Soil microbial response to photo-degraded C 60 fullerenes * Timothy D. Berry a , Andrea P. Clavijo b , Yingcan Zhao c , Chad T. Jafvert c , Ronald F. Turco b , Timothy R. Filley a, * a Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette 47907, IN, USA b Department of Agronomy, Purdue University, West Lafayette 47907, IN, USA c Lyles School of Civil Engineering and Division of Environmental and Ecological Engineering, Purdue University, West Lafayette 47907, IN, USA article info Article history: Received 29 April 2015 Received in revised form 15 December 2015 Accepted 15 December 2015 Available online xxx Handling Editor: B. Nowack Keywords: Carbon nanomaterials Soil Fullerenes Microbial degradation Emerging pollutants Photo decay abstract Recent studies indicate that while unfunctionalized carbon nanomaterials (CNMs) exhibit very low decomposition rates in soils, even minor surface functionalization (e.g., as a result of photochemical weathering) may accelerate microbial decay. We present results from a C 60 fullerene-soil incubation study designed to investigate the potential links between photochemical and microbial degradation of photo-irradiated C 60 . Irradiating aqueous 13 C-labeled C 60 with solar-wavelength light resulted in a complex mixture of intermediate products with decreased aromaticity. Although addition of irradiated C 60 to soil microcosms had little effect on net soil respiration, excess 13 C in the respired CO 2 demonstrates that photo-irradiating C 60 enhanced its degradation in soil, with ~0.78% of 60 day photo-irradiated C 60 mineralized. Community analysis by DGGE found that soil microbial community structure was altered and depended on the photo-treatment duration. These findings demonstrate how abiotic and biotic transformation processes can couple to influence degradation of CNMs in the natural environment. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Since the discovery of the first fullerenes in 1985, manufactured carbon nanomaterials (CNMs) have resulted in significant material advances in the fields of bioengineering and microelectronics (Kroto et al., 1985). These nanoscale materials, with a rigid frame- work composed entirely of condensed aromatic carbon rings, can be found in many geometric configurations ranging from planar graphene sheets to spherical buckminsterfullerene (C 60 fullerene) and can be chemically modified to generate a wide variety of car- bon nanomaterials (Nakamura and Isobe, 2003). The small size and high surface area of these nanomaterials makes them attractive components in a variety of applications ranging from drug delivery to inclusion in next-generation photovoltaic panels (Bakry et al., 2007; Mwaura et al., 2005; Thompson and Frechet, 2008). In recent years, CNMs have become increasingly prevalent in manufacturing due to their robust physical properties, variety of available chemical modifications, and the versatility that these modifications confer on electrical and biological interactions (Guldi and Asmus, 1997). Despite these advances in the synthesis and application of carbon nanomaterials, little is still known about the fate of CNMs that might enter the environment following acci- dental release, disposal in landfills, or accumulation in biosolids (Westerhoff et al., 2013). The same highly condensed structure that makes nanomaterials ideal as structural components makes them relatively resistant to biodegradation. As a result of this environ- mental recalcitrance, nanomaterials have the potential to accu- mulate in soils and sediments following environmental releases (Batley et al., 2013). Recent work has illustrated a wide range of interactions and reactions of CNMs in the environment that occur as a result of their physiochemical properties (e.g., particle size, surface functionali- zation, metal content, etc.). For example, the surface functionali- zation of CNMs has been found to play a particularly significant role in the stability of CNM homo-aggregates in suspension, and thus their solubility, as the aggregation of CNM into clusters results in flocculation (Batley et al., 2013; Smith et al., 2009). The formation of aggregates renders long-term suspensions of nanomaterials in aqueous environments unlikely unless they are stabilized by interaction with other environmental compounds such as dissolved * This paper has been recommended for acceptance by B. Nowack. * Corresponding author. E-mail address: filley@purdue.edu (T.R. Filley). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol http://dx.doi.org/10.1016/j.envpol.2015.12.025 0269-7491/© 2015 Elsevier Ltd. All rights reserved. Environmental Pollution 211 (2016) 338e345