Carbon black is not black carbon

We were most interested to read the recent article entitled ‘Carbon black-benzo(a)pyrene complex-induced apoptosis and autophagy blockage in rat alveolar macrophages’ (Meng et al. 2020). We would like to point out an important error in the article, in which the authors incorrectly state that carbon black is present in fumes formed by cooking foods and the burning of biomass and fossil fuels. The authors lead their abstract with the following incorrect statement: ‘Cooking of foods and the burning of biomass and fossil fuels in stoves are the main sources of cooking fumes, with carbon black and polycyclic aromatic hydrocarbons as main components.’ Contrary to the authors’ assertions, carbon black (CAS 1333-86-4) is not formed from cooking, but instead is a well-defined chemical substance that is intentionally manufactured on an industrial scale. It is formed by the pyrolysis of hydrocarbon feedstocks at high temperatures under strictly controlled process conditions. In the enclosed furnace black process of manufacturing carbon black (which is the major manufacturing process), preheated feedstock (typically decant oil from gasoline production), preheated air, and gas enter a closed reactor in which partial combustion at 1400–1800 C takes place. The carbon-rich product is quenched with water and passed through heat exchangers that preheat the combustion air. Altering the reactor temperatures and/or residence times produces the different grades of carbon black (Wang et al. 2003; McCunney et al. 2012). In our view, Meng et al. (2020) are mistaking carbon black with black carbon – also referred to as soot – which by definition, is an undesired carbonaceous byproduct of incomplete combustion of fossil fuels and biomass. Anthropogenic sources of black carbon or soot include residential combustion sources, such as oil furnaces, fireplaces, and woodstoves in developed countries, and simple cookstoves and open fires in developing countries. While carbon black consists almost exclusively of pure elemental carbon (>97%), black carbon or soot is a heterogeneous material consisting of less than 60% elemental carbon, a large portion of inorganic impurities (ash and metals) and a range of organic carbon species (Watson and Valberg 2001; Long, Nascarella, and Valberg 2013). Therefore, it is misleading to state that the toxicology studies conducted using industrially-produced carbon black are in any way reflective of the potential toxicity of cooking fumes.