The main challenge of my work is the development of solutions that allow rapid detection and identification of natural alpha-particle emitting radionuclides, such as isotopes of polonium, radium, uranium and thorium as well as artificial radionuclides such as plutonium and americium in various samples. On the other hand, also fission products such as Cs-137 and Sr-90 are very important. All mention radionuclides are present at low levels in food and foodstuffs.
Since many analytical methods and approaches are not yet standardized, and certified reference materials are not available, metrological support providing validation and standardization of methods is essential to the accurate determination of radionuclides in food and foodstuffs.
Due to the low-level activity concentrations of radionuclides in food and foodstuff, their accurate determination often requires extensive radiochemical separation. To effectively separate the radionuclides of interest from the sample matrix and other interfering radionuclides, different selective precipitation techniques and/or different ion exchange and/or extraction chromatography techniques have to be applied before the measurements can be conducted.
The radiometrical techniques used to quantify the radionuclide(s) of interest are: i) Radiochemical neutron activation analysis (RNAA) and instrumental neutron activation analysis (INAA), ii) alpha-particle spectrometry, iii) beta counting, iv) liquid scintillation counting and v) gamma spectrometry.
My current studies among other include: i) development of a fast lithium borates thermal fusion decomposition procedure, ii) determination of activity concentrations of alpha-particle emitting radionuclides in baby formulas, iii) determination of a low-level 237Np in environmental samples, iv) determination of uranium radioisotopes and 210Po in soil an cabbage collected in the vicinity of the former Žirovski Vrh uranium mine, v) development of an accurate method for determination of 228Ra activity concentration in water and vi) routine radiochemical analysis of environmental samples including various food and foodstuffs.
Since the last few years titanium dioxide (TiO2) has become a common additive in food stuff and personal care products. Even though its use as food-grade colorant (E171) is regulated by the European Directive 94/36/EC, a recent study by Weir et al. highlighted the presence of TiO2 in many commercial products, which contributes to the raise of the daily human exposure towards it. The study reported that up to the 36% of the extracted TiO2 was constituted of nano-sized particles. Due to the numerous warning studies about the toxicity of nano-TiO2 particles, the scientific community has started having concerns about the health risks for the consumers.
Being aware that E171 is diffusely used as white pigment and thickening agent, TiO2-based food colours and additives were chosen as study substances. The main objective of the project is to extract and physico-chemically characterise titania E171 contained in different commercial sources, such as chewing gums, food colours, cake decorations…
The extraction of titania powders from food will be achieved by different analytical methods, in order to optimise the yield and the purity of the recovered particles. The accomplishment and optimization of the powder extraction will be monitored by Fourier-Transformed Infrared (FT-IR) spectroscopy. The presence of remaining organics mixed with the food-grade titanium dioxide will be followed up throughout the extraction process steps.
Next, the dried powders will be physico-chemically characterised. Scanning Electron Microscopy (SEM), Particle Size Distribution analysis, Brunauer, Emmett and Teller (BET) analysis will be applied to study the particle morphology, size and size distribution, surface area; X-ray Diffractometry (XRD), Energy-Dispersive X-ray (EDX) spectroscopy and FT-IR spectroscopy will reveal the chemical and phase composition of the dry powders. Measurements of zeta potential (ZP) titration curves in water, physiological solution and artificial saliva will disclose the surface charge of the particles in different pH conditions and, accordingly, their state of aggregation in liquids.
As a semiconductor, nano-sized TiO2 undergoes photocatalysis, if activated by UV light; thus, our purpose will be also to study the photocatalytic activity of the E171-based powders under UV light, following the degradation of the other organic components which constitute the food colorants. Pure TiO2 food-grade white pigments from different brands will be used to assess the organic degradation of caffeine (used as model molecule) upon UV irradiation. Their photocatalytic activity will be related to their physico-chemical properties.
If confirmed by the present study, the portion of particles in the range of nanosize deserves attention, due to the potential toxic effects. In fact, the nanoparticles can interact with the gastrointestinal tract. In theory, it can be supposed that the TiO2 powders can be cell-internalised in the stomach, due to the positive charge acquired by the (nano)particles at high acidic pH; the ZP titration curves will help predicting the particle behaviour once dispersed in liquid.
Further biological studies will be aimed at in vitro cell toxicity and risk assessment of the TiO2 (nano)particles isolated from food and/or purchased as food-grade powder. Finally, collaborations within the IsoFood associated groups are expected to broaden the possible available techniques (e.g. microwave-assisted digestion, field flow fractionation, atomic adsorption, inductively coupled plasma-mass spectrometry).