Alteration of Hordeum vulgare and Sinapis alba germination and early growth in response to airborne low-metallic automotive brake wear debris

Road transportation significantly contributes to environmental pollution, both in terms of exhaust and non-exhaust (brake wear) emissions. As was proven, brake wear debris is released in a wide variety of sizes, shapes, and compositions. Although studies confirming the possible adverse health and environmental impact of brake wear debris were published, there is no standardized methodology for their toxicity testing, and most studies focus only on one type of brake pad and/or one test. The lack of methodology is also related to the very small amount of material released during the laboratory testing. For these reasons, this study deals with the mixture of airborne brake wear debris from several commonly used low-metallic brake pads collected following the dynamometer testing. The mixture was chosen for better simulation of the actual state in the environment and to collect a sufficient amount of particles for thorough characterization (SEM, XRPD, XRF, chromatography, and particle size distribution) and phytotoxicity testing. The particle size distribution measurement revealed a wide range of particle sizes from nanometers to hundreds of nanometers, elemental and phase analysis determined the standard elements and compounds used in the brake pad formulation. The Hordeum vulgare and Sinapis alba were chosen as representatives of monocotyledonous and dicotyledonous plants. The germination was not significantly affected by the suspension of brake wear debris; however, the root elongation was negatively influenced in both cases. Sinapis alba (IC50 = 23.13 g L-1) was more affected than Hordeum vulgare (IC50 was not found in the studied concentration range) the growth of which was even slightly stimulated in the lowest concentrations of brake wear debris. The plant biomass was also negatively affected in the case of Sinapis alba, where the IC50 values of wet and dry roots were determined to be 44.83 g L-1 and 86.86 g L-1, respectively.

Determination of Oxidative Potential Caused by Brake Wear Debris in Non-Cellular Systems

Wear debris from automotive brake systems represents a major source of non-exhaust emissions from road traffic and its production increases with number of cars worldwide. However, impact of brake wear debris on the environment and organisms is still not clear. One of the most possible ways by which these particles may affect living organisms is oxidative stress. Production of reactive oxidative species may cause damage of basic cell components, lipids, proteins, etc. Aim of this study is to perform characterization of airborne and nonairborne fractions of brake wear debris generated during standard dynamometer tests and evaluation of its potential to induce oxidative stress via lipid peroxidation and carbonylation of proteins in non-cellular system. Elemental and phase composition were determined by scanning electron microscopy, Raman microspectroscopy, and X-ray powder diffraction analysis. Carbon in amorphous form and graphite, copper, and iron in form of oxides were identified as major components in both studied fractions. Characteristic size of studied wear particles was evaluated by dynamic light scattering. Both airborne and nonairborne samples showed ability to induce oxidative stress which results from determination of carbonylated proteins.

Toxicity of the Zinc Oxide and Vermiculite/Zinc Oxide Nanomaterials

Nanomaterials and nanocomposite materials on the base of zinc oxide (ZnO) are being produced and applied in our daily life at a rapid pace mainly as additives to the different polymer materials. The antibacterial behaviors of ZnO nanoparticles are intensively studied but related health and environmental toxicity assessments are lagging behind. The aim of this work was evaluated the toxic effect of self-synthesized samples (ZnO nanoparticles, vermiculite/ZnO nanocomposite) and one commercial sample of the ZnO nanoparticles, to induce oxidative stress via lipid peroxidation. This ability is one of the indicators of material toxicity. The toxicity results were compared with the results of titanium dioxide nanoparticles as a validated toxic standard. The effect of the major nanoparticles properties as particle and crystallite size, shape, specific phase and composition were evaluated using the dynamic laser diffraction, scanning electron microscopy and X-ray diffraction analysis. The attention was also focused on the influence of the vermiculite (as matrix of nanocomposite samples) and temperature of the nanostructured materials preparation. All samples containing vermiculite are not able to induce peroxidation of lipids in comparison to TiO₂ nanoparticles. However, samples of ZnO nanoparticles demonstrate the ability to induce oxidative stress via lipid peroxidation, which decreases with the increasing temperature of preparation and for commercial ZnO was higher than for prepared ZnO nanoparticles.