Giovanna Armiento

Zinc Oxide Nanorods-Decorated Graphene Nanoplatelets: A Promising Antimicrobial Agent against the Cariogenic Bacterium Streptococcus mutans

Nanomaterials are revolutionizing the field of medicine to improve the quality of life due to the myriad of applications stemming from their unique properties, including the antimicrobial activity against pathogens. In this study, the antimicrobial and antibiofilm properties of a novel nanomaterial composed by zinc oxide nanorods-decorated graphene nanoplatelets (ZNGs) are investigated. ZNGs were produced by hydrothermal method and characterized through field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) techniques. The antimicrobial activity of ZNGs was evaluated against Streptococcus mutans, the main bacteriological agent in the etiology of dental caries. Cell viability assay demonstrated that ZNGs exerted a strikingly high killing effect on S. mutans cells in a dose-dependent manner. Moreover, FE-SEM analysis revealed relevant mechanical damages exerted by ZNGs at the cell surface of this dental pathogen rather than reactive oxygen species (ROS) generation. In addition, inductively coupled plasma mass spectrometry (ICP-MS) measurements showed negligible zinc dissolution, demonstrating that zinc ion release in the suspension is not associated with the high cell mortality rate. Finally, our data indicated that also S. mutans biofilm formation was affected by the presence of graphene-zinc oxide (ZnO) based material, as witnessed by the safranin staining and growth curve analysis. Therefore, ZNGs can be a remarkable nanobactericide against one of the main dental pathogens. The potential applications in dental care and therapy are very promising.

High geochemical background of potentially harmful elements in soils and sediments: implications for the remediation of contaminated sites

Geochemical background concentrations of potentially harmful elements and species (PHES) may have a high spatial variability and their natural levels can be higher than those caused by anthropogenic sources of pollution. Therefore, the use of a threshold value for assessing contamination can be inadequate and local variability should be considered. In Europe, soil quality standards are widely variable. In Italy concentration levels exceeding threshold values (TVs) are allowed only if the natural concentrations for a given area are higher than those specified by law. For sediments, in Italian law TVs have not been yet established but TVs with local validity are used for contamination assessment in areas with different geochemistry. A short outline of the worldwide regulatory frameworks is presented with the intent of singling out suitable approaches and priority actions needed to tackle the weak points in law, following the indications of the scientific community and stressing the importance of assessing the real hazard using tools for the evaluation of site-specific mobility and toxicity of PHES. Cases of areas with high PHES background concentration are presented as evidence of this widespread phenomenon and of the need to find effective approaches and solutions.

High geochemical background of potentially harmful elements. The ''geochemical risk'' and ''natural contamination'' of soils and water: awareness and policy approach in Europe with a focus on Italy

A brief review on the occurrence of high natural concentrations of potentially toxic elements (PHEs) in soils and water is presented, analysing also various approaches and strategies applied in different Countries to address the problem of “natural” contamination. Starting from the well known case of arsenic, the situation for other elements such as beryllium, uranium and nickel, among the most interesting, is analysed. The analysis is based on already evidenced geochemical anomalies and on the possible evolution both in the estimate of their toxicological effects and the redefinition (lowering) of the limits at the moment imposed by legislation or suggested by guidelines. New data obtained in the ENEA laboratory in the last years on arsenic and beryllium are presented. The growing need of “geochemical maps” at regional, national and European level and of a continuous monitoring activity is highlighted. At the same time the importance of considering concentration and speciation of elements and how an element is bound and under what circumstances it may be bioavailable and able to damage the ecosystem, is recalled. Finally it is suggested to concentrate efforts on the development of screening methodologies that could play a key role in the characterisation of contamination and on standardising fast procedures that enable a guided real-time survey. The clear definition of a “geochemical risk” requires a complex and multidisciplinary approach, so the emerging role of Medical Geology is underlined.

Toxicity of the readily leachable fraction of urban PM2.5 to human lung epithelial cells: Role of soluble metals

Fine airborne particulate matter (PM2.5) has been repeatedly associated with adverse health effects in humans. The PM2.5 soluble fraction, and soluble metals in particular, are thought to cause lung damage. Literature data, however, are not consistent and the role of leachable metals is still under debate. In this study, Winter and Summer urban PM2.5 aqueous extracts, obtained by using a bio-compatible solution and different contact times at 37 °C, were used to investigate cytotoxic effects of PM2.5 in cultured lung epithelial cells (A549) and the role played by the leachable metals Cu, Fe, Zn, Ni, Pb and Cd. Cell viability and migration, as well as intracellular glutathione, extracellular cysteine, cysteinylglycine and homocysteine concentrations, were evaluated in cells challenged with both PM2.5 extracts before and after ultrafiltration and artificial metal ion solutions mimicking the metal composition of the genuine extracts. The thiol oxidative potential was also evaluated by an abiotic test. Results demonstrate that PM2.5 bioactive components were released within minutes of PM2.5 interaction with the leaching solution. Among these are i) low MW (<3 kDa) solutes inducing oxidative stress and ii) high MW and/or water-insoluble compounds largely contributing to thiol oxidation and to increased homocysteine levels in the cell medium. Cu and/or Ni ions likely contributed to the effects of Summer PM2.5 extracts. Nonetheless, the strong bio-reactivity of Winter PM2.5 extracts could not be explained by the presence of the studied metals. A possible role for PM2.5 water-extractable organic components is discussed.

A field screening test for the assessment of concentrations and mobility of potentially toxic elements in soils: a case study on urban soils from Rome and Novi Sad

The increasing demand for environmental pollution control results in the development and use of new procedures for the determination of dangerous chemicals. Simple screening methods, which can be used directly in the field for a preliminary assessment of soil contamination, seem to be extremely advantageous. In our laboratory, we developed and optimized a rapid test for a preliminary evaluation of both the concentration and the mobility of some potentially toxic metals in soils. This screening test consists of a single extraction of the soil sample with a buffer solution, followed by the titration of the extracted solution with dithizone to determine the contents of bi-valent heavy metals (such as Pb, Cu, Zn, and Cd). This screening method was then directly applied in the field during the sampling campaign in the framework of an Italian–Serbian collaborative project, finalized in the study of metal availability in soils. The results obtained in the field with the rapid test were compared with those obtained in the laboratory following the conventional procedure commonly used to evaluate metal bioavailability (diethylenetriaminepentaacetic extraction). Moreover, selected samples were analyzed sequentially in the laboratory using the standardized BCR three-step sequential extraction procedure. The screening test gave results conceptually in good agreement with those obtained via the BCR procedure. These preliminary data show that the proposed screening test is a reliable method for the preliminary rapid evaluation of metal total concentrations and of potential metal mobility in soils, supporting sampling activities directly in the field.