In silico evaluation of new mangiferin-based Positron Emission Tomography radiopharmaceuticals through the inhibition of metalloproteinase-9.

Metalloproteinase-9 (MMP-9) is a key protein in cancer advancement and metastasis owing to its ability to degrade some extracellular matrix components. Mangiferin, a natural polyphenolic compound, has demonstrated through experimental and theoretical studies to be a great anticancer agent for the selective inhibition of MMP-9. This work aimed to evaluate the utility of several fluorinated compounds obtained from MF as possible Positron Emission Tomography (PET) radiopharmaceuticals oriented to MMP-9. Density Functional Theory calculations of MF were made to obtain the most active sites toward electrophilic and nucleophilic reactions and propose a synthetic route to produce its fluorinated derivatives. The reactivity study allowed us to propose a late-stage synthetic route based on click chemistry to obtain three fluorinated MF-based derivatives. Molecular docking calculations suggested that the derivative F-propyl-MF could be suitable as PET radiopharmaceutical owing to the establishment of a five-coordinated complex with the catalytic Zn atom belonging to the active site of MMP-9, crucial factor in the inhibition of MMP-9.

Characterization of sargassum accumulated on Dominican beaches in 2021: Analysis of heavy, alkaline and alkaline-earth metals, proteins and fats.

This paper presents the characterization of sargassum that reached the shores of eight Dominican beaches in 2021. The analysis of heavy, alkaline and alkaline-earth metals was performed by ICP-OES. Twelve heavy metals were studied, with the highest concentrations corresponding to Fe, As, and Zn. Regarding the alkaline and alkaline-earth metals, the highest concentrations were detected for Ca, K, Na and Mg. The high values of arsenic and alkali and alkaline-earth metal salts do not suggest using these algae in agriculture. It is recommended to carry out arsenic speciation studies to assess whether the form in which it is found is bioavailable for plants and animals. The heavy metal contamination index was determined, which ranged between 0.318 and 3.279. Finally, for the first time in the country, the organic fraction of sargassum was analyzed.

Competitive formation of molecular inclusion complexes of chlordecone and ß-hexachlorocyclohexane with natural cyclodextrins: DFT and molecular dynamics study.

CONTEXT: Chlordecone (CLD) and ß-hexachlorocyclohexane (ß-HCH) are chlorinated pesticides that coexist as persistent organic pollutants in the groundwater of several countries in the Caribbean, being an environmental issue. This work evaluates theoretically the competitive formation of host-guest complexes pesticides@cyclodextrines (CDs) as an alternative for water purification and selective separation of pesticides. METHODS: Quantum mechanical calculations based on density functional theory (DFT) and classical molecular dynamics (MD) simulations were used to achieve information on geometries, energies, structure, and dynamics of guest-host complexes in the gas phase, implicit solvent medium, and in aqueous solutions. RESULTS: DFT studies showed that interactions of both pesticides with CDs are mediated by steric factors and guided by maximization of the hydrophobic interactions either with the other pesticide or with the CD cavity's inner atoms. MD results corroborate the formation of stable complexes of both pesticides with the studied CDs. α-CD exhibited a preference for the smaller ß-HCH molecule over the CLD that could not perturb the formed complex. CONCLUSIONS: The simulation of competitive formation with γ-CD illustrated that this molecule could accommodate both pesticides inside its cavity. These results suggest that CDs with smaller cavity sizes such as α-CD could be used for selective separation of ß-HCH from CLD in water bodies, while γ-CD could be used for methods that aim to remove both pesticides at the same time.

Adsorption of Hexavalent Chromium Using Activated Carbon Produced from Sargassum ssp.: Comparison between Lab Experiments and Molecular Dynamics Simulations.

Adsorption is one of the most successful physicochemical approaches for removing heavy metal contaminants from polluted water. The use of residual biomass for the production of adsorbents has attracted a lot of attention due to its cheap price and environmentally friendly approach. The transformation of Sargassum-an invasive brown macroalga-into activated carbon (AC) via phosphoric acid thermochemical activation was explored in an effort to increase the value of Sargassum seaweed biomass. Several techniques (nitrogen adsorption, pHPZC, Boehm titration, FTIR and XPS) were used to characterize the physicochemical properties of the activated carbons. The SAC600 3/1 was predominantly microporous and mesoporous (39.6% and 60.4%, respectively) and revealed a high specific surface area (1695 m2·g-1). To serve as a comparison element, a commercial reference activated carbon with a large specific surface area (1900 m2·g-1) was also investigated. The influence of several parameters on the adsorption capacity of AC was studied: solution pH, solution temperature, contact time and Cr(VI) concentration. The best adsorption capacities were found at very acid (pH 2) solution pH and at lower temperatures. The adsorption kinetics of SAC600 3/1 fitted well a pseudo-second-order type 1 model and the adsorption isotherm was better described by a Jovanovic-Freundlich isotherm model. Molecular dynamics (MD) simulations confirmed the experimental results and determined that hydroxyl and carboxylate groups are the most influential functional groups in the adsorption process of chromium anions. MD simulations also showed that the addition of MgCl2 to the activated carbon surface before adsorption experiments, slightly increases the adsorption of HCrO4- and CrO42- anions. Finally, this theoretical study was experimentally validated obtaining an increase of 5.6% in chromium uptake.

Explaining the interaction of mangiferin with MMP-9 and NF-ƙß: a computational study.

Mangiferin is a glycosylated xanthone widely distributed in nature, which exhibits wide pharmacological activities, highlighting its anti-cancer properties. Mangiferin interferes with inflammation, lipid, and calcium signaling, which selectively inhibits multiple NFkB target genes as interleukin-6, tumor necrosis factor, plasminogen, and matrix metalloproteinase, among others. In this work, the interactions of this polyphenol with MMP-9 and NF-κß are characterized by using computational chemistry methods. The results show MMP-9 inhibition by mangiferina is characterized for the interact with the catalytic Zn atom through a penta-coordinate structure. It is also demonstrated through a strong charge transfer established between mangiferin and Zn in the QM/MM study. Concerning the mangiferin/NF-κß system, the 92.3% of interactions between p50 sub-unity and DNA are maintained with a binding energy of - 8.04 kcal/mol. These findings indicate that mangiferin blocks the p50-p65/DNA interaction resulting in the loss of the functions of this hetero-dimeric member and suggesting inhibition of the cancer progression. Experimental results concerning the anti-cancer properties of mangiferin show that this natural compound can inhibit selectively MMP-9 and NF-ƙß. Although the anti-tumor properties of mangiferin are well defined, its molecular mechanisms of actions are not described. In this work, a computational study is carried out to characterize the interactions of mangiferin with these molecular targets. The results obtained corroborate the anti-proliferative and anti-apoptotic activity of mangiferin and provide a depiction of its mechanisms of action.

In silico development of new PET radiopharmaceuticals from mTOR inhibitors.

Rapamycin (or sirolimus) is a macrolide that has shown to be useful as an immunosuppressant and that was studied in metabolic, neurological, or genetic disorders. Rapamycin is a specific natural inhibitor of the mechanistic target of rapamycin (mTOR) that is a kinase protein playing a pivotal role in cell growth and proliferation by activation of several metabolic processes. This work aimed to evaluate the utility of several compounds obtained from rapamycin and its semi-synthetic analogs everolimus and temsirolimus as possible radiopharmaceuticals oriented to this protein. Density Functional Theory calculations of these molecules were made and further analysis of the dual descriptor, charges populations, and of the electrostatic potential surfaces were performed. Molecular docking simulations were used to evaluate the interactions of the rapamycin with the studied candidates. They allowed us to propose two strategies for the synthesis of novel compounds based on electrophilic reactions. Molecular docking results also helped us to eliminate molecules that did not interact correctly with the target. Finally, we found for the first time, that the novel compounds synthesized through the electrophilic addition reaction that employed 18F-selectfluor, should maintain the biological activity of original compounds and could be suitable as Positron Emission Tomography radiopharmaceuticals targeting mTOR Complex1 system.

Role of Basic Surface Groups of Activated Carbon in Chlordecone and ß-Hexachlorocyclohexane Adsorption: A Molecular Modelling Study.

The influence of nitrogen-containing surface groups (SGs) onto activated carbon (AC) over the adsorption of chlordecone (CLD) and ß-hexachlorocyclohexane (ß-HCH) was characterized by a molecular modelling study, considering pH (single protonated SGs) and hydration effect (up to three water molecules). The interactions of both pollutants with amines and pyridine as basic SGs of AC were studied, applying the multiple minima hypersurface (MMH) methodology and using PM7 semiempirical Hamiltonian. Representative structures from MMH were reoptimized using the M06-2X density functional theory. The quantum theory of atoms in molecules (QTAIM) was used to characterize the interaction types in order understanding the adsorption process. A favorable association of both pesticides with the amines and pyridine SGs onto AC was observed at all pH ranges, both in the absence and presence of water molecules. However, a greater association of both pollutants with the primary amine was found under an acidic pH condition. QTAIM results show that the interactions of CLD and ß-HCH with the SGs onto AC are governed by Cl···C interactions of chlorine atoms of both pesticides with the graphitic surface. Electrostatic interactions (H-bonds) were observed when water molecules were added to the systems. A physisorption mechanism is suggested for CLD and ß-HCH adsorption on nitrogen-containing SGs of AC.

SARS-CoV-2 en aguas residuales y superficiales: ¿cómo lidiar con el problema? / Sars-cov-2 in wastewater and surface water: how to deal with the problem?

Introducción: hoy la humanidad sufre uno de los peores episodios debido a la pandemia causada por el SARS-CoV-2. Su alta infectividad, rápida propagación y persistencia en ciertas superficies dificultan el combate de este virus. Su presencia en aguas residuales y posible transmisión fecal-oral podría ser una nueva amenaza para la salud pública. Objetivo: alertar a la comunidad científica internacional y a los gobiernos sobre la presencia de SARS-CoV-2 en las aguas residuales y sobre qué hacer para evitar su propagación por este medio. Métodos: se realizó una revisión de artículos referenciados en SCOPUS y Web of Science desde el año 2019 relacionados con la presencia del virus en aguas residuales y superficiales. Resultados y discusión: es necesario establecer sistemas de monitoreo, utilizar métodos analíticos sensibles y rápidos para la detección del virus en las aguas residuales y superficiales. Asimismo, implantar protocolos de inactivación del virus en las unidades de salud y en las plantas de tratamiento de aguas. Se recomiendan procesos con oxidantes químicos, radiación ultravioleta, fotocatálisis, foto-Fenton, ozono o filtración por membrana. Además, se debe alertar a la población sobre la importancia del lavado y de la desinfección de productos agrícolas, así como del cuidado en su manejo por parte de los trabajadores agrícolas

Introduction: Today, humanity suffers one of the worst episodes due to a pandemic caused by the SARS-CoV-2. Its high infectivity and rapid spread combined with its persistence on certain surfaces difficult to fight this virus. Its presence in wastewater and possible fecal-oral transmission could be a new public health threat. Objective: To alert the international scientific community and governments about the presence of SARS-CoV-2 in wastewater, and what to do to prevent its spread by this means. Methods: A review of articles referenced in SCOPUS and Web of Science since 2019 related to the presence of the virus in wastewater and surface water was performed. Results and discussion: It is necessary to establish monitoring systems with the use of sensitive and rapid analytical methods for the on-site detection of viruses in wastewaters and surface waters. It should be established virus inactivation protocols at the health units, and water treatment plants, where are recommended processes with chemical oxidants, ultraviolet radiation, photocatalysis, photo-Fenton, ozone, or membrane filtration. It is necessary to alert the population about the importance of washing and disinfecting agricultural products, mainly vegetables and fruits, as well as the care in its handling by agricultural workers

Caracterización clínica, endoscópica e histológica del cáncer colorrectal en un grupo de pacientes cubanos / Clinical, endoscopic and histological characterization of colorectal cancer in a group of Cuban patients

Introducción: el cáncer colorrectal representa el tercero en incidencia en ambos sexos a nivel mundial, por ellos es importante realizar estudios epidemiológicos del mismo. Objetivo: caracterizar clínica, endoscópica e histológicamente el cáncer colorrectal en pacientes atendidos en el Centro de Investigaciones Médico Quirúrgicas, Cuba. Métodos: estudio observacional, descriptivo y retrospectivo a 52 pacientes (31 hombres y 21 mujeres) con cáncer colorrectal diagnosticados entre 2012 y 2014. Se recolectaron los datos de historias clínicas y estudios endoscópicos, imagenológicos y anatomopatológicos. La media de edad fue 66,73 años. Resultados: el antecedente y/o presencia de pólipos en el colon predominó con 55.8 %. La enterorragia se presentó en 38.5 %, la oclusión intestinal y el dolor abdominal en 17.3 %. Durante la colonoscopia, se encontró el 47.7% con lesión ulcerada y el lugar más comprometido fue el colon descendente. El adenocarcinoma se encontró en 90.4 % de los pacientes. Conclusiones: los antecedentes personales de pólipos colorrectales, el hábito de fumar, la diabetes mellitus tipo 2 y la obesidad fueron los factores de riesgo más encontrados. La forma de presentación más frecuente fue la enterorragia, seguida por la oclusión intestinal y las regiones del colon más afectadas fueron la descendente y la ascendente, respectivamente. El diagnóstico histológico fue en el mayor de los casos un adenocarcinoma. Existe una mayor frecuencia del diagnóstico en etapas avanzadas de la enfermedad

Introduction: Colorectal cancer represents the third in incidence in both sexes worldwide. For this reason, it is essential to carry out epidemiological studies of it. Objective: To characterize clinically, endoscopically and histologically colorectal cancer in patients treated at the Surgical Medical Research Center, Cuba. Methods: An observational, descriptive, and retrospective study of 52 patients (31 men and 21 women) with colorectal cancer diagnosed between 2012 and 2014 was carried out. Data from clinical histories, endoscopic imaging, and pathological studies were collected. The average age was 66.7 years Results: The antecedent and presence of polyps in the colon predominated with 55.8%. Enterorrhagia occurred in 38.5% of patients, intestinal occlusion, and abdominal pain in 17.3%. During the colonoscopy, 47.7% of patients were found with an ulcerated lesion, and the most compromised place was the descending colon (38.5%). Adenocarcinoma was found in 90.4% of patients. Conclusions: Personal history of colorectal polyps, smoking, type 2 diabetes mellitus, and obesity were the most common risk factors. The most common form of presentation was enterorrhagia, followed by intestinal occlusion, and the most affected regions of the colon were descending and ascending. The histological diagnosis was, in most cases, an adenocarcinoma. There was a higher frequency of diagnosis in advanced stages of the disease

Theoretical Evaluation of the Molecular Inclusion Process between Chlordecone and Cyclodextrins: A New Method for Mitigating the Basis Set Superposition Error in the Case of an Implicit Solvation Model.

The aim of this work is to describe the molecular inclusion of chlordecone with α-, ß-, and γ-cyclodextrin in aqueous solution using quantum mechanics. The guest-host complexes of chlordecone and cyclodextrins are modeled in aqueous solution using the multiple minima hypersurface methodology with a PM6-D3H4X semiempirical Hamiltonian, and the lowest energy minima obtained are reoptimized using the M06-2X density functional and the intermolecular interactions described using quantum theory of atoms in molecules (QTAIM). The studied complexes are classified according to the degree of inclusion, namely, total occlusion, partial occlusion, and external interaction. More stable complexes are obtained when γ-CD is used as the host molecule. The interactions characterized through QTAIM analysis are all of electrostatic nature, predominantly of dispersive type. In this work, a method based on the counterpoise correction is also discussed to mitigate the basis set superposition error in density functional theory calculations when using an implicit solvation model.

Guest-host complexes of 1-iodochlordecone and ß-1-iodo-pentachlorocyclohexane with cyclodextrins as radiotracers of organochlorine pesticides in polluted water.

The chlordecone (CLD) and the ß-hexachlorocyclohexane (ß-HCH) are persistent organic pollutants with a great environmental stability that cause severe affectations to health. The concentration of these pesticides in the environment is low, which represent a problem for their determination, even for the modern analytical methods. The labeling of these compounds with an iodine radioisotope for their use as radiotracers is a potential solution to this problem. The present work studies the interaction of 1-iodochlordecone (I-CLD) and ß-1-iodo-pentachlorocyclohexane (I-ß-HCH) with cyclodextrins (CDs), during the formation of molecular inclusion complexes pesticide@CDs. The methodology of multiple minima hypersurfaces, quantic calculations based on density functional theory and a topologic study of electronic density were used to corroborate the stability of I-CLD@CDs and I-ß-HCH@CDs complexes. Three main types of guest-host complexes in relation to the occlusion grade were observed: with total occlusion, with partial occlusion and external interaction without occlusion. The more stable complexes are obtained when the γ-CD is the host molecule. The formed complexes with radiolabelled pollutants are analogous with the ones reported in previous works. These results confirm the utility of these complexes for the removal of organochlorine pesticides from polluted water and, also, demonstrate the possibility of using the I-CLD and the I-ß-HCH as possible radiotracers for these pollutants in further studies with environmental proposes.

Enhancement of ciprofloxacin degradation in aqueous system by heterogeneous catalytic ozonation.

Fluoroquinolones are extensively used in medicine due to their antimicrobial activity. Their presence in water inhibits microorganism activity in conventional wastewater treatment plants. This study aims to evaluate the technical feasibility of applying heterogeneous catalytic ozonation to eliminate ciprofloxacin (CIP) as a representative of fluoroquinolone antibiotics normally present in municipal wastewater discharges. Experiments were conducted in a semi-batch stirred slurry reactor, using 0.7 L of 100 mg L-1 CIP aqueous solution, at pH 3 and 30 °C. Experimental results show that single ozonation can easily oxidise CIP molecules (68%) within the first 5 min, leading to the generation of refractory oxidation by-products. However, when heterogeneous catalytic ozonation is applied using iron oxide supported on MFI synthetic zeolite, total degradation of CIP is observed at 5 min and a higher mineralisation rate is obtained. A novel sequential process is developed for CIP mineralisation. In a first step, a flash single ozonation is applied and CIP molecules are broken down. Then, a catalytic ozonation step is conducted by adding the Fe/MFI catalyst into the reactor. As a result of catalyst addition, 44% of Total Organic Carbon (TOC) is eliminated within the first 15 min, compared to single ozonation where only 13% of TOC removal is reached in the same time. The application of this sequential process to a real wastewater effluent spiked with CIP leads to 52% of TOC removal.

Explaining the interactions between metaldehyde and acidic surface groups of activated carbon under different pH conditions.

Metaldehyde (MA) is an organic compound widely used in agriculture all around the world as molluscicide. There are growing concerns that relatively high levels of MA have been detected in surface water, which could be ascribed to the fact that it is transparent to common wastewater treatment processes. A theoretical study of the influence of activated carbon (AC) surface groups (SGs) on MA adsorption is done in order to help to understand the process and to evaluate the influence of the acid SGs over the adsorption in AC filters. Multiple Minima Hypersurface methodology was employed in order to study the interactions of the MA with acid SGs (hydroxyl and carboxyl) at acidic and neutral pH, and at different hydration conditions explicitly taking into account the solvent influence. Selected structures were re-optimized using Density Functional Theory and posteriorly refined to achieve a well-defined electron density to characterize the interactions by the Quantum Theory of Atoms in Molecules approach. The obtained results showed that the presence of SGs enhances the adsorption process. The deprotonated carboxyl and hydroxyl SGs of AC models show the strongest interactions, suggesting greater adsorption at neutral pH which is in concordance with experimental data. The main interactions are of a dispersive nature between the pesticide and the π-cloud of the AC and hydrogen bonds between the MA and the acid SGs suggesting that the adsorption process is driven by a physisorption mechanism. Water acts as an intermediary between the AC and MA and competing with it for the adsorption sites.

Photo-Fenton reaction at mildly acidic conditions: assessing the effect of bio-organic substances of different origin and characteristics through experimental design.

Urban-waste bio-organic substances (UW-BOS) have been shown to be capable of extending the photo-Fenton reaction to mildly acidic conditions. In this study, the effects of pH (3-7), UW-BOS, H2O2 and iron concentrations on the photo-Fenton process were systematically assessed using a Doehlert experimental design and response surface methodology for two UW-BOS (CVT230 and FORSUD). Solutions of the model antibiotic sulfadiazine (SDZ) were irradiated in a solar simulator equipped with a 550 W Xenon lamp. The results showed that for UW-BOS contents below 30 mg L-1, SDZ removal proceeds at pH 5 with similar rates for both CVT230 and FORSUD, regardless of Fe(III) concentration. For 50 mg L-1 of UW-BOS or higher, CVT230 performs better than FORSUD, even for low Fe(III) content (1-3 mg L-1). In contrast, half-life times of 35-40 min can only be achieved under mildly acidic conditions with FORSUD for iron concentrations higher than 10 mg L-1. The better performance of CVT230 can be associated with its high hydrophilic/hydrophobic ratio, low E2:E3, higher iron content and possibly higher yields of triplet reactive species generation upon solar irradiation. The most appropriate conditions for each UW-BOS studied are discussed for the first time, which are advantageous for possible engineered applications.

Evaluation of the molecular inclusion process of ß-hexachlorocyclohexane in cyclodextrins.

The present work aimed to study the guest-host complexes of ß-hexachlorocyclohexane (ß-HCH), a pesticide with high environmental stability that can cause severe health problems, with the most common cyclodextrins (α-, ß-, and γ-CDs). The formation reactions of these molecular inclusion complexes were addressed in this research. The multiple minima hypersurface methodology, quantum calculations based on density functional theory and a topological exploration of the electron density based on the quantum theory of atoms in molecules approach were used to characterize the interaction spaces of the pollutant with the three CDs. Additionally, charge distribution, charge transfer and dual descriptor analyses were employed to elucidate the driving forces involved in the formation of these molecular inclusion complexes. Three types of fundamental interactions were observed: total occlusion, partial occlusion and external interaction (non-occlusion). Finally, experiments were performed to confirm the formation of the studied complexes. The most stable complexes were obtained when γ-CD was the host molecule. The interactions between the pesticide and CDs have fundamentally dispersive natures, as was confirmed experimentally by spectroscopic results. All the obtained results suggest the possibility of using CDs for the purification and treatment of water polluted with ß-HCH.

Theoretical study on the interactions between chlordecone hydrate and acidic surface groups of activated carbon under basic pH conditions.

A theoretical study of the influence of acidic surface groups (SG) of activated carbon (AC) on chlordecone hydrate (CLDh) adsorption is presented, in order to help understanding the adsorption process under basic pH conditions. A seven rings aromatic system (coronene) with a functional group in the edge was used as a simplified model of AC to evaluate the influence of SG in the course of adsorption from aqueous solution at basic pH conditions. Two SG were modeled in their deprotonated form: carboxyl and hydroxyl (COO- and O-), interacting with CLDh. In order to model the solvation process, all systems under study were calculated with up to three water molecules. Multiple Minima Hypersurface (MMH) methodology was employed to study the interactions of CLDh with SG on AC using PM7 semiempirical Hamiltonian, to explore the potential energy surfaces of the systems and evaluate their thermodynamic association energies. The re-optimization of representative structures obtained from MMH was done using M06-2X Density Functional Theory. The Quantum Theory of Atoms in Molecules (QTAIM) was used to characterize the interaction types. As result, the association of CLDh with acidic SG at basic pH conditions preferentially occurs between the two alcohol groups of CLDh with COO- and O- groups and by dispersive interactions of chlorine atoms of CLDh with the graphitic surface. On the other hand, the presence of covalent interactions between the negatively charged oxygen of SG and one hydrogen atom of CLDh alcohol groups (O-⋯HO interactions) without water molecules, was confirmed by QTAIM study. It can be concluded that the interactions of CLDh with acidic SG of AC under basic pH conditions confirms the physical mechanisms of adsorption process.

Optimization of ciprofloxacin degradation in wastewater by homogeneous sono-Fenton process at high frequency.

Emerging pollutants such as pharmaceuticals have been focusing international attention for a few decades. Ciprofloxacin (CIP) is a common drug that is widely found in hospital and wastewater treatment plants effluents, as well as in rivers. In this work, the feasibility of CIP degradation by ultrasound process at high frequency is discussed and sonolysis, sonolysis with hydrogen peroxide and sono-Fenton are evaluated. The amounts of hydrogen peroxide and ferrous ions (Fe2+) needed were optimized using response surface methodology. Best results were obtained with the sono-Fenton process resulting in a total pharmaceutical degradation within 15 min and a mineralization greater than 60% after 1 h. Optimal conditions were tested on a real matrix from a municipal wastewater treatment plant. Even if the degradation of the pollutants by sono-Fenton was hampered, the removal efficiency of both CIP and total organic carbon (TOC) is interesting as an increase in the biodegradability of the wastewater is found. These results show that sono-Fenton oxidation can be a promising pretreatment process for pharmaceutical-containing wastewaters.

Degradation of chlordecone and beta-hexachlorocyclohexane by photolysis, (photo-)fenton oxidation and ozonation.

Intensive use of chlorinated pesticides from the 1960s to the 1990s has resulted in a diffuse contamination of soils and surface waters in the banana-producing areas of the French West Indies. The purpose of this research was, for the first time, to examine the degradation of two of these persistent pollutants - chlordecone (CLD) and beta-hexachlorocyclohexane (ß-HCH) in 1 mg L-1 synthetic aqueous solutions by means of photolysis, (photo-) Fenton oxidation and ozonation processes. Fenton oxidation is not efficient for CLD and yields less than 15% reduction of ß-HCH concentration in 5 h. Conversely, both molecules can be quantitatively converted under UV-Vis irradiation reaching 100% of degradation in 5 h, while combination with hydrogen peroxide and ferrous iron does not show any significant improvement except in high wavelength range (>280 nm). Ozonation exhibits comparable but lower degradation rates than UV processes. Preliminary identification of degradation products indicated that hydrochlordecone was formed during photo-Fenton oxidation of CLD, while for ß-HCH the major product peak exhibited C3H3Cl2 as most abundant fragment.

The impact of humic acid on metaldehyde adsorption onto powdered activated carbon in aqueous solution.

Metaldehyde has been detected in surface water and drinking water in the UK, exceeding the EU and UK standard of 0.1 µg L-1. The presence of natural organic matter (NOM) is considered to affect the removal efficiency of metaldehyde using traditional treatment methods such as adsorption by granular activated carbon. This paper selected humic acid (HA) to represent NOM and investigated the single and binary adsorption systems of metaldehyde and HA by powdered activated carbon (PAC). Metaldehyde was effectively removed by PAC in both systems. Since the percentage removal of metaldehyde was only 3% lower in the binary adsorption system, HA was therefore not considered as a significant compound competing with metaldehyde for adsorption sites on PAC. An adsorption equilibrium study and kinetic study for metaldehyde in a single system suggested that the Langmuir isotherm and the pseudo-second order kinetic model were more suitable in this case than the Freundlich isotherm and the pseudo-first order kinetic model. The two models revealed that the maximum adsorption capacity (q m) of metaldehyde by PAC was 28.3 mg g-1 and the adsorption rate (k 2) was 0.16 g mg-1 min-1. The effect of pH of metaldehyde solution was also investigated in a single system. Higher percentage removal of metaldehyde was found under alkaline conditions. In contrast to metaldehyde, HA was not effectively and efficiently removed by PAC in both systems, even with higher PAC dosages and longer contact times. Hence, the microporous and mesoporous PAC was suitable for removing metaldehyde even in the binary system.