Suspended particulate matter determines physical speciation of Fe,Mn, and trace metals in surface waters of Loire watershed

This study investigates the spatiotemporal variability of major and trace elements, dissolved organic carbon (DOC), total dissolved solids (TDS), and suspended particulate matter (SPM) in surface waters of several hydrosystems of the Loire River watershed in France. In particular, this study aims to delineate the impact of the abovementioned water physicochemical parameters on natural iron and manganese physical speciation (homoaggregation/heteroaggregation) among fine colloidal and dissolved (<?10 nm), colloidal (10–450 nm) and particulate (>?450 nm) phases in Loire River watershed. Results show that the chemistry of the Loire River watershed is controlled by two end members: magmatic and metamorphic petrographic context on the upper part of the watershed; and sedimentary rocks for the middle and low part of the Loire. The percentage of particulate Fe and Mn increased downstream concurrent with the increase in SPM and major cations concentration, whereas the percentage of colloidal Fe and Mn decreased downstream. Transmission electron microscopy analyses of the colloidal and particulate fractions (from the non-filtered water sample) revealed that heteroaggregation of Fe and Mn rich natural nanoparticles and natural organic matter to the particulate phase is the dominant mechanism. The heteroaggregation controls the partitioning of Fe and Mn in the different fractions, potentially due to the increase in the ionic strength, and divalent cations concentration downstream, and SPM concentration. These findings imply that SPM concentration plays an important role in controlling the fate and behavior of Fe and Mn in various sized fractions.

Physical speciation by heteroaggregation of (Fe-Mn) compounds: high [SPM]?→?[Fe-Mn] particulate faction; low {SPM]?→?[Fe-Mn] colloid-dissolved fraction.

     

Predicting Pb bioavailability to freshwater microalgae in the presence of fulvic acid: algal cell density as a variable

In order to better understand the relationship between lead speciation and its bioavailability in natural waters, the interactions between Pb(II), fulvic acid and the freshwater alga, Chlorella kesslerii were studied at various algal cell densities. An increase in cellular lead or fulvic acid adsorbed to algae was observed with decrease of the cell density from ca. 10(7) to 10(5)cells ml(-1). In the presence of fulvic acid, cellular Pb was greater than that expected for the same free lead ion concentrations in the absence of fulvic acid in agreement to our previous study. This effect was found to be more pronounced at lower cell density, in accordance with increased fulvic acid adsorption to algae. Good fit between experimental observations and model predictions of cellular Pb at various cell densities, was observed by assuming that fulvic acid adsorbed to algae give rise to additional binding sites for Pb(II). The findings of this study indicate that a further extension of the biotic ligand model which includes the formation of a ternary complex and cell density (or concentration) as an input parameter is needed to improve its site-specific predictive capacity, especially in the case of dissolved organic matter-rich surface waters. This extension of predictive capacity would allow to reduce the deviations from the BLM model predictions for microalgae in the presence of dissolved organic matter and hence will serve as a mechanistic tool for establishing ambient site-specific water quality criteria.     

Molecular size distribution of natural organic matter in raw and drinking waters.

The purpose of this study was to compare the molecular size distribution (MSD) of natural organic matter (NOM) in raw waters (RW) and drinking waters (DW), and to find out the differences between MSD after different water treatment processes. The MSD of NOM of 34 RW and DW of Finnish waterworks were determined with high-performance size-exclusion chromatography (HPSEC). Six distinct fractions were generally separated from water samples with the TSK G3000SW column, using sodium acetate at pH 7 as an eluent. Large and intermediate humic fractions were the most dominant fractions in surface waters (lakes and rivers), while in artificially recharged groundwaters and natural groundwaters intermediate and small fractions predominated. Water treatment processes removed the two largest fractions almost completely shifting the MSD towards smaller molecular size in DW. Granular activated carbon (GAC) filtration, ozonation, and their combination reduced all humic fractions compared to the conventional treatment. Humic fractions correlated with total organic carbon (TOC) content and chemical oxygen demand, this being especially true in RW. The results demonstrate that the HPSEC method can be applied for a qualitative and also for rough estimate quantitative analyzes of NOM directly from RW and DW samples without sample pretreatment.     

Cu(II) acute toxicity to the rotifer Brachionus calyciflorus, as affected by fulvic acids of freshwater origin

Natural fulvic acids (FA) from the Rio Santiago, an affluent of the Rio de la Plata estuary, were isolated by adsorption on XAD-2 at pH 2, and were then characterized by IR and fluorescence spectra, acidity and complexing capacity to Cu(II). The effect of the interaction between FA and Cu(II) on the acute toxicity of this heavy metal was assayed with the rotifer Brachionus calyciflorus in standardized in-vitro tests. A CuSO(4).5H(2)O concentration of 0.080 ppm produced 89.2% mortality in the absence of FA. At FA/Cu ratios >/= 1 no mortality was observed. Based on the values of the FA-Cu binding parameters and acute toxicity inhibition, it was possible to predict the effect of dissolved organic matter on the toxicity of copper in this surface freshwater body.     

Characterization of H+ and Cd2+ binding properties of the bacterial exopolysaccharides

The proton and Cd binding capacities of microbially produced exopolysaccharides, EPS, were quantified by the determination of stability constants and the concentration of complexing sites using H(+) or Cd(2+) selective electrodes in dynamic titrations. The influence of ionic strength, pH and the Cd to EPS ratio was evaluated over large concentration ranges. The applicability of the non-ideal competitive adsorption isotherm combined with a Donnan electrostatics approach was tested with respect to the EPS. Proton and cadmium binding data were compared with literature data examining other ubiquitous environmental ligands including humic substances, alginate, bacteria, etc. Subsequent modelling of Cd speciation in aquatic (fresh and marine waters) and soil systems suggested that the exopolysaccharides would play non-negligible role, under most conditions. The quantitative information provided in this paper thus represents an important advance in our understanding of Cd transport, bioavailability and impact in aquatic and terrestrial systems.     

Effects of aquatic humic substances on a hydrophobic ultrafiltration membrane

Natural humic surface water (pH 5.9), ion exchanged samples of the same water (pH 5.5), and aqueous solutions of isolated humic substances at pH 4.5, 5.5 and 6.5, respectively, were ultrafiltered (15°C, 0.5 bar) using hydrophobic polysulfone membranes (GR51) in a cross-flow flat sheet module. The used membrane did not completely retain natural organic matter from the surface water and the addition of complexing metals did not affect the retention any further. The changes which were induced in the membranes during each filtration run were studied by simultaneous streaming potential and flux measurements in 0.01 M KCl solutions. Zeta potentials were calculated based on the streaming potentials and the results showed changes towards more negative values for all the samples due to adsorption of organic matter onto the surface of the membrane pores. Humic acid affected the membrane charges more than fulvic acid. High ionic strength and low pH enhanced flux reduction and fouling. Filtration of natural waters caused more pore plugging and flux reduction than filtration of solutions of the isolated humic substances.     

Mobilization of soil organic matter by complexing agents and implications for polycyclic aromatic hydrocarbon desorption

Complexing agents are frequently used in treatment technologies to remediate soils, sediments and wastes contaminated with toxic metals. The present study reports results that indicate that the rate and extent of soil organic matter (SOM) as represented by dissolved natural organic carbon (DNOC) and polycyclic aromatic hydrocarbon (PAH) desorption from a contaminated soil from a manufactured gas plant (MGP) site can be significantly enhanced with the aid of complexing agents. Desorption of DNOC and PAH compounds was pH dependent, with minimal release occurring at pH 2-3 and maximal release at pH 7-8. At pH-6, chelate solutions were shown to dissolve large amounts of humic substances from the soil compared to controls. The complexing agents mobilized polyvalent metal ions, particularly Fe and Al from the soil. Metal ion chelation may disrupt humic (metal ion)-mineral linkages, resulting in mobilization of SOM and accompanying PAH molecules into the aqueous phase; and/or reduce the degree of cross-linking in the soil organic matter phase, which could accelerate PAH diffusion.     

Occurrence and distribution of polybrominated diphenyl ethers (PBDEs) in the dissolved and suspended phases of the sea-surface microlayer and seawater in Hong Kong, China

This study reports the first data on the concentration and distribution of polybrominated diphenyl ethers (PBDEs) in the sea-surface microlayer (SML), and their enrichment relative to bulk seawater, for coastal waters in the marine environment of Hong Kong, China. Samples were collected in March 2005 at five sample locations and analysed for eight congeners of primary interest, i.e. BDE 28, 47, 99, 100, 153, 156, 183 and 209. Concentration ranges of summation operatorPBDE in the dissolved phase (DP, defined as sum of truly dissolved and colloidal phase) and suspended particulate matter (SPM) of seawater were 31.1-118.7 pg/l (mean 70.7 pg/l), and 25.7-32.5 pg/l (mean 28.1 pg/l), respectively. Concentrations in the SML were generally higher by factor of 1.3-3.6 in the DP (concentration range from 40.2 to 228.2 pg/l, mean 149.2 pg/l) and by 0.3-2.1 in the SPM (concentration range 8.1-69.1 pg/l, mean 38.2 pg/l). Concentrations of PBDEs were general low and below detection limits in samples of an oceanic character and highest in the sheltered waters of Victoria Harbour. The congeners BDE 28, 47, 100 and 183 were most abundant, where BDE 209 was detected only in trace amounts. It is suggested that Hong Kong's marine waters show relatively low levels of PBDE contamination, and these compounds may originate from the disposal of electronic waste in southern China, as well as untreated discharge of wastewater locally.     

Detection of PCBs in natural waters by front face fluorometry on solid sorbent on account of their fluorescence quantum yields and interaction with humic substances

A method for the detection of PCBs in natural water, based on extraction/concentration with tab shaped elements cut from C18 fiber glass SPE disks coupled with a fluorescence detection has been evaluated. The potential of the method was estimated through the measurement of the fluorescence quantum yields in acetonitrile and limits of detection (LOD) of 11 PCBs congeners and Arochlors 1221 and 1242 in pure water. Most of the LOD values are within the range of PCB concentrations found in highly polluted waters (<1microg l(-1)) and thus confer some interest to the method. However, as expected, naturally present humic substances was shown to compete with the solid phase for PCBs adsorption thus reducing the capability of the method when applied to natural waters. A Stern-Volmer plot of the fluorescence signal reduction in the presence of various type of humic substances leads to apparent sorption coefficients (K(DOC)) significantly higher than the literature values determined for PCBs or for polycyclic aromatic hydrocarbons, indicating that besides complexing PCBs, humic substances may also block some of the adsorption sites at the sorbent surface. An increase of the pH up to 11 was shown to reduce the negative effect of humic substances but their preliminary total denaturation or destruction appears as a prerequisite condition for taking full advantage of the present method.     

Photodegradation of sulfonamide antibiotics in simulated and natural sunlight: Implications for their environmental fate

The photochemical fate of seven sulfonamides was investigated in matrices representative of natural water bodies under various light sources. Fundamental photolysis parameters such as molar absorption coefficient, quantum yield (QY) and first-order rate constants were determined. The photolysis decay rate was dependent on the protonation state of the molecule, pH of the water sample and dissolved organic matter. Natural organic matter was the most significant factor in the indirect photolysis of sulfonamides. Half-lives were in the range of minutes at 254 nm to days under natural sunlight. Under natural sunlight, all sulfonamides showed higher removal rates in natural waters implying that indirect photolysis is the predominant mechanism.     

Source extraction information from air quality data monitored in an Argentinean steel mill

A statistical analysis of a series of ambient air concentrations of suspended particulate matter (SPM) and NO2 is presented. Measurements were taken at four sites that belong to an Argentinean steel mill and in another site located in its vicinity. The air pollutants were measured during a three-week exploratory sampling. The monitoring sites were selected on the basis of relevant characteristics of the emission sources and the corresponding climatological statistics of the last decade. Suspended particulate matter with aerodynamic diameter of less than 10 microm (PM10) and NO2 were continuously measured at only one site, while 1-hr samples of NO2 and 24-hr samples of total SPM and SO2 were collected at the other sites. The registered concentrations show that SPM was the pollutant of major concern. A first estimate about the nature of the contribution of the different sources of particles and NO2 present in the area was obtained through the statistical analysis of measured concentration data coupled with prevalent meteorological variables.     

Metal extractability patterns to evaluate (potentially) mobile fractions in periurban calcareous agricultural soils in the Mediterranean area—analytical and mineralogical approaches

A set of periurban calcareous agricultural Mediterranean soils was spiked with a mixture of Cd, Cu, Pb and Zn at two levels within the limit values proposed by current European legislation, incubated for up to 12 months, and subjected to various one-step extraction procedures to estimate mobile (neutral salts) and potentially mobile metal fractions (complexing and acidic extraction methods). The results obtained were used to study metal extractability patterns according to the soil characteristics. The analytical data were coupled with mineralogical investigations and speciation modelling using the Visual Minteq model. The formation of soluble metal-complexes in the complexing extracts (predicted by the Visual Minteq calculations) led to the highest extraction efficiency with complexing extractants. Metal extractability patterns were related to both content and composition of carbonate, organic matter, Fe oxide and clay fractions. Potentially mobile metal fractions were mainly affected by the finest soil fractions (recalcitrant organic matter, active lime and clay minerals). In the case of Pb, scarce correlations between extractable Pb and soil constituents were obtained which was attributed to high Pb retention due to the formation of 4PbCO₃·3PbO (corroborated by X-ray diffraction). In summary, the high metal proportion extracted with complexing agents highlighted the high but finite capacity to store potentially mobilizable metals and the possible vulnerability of these soils against environmental impact from metal accumulation.     

Adsorption of natural organic matter from waters by iron coated pumice

Natural pumice particles were used as granular support media and coated with iron oxides to investigate their adsorptive natural organic matter (NOM) removal from waters. The impacts of natural pumice source, particle size fraction, pumice dose, pumice surface chemistry and specific surface area, and NOM source on the ultimate extent and rate of NOM removal were studied. All adsorption isotherm experiments were conducted employing the variable-dose completely mixed batch reactor bottle-point method. Iron oxide coating overwhelmed the surface electrical properties of the underlying pumice particles. Surface areas as high as 20.6m(2)g(-1) were achieved after iron coating of pumice samples, which are above than those of iron coated sand samples reported in the literature. For all particle size fractions, iron coating of natural pumices significantly increased their NOM uptakes both on an adsorbent mass- and surface area-basis. The smallest size fractions (<63 microm) of coated pumices generally exhibited the highest NOM uptakes. A strong linear correlation between the iron contents of coated pumices and their Freundlich affinity parameters (K(F)) indicated that the enhanced NOM uptake is due to iron oxides bound on pumice surfaces. Iron oxide coated pumice surfaces preferentially removed high UV-absorbing fractions of NOM, with UV absorbance reductions up to 90%. Control experiments indicated that iron oxide species bound on pumice surfaces are stable, and potential iron release to the solution is not a concern at pH values of typical natural waters. Based on high NOM adsorption capacities, iron oxide coated pumice may be a promising novel adsorbent in removing NOM from waters. Furthermore, due to preferential removal of high UV-absorbing NOM fractions, iron oxide coated pumice may also be effective in controlling the formation of disinfection by-products in drinking water treatment.     

Effects of photodegradation of dissolved organic matter on the binding of benzo(a)pyrene

Dissolved organic matter (DOM) in natural waters can bind various organic pollutants, and the affinity of this binding is strongly influenced by the chemical characteristics of the DOM and water pH. This study examined the effects of photochemically induced alteration of the DOM's chemical properties and water pH on the binding of benzo(a)pyrene (BaP). Time- and pH-series of solar-simulated irradiations were performed on a natural water sample and aqueous DOM solutions prepared from aquatic and soil humic substances. The binding affinity of BaP, expressed as a partition coefficient of a compound to DOM, decreased substantially after the DOM samples were irradiated over environmentally relevant radiation doses and pH ranges. The lowering of the pH due to the photoproduction of acidic products often partly offsets the reduction of the binding affinity caused by direct photoalteration of the DOM's chemical structure. The decrease of the binding affinity, after correction for the photoinduced pH change, was positively correlated with the decrease in the molecular weight and the aromaticity of the DOM in the course of irradiation. Increasing O(2) abundance accelerated the decrease of the binding affinity as a result of enhanced DOM photodegradation. Visible light played a more important role in reducing the molecular weight and aromaticity of the DOM than in reducing the content of dissolved organic carbon (DOC) via photoremineralization while the reverse was true for UV radiation, indicating that photochemical reduction of the binding affinity may occur in natural waters at depths greater than UV radiation can reach. A decrease of the affinity of DOM for binding BaP will increase the free dissolved fraction of BaP and thus its availability and toxicity to aquatic organisms. The results from this study may have similar implications for organic pollutants other than BaP.     

Metal concentrations in Kandalaksha Bay, White Sea (Russia) following the spring snowmelt

Elevated concentrations of dissolved and particulate Cd, Cu, Pb and Zn have been determined in the waters of Kandalaksha Bay (White Sea, Russia), following the ice melt in the spring of 2000. Dissolved metal maxima in the surface waters were observed at some stations and concentrations generally decreased with depth. The suspended particulate matter (SPM) comprised a non-lithogenic fraction in the range 12-83%, and had elevated metal concentrations that showed no trend with depth or salinity and was compositionally distinct from the sediments. A log-linear relationship existed between the concentrations of metals in sediments and in SPM and their respective Al concentrations, indicating a source of metal-rich particles, with low Al content, to the Bay. The results suggest that Kandalaksha Bay has been impacted by industrial activity on the Kola Peninsula and that restricted water exchange will hinder its recovery from metal contamination.     

Fluorescence and DOC contents of estuarine pore waters from colonized and non-colonized sediments: effects of sampling preservation

The influence of the colonization of salt marsh sediments with Halimione portulacoides was evaluated by analysing the fluorescent dissolved organic matter (FDOM) in sediment pore waters from a salt marsh at different depths. Cores of sediments at colonized and non-colonized sites were collected from a coastal lagoon (Ria de Aveiro, Portugal). The DOC content of extracted pore waters was determined and characterized by synchronous molecular fluorescence (Deltalambda=60nm) and UV-visible spectroscopies. The common practice of freezing sediment cores for further and later chemical investigation was shown not to be an appropriate methodology of sample preservation. On the contrary, freezing of extracted and filtered pore water seemed not to affect either the DOC content or the fluorescence properties of pore waters. Two types of fluorescent substances were found in the pore waters spectra; one corresponding to humic-like substances and another one resembling proteins. However, major differences were found in the spectra of pore waters depending on both depth and the presence/absence of vegetation colonization.     

Fractionation and composition of colloidal and suspended particulate materials in rivers

The association of pollutants (nutrients, heavy metals and organic compounds) with colloidal and suspended particle matter (SPM) plays a dominant role in determining their transport, fate, biogeochemistry, bioavailability and toxicity in natural waters. A scheme for the fractionation and composition of colloidal and SPM from river waters has been tested. All four separation methods, i.e. sieving, continuous flow centrifugation, tangential flow filtration, sedimentation field-flow fractionation, were for the first time used to separate five size particulate fractions from river. Significant (gram) amounts of colloidal material (<1 microm) in three size ranges, nominally 1-0.2, 0.2-0.006 and 0.006-0.003 microm were obtained. The separation scheme was able to process large samples (100 l), within reasonable times (1 day) and the apparatus was portable. The aquatic colloid size was also characterized with high resolution by using sedimentation field-flow fractionation technique. The mass-based particle size distribution for the water sample showed a broad size distribution between 0.05 and 0.4 microm with the maximum around 0.14 microm. There was a systematic increase in the content of organic carbon (estimated by loss on ignition), Mg, Ca, Na, Cu and Zn with decreasing particle size, highlighting the importance of the colloidal (<1 microm) fraction. It was concluded that the colloidal Cu and Zn concentrations in rivers might be much higher than those reported before.     

Aging and temperature effects on DOC and elemental release from a metal contaminated soil

The combined effect of time and temperature on elemental release and speciation from a metal contaminated soil (Master Old Site, MOS) was investigated. The soil was equilibrated at 10, 28, 45, 70 and 90 degrees C for 2 days, 2 weeks, and 2 months in the laboratory. Dissolved organic carbon (DOC), total soluble elements (by ICP), and labile metals (by DPASV) were determined in the filtered (0.22 microm) supernatants. For the samples equilibrated at 90 degrees C, DOC fractions were size fractionated by filtration and centrifugation; a subsample was only centrifuged while another was also filtered through a 0.45 microm filter. Analyses of the supernatants (ICP, DPASV, DOC) were performed on all size fraction subsamples. Dissolved organic carbon (DOC) increased both with temperature and incubation time; however, metal behavior was not as uniform. In general, total soluble metal release (ICP) paralleled the behavior of DOC, increasing with both time and temperature, and confirming the importance of soil organic matter (SOM) in metal retention. Voltammetric analysis (dpasv) of Cu and Zn showed that very little of these metals remains labile in solution due, presumably, to complexation with dissolved organic matter. Labile concentrations of Cd, on the other hand, constituted a significant portion (50%) of total soluble Cd. Copper and Al increased in solution with time (up to 2 months) and temperature up to 70 degrees C; however, at 90 degrees C the soluble concentration declined sharply. The same behavior was observed after equilibration for longer periods of time (550 days) at lower temperatures (23 and 70 degrees C). While concentrations of labile Cu and total soluble Cu and Al increased in the unfiltered samples, the trend remained the same. DPASV analysis showing shifts in labile Cu complexes with temperature and time, together with the results from the unfiltered samples, lead to the hypothesis that Cu was complexing with large polymers that could form at the elevated temperature, and thus be removed from the analyzed solution. It is possible that Cu and Al released by SOM oxidation has re-sorbed or complexed to more recalcitrant organic matter or to mineral phases. Variations in the relative molecular size fractions present within the DOC pool produced by increased time and temperature may influence the element-DOC complexes present in solution and their behavior in soil environments.     

北运河表层沉积物对重金属Cu、Pb、Zn的吸附

首先分析了北运河6个采样点表层沉积物中重金属含量及相关基本特征。通过实验室模拟实验,利用分配系数Kd评价沉积物对重金属Cu、Pb、Zn的吸附特性,进一步考察了水体pH变化和有机质对重金属在北运河沉积物上吸附的影响。结果表明,沉积物中重金属的含量顺序为Zn>Cu>Pb,去除有机质后,沉积物对重金属的吸附能力显著降低,但各采样点中的重金属含量,沉积物对重金属吸附能力,以及沉积物中的有机质含量并没有明显相关性,这可能是因为不同采样点中有机质种类与结构不同导致的。总之,北运河沉积物对Pb有很强的吸附能力,其次是Cu和Zn,而且,Cu、Zn、Pb的吸附量随着pH的升高逐渐增大,水体pH值对于Zn的吸附影响更大。     

Removal of metal ions from the complexed solutions in fixed bed using a strong-acid ion exchange resin

Fixed bed removal of equimolar metal ions (Co²⁺, Ni²⁺, Mn²⁺, Sr²⁺) from aqueous solutions using a strong-acid resin was examined. The solution contained a water-soluble complexing agent including ethylenediaminetetraacetic acid, nitrilotriacetic acid, and citric acid. Experiments were performed under different solution pH and molar concentration ratios of complexing agent to the total metals. It was shown from batch studies that the equilibrium exchange of metals and the resin mainly depended on solution pH, and partly on the type of complexing agent used. A mass transfer model was proposed to describe the breakthrough curves of the resin bed, which contained two parameters (τ and k) estimated from the observed breakthrough data. The calculated breakthrough curves agreed well with the measured ones (standard deviation <6%). In fixed bed tests at low pH (=2), the type of complexing agent had little effect on the breakthrough data. For a given complexing agent, the metal with a larger overall formation constant (K_f) showed a smaller exchange capacity. For a given metal ion, the complexing agent with a larger K_f also revealed a smaller exchange capacity.