9. Carbon Allotropes in the Environment and Their Toxicity

As well as other contaminants (particular matter, heavy metal ions, toxic gases, etc.), carbon allotropes are severe contaminants in air, water, and soil. For example, for diesel vehicles, the black carbon (BC), organic carbon (OC), and other inorganic components of fine particulate matter (PM), as well as carbon monoxide (CO), nitrogen oxides (NO_x), sulfur dioxide (SO₂), ethane, acetylene, benzene, toluene, and other compounds, are typical contaminants under real-world driving conditions [1]. Among carbon allotropes in the environment, the most important carbons in the elemental form are black carbon (mainly), carbon nanotubes, graphene, and fullerenes in lesser quantities. Engineered carbon nanoparticles range from the well-established multi-ton production of carbon black (CB) and other carbon allotropes for applications in plastics and car tires to microgram quantities of fluorescent quantum dots used as markers in biological imaging. All of them possess distinct toxicity, depending on many factors (type of allotrope, particle size, form, structural defects, coating molecules, grade of functionalization, etc.). So, the nanotoxicology, as a scientific discipline, shall be quite different from occupational hygiene in approach and context. Understanding the toxicity of carbon nanomaterials and nano-enabled products is important for human and environmental health and safety as well as public acceptance.