Background:A rich body of literature exists that has demonstrated adverse human health effects following exposure to ambient air particulate matter (PM), and there is strong support for an important role of ultrafine (nanosized) particles. At present, relatively few human health or epidemiology data exist for engineered nanomaterials (NMs) despite clear parallels in their physicochemical properties and biological actions in in vitro models.Objectives:NMs are available with a range of physicochemical characteristics, which allows a more systematic toxicological analysis. Therefore, the study of ultrafine particles (UFP, <100 nm in diameter) provides an opportunity to identify plausible health effects for NMs, and the study of NMs provides an opportunity to facilitate the understanding of the mechanism of toxicity of UFP.Methods:A workshop of experts systematically analyzed the available information and identified 19 key lessons that can facilitate knowledge exchange between these discipline areas.Discussion:Key lessons range from the availability of specific techniques and standard protocols for physicochemical characterization and toxicology assessment to understanding and defining dose and the molecular mechanisms of toxicity. This review identifies a number of key areas in which additional research prioritization would facilitate both research fields simultaneously.Conclusion:There is now an opportunity to apply knowledge from NM toxicology and use it to better inform PM health risk research and vice versa. https://doi.org/10.1289/EHP424

Aims: To assess hazards associated with exposure to dust in the London Underground railway and to provide an informed opinion on the risks to workers and the travelling public of exposure to tunnel dust. Methods: Concentrations of dust, as mass (PM 2.5 ) and particle number, were measured at different underground stations and in train cabs; its size and composition were analysed; likely maximal exposures of staff and passengers were estimated; and in vitro toxicological testing of sample dusts in comparison with other dusts was performed. Results: Concentrations on station platforms were 270-480 mg/m 3 PM 2.5 and 14 000-29 000 particles/ cm 3 . Cab concentrations over a shift averaged 130-200 mg/m 3 and 17 000-23 000 particles/cm 3 . The dust comprised by mass approximately 67% iron oxide, 1-2% quartz, and traces of other metals, the residue being volatile matter. The finest particles are drawn underground from the surface while the coarser dust is generated by interaction of brakes, wheels, and rails. Taking account of durations of exposure, drivers and station staff would have maximum exposures of about 200 mg/m 3 over eight hours; the occupational exposure standard for welding fume, as iron oxide, is 5 mg/m 3 over an eight hour shift. Toxicology showed the dust to have cytotoxic and inflammatory potential at high doses, consistent with its composition largely of iron oxide. Discussion: It is unjustifiable to compare PM 2.5 exposure underground with that on the surface, since the adverse effects of iron oxide and combustion generated particles differ. Concentrations of ultrafine particles are lower and of coarser (PM 2.5 ) particles higher underground than on the surface. The concentrations underground are well below allowable workplace concentrations for iron oxide and unlikely to represent a significant cumulative risk to the health of workers or commuters.

The toxicology of nanoparticles (NPs) is an area of intense investigation that would be greatly aided by improved understanding of the relationship between NP structure and inflammogenicity. To evaluate how their physicochemical parameters influence toxicity, we assembled a panel of 15 metal/metal oxide NPs and attempted to relate various physicochemical parameters, including zeta potential (ζP) and solubility, to lung inflammogenicity. The acute pulmonary inflammogenicity of the 15 NPs showed a significant correlation with one of two structural parameters-ζP under acid conditions for low-solubility NPs and solubility to toxic species for high-solubility NPs. ζP is the electrical potential created between the surface of a particle, with its associated ions, and the medium it exists in and provides information concerning the particle surface charge. We suggest that inside the phagolysosome under acid conditions, a high positive ζP may allow NPs to damage the integrity of the phagolysosomal membrane leading to inflammation. In the case of high-solubility NPs, inflammogenicity depends on the ions that are produced during dissolution of NP inside the acidic phagolysosomes; if the ions are toxic, then phagolysosomes will be destabilized and cause inflammation. These two parameters may have utility in preliminary assessment of the potential lung inflammation hazard of the large number of NPs that require testing.

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Carbon nanotubes (CNTs) possess many unique electronic and mechanical properties and are thus interesting for numerous novel industrial and biomedical applications. As the level of production and use of these materials increases, so too does the potential risk to human health. This study aims to investigate the feasibility and challenges associated with conducting a human health risk assessment for carbon nanotubes based on the open literature, utilising an approach similar to that of a classical regulatory risk assessment. Results indicate that the main risks for humans arise from chronic occupational inhalation, especially during activities involving high CNT release and uncontrolled exposure. It is not yet possible to draw definitive conclusions with regards the potential risk for long, straight multi-walled carbon nanotubes to pose a similar risk as asbestos by inducing mesothelioma. The genotoxic potential of CNTs is currently inconclusive and could be either primary or secondary. Possible systemic effects of CNTs would be either dependent on absorption and distribution of CNTs to sensitive organs or could be induced through the release of inflammatory mediators. In conclusion, gaps in the data set in relation to both exposure and hazard do not allow any definite conclusions suitable for regulatory decision-making. In order to enable a full human health risk assessment, future work should focus on the generation of reliable occupational, environmental and consumer exposure data. Data on toxicokinetics and studies investigating effects of chronic exposure under conditions relevant for human exposure should also be prioritised.