Mixtures of Chemical Pollutants at European Legislation Safety Concentrations: How Safe Are They?

The risk posed by complex chemical mixtures in the environment to wildlife and humans is increasingly debated, but has been rarely tested under environmentally relevant scenarios. To address this issue, two mixtures of 14 or 19 substances of concern (pesticides, pharmaceuticals, heavy metals, polyaromatic hydrocarbons, a surfactant, and a plasticizer), each present at its safety limit concentration imposed by the European legislation, were prepared and tested for their toxic effects. The effects of the mixtures were assessed in 35 bioassays, based on 11 organisms representing different trophic levels. A consortium of 16 laboratories was involved in performing the bioassays. The mixtures elicited quantifiable toxic effects on some of the test systems employed, including i) changes in marine microbial composition, ii) microalgae toxicity, iii) immobilization in the crustacean Daphnia magna, iv) fish embryo toxicity, v) impaired frog embryo development, and vi) increased expression on oxidative stress-linked reporter genes. Estrogenic activity close to regulatory safety limit concentrations was uncovered by receptor-binding assays. The results highlight the need of precautionary actions on the assessment of chemical mixtures even in cases where individual toxicants are present at seemingly harmless concentration

Mixtures of chemical pollutants at European legislation safety concentrations: how safe are they?

The risk posed by complex chemical mixtures in the environment to wildlife and humans is increasingly debated, but has been rarely tested under environmentally relevant scenarios. To address this issue, two mixtures of 14 or 19 substances of concern (pesticides, pharmaceuticals, heavy metals, polyaromatic hydrocarbons, a surfactant, and a plasticizer), each present at its safety limit concentration imposed by the European legislation, were prepared and tested for their toxic effects. The effects of the mixtures were assessed in 35 bioassays, based on 11 organisms representing different trophic levels. A consortium of 16 laboratories was involved in performing the bioassays. The mixtures elicited quantifiable toxic effects on some of the test systems employed, including i) changes in marine microbial composition, ii) microalgae toxicity, iii) immobilization in the crustacean Daphnia magna, iv) fish embryo toxicity, v) impaired frog embryo development, and vi) increased expression on oxidative stress-linked reporter genes. Estrogenic activity close to regulatory safety limit concentrations was uncovered by receptor-binding assays. The results highlight the need of precautionary actions on the assessment of chemical mixtures even in cases where individual toxicants are present at seemingly harmless concentrations

Electrochemical etching of graphite tips for potential use in nanoscience

The main goal is to find an easy, and more importantly, cheap process of producing sharp tips for the potential use in an atomic force microscope (AFM) or as a source of electrons utilizing cold field emission. This objective is being achieved by the method named electrochemical etching, and the used material is cheap and easily accessible. For this experiment, graphite leads of different hardnesses were used, etched with two types of etching solutions. The first solution contained potassium hydroxide (KOH) dissolved in water and the second contained sodium hydroxide (NaOH), also dissolved in water. Different ratios of chemicals were tried for the manufacturing process. Hardnesses of leads were 2B, B, and HB. After the process of etching, products were examined with a scanning electron microscope (SEM). The radius of tips was measured, and results were compared and evaluated. Stating on the output data of tips, it can be said, that goal was achieved, and tips can be used for their potential purpose. There would be needed another research about how well they fit to work

Effects of Structure and Composition of Adsorbents on Competitive Adsorption of Gaseous Emissions: Experiment and Modeling

Dangerous gases arising from combustion processes must be removed from the air simply and cheaply, e.g., by adsorption. This work is focused on competitive adsorption experiments and force field-based molecular modeling of the interactions at the molecular level. Emission gas, containing CO, NO, SO2, and CO2, was adsorbed on activated carbon, clay mineral, silicon dioxide, cellulose, or polypropylene at two different temperatures. At 20 °C, activated carbon had the highest NO and SO2 adsorption capacity (120.83 and 3549.61 μg/g, respectively). At 110 °C, the highest NO and SO2 adsorption capacity (6.20 and 1182.46 μg/g, respectively) was observed for clay. CO was adsorbed very weakly, CO2 not at all. SO2 was adsorbed better than NO, which correlated with modeling results showing positive influence of carboxyl and hydroxyl functional groups on the adsorption. In addition to the wide range of adsorbents, the main novelty of this study is the modeling strategy enabling the simulation of surfaces with pores of controllable sizes and shapes, and the agreement of the results achieved by this strategy with the results obtained by more computationally demanding methods. Moreover, the agreement with experimental data shows the modeling strategy to be a valuable tool for further adsorption studies

Effect of crystal structure on nanofiber morphology and chemical modification; design of CeO2/PVDF membrane

Layered crystal structures tend to form flat platelet-like crystallites, and nanofibers having such a structure exhibit strip-like morphology. Crystallographic plane forming the dominant flat surface of the nanofibers can be used for surface modification with catalytically active nanoparticles capable of anchoring to the dominant flat surface. In this study, polyvinylidene fluoride (PVDF) nanofibers exhibiting strip-like morphology and longitudinal folding were prepared using wire electrospinning, and surface modified with CeO2 nanoparticles. Experimental characterization of the CeO2/PVDF membrane using (high-resolution) scanning electron microscopy and X-ray photoelectron spectroscopy was supplemented by a force field-based molecular modeling. The modeling has shown that the dominant PVDF(100) plane is suitable for anchoring the CeO2 nanoparticles. In this respect, the PVDF(100) plane is comparable to the less exposed fluorine-oriented PVDF(010) plane, and both planes show stronger interaction with CeO2 compared to hydrogen-oriented PVDF(010) plane. Molecular modeling also revealed preferred crystallographic orientations of anchored CeO2 nanoparticles: these are the catalytically active planes (100), (110), and (111). The successful surface modification and the finding that CeO2 nanoparticles on the dominant PVDF(100) surface can preferentially exhibit these crystallographic orientations thus provides the possibility of various practical applications of the CeO2/PVDF membrane.Web of Science110art. no. 10756

The influence of structural properties on the adsorption capacities of microwave-assisted biochars for metazachlor removal from aqueous solutions

Biochars, carbonaceous materials prepared without the usage of chemical agents, are porous materials capable of adsorbing pollutants from ground-and surface waters. In this study, biochars prepared from various types of agricultural biomass were tested for the adsorptive removal of herbicide metazachlor from an aqueous environment. Banana wastes, red mombin seeds, corncob, cocoa pod husk, and coffee husk were used as precursors. Biochars were prepared with the aid of microwave treatment. The effect of precursor type on structure and adsorption was examined. Adsorption was controlled by a multistep mechanism, adsorption kinetics followed predominantly the pseudo-second-order model, adsorption isotherms suited to both Langmuir and Freundlich isotherms, depending on the particular biochar. Significant differences between the structural properties and adsorption capacities of the examined biochars were observed. The best adsorption properties for metazachlor uptake were observed for banana waste-based biochar, which had large, elongated pores, highest volume of micropores and one of the highest contents of polar functional groups. The maximum adsorption capacity, calculated from Langmuir isotherm, was 146.01 mg.g(-1), The adsorption capacity at equilibrium, obtained by kinetic measurements, was 27.25 mg.g(-1), the kinetic constant was 5.14.10- 3 dm3.min(-1) (both calculated from pseudo-second order model). Molecular modeling revealed that metazachlor molecules preferably entered two layer wide cavities containing one COOH group with their pyrazole rings.Web of Science103art. no. 10800