Even non-reactive particles like asbestos can cause a persistent inflammatory response eventually leading to cancer, chronic fatigue, malaise, etc. The ones that get the most attention these days are PM-2.5: tiny particles or droplets in the air that are two and one half microns or less in width, penetrate alveoli, and go straight into your blood stream.

More info: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4740125/

In about a decade or two brake dust pollution will be more recognized as a severe public health problem. It's not on the hype cycle yet. https://pubmed.ncbi.nlm.nih.gov/32593898/

Not just brake dust (which is probably solvable), but also rubber from tires.

But pure carbon is somewhat reactive, so maybe it could be cleaned by the body. Is it not?

Not sure, but there is definite collateral damage because it is biologically active.

From Fig 2. of https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7789336/

Mechanism of DNA methylation and histone modification alterations induced by nanomaterials and nanoparticles:

Exposure to NMs and NPs alters the functioning of chromatin-modifying proteins, e.g., DNA methylation and demethylation machinery, and histone-modifying enzymes, causing changes in the pattern of DNA methylation and histone modifications.

One of the most common effects of NMs and NPs is the induction of cellular stress, e.g., oxidative and endoplasmic reticulum stress, and metabolic disturbances, e.g., one-carbon metabolism and the citric acid cycle.

These events are causing DNA damage and repair response and metabolic alterations affecting the functioning of chromatin-modifying enzymes.

Any or all of these events may result in hypomethylation of DNA and altered histone modification patterns.

Additionally, exposure to NMs and NPs causes activation of the inflammatory response that, in turn, may cause DNA hypermethylation and histone modification changes

Benzene and similar flat aromatic carbon-based compounds are mutagenetic (cancer- and birth defect- causing) because they can slip between base pairs in DNA and disrupt replication.

I wonder whether graphene, itself a flat carbon compound, has the same affinity for DNA?

Molecular bond in benzene is little special. Maybe that's the source of mutagenic properties?

Carbon nanotubes are known to cause lung tumors.

Pure carbon really isn't something that a lot of organisms ever encounter.

Study on rats confirming this https://particleandfibretoxicology.biomedcentral.com/article...

You'd think, but in fact biochemistry is quite bad at disposing of pure carbon compounds. You can test this: stick a pencil lead into some compost for a week and pull it out.

I still have a piece of pencil lead stuck in my finger from 24 years ago, though it has gotten smaller. And I know someone with a piece more than twice that old.

Doesn't it contain a lot of clay?