RESUMO

The UV/monochloramine (UV/NH2Cl) process, while efficiently eliminating micropollutants, produces toxic byproducts. This study utilized Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to investigate molecular-level changes in natural organic matter (NOM) and to disclose formation pathways of nitro(so) and chloro byproducts in the UV/NH2Cl process. The UV/NH2Cl process significantly increased the saturation and oxidation levels and altered the elemental composition of NOM. Using 15N labeling and a screening workflow, nitro(so) byproducts with nitrogen originating from inorganic sources (i.e., reactive nitrogen species (RNS) and/or NH2Cl) were found to exhibit total intensities comparable to those from NOM. RNS, rather than NH2Cl, played a significant role in incorporating nitrogen into NOM. Through linkage analysis, nitro(so) addition emerged as an important reaction type among the 25 reaction types applied. By using phenol as a representative model compound, the nitro byproducts were confirmed to be mainly generated through the oxidation of nitroso byproducts instead of nitration. Machine learning and SHAP analysis further identified the major molecular indices distinguishing nitro(so) and chloro precursors from non-precursors. This study enhances our fundamental understanding of the mechanisms driving the generation of nitro(so) and chloro byproducts from their precursors in complex NOM during the UV/NH2Cl process.

Assuntos

RESUMO

BACKGROUND: Understanding the interaction mechanisms and the relevant binding constants between humic acids and emerging or regulated pollutants is of utmost importance in predicting their geochemical mobility, bioavailability, and degradation. Fluorescence spectroscopy, UV-vis spectroscopy, equilibrium dialysis, and solid-phase extraction combined with liquid chromatography-mass spectrometry have been employed to elucidate interactions of humic acids with organic micropollutants, especially pharmaceutical drugs. These methods demand large sample volumes, long equilibration times, and laborious extraction steps which may imply analytical errors. Monolithic high-performance affinity chromatography is an alternative and simpler method to investigate these interactions and determine the binding constants. RESULTS: Polymer monoliths based on aminated glycidyl methacrylate and ethylene glycol dimethacrylate served to immobilize Cu(II) and then humic acid to produce monolithic affinity chromatography columns with humic acid as the active interaction phase. About 86.5 mg of humic acid was immobilized per gram of polymer. The columns enabled a comparison of the binding strength of humic acid with herbicides and emerging pollutants at 25 °C and pH 6.0 ± 0.1. Paracetamol, acetylsalicylic acid, and salicylic acid did not retain. Among the compounds that interacted with humic acid, the order of increasing affinity, estimated by the global affinity constant (nKa) or partition coefficient (KD) was: caffeine < simazine < atrazine âˆ¼ propazine < benzophenone. The nKa (L mol-1) values ranged from (4.9 ± 0.3) × 102 for caffeine to (1.9 ± 0.3) × 103 for benzophenone, whereas KD (L kg-1) varied from 14 ± 1 to 56 ± 8 for the same compounds. SIGNIFICANCE AND NOVELTY: To our knowledge, this is the first paper demonstrating the use of a monolithic platform to immobilize supramolecular structures of humic acids exploiting immobilized metal affinity to comparatively evaluate their affinity towards emerging pollutants exploiting the concepts of high-performance affinity chromatography. The proposed approach needs only small amounts of humic acid, which is a relevant feature in preparing columns with humic substances isolated and purified from remote areas.

Assuntos

RESUMO

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.

Assuntos

RESUMO

The presence of microcontaminants in the water supply system offers adverse impacts. This study analyzed the performance of two powdered activated carbons (PAC1 and PAC2) in the removal of 2,4-D herbicide in ultrapure water (UW) and natural water (NW) to verify the influence of natural organic matter (NOM) on the adsorptive process. The properties of PAC1 and PAC2 were analyzed by textural analysis, FTIR, TG, pH, XDR, NMR. The specific surface area of PAC2 was lower than PAC1 and PAC2 showed better adsorption capacity in UW (37.04 mg.g-1) and in NW (8.06 mg.g-1). The results of experiments performed in natural water showed that both activated carbons had reduced 2,4-D adsorption capacity in the presence of NOM, since it may compete for the same adsorption sites or block the access of the 2,4-D molecule to the pores of the activated carbon. PAC2 showed a higher mesopores percentage, decreasing the effects caused by NOM in 2,4-D adsorption. The use of activated carbons with varying pore sizes for the removal of microcontaminants is recommended, especially in NW. This result contributes to the choice of the adsorbent type to be applied in water treatment plants.

Assuntos

RESUMO

The sorption of dissolved organic matter (DOM) depends on its interaction with the soil matrix. In hydromorphic podzols, DOM reacts mainly with aluminium (Al), which is responsible for the formation of the Bh-horizon in the subsoil. In this work, we investigated whether the retention of DOM in the soil during the podzolization process is selective in relation to the molecular composition of DOM. A column experiment was conducted to study the selective retention of sorption and desorption processes under controlled conditions. Materials used in the column experiment were representative for Brazilian coastal podzols under tropical rainforest. Materials were collected from this tropical coastal podzol ecosystem, and included soil from E- and Bh-horizons, and DOM from a stream (Stream), peat water (Peat), litter (Litter) and charred litter (Char). To evaluate selective retention of DOM, both the initial DOM and its leachates were analyzed by Fourier transform infrared spectra absorption (FTIR) and pyrolysis gas-chromatography/mass spectrometry (Py-GC/MS). The results showed preferential retention of DOM associated with biopolymers for soil columns with E-horizon material (E), E with Al nitrate (E-n), E with kaolinite (E-k) and E with gibbsite (E-h), except for Char. The composition of leachates after percolation through B horizon columns was mainly determined by desorption, and had a relatively large contribution from phenolic and carboxylic groups associated with Al and low molecular weight aromatic and N-containing pyrolysis products, while products from macromolecular materials such as cellulose were selectively retained in the columns for all DOM types. DOM from the Stream (taken during the rainy season) resembled that of desorbed OM from the B columns, reinforcing substantial desorption in the field as well. Our results suggest that sorption and desorption of OM in the hydromorphic Bh-horizon is continuous and that the selectivity of sorption is dependent on DOM source.

Assuntos

RESUMO

Novel pre-coagulation-sedimentation integrated with ultraviolet activated sodium percarbonate (SPC) (Fe(III)-UV/SPC) processes are promising methods for ultrafiltration (UF) pretreatment to ensure the safety of rural drinking water and mitigate UF membrane fouling. The process of surface water purification using the integrated coagulation-advanced oxidation processes (AOPs)-UF system relies on the idea that pre-coagulation can remove hydrophobic macromolecular organic compounds, thus facilitating the oxidation of hydrophilic molecules or medium-sized macromolecules to improve the utilization efficiency of free radicals in AOPs. Compared with the UV/SPC process, the removal rates of UV254 and DOC in the Fe(III)-UV/SPC process (Fe(III) = 0.1 mM, SPC = 0.5 mM) were increased from 87.39 % to 41.45 %-93.56 % and 52.51 %, respectively. Furthermore, the dosage of SPC was reduced from 0.75 mM in UV/SPC process to 0.5 mM due to effects of pre-coagulation. The free radical quenching experiment showed that a significant radical sink of reactions with organic contaminants was formed by •OH and CO3•- in the UV/SPC process, rather than a single specific radical. The destruction of the cake layer structure, reduction in contaminant concentration, and appearance of many permeable holes on the membrane surface were the main reasons for the alleviation of UF membrane fouling. Finally, the trans-membrane pressure and reversible membrane resistance decreased from 22.33 kPa to 3.68 × 1011 m-1 to 18.28 kPa and 0.93 × 1011 m-1, respectively. These results provide new insights into the behavior of membrane fouling control and offer technical references for the long-term stable operation of the UF process.

Assuntos

RESUMO

RESUMO Estudos recentes vêm demonstrando que a aplicação de cloro poderia levar à formação de trihalometanos (THM), que ocorre quando o cloro reage com a matéria orgânica natural, também denominada de precursora de THM e presente em águas naturais. A United States Environmental Protection Agency (USEPA) classificou os THM como prováveis carcinogênicos para humanos. Com o objetivo de avaliar os níveis de THM na água destinada ao abastecimento público na cidade de Cáceres/MT, foram coletadas amostras de água em três pontos distintos: P1 na água bruta, P2 na saída do reservatório e P3 na rede de abastecimento, por um período de um ano (agosto de 2018 a junho de 2019), com frequência bimestral. Além dos THM, foram monitorados os parâmetros de turbidez, cor, pH e cloro residual livre. Os resultados de água bruta demonstraram que o fenômeno natural denominado "decoada" aumentou as concentrações de turbidez e cor aparente no período enchente/cheia pelo intenso processo de decomposição que ocorre nesse momento, elevando os níveis de matéria orgânica na água bruta. Quanto à água tratada, valores de turbidez fora do preconizado foram detectados. Os níveis de THMs chegaram próximo (0,09518 mg.L-1 - P2) de atingir o VMP de 0,1 mg.L-1 em consequência da presença de precursores. Os valores de THM foram maiores em P2 pelo fato de esse ponto apresentar medição maior de cloro residual livre em relação a P3. Todavia, notou-se uma forte correlação entre THM e turbidez (p < 0,05 e R² = 0,67), o que demonstra que o parâmetro de turbidez pode ser um indicativo da presença de precursores de THM.

ABSTRACT Recent studies have shown that the application of chlorine could lead to the formation of trihalomethanes (THM), which occurs when chlorine reacts with natural organic matter (NOM), also known as precursors of THM, present in natural waters. The United States Environmental Protection Agency (USEPA) has classified THM as probable carcinogens for humans. In order to assess the levels of trihalomethanes in water destined for public supply in the city of Cáceres, state of Mato Grosso, Brazil, water samples were collected from three different points: P1, at raw water; P2, at the outlet of the reservoir; and P3, at the supply network, for a period of one year (from August 2018 to June 2019), with bimonthly frequency. In addition to THM, the parameters of turbidity, color, pH, and free residual chlorine were monitored. The results of raw water demonstrated that the natural phenomenon called "decoada" increased the concentrations of turbidity and apparent color in the flood/spate period, due to the intense decomposition process that occurs in this period, increasing the levels of organic matter in raw water. As for treated water, turbidity values outside the recommended values were detected. THM levels (0.09518 mg.L-1 - P2) almost reached the MPV of mg.L-1, as a result of the presence of precursors. The THM values were higher in P2 because this point presents a higher concentration of free residual chlorine in relation to P3. However, there was a strong correlation between THM and turbidity (p < 0.05 and R² = 0.67), thus demonstrating that the turbidity parameter may be indicative of the presence of THM precursors.

RESUMO

Humic substances are redox-active organic molecules, which play pivotal roles in several biogeochemical cycles due to their electron-transferring capacity involving multiple abiotic and microbial transformations. Based on the redox properties of humic substances, and the metabolic capabilities of microorganisms to reduce and oxidize them, we hypothesized that they could mediate the anaerobic oxidation of methane (AOM) coupled to the reduction of nitrous oxide (N2O) in wetland sediments. This study provides several lines of evidence indicating the coupling between AOM and the reduction of N2O through an extracellular electron transfer mechanism mediated by the redox active functional groups in humic substances (e.g., quinones). We found that the microbiota of a sediment collected from the Sisal wetland (Yucatán Peninsula, southeastern Mexico) was able to reduce N2O (4.6 ± 0.5 µmol N2O g sed. -1 day-1) when reduced humic substances were provided as electron donor in a close stoichiometric relationship. Furthermore, a microbial enrichment derived from the wetland sediment achieved simultaneous 13CH4 oxidation (1.3 ± 0.1 µmol 13CO2 g sed. -1 day-1) and N2O reduction (25.2 ± 0.5 µmol N2O g sed. -1 day-1), which was significantly dependent on the presence of humic substances as an extracellular electron shuttle. Taxonomic characterization based on 16S rRNA gene sequencing revealed Acinetobacter (a É£-proteobacterium), the Rice Cluster I from the Methanocellaceae and an uncultured archaeon from the Methanomicrobiaceae family as the microbes potentially involved in AOM linked to N2O reduction mediated by humic substances. The findings reported here suggest that humic substances might play an important role to prevent the emission of greenhouse gases (CH4 and N2O) from wetland sediments. Further efforts to evaluate the feasibility of this novel mechanism under the natural conditions prevailing in ecosystems must be considered in future studies.

RESUMO

RESUMO O objetivo deste trabalho foi avaliar, por meio dos testes rápidos de coluna em escala reduzida, a capacidade de adsorção do carvão ativado granular (CAG) na remoção do ácido 2,4-diclorofenoxiacético (2,4-D) em amostras de água ultrapura e de água filtrada proveniente de estação de tratamento de água. Os valores da capacidade de adsorção obtidos a partir de amostras de água ultrapura foram 67% superiores aos obtidos para água com presença de matéria orgânica natural (MON). A MON influenciou fortemente a remoção de 2,4-D competindo pelos sítios de adsorção do carvão ativado e diminuiu a capacidade de adsorção para 7,43 mg 2,4-D por grama de CAG. Para a concentração de 2,4-D no afluente igual a 7089 ± 104 µg.L-1 e relação volumeágua/volumeCAG estimado em 766, foi possível produzir água com concentração de 2,4-D inferior a 30 µg.L-1, como recomendado pela Portaria Brasileira de Potabilidade de Água, do Ministério da Saúde (Portaria MS nº 2.914/2011).

ABSTRACT The aim of this study was to assess by means of rapid tests of small-scale column the adsorption capacity of granular activated carbon (GAC) for removal of 2,4-dichlorophenoxyacetic acid (2,4-D) from samples of ultrapure water and filtered water from a water treatment plant. The adsorption capacities values obtained from distilled water samples were 67% higher than those obtained for water having natural organic matter (NOM). NOM strongly influenced the removal of 2,4-D, competing for GAC adsorption sites, and decreasing its adsorption capacity to 7 mg 2,4-D g-1 CAG. For 2,4-D concentration of 7089 ± 104 µg L-1 and the water treated volume/GAC volume at 766, it was possible to produce treated water with 2,4-D concentration less than 30 µg L-1 as recommended by Brazilian Drinking Water Legislation of the Ministry of Health (Portaria MS 2914/2011).

RESUMO

Key pathways for the anaerobic oxidation of methane (AOM) have remained elusive, particularly in organic rich ecosystems. In this work, the occurrence of AOM driven by humus-catalyzed dissimilatory iron reduction was investigated in sediments from a coastal mangrove swamp. Anoxic sediment incubations supplied with both goethite (α-FeOOH) and leonardite (humic substances (HS)) displayed an average AOM rate of 10.7 ±â€¯0.8 µmol CH4 cm-3 day-1, which was 7 and 3 times faster than that measured in incubations containing only goethite or HS, respectively. Additional incubations performed with 13C-methane displayed Pahokee Peat HS-mediated carbonate precipitation linked to 13CH4 oxidation and ferrihydrite reduction (~1.3 µmol carbonate cm-3 day-1). These results highlight the role of HS on mitigating greenhouse gases released from wetlands, not only by mediating the AOM process, but also by enhancing carbon sequestration as inert minerals (calcite, aragonite and siderite).

RESUMO

Dissolved organic carbon (DOC) represents a heterogeneous group of naturally-occurring molecules in aquatic environments, and recent studies have evidenced that optically dark DOCs can exert some positive effects on ionoregulatory homeostasis of aquatic organisms in acidic waters. We investigated the effects of Luther Marsh DOC, a dark allochthonous DOC, on ion regulation and N-waste excretion of zebrafish acutely exposed to either neutral or low pH in ion-poor water. In the first experiment, simultaneous exposure to pH 4.0 and DOC greatly attenuated the stimulation of Na+ diffusive losses (J outNa ), and prevented the blockade of Na+ uptake (J inNa ) seen in zebrafish exposed to pH 4.0 alone, resulting in much smaller disturbances in Na+ net losses (J netNa ). DOC also attenuated the stimulation of net Cl- losses (J netCl ) and ammonia excretion (J netAmm ) during acidic challenge. In the second experiment, zebrafish acclimated to DOC displayed similar regulation of J inNa and J outNa , and, therefore, reduced J netNa at pH 4.0, effects which persisted even when DOC was no longer present. Protective effects of prior acclimation to DOC on J netCl and J netAmm at pH 4.0 also occurred, but were less marked than those on Na+ balance. Urea fluxes were unaffected by the experimental treatments. Overall, these effects were clearly beneficial to the ionoregulatory homeostasis of zebrafish at low pH, and were quite similar to those seen in a recent parallel study using darker DOC from the upper Rio Negro. This suggests that dark allochthonous DOCs share some chemical properties that render fish tolerant to ionoregulatory disturbances during acidic challenge.

Assuntos

RESUMO

Polymeric nanoparticles have been developed for several applications, among them as carrier system of pesticides. However, few studies have investigated the fate of these materials in the environment in relation to colloidal stability and toxicity. In nature, humic substances are the main agents responsible for complexation with metals and organic compounds, as well as responsible for the dynamics of these nanoparticles in aquatic and terrestrial environments. In this context, the evaluation of the influence of aquatic humic substances (AHS) on the colloidal stability and toxicity of polymeric nanoparticles of chitosan/tripolyphosphate with or without paraquat was performed. In this study, the nanoparticles were prepared by the ionic gelation method and characterized by size distribution measurements (DLS and NTA), zeta potential, infrared and fluorescence spectroscopy. Allium cepa genotoxicity studies and ecotoxicity assays with the alga Pseudokirchneriella subcapitata were used to investigate the effect of aquatic humic substances (AHS) on the toxicity of this delivery system. No changes were observed in the physical-chemical stability of the nanoparticles due to the presence of AHS using DLS and NTA techniques. However some evidence of interaction between the nanoparticles and AHS was observed by infrared and fluorescence spectroscopies. The ecotoxicity and genotoxicity assays showed that humic substances can decrease the toxic effects of nanoparticles containing paraquat. These results are interesting because they are important for understanding the interaction of these nanostructured carrier systems with species present in aquatic ecosystems such as humic substances, and in this way, opening new perspectives for studies on the dynamics of these carrier systems in the ecosystem.

Assuntos

RESUMO

This work reports on the changes in compositions of humic acids (HAs) and fulvic acids (FAs) during photocatalytic degradation. The HAs and FAs were obtained from the XAD-resin fractionation of natural-organic matter (NOM) from a bog lake (Lake Hohloh, Black Forest, Germany). Degussa P-25 titanium dioxide (TiO2) in a suspension and a solar UV simulator (batch reactor) were used in the experiments. The photocatalytic degradation of the HAs and FAs were monitored using size-exclusion chromatography (SEC) equipped with dissolved organic carbon (DOC) and ultraviolet (UV254) detection (SEC-DOC and SEC-UV254) and UV-Vis spectrophotometry. The evolutions of the photocatalytic degradations of the HA and FA fractions were selective. The photocatalytic degradation started with the degradations of high molecular weight compounds with relatively high UV254 absorbances in the HA and FA fractions to yield low molecular weight compounds showing less specific UV254 absorbances. Observance of the same tendency for the original NOM from Lake Hohloh indicates that these XAD-fractions still having complex compound mixtures. However, the larger molecular weight fractions of the FAs showed higher preferential adsorptions onto TiO2, which caused their faster degradation rates. Furthermore, FAs showed a greater reduction of the total THM formation potential (TTHMFP) and the organic halogen compounds adsorbable on activated carbon formation potential (AOXFP), in comparison with the HAs.

Assuntos

RESUMO

A atrazina é um dos herbicidas mais utilizados no mundo, sendo encontrada em águas superficiais e subterrâneas. Pertence à classe das s-triazinas, possui potencial carcinogênico e apresenta toxicidade como disruptor endócrino. A reconhecida limitação dos processos de tratamento de água, os quais empregam a coagulação química na remoção da atrazina e os efeitos na saúde, motivou este trabalho, considerando a adsorção em carvão ativado como tecnologia alternativa. O estudo experimental consistiu na caracterização física do carvão ativado e nos ensaios de adsorção em águas de diferentes conteúdos orgânicos. Foi possível verificar a capacidade do carvão ativado em remover atrazina, e o mecanismo de adsorção foi influenciado pela variação da qualidade das matrizes de água gerando isotermas com características distintas.

Atrazine is one of the most widely herbicides used in the world, being found in surface water and groundwater. It belongs to the s-triazines class classified as possible carcinogenic potential and toxicity presents as an endocrine disruptor. The acknowledged limitation of the water treatment processes, which employ chemical coagulation in atrazine removal and the risks to health, has motivated this work taking into regards the adsorption of activated carbon as an alternative technology. The experimental study consisted of physical characterization of activated carbon and of adsorption tests in waters of different organic content. It was possible to verify the capacity of activated carbon to remove atrazine, and the adsorption mechanism was influenced by the quality variation of water matrices generating isotherms with different characteristics.