Graphite is a naturally occurring mineral form of the element carbon. It is an allotrope of carbon, meaning it has the same chemical composition as diamond and coal, but a different crystal structure.
Is graphite toxic?
In its natural mineral form, graphite is considered non-toxic and inert. However, graphite powders can present some health hazards when inhaled over prolonged periods of time or in large doses. The main concerns for human health are related to inhalation of fine graphite dust particles.
Lung effects
When inhaled, graphite particles can embed in lung tissue, leading to a benign condition called graphite pneumoconiosis. This causes a buildup of scar tissue in the lungs, which reduces lung capacity over time. Symptoms include coughing, shortness of breath, and decreased lung function. It usually takes many years of prolonged exposure for graphite pneumoconiosis to develop.
Studies on workers exposed to graphite dust in occupations like mining have shown increased rates of respiratory disease like bronchitis. However, graphite exposure was often accompanied by exposure to other mineral dusts as well, making it difficult to isolate the effects to graphite alone.
Cancer risk
There are conflicting reports on whether graphite dust exposure increases cancer risk. Some studies have linked high levels of graphite exposure over many years to increased lung cancer rates. However, graphite has not been officially classified as a carcinogen.
Part of the uncertainty stems from the fact that graphite is often contaminated with impurities like silica or sulfides which may influence its toxicity. Additionally, graphite miners were also exposed to radon gas, a known carcinogen. So it is hard to separate out the effects of pure graphite from other exposures in occupational studies.
Other effects
Fine graphite particles can be irritating to the eyes and skin, causing symptoms like itching and watering of the eyes. Ingesting graphite is not thought to be harmful, although high oral doses may cause temporary intestinal obstruction or distension.
Is graphite absorbed by the body?
In its natural mineral form, graphite is inert and insoluble in water and body fluids. This means it is not absorbed at significant levels by the gastrointestinal tract if ingested, the lungs if inhaled, or through the skin.
However, nanosized graphite particles engineered for commercial use can exhibit higher absorption depending on the particle size, coating, and route of exposure. Once absorbed, graphene nanoparticles can distribute to organs like the liver, spleen, kidneys, and lungs.
The health impacts of absorbed nanographite are not fully characterized yet. There are some concerns these tiny particles may cause oxidative stress or inflammation at high doses. But more research is needed.
Does graphite accumulate in the body?
Since natural graphite is not well absorbed, it does not tend to bioaccumulate in bodily tissues. Most inhaled graphite dust is either exhaled immediately or trapped in mucus and cleared from the lungs. Small amounts that do embed in lung tissue persist as inert deposits.
Nanosized graphite particles can accumulate in certain organs if they are not readily cleared from the body. This has been seen mainly in animal studies after intravenous injection of graphene. The liver and spleen appear to be the main sites of accumulation.
The buildup of high levels of nanographite could potentially lead to chronic toxicity effects. However, this has not been demonstrated in humans and there are no established safety limits for accumulation in the body.
Can graphite be toxic if ingested?
Graphite is considered non-toxic if ingested. In its bulk mineral form, graphite has low solubility in water and body fluids. It largely passes through the gastrointestinal tract unchanged without releasing toxic chemicals.
A review of clinical case reports found graphite ingestion does not typically cause any symptoms or adverse health effects. In most cases, the graphite was simply excreted in feces within a couple days.
In rare instances after swallowing large amounts of graphite, temporary intestinal complications like obstruction can occur. Surgery may be required in extreme cases. But overall graphite is less toxic than other forms of carbon like activated charcoal when ingested.
Risks of nanographite ingestion
Engineered nanosized graphite particles could theoretically be absorbed from the GI tract and cause toxicity at high doses. But there is little research on ingested nanographite in humans.
Given the low toxicity of other inert nanoparticulates like titanium dioxide, major adverse effects seem unlikely. But more studies are needed specifically looking at the oral toxicity of graphite nanoparticles.
Can graphite penetrate the skin?
Intact skin acts as an effective barrier preventing graphite absorption or penetration in most cases. Graphite is not thought to be dermally absorbed based on its physical and chemical properties.
However, high pressure injection of fine graphite suspensions under the skin or into tissues could allow penetration. Graphite foreign bodies deposited this way incite a typical inflammatory response followed by fibrosis.
Nanosized graphite particles in some skin cosmetic preparations may theoretically permeate superficial skin layers. But absorption likely remains very low.
Skin irritation
While not absorbed through normal skin, graphite dust or particles can be irritating with repeated or prolonged skin contact. Symptoms may include itching, redness, drying, and dermatitis.
Workers in occupations with graphite exposure report higher rates of skin effects like melanosis, keratosis and acneiform eruptions. However, skin protection measures are often lacking in these settings.
Does graphite cause kidney damage?
There is no good evidence that natural graphite exposure causes kidney damage or impairment of kidney function at typical environmental exposures in humans.
Some rodent studies using high intravenous doses of graphene sheets or carbon nanotubes showed accumulation in the kidneys and indicators of possible toxicity like inflammatory changes. But effects in humans after oral or inhalation routes are expected to be less pronounced.
People with high occupational graphite exposure did not show consistent signs of kidney injury. Any kidney effects were likely related to contaminants or co-exposures rather than graphite itself.
Is graphite safe during pregnancy?
There are no studies examining graphite exposure specifically during pregnancy. However, based on general toxicity studies, graphite is not thought to pose significant reproductive or developmental risks.
No accumulation or specific effects on the fetus or pregnancy outcomes have been reported in women exposed occupationally or environmentally to graphite dusts. Graphite particles are not readily transferred across the placenta.
High dose animal studies with nanosized graphite did not find strong evidence of embryo or fetal toxicity. More research is still needed. But current data suggests graphite is likely to have low reproductive toxicity.
Can you be allergic to graphite?
Graphite allergy is very rare, but skin sensitization is theoretically possible. A few cases of skin rashes and hives have been reported in workers repeatedly exposed to graphite powders.
However, patch testing with graphite samples in suspected sensitization cases has usually been negative. Many apparent “allergic” reactions may actually represent irritant contact dermatitis rather than true immunologic hypersensitivity.
Airborne graphite could potentially aggravate preexisting respiratory conditions like asthma as well. But in general, graphite is less allergenic than other forms of carbon.
Is graphite safe to use in medical implants?
Graphite has been used extensively for decades in medical devices and implants due to its stability, strength, and biocompatibility. These include uses like:
- Bone fracture fixation plates
- Dental root implants
- Prosthetic heart valves
- Mechanical heart pumps
When used as a bulk material, graphite elicits minimal immune system response in the body. Encapsulated graphite implants become surrounded by a fibrous tissue lining and integrate well with minimal toxicity.
The long history of safe graphite use in implants suggests it is generally considered biocompatible. However, quality controls are needed as contaminants could influence bioreactivity.
Nanoparticle toxicity concerns
Nanosized graphite particles may demonstrate different biological behavior and toxicity profiles. The higher chemical reactivity and mobility of nanoparticles could lead to inflammatory or oxidative stress effects at the implant site.
Criteria like nanoparticle size, shape and surface coating affect biocompatibility. More research is needed specifically on graphite nanoparticle implant safety and interactions with surrounding tissues.
Does graphite cause cognitive or neurological effects?
There is no evidence that inhaled, ingested or dermally absorbed graphite causes direct neurological or cognitive toxicity, based on human data.
Workers heavily exposed to fine graphite dusts did not display higher rates of cognitive impairment or neurobehavioral effects. Consumer exposures through products like pencils are even less concerning.
High doses of graphene particles injected directly into the brains of lab animals found signs neuroinflammation and oxidative stress. But real-world exposures are much lower and don’t provide direct brain access.
Does graphite affect fertility or sexual function?
There is no human or animal evidence suggesting graphite exposure affects fertility or sexual function in either males or females.
Studies have not found reduced fertility, sperm abnormalities, or increased miscarriage rates in workers exposed regularly to graphite dusts. Graphite does not accumulate appreciably in reproductive organs.
High doses of graphene sheets injected into lab animal testes showed temporary inflammation effects but did not impair fertility or sperm counts. Realistic exposures from environmental sources or products would be far lower.
Conclusion
In summary, natural graphite and synthesized graphite nanoparticles have low toxicity when inhaled or ingested at typical environmental or occupational levels. While high concentrations of graphite dust require precautions, graphite is considerably less dangerous than other forms of carbon and minerals.
When embedded in the body, graphite is biologically inert and does not cause significant immune system reactivity. This makes it suitable and safe for many medical uses. However, higher purity standards and more research on nanoparticle bioreactivity are still warranted.
While accidental or suicidal graphite poisoning can require emergency treatment, the material does not appear to be absorbed readily or cause lasting organ damage. Main symptoms are related to temporary intestinal obstruction. Skin and eye irritation can also occur with direct contact.
Overall, the health risks of natural graphite exposure appear relatively low based on extensive use history and current toxicology data. With responsible workplace safety practices and purity quality controls, graphite can be considered a non-toxic material for diverse commercial, industrial and medical applications.
