Oxidative and Toxicological Evolution of Engineered Nanoparticles with Atmospherically Relevant Coatings
- DOI
- Language of the publication
- English
- Date
- 2019-02-22
- Type
- Article
- Author(s)
- Liu, Qifan
- Liggio, John
- Breznan, Dalibor
- Thomson, Errol M.
- Kumarathasan, Premkumari
- Vincent, Renaud
- Li, Kun
- Li, Shao-Meng
- Publisher
- American Chemical Society
Abstract
The health impacts associated with engineered nanoparticles (ENPs) released into the atmosphere have not been adequately assessed. Such impacts could potentially arise from the toxicity associated with condensable atmospheric secondary organic material (SOM), or changes in the SOM composition induced by ENPs. Here, these possibilities are evaluated by investigating the oxidative and toxicological evolution of TiO2 and SiO2 nanoparticles which have been coated with SOM from the O3 or OH initiated oxidation of α-pinene. It was found that pristine SiO2 particles were significantly more cytotoxic compared to pristine TiO2 particles. TiO2 in the dark or under UV irradiation catalytically reacted with the SOM, increasing its O/C by up to 55% over photochemically inert SiO2 while having negligible effects on the overall cytotoxicity. Conversely, the cytotoxicity associated with SiO2 coated with SOM was markedly suppressed (by a factor of 9, at the highest exposure dose) with both increased SOM coating thickness and increased photochemical aging. These suppressing effects (organic coating and photo-oxidation of organics) were attributed to a physical hindrance of SiO2-cell interactions by the SOM and enhanced SOM viscosity and hydrophilicity with continued photo-oxidation, respectively. These findings highlight the importance of atmospheric processes in altering the cytotoxicity of ENPs.
Plain language summary
Health Canada is responsible for the assessment and management of health risks to Canadians associated with exposure to products and chemicals in the environment. Engineered nanoparticles (ENPs) have gained interest due to potential human health and terrestrial/aquatic ecosystem impacts. However, health impacts of atmospheric ENPs have not been adequately assessed. Secondary organic material (SOM) in the atmosphere can coat ENPs, or ENPs can change the chemical composition of SOM potentially altering toxicity characteristics. We have tested the impacts of titanium dioxide (TiO2) and silicon dioxide (SiO2) ENPs exposed to the atmosphere, on compositional changes of SOM coating on ENPs, and resulting cellular effects. The ENPs were coated with SOM of varying thickness formed by ozone/hydroxyl radical-initiated oxidation of alpha-pinene, a compound released by vegetation. SOM compositional changes were monitored for variable coating thickness and aging time (equivalent to 0.5–8.0 days in the atmosphere). Toxicity of SOM-coated nanoTiO2 and nanoSiO2 in mouse-derived macrophages was examined using assays that measure cell membrane damage, energy levels and metabolic activity. The results showed that nanoTiO2 reacted with the SOM, increasing the amount of oxygen in the SOM coating, compared to uncoated nanoSiO2. Also, based on these assays, these SOM-coated nanoTiO2 did not appear to affect cell health, suggesting that the SOM coating itself may be non-toxic. In contrast, the toxicity associated with SOM-coated nanoSiO2 decreased with increased SOM coating thickness and aging. These effects may have resulted from non-toxic SOM coating preventing nanoSiO2 from directly interacting with the cells or from enhanced SOM hydrophilicity (increased interaction with water molecules). These findings highlight the importance of atmospheric processes in altering the toxicity of ENPs, adding value to the risk assessment processes by Health Canada and Environment and Climate Change Canada on ENPs which may be released to the atmosphere.
Subject
- Health,
- Health and safety