Frequent exposure to graphene oxide is hazardous to the lungs

Background 

Graphene is chemically defined as a single-atom-thick layer of monocrystalline graphite, a two-dimensional sheet of sp2-bonded carbon atoms arranged in a hexagonal pattern.  

Following the first isolation and characterization of graphene,  

• research and production of “graphene-related” nanomaterials (one external dimension in the nanoscale) have expanded exponentially. 

• The total forecasted global market for graphene-based materials is tens of billions and hundreds of billions of dollars for large-area graphene and bulk or flake graphene, respectively. Applications are led by the field of electronics for large-area graphene and use in filtration by both the petroleum and gas industry and the water/wastewater treatment industry for bulk/flake graphene.  

• The global market is predicted to grow considerably in the next 10 years. The current and potential applications of graphene nanomaterials are numerous including, but not limited to, use in electronics, energy storage, lighting, filtration, aerospace engineering, sensors, structural engineering composites, and health. 

Study 

In a 2020 study for the EU's Graphene Flagship project, a team from the National Graphene Institute of the University of Manchester in the UK demonstrated that a single exposure to micrometer-sized graphene oxide caused a negative reaction in rodent lungs, with inflammation lasting in some places for as long as 90 days. Animals exposed to nanometer-sized sheets, on the other hand, were totally recovered 28 days after exposure. 

The' potential for inhalation toxicity of graphene oxide sheets is significantly influenced by their width, according to a mouse study from the Manchester team. The team proposes that when building safer two-dimensional materials for commercial uses, the results, which reveal DNA damage with repeated high-dose exposure, should be taken into consideration. 

Numerous commercial products comprising composites, dispersions, or spray coatings have already been developed as a result of graphene oxide's low cost of manufacture. Other prospective uses for graphene oxide include the deposition of films on substrates in flexible electronics, solar cells, and chemical sensors. In their research paper, the experts note that there are still issues with the substance's safety profile. Although several studies have examined the genotoxic potential of graphene oxide on lung cells in vitro, there aren't many in vivo lung investigations, and the main characteristics that might contribute to toxicity are still up for debate.    

Chronic exposure  

The Manchester researchers assessed whether chronic exposure to graphene oxide could result in genotoxicity in their most recent study, which was also partially sponsored by the Graphene Flagship project:  

Animals were given high doses of graphene oxide sheets once for a maximum of 28 days or several times for a maximum of 84 days. For both exposure sets, graphene oxide sheets of equivalent thickness and physicochemical properties were employed in the micrometer- and nanometer-sized (LGO) and USGO, respectively. A low dose of 3 micrograms reflects a realistic working exposure, whereas a high dose of 30 micrograms includes the adverse circumstance. 

In contrast to an earlier study's investigation of the entire lung, the more recent study used immunostaining to pinpoint specific areas of DNA damage. Although total tissue analysis is typically the standard method, the researchers assert that it tends to produce a distorted image and underestimate local detrimental effects since nanomaterials cluster together to accumulate in various lung sections. 

Overall, the results indicate that: - 

• while LGO sheets may have long-term genotoxic effects, rodent lungs can quickly recover from exposure to USGO sheets.  

• A single high dose of LGO sheets left the rats quickly recovering, but repeated exposure led to long-term DNA double strand breakage.  

• The researcher's hypothesis that two pathways contributing to the long-term DNA damage are oxidative stress and inflammation.   

According to the researchers, the study lays some foundations for a deeper comprehension of the major elements that reduce lung injury following exposure to graphene oxide sheets. They write in the journal Particle and Fibre Toxicology that the study also “emphasises the importance of their lateral dimensions, which will be a crucial consideration for the risk classification of these materials and towards designing safer two-dimensional materials for future commercial applications."   

Research on graphene and graphene oxide is being done for the European Union Observatory for Nanomaterials (Euon). The work package on environment and health for the Graphene Flagship will be completed in 2023.