Effects of plants on the removal of hexavalent chromium in wetland sediments

Comparative spatially explicit approach for testing effects of soil chemicals on terrestrial wildlife bioindicator demographics

Wildlife species are often used as bioindicators to evaluate the extent and severity of environmental contamination and the effectiveness of remediation practices. A common approach for investigating population- or community-level impacts on bioindicators compares demographic parameter estimates (e.g., population size or density) between sites that were subjected to different levels of contamination. However, the traditional analytical method used in such studies is nonspatial capture-recapture, which results in conclusions about potential relationships between demographics and contaminants being inferred indirectly. Here, we extend this comparative approach to the spatially explicit framework, allowing direct estimation of said relationships and comparisons between study areas, by applying spatial capture-recapture (SCR) models to bioindicator (deer mice [Peromyscus spp.]) detection data from two study areas that were subjected to different industrial activities and remediation practices. Bioindicator density differed by 178% between the neighboring study areas, and the area with the highest soil concentrations of polychlorinated biphenyls, chromium, and zinc had the highest bioindicator density. Under the traditional nonspatial approach, we might have concluded that soil chemical levels had negligible influences on demographics. However, by modeling density as a spatial function of select chemical concentrations using SCR models, we found strong support for a positive relationship between density and soil chromium concentrations in one study area (β = 0.82), which was not masked by or associated with habitat-related metrics. To obtain reliable inferences about potential effects of environmental contamination on bioindicator demographics, we contend that a comparative spatially explicit approach using SCR ought to become standard.

Comparative study on the performance of Typha latifolia and Cyperus Papyrus on the removal of heavy metals and enteric bacteria from wastewater by surface constructed wetlands

Semi-arid countries continue to face water scarcity, especially with the current global climatic changes. This scarcity has continuously increased over the last five decades in countries like Egypt, Syria, Libya and Jordan, where the agriculture sector consumes more than 85% of the country's water resources. The problem of water scarcity in Egypt is further challenged by high levels of urbanization, increasing industrial uses, and the high cost of advanced treatment processes. These challenges lead to the utilization of untreated or poorly treated wastewater for irrigation of agricultural crop fields. Thus, the current study proposes the use of an eco-friendly technology consisting of a constructed wetland planted with Typha latifolia and Cyperus papyrus supported with zeolite substrate for water purification, to curb this challenge. The results showed that, the removal efficiency of COD, BOD, TSS, and ammonia were 68.5%, 71%, 70%, and 82.3%, respectively by Typha latifolia bed. On the other hand, the removal efficiency of COD, BOD, TSS and ammonia were 85.5%, 86.2%, 83.9% and 92.3% respectively by Cyperus papyrus bed. As a result, bacteriological parameters were reduced to 99.9%, and complete removal of Salmonella sp was achieved during three days by Cyperus papyrus. Box-Behnken design was utilized to optimize independent factors, including contact time (24-72h) and initial concentration of metals (15-45 mg L^-1) and their responses. The removal efficiency of Cu and Zn were 72% and 84%, respectively of the optimum reaction time (72 h), with 16 plant stems and an initial metal concentration of 15 mg L^-1.

Simultaneous Removal of Trivalent Chromium and Hexavalent Chromium from Soil Using a Modified Bipolar Membrane Electrodialysis System

In this study, a modified bipolar membrane electrodialysis system equipped with a "back-to-back" soil compartment was fabricated for simultaneous removal of trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) from contaminated soils. The results showed that the soil solution pH had a significant effect on the Cr(III) and Cr(VI) desorption, and the desorption data fit well with the Elovich kinetic model. Current density had an obvious effect on Cr(III) and Cr(VI) removal, cell voltage, soil pH, current efficiency, and specific energy consumption, and the optimal current density was 2.0 mA/cm². The removal efficiencies of Cr(III) and Cr(VI) were both 99.8%, while Cr(III) and Cr(VI) recoveries were somewhat lower at 87 and 90%, respectively, because some Cr(III) and Cr(VI) were adsorbed by the membranes. An energy consumption analysis indicates that the back-to-back soil compartment equipped system increased the current efficiency and decreased the specific energy consumption. When a system equipped with two back-to-back soil compartments was used to remove chromium from soil, the current efficiency increased to 28.8% and the specific energy consumption decreased to 0.048 kWh/g. The experimental results indicate that the proposed process has the potential to be an effective technique for the treatment of soil contaminated with heavy metals.

Pennisetum sinese: A Potential Phytoremediation Plant for Chromium Deletion from Soil

Chromium is one of the major pollutants in water and soil. Thus, it is urgent to develop a new method for chromium removal from the environment. Phytoremediation is a promising approach for heavy metal pollution recovery. As a perennial giant grass with a fast growth rate, Pennisetum sinese has been widely used as livestock feed, mushroom culture medium and biomass energy raw material. Interestingly, we have found a high adsorption capacity of P. sinese for chromium. P. sinese was treated with different concentrations of chromium for 15 days. Results showed that P. sinese plantlets grew well under low concentrations (less than 500 μM) of chromium (VI). The plantlet growth was inhibited when treated with high concentrations of chromium (more than 1000 μM). Up to 150.99 and 979.03 mg·kg−1 DW of chromium accumulated in the aerial part and root, respectively, under a treatment of 2000 μM Cr. The bioaccumulation factor (BCF) of P. sinese varied from 10.87 to 17.56, and reached a maximum value at the concentration of 500 μM. The results indicated that P. sinese showed strong tolerance and high accumulation capability under Cr stress. Therefore, the chromium removal potential of P. sinese has a great application prospect in phytoremediation.

Evapotranspiration from Horizontal Subsurface Flow Constructed Wetlands Planted with Different Perennial Plant Species

This paper presents the results of an experiment carried out in Southern Italy (Sicily) on the estimation evapotranspiration (ET) in pilot constructed wetlands planted with different species (Chrysopogon zizanioides, Myscanthus x giganteus, Arundo donax, Phragmites australis, and Cyperus papyrus). In the two monitored growing seasons, reference ET0 was calculated with the Penman-Monteith formula, while actual ET and crop coefficients were measured through a water balance and the FAO 56 approach, respectively. The highest average seasonal ET value was observed in Phragmites australis (17.31 mm d−1) followed by Arundo donax (11.23 mm day−1) Chrysopogon zizanioides (8.56 mm day−1), Cyperus papyrus (7.86 mm day−1), and Myscanthus x giganteus (7.35 mm day−1). For all plants, crop coefficient values showed different patterns in relation to growth stages and were strongly correlated with phenological parameters. Myscanthus x giganteus and Arundo donax showed a water use efficiency values significantly higher than those observed for the other tested species. Results of this study may contribute to select appropriate plant species for constructed wetlands located in semi-arid regions, especially when the use of reclaimed water and/or the use of aboveground biomass are planned.

Removal of dissolved chromium from synthetic mine effluent: A mesocosm experiment

Dispersion of hexavalent chromium (Cr(VI)) in streams around nickel laterite mines, which are mostly located in the tropics, may pose serious risks for the environment and human health. In an earlier study, a local natural wetland effectively removed Cr from a nickel mine environment in Indonesia. In order to understand the processes and conditions that would facilitate the establishment of operational constructed wetlands that would remove Cr from mine water discharge, we used two native macrophyte species from the same wetland, Lepironia articulata and Machaerina rubiginosa, in a series of mesocosm experiments to follow the distribution of Cr species in water, substrate and plants. A 1 m³ mesocosm was charged with a sand/compost mixture to a depth of 0.5 m, filled to within 0.1 m from the top by water with Cr concentrations of about 1.0 mg L^-1, similar to mine discharge water, and plants were introduced to part of the substrate surface. Stage 1 of the experiment supplied and removed fresh water continuously by surface flow, maintaining a residence time of 12 h. In stages, the water was recirculated (Stage 2), more plants were added (Stage 3) and outflow conditions were changed from totally surface to partially from beneath the substrate (Stage 4). All stages lowered Cr concentrations at the surface water outflow, but Cr concentrations were lower again close to the sediment/water interface. Due to the reduction of Cr(VI), the Cr concentrations in substrate pore water were higher near the surface compared to those at depth, and the pore water concentrations of Cr(VI) and total Cr were higher in the vegetated area compared to the non-vegetated area. Higher plant density and mixed species composition of the macrophytes did not increase the efficiency of Cr(VI) removal from the system. The hybrid system, comprising surface and below-substrate outflow (Stage 4), removed hexavalent chromium at a much higher rate than surface outflow only.

Wetlands for wastewater treatment and subsequent recycling of treated effluent: a review

Due to water scarcity challenges around the world, it is essential to think about non-conventional water resources to address the increased demand in clean freshwater. Environmental and public health problems may result from insufficient provision of sanitation and wastewater disposal facilities. Because of this, wastewater treatment and recycling methods will be vital to provide sufficient freshwater in the coming decades, since water resources are limited and more than 70% of water are consumed for irrigation purposes. Therefore, the application of treated wastewater for agricultural irrigation has much potential, especially when incorporating the reuse of nutrients like nitrogen and phosphorous, which are essential for plant production. Among the current treatment technologies applied in urban wastewater reuse for irrigation, wetlands were concluded to be the one of the most suitable ones in terms of pollutant removal and have advantages due to both low maintenance costs and required energy. Wetland behavior and efficiency concerning wastewater treatment is mainly linked to macrophyte composition, substrate, hydrology, surface loading rate, influent feeding mode, microorganism availability, and temperature. Constructed wetlands are very effective in removing organics and suspended solids, whereas the removal of nitrogen is relatively low, but could be improved by using a combination of various types of constructed wetlands meeting the irrigation reuse standards. The removal of phosphorus is usually low, unless special media with high sorption capacity are used. Pathogen removal from wetland effluent to meet irrigation reuse standards is a challenge unless supplementary lagoons or hybrid wetland systems are used.

Phosphate enhanced abiotic and biotic arsenic mobilization in the wetland rhizosphere

Although abiotic process of competitive sorption between phosphate (P) and arsenate (As(V)), especially onto iron oxides, are well understood, P-mediated biotic processes of Fe and As redox transformation contributing to As mobilization and speciation in wetlands remain poorly defined. To gain new insights into the effects of P on As mobility, speciation, and bioavailability in wetlands, well-controlled greenhouse experiments were conducted. As expected, increased P levels contributed to more As desorption, but more interestingly the interactions between P and wetland plants played a synergistic role in the microbially-mediated As mobilization and enhanced As uptake by plants. High levels of P promoted plant growth and the exudation of labile organic carbon from roots, enhancing the growth of heterotrophic bacteria, including As and Fe reducers. This in turn resulted in both, more As desorption into solution due to reductive iron dissolution, and a higher fraction of the dissolved As in the form of As(III) due to the higher number of As(V) reducers. Consistent with the dissolved As results, arsenic-XANES spectra from solid medium samples demonstrated that more As was sequestered in the rhizosphere as As(III) in the presence of high P levels than for low P levels. Hence, increased P loading to wetlands stimulates both abiotic and biotic processes in the wetland rhizosphere, resulting in more As mobilization, more As reduction, as well as more As uptake by plants. These interactions are important to be taken into account in As fate and transport models in wetlands and management of wetlands containing As.

Effect of dissimilatory iron and sulfate reduction on arsenic dynamics in the wetland rhizosphere and its bioaccumulation in wetland plants (Scirpus actus)

Microbial redox transformations of arsenic (As) are coupled to dissimilatory iron and sulfate reduction in the wetlands, however, the processes involved are complex and poorly defined. In this study, we investigated the effect of dissimilatory iron and sulfate reduction on As dynamics in the wetland rhizosphere and its bioaccumulation in plants using greenhouse mesocosms. Results show that high Fe (50μM ferrihydrite/g solid medium) and SO₄^2- (5mM) treatments are most favorable for As sequestration in the presence of wetland plants (Scirpus actus), probably because root exudates facilitate the microbial reduction of Fe(III), SO₄^2-, and As(V) to sequester As(III) by incorporation into iron sulfides and/or plant uptake. As retention in the solid medium and accumulation in plants were mainly controlled by SO₄^2- rather than Fe levels. Compared to the low SO₄^2- (0.1mM) treatment, high SO₄^2- resulted in 2 times more As sequestered in the solid medium, 30 times more As in roots, and 49% less As in leaves. An As speciation analysis in pore water indicated that 19% more dissolved As was reduced under high SO₄^2- than low SO₄^2- levels, which is consistent with the fact that more dissimilatory arsenate-respiring bacteria were found under high SO₄^2- levels.

Uranium fate in wetland mesocosms: Effects of plants at two iron loadings with different pH values

Small-scale continuous flow wetland mesocosms (∼0.8 L) were used to evaluate how plant roots under different iron loadings affect uranium (U) mobility. When significant concentrations of ferrous iron (Fe) were present at circumneutral pH values, U concentrations in root exposed sediments were an order of magnitude greater than concentrations in root excluded sediments. Micro X-ray absorption near-edge structure (μ-XANES) spectroscopy indicated that U was associated with the plant roots primarily as U(VI) or U(V), with limited evidence of U(IV). Micro X-ray fluorescence (μ-XRF) of plant roots suggested that for high iron loading at circumneutral pH, U was co-located with Fe, perhaps co-precipitated with root Fe plaques, while for low iron loading at a pH of ∼4 the correlation between U and Fe was not significant, consistent with previous observations of U associated with organic matter. Quantitative PCR analyses indicated that the root exposed sediments also contained elevated numbers of Geobacter spp., which are likely associated with enhanced iron cycling, but may also reduce mobile U(VI) to less mobile U(IV) species.

Ailanthus Altissima and Phragmites Australis for chromium removal from a contaminated soil

The comparative effectiveness for hexavalent chromium removal from irrigation water, using two selected plant species (Phragmites australis and Ailanthus altissima) planted in soil contaminated with hexavalent chromium, has been studied in the present work. Total chromium removal from water was ranging from 55 % (Phragmites) to 61 % (Ailanthus). After 360 days, the contaminated soil dropped from 70 (initial) to 36 and 41 mg Cr/kg (dry soil), for Phragmites and Ailanthus, respectively. Phragmites accumulated the highest amount of chromium in the roots (1910 mg Cr/kg(dry tissue)), compared with 358 mg Cr/kg(dry tissue) for Ailanthus roots. Most of chromium was found in trivalent form in all plant tissues. Ailanthus had the lowest affinity for Cr(VI) reduction in the root tissues. Phragmites indicated the highest chromium translocation potential, from roots to stems. Both plant species showed good potentialities to be used in phytoremediation installations for chromium removal.

Cr(VI) and COD removal from landfill leachate by polyculture constructed wetland at a pilot scale

Four subsurface horizontal-flow constructed wetlands (CWs) at a pilot scale planted with a polyculture of the tropical plants Gynerium sagittatum (Gs), Colocasia esculenta (Ce) and Heliconia psittacorum (He) were evaluated for 7 months. The CW cells with an area of 17.94 m(2) and 0.60 m (h) each and 0.5 m of gravel were operated at continuous gravity flow (Q = 0.5 m(3) day(-1)) and a theoretical HRT of 7 days each and treating landfill leachate for the removal of filtered chemical oxygen demand (CODf), BOD5, TKN, NH4 (+), NO3 (-), PO4 (3-)-P and Cr(VI). Three CWs were divided into three sections, and each section (5.98 m(2)) was seeded with 36 cuttings of each species (plant density of six cuttings per square metre). The other unit was planted randomly. The final distributions of plants in the bioreactors were as follows: CW I (He-Ce-Gs), CW II (randomly), CW III (Ce-Gs-He) and CW IV (Gs-He-Ce). The units received effluent from a high-rate anaerobic pond (BLAAT®). The results show a slightly alkaline and anoxic environment in the solid-liquid matrix (pH = 8.0; 0.5-2 mg L(-1) dissolved oxygen (DO)). CODf removal was 67 %, BOD5 80 %, and TKN and NH4 (+) 50-57 %; NO3 (-) effluents were slightly higher than the influent, PO4 (3-)-P (38 %) and Cr(VI) between 50 and 58 %. CW IV gave the best performance, indicating that plant distribution may affect the removal capacity of the bioreactors. He and Gs were the plants exhibiting a translocation factor (TF) of Cr(VI) >1. The evaluated plants demonstrated their suitability for phytoremediation of landfill leachate, and all of them can be categorized as Cr(VI) accumulators. The CWs also showed that they could be a low-cost operation as a secondary system for treatment of intermediated landfill leachate (LL).

Enhanced semipermanent dialysis samplers for long-term environmental monitoring in saturated sediments

The ability to sample in situ natural environmental processes has proven to be challenging when working with redox-sensitive contaminates in saturated sediments in wetland systems, especially within the rhizosphere, where sharp redox gradients are common. Many traditional approaches are invasive and disturb natural sediment chemistry. Through laboratory and field studies, the work presented in this study demonstrates a novel semipermanent dialysis sampler that allows for long-term, anaerobic monitoring of shallow sediments. Dialysis samplers were deployed and tested for over 1 year while being exposed to extremes in climate. These newly designed devices produce statistically reproducible data and capture sensitive redox trends. Results from the newly designed samplers were compared to conventional samplers. Initially, both the new and old designs yielded statistically similar data, but these data diverged over a period of months. The new devices are less invasive, so data gathered from these devices are more likely to be a closer representation of true conditions in the subsurface. By giving reliable data from a consistent location in space, these new samplers represent a significant step forward in capturing spatial and temporal variability in wetland redox chemistry during long-term monitoring.

Evapotranspiration from pilot-scale constructed wetlands planted with Phragmites australis in a Mediterranean environment

This article reports the results of evapotranspiration (ET) experiments carried out in Southern Italy (Sicily) in a pilot-scale constructed wetland (CW) made of a combination of vegetated (Phragmites australis) and unvegetated sub-surface flow beds. Domestic wastewater from a conventional wastewater treatment plant was used to fill the beds. Microclimate data was gathered from an automatic weather station close to the experimental plant. From June to November 2009 and from April to November 2010, ET values were measured as the amount of water needed to restore the initial volume in the beds after a certain period. Cumulative reference evapotranspiration (ET(0)) was similar to the cumulative ET measured in the beds without vegetation (ET(con)), while the Phragmites ET (ET (phr) ) was significantly higher underlining the effect of the vegetation. The plant coefficient of P. australis (K(p)) was very high (up to 8.5 in August 2009) compared to the typical K(c) for agricultural crops suggesting that the wetland environment was subjected to strong "clothesline" and "oasis" effects. According to the FAO 56 approach, K(p) shows different patterns and values in relation to growth stages correlating significantly to stem density, plant height and total leaves. The mean Water Use Efficiency (WUE) value of P. australis was quite low, about 2.27 g L(-1), probably due to the unlimited water availability and the lack of the plant's physiological adaptations to water conservation. The results provide useful and valid information for estimating ET rates in small-scale constructed wetlands since ET is a relevant issue in arid and semiarid regions. In these areas CW feasibility for wastewater treatment and reuse should also be carefully evaluated for macrophytes in relation to their WUE values.

Distribution and mass balance of hexavalent and trivalent chromium in a subsurface, horizontal flow (SF-h) constructed wetland operating as post-treatment of textile wastewater for water reuse

In this study, during a two-year period, we investigated the fate of hexavalent and trivalent chromium in a full-scale subsurface horizontal flow constructed wetland planted with Phragmites australis. The reed bed operated as post-treatment of the effluent wastewater from an activated sludge plant serving the textile industrial district and the city of Prato (Italy). Chromium speciation was performed in influent and effluent wastewater and in water-suspended solids, at different depths and distances from the inlet; plants were also analyzed for total chromium along the same longitudinal profile. Removals of hexavalent and trivalent chromium equal to 72% and 26%, respectively were achieved. The mean hexavalent chromium outlet concentration was 1.6 ± 0.9 μg l(-1) and complied with the Italian legal limits for water reuse. Chromium in water-suspended solids was in the trivalent form, thus indicating that its removal from wastewater was obtained by the reduction of hexavalent chromium to the trivalent form, followed by accumulation of the latter inside the reed bed. Chromium in water-suspended solids was significantly affected by the distance from the inlet. Chromium concentrations in the different plant organs followed the same trend of suspended solids along the longitudinal profile and were much lower than those found in the solid material, evidencing a low metal accumulation in P. australis.

Accumulation and tolerance characteristics of chromium in a cordgrass Cr-hyperaccumulator, Spartina argentinensis

The cordgrass Spartina argentinensis, which occurs in inland marshes of the Chaco-Pampean regions of Argentina, has been found to be a new chromium hyperaccumulator. A glasshouse experiment was designed to investigate the effect of Cr(6+) from 0 to 20 mmol l(-1) on growth and photosynthetic apparatus of S. argentinensis by measuring chlorophyll fluorescence parameters, gas exchange and photosynthetic pigment concentrations. Boron, calcium, chromium, copper, iron, manganese, magnesium, potassium and phosphorous concentrations were also determined. S. argentinensis showed phytotoxicity at tiller concentration of 4 mg g(-1) Cr, and symptoms of stress at tiller concentration of 1.5 mg g(-1) Cr, as well as reductions in leaf gas exchange, in chlorophyll a fluorescence parameters, in photosynthetic pigment contents and in the uptake of essential nutrients. Reductions in net photosynthetic rate could be accounted for by non-stomatal limitations. Moreover, the bioaccumulator factors exceeded greatly the critical value (1.0) for all Cr treatments, and the transport factors indicated that this species has a higher ability to transfer Cr from roots to tillers at higher Cr concentrations. These results confirmed that S. argentinensis is a chromium hyperaccumulator and that it may be useful for restoring Cr-contaminated sites.

Isolation and characterization of hexavalent chromium-reducing rhizospheric bacteria from a wetland

Scirpus americanus Pers. occurs naturally in "San Germán," a pond that serves as a receptor of industrial wastewater in Guanajuato, México. This plant accumulates metals mainly in the root: concentrations (mg/kg) of Cr, As, Cd and Se were 970, 49, 41, and 85 respectively. Analysis of rhizosphere samples indicated bacterial population of 10(8) cfu g(-1) in media with 0.2 mM Cr(VI) and 10 mM sodium gluconate. Thirteen isolates were obtained and phylogenetic analyses (16S rRNA) indicated they corresponded to genera of Agrobacterium, Arthrobacter, Microbacterium, Curtobacterium, Rhodococcus, Xanthomonas and Pseudomonas. Cr(VI) reduction was evaluated using the diphenyl carbazide method. The isolates accomplished 5-40% (20 microM) of reduction in assays of resting cell and tolerated 0.5-5.0 mM Cr(VI). Eight strains used nitrate and thirteen used iron and chromium as electron acceptors to grow under anaerobic conditions. Cr(VI) reduction by five strains occurred at pH values (7-9) and NaCl concentrations (0.5-1.0 M) in basal medium. A mixed culture of strains (S17 and S28) reached a chromium removal of 100% at 0.2 mM Cr(VI) initial concentration. Aerobically, this consortium was capable of 93.8% Cr(VI) reduction of 81 microg L(-1) Cr(VI) of the industrial effluent, indicating their possible use in environmental cleanup.

Phycoremediation of Chromium (VI) by Nitella and impact of calcium encrustation

This article discusses the applicability of the Charophyte, Nitella pseudoflabellata in the remediation of Cr (VI) contaminated waters at different calcifying potentials. Its growth was found to be positively correlated with Ca in water (CaW), but marginally significant in the presence of Cr (VI) in water (CrW). High CaW resulted in calcite encrustation on the plant cell wall. CaW was found to be aiding Cr (VI) fixation in the long run, as this correlated positively with both CaW and CrW. However, Ca interfered with passive Cr (VI) accumulation in live plant matter at low CrW concentrations (<or=0.2mg/L). Biosorption by dead plant matter seemed to be the major mechanism as the dead plant organs contained >1mg/g Cr dry weight of plant. Cr (VI) concentrations greater than 0.4 mg/L were too toxic, showing maximum quantum efficiency of PSII photochemistry (F(v)/F(m)) values<0.63. The opposite was noticed (F(v)/F(m)>0.76) when Cr (VI) was less than 0.2mg/L. Elongation curve patterns based on shoot lengths showed similar scenarios. In all cases high CaW units with calcite encrustation found to be least affected by Cr (VI) toxicity. Optimum remediation was obtained using a combination of high Ca and Cr (VI) in the case of passive (short-term) operation and low Ca and Cr (VI) for active (long-term) operation. Under the passive scenario, plants accumulated above 1.2mg/g Cr dry weight whereas in the active case, accumulation was 0.8 mg/g Cr dry weight. We conclude that Nitella-mediated Cr (VI) remediation is a promising technique within the range and conditions investigated.

Trace metal behaviour in estuarine and riverine floodplain soils and sediments: a review

This paper reviews the factors affecting trace metal behaviour in estuarine and riverine floodplain soils and sediments. Spatial occurrence of processes affecting metal mobility and availability in floodplains are largely determined by the topography. At the oxic-anoxic interface and in the anoxic layers of floodplain soils, especially redox-sensitive processes occur, which mainly result in the inclusion of metals in precipitates or the dissolution of metal-containing precipitates. Kinetics of these processes are of great importance for these soils as the location of the oxic-anoxic interface is subject to change due to fluctuating water table levels. Other important processes and factors affecting metal mobility in floodplain soils are adsorption/desorption processes, salinity, the presence of organic matter, sulphur and carbonates, pH and plant growth. Many authors report highly significant correlations between cation exchange capacity, clay or organic matter contents and metal contents in floodplain soils. Iron and manganese (hydr)oxides were found to be the main carriers for Cd, Zn and Ni under oxic conditions, whereas the organic fraction was most important for Cu. The mobility and availability of metals in a floodplain soil can be significantly reduced by the formation of metal sulphide precipitates under anoxic conditions. Ascending salinity in the flood water promotes metal desorption from the floodplain soil in the absence of sulphides, hence increases total metal concentrations in the water column. The net effect of the presence of organic matter can either be a decrease or an increase in metal mobility, whereas the presence of carbonates in calcareous floodplain soils or sediments constitutes an effective buffer against a pH decrease. Moreover, carbonates may also directly precipitate metals. Plants can affect the metal mobility in floodplain soils by oxidising their rhizosphere, taking up metals, excreting exudates and stimulating the activity of microbial symbionts in the rhizosphere.

Influence of plants on the reduction of hexavalent chromium in wetland sediments

This work addresses the effect that plants (Typha latifolia and Carex lurida) have on the reduction of Cr(VI) in wetland sediments. Experiments were carried out using tubular microcosms, where chemical species were monitored along the longitudinal flow axis. Cr(VI) removal was enhanced by the presence of plants. This is explained by a decrease in the redox potential promoted by organic root exudates released by plants. Under these conditions sulfate reduction is enhanced, increasing the concentration of sulfide species in the sediment pore water, which reduce Cr(VI). Evapotranspiration induced by plants also contributed to enhance the reduction of Cr(VI) by concentrating all chemical species in the sediment pore water. Both exudates release and evapotranspiration have a diurnal component that affects Cr(VI) reduction. Concentration profiles were fitted to a kinetic model linking sulfide and Cr(VI) concentrations corrected for evapotranspiration. This expression captures both the longitudinal as well as the diurnal Cr(VI) concentration profiles.

The calcium binding protein ALG-2 binds and stabilizes Scotin, a p53-inducible gene product localized at the endoplasmic reticulum membrane

ALG-2 (apoptosis linked gene 2 product) is a calcium binding protein for which no clear cellular function has been established. In this study we identified Scotin as a novel ALG-2 target protein containing 6 PXY and 4 PYP repeats, earlier identified in the ALG-2 binding regions of AIP1/ALIX and TSG101, respectively. An in vitro synthesized C-terminal fragment of Scotin bound specifically to immobilized recombinant ALG-2 and tagged ALG-2 and Scotin were shown by immunoprecipitation to interact in MCF7 and U2OS cell lines. Furthermore ALG-2 bound to endogenous Scotin in extracts from mouse NIH3T3 cells. Overexpression of ALG-2 led to accumulation of Scotin in MCF7 and H1299 cells. In vitro and in vivo binding of ALG-2 to Scotin was demonstrated to be strictly calcium dependent indicating a role of this interaction in calcium signaling pathways.