Response of Soil Microorganisms to As-Produced and Functionalized Single-Wall Carbon Nanotubes (SWNTs) Zhonghua Tong, †,⊥ Marianne Bischoff, † Loring F. Nies, ‡ Phillip Myer, ∥ Bruce Applegate, §,∥ and Ronald F. Turco †, * † College of Agriculture − Laboratory for Soil Microbiology, ‡ School of Civil Engineering, § Department of Food Science, ∥ Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, United States ⊥ Department of Chemistry, University of Science & Technology of China, Hefei, Anhui 230026, China * S Supporting Information ABSTRACT: The use of single-wall carbon nanotubes (SWNTs) in manufacturing and biomedical applications is increasing at a rapid rate; however data on the effects of a potential environmental release of the materials remain sparse. In this study, soils with either low or high organic matter contents as well as pure cultures of E. coli are challenged with either raw as-produced SWNTs (AP-SWNTs) or SWNTs functionalized with either polyethyleneglycol (PEG-SWNTs) or m-polyaminobenzene sulfonic acid (PABS-SWNTs). To mimic chronic exposure, the soil systems were challenged weekly for six weeks; microbial activities and community structures for both the prokaryote and eukaryote community were evaluated. Results show that repeated applications of AP-SWNTs can affect microbial community structures and induce minor changes in soil metabolic activity in the low organic matter systems. Toxicity of the three types of SWNTs was also assessed in liquid cultures using a bioluminescent E. coli-O157:H7 strain. Although decreases in light were detected in all treated samples, low light recovery following glucose addition in AP-SWNTs treatment and light absorption property of SWNTs particles suggest that AP-SWNTs suppressed metabolic activity of the E. coli, whereas the two functionalized SWNTs are less toxic. The metals released from the raw forms of SWNTs would not play a role in the effects seen in soil or the pure culture. We suggest that sorption to soil organic matter plays a controlling role in the soil microbiological responses to these nanomaterials. ■ INTRODUCTION Since their isolation and characterization in 1991, 1 single-wall carbon nanotubes (SWNTs) have been subjected to hundreds of research studies addressing their intrinsic behavior and potential use. 2 SWNTs are composed of graphite sheets rolled into hollow cylinders with nanosized diameters and can be uncapped or capped using fullerenes. They are now used for purposes ranging from electronics to building materials. With their expanding role in manufacturing, some environmental exposure is likely raising concerns about their potential environmental risk. 3 Understanding the potential environmental consequences of environmental exposure of SWNTs is warranted as their toxicity has been reported. For example, SWNTs have been shown to induce dose-dependent lesions in the lungs of mice 4 and human cervical carcinoma HeLa cell apoptosis. 5 Roberts et al. showed that SWNTs solubilized with lysophophatidylcho- line could induce mortality in Daphnia magna. 6 SWNTs have also been shown to cause respiratory toxicity and some physiological changes in rainbow trout. 7 Antimicrobial activity of SWNTs has also been demonstrated and attributed to cell membrane damage following contact with the SWNTs. 8 Pristine SWNTs are minimally soluble in water and most organic solvents; the solubility of small diameter SWNTs is only 95 and 1 mg L −1 in 1,2-dichlorobenzene and toluene, respectfully. 9,10 Bundled SWNTs strongly resist dispersion in water and, if dispersed, tend to reaggregate or aggregate with macromolecules or deposit on surfaces. 10 To overcome this issue, most technical applications of SWNTs take advantage of the use of end-group and sidewall functionalization to improve dispersion. 11 Noncovalent solubilization can also be achieved by wrapping the SWNTs in an organic polymer. 12 Function- alized SWNTs (f-SWNTs) have been shown to be less cytotoxic, which improves their biocompatibility for potential pharmaceutical applications. 13,14 To date, few studies have Received: August 10, 2012 Revised: November 16, 2012 Accepted: November 19, 2012 Published: November 19, 2012 Article pubs.acs.org/est © 2012 American Chemical Society 13471 dx.doi.org/10.1021/es303251r | Environ. Sci. Technol. 2012, 46, 13471−13479