Assessing nanoparticle risk poses prodigious challenges

Development of New Health Risk Assessment of Nanoparticles: EPA Health Risk Assessment Revised

The concentration of nanoparticles in the ambient air can lead to induced toxicities; however, it appears that nanoparticles’ unique properties are completely omitted when assessing health risks. This paper aims to enhance the EPA health risk assessment by incorporating two new variables that consider the size of nanoparticles: the toxicity multiplier and the size multiplier. The former considers the qualitative aspect of the size of particles within a concentration, whilst the latter takes into account the effects associated with the number of particles of the specific i-th size distribution interval. To observe the impact of the new variables, a case study was performed. The studied element was cadmium, which was measured using ICP-MS to discover concentrations of size fractions, ranging from <15.1 to <9830 nm. Next, the cadmium concentration is assessed using both the current state-of-the-art method and the proposed method with adjustments. Based on the new approach, the final risk was 1.1 × 10−5, which was almost 24 times higher compared with the current method. The contribution of nanoparticles to the risk value grew from barely 6% to an alarming 88%. Therefore, the enhanced method can lead to more realistic results when assessing the health risks of nanoparticles.

No genome-wide DNA methylation changes found associated with medium-term reduced graphene oxide exposure in human lung epithelial cells

The presence of nanomaterials in our everyday life is ever increasing, and so too are concerns about the possible health consequences of exposure to them. While evidence of their biological activity is growing, there is still scant knowledge of the epigenetic mechanisms that could be at play in these processes. Moreover, the great variability in the chemical and physical structures of these compounds handicaps the study of their possible health risks. Here we have synthesized reduced graphene oxide (rGO) through the thermal exfoliation/reduction of graphite oxide, and characterized the resulting material. We have then made use of Illumina's MethylationEPIC arrays and bisulphite pyrosequencing to analyse the genome-wide and global DNA methylation dynamics associated with the medium-term exposure of human lung epithelial cells to rGO at concentrations of 1 and 10 µg/mL. The results show no genome-wide or global DNA methylation changes associated with either condition. Our observations thus suggest that medium-term rGO exposure does not have significant effects on the DNA methylation patterns of human lung epithelial cells.

Particle size distributions by transmission electron microscopy: an interlaboratory comparison case study

This paper reports an interlaboratory comparison that evaluated a protocol for measuring and analysing the particle size distribution of discrete, metallic, spheroidal nanoparticles using transmission electron microscopy (TEM). The study was focused on automated image capture and automated particle analysis. NIST RM8012 gold nanoparticles (30 nm nominal diameter) were measured for area-equivalent diameter distributions by eight laboratories. Statistical analysis was used to (1) assess the data quality without using size distribution reference models, (2) determine reference model parameters for different size distribution reference models and non-linear regression fitting methods and (3) assess the measurement uncertainty of a size distribution parameter by using its coefficient of variation. The interlaboratory area-equivalent diameter mean, 27.6 nm ± 2.4 nm (computed based on a normal distribution), was quite similar to the area-equivalent diameter, 27.6 nm, assigned to NIST RM8012. The lognormal reference model was the preferred choice for these particle size distributions as, for all laboratories, its parameters had lower relative standard errors (RSEs) than the other size distribution reference models tested (normal, Weibull and Rosin-Rammler-Bennett). The RSEs for the fitted standard deviations were two orders of magnitude higher than those for the fitted means, suggesting that most of the parameter estimate errors were associated with estimating the breadth of the distributions. The coefficients of variation for the interlaboratory statistics also confirmed the lognormal reference model as the preferred choice. From quasi-linear plots, the typical range for good fits between the model and cumulative number-based distributions was 1.9 fitted standard deviations less than the mean to 2.3 fitted standard deviations above the mean. Automated image capture, automated particle analysis and statistical evaluation of the data and fitting coefficients provide a framework for assessing nanoparticle size distributions using TEM for image acquisition.