Abstract
Abstract. The exceptional sorptive ability of carbon nanomaterials (CNMs) for hydrophobic organic contaminants (HOCs) is driven by their characteristically large reactive surface areas and highly hydrophobic nature. Given these properties, it is possible for CNMs to impact on the persistence, mobility and bioavailability of contaminants within soils, either favourably through sorption and sequestration, hence reducing their bioavailability, or unfavourably through increasing contaminant dispersal. This review considers the complex and dynamic nature of both soil and CNM physicochemical properties to determine their fate and behaviour, together with their interaction with contaminants and the soil microflora. It is argued that assessment of CNMs within soil should be conducted on a case-by-case basis and further work to assess the long-term stability and toxicity of sorbed contaminants, as well as the toxicity of CNMs themselves, is required before their sorptive abilities can be applied to remedy environmental issues.
Highlights
With the continued upscaling of carbon nanomaterial (CNM) production (Nowack and Bucheli, 2007) as well as the diverse array of consumer (Sharma and Ahuja, 2008), medical (Peretz and Regev, 2012) and industrial applications in which they are increasingly becoming incorporated, widespread environmental release of these physically and chemically unique macromolecules has become inevitable (Köhler et al, 2008)
Significant inhibitory effects on the degradation of 14C-2,4-DCP when pre-sorbed to carbon nanotubes (CNTs) occurred at a CNT concentration of 20 mg kg−1. These results show that CNT interactions with contaminants within the soil environment reduced the number of available sorption sites, with their sorptive ability further reduced by CNM aggregation and interaction with soil components such as humic substances, dissolved form (DOM), peptone and TA, which potentially coat CNTs modifying surface polarity, reducing surface area and reducing hydrophobic organic compounds (HOCs) sorption capacity as discussed in Sect. 4.1
While the toxicity of CNMs in soil is dependent on their bioaccessibility in addition to retention of reactivity, if agglomerates of CNMs are present with a reduced cytotoxic nature, it is conceivable that interstitial gaps in the agglomerate with mesopore dimensions will result in their increased suitability for the sorption of microorganisms (Agnihotri et al, 2005; Upadhyayula and Gadhamshetty, 2010)
Summary
With the continued upscaling of carbon nanomaterial (CNM) production (Nowack and Bucheli, 2007) as well as the diverse array of consumer (Sharma and Ahuja, 2008), medical (Peretz and Regev, 2012) and industrial applications in which they are increasingly becoming incorporated, widespread environmental release of these physically and chemically unique macromolecules has become inevitable (Köhler et al, 2008). Understanding the interactions between CNMs, soils and components therein is an urgent and essential aspect of any risk assessment process In their pristine form, CNMs are broadly characterised by their large reactive surface areas, highly hydrophobic characteristics and high degree of biogeochemical recalcitrance. They are known to be toxic to various soil microbiota (Riding et al, 2012a, b), and possess a high affinity for the sorption of a range of hydrophobic organic compounds (HOCs), such as polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) (Pan and Xing, 2010).
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