The large-scale production and spread applications of carbon nanomaterials in the past few years have led to a very high proportion of carbon store in these materials worldwide, which may be imported into the carbon cycle. Carbon nanomaterials can enter living organisms, the atmosphere, soil, water and sediments, without being unchanged or degraded during their transfer. Here, we show that there is a scientific basis for researchers and policy-makers to be concerned about the potential impact of carbon nanomaterials on the carbon cycle and integrate them into the map of carbon cycle.

Carbon nanomaterials possess unique physical-chemical properties and have been applied in numerous areas [1–۹]. Significant commercial interest has stimulated an increase in production capacity of carbon nanomaterials, and demand is still continually increasing [10,11]. Given that the main component of carbon nanomaterials such as carbon nanotubes, graphene and fullerene is carbon, a high proportion of the Earth’s carbon has been moved into these materials. Until now, however, they have not been considered as a potentially important part of carbon cycle because they are new emerging materials. The specific issue that we are addressing is whether carbon nanomaterials will play a role in carbon cycle. Herein, we provide three pieces of scientific evidence that demonstrate their potential role in carbon cycle: The first issue is that the carbon amount in carbon nanomaterials will become very large as the production of carbon nanomaterials continuously increases. It has been reported thatthe estimated production capacity of carbon nanotubes in 2011 was >4.5 kiloton/year, which is about 10 times more than that in 2006 [3]. For graphene films and small graphene sheets, the annual production capacity in China was reported to be more than 110,000 m2 and 0.4 kiloton, respectively [5]. The estimated annual U.S. production of fullerenes was 0.002–۰٫۰۸۰ kiloton/year [7]. Adding up all types of carbon nanomaterials for decades at a global scale, the carbon amount stored in these materials would become very considerable. Mass production and wide applications of carbon nanomaterials give rise to the possibility that they find their way into the carbon cycle. Thus, we cannotignore the role of carbon possessed by carbon nanomaterials when exploring the carbon cycle (Fig. 1). The second piece of scientific evidence is that carbons derived from carbon nanomaterials can transfer in the environment and widely distribute in the world. They are able tomove via food chains or physical-chemical processes [12], increasing the complexity to investigate carbon-transfer routes. The carbon from carbon nanomaterials faces two fates: remain unchanged or decompose. Some microbes can utilize carbon nanomaterials as a carbon source [13,14], generating CO2 that can enter the atmosphere [15]. Although the degradation rate of carbon nanomaterials is often low [16], the carbon arising from this process is considerable due to the large volume of carbon nanomaterials being generated in the world. It is noteworthy that carbon nanomaterials can also interact with environmental substances, which can become an obstacle to quantifying themaccurately [12].Itisnot easy to track carbonmovement associated with carbon nanomaterials in the environment. Carbon transfer routes for carbon nanomaterials and how these integrate with the whole carbon cycle now need to be investigated. The third issue is that carbon nanomaterials have a direct influence on the carbon cycle because of the adverse effect they have on fungi and bacteria [17]. Thus, the environmental release of carbon nanomaterials will affect carbon transport and balance.