A simple and rapid dispersive solid-phase extraction method coupled with furnace atomic absorption spectrometry detection was developed for selective separation and preconcentration of ultra-trace amounts of lead ions using modified magnetic graphene oxide such as the pseudo imprinted polymer sorbent in real water and food samples. Some effective parameters in the extraction of lead were selected and optimized. The optimum experimental conditions of the proposed method were: pH, 5.0; amount of absorbent, 1 mg; eluent type and its volume, 50 μL of 0.4 mol L⁻¹ hydrochloric acid; sample solution volume, 30.0 mL. Under the optimum conditions, a high preconcentration factor of 600 was obtained for 30.0 mL of sample solution. The relative standard deviation for seven 20 ng L⁻¹ replicates of lead was 2.4% and the detection limit was 0.18 ng L⁻¹. The proposed method was applied for the determination of lead ions in real water and food samples, and its accuracy was assessed through the analysis of a certified reference water (ERA 1340) and recovery experiments.

In this research work, for the first time, a new mode of dispersive solid-phase extraction named syringe to syringe magnetic dispersive micro-solid phase extraction is introduced as an efficient, simple, rapid, and eco-friendly sample extraction method. A nickel–aluminum layered double hydroxide coated on magnetic nanoparticles (Fe₃O₄@Ni–Al–CO₃-LDH), as an efficient nanosorbent, was synthesized and successfully applied for the concurrent extraction of trace amounts of Cd²⁺ and Pb²⁺ ions in food and water samples prior to their determination using a microsampling-flame atomic absorption spectrometry technique. After extraction and magnetic separation, the elution step was easily performed through dissolving the magnetic layered double hydroxide (LDH) containing the target analytes in an acidic solution. Also the use of a magnetic LDH overcomes the difficulty of phase separation that decreases the extraction time. The optimum conditions efficiently evaluated via the response surface methodology (RSM) were pH 7.0, 13.7 mg of the nanosorbent, 16 extraction cycles, 125 μL of 3.8 mol L⁻¹ trifluoroacetic acid, and an ultrasonic time of 75 s. According to the optimum conditions obtained in above, good linear ranges (0.75–35 ng mL⁻¹ for Cd²⁺ ions and 4.0–370 ng mL⁻¹ for Pb²⁺ ions) with coefficient of determination (R²) values higher than 0.995 were obtained. The limits of detection were found to be 0.25 and 1.0 ng mL⁻¹ for Cd²⁺ and Pb²⁺, respectively. The preconcentration factor for the target analytes was 80 in a 10 mL sample solution. The obtained results indicated the high quality of the developed procedure for the much-needed quantification of the aforementioned metal ions in food and water samples.

A simple, fast, green, sensitive and selective ultrasonic assisted deep eutectic solvent liquid-phase microextraction technique was used for preconcentration and extraction of cadmium (Cd) in water and food samples by electrothermal atomic absorption spectrometry (ETAAS). In this technique, a synthesized reagent (Z)-N-(3,5-diphenyl-1H-pyrrol-2-yl)-3,5-diphenyl-2H-pyrrol-2-imine (Azo) was used as a complexing agent for Cd. The main factors effecting the pre-concentration and extraction of Cd such as effect of pH, type and composition of deep eutectic solvent (DES), volume of DES, volume of complexing agent, volume of tetrahydrofuran (THF) and ultrasonication time have been examined in detail. At optimum conditions the value of pH and molar ratio of DES were found to be 6.0 and 1:4 (ChCl:Ph), respectively. The detection limit (LOD), limit of quantification (LOQ), relative standard deviation (RSD) and preconcentration factor (PF) were observed as 0.023 ng L−1, 0.161 ng L−1, 3.1% and 100, correspondingly. Validation of the developed technique was observed by extraction of Cd in certified reference materials (CRMs) and observed results were successfully compared with certified values. The developed procedure was practiced to various food, beverage and water samples.

The research “Use of pesticides in Fresh Water Aquaculture in the Mekong Delta, Vietnam, and impacts on environment and food safety” consisted of four sections. To evaluate the pressure of drugs and chemicals in the environment, two surveys were performed in the Mekong Delta. The first was focused on rice and rice-fish system and was conducted in 2009. The second, an in depth survey, conducted in 2013, focused on rice-fish, striped catfish and red-tilapia systems. Results showed that, for the rice-fish system, most rice fish farmers grew 2 rice crops and 1 fish crop per year. Pesticides were applied generally 3 times per crop. Farmers normally applied pesticides based on the recommended doses of producers. Chess 50WG (containing 500g/kg pymetrozine, produced by Syngenta, Vietnam), Bassa 50EC (containing 500g/L fenobucard, produced by Việt Thắng Bắc Giang (Vithaco), Vietnam) and Kinalux (containing 250g/L quinalphos, produced by United Phosphorus Ltd., India) were the most common used commercial pesticides in rice crop, rice-fish crop and distributors as well. According to the majority of the distributors, the use of pesticides will increase in future. The in-depth survey showed that much more active compounds were used in 2013 compared to 2009, but, all of the active compounds belonged to the approved list of Vietnamese government. Few farmers used chemicals during fish crop. Farmers reported their awareness towards the use of agrochemicals in terms of health effects. The survey showed that the farmers select an agrochemical based on their experience. The study on red-tilapia demonstrated that many different types of disinfectants and antimicrobials are used. Further, the cost-effectiveness of such pesticide use, especially for feed supplement products, antimicrobials and disinfectants, is questionable and should be assessed. There is an urgent need to improve the farmer’s knowledge and their access to advisory services on careful use of disinfectants and antimicrobials. All visited striped catfish farms applied drugs and chemicals with seven types of antibiotics during the fish production. Enrofloxacin, sulfamethoxazole and trimethoprim were reported to be the most used chemicals by farmers to treat Bacillary Necrosis of Pangasius (BNP). The survey and practical situation demonstrated that quinalphos, trifluralin and dichlorvos were commonly used in rice fish system and, consequently, may contaminate aquaculture products. A Gas chromatography – mass spectrometry (GC-MS) analytical method was developed and validated according to European guidelines (SANTE/11945/2015) for the determination of residues of those pesticides in water. The developed method was then optimized using a gas chromatography – electron capture detector (GC ECD) technique to make the method more applicable in Vietnam. The developed method was used to analyze water samples collected from the aquaculture system in April 2013, at the beginning of the rainy season. Results showed that only 9 % of the total water samples analyzed contained residues of quinalphos, but only in water from rice fish systems. The other two pesticides, trifluralin and dichlorvos, were not detected. A comparison between GC-MS and GC-ECD indicated that GC-ECD is less sensitive than GC-MS. However, for samples with concentrations detectable with both techniques, no significant difference was observed between the results obtained using both equipments GC-ECD and GC-MS. The next step was to determine the distribution and elimination of quinalphos, the active substance of a popular insecticide used in the Mekong Delta, according to the first survey. An experiment was set up in a rice-fish integrated system in Can Tho City, Vietnam. Quinalphos was applied twice in a dose of 42.5 g per 1000 m2, according to the producer recommendations. Samples (fish, water and sediment) were collected at time intervals and were analyzed by GC-ECD. The results showed that quinalphos residues in fish muscles were much higher than those in the water and the bioconcentration factor (logBCF) was above 2 for the fish. The half-lives, after the first and second quinalphos applications, were 12.2 and 11.1 days for sediment, 2.5 and 1.1 days for silver barb, 1.9 and 1.3 days for common carp, and 1.1 and 1.0 days for water, respectively. Finally, as a case study including 3 commonly used pesticides (quinalphos, trifluralin and dichlorvos), dioxins and one forbidden antibiotic (chloramphenicol), the risk for the consumer, linked to the chemical contamination of the aquaculture related environment was evaluated. Sediments samples were collected including 10 samples collected from catfish ponds in An Giang Province and 12 samples randomly collected from rice-fish systems in Can Tho City. Analytical results showed that 3 from the 13 water samples collected from rice field were contaminated with low levels of quinalphos (with concentrations of 0.11, 0.08 and 0.04 μg/L). The other investigated pesticides were not detected in any sample. For chloramphenicol (CAM) residues in fish samples, analysis was performed on 36 fish samples of catfish (18 samples included 9 from small scale and 9 from large scale systems), snakehead (9 samples) and climbing perch (9 samples) collected at the beginning, middle and at the end of culture period. Results showed that one sample of climbing perch and one sample of snakehead were contaminated with traces of CAM (concentrations of 0.17 and 0.19 µg/kg, respectively). It appeared that CAM was not detected in catfish samples neither from the beginning to the end of the crop, nor from small and large scale systems. Dioxins were not detected in any of the collected sediments samples. In order to assess the general risk for the Vietnamese consumer of fish, a survey was performed in Can Tho City, using a questionnaire designed to collect information. A large part of interviewees (77%) stated that they like to eat fish. The number of days of eating fish was 3.4 days per week. In this study, the average amount of fish consumption ranged between 90 and 140 g per day. It was shown that the daily intake of trifluralin of interviewed people was 0.05 µg/kg body weight/day. This level of exposure was much lower than the acceptable daily intake (ADI) (15 µg/kg/day) (EFSA, 2015). However, trifluralin has not been approved in EU, so the presence of residues of trifluralin in aquatic product, even if they cause no problem for the consumer, would be a problem for aquatic product export. | Deltaquasafe Project

El objetivo del presente trabajo fue determinar cuál de las dietas brindadas a la especie en investigación durante el cultivo del paco fue la mejor, donde fueron cultivas en estanques de un área de 1000 m2, donde se emplearon una población de 1000 peces/estanques, los cuales fueron distribuidos a los 9 socios de la Asociación Tres Fronteras, quienes fueron considerados dentro del estudios por tener estanques de la misma división la cual permitía realizar la investigación presente. A cada socio se le entrego 1000 alevinos, donde se tendría que alimentar con estos diferentes tratamientos propuestos, como el tratamiento 1 (T1) que consistía en un alimento balanceado sin considerar ningún aditivo, el tratamiento 2 (T2) que consistía en un alimento balanceado mezclado con un aditivo (el aditivo era un suplemento de concentrado de pescado) y el tratamiento 3 (T3) que era un alimento balanceado mezclado con el aditivo (concentrado de pescado) más la adición de enzimas digestoras de materia orgánica (prebiótico) en el agua de cultivo, cada tratamiento era brindado a tres estanques diferentes, cuyo tiempo de evaluación termino en 90 días, donde se empleó un muestreo estadístico al azar y se evaluaba el crecimiento y la supervivencia cada 7 días, con la finalidad de determinar cuál de los tratamientos empleados daba mejores resultados | Tesis

This study investigated the feasibility of using an invasive snail, Pomacea canaliculata, as a food source and water purifier for the commercial breeding of the loach Misgurnus anguillicaudatus. The predatory potential of M. anguillicaudatus (3.5–5.5 g) against hatchling snails was evaluated in aquaria and simulated paddy fields. Some hatchling snails left the water to avoid being preyed upon by the loaches, and approximately 10 hatchlings died per day in the presence of five loaches in aquaria, whereas a weaker snail control effect was observed in the simulated paddy fields. The growth of rice seedlings (Oryza sativa) was not reduced by the presence of hatchling snails alone, but the shoot biomass of seedlings coexisting with snails was promoted after introducing the loaches. Additionally, the presence of P. canaliculata adults improved the aquatic environment in the short term for loach breeding by decreasing the turbidity of the water. Importantly, M. anguillicaudatus (12–18 g) mortality decreased and its weight increased in the presence of adult snails.

A novel green solvent-based ultrasonic assisted dispersive liquid–liquid microextraction (GS-UADLLME) method was developed for the preconcentration of cadmium and lead ions in various real samples prior to determination by graphite furnace atomic absorption spectrometry (GFAAS). In order to extract trace amounts of cadmium and lead ions, 2-amino-3-sulfhydrylpropanoic acid (l-cysteine) (as a green ligand), tetrafluoroborate ion (BF₄⁻) (as an ion pair agent) and 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF₄] (as acceptor phase) were used. Different effective factors in the microextraction procedure such as pH of the sample solution, sample solution volume, acceptor phase volume, l-cysteine and tetrafluoroborate concentrations, centrifugation conditions and salting addition were thoroughly optimized. Under the optimum conditions, the calibration graphs were linear in the range of 0.8–180 and 2.5–190 ng L⁻¹ with a correlation coefficient (r²) higher than 0.9967 for the measurement of cadmium and lead ions, respectively. The limits of detection for the determination of Cd(ii) and Pb(ii) for the proposed method were 0.2 and 0.7 ng L⁻¹, respectively. The relative standard deviations (n = 5) for the analyte determination were lower than 3.4%. In order to investigate the method’s accuracy, cadmium and lead contents of a certified reference material, SRM 1643e (NIST), were determined and the results from the proposed method were in very good agreement with the certified values. The suggested method was successfully applied to the determination of cadmium and lead ions in real samples such as real water, soil, rice and tea samples.

O objetivo geral deste trabalho foi implementar o uso de ferramentas estatísticas na otimização do processo de eletrocoagulação para o tratamento de águas superficiais; comparar os mecanismos de coagulação dominantes na eletrocoagulação com eletrodos de alumínio e no tratamento convencional com sulfato de alumínio; e avaliar técnica e economicamente o uso da eletrocoagulação baseada em energia fotovoltaica como tratamento complementar à remoção de poluentes de águas para consumo humano. Inicialmente os modelos e condições ótimas de operação para a eletrocoagulação foram baseados na metodologia de “superfície de resposta” usando o delineamento composto central. A função “desejabilidade” foi utilizada para encontrar as condições operacionais que levassem ao aumento da remoção de cor aparente, da demanda química de oxigênio (DQO) e da turbidez, de maneira simultânea. Foi possível cumprir o padrão estético/organoléptico estipulado para esta etapa do processo (cor < 15 uH, DQO < 18 e turbidez < 5 uT) considerando três amostras de água (turbidez inicial baixa, média e alta). Em uma segunda etapa, gráficos de isoeficiência para remoção de poluentes foram utilizados para determinar e comparar os mecanismos de coagulação atuantes na coagulação convencional e na eletrocoagulação. Para águas com turbidez inicial baixa o mecanismo de adsorção de cargas mostrou eficiências de remoção maiores nos dois tratamentos estudados. Para águas com turbidez inicial média e alta, o mecanismo de varredura mostrou-se eficiente nas duas tecnologias utilizadas. Na terceira fase, a metodologia de superfície de resposta foi utilizada para desenvolver modelos matemáticos considerando os efeitos dos parâmetros intensidade de corrente e tempo de eletrólise (i.t) sobre a remoção da cor aparente e turbidez de uma amostra de água proveniente do rio Turvo Sujo. As condições de desenho e operação para o sistema integrado eletrocoagulação-sistema fotovoltaico (EC-SF) foram estabelecidas assumindo o conceito de reprodutibilidade das condições quando conhecidos os parâmetros de uma única célula eletrolítica. A metodologia estatística utilizada mostrou-se eficiente para a previsão dos melhores valores do binômio i.t, permitindo o cumprimento do padrão estético/organoléptico (cor < 15 uH e turbidez < 5 uT). O desenho de um sistema EC-SF que suprisse a necessidade de consumo de 50 pessoas foi realizado para avaliação do custo do tratamento. Para isto foram considerados o custo do material do eletrodo e o custo de energia elétrica, obtendo-se um custo de R$ 0,70 m -3 de água clarificada. A correlação existente entre as respostas analisadas permitiu encontrar condições especificas dos parâmetros, auxiliando a determinação de pontos de trabalho seguros na operação. A eletrocoagulação mostrou-se eficiente para clarificar águas naturais com diferentes características de turbidez inicial. No que diz respeito aos mecanismos de coagulação encontrados, para águas com turbidez inicial média e alta, o mecanismo de varredura mostrou-se eficiente nas duas tecnologias utilizadas. No entanto, a amplitude de eficiência de remoção, quando utilizada a coagulação convencional, abrange uma área maior do que quando utilizada a eletrocoagulação. Isto implica em uma maior segurança operacional quando ocorrem eventuais flutuações das características da água bruta, bem como no controle da dosagem de coagulante empregado. A metodologia de superfície de resposta permitiu encontrar condições ótimas para os parâmetros de operação, auxiliando na determinação dos parâmetros relativos às necessidades energéticas e de dimensionamento de um sistema fotovoltaico integrado à célula eletrolítica. Assim é possível instalar o sistema EC-SF em qualquer localização onde existam níveis satisfatórios de irradiação como uma alternativa inovadora que ao mesmo tempo ofereça uma opção sustentável ao tratamento de águas em zonas rurais utilizando energias renováveis. | The general objective of this work was to implement the use of statistical tools in the optimization of the electrocoagulation process in surface waters. Also, to compare the dominant coagulation mechanisms in electrocoagulation with aluminium electrodes and in the conventional treatment with aluminium sulphate. Even, technically and economically evaluate the use of electrocoagulation based on photovoltaic energy as a complementary treatment to pollutants removal from water for human consumption. Initially the models and optimal operating conditions for electrocoagulation were based on the response surface methodology using the central composite design. The desirability function was used to find the operating conditions that lead to increased apparent color removal, Chemistry Oxygen Demand (COD) and turbidity simultaneously. It was possible to comply with the aesthetic / organoleptic standard stipulated for this stage of the process (color <15 uH, COD <18 and turbidity <5 uT) considering the three types of studied waters (initial turbidity; low, medium and high). In a second step, isoefficiency plots for pollutants removal were used to determine and compare the coagulation mechanisms acting on conventional coagulation and electrocoagulation. For waters with low initial turbidity, the adsorption mechanism showed higher removal efficiencies in both studied treatments. For water with medium and high initial turbidity, the scanning mechanism was common in both used technologies. In the third step, the response surface methodology was used to develop mathematical models considering the effects of the current intensity and electrolysis time (i.t) parameters on the apparent colour and turbidity removal of a dirty river water sample. The design and operation conditions for the EC-SF integrated system were established assuming the reproducibility concept of the conditions when the parameters of a single electrolytic cell were known. The used statistical methodology proved to be efficient for predicting the best values of the “i.t” binomial, allowing compliance with the aesthetic / organoleptic standard (colour <15 uC and turbidity <5 Ut). The design of an EC-SF system that met the need for consumption of 50 people was conducted to evaluate the cost of treatment. To this, were considered the cost of the electrode material and the cost of electricity for determining a rate of R$ 0,7 m -3 of clarified water. The correlation between the analysed answers allowed to find specific conditions of the parameters, helping to determine safe working points in the operation. Electrocoagulation was efficient to clarify natural waters with different characteristics of initial turbidity. Regarding the coagulation mechanisms found for water, with medium and high initial turbidity, the scanning mechanism was common in both used technologies. However, the breadth of removal efficiency, when using conventional coagulation, covers a larger area than when using electrocoagulation. This may imply greater operational safety, when eventual fluctuations in the raw water characteristics occur, as well as in the dosage control of the employed coagulant. The response surface methodology allowed finding optimum conditions for the operation parameters, helping to determine the parameters related to the energy requirements and the design of a photovoltaic system integrated to the electrolytic cell. Thus, it is possible to install the EC-SF system in any location where irradiation satisfactory levels are reached. Becoming it in an innovative alternative that offers a sustainable option to the water treatment in rural areas using renewable energies. | Coordenação de Aperfeiçoamento de Pessoal de Nível Superior