Adsorption for removal of Cd(II) from effluents

The adsorption of Cd(II) onto wollastonite has been reported. Adsorption increased from 55.7 to 93.6% by decreasing the concentration of Cd(II) from 2.0 x 10^‐4M to 0.5 x 10^‐4M. The rearranged Lagergren equation has been used for dynamic modelling of the process. However, the value of rate constant at 30°C was found to be 3.17 x 10^‐2min^‐1. Equilibrium modelling was carried out using the Freundlich isotherm equation and constants have been calculated. Thermodynamic studies were carried out and values of standard free energy (?G°), enthalpy (?H°) and entropy (AS°) were calculated at various temperatures. Low temperatures favour the uptake of Cd(II) in the process.     

Equilibrium and kinetic modelling of Cd(II) biosorption by algae Gelidium and agar extraction algal waste

In this study an industrial algal waste from agar extraction has been used as an inexpensive and effective biosorbent for cadmium (II) removal from aqueous solutions. This biosorbent was compared with the algae Gelidium itself, which is the raw material for agar extraction. Equilibrium data follow both Langmuir and Redlich-Peterson models. The parameters of Langmuir equilibrium model are q(max)=18.0 mgg(-1), b=0.19 mgl(-1) and q(max)=9.7 mgg(-1), b=0.16 mgl(-1), respectively for Gelidium and the algal waste. Kinetic experiments were conducted at initial Cd(II) concentrations in the range 6-91 mgl(-1). Data were fitted to pseudo-first- and second-order Lagergren models. For an initial Cd(II) concentration of 91 mgl(-1) the parameters of the pseudo-first-order Lagergren model are k(1,ads)=0.17 and 0.87 min(-1); q(eq)=16.3 and 8.7 mgg(-1), respectively, for Gelidium and algal waste. Kinetic constants vary with the initial metal concentration. The adsorptive behaviour of biosorbent particles was modelled using a batch reactor mass transfer kinetic model. The model successfully predicts Cd(II) concentration profiles and provides significant insights on the biosorbents performance. The homogeneous diffusivity, D(h), is in the range 0.5-2.2 x10(-8) and 2.1-10.4 x10(-8)cm(2)s(-1), respectively, for Gelidium and algal waste.     

Adhesion of Campylobacter jejuni and Mycobacterium avium onto polyethylene terephtalate (PET) used for bottled waters

Adhesion of the bacteria Campylobacter jejuni and Mycobacterium avium onto polyethylene terephtalate (PET), a polymer widely used within the bottled water industry was measured in two different groundwater solutions. From this, it was found that whilst the percentage cell adhesion for a given strain did not change between groundwater types, substantial variation was obtained between the two bacterial species tested: M. avium (10-30% adhered cells) and C. jejuni (1-2%) and no major variations were measured as a function of groundwater composition for a given strain. To explain this, the interfacial electro-hydrodynamic properties of the bacteria were investigated by microelectrophoresis, with the resultant data analysed on the basis of electrokinetic theory for soft biocolloidal particles. The results obtained showed that M. avium carries a significant volume charge density and that its peripheral layer exhibits limited hydrodynamic flow permeation compared to that of C. jejuni. It was also demonstrated that steric hindrance to flow penetration and the degree of hydrophobicity within/of the outer bacterial interface are larger for M. avium cells. In line with this, the larger amount of M. avium cells deposited onto PET substrates as compared to that of C. jejuni can be explained by hydrophobic attraction and chemical binding between hydrophobic PET and outer soft surface layer of the bacteria. Hydrophobicity of PET was addressed by combining contact angle analyses and force spectroscopy using CH₃-terminated AFM tip.     

Effect of moderate pre-oxidation on the removal of Microcystis aeruginosa by KMnO4-Fe(II) process: significance of the in-situ formed Fe(III)

This study developed a novel KMnO₄-Fe(II) process to remove the cells of Microcystis aeruginosa, and the mechanisms involved in have been investigated. At KMnO₄ doses of 0-10.0 μM, the KMnO₄-Fe(II) process showed 23.4-53.3% higher efficiency than the KMnO₄-Fe(III) process did. This was first attributed to the moderate pre-oxidation of M. aeruginosa by KMnO₄, achieved by dosing Fe(II) after a period of pre-oxidation, to cease the further release of intracellular organic matter (IOM) and the degradation of dissolved organic matter (DOM). The extensive exposure of M. aeruginosa to KMnO₄ in KMnO₄-Fe(III) process led to high levels and insufficient molecular weight of DOM, inhibiting the subsequent Fe(III) coagulation. Additionally, Fe(II) contributed to lower levels of the in-situ formed MnO₂, the reduction product of KMnO₄ which adversely affected algae removal by Fe(III) coagulation. However, the in-situ formed Fe(III), which was derived from the oxidation of Fe(II) by KMnO₄, in-situ MnO₂, and dissolved oxygen, dominated the remarkably high efficiency of KMnO₄-Fe(II) process with respect to the removal of M. aeruginosa. On one hand, in-situ formed Fe(III) had more reactive surface area than pre-formed Fe(III). On the other hand, the continuous introduction of fresh Fe(III) coagulant showed higher efficiency than one-off dosage of coagulant to destabilize M. aeruginosa cells and to increase the flocs size. Moreover, the MnO₂ precipitated on algae cell surfaces and contributed to the formation of in-situ formed Fe(III), which may act as bridges to enhance the removal of M. aeruginosa.     

Imposex and butyltin body burden in Nassarius nitidus (Jeffreys, 1867), in coastal waters within the Basque Country (northern Spain)

Levels of imposex (superimposition of male characters, upon females) and the presence of sterile females are assessed in the gastropod Nassarius nitidus (Jeffreys, 1867), at 22 locations in the Basque Country (northern Spain). At 18 of these localities, butyltin bioaccumulation (tributyltin (TBT); dibutyltin; monobutyltin) was analysed using isotope dilution and GC-ICP-MS. Higher imposex levels and TBT body burden were found in confined harbours, with a large vessel traffic or the presence of a fishing fleet or a shipyard. For the first time, four apparently sequential types of aborted capsules are described in this species. Another novelty is the interspecific comparison between imposex intensities in sympatrically living populations of N. nitidus and N. reticulatus. This showed that sensitivity to TBT pollution of both species is relatively similar (in terms of Relative Penis Length Index). Since N. nitidus has a restricted habitat distribution due to its low presence in wave-exposed habitats, its complementary use with other species is recommended for its use in TBT monitoring programmes.     

Removal of arsenic from water: Effect of calcium ions on As(III) removal in the KMnO4–Fe(II) process

A novel KMnO₄–Fe(II) process was developed in this study for As(III) removal. The optimum As(III) removal was achieved at a permanganate dosage of 18.6 μM. At the optimum dosage of permanganate, the KMnO₄–Fe(II) process was much more efficient than the KMnO₄–Fe(III) process for As(III) removal by 15–38% at pH 5–9. The great difference in As(III) removal in these two processes was not ascribed to the uptake of arsenic by the MnO₂ formed in situ but to the different properties of conventional Fe(III) and the Fe(III) formed in situ. It was found that the presence of Ca²⁺ had limited effects on As(III) removal under acidic conditions but resulted in a significant increase in As(III) removal under neutral and alkaline conditions in the KMnO₄–Fe(II) process. Moreover, the effects of Ca²⁺ on As(III) removal in the KMnO₄–Fe(II) process were greater at lower permanganate dosage when Fe(II) was not completely oxidized by permanganate. This study revealed that the improvement of As(III) removal at pH 7–9 in the KMnO₄–Fe(II) process by Ca²⁺ was associated with three reasons: (1) the specific adsorption of Ca²⁺ increased the surface charge; (2) the formation of amorphous calcium carbonate and calcite precipitate that could co-precipitate arsenate; (3) the introduction of calcium resulted in more precipitated ferrous hydroxide or ferric hydroxide. On the other hand, the enhancement of arsenic removal by Ca²⁺ under acidic conditions was ascribed to the increase of Fe retained in the precipitate. FTIR tests demonstrated that As(III) was removed as arsenate by forming monodentate complex with Fe(III) formed in situ in the KMnO₄–Fe(II) process when KMnO₄ was applied at 18.6 μM. The strength of the “non-surface complexed” As–O bonds of the precipitated arsenate species was enhanced by the presence of Ca²⁺ and the complexation reactions of arsenate with Fe(III) formed in situ in the presence or absence of Ca²⁺ were proposed.     

Patterns of metal bioaccumulation in two filter-feeding macroinvertebrates: Exposure distribution, inter-species differences and variability across developmental stages

This study focused on the metal bioaccumulation of two aquatic insects (Ephoron virgo and Hydropsyche spp.) in order to evaluate the spatial distribution of metals, the interspecific differences between both filter-feeders and the bioaccumulation dynamics during E. virgo development stages. Hg, Cd, Ni, Cr, As, Pb, Cu, Ti, Zn and Mn were quantified in insects and in suspended particulate matter (SPM) sampled downstream and upstream of a chemical plant, where more than 300,000 t of polluted sediments are deposited. Hg concentrations were one order of magnitude higher downstream of the sediment dump, which showed that the Hg pollution originated in the chemical plant. Cd, Ni, Cr, Pb, Ti, Zn and Mn in invertebrates revealed that metal pollution was present upstream in other parts of the river. Interspecific differences were observed for all metals but Mn; significantly higher concentrations were observed in E. virgo over Hydropsyche exocellata, except for Cd, which showed 10-fold higher values. Hg and Cd increased until E. virgo nymphs reached 11 mm and decreased afterwards in late instars when nymphs were about to emerge. Cr, Pb, Ti and Mn decreased along early instars followed by a steady state in late instars. Similar values were obtained for Cu, As and Zn along all instars. Sexual differences between males and females of E. virgo were observed for Cd, Cu and Mn. Hg and Cd persistence was strong across developmental stages since high concentrations were found in eggs and emerging adults. Because the behavior of different metals varied for the two species and during the developmental stages of E. virgo, care should be taken in the interpretation of insect metal concentrations when analyzing the food chain transfer of metals in river ecosystems.     

Detection of genotoxicity in the marine environment: a preliminary feasibility study using primary mussel tissue culture

The purpose of this study was to evaluate the feasibility and potential usefulness of primary cultures of somatic tissues from adult mussel by means of sister chromatid exchange induction (SCE). This research is an initial pilot study carried out with mussel mantle tissue using seawater artificially contaminated with cadmium and polluted seawater from the port of Arcachon. With regard to cadmium concentration, mean SCE numbers showed a progressive increase from 1.07 +/- 0.18 per diploid cell in controls (i.e. cultures without contaminant) to 2.91 +/- 0.42 per diploid cell for the highest concentration, 10 - 4 M. With regard to the medium prepared with seawater from the port of Arcachon, the mean SCE number reached a value of 5.85+/- 0.85 per diploid cell. The analysis of SCEs induced by cadmium showed DNA responses even at the lowest concentration (i.e. 10 - 7 M). The study demonstrates the feasibility of the sister chromatid exchange (SCE) approach based upon primary mussel tissue culture, for the genotoxicity testing of contaminated seawater. Highlights from this procedure are (1) the presence of an active cell proliferation, (2) the use whole-water samples, (3) the possibility of culturing without serum, (4) the absence of cell dissociation before culturing and (5) a cellular proliferation which can be obtained in cultures carried out in a medium containing seawater whose salinity is comprise between 28 and 35 per thousand.     

(210)Po and (210)Pb in the tissues of the deep-sea hydrothermal vent mussel Bathymodiolus azoricus from the Menez Gwen field (Mid-Atlantic Ridge)

The hydrothermal deep-sea vent fauna is naturally exposed to a highly specific environment enriched in potentially toxic species such as sulfides, metals and natural radionuclides due to the convective seawater circulation inside the oceanic crust and its interaction with basaltic or ultramafic host rocks. However, data on radionuclides in biota from such environment are very limited. An investigation was carried out on tissue partitioning of ²¹⁰Po and ²¹⁰Pb, two natural radionuclides within the ²³⁸U decay chain, in Bathymodiolus azoricus specimens from the Mid-Atlantic Ridge (Menez Gwen field). These two elements showed different distributions with high ²¹⁰Pb levels in gills and high ²¹⁰Po levels in both gills and especially in the remaining parts of the body tissue (including the digestive gland). Various factors that may explain such partitioning are discussed. However, ²¹⁰Po levels encountered in B. azoricus were not exceptionally high, leading to weighted internal dose rate in the range 3 to 4 μGy h^− 1. These levels are slightly higher than levels characterizing coastal mussels (~ 1 μGy h^− 1).     

Testing the validity of a Cd soil quality standard in representative Mediterranean agricultural soils under an accumulator crop

The validity of a quality standard for cadmium (Cd) in representative agricultural Mediterranean soils under an accumulator crop (Lactuca sativa L.) is evaluated in this work considering both its effect on the crop growth (biomass production) and the metal accumulation in the edible part of the plant. Four soils with different properties relevant to regulate the behaviour of heavy metals were selected from the Valencian Region, a representative area of the European Mediterranean Region. For all soils, the effective concentration of added Cd causing 50% inhibition (EC₅₀) on the biomass production was much higher than the minimum legal concentration used to declare soils as contaminated by cadmium, i.e. 100 times the baseline value for Cd, in Spain (Spanish Royal Decree 9/2005). As expected, Cd toxicity in the crop was higher in the soils having less carbonate content. On the other hand, for all soils, from the second dose on, which represents 10-times the baseline value for Cd, the metal content in crops exceeded the maximum level established for leaf crops by the European legislation (Regulation EC no. 466/2001). Soil salinity and coarse textures make the accumulation of Cd in the edible part of the plant easier. Therefore, the legal baseline soil cadmium content established by the Spanish legislation seems not valid neither from the point of view of the effect on the crop growth nor from the point of view of the metal accumulation in the edible part of the plant. In order to realistically declare contaminated soils by heavy metals, soil quality standards should be proposed taking into account the soil properties. Further research in other agricultural areas of the region would improve the basis for proposing adequate soil quality standards for heavy metals as highlighted by the European Thematic Strategy for Soil Protection.     

Magnetic binary oxide particles (MBOP): a promising adsorbent for removal of As (III) in water

Magnetic binary oxide particles (MBOP) synthesized using chitosan template has been investigated for uptake capacity of arsenic (III). Batch experiments were performed to determine the rate of adsorption and equilibrium isotherm and also effect of various rate limiting factors including adsorbent dose, pH, optimum contact time, initial adsorbate concentration and influence of presence cations and anions. It was observed that uptake of arsenic (III) was independent of pH of the solution. Maximum adsorption of arsenic (III) was ∼99% at pH 7.0 with dose of adsorbent 1 g/L and initial As (III) concentration of 1.0 mg/L at optimal contact time of 14 h. The adsorption equilibrium data fitted well to Langmuir and Freundlich isotherm. The maximum adsorption capacity of adsorbent was 16.94 mg/g. With increase in concentration of Ca²⁺, Mg²⁺ from 50 mg/L to 600 mg/L, adsorption of As (III) was significantly reduced while for Fe³⁺ the adsorption of arsenic (III) was increased with increase in concentration. Temperature study was carried out at 293 K, 303 K and 313 K reveals that the adsorption process is exothermic nature. A distinct advantage of this adsorbent is that adsorbent can readily be isolated from sample solutions by application of an external magnetic field. Saturation magnetization is a key factor for successful magnetic separation was observed to be 18.78 emu/g which is sufficient for separation by conventional magnate.     

Antimicrobial resistance of fecal bacteria in waters of the Seine river watershed (France)

We studied the prevalences of antimicrobial resistance (AR) and multiple antimicrobial resistance (MAR) among the fecal bacteria found in the rivers of a large watershed under strong anthropogenic pressures, the Seine river watershed (France). Two groups of fecal indicator bacteria, Escherichia coli and intestinal enterococci, were tested for their susceptibility to 16 and 10 antimicrobials respectively, using the disk diffusion method. We found that 42% of the 214 E. coli river isolates were AR (resistant to at least one antimicrobial) and 35% were MAR (resistant to at least two antimicrobials). Among the 148 intestinal enterococci isolates from rivers, 83% were AR and 49% were MAR. We also investigated the sources of AR fecal bacteria found in the rivers of the watershed. A total of 715 E. coli isolates and 476 intestinal enterococci isolates were collected in point sources (municipal and hospital wastewaters) and non-point sources (surface runoff and soil leaching waters from agricultural or forest areas). For E. coli, the prevalence of AR differed widely from source to source and ranked in this order: hospital wastewaters (71%) > municipal wastewaters (44%) > agricultural non-point sources (16%) > forest non-point sources (2%). The prevalence of MAR ranked similarly, and the same trend was observed for intestinal enterococci. The AR level of fecal bacteria in the sources was related to their expected exposure level to antimicrobials before their release into the environment. A MAR index was calculated for every source and a good discrimination between them was thus obtained. At the global scale of the Seine river watershed, domestic wastewaters seemed more likely to be the predominant source of the AR fecal bacteria found in the rivers. This was corroborated by the similarity of the MAR indices from river and municipal wastewater isolates for both fecal indicators.     

Mercury bioacumulation in four tissues of Podocnemis erythrocephala (Podocnemididae: Testudines) as a function of water parameters

A number of environmental factors influence the dynamics of Hg in aquatic ecosystems, yet few studies have examined these factors for turtles, especially from South America. Red-headed river turtle (Podocnemis erythrocephala) is easy to capture in the black waters of Rio Negro, making it the turtle species that is consumed most often by people of the region. In this study, environmental factors and turtle size were investigated to determine their influence on the Hg concentration in blood, muscle, liver and carapace of the red-headed river turtle. Factors investigated included turtle length, pH, dissolved organic carbon and availability of potential methylation sites (floodplain forests and hydromorphic soils). The study was conducted in the Rio Negro basin, where we collected water and turtle blood, muscle, liver and carapace samples from 12 tributaries for chemical analysis. Through radar imagery and existing soil maps with GIS, the percentage of alluvial floodplains and hydromorphic soils (potential methylation sites) was estimated for each drainage basin at sampling points. The mean Hg concentration in blood of P. erythrocephala was 1.64 ng g^− 1 (SD = 1.36), muscle 33 ng g^− 1 (SD = 11), liver 470 ng g^− 1 (SD = 313) and carapace 68 ng g^− 1 (SD = 32). Sex or length did not influence the Hg concentration in P. erythrocephala blood, muscle and liver, but Hg increased in carapace tissue when length size increased (ANCOVA p = 0.007). In the multiple regression analysis, none of the environmental factors studied had a significant relation with blood, muscle, liver and carapace. P. erythrocephala moves among habitats and in the open and interconnected aquatic systems of the Amazon basin, characterized by high levels of limnological variability, a good bioindicator of Hg concentration needs to be relatively sedentary to represent a specific habitat. However, the levels of Hg in liver were sufficient to pose a potential risk to humans that consume them, suggesting the usefulness of P. erythrocephala as a bioindicator.     

Possible interaction between a rodenticide treatment and a pathogen in common vole (Microtus arvalis) during a population peak

A common vole (Microtus arvalis) population peak in Northern Spain in 2007 was treated with large scale application of chlorophacinone, an anticoagulant rodenticide of the indandione family. Voles found dead and trapped alive were collected in treated and untreated areas. Residues of chlorophacinone were analyzed in liver of voles by HPLC-UV. Also, the presence of the pathogen Francisella tularensis was analyzed by PCR in samples of vole spleen. Chlorophacinone (82-3800 ng/g; wet weight liver) was only detected in voles found dead in treated areas (55.5%). The prevalence of F. tularensis in voles found dead in treated areas was also particularly high (66.7%). Moreover, chlorophacinone levels were lower in voles that were PCR-positive for F. tularensis (geometric mean [95% CI], 418 [143-1219] ng/g) than in those that were PCR-negative (1084 [581-2121] ng/g). Interactions between pathogens and rodenticides might be considered to reduce the doses used in baits or to avoid the use of the more toxic 2nd generation anticoagulant rodenticides.     

The influence of biofilms on the migration of uranium in acid mine drainage (AMD) waters

The uranium mine in Königstein (Germany) is currently in the process of being flooded. Huge mass of Ferrovum myxofaciens dominated biofilms are growing in the acid mine drainage (AMD) water as macroscopic streamers and as stalactite-like snottites hanging from the ceiling of the galleries. Microsensor measurements were performed in the AMD water as well as in the biofilms from the drainage channel on-site and in the laboratory. The analytical data of the AMD water was used for the thermodynamic calculation of the predominance fields of the aquatic uranium sulfate (UO₂SO₄) and UO₂⁺⁺ speciation as well as of the solid uranium species Uranophane [Ca(UO₂)₂(SiO₃OH)₂?5H₂O] and Coffinite [U(SiO₄)_1 − x(OH)_4x], which are defined in the stability field of pH > 4.8 and Eh < 960 mV and pH > 0 and Eh < 300 mV, respectively. The plotting of the measured redox potential and pH of the AMD water and the biofilm into the calculated pH-Eh diagram showed that an aqueous uranium(VI) sulfate complex exists under the ambient conditions. According to thermodynamic calculations a retention of uranium from the AMD water by forming solid uranium(VI) or uranium(IV) species will be inhibited until the pH will increase to > 4.8. Even analysis by Energy-filtered Transmission Electron Microscopy (EF-TEM) and electron energy loss spectroscopy (EELS) within the biofilms did not provide any microscopic or spectroscopic evidence for the presence of uranium immobilization. In laboratory experiments the first phase of the flooding process was simulated by increasing the pH of the AMD water. The results of the experiments indicated that the F. myxofaciens dominated biofilms may have a substantial impact on the migration of uranium. The AMD water remained acid although it was permanently neutralized with the consequence that the retention of uranium from the aqueous solution by the formation of solid uranium species will be inhibited.     

In situ feeding assay with Gammarus fossarum (Crustacea): Modelling the influence of confounding factors to improve water quality biomonitoring

In situ feeding assays implemented with transplanted crustacean gammarids have been claimed as promising tools for the diagnostic assessment of water quality. Nevertheless the implementation of such methodologies in biomonitoring programs is still limited. This is explained by the necessity to improve the reliability of these bioassays. The present study illustrates how modelling the influence of confounding factors could allow to improve the interpretation of in situ feeding assay with Gammarus fossarum. We proceeded in four steps: (i) we quantified the influence of body size, temperature and conductivity on feeding rate in laboratory conditions; (ii) based on these laboratory findings, we computed a feeding inhibition index, which proved to be robust to environmental conditions and allowed us to define a reference statistical distribution of feeding activity values through the data compilation of 24 in situ assays among diverse reference stations at different seasons; (iii) we tested the sensitivity of the feeding assay using this statistical framework by performing 41 in situ deployments in contaminated stations presenting a large range of contaminant profiles; and (iv) we illustrated in two site-specific studies how the proposed methodology improved the diagnosis of water quality by preventing false-positive and false-negative cases mainly induced by temperature confounding influence. Interestingly, the implementation of the developed protocol could permit to assess water quality without following an upstream/downstream procedure and to compare assays performed at different seasons as part of large-scale biomonitoring programs.     

Rapid QPCR-based assay for fecal Bacteroides spp. as a tool for assessing fecal contamination in recreational waters

Concentrations of fecal indicator bacteria (FIB; e.g. Escherichia coli, and Enterococcus sp.) can only be used in limited ways for determining the source of fecal contamination in recreational waters because they cannot distinguish human from non-human fecal contamination. Several Bacteroides spp. have been suggested as potential alternative indicators. We have developed a rapid, culture-independent method for quantifying fecal Bacteroides spp. using quantitative PCR (QPCR) targeting the 16S rRNA gene. The assay specifically targets and quantifies the most common human Bacteroides spp. The details of the method are presented, including analyses of a wide range of fecal samples from different organisms. Specificity and performance of the QPCR assay were also tested via a laboratory experiment where human sewage and gull guano were inoculated into a range of environmental water samples. Concentrations of fecal Bacteroides spp., total Enterococcus sp., Enterococcus faecium, Enterococcus faecalis, and Enterococcus casseliflavus were measured using QPCR, and total Enterococcus sp. and E. coli were quantified by membrane filtration (MF). Samples spiked with gull guano were highly concentrated with total Enterococcus sp., E. coli, E. faecalis, and E. casseliflavus, demonstrating that these indicators are prominent in animal feces. On the other hand, fecal Bacteroides spp. concentrations were high in samples containing sewage and were relatively low in samples spiked with gull guano. Sensitivity and specificity results suggest that the rapid fecal Bacteroides spp. QPCR assay may be a useful tool to effectively predict the presence and concentration of human-specific fecal pollution.     

Study on Fe(VI) species as a disinfectant: quantitative evaluation and modeling for inactivating Escherichia coli

Ferrate (Fe(VI)) has high potentials as a multi-purpose water treatment chemical acting as an oxidant, coagulant, and disinfectant, but little detail has been reported concerning its biocidal ability. In this study, the inactivation efficiencies of three Fe(VI) species (H(x)FeO(4)(x-2), x=0, 1, 2) are quantified using Escherichia coli as a model microorganism. E. coli inactivation by Fe(VI) was performed in solutions buffered with 25 mM phosphate in the pH range of 5.6-8.2 and at 25 degrees C. Kinetics of E. coli inactivation were successfully fitted to the Modified Delayed Chick-Watson model in the tested pH range, indicating that log inactivation level of E. coli is linearly proportional to exposure amount of E. coli to Fe(VI). The rate constant of E. coli inactivation by Fe(VI) (k(obs)) that was obtained from the linear regression increased non-linearly from 0.33 to 6.25 l(mg min)(-1) with decreasing pH from 8.2 to 5.6. From the measured pH dependency of k(obs) and the known acidity constants of Fe(VI) species (pK(a), H(2)FeO(4)=3.50 and pK(a), HFeO(4)(-)=7.23), HFeO(4)(-) and H(2)FeO(4) were found to be 3 and 265 times as effective as FeO(4)(2-) in E. coli inactivation, respectively.     

Boron removal by the duckweed Lemna gibba: a potential method for the remediation of boron-polluted waters

Boron (B) is often found in polluted and desalinated waters. Despite its potentially environmental damaging effects, efficient treatments are lacking. The duckweed Lemna gibba has been shown to remove toxic elements from water; however, its applicability to B removal is unknown. In this study, L. gibba was examined for its tolerance to B in water and its B removal efficiency. Duckweed plants were grown in outdoor 12-day batch experiments in nutrient solution containing 0.3-10 mg B L(-1). Plant biomass production was not affected by B over the tested concentrations during the 12-day cultivation period. Boron removal and the bioconcentration factor of B in L. gibba were highest at initial B concentrations below 2 mg L(-1), and decreased as the initial B concentration increased. Boron content in the plants at the end of the experiment ranged between 930 and 1900 mg kg(-1) dry weight, and was comparable to that of wetland plants reported to be good B accumulators. Boron removal by L. gibba may therefore be a suitable option for the treatment of water containing B concentrations below 2 mg L(-1).