An eco-friendly and sustainable support of agave-fibers functionalized with graphene/TiO2:SnO2 for the photocatalytic degradation of the 2,4-D herbicide from the drinking water.

In this research, we evaluated the photocatalytic performance of biodegradable composites for the removal of the 2,4-Dichlorophenoxyacetic acid (2,4-D) herbicide. The composite was composed by agave fibers (AgF), graphene-microplates (GM) and titanium dioxide TiO2/SnO2 (TSn) nanoparticles (NPs) and was named TSn + AgF/GM. Both, the TSn NPs and the GM were deposited on the AgF using the Dip-coating method. According to the analysis by X-Ray Diffraction (XRD), the crystalline phase for the TiO2 and SnO2 was anatase and tetragonal-rutile, respectively. The Scanning Electron Microscopy (SEM) images demonstrated that the AgF were completely saturated by the GM (which had average dimensions of 15 µm × 22 µm) and by conglomerations of TSn NPs with average size of 642 nm. The TSn NPs and the TSn + AgF/GM composite were evaluated for the photocatalytic degradation of the 2,4-D herbicide under ultraviolet-visible (UV-Vis) light and found a maximum degradation of 98.4 and 93.7% (after 4 h) for the TSn NPs and the TSn + AgF/GM composite, respectively. Reuse cycles were also performed and the degradation percentage decreased by 13.1% and by 7.8% (after 3 cycles of reuse) when the TSn NPs and the TSn + AgF/GM composite are employed, respectively. Scavenger experiments were also carried out and found that the oxidizing agents are mainly produced in the order of: •OH>•O2- > h+; then, the main oxidizing agents generated during the photocatalytic reaction were the hydroxyl radicals. Thus, the photocatalytic system studied in this work for the degradation of 2,4-D could pave the way for the development of new eco-friendly/floatable photocatalysts, which can be applied in wastewater-treatment plants.

Removing 2,4-D micropollutant herbicide using powdered activated carbons: the influence of different aqueous systems on adsorption process.

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.

High-performance of activated biocarbon based on agricultural biomass waste applied for 2,4-D herbicide removing from water: adsorption, kinetic and thermodynamic assessments.

Activated biocarbons were prepared using biomass wastes: sugarcane bagasse, coconut shell and endocarp of babassu coconut; as a renewable source of low-cost raw materials and without prior treatments. These activated biocarbons were characterized by textural analysis, solid-state 13C nuclear magnetic resonance spectroscopy, X-ray diffraction and scanning electronic microscopy. Textural analysis results revealed that those activated biocarbons were microporous, with specific surface area values of 547, 991 and 1,068 m2 g-1 from sugarcane bagasse, coconut shell and endocarp of babassu coconut, respectively. The innovation of this work was to evaluate which biomass residue was able to offer the best performance in removing 2,4-dichlorophenoxyacetic acid herbicide (2,4-D) from water by adsorption. Adsorption process of 2,4-D was investigated and the Langmuir and Redlich-Peterson models described best the adsorption process, with R2 values within 0.96-0.99. The 2,4-D removal performance were 97% and 99% for the coconut and babassu biocarbons, respectively. qM parameter values obtained from Langmuir model were 153.9, 233.0 and 235.5 mg g-1 using sugarcane bagasse, coconut shell and endocarp of babassu, respectively. In addition, the adsorption kinetics were described nicely by the second-order model and the Gibbs free energy parameter values were negative, pointing to a spontaneous adsorption, as well.

Effects of the 2, 4-D herbicide on gills epithelia and liver of the fish Poecilia vivipara / Efeitos do herbicida 2, 4-D no epitélio das brânquias e no fígado do peixe Poecilia vivípara

The 2,4-dichlorophenoxyacetic acid, usually named 2,4-D is one of the most widely used herbicides in the world. Acute toxicity of 2,4-D herbicide was investigated through its effects on guppies (Poecilia vivipara Bloch et Schneider 1801). Fish were exposed to the herbicide at concentrations of 10, 20 and 40µl per liter of water for 24 hours to determine its effects on gills and liver epithelia. The estimated LC50 was 34.64µl of 2,4-D per liter of water. Histochemical analyses and Feulgen's reaction were conducted to detect glycoconjugates and DNA, respectively, in gills and liver epithelia. Histochemistry revealed qualitative variations of glycoconjugates present on mucous cells and granules. The four types of mucous cells contained neutral granules, acids, or both. Increasing amounts of syalomucins were observed from the control group to the group exposed to the highest concentration of 2,4-D, suggesting increased mucous viscosity and the formation of plaques that could inhibit gas exchange and osmoregulation. Lamellar fusion observed in the group exposed to 40µl of 2,4-D suggests a defense mechanism. Hepatocytes showed vacuolization in the 10 and 20µl/L groups. The 40 µl/L group showed normal hepatocytes as well as changed ones, many Ito cells, micronuclei, and nuclear swelling. These effects may be associated with toxicity or adaptative processes to cellular stress. The data from this study indicates the importance of assessing similar risks to aquatic species and suggests that Poecilia vivipara is an adequate biological model for analysis of environmental contamination.(AU)

A toxicidade aguda do herbicida 2,4-D foi investigada através dos efeitos no peixe Poecilia vivípara (Bloch et Schneider, 1801). Grupos de peixes foram expostos ao herbicida nas concentrações de 10, 20 e 40µl por litro de água, durante 24 horas. As brânquias e o fígado foram estudados. A concentração letal média (CL50) do herbicida para a espécie em questão foi de 34,64µl/l. Foram realizadas colorações histoquímicas e coloração de Feulgen para identificar glicoconjugados e DNA, respectivamente, nos tecidos acima citados. Os métodos histoquímicos revelaram os tipos de glicoconjugados presentes nas células mucosas e nos grânulos. Os quatro tipos de células mucosas apresentaram glicoconjugados neutros, ácidos, ou ambos em um mesmo tipo celular. Observou-se a presença crescente de sialomucinas do grupo controle até o grupo exposto a maior concentração de 2,4-D, sugerindo aumento da viscosidade do muco e, consequentemente, formação de placas que impedem as trocas gasosas e a osmorregulação. A fusão lamelar observada no grupo exposto a 40µl de 2,4-D sugere ser um mecanismo de defesa. Os hepatócitos apresentaram processo de vacuolização nos grupos 10 e 20µl/l. No grupo de 40µl/l, observou-se a presença de células de Ito, micronúcleos e hepatócitos normais e outros com edema nuclear. Este estudo indica a importância da avaliação de riscos semelhantes a espécies aquáticas e sugere a espécie Poecilia vivipara como modelo biológico adequado para análises de contaminação ambiental.(AU)

Effects of the 2, 4-D herbicide on gills epithelia and liver of the fish Poecilia vivipara / Efeitos do herbicida 2, 4-D no epitélio das brânquias e no fígado do peixe Poecilia vivípara

The 2,4-dichlorophenoxyacetic acid, usually named 2,4-D is one of the most widely used herbicides in the world. Acute toxicity of 2,4-D herbicide was investigated through its effects on guppies (Poecilia vivipara Bloch et Schneider 1801). Fish were exposed to the herbicide at concentrations of 10, 20 and 40µl per liter of water for 24 hours to determine its effects on gills and liver epithelia. The estimated LC50 was 34.64µl of 2,4-D per liter of water. Histochemical analyses and Feulgen's reaction were conducted to detect glycoconjugates and DNA, respectively, in gills and liver epithelia. Histochemistry revealed qualitative variations of glycoconjugates present on mucous cells and granules. The four types of mucous cells contained neutral granules, acids, or both. Increasing amounts of syalomucins were observed from the control group to the group exposed to the highest concentration of 2,4-D, suggesting increased mucous viscosity and the formation of plaques that could inhibit gas exchange and osmoregulation. Lamellar fusion observed in the group exposed to 40µl of 2,4-D suggests a defense mechanism. Hepatocytes showed vacuolization in the 10 and 20µl/L groups. The 40 µl/L group showed normal hepatocytes as well as changed ones, many Ito cells, micronuclei, and nuclear swelling. These effects may be associated with toxicity or adaptative processes to cellular stress. The data from this study indicates the importance of assessing similar risks to aquatic species and suggests that Poecilia vivipara is an adequate biological model for analysis of environmental contamination.

A toxicidade aguda do herbicida 2,4-D foi investigada através dos efeitos no peixe Poecilia vivípara (Bloch et Schneider, 1801). Grupos de peixes foram expostos ao herbicida nas concentrações de 10, 20 e 40µl por litro de água, durante 24 horas. As brânquias e o fígado foram estudados. A concentração letal média (CL50) do herbicida para a espécie em questão foi de 34,64µl/l. Foram realizadas colorações histoquímicas e coloração de Feulgen para identificar glicoconjugados e DNA, respectivamente, nos tecidos acima citados. Os métodos histoquímicos revelaram os tipos de glicoconjugados presentes nas células mucosas e nos grânulos. Os quatro tipos de células mucosas apresentaram glicoconjugados neutros, ácidos, ou ambos em um mesmo tipo celular. Observou-se a presença crescente de sialomucinas do grupo controle até o grupo exposto a maior concentração de 2,4-D, sugerindo aumento da viscosidade do muco e, consequentemente, formação de placas que impedem as trocas gasosas e a osmorregulação. A fusão lamelar observada no grupo exposto a 40µl de 2,4-D sugere ser um mecanismo de defesa. Os hepatócitos apresentaram processo de vacuolização nos grupos 10 e 20µl/l. No grupo de 40µl/l, observou-se a presença de células de Ito, micronúcleos e hepatócitos normais e outros com edema nuclear. Este estudo indica a importância da avaliação de riscos semelhantes a espécies aquáticas e sugere a espécie Poecilia vivipara como modelo biológico adequado para análises de contaminação ambiental.