Eduarda B.H. Santos

Kinetic approach to heavy metal mobilization assessment in sediments: choose of kinetic equations and models to achieve maximum information.

Studies of trace metal mobilization in sediments are generally performed using sequential extraction schemes at equilibrium. In the present work, a kinetic fractionation of trace metals in sediments has been developed to assess that information. The extraction rate data have been obtained using a single extraction scheme with EDTA and following a protocol previously optimized. Two kinetic equations and two kinetic models were used to fit the experimental data. The two constants equation fits well the extraction rate data used in this work but does not present any physico-chemical meaning. The diffusion model and the two first-order reactions model allow determining which parameter (the reaction between the metal M and the EDTA or the diffusion of the complex M/EDTA) is rate limiting in the trace metal extraction by EDTA. It appears that the two first-order reactions model is more efficient than the diffusion model to fit the present extraction rate data so it can be deduced that the diffusion of the complex M/EDTA is not the limiting step of the trace metal extraction by EDTA in estuarine sediments. In a second part, relationships between the fraction of metals determined with the two first-order reactions model and the sediments composition were established.

The influence of pulp and paper mill effluents on the composition of the humic fraction of aquatic organic matter

The humic fraction of dissolved organic matter was isolated from three sites of River Vouga (Portugal) and its lagoon, corresponding to unpolluted water and water contaminated with pulp mill effluent. Humic substances were characterized by elemental analysis, Fourier transform infrared spectroscopy, CPMAS-13C-NMR spectroscopy and potentiometric titration. The fulvic acids isolated from the most contaminated site exhibit several structural features characteristic of lignosulphonic acids, such as a high sulphur content, the presence of sulphonic groups, higher phenol and methoxyl contents, higher aromaticity and lower carboxyl content than the fulvic acids upstream of the discharge from the pulp mill effluent. The humic substances further downstream still show some of those structural characteristics but they are preferentially shown in the humic acids than in the fulvic acids. These results highlight the importance of the contribution of anthropogenic sources of organic matter to the composition of humic substances from surface waters.

Sorption-desorption behavior of atrazine on soils subjected to different organic long-term amendments.

Sorption of atrazine on soils subjected to three different organic amendments was measured using a batch equilibrium technique. A higher K(F) value (2.20 kg(-1)(mg L(-1))(-N)) was obtained for soil fertilized with compost, which had a higher organic matter (OM) content. A correlation between the K(FOC) values and the percentage of aromatic carbon in OM was observed. The highest K(FOC) value was obtained for the soil with the highest aromatic content. Higher aromatic content results in higher hydrophobicity of OM, and hydrophobic interactions play a key role in binding of atrazine. On the other hand, the soil amended with farmyard manure had a higher content of carboxylic units, which could be responsible for hydrogen bonding between atrazine and OM. Dominance of hydrogen bonds compared to hydrophobic interactions can be responsible for the lower desorption capacity observed with the farmyard manure soil. The stronger hydrogen bonding can reduce the leaching of atrazine into drinking water resources and runoff to rivers and other surface waters.

First spectroscopic study on the structural features of dissolved organic matter isolated from rainwater in different seasons

The complexity of rainwater dissolved organic matter (DOM) and the large percentage considered uncharacterized has made it difficult to determine the role of rainwater DOM in regional and global carbon budgets. Recent studies have concentrated on determining the structural characteristics of the bulk DOM in rainwater, but a comparison between the structural characteristics of rainwater DOM from different seasons is lacking. In this work, DOM was extracted from rainwater collected in different seasons by a procedure based on adsorption onto DAX-8 resin and a comparison between the spectroscopic characteristics of extracted DOM was performed using UV-visible, excitation-emission matrix (EEM) fluorescence and (1)H NMR spectroscopies. Similar structural characteristics were observed for extracted DOM from the different seasons: high content of aliphatic structures, hydroxy and alkoxy groups, carbonyl groups and unsaturated carbon atoms, and low content of aromatic structures when compared with aliphatic structures. The obtained results suggest a model of chemical structures for the extracted DOM from rainwater, as consisting mainly of aliphatic chains, with COOH, -CH(2)OH, -COCH(3), or -CH(3) terminal groups, and with only a minor aromatic component. Moreover, this study suggests that the DOM extracted from rainwater has higher aliphatic character and lower aromatic content than aquatic humic substances. Thus, the chemical characteristics of aquatic humic substances may not be good models for DOM extracted from rainwater.

A solid-phase extraction procedure for the clean-up of thiram from aqueous solutions containing high concentrations of humic substances.

A simple solid-phase extraction (SPE) procedure with an octadecyl bonded phase silica (C(18)) was developed for clean-up of the fungicide thiram from aqueous solutions containing high concentrations of humic substances, for future studies of thiram adsorption onto solid humic substances or soils. Suspensions of humic acids and soil, in aqueous 0.01M CaCl(2) solution, were prepared and used as samples. These extracts were spiked with thiram and immediately applied to a C(18)-SPE cartridge. Thiram was eluted with chloroform and its concentration measured by spectrophotometry at 283nm. Non-spiked aqueous extracts (blanks) and a control sample of thiram in 0.01M CaCl(2) aqueous solution were also prepared and submitted to the same SPE procedure. The results show that humic substances are extensively retained by the C(18) cartridge but are not eluted with CHCl(3). Recoveries of 100-104% were obtained for thiram in the presence of humic substances. The SPE procedure described in this work is an efficient clean-up step to remove the interference of humic substances absorbance and to be coupled to any spectrophotometric or HPLC-UV method, usually used for thiram analysis in food extracts.

BDE-209: kinetic studies and effect of humic substances on photodegradation in water.

BDE-209 is a brominated flame retardant and a priority contaminant, which has been found in several environmental matrices, namely, in water. To date, there are no quantum yield data for BDE-209 photodegradation by sunlight in water, to allow predicting half-life times in aquatic systems. In this work, the kinetics of BDE-209 photodegradation in water was studied and the influence of different fractions of aquatic humic substances (HS) was evaluated. Aqueous solutions of BDE-209 exposed for different periods of time to simulated sunlight were analyzed by HPLC-UV after being concentrated using dispersive liquid-liquid microextraction (DLLME) or solid-phase extraction (SPE). The photodegradation of BDE-209 in aqueous solution followed pseudo-first-order kinetics. The average quantum yield obtained of 0.010 ± 0.001 (about 20-fold lower than the quantum yield determined in ethanol) allow to predict an outdoor half-life time of 3.5 h. The photodegradation percentage of BDE-209 was not significantly affected by the XAD-4 fraction of HS, but it decreased substantially in the presence of humic and fulvic acids. Light screening by the humic substances could not explain this delay, which is probably the result of the association of the compound with the hydrophobic sites of the humic material.

Fluorescence as a Tool for Tracing the Organic Contamination from Pulp Mill Effluents in Surface Waters

Three-dimensional fluorescence spectra of water samples from an eucalyptus bleached kraft pulp mill and from a river, upstream and downstream of the discharge of the effluent, revealed the existence of a peak at δexc = 280 nm and δem = 340 nm Δδ = 60 nm), characteristic of effluentπs organic matter. Humic substances were isolated from the effluent by sequential adsorption onto resins XAD-8 and XAD-4 in series. Their synchronous fluorescence spectra with Δδ = 60 nm do also exhibit an intense signal at δexc = 280 nm (≈ 300 nm in the humic acid fraction). The peak is absent in the spectra of humic substances isolated from a non-polluted site of the river, but it is clearly seen in the spectra of the humic substances from a site downstream of the discharge of the effluent. Synchronous fluorescence spectra (Δδ = 60 nm) of water samples from the river and its lagoon were recorded and revealed to be an easy and fast way of tracing the organic contamination from the effluent. Fluoreszenzspektroskopie zum Nachweis der organischen Kontamination von Oberflachengewassern durch Abwasser der Zellstoffindustrie Die dreidimensionalen Fluoreszenzspektren des Ablaufs einer Eukalyptus-verarbeitenden Zellstofffabrik sowie des Vorfluters oberhalb und unterhalb der Einleitungsstelle weisen einen Peak bei δex = 280 nm und δem = 340 nm (Δδ = 60 nm) auf, der fur die organischen Abwasserinhaltsstoffe der Zellstofffabrik charakteristisch ist. Durch sequentielle Adsorption an XAD-8- und XAD-4-Harz wurden Huminstoffe aus dem Ablauf isoliert. Ihre synchronen Fluoreszenzspektren mit Δδ = 60 nm zeigen ebenfalls ein intensives Signal bei δex = 280 nm bzw. bei ca. 300 nm fur die Huminsaurefraktion. Dieser Peak fehlt in Spektren von Huminstoffen, die aus einem nicht kontaminierten Abschnitt des Flusses isoliert wurden, ist aber in den Spektren von Huminstoffen, die aus einem Flussabschnitt unterhalb der Einleitungsstelle isoliert wurden, deutlich zu erkennen. Anhand der Synchronspektren (Δδ = 60 nm) von Wasserproben aus dem Fluss und der Lagune lasst sich somit die organische Kontamination durch das Abwasser leicht und schnell verfolgen.

The inner filter effects and their correction in fluorescence spectra of salt marsh humic matter

The inner filter effects in synchronous fluorescence spectra (Δλ=60 nm) of sedimentary humic substances from a salt marsh were studied. Accordingly to their type and the influence of plant colonization, these humic substances have different spectral features and the inner filter effects act in a different manner. The fluorescence spectra of the humic substances from sediments with colonizing plants have a protein like band (λexc=280 nm) which is strongly affected by primary and secondary inner filter effects. These effects were also observed for the bands situated at longer wavelengths, i.e., at λexc=350 nm and λex=454 nm for the fulvic acids (FA) and humic acids (HA), respectively. However, they are more important for the band at 280 nm, causing spectral distortions which can be clearly seen when the spectra of solutions 40 mg L(-1) of different samples (Dissolved Organic Carbon - DOC~20 mg L(-1)) are compared with and without correction of the inner filter effects. The importance of the spectral distortions caused by inner filter effects has been demonstrated in solutions containing a mixture of model compounds which represent the fluorophores detected in the spectra of sedimentary humic samples. The effectiveness of the mathematical correction of the inner filter effects in the spectra of those solutions and of solutions of sedimentary humic substances was studied. It was observed that inner filter effects in the sedimentary humic substances spectra can be mathematically corrected, allowing to obtain a linear relationship between the fluorescence intensity and humic substances concentration and preventing distortions at concentrations as high as 50 mg L(-1) which otherwise would obscure the protein like band.

Spectroscopic properties of sedimentary humic acids from a salt marsh (Ria de Aveiro, Portugal): comparison of sediments colonized by Halimione portulacoides (L.) Aellen and non-vegetated sediments

The influence of the colonization of salt marsh sediments with Halimione portulacoides, on the composition of the sedimentary humic acids was evaluated. For this purpose, cores of colonized and non-colonized sediments from a salt marsh in Ria de Aveiro (Portugal) were collected, and the humic acids of different layers were extracted and characterized by Fourier transform infrared, synchronous molecular fluorescence (Δλ = 60 nm) and UV-visible spectroscopies and also by elemental analysis. The infrared spectra suggest the presence of more peptide residues and carbohydrates in the sedimentary humic acids from surface and around the plant roots at the site colonized by H. portulacoides, when compared with the humic acids from the depth-equivalent sediment layers at the non-colonized site. The higher content of protein-type materials is confirmed by the lowest values of C/N ratios and the highest relative intensities of a band at λexc = 280 nm in the fluorescence spectra. The lowest ε280 values obtained in the UV-visible spectra, and the infrared spectra suggest a lower aromatic content of the humic acids from the colonized site.

Humic substances' proton-binding equilibria: assessment of errors and limitations of potentiometric data

The variability of experimental procedures referred to in the literature for the potentiometric acid‐base titrations of humic substances was analysed and the corresponding implications on the titration data were studied. Hysteresis phenomena were observed in the titrations of all the studied samples: two samples of fulvic acids isolated from two different points of river Vouga (Portugal), one XAD-4 fraction isolated from one of those points and the Swannee river reference fulvic acid. Due to those phenomena, carboxyl contents and charge‐pH curves calculated from direct and back-titrations can be considerably different. Other sources of variability, such as changes of the moisture content of samples, different calibration procedures or different equations for the calculation of activity coefficients, are also shown to lead to large variations in the calculated carboxyl contents and charge‐pH curves. # 1999 Elsevier Science B.V. All rights reserved.