Aquatic Humic Substances Research Articles

Seasonal studies of aquatic humic substances from Amazon rivers: characterization and interaction with Cu (II), Fe (II), and Al (III) using EEM-PARAFAC and 2D FTIR correlation analyses.

Aquatic humic substances (AHS) are defined asan important components of organic matter, being composed as small molecules in a supramolecular structure and can interact with metallic ions, thereby altering the bioavailability of these species. To better understand this behavior, AHS were extracted and characterized from Negro River, located near Manaus city and Carú River, that is situated in Itacoatiara city, an area experiencing increasing anthropogenic actions; both were characterized as blackwater rivers. The AHS were characterized by 13C nuclear magnetic ressonance and thermochemolysis GC-MS to obtain structural characteristics. Interaction studies with Cu (II), Al (III), and Fe (III) were investigated using fluorescence spectroscopy applied to parallel factor analysis (PARAFAC) and two-dimensional correlation spectroscopy with Fourier transform infrared spectroscopy (2D-COS FTIR). The AHS from dry season had more aromatic fractions not derived from lignin and had higher content of alkyls moities from microbial sources and vegetal tissues of autochthonous origin, while AHS isolated in the rainy season showed more metals in its molecular architecture, lignin units, and polysacharide structures. The study showed that AHS composition from rainy season were able to interact with Al (III), Fe (III), and Cu (II). Two fluorescent components were identified as responsible for interaction: C1 (blue-shifted) and C2 (red-shifted). C1 showed higher complexation capacities but with lower complexation stability constants (KML ranged from 0.3 to 7.9 × 105) than C2 (KML ranged from 3.1 to 10.0 × 105). 2D-COS FTIR showed that the COO- and C-O in phenolic were the most important functional groups for interaction with studied metallic ions.

Environmental condition-dependent effects of aquatic humic substances on the distribution of phenanthrene in microplastic-contaminated aquatic systems

Numerous studies have focused on the interaction between microplastics (MPs) and phenanthrene (PHE) in aquatic environments. However, the intricate roles of aquatic humic substances (HS), which vary with environmental conditions, in influencing PHE-MP interactions are not yet fully understood. This study investigates the variable and environmentally sensitive roles of HS in modifying the interactions between PHE and polyethylene (PE) MPs under laboratory-simulated aquatic conditions with varying solution chemistry, including pH, HS types, HS concentrations, and ionic strength. Our findings show that the presence of HS significantly reduces the adsorption of PHE onto both pristine and aged PE MPs, with a more pronounced reduction observed in aged PEs. This effect is highlighted by a notable decrease in the partitioning coefficient (Kd) of PHE, which falls from 2.60 × 104 to 1.30 × 104 L/kg on MPs in the presence of HS. The study also demonstrates that alterations in the net charge of HS solutions are crucial in modifying PHE distribution onto PEs. An initial decrease in Kd values at higher pH levels is reversed when HS is introduced. Furthermore, an increase in HS concentrations is associated with lower Kd values. In conditions of higher ionic strength, the retention of PHE by HS is intensified, likely due to an enhanced salting-out effect. This research highlights the significant role of aquatic HS in modulating the distribution of PHE in MP-polluted waters, which is highly influenced by various solution chemistry factors. The findings are vital for understanding the fate of PHE in MP-contaminated aquatic environments and can contribute to refining predictive models that consider diverse solution chemistry scenarios.

Interactions of ferrate(VI) and aquatic humic substances in water treatment

Aquatic humic substances, encompassing humic acid (HA) and fulvic acid (FA), can influence the treatment of ferrate(VI), an emerging water treatment agent, by scavenging Fe(VI) to accelerate its decomposition and hinder the elimination of target micro-pollutants. Meanwhile, HA and FA degrade the water quality through the transformation to disinfection byproducts over disinfection, contribution to water color, and enhanced mobility of toxic metals. However, the interplay with ferrate(VI) and humic substances is not well understood. This study aims to elucidate the interactions of ferrate(VI) with HA and FA for harnessing ferrate(VI) in water treatment. Laboratory investigations revealed distinctive biphasic kinetic profiles of ferrate(VI) decomposition in the presence of HA or FA, involving a 2nd order kinetic reaction followed by a 1st-order kinetic reaction. Both self-decay and reactions with the humic substances governed the ferrate(VI) decomposition in the initial phase. With increasing dissolved organic carbon (DOC), the contribution of self-decomposition to ferrate(VI) decay declined, while humic substance-induced ferrate(VI) consumption increased. To assess relative contributions of the two factors, DOC50% was first introduced to represent the level at which the two factors equally contribute to the ferrate(VI) loss. Notably, DOC50% (11.90 mg/L for HA and 13.10 mg/L for FA) exceeded typical DOC in raw water, implying that self-decay predominantly governs ferrate(VI) consumption. Meanwhile, ferrate(VI) could degrade and remove HA and FA across different molecular weight (MW) ranges, exhibiting treatment capabilities that are either better or, at least, equivalent to ozone. The ferrate(VI) treatment attacked high MW, hydrophobic organic molecules, accompanied by the production of low MW, more hydrophilic compounds. Particularly, FA was more effectively removed due to its smaller molecular sizes, higher solubility, and lower carbon contents. This study provides valuable insights into the effective utilization of ferrate(VI) in water treatment in presence of humic substances.

Impact of aquatic humic substances on speciation and toxicity of arsenic and cobalt to Ceriodaphnia dubia.

Humic substances (HS) interact with trace metals such as As and Co, affecting their mobility and availability in aquatic systems. However, their combined effects on toxicity to aquatic organisms are not totally understood. The objective of this study was to evaluate the toxicity of Co(II) and As(III) to the water flea Ceriodaphnia dubia in the presence of HS, considering element speciation. Toxicity assays were performed in the presence and absence of HS at two different concentrations of As(III) (10 and 20 μg/L) and Co(II) (50 and 100 μg/L). The free As(III) and Co(II) (< 1 kDa, fraction most potentially bioavailable) in the test solutions were determined via ultrafiltration. While free Co(II) decreased by approximately 80% in the presence of HS, free As(III) decreased just by 1%. Despite the higher percentage of As(III) potentially bioavailable, the presence of HS reduced significantly the toxicity of As at 20 μg/L (no toxicity was observed at 10 μg/L). This was attributed to direct effects of HS such as hormesis, hormone-like effects of HS and/or formation of protective coating. These effects also stimulated the reproduction, including in the assays in the absence of As and Co. HS reduced the toxicity of Co(II) at both test concentrations. The results of this investigation support that HS should be considered when safe limits for As and Co are defined.

Calibration of high performance size exclusion chromatography (HPSEC) for molecular weight estimation of aquatic humic substances

Three high performance size exclusion chromatography (HPSEC) columns were compared, along with mobile phase chemistry and calibration standards, for the determination of apparent molecular weight (AMW) of aquatic humic substances using a UV absorbance detector (λ = 254 nm). The addition of 10 % organic solvent did not influence peak elution times of sodium polystyrene sulfonate (PSS) standards or chromatograms of Suwannee River humic acid (SRHA) or fulvic acid (SRFA) but did result in an additional peak being detected in a treated municipal wastewater sample (WWT). Mobile phase concentration was found to have a greater effect on peak position of PSS standards and SRHA than mobile phase pH or sample injection volume. Several chemicals of known molecular weight were tested alongside PSS standards, with salicylic acid (138.1 Da) and 4-chlorobenzoic acid (156.6 Da) resulting in retention times that aligned with the PSS MW standards. Of the three columns tested, the two with comparable pore sizes (i.e., 250 and 300 Å) were found to result in similar peak elution times and highly linear calibration curves over the range of 210–17,000 Da, while the column with the smaller pore size (i.e., 100 Å) gave better peak separation in the low AMW range (i.e., < 1000 Da). Estimations of AMW of SRHA using various sets of calibration standards on one of the three columns tested ranged from 1080 to 2799 Da using 0.02 M NH4CH3CO2 as eluent and 60-µL injections. AMW of SRFA ranged from 939 to 2434 Da for the same conditions.

Combined effects of humic substances and clay minerals on U(VI) bioreduction

In the last several decades, microbial reduction of U(VI) to U(IV) has been applied as a method to remediate uranium contamination in situ. The U(VI) bioreduction kinetics and resulting U(IV) speciation are affected by various environmental factors, such as humic substances (HS) and Fe-bearing clay minerals. Previous studies have largely focused on their individual effects on U(VI) bioreduction. However, HS and Fe(III)-bearing clay minerals often co-exist at uranium contaminated sites, their joint effects may be different from the sum of their individual ones, due to either synergistic or antagonistic interactions between the two. In this work, we investigated the combined effects of HS and Fe(III)-bearing clay minerals (Fe-rich nontronite and Fe-poor montmorillonite) on U(VI) reduction by Shewanella putrefaciens and the resulting U(IV) speciation. HS alone exhibited an inhibitory effect on U(VI) bioreduction, likely because HS retained a fraction of electrons from microbial oxidation of lactate. The resulting U(IV) was in the form of aqueous U(IV)-HS complex. Clay minerals alone also inhibited U(VI) bioreduction because a fraction of reduced U(IV) was likely re-oxidized by structural Fe(III) and thus electrons were partially diverged from U(VI) to structural Fe(III). Bioreduced U(IV) was in a solid phase. However, in the presence of both HS and clay minerals, their combined effect of inhibition on U(VI) bioreduction was not a simple addition of the two individual ones. In the co-presence of clay minerals and a low concentration of HS (10 and 20 mg C/L), their combined inhibition effect on U(VI) bioreduction was stronger than that of HS but weaker than that of clays. The stronger inhibition than that of HS alone was due to electron diversion by clay minerals. The weaker inhibition than that of clays alone was because HS and/or Fe(III)-HS/Fe(II)-HS served as electron shuttles to accelerate the rate of Fe(III) reduction. These double shuttles decreased the ability of structural Fe(III) in clays to diverge electrons from U(VI) and thus partially negated the inhibitory effect of clay minerals. In the co-presence of clay minerals and a high concentration of HS (100 mg C/L), their combined effect on U(VI) bioreduction was initially similar to that in the low concentration of HS scenario. However, over extended time, clay minerals partially negated the inhibitory effect of HS, likely because clay minerals adsorbed a fraction of HS and thus lowered the ability of residual aqueous HS to retain electrons. Biogenic U(IV) was sequestered in solid in the presence of Fe-rich nontronite and HS but partially remained soluble in the presence of Fe-poor montmorillonite and HS. This study highlights the importance of the complex interaction between HS and Fe-bearing clays in bioreduction of U(VI) and speciation of the resulting U(IV).

Prediction of polarity-dependent environmental behaviors of humic substances (HS) using a HS hydrophobicity index based on hydrophilic interaction chromatography

A variety of analytical methods have been applied to describe the properties of aquatic humic substances (HS). However, there are only a few methods available to probe HS hydrophobicity because of the heterogeneous character of HS. In this study, hydrophilic interaction chromatography (HILIC) equipped with a UV detector was employed to describe the heterogeneous distribution of HS with respect to its hydrophobicity and to suggest a representative HS hydrophobicity index. To this end, various mobile phases were explored to achieve the optimal separation capability of HILIC. The highest resolution was obtained with a mobile phase comprising acetonitrile and water at a ratio of 70:30 (v:v). A calibration curve was successfully constructed using eight different HS precursor compounds, which allowed for the successful conversion of the retention time (RT) into the octanol-water partition coefficient (Kow) (log Kow = −2.83 × (RT) + 17.44, R2 = 0.950). Several possible HS hydrophobicity indices were derived from the HILIC chromatogram. Among those, the weight-average log KOW value exhibited the strongest negative correlation with the well-known polarity index, (O + N)/C ratios, of seven reference HS samples. This new HILIC-based index (i.e., average log KOW) also presented a good relationship with the HS binding coefficients with pyrene as well as the extent of HS adsorption onto kaolinite at a given solution chemistry (i.e., at a high ionic strength and a neutral pH), both of which are known to be largely governed by the hydrophobic nature of HS. This study demonstrated that the average KOW value based on HILIC is an intuitive and robust HS hydrophobicity index to fully represent the heterogeneous distribution of hydrophobicity within a bulk HS and could be applied to predict many environmental behaviors related to HS hydrophobicity or HS polarity.

Change in adsorption behavior of aquatic humic substances on microplastic through biotic and abiotic aging processes

Interactions between microplastics (MPs) and humic substances (HS) are inevitable in MP-contaminated aquatic environment because of the ubiquitous presence of HS. In this study, we explored the effects of abiotic and biotic aging processes on the adsorption behavior of aquatic HS on MPs. Aging experiments were conducted using polyethylene (PE) as a representative MP, in which UV irradiation and microbial incubation were applied for 15 to 18 days to mimic the natural abiotic and biotic aging processes. Surface modifications after the aging treatments were evidenced by the appearance of CO, CO, O-C=O, and -OH groups; the formation of grooves on UV-aged PE; and the formation of biofilms on the surface of bio-aged PE. The specific surface areas of both treated PE MPs increased with aging. Higher HS adsorption on PE surface was observed after the aging treatments, with a highest kinetic rate for UV-aged PE than that for bio-aged PE. The adsorption isotherm models revealed that the aging processes enhanced the HS adsorption tendency, as evidenced by the highest adsorption capacity for UV-aged PE (~187 μg C/m2), followed by bio-aged PE (~157 μg C/m2) and pristine PE (~87.5 μg C/m2) for a comparable extended aging period (15–18 days). The difference was more pronounced at a lower pH. The enhanced HS adsorption was mainly attributed to the formation of hydrogen bonds, whereas HS adsorption on pristine PE was dominated by hydrophobic interactions and weak van der Waals interactions. Among the two identified fluorescent components (terrestrial humic-like C1 and protein-like C2), C1 exhibited a higher affinity for adsorption onto PE irrespective of aging. Our findings provide insights into the substantial changes that occur in the interactions between MPs and aquatic organic matter with aging processes, which may alter the fate and environmental impacts of MPs in many aquatic systems.

Activation of persulfate by humic substances: Stoichiometry and changes in the optical properties of the humic substances

Persulfate activation through electron transfer from humic substances (HS) was investigated. Persulfate consumption in the presence of standard HS and HS model compounds linearly correlated with the phenol contents of the HS. Redox-active carbonyl groups such as aromatic ketones and quinone also contributed to persulfate consumption by donating electrons while being reduced. Phenols activated persulfate through direct electron transfer from the phenolate forms but reduced ketones activated persulfate through reactions between their organic radicals and persulfate. Persulfate was activated more by terrestrially derived aquatic HS containing large numbers of phenol groups than by other species, and this caused more benzene oxidation to occur in the presence of terrestrially derived aquatic HS than in the presence of other species. Larger amounts of sulfate radicals were scavenged by soil-derived HS than other types of HS because soil-derived HS were composed of larger molecules than other types of HS. The fluorescence regional integration volume for HS reacted with persulfate linearly correlated with persulfate consumption. Decreases in the fluorescence regional integration value could be used to predict persulfate activation through electron transfer from HS to persulfate if the electron-donating capacity cannot be determined. Persulfate activation by HS is expected to be stoichiometrically more advantageous than conventional persulfate–Fe2+ processes when treating an aquifer containing large amounts of electron-rich HS.

Complejación de metales por sustancias húmicas acuáticas como proceso natural, tomando como caso de estudio el Lago de Xochimilco

&#x0D; Abstract 22&#x0D; This work discusses the importance of organic matter, specifically Aquatic Humic Substances (SHA) 23 within the speciation and distribution of metals within an aquatic system, in this case Xochimilco 24 Lake, a site with great ecological importance. This lake is the natural habitat of the endemic species 25 “axolotl” (ajolote). In this research, complexation reactions between SHA and metals (Cu, Mn, Pb 26 and Zn) were carried out under different reaction conditions, the source of AHS was water samples 27 taken in Xochimilco Lake in presence and absence of pH buffer dissolution and varying the 28 concentration of metals. The results show that there is a direct competition between the major 29 elements and trace elements to react with the AHS. Under the pH conditions of Xochimilco Lake 30 complexes formation is possible. 31

Humus formation in soils of the Lena River Delta

The aim of the study. Nowadays close attention is paid to polar soils due to the expected landscape transformation rate under the predicted climate crisis. Intensive degradation of permafrost and the release of nutrients from their frozen state can lead to an increase in the emission of greenhouse gases into the atmosphere, as well as the loss of landscapes. The aim of the study was to investigate the peculiarities of organic residues formation and humification degree as well as humus structure and functioning in soil the Lena River Delta. &#x0D; Location and time of the study. The study was conducted on the Samoylov and Sardach Islands in the Lena River Delta (Yakutia, Russia). Field studies were performed during the summer of 2019. &#x0D; Objects and methodology. Soils of the Lena River Delta from the Samoylov Island (flooded area) and Sardakh (non-flooded zone), i.e. Subaquatic Fluvisol (Arenic) and Histic Cryosol (Siltic) were the objects of the study, respectively. To examine the features of humification chemical-analytical, sedimentation, micromorphological methods were used, as well as CP/MAS 13C-NMR spectroscopy. &#x0D; Main results. The data obtained indicate a high diversity of soils and soil formation conditions in the Lena River Delta. Under non-flooded conditions Histic Cryosol (Siltic) were formed in the flooded parts of the Samoylov Island, Subaquatic Fluvisol (Arenic) were formed. These soils play an important role in the global carbon cycle, accumulation, transformation and deposition of condensed high- and low molecular mass organic compounds in the composition of soils and permafrost. The main soil micromorphology features were identified. In the young landscapes the soil microstructure was represented by poorly sorted sand with a circular type of optical orientation of the soil plasma (which indicated the influence of the river), as well as vertically oriented micas (muscovite/biotite). Soils influenced by the floodplain process were characterized by the presence of coarse amorphous humus. Due to the long-term effect of the freezing/thawing processes on the permafrost-affected soils the biogenic aggregates were formed. In such organo-mineral microaggregates humus is fixed in the composition of mineral components consisting of particles of quartz, micas and Mn-Fe nodules and is in a stable state (physical stabilization of humus). To analyze the molecular composition the 13C NMR spectroscopy method was used. According to 13C NMR spectroscopy data, up to 37% of aromatic structural fragments accumulated in soils, which indicates the process of condensation of molecules in humic acids, thus showing a relatively high level of humus stabilization in the soils of the Lena River delta. From the data obtained, three main groups of chemical structural fragments that accumulate in the delta soils can be distinguished, such as C,H - alkyls ((CH2)n/CH/C and CH3), aromatic compounds (C–C/C–H, C–O) and the OCH group (OCH/OCq). In the studied humic preparations aliphatic structural fragments of HAs (63–64%) predominated, which indicated a deficiency of lignin and lignin-like compounds in the composition of humification precursors. The predominance of aliphatic structures is typical of humic substances formed under reduction conditions, including the aqueous humic substances, as well as in soils, the precursors of humification of which are typical tundra vegetation (mosses and lichens) with a predominance of carbohydrates (up to 80%). A significant amount of aromatic fragments accumulated in the delta in the alluvial soils of the first terrace of the river (flooded zone). This is apparently due to the formation of vascular plants in the flooded areas of the Lena River Delta. The chemical composition of vascular plants includes components such as tannins, flavonoids and lignin (arenas). Thus in the samples formed under vascular plants with a lignin content of about 30%, an increase in signals in the range of 110-160 ppm were observed. Aromatic and carboxyl fragments in the structure of HA were formed during the transformation of lignin, which leads to the resistance of HAs to biodegradation.&#x0D; Conclusion. Under the floodplain condition humus is represented by coarse amorphous forms, whereas without the influence of flooding humus is fixed in mineral microaggregates. Specific humic acids composition in the studied regions is determined by bioclimatic conditions, cryogenic processes and the composition of humification precursors. High abundance of aromatic structures in humus substances suggests relatively stable humus status (most likely due to the putative condensation of humic acids) in the Lena River Delta during the study period.

A Systematic Study of the Antioxidant Capacity of Humic Substances against Peroxyl Radicals: Relation to Structure.

Humic substances (HS) are natural supramolecular systems of high- and low-molecular-weight compounds with distinct immunomodulatory and protective properties. The key beneficial biological activity of HS is their antioxidant activity. However, systematic studies of the antioxidant activity of HS against biologically relevant peroxyl radicals are still scarce. The main objective of this work was to estimate the antioxidant capacity (AOC) of a broad set of HS widely differing in structure using an oxygen radical absorption capacity (ORAC) assay. For this purpose, 25 samples of soil, peat, coal, and aquatic HS and humic-like substances were characterized using elemental analysis and quantitative 13C solution-state NMR. The Folin–Ciocalteu method was used to quantify total phenol (TP) content in HS. The determined AOC values varied in the range of 0.31–2.56 μmol Trolox eqv. mg−1, which is close to the values for ascorbic acid and vitamin E. Forward stepwise regression was used to reveal the four main factors contributing to the AOC value of HS: atomic C/N ratio, content of O-substituted methine and methoxyl groups, and TP. The results obtained clearly demonstrate the dependence of the AOC of HS on both phenolic and non-phenolic moieties in their structure, including carbohydrate fragments.

Aquatic humic substances dynamics in surface water of bog pools in Ozegahara Mire

Aquatic humic substances dynamics in surface water of bog pools in Ozegahara Mire

Relationships between the Physicochemical Properties of Dissolved Organic Matter and Its Reaction with Sodium Borohydride.

The reaction of dissolved organic matter (DOM) with sodium borohydride has been used to understand the geographic origin of DOM and investigate the photophysical model underlying DOM's optical properties. However, the physicochemical properties of DOM (e.g., molecular size and charge) that influence the kinetics and ultimate reducibility of DOM by borohydride remain poorly characterized. Herein, we studied the kinetics of DOM-borohydride reactions by recording absorbance and fluorescence spectra at a high temporal frequency (every ∼10 min for 24 h) for a diverse set of DOM isolates of aquatic and soil origin. The reducibility of DOM by sodium borohydride (as judged by relative removal of initial absorbance) varied appreciably among the DOM samples studied, with soil humic substances being less reducible than aquatic humic substances and natural organic matter. While statistically significant correlations were found between the reducibility of DOM and descriptors of molecular size, these descriptors were not able to differentiate the reducibility of soil versus aquatic DOM isolates that had similar bulk properties. Thus, it appears that the extent of absorbance removal by borohydride is largely driven by the origin of the humic substance isolate (aquatic vs soil) instead of molecular size or charge. Borohydride reduction resulted in increased fluorescence emission across UV and visible excitation wavelengths. However, the enhanced emission at visible excitation decreased over a time period of hours to days, suggesting that reduction of an important subset of DOM chromophores is reversible. This reversibility in fluorescence emission is consistent with the small role of quinones in the absorbance of DOM but suggests a more important role for quinone-containing charge-transfer contacts in the fluorescence of DOM, particularly at visible excitation wavelengths.

Atmospheric Humic‐Like Substances (HULIS) Act as Ice Active Entities

AbstractWe investigated the ice nucleation activities of humic‐like substances (HULIS), an important component of organic aerosol (OA), derived from atmospheric and biomass burning aerosols, and produced from aqueous‐phase chemical reactions. Respective HULIS can effectively trigger heterogeneous IN under mixed‐phase cloud conditions. HULIS ice active entities (IAE) were aggregates in size between 0.02 and 0.10 μm. At −20°C, the IAE numbers per unit HULIS mass varied from 213 to 8.7 × 104 mg−1. Such results were different than those detected in aquatic humic substances (HS) from previous studies, implying using HS as surrogates may not robustly estimate the IAE concentrations in the real atmosphere. Combining the abundance of atmospheric HULIS with the present results suggests that HULIS could be an important IAE contributor in the atmosphere where other ice nucleating particle species, such as dust and biological particles, are either low in concentration or absent.

Differences in quinone redox system of humic substances between endemic and disease-free areas in Kashin-Beck disease-affected Changdu Region, Tibet, China.

Kashin-Beck disease (KBD) is an endemic disease in China with the highest incidence rate in Tibet region. Promoted generation of oxygen free radicals by semiquinone structure of humic substance (HS) in drinking water was considered to be one of its pathogeneses. Therefore, detailed analysis of HS was performed in water and sediment samples collected from three endemic and three disease-free areas in Changdu Region, Tibet, China. After purification of the HS in the samples, the fractions of HS were characterized using electron paramagnetic resonance, 13C nuclear magnetic resonance, fluorescence spectroscopy with parallel factor analysis and Fourier transform infrared spectroscopy (FTIR). The organic carbon content of HS did not show a significant difference between endemic and disease-free areas or correlation with KBD-associated morbidity. Except FTIR, all techniques succeeded in characterization of the quinone redox system, indicating their validity and consistency. The quinone redox system in aquatic HS exhibited significantly higher level of the following indexes in endemic areas than disease-free areas: semiquinone radical content of fulvic acid (FA) (p < 0.05), aromaticity of FA (p < 0.05), fluorescence intensity (per gram carbon) of reduced quinone-like component of FA (p < 0.05) and humic acid (HA) (p < 0.1). Semiquinone radical content (r = 0.781, p < 0.1), aromaticity of FA (r = 0.891, p < 0.05), intensity of oxidized quinone-like component (r = 0.875, p < 0.05) and reduced quinone-like component of FA (r = 0.793 p < 0.1) showed medium to strong correlation with KBD-associated morbidity. Generally, the content of reduced quinone and aquatic FA showed stronger differences between endemic and disease-free areas than oxidized quinone and aquatic HA, respectively. The quinone redox system in sediment HS did not show any significant relationship with KBD. The present study is a successful attempt to combine the three indexes, semiquinone radical content, aromaticity and fluorescence intensity, in characterizing quinone redox system in HS, facilitating more comprehensive understanding of the characteristics of HS in KBD-affected regions.

Interaction of Pb, Ni and Cd with Aquatic Humic Substances of Amazonian Blackwater Rivers

In this study, the extraction and characterization of aquatic humic substances (AHS) from two blackwater rivers in the Amazon basin was carried out in order to assess the seasonal effects in the AHS structure. In addition, an investigation of the complexing capacities (CC) of the structures containing the metal ions CdII, NiII and PbII was also done. The characterization (of the AHS) was done using UV-Vis, molecular fluorescence, and infrared spectroscopy. AHS from the Negro River showed more aromatic characteristics in its structures and molecular weight, than the AHS from the Caru River. The AHS studied presented a seasonal pattern characterized by higher humification levels during the rainy season. For all the metals, the AHS complexing capacity was higher for the Negro River. The highest complexing capacities were observed for the NiII assays, which were 0.56 and 0.12 µmol NiII mg-1 dissolved organic carbon (DOC), for AHS RN and AHS RC-II, respectively. We concluded that the transport, bioavailability, and toxicity, of these metal species should be higher for Caru River.

New insights on the relation between zooplankton and humic substances in tropical freshwater ecosystems.

Aquatic humic substances (HS) represent about 60-95% of the dissolved organic carbon (DOC) present in coastal environments of northern Rio de Janeiro state, Brazil. Although they are important regulators of processes involving aquatic communities, the response of the zooplankton community to their presence remains poorly understood, especially in natural tropical environments. Therefore, our objective was to elucidate zooplankton community responses along a natural gradient of HS. Such natural humic gradient was obtained in coastal freshwater environments with distinct DOC concentrations (20-200 mg L-1). Results show a decrease in zooplankton density and biomass along the HS gradient. However, microphages organisms (e.g. non-predatory rotifers and smaller testate amoeba, such as Difflugia) were most present in environments with higher concentration of HS, probably due to a stronger importance of the microbial-loop in these environments. Some species - such as Scapholeberis armata (Cladocera) and Lecane boettgeri (Rotifera) were only accounted for environments with high HS concentration, illustrating their potential as bioindicators for HS presence. Nevertheless, we were able to observe the effects of HS on the structure and composition of primary consumers and how these substances might indirectly affect species dynamics. We point out to new findings in highly humic tropical environments, which are still poorly studied and understood.

Ozonation of natural organic matter and aquatic humic substances: the effects of ozone on the structural characteristics and subsequent trihalomethane formation potential

Abstract The effect of ozonation on the structural and chemical characteristics of natural organic matter (NOM) and its isolated humic fractions, humic acid (HA) and fulvic acid, were studied using Fourier transform infrared coupled to attenuated total reflectance (FTIR-ATR), ultraviolet/visible (UV/Vis) spectroscopy, and synchronous scanning fluorescence (SSF) spectroscopy. The results were linked to the effect of ozonation on trihalomethane formation potential (THMfp) reduction for water standards with high THM precursors. Results showed that ozonation at a dose of 1 mg ozone/mg dissolved organic carbon (DOC) was capable of reducing DOC, UV absorbance at 254 nm (UV254), and THMfp by up to 42%, 95%, and 89% for the HA water standard, respectively. The study of UV/Vis, FTIR-ATR, and SSF revealed trends showing that ozone can alter the composition of DOC in the water standards, causing a significant reduction in aromaticity. The reduction of UV254 for each ozonated sample also affirms that ozone mainly targets aromatic moieties contained in NOM. FTIR-ATR results showed that the reduction of unsaturated functional groups, including aromatic rings and C = C bonds in the water standards tested, were the main components impacted by ozone application. SSF results also revealed that ozonation decreases the fluorescence intensity of the maximum peak – as well as the whole spectra.

EXTRAÇÃO E CARACTERIZAÇÃO DE SUBSTÂNCIAS HÚMICAS AQUÁTICAS (SHA) EXTRAÍDAS DE AMOSTRAS COLETADAS NO PARQUE NACIONAL SERRA DE ITABAIANA, SERGIPE, BRASIL

Este trabalho descreve o estudo da capacidade de complexação (CC) das substâncias húmicas aquáticas (SHA) extraídas de amostras de água coletadas no Parque Nacional Serra de Itabaiana (Sergipe) pelos íons metálicos Mn, Ni, Zn, Cu e Pb, bem como a avaliação da concentração dos metais totais das amostras de água. Os parâmetros físicos e químicos das amostras de água foram determinados por pH, temperatura, condutividade elétrica e COD, assim como a determinação dos metais totais foram quantificados por ICP OES. As SHA foram extraídas com resina XAD 8, segundo o procedimento reconhecido pela International Humic Substances Society (IHSS), e foram caracterizadas por TGA, análise elementar e por FTIR. Posteriormente foi estudado a CC das SHA pelos íons metálicos Cu, Mn, Ni, Pb e Zn pelo método de ultrafiltração. O valor do pH da amostra estudada apresentou valor abaixo dos estabelecidos pela Resolução CONAMA N° 357. No entanto, o valor da condutividade elétrica está em conformidade com a Portaria N° 2914 do Ministério da Saúde. As concentrações dos metais totais estão em acordo com a Resolução CONAMA N° 357, exceto para o Pb. As SHA apresentaram três processos principais de perda de massa (de acordo com as curvas TGA/DTGA), e o espectro FTIR apresentou bandas características de SHA. A CC das SHA por íons metálicos estabeleceu a seguinte ordem decrescente: Mn(II) &gt; Ni(II) &gt; Zn(II) &gt;&gt; Cu(II) &gt; Pb(II). Esses resultados reforçam que as SHA podem ser classificadas como agentes complexantes naturais que desempenham uma função importante no meio ambiente.