Graphene consists of a single layer of carbon atoms arranged in a hexagonal lattice, offering extraordinary properties like immense strength and high electrical conductivity. These qualities have positioned it as a key component in fields ranging from electronics to medicine. However, the increasing use of this nanomaterial has led to questions regarding its safety and its potential impact on human health. Determining the toxicity of graphene is not straightforward, as the answer depends heavily on the specific form of the material and how it interacts with the biological environment.
How Material Characteristics Influence Safety
The term “graphene” is not used to describe one material but a family of materials, and toxicity is highly dependent on the physical and chemical properties of a specific variant. This class of materials is often referred to as graphene-family nanomaterials (GFNs). Different forms of graphene, such as single-layer graphene, few-layer graphene (FLG), and graphene oxide (GO), exhibit different behaviors in the body.
One of the most significant factors is the number of layers, as truly two-dimensional materials interact differently with cells than thicker stacks. Graphene oxide (GO), a derivative with oxygen-containing groups, is more water-soluble than pristine graphene, which affects its dispersion and cellular uptake. The lateral size, or the width and length of the carbon sheet, also influences safety, as smaller pieces are generally easier for the body’s immune cells to process and clear. Furthermore, the addition of chemical groups, known as surface functionalization, can fundamentally change a material’s reactivity and biocompatibility. For instance, functionalizing GO with polyethylene glycol (PEG) has been shown to reduce inflammatory and toxic responses in the lungs.
Pathways for Human Exposure
Human contact with graphene is primarily a concern in occupational settings, where workers may be exposed during manufacturing or handling of dry powders. Inhalation is considered the most significant exposure route, as airborne nanoparticles can penetrate deep into the lungs. Studies have measured airborne GFN concentrations in production workplaces, highlighting the need for protective measures in these environments.
Dermal contact is another potential pathway, although intact skin generally acts as an effective barrier against external exposure. The risk from skin contact depends on the concentration and duration of exposure, with high concentrations over prolonged periods potentially causing minor membrane damage to skin cells. Incidental ingestion is also possible, such as from environmental runoff or food packaging applications. However, studies on oral administration suggest that the intestinal absorption of graphene-based materials is generally very limited.
Cellular and Organ System Responses
Toxicity in the body is often triggered by the material’s physicochemical properties interacting with biological systems. A primary mechanism of harm for many nanomaterials, including graphene, is the induction of oxidative stress. Graphene can interact with cellular components to generate reactive oxygen species (ROS), which are unstable molecules that can cause damage to cell structures and DNA.
The physical structure of graphene sheets can also lead to harm, as the sharp edges of the sheets may physically damage cell membranes through direct contact. This physical interaction is especially relevant for smaller, sharper flakes. The immune system reacts to the presence of graphene, which can trigger an inflammatory response. In the lungs, this inflammation has raised concerns about effects such as pulmonary fibrosis, similar to the responses seen with other fibrous materials.
Once in the bloodstream, GFNs are subject to biodistribution, and their ultimate fate depends on their properties. They tend to accumulate in organs that are part of the reticuloendothelial system, such as the liver and spleen. Smaller, functionalized materials are generally more efficiently cleared, often through renal or fecal excretion. However, few-layer graphene (FLG) instilled in the lungs has been shown to persist, with a significant amount remaining after several weeks.
Practical Safety Guidelines and Current Regulation
Given the potential for occupational exposure, mitigating risk involves strict adherence to safety protocols. Handling procedures focus on reducing the release of airborne particles, often by using wet handling techniques to prevent dust formation. Essential safety measures include local exhaust ventilation, closed systems, and the mandatory use of personal protective equipment (PPE), such as FFP3 respiratory masks and nitrile gloves.
While there are no specific laws solely dedicated to graphene toxicity, the material is regulated under existing frameworks for chemicals and nanomaterials. In Europe, regulatory bodies like the European Chemicals Agency (ECHA) and national agencies apply existing guidelines to ensure the safe development and use of nanomaterials. The focus is on risk management, which requires a thorough hazard assessment combined with an evaluation of real-world exposure levels.
For the general consumer, the risk from products containing graphene is considered minimal. In consumer goods, graphene is typically embedded within a composite material, which prevents it from being released as a free nanoparticle. This encapsulation significantly reduces the chance of human exposure compared to the direct handling of dry powders in industrial settings. Safety guidelines encourage a “safe-by-design” approach, where material properties are optimized to minimize any adverse biological impact from the outset.