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O objetivo desta dissertação de mestrado consistiu em estudar as possíveis interações entre os microplásticos e outros contaminantes, em solos, ao longo do tempo. Para tal, foram realizados vários ensaios experimentais com solo standard, microplásticos (polietileno de baixa densidade), e diferentes concentrações de retardante de chama (fosfato de trifenilo), pesticida, (malatião) e água. Um filme bastante utilizado na cultura de morangueiros é o polietileno e, por isso, os microplásticos deste polímero foram selecionados para estes estudos. Quanto ao fosfato de trifenilo, este foi selecionado por ser um aditivo de plástico muito utilizado na produção de polímeros. Relativamente ao pesticida, escolheu-se o pesticida organofosforado por ser comumente utilizado na cultura dos morangueiros e também porque a sua presença em morangos está reportada em alguns estudos. Por último, foi também estudada a presença da água com o objetivo de simular as condições reais, de rega e chuvas de um ambiente agrícola. Conforme descrito anteriormente, foram estudadas 3 variáveis (em 3 níveis de concentração de retardante de chama, pesticida e água) simulando diferentes ambientes agrícolas na presença de solo e microplásticos. Para otimizar o desenho experimental e minimizar o tempo de experiências, recorreu-se ao Design Expert 11.1.2.0, que é um software de estatística que utiliza como ferramenta o planeamento fatorial. De forma a estudar as interações entre as diferentes variáveis, ao longo do tempo foram realizadas 15 experiências (número determinado pelo Design Expert 11.1.2.0), com contaminações em diferentes proporções de retardante de chama, pesticida e água. Cada uma das experiências teve 5 pontos de amostragem, o que correspondeu a 5 frascos por experiência. As amostragens e subsequentes análises foram feitas aos dias 0, 7, 14, 21 e 28. Após a preparação de todos os ensaios experimentais, estes foram colocados numa camara de fitoclima, que simula o dia e a noite, operando em ciclos alternados de 16 h com luz (12000 lx; 24 ± 2 °C) e de 8 h sem luz (16 ± 2 °C). No tempo correspondente, os vasos foram analisados. Para tal, foi validada uma metodologia analítica para a realização de extrações sólido-líquido, pelo método de QuEChERS modificado, de forma a se extraírem os poluentes fosfato de trifenilo e malatião, dos solos com micropláticos. De seguida, estes foram separados e quantificados através de cromatografia gasosa. Paralelamente a este estudo, também se realizaram algumas experiências para a separação de microplásticos do solo, utilizando soluções salinas de NaCl (0,3 g/cm3 ) e H2O2 (30%). Estes estudos de separação foram avaliados qualitativamente, recorrendo à microscopia ótica. Neste estudo, os resultados demonstraram uma diminuição na concentração de malatião ao longo do tempo e formulou-se a hipótese de que o malatião apresenta uma forte afinidade com os microplásticos, devido ao carácter hidrofóbico de ambos, formando-se um complexo de adsorção. No entanto, outros fenómenos relacionados com as condições do meio (pH, percentagem de humidade) ou mesmo com as características do solo, podem ter levado a uma degradação do pesticida. A concentração do malatião sofreu uma diminuição significativa ao longo do tempo, sendo difícil ou impossível (por ter ocorrido a sua degradação por exemplo) de extrair dos vasos experimentais. Relativamente aos resultados obtidos para o fosfato de trifenilo, formulou-se a hipótese de que a percentagem de humidade do solo possa favorecer a sua adsorção. Também se verificou que as ligações que estabelece com os microplásticos favorecem a sua dessorção. No entanto, outros fenómenos de degradação do fosfato de trifenilo podem ter ocorrido. A concentração deste aditivo de plástico sofreu um aumento significativo ao longo das experiências, uma vez que foi facilmente extraído dos vasos experimentais, no entanto, também se podem se ter formado produtos de degradação. Este trabalho permitiu concluir que diversas interações entre microplásticos, aditivos de plásticos e pesticidas podem ocorrer nos sistemas agrícolas e que são precisos mais estudos para as interpretar e perceber.
The aim of this master's thesis was to study the possible interactions between microplastics and other contaminants, in agricultural soils, over time. For this purpose, several experiments were carried out in open pots with standard soil, with microplastics (low density polyethylene), and different concentrations of flame retardant (triphenyl phosphate), pesticide, (malathion) and water. Polyethylene is widely used in strawberry culture as mulch film and, therefore, it was the microplastic selected for these studies. Triphenyl phosphate was selected because it is a plastic additive widely used in polymer production. Regarding pesticide, the organophosphorus pesticide was chosen since it is commonly used in strawberry crops and because its presence in strawberries is reported in some studies. Finally, the presence of water was also studied to simulate the real conditions of an agricultural crop. As described previously, 3 variables (at 3 concentration levels of flame retardant, pesticide, and water) were studied simulating different agricultural environments in the presence of soil and microplastics. To optimize the experimental design and minimize the experimental time, Design Expert 11.1.2.0 was used, which is a statistical software that uses factorial planning as a tool. To study the interactions between the different variables, over time 15 experiments (number determined by Design Expert 11.1.2.0) were carried out, with contaminations at different proportions of flame retardant, pesticide, and water. Each of the experiments had 5 sampling points, corresponding to 5 vials per experiment. Sampling and subsequent analysis were done at days 0, 7, 14, 21 and 28. The experimental pots were placed in a phytoclimatic chamber, which simulates day and night, operating on alternating cycles of 16 h of light (12000 lx; 24 ± 2 °C) and 8 h of darkness (16 ± 2 °C). At the corresponding time, the vessels were analyzed. To this end, an analytical methodology was validated to perform solid-liquid extractions by a modified QuEChERS method, to extract triphenyl phosphate and malathion, from the soils with microplastics These were then separated and quantified by gas chromatography. Parallel to this study, some experiments for the separation of microplastics from soil, using saline solutions (0.3 g/cm3 ) and H2O2 (30%) were also carried out. These separation studies were qualitatively evaluated using optical microscopy. In this study, the results showed a decrease in malathion concentration over time. It was hypothesized that malathion shows a strong affinity with microplastics, due to the hydrophobic character of both, that leads to the formation of an adsorption complex. However, other phenomena may have occurred, since conditions of the medium such as pH, the percentage of moisture or even the characteristics of the soil, may have contributed to the pesticide’s degradation. The concentration of malathion suffered a significant decrease throughout the experiments, being difficult or impossible (by degradation for example) to extract from the experimental pots. Regarding the results obtained for triphenyl phosphate, it was hypothesized that the percentage of moisture in the soil may favor its adsorption. A weak interaction with microplastics was also found. However, other degradation phenomena of triphenyl phosphate may have occurred. The concentration of this plastic additive underwent a significant increase throughout the experiments, as it was easily extracted from the experimental vessels, however, degradation products may have also been formed. This work allowed the conclusion that several interactions between microplastics, plastics additives and pesticides can occur in agricultural systems and that more studies are needed to clarify them.
The aim of this master's thesis was to study the possible interactions between microplastics and other contaminants, in agricultural soils, over time. For this purpose, several experiments were carried out in open pots with standard soil, with microplastics (low density polyethylene), and different concentrations of flame retardant (triphenyl phosphate), pesticide, (malathion) and water. Polyethylene is widely used in strawberry culture as mulch film and, therefore, it was the microplastic selected for these studies. Triphenyl phosphate was selected because it is a plastic additive widely used in polymer production. Regarding pesticide, the organophosphorus pesticide was chosen since it is commonly used in strawberry crops and because its presence in strawberries is reported in some studies. Finally, the presence of water was also studied to simulate the real conditions of an agricultural crop. As described previously, 3 variables (at 3 concentration levels of flame retardant, pesticide, and water) were studied simulating different agricultural environments in the presence of soil and microplastics. To optimize the experimental design and minimize the experimental time, Design Expert 11.1.2.0 was used, which is a statistical software that uses factorial planning as a tool. To study the interactions between the different variables, over time 15 experiments (number determined by Design Expert 11.1.2.0) were carried out, with contaminations at different proportions of flame retardant, pesticide, and water. Each of the experiments had 5 sampling points, corresponding to 5 vials per experiment. Sampling and subsequent analysis were done at days 0, 7, 14, 21 and 28. The experimental pots were placed in a phytoclimatic chamber, which simulates day and night, operating on alternating cycles of 16 h of light (12000 lx; 24 ± 2 °C) and 8 h of darkness (16 ± 2 °C). At the corresponding time, the vessels were analyzed. To this end, an analytical methodology was validated to perform solid-liquid extractions by a modified QuEChERS method, to extract triphenyl phosphate and malathion, from the soils with microplastics These were then separated and quantified by gas chromatography. Parallel to this study, some experiments for the separation of microplastics from soil, using saline solutions (0.3 g/cm3 ) and H2O2 (30%) were also carried out. These separation studies were qualitatively evaluated using optical microscopy. In this study, the results showed a decrease in malathion concentration over time. It was hypothesized that malathion shows a strong affinity with microplastics, due to the hydrophobic character of both, that leads to the formation of an adsorption complex. However, other phenomena may have occurred, since conditions of the medium such as pH, the percentage of moisture or even the characteristics of the soil, may have contributed to the pesticide’s degradation. The concentration of malathion suffered a significant decrease throughout the experiments, being difficult or impossible (by degradation for example) to extract from the experimental pots. Regarding the results obtained for triphenyl phosphate, it was hypothesized that the percentage of moisture in the soil may favor its adsorption. A weak interaction with microplastics was also found. However, other degradation phenomena of triphenyl phosphate may have occurred. The concentration of this plastic additive underwent a significant increase throughout the experiments, as it was easily extracted from the experimental vessels, however, degradation products may have also been formed. This work allowed the conclusion that several interactions between microplastics, plastics additives and pesticides can occur in agricultural systems and that more studies are needed to clarify them.
Description
Keywords
Microplásticos Aditivos de plástico Retardante de chama Pesticidas Ambiente Solos Sustentabilidade Cromatografia gasosa Microplastics Plastic additives Flame retardant Pesticides Environment Soil Sustainability Gas chromatography