Carbon black

Endpoint summary

Description of key information

Carbon black is substantially elemental carbon. It has no functional groups that could bring about solubility in water and organic solvents. Its vapour pressure is negligible. It cannot be further degraded by hydrolysis, light or by photodegradation in air or in surface water. These physico-chemical properties are reason why important parameters like water solubility, octanol/water partition coefficient, dissociation constant or adsorption/desorption which are relevant for environmental fate and distribution cannot be analytically measured.

As an inorganic substance with the chemical structure "C", carbon black cannot be used as a carbon source and will not be biodegraded by microorganisms. Biodegradation testing has therefore no meaning for inorganic substances, including inorganic nanomaterials.

Based on the physico-chemical properties it is expected that carbon black will not partition into air or water in significant amounts. Also, a potential for distribution via water or air, respectively, can be dismissed due to agglomeration and sedimentation of carbon black particles. The deposition in soil or sediments is therefore the most relevant compartment of fate of carbon black in the environment. The major source of carbon black emission to the environment from products will be as a component of tyre dust. Carbon black constitutes approximately 22% of the mass of a tyre, which equates to less than 30% of tyre dust (Hird et al. 2002). A tyre loses from 10% to 20% of its weight in use, with passenger car tyres showing a higher percentage loss than commercial vehicles. In the UK, where the average passenger car travelled approximately 20,000 km in 1998, an average abrasion of 172 kg of rubber per km of road is calculated, although rubber loss will be greater on motorways where the traffic volume is greater, and in breaking areas around junctions. Larger particles fall onto the road surface and are washed into the drainage system during wet weather (Hird et al. 2002;TRL Limited 2002). Both shredded tyres (Park et al. 1996) and carbon black (Risby et al. 1988) have been shown to significantly adsorb organic pollutants associated with fuel exhaust, thus potentially improving the quality of highway run-off. Aqueous desorption of adsorbed organics of various polarities from carbon black has been shown to be negligible (Risby et al. 1988). Thus, leaching of relatively non-polar hydrocarbons such as PAHs from carbon black in tyre dust is not expected to occur in the environment.

Carbon black release due to mechanical treatment was also studied with 11 acrylate coatings and 11 polypropylene composites; there was no correlation to the primary pigment particle size found (Göhler et al. 2013).

References:

Göhler D, Nogowski A, Fiala P, Stintz M (2013). Nanoparticle release from nanocomposites due to mechanical treatment at two stages onf the life-cycle. J. phys. conf. Ser. 429, 012045.

Hird AB, Griffiths PJ, Smith RA (2002) Tyre waste and resource management: a mass balance approach. Viridis Report VR2, ISSN 1478-0143.

Park JK, Kim JY, Edil TB (1996) Mitigation of organic compound movement in landfills by shredded tires. Water Environment Research 68(1):4-10.

Risby TH, Sehnert SS, Long J, Dhingra BS (1988) Model for the Release of Adsorbed Molecules from the surfaces of Airborne Particulate Matter Based on Liquid-Phase Desorption from Amorphous Carbon Blacks. Environmental Health Perspectives 77 77:141-140

TRL Limited (2002) The status of post-consumer tyres in the European Union. A summary report based on work by Dr. V. L. Schulman. Viridis report VR3. ISSN 1478-0143.

Additional information

Carbon and its components are widely distributed in nature. The estimation is that carbon forms 0.032% of the earth’s crust. Free carbon is found in big reservoirs like hard coal, an amorphous form of the element with other complex compounds of carbon-hydrogen-nitrogen. Pure crystalline carbon is found in the form of graphite and diamond. Carbon is an essential element in the components of all living organisms. The remains of live plants and animals form deposits of petroleum, asphalt and bitumen. The natural gas deposits contain compounds formed by carbon and hydrogen.