zn, respectively. In water, the mean concentration values of these metals were arranged in the following descending order: Pb > Cu > Zn > Cd. The heavy metal concentrations in tissues of M. meretrix were within the acceptable standards set by the US Environmental Protection Agency, the Commission Européenne, and the Food and Drug Administration of the USA. From the human public health point of view, these results seem to show no possibility of acute toxicities of Cd, Cu, Pb, and Zn if the edible clam is consumed. It is recommended that relevant authorities should carry out a continual assessment on the levels of these pollutants in the studied area.     

Potential of Aquatic Macrophytes as Bioindicators of Heavy Metal Pollution in Urban Stormwater Runoff

The concentrations of heavy metals in water, sediments, soil, roots, and shoots of five aquatic macrophytes species (Oenanthe sp., Juncus sp., Typha sp., Callitriche sp.1, and Callitriche sp.2) collected from a detention pond receiving stormwater runoff coming from a highway were measured to ascertain whether plants organs are characterized by differential accumulations and to evaluate the potential of the plant species as bioindicators of heavy metal pollution in urban stormwater runoff. Heavy metals considered for water and sediment analysis were Cd, Cr, Cu, Ni, Pb, Zn, and As. Heavy metals considered for plant and soil analysis were Cd, Ni, and Zn. The metal concentrations in water, sediments, plants, and corresponding soil showed that the studied site is contaminated by heavy metals, probably due to the road traffic. Results also showed that plant roots had higher metal content than aboveground tissues. The floating plants displayed higher metal accumulation than the three other rooted plants. Heavy metal concentrations measured in the organs of the rooted plants increased when metal concentrations measured in the soil increased. The highest metal bioconcentration factors (BCF) were obtained for cadmium and nickel accumulation by Typha sp. (BCF = 1.3 and 0.8, respectively) and zinc accumulation by Juncus sp. (BCF = 4.8). Our results underline the potential use of such plant species for heavy metal biomonitoring in water, sediments, and soil.     

Phytoremediation of Pb in the sediment of a mangrove ecosystem

Purpose

Coal-fuelled power plants can discharge hazardous materials, particularly heavy metals such as lead (Pb). An alternative way of reducing Pb concentration from contaminated sediments is through phytoremediation. Presently, there are few research findings on the phytoremediation potential of mangroves on metals like Pb. The study was conducted to survey and identify mangroves that thrive near the coal-fired power plant and to assess the phytoremediation potential of mangroves on Pb in sediment.

Materials and methods

The study sites were located in the mangrove ecosystems of Sitio Oyon and Sitio Asinan in Masinloc, Zambales, Philippines. The first stage of our study was to survey and identify the mangrove species. The second stage was to assess the levels of Pb in the sediments, water, and tissues of mangrove trees. The diversity assessment of the mangrove species was done through the use of 10?×?12 m quadrat technique. Water and sediment samples from each mangrove ecosystem were collected using composite sampling methods.

Results and discussion

Three mangrove species were identified in the study sites: Avicennia marina, Rhizophora stylosa, and Sonneratia alba. The order of importance of the mangrove trees in the two sampling locations, based on an importance value index (IVI), were as follows: SA (IVI?=?171.20)?>?AM (77.79)?>?RS (51.01). The total uptake of Pb from sediments near the power plants varied significantly (p?≤?0.001) among the three mangrove species. S. alba had the highest Pb uptake of 48.4 kg ha^?1 followed by A. marina (23.1 kg ha^?1), and R. stylosa (2.4 kg ha^?1). These three mangrove species have the potential to phytoremediate Pb in the sediment.

Conclusions

The three mangrove species present in the coastal ecosystem near the electric power plant—A. marina, R. stylosa, and S. alba—were potential phytoremediators of sediment Pb. The present study indicated that the mangroves possess beneficial characteristics that remove Pb from contaminated sediments in areas directly affected by coal-fired power plants, and thus have potential phytoremediation properties.     

A comparison study on heavy metal/metalloid stabilization in Maozhou River sediment by five types of amendments

Purpose

River sediment pollution by heavy metals/metalloids has attracted widespread attention due to a serious threat to the ecosystem and human health. As an effective and economical alternative, the stabilization method was considered by previous studies for the remediation of sediments polluted by metals/metalloids. However, a comprehensive study is required for an extensive comparison on the effects of metal/metalloid immobilization based on the application of different materials as sediment amendments.

Materials and methods

In this study, the Maozhou River was selected as the study area, and the stabilization method was applied for the remediation of the river sediment polluted by metals and metalloids. Five materials (CaCO₃, Ca(OH)₂, zeolite, kaolin, FeCl₂) were selected as amendments for the metal/metalloid stabilization in the collected sediment. A modified BCR procedure was employed for the speciation analysis of heavy metals and metalloid in the sediment before and after remediation. A TCLP (toxicity characteristic leaching procedure) investigation was performed to further evaluate the immobilization of heavy metals in acidic environment.

Results and discussion

The sediment of the Maozhou River was heavily polluted by heavy metals and metalloid. The speciation of As, Pb, Cr, and Mn mainly exists as residual fraction (F4), while that of Ni, Cu, and Zn was identified as exchangeable metal and carbonate-associated fraction (F1) and fraction associated with Fe-Mn oxides (F2). Moreover, the F2 fraction of Co was observed as the major speciation. Through the application of five materials (CaCO₃, Ca(OH)₂, zeolite, kaolin, FeCl₂) as sediment amendments, the metal/metalloid speciation was transferred into F4. When five amendments were compared, the stabilization effect can be ordered as CaCO₃?>?zeolite?>?FeCl₂?>?kaolin?>?Ca(OH)₂ based on the modified BCR results. TCLP results showed that using Ca(OH)₂ and CaCO₃ as amendments can significantly reduce the metal leachability in an acidic environment, while zeolite is effective for most of the heavy metals and metalloid.

Conclusions

The results showed that the sediment of the Maozhou River was seriously polluted by a variety of heavy metals and metalloids. This study provided extensive information on the speciation of metals or metalloid and the effect of various amendments on metals and metalloid stabilization, which can be of vital importance for further remediation of metal/metalloid-polluted sediment.

     

The effects of cattle grazing on tall-herb fen vegetation and molluscs

The effects of light year-round cattle grazing on tall-herb fen vegetation and wetland molluscs were compared to the effects of non-intervention over a period of four years using grazing exclosures. The distribution of cattle within the area of fen was investigated by plotting the position of the herd at 3-4 day intervals throughout the year. Cattle distributed themselves randomly throughout the fen in spring, autumn and winter, but showed a more aggregated distribution in summer. Grazing reduced the biomass of Phragmites australis and increased stem densities of Glyceria maxima, resulting in a shift of dominance from Phragmites to Glyceria. Plant species-richness was also significantly higher in areas open to grazing.Grazing decreased total densities of molluscs and substantially reduced densities of the rare snail Vertigo moulinsiana. V. moulinsiana was particularly associated with areas of fen that had a high water table and high biomass of ungrazed Carex riparia. However, because of the patchy nature of the grazing, V. moulinsiana survived at reasonably high densities in patches of ungrazed vegetation within the grazing unit.     

Chicory (Cichorium intybus L.) and dandelion (Taraxacum officinale Web.) as phytoindicators of cadmium contamination

Chicory (Cichorium intybus L.) and dandelion (Taraxacum officinale Web.) were demonstrated to be potential indicator plants for heavy metal contaminated sites. Chicory, grown with 0.5–50 μM cadmium (Cd) in nutrient solution, accumulated 10–300 μM Cd g^?1 in shoots and 10–890 μg Cd μg^?1 in roots and rhizomes. With dandelion, 20–410 μg Cd μg^?1 was found in shoots and 20–1360 μg Cd μg^?1 in roots and rhizomes. An inverse correlation existed between chlorophyll and Cd concentrations in shoots of both species. Accumulation of Cd from nutrient solution was similar with the counter-anions SO₄ ^2?, Cl^1? and NO₃ ^? in chicory. In chicory grown in Cd-amended (11.2 kg Cd ha^?1 applied five years previously) soils, Cd concentrations were substantially higher than in controls in all plant parts following the order: leaf > caudex > stem > root and rhizome. The above trend was the opposite of that observed in solution culture, where Cd accumulation was higher in roots and rhizomes than in shoots. Higher cadmium accumulation was found from a Cd-treated sand (Grossarenic Paleudult) than from a loamy sand (Typic Kandiudult) soil type. Chicory and dandelion are proposed indicator plants of cadmium contamination, and both have the potential to be an international standard heavy phytomonitor species of heavy metal contaminantion.