Seasonality in estuarine sources of methylated arsenic

The effect of seasonal temperature change on the release of methylated arsenic from macroalgae, phytoplankton and sediment porewaters has been investigated by a series of controlled laboratory experiments. The appearance of dissolved arsenic species in the overlying waters was monitored using a coupled hydride generation/GC AA analytical technique. The liberation of dissolved arsenic species by the macroalgae Ascophyllum nodosum was examined under estuarine conditions at 5 °C and 15 °C. At the lower temperature the release rates were 0.2 μg kg^?1 h^?1 (wet weight of material) for monomethylarsenic (MMA) and 0.5 μg kg^?1 h^?1 for dimethylarsenic (DMA), whereas at 15 °C the rates were 0.4 μg kg^?1 h^?1 and 3.2 μg kg^?1h^?1, respectively. Incubation experiments were also carried out at 15 °C using the diatom Skeletonema costatum. During the log growth phase, when chlorophyll a concentrations were in the range 1-5 μg dm^?3, the rate of appearance of DMA in the water was ～3 ng dm^?3 h^?1. Sediment samples from the freshwater and seawater end-members of the Tamar Estuary, UK, were incubated under natural conditions at 5 °C and 15 °C. The freshwater sediments released DMA in preference to MMA; the concentrations of both species increased exponentially and reached a steady state in the overlying water after 250 h. Considerably more DMA was produced at 15 °C than at 5 °C, whilst the amount of MMA produced appeared to be insensitive to the temperature increase. In contrast, the seawater sediments always produced more MMA than DMA and the increase in temperature had little effect on the production of either MMA or DMA. The results of the laboratory experiments were compared with field observations in temperate estuaries, including the Tamar Estuary. The implications of changes of water temperature on the fate of arsenic in estuaries is discussed and modifications to the estuarine arsenic cycle are proposed.     

Analysis of tributyltin in estuarine sediments and oyster tissue,Crassostrea virginica

An analytical method to determine tributyltin (TBT) in oyster tissue, Crassostrea virginica, and estuarine sediments is described. Recoveries of TBT from oysters range from 86 to 102% when samples are fortified at concentrations ranging from 22 to 890 μg kg^?1 (wet weight); recoveries from sediment range from 92 to 105% for samples fortified from 20 to 500 μg kg^?1 (dry weight). Feral oysters and natural sediments were analysed and shown to be contaminated with TBT. Oysters collected near a marina contained concentrations as high as 1.5 mg kg^?1 (wet weight).     

The Employ of Multiple Voltammetric Pulses for the Study of the Adsorption of Bipyridilium Pesticides in River Sediment

The multiple square‐wave voltammetry (MSWV) allied to gold microelectrode (Au‐ME) was used to establish an electroanalytical procedure for the determination of the paraquat and diquat pesticides in river sediment samples. For both pesticides, two reduction peaks, at around ?0.70 V (peak 1) and around ?1.00 V vs. Ag/AgCl 3.00 mol L^?1 (peak 2), with profile of the totally reversible redox process, were observed. The experimental and voltammetric conditions showed that the best conditions to reduce paraquat and diquat were a pH of 6.0, a frequency of 250 s^?1, a scan increment 2 mV, a square‐wave amplitude of 50 mV and pulse number of 8 pulses of potential in each step of staircase of potential. Under such conditions, the detection limit of 0.044 μg L^?1 (0.044 ppb) and 0.360 μg L^?1 (0.360 ppb ) for peak 1 and peak 2 of paraquat and 0.159 μg L^?1 (0.159 ppb) and 0.533 μg L^?1 (0.533 ppb) for peak 1 and peak 2 of diquat, respectively, were obtained. These results are an order of magnitude of about two less than those obtained and published in the literature. Also, the electroanalytical procedure proposed was applied for the determination of adsorption isotherms of pesticides on river sediments samples collected from Mogi‐Guaçu River in Sao Paulo State, Brazil. The experimental data were fitted using the Langmuir and Freundlich isotherms models; and the results indicated low intensities of adsorption process of the pesticides in the samples employed with distribution coefficients (K_d) lower 5.0, and paraquat showed slightly higher affinity than diquat in the sediments. The increase in organic matter and organic carbon leads to an increase in the K_d values, and consequently an increase in the organic matter constant (K_OM) organic carbon constant (K_OC) values. All results demonstrated that isotherms “L” type in the Giles classification were obtained, indicating that sediments have a medium affinity for the pesticides, and no strong competition from the solvent used (in this case Na₂SO₄) for adsorption sites occurs.     

The distribution coefficient of60Co in sediments from the Solway Firth, UK

The behaviour of⁶⁰Co in sea water and sediments typical of the Solway Firth has been investigated. The distribution coefficient,K _d, of⁶⁰Co²⁺ in sediments was determined using the batch sorption method and theK _d variation with aqueous phase composition, sediment type and pH has been studied. Adsorption of⁶⁰Co by sediments was found to be highest in de-ionised water and lower in NaCl solution (31 salinity). Adsorption was lowest in natural sea water, where theK _d range was 2,270 to 2,750. Variation ofK _d with sediment grain size was observed. It was shown that⁶⁰Co adsorption was strongly dependent on pH in de-ionised water, with less variation in NaCl solution. Variance of⁶⁰CoK _d values were lowest in sea water in the range pH 5–8 indicating a more conservative behaviour of⁶⁰Co than previously recognised. Hence⁶⁰Co dispersion will be predominantly govemed by tidal behaviour.     

The determination of chlorinated long-chain paraffins in water,sediment and biological samples

Methods are described for the routine determination of traces of industrial chloro-n-paraffins having 13–30 carbon atoms and chlorine contents of 42–45% (frw/w), in environmental samples of water, sediments and biota. The procedures are based on thin-layer chromatography detection and measurement. All samples are cleaned up by liquid—solid adsorption chromatography and thin-layer chromatography but those rich in lipids require preliminary solvent extraction. The methods distinguish between chloro-n-paraffins based on long carbon chains (C₂₀–C₃₀) and those based on shorter chains (C₁₃–C₁₇). The methods cover the ranges 500 ng l^?1 to 8 μg l^?1 for water (i.e. from about the solubility limit upwards) and 50 μg kg^?1 to 16 mg kg^?1 for sediments and biota. The precision of the methods ranges from ± 50% relative at the lowest concentrations to ± 12% relative at the highest. Recoveries are about 90% for water, 80% for sediments and between 80 and 90% for biota according to sample type.     

Levels of polycyclic aromatic hydrocarbons,polychlorinated byphenyls,methylmercury and butyltins in the natural UNESCO reserve of the biosphere of Urdaibai (Bay of Biscay,Spain)

Polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), methylmercury (MeHg⁺) and butyltins (mono-, di- and tri-butyltin, MBT, DBT and TBT) were monitored in oysters (Crassostrea sp.) and sediments collected in different sampling points of the UNESCO reserve of the biosphere of Urdaibai (Bay of Biscay) from March 2006 to June 2007. In the case of oyster samples, concentrations in the 290–1814 µg kg^?1 (PAHs), 70–475 µg kg^?1 (PCBs), 75–644 µg kg^?1 (MeHg⁺) and 200–1300 µg kg^?1 (as a sum of the three butyltins) ranges were obtained. In most samples TBT was the most abundant butyltin, followed by DBT and MBT. It should be highlighted that most samples exceeded the highest range (367 µg kg^?1) found in the last mussel watch programme carried out by the National Oceanic and Atmospheric Administration (NOAA) for butyltins in oyster samples. This could be due to the presence of a shipyard in the estuary. Sediment concentrations ranged as follows: total PAHs (856–3495 µg kg^?1) and total PCBs (58–220 µg kg^?1). Organometallic species were always below the limits of detection (LODs) (0.24 µg kg^?1 for MeHg⁺, 0.6 µg kg^?1 for MBT, 0.48 µg kg^?1 for DBT and 1.1 µg kg^?1 for TBT). In both sediment and oyster PAH sources were mostly combustion. In the case of PCBs, 4-6 chlorine-atom congeners were the most abundant ones. Slight differences in the profile of PAHs as well as PCBs can be detected when the matrices were compared with each other. Finally, in the case of PAHs, sediment and water column played the main role in the accumulation pathway into the organisms in all the sampling stations.     

Dissolved butyltins in marine waters of the netherlands three years after the ban

In 1990 the Dutch government banned the use of tributyltin-containing antifouling paint for ships up to 25m long. Concentrations of dissolved (<0.45 μm) tributyltin and its degradation products di- and mono-butyltin were determined in six selected marinas during three consecutive years with a frequency of five times a year, starting in 1990. The highest butyltin concentrations were found in Scharendijke located in the salt water lake Grevelingen: up to 2500 ng dm^?3. In tidal-water marinas butyltin concentrations were in the order of 50–300 ng dm^?3, depending on the boating and dredging activity. In some marinas higher butyltin concentrations were found during the summer period, probably indicating the illegal use of tributyltin-containing antifouling paints. No clear trend of decrease in dissolved tributyltin concentrations in the different marinas has been found. Due to the equilibrium between the butyltins dissolved in the water and the butyltins adsorbed onto the sediment, water concentrations will remain more or less constant.     

Adsorption of La,Eu and Lu on raw and modified red clay

Adsorption of La, Eu, and Lu on red clay was studied in an initial concentration range of 10^?4–10^?3 mol/dm³ and a pH range of 2–10. Among the different forms of red clay: T-clay (thermally modified), R-clay (raw, unmodified), Na-clay (sodium form), H-clay (acid form), and HDTMA-clay (surfactant-modified form), T-clay was found to be the most effective adsorbent of the lanthanides studied. The adsorption/desorption isotherms, i.e. log K _d versus log c _eq dependencies, had a linear character. Among the investigated lanthanides, Eu was most strongly bound by the clay surface and, therefore, parameters a (slopes of the lines log K _d = alog c _eq + b) of Eu were the highest compared to those for La and Lu. Desorption isotherms were located above adsorption isotherms, which resulted from chemiadsorption of the investigated lanthanides. Changes in lanthanide adsorption with pH were successfully modelled based on the molar fractions of Ln³⁺, LnOH²⁺, LnCO₃ ⁺, and Ln(CO₃) ₂ ^? species in the aqueous phase [Ln—lanthanide(III)].     

Conversion of arsenite and arsenate to methylarsenic and dimethylarsenic compounds by homogenates prepared from livers and kidneys of rats and mice

Pooled livers and pooled kidneys from rats or mice were homogenized and spiked with arsenite or arsenate in the concentration range 1.3–20 μmol dm^?3. Methylarsenic and dimethylarsenic compounds were determined by the hydride generation technique in the homogenates after a 90 min incubation at 37°C. The rat homogenates methylated arsenite and arsenate more efficiently than the mouse homogenates. Monomethylated arsenic was present in larger amounts than dimethylated arsenic in the rat homogenates. In the absence of reduced glutathione (GSH), no methylation occurred. Addition of GSH promoted monomethylation and dimethylation, whereas dithiothreitol and mercaptoethanol (10 mmol dm^?3) fostered only monomethylation. The amounts of monomethylated arsenic in the rat liver homogenates increased with increasing arsenite concentration (1.3–20 μmol dm^?3) however, the percentage of arsenic that had been methylated decreased. A similar trend, but with much less monomethylarsenic formed, was observed for arsenate-spiked homogenates. Rat kidney homogenates methylated arsenite and arsenate to a much smaller extent than rat liver homogenates. The K_m values for the monomethylation in rat liver homogenates were found to be 5.3 μmol dm^?3 for arsenite and 59 μmol dm^?3 for arsenate.     

Speciation of butyltins in fish and sediment by means of gas chromatography with flame photometric detection

A modified method for the determination of tributyl-, dibutyl-, and monobutyl-tin in fish and sediment samples is proposed. The samples are digested with hydrochloric acid and the butyltin compounds are extracted into a tropolone solution in pentane and pentylated by a Grignard reaction. The products are cleaned up by washing with a sodium hyrdoxide solution, dried over sodium sulphate, concentrated by evaporation and analysed by gas chromatography with flame photometric detection, using an interence filter at 610 nm. Problems peculiar to the fish and sediment samples are overcome by this improved clean-up procedure. The limit of detection for tributyltin in fish is 0.04 m?g g^?1 and the reproducibility at 0.06 μg g^?1, expressed as the relative standard deviation, is 6.8%. Contaminated sediment samples were found to contain the mixed methylbutyl-tin compounds Me₂BuSn⁺ and MeBu₂Sn⁺.     

Nanofibrillar Cellulose‐Chitosan Composite Film Electrodes: Competitive Binding of Triclosan,Fe(CN)63−/4−, and SDS Surfactant

Glassy carbon electrodes are modified with a thin film of a cellulose‐chitosan nanocomposite. Cellulose nanofibrils (of ca. 4 nm diameter and 250 nm length) are employed as an inert backbone and chitosan (poly‐D ‐glucosamine, low molecular weight, 75–85% deacetylated) is introduced as a structural binder and “receptor” or molecular binding site. The composite films are formed in a solvent evaporation method and prepared in approximately 0.8 μm thickness. The adsorption of three molecular systems into the cellulose‐chitosan films is investigated and approximate Langmuirian binding constants are evaluated: i) Fe(CN)₆^4? (K_Ferrocyanide=2.2×10³ mol^?1 dm³ in 0.1 M phosphate buffer at pH 6) is observed to bind to ammonium chitosan functionalities (present at pH<7), ii) triclosan (K_Triclosan=2.6×10³ mol^?1 dm³ in 0.1 M phosphate buffer pH 9.5) is shown to bind only weakly and under alkaline conditions, and iii) the anionic surfactant dodecylsulfate (K_SDS=3.3×10⁴ mol^?1 dm³ in 0.1 M phosphate buffer pH 6) is shown to bind relatively more strongly in acidic media. The competitive binding of Fe(CN)₆^4? and dodecylsulfate anions is proposed as a way to accumulate and indirectly determine the anionic surfactant.     

Determination of Volatile Halogenated Compounds in Tap and Surface Waters from the Gdańsk District

Abstract

The present method is based on preconcentration of organic contaminants on XAD-4 as sorbent, thermal desorption, mineralization and coulometric argentometric titration for the final determination of halides. The results were calculated as the total parameter VOX (volatile organic halogen) expressed as chlorine. The method has been used for the VOX determination in tap water, Vistula river water and Baltic Sea water. Sampling of the Baltic Sea water has been carried out during the research cruise of the r/v ‘Oceania’. The relatively high anthropogenic pollution of the river Vistula (c _vox = 11–45 μg Cl/cd³), Gulf of Gdańsk (c _vox = 0.6–4.5 μg Cl/dm³) and the Pomerania Bay (c _vox = 2 μg Cl/dm³) has been determined. The VOX concentration in the tap water varied between 13 and 56 μg/dm³; that is, this water is seriously polluted by volatile organic halogen compounds.     

IONIC STRENGTH EFFECTS ON THE GROUND STATE COMPLEXATION and TRIPLET STATE ELECTRON TRANSFER REACTION BETWEEN ROSE BENGAL and METHYL VIOLOGEN

Abstract— The equilibrium constants, K_c, for complexation between methyl viologen dication (MV²+) and Rose Bengal, or Eosin Y, decrease with increasing ionic strength. At zero ionic strength K_c is 6500 (± 500) mol^?1 dm³ for Rose Bengal and 3200 (± 200) mol^?1 dm³ for Eosin Y, and these values decrease to 1500 (± 100) and 680 (± 40) mol^?1 dm³, respectively, at an ionic strength of 0.1 mol dm^?3. K_c is independent of pH between 4.5 and 10. ΔH is -25 (± 1) kJ mol^?1 for complexation with either dye, whereas ΔS is -15 (± 3) J K^?1 mol^?1 for Rose Bengal, and - 23 (± 3) J K^?1 mol^?1 for Eosin Y. The complexation constant for Rose Bengal and the neutral viologen, 4,4'-bipyridinium-N, N'-di(propylsulphonate), (4,4'-BPS), is 420 (± 35) mol^?1 dm³, and independent of ionic strength. No complexation could be observed for either Rose Bengal or Eosin with another neutral viologen, 2,2'-bipyridinium-N,N'-di(propylsulphonate), (2,2'-BPS). MV²+ quenches the triplet state of Rose Bengal with a rate constant of 7 × 10⁹ mol^?1 dm³ s^?1, and this rate constant decreases slightly as ionic strength increases. The cage escape yield following quenching, Φ_cc is very low (Φ_cc= 0.02 (± 0.005), and independent of ionic strength. 4,4'-BPS quenches the triplet state of Rose Bengal with a rate constant of 2.2 (± 0.1) × 10⁹ mol^?1 dm³ s^?1, and gives a cage escape yield of 0.033 (± 0.006). 2,2'-BPS quenches the Rose Bengal triplet with a rate constant of 6 (± 1) × 10⁸ mol^?1 dm³ s^?1 and gives a cage escape yield of 0.07 (± 0.01). Conductivity measurements indicate that MV²+(Cl^?)₂ is completely dissociated at concentrations below 2 × 10^?2 mol dm^?3.     

Comparison of carbon aerogel and carbide-derived carbon as electrode materials for non-aqueous supercapacitors with high performance

Two porous carbon materials, one synthesised by pyrolysis of an organic aerogel prepared using sol–gel method and the other synthesised from molybdenum carbide by high temperature chlorination method, were tested as supercapacitor electrode materials in a non-aqueous tetraalkylammonium salt-based electrolyte. The gravimetric capacitance values calculated for the carbon aerogel (CAG)-based system were almost two times smaller (~55?F?g^?1) compared to carbide-derived carbon (C(Mo₂C))-based system (~125?F?g^?1). However, due to the very wide region of ideal polarizability, 3.6?V for C(Mo₂C) and 3.8?V for CAG-based test cells, very high energy densities up to 63?Wh?kg^?1 (34?Wh?dm^?3) and power densities up to 757?kW?kg^?1 (314?kW?dm^?3) were estimated for these systems, respectively. CAG-based system shows very short characteristic charge/discharge time constant values (0.05?s).     

The Nonreversibility of Adsorption-Desorption of Dieldrin and Lindane on Chitin in Seawater

Abstract

Adsorption and desorption of dieldrin and lindane on chitin were investigated in seawater batch tests as a function of chitin concentration, temperature, pH and salinity. For chitin concentrations ranging from 0.5 g l^?1 to 12.5 g l^?1, the pesticide concentrations were varied from 4 μgl^?1 to 65 μg^?1 for dieldrin and from 40 μl^?1 to 680 μg l^?1 for lindane. Both dieldrin and lindane show adsorption-desorption hysteresis at low chitin concentration. At high chitin concentrations (m > 6.25 g l^?1 for dieldrin and m > 10 gl^?1 for lindane) both pesticides exhibit reversible behaviour. However, only lindane adsorption is affected by chitin concentration. These types of behaviour remain fixed in prewashed chitin. However, an increase in the temperature and a decrease in the salinity made the process become reversible. A resistant-reversible two component model has been applied to account for these types of behaviour and provides a way to explain most of the observed effects by defining mass independent distribution coefficients.     

A simplified procedure for the determination of butyltin species in water

A method is described for the analysis of solutions containing inorganic tin and butyltin compounds. It can be used to determine total tin at a concentration of 20 ng dm^?3 using a 5 dm³ sample. The method is based on solvent extraction with dichloromethane containing tropolone and determination of the tin as inorganic tin by atomic absorption spectroscopy using electrothermal atomization. The extracted butyltin compounds can be separated by paper chromatography and the tin content of the individual spot determined as above. Observations on the stability of butyltin compounds in water at the ～2 mg dm^?3 (Sn) are included.     

Continuous sorption of synthetic dyes on dried biomass of microalga Chlorella pyrenoidosa

The sorption of thioflavine T (TT) and malachite green (MG) cationic synthetic dyes on dried biomass of green microalga (Chlorella pyrenoidosa) immobilised in polyurethane foam under continuous column systems conditions using spectrophotometric methods of detection was investigated. Data characterising the sorption of TT and MG on microalgal biomass immobilised in polyurethane foam in a column system from single (C ₀ = 25 μmol dm^?3) or binary equimolar (C ₀ = 25 μmol dm^?3) dye solutions in the form of breakthrough curves were well described by the Thomas (R ² = 0.994–0.912), Yoon-Nelson (R ² = 0.994–0.911), and Clark (R ² = 0.993–0.911) models. Useful parameters characterising the sorption column system were obtained from these mathematical models. The Thomas model, in particular, provided the Q _max (maximal sorption capacity in μmol g^?1) parameter for characterisation of biosorbent and also for evaluation of competitive effects in the TT and MG dyes sorption. For the purposes of biomass regeneration, a one-step desorption of the dyes studied from the microalgal biomass in batch and continuous column systems was performed. Efficiency of TT desorption from microalgal biomass increased in the order: deionised H₂O (50.7 %), 99.5 vol. % 1,4-dioxane (67 %), 20 mmol dm^?3 NiCl₂ (83 %), 96 vol. % ethanol (85 %), 0.1 mol dm^?3 HCl (89 %), 1 mol dm^?3 acetic acid (89 %). In the case of MG, the desorption efficiency increased in the order: deionised H₂O (13 %), 20 mmol dm^?3 NiCl₂ (50 %), 0.1 mol dm^?3 HCl (91 %), 99.5 vol. % 1,4-dioxane (94 %), 1 mol dm^?3 acetic acid (99 %), 96 vol. % ethanol (> 99 %). The presence of carboxyl, phosphoryl, amino, and hydroxyl groups, the important functional groups for sorption of cationic xenobiotics, was also confirmed on the algae biomass surface by potentiometric titration and ProtoFit modelling software. The data obtained showed that the dried immobilised algae biomass could be used as a sorbent for removing toxic xenobiotics from liquid wastewaters or contaminated waters and also presenting the possibilities of mathematical modelling of sorption processes in continuous column systems in order to obtain important parameters for use in practice.     

Electrochemical Determination of Vitamin D3 in Pharmaceutical Products by Using Boron Doped Diamond Electrode

A sensitive square‐wave voltammetry method was developed to determine cholecalciferol (vitamin D₃) in pharmaceutical products at boron‐doped diamond electrode as a working electrode. Vitamin D₃ provided a well‐defined voltammetric peak at around +1.00 V (vs. Ag/AgCl, 3.5 mol dm^?3) in 0.02 mol dm^?3 Britton‐Robinson buffer pH 5.0 prepared in 50 % ethanol. The influence of various factors such as type and pH of the supporting electrolyte, scan rate and square‐wave parameters were studied and optimized. Under optimum conditions, the oxidation peak current increased linearly with the concentration of vitamin D₃ over the range of 2 to 200 μmol dm^?3. The calculated limit of detection and limit of quantitation were 0.17 μmol dm^?3 and 0.51 μmol dm^?3, respectively. The boron‐doped diamond electrode exhibited specific recognition capability for cholecalciferol amongst possible interferences, and the determination of vitamin D₃ was possible in samples such as commercial pharmaceutical products without complicated sample pretreatments.     

Factors affecting interaction of radiocesium with freshwater solids

The paper aims at the analysis of principal factors affecting the interaction of radiocesium with freshwater solids, important for the migration of radiocesium in rivers. Uptake of radiocesium by bottom sediments and suspended solids from small streams was studied as a function of pH and composition of aqueous phase, of the concentration of cesium in water and of the composition of freshwater solids, using laboratory model experiments. pH had negligible effect on the uptake in the pH range 5–9, the uptake decreased at pH values less than 3–5 depending on the nature and concentration of the solids. Addition of cations suppressed the uptake in the order K⁺>Na⁺>Ca²⁺, the suppression began at 0.001, 0.01 and 0.1 mol.dm^?3 concentration, respectively. Increase in cesium concentration in water caused a decrease of radiocesium uptake, but at very low concentrations of cesium combined with higher concentration of sediment (2g·dm^?3) the uptake was independent of cesium concentration. Removal of carbonates, oxidic coatings and organic matter from a sediment did not affect the sorption properties of the sediment. The nature of the effects found confirms that cesium is sorbed mainly by clay components of freshwater solids. Results obtained are compared with literature data and conclusions are drawn on the importance of the factors studied for modelling of radiocesium migration in rivers.