Submitted to: Journal of Hazardous Materials
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/13/2013
Publication Date: 10/15/2013
Citation: Shrestha, B., Acosta Martinez, V., Cox, S., Li, S., Canas, J. 2013. An evaluation of the impact of multi-walled carbon nanotubes on soil microbial community structure and functional diversity. Journal of Hazardous Materials. 261:188-197. Interpretive Summary: The use of nanomaterials, including carbon nanotubes (CNTs), is increasing due to their unique and versatile physicochemical, mechanical, and electrical properties with diverse applications in superconductor materials, construction industry, optical devices, biomedical field, and agriculture. However, their impact on the environmental quality is still not well understood. A semi-arid soil was treated with multi-walled carbon nanotubes (MWCNTs) at four different concentrations (10, 100, 1000 and 10000 mg MWCNTs kg-1soil), and incubated with a control (soil only) for 90 d. We evaluated soil-basal respiration, microbial community structure and enzymatic activities involved in nutrient cycling over time. Our results indicated no long term effects of different MWNT concentrations up to 1000 mg MWNTs kg-1soil in soil respiration and enzymatic activities. Potential changes in soil microbial community structure (i.e., increases in fungal markers and Actinobacteria) were observed at 10000 MWNTs kg-1 soil without major changes in soil metabolic functioning. Other changes within bacterial populations suggest a possible shift in soil microbial community structure to more tolerant genera in the presence of extremely high MWNT concentrations.
Technical Abstract: Increasing application of carbon nanotubes (CNTs) triggers the need for an assessment of their effects on organisms in the environment. Soil microbial communities play a significant role in soil organic matter dynamics and nutrient cycling. This study evaluated the impacts of multi-walled carbon nanotubes (MWNT) on microbial community composition and functionality in a sandy loam soil over 90 d. Results indicated no effects of MWNT concentrations up to 1000 mg kg-1 on soil respiration, enzymatic activities, and microbial community composition. However, increases in fungal fatty acid methyl ester (FAME) markers were observed at the highest concentration (10,000 mg kg-1). In addition, pyrosequencing demonstrated an increased abundance of some genera at the highest concentration that are considered potential degraders of polycyclic aromatic hydrocarbons (PAHs), like Rhodococcus, Cellulomonas and Nocardioides (Actinobacteria) and Pseudomonas (Gammaproteobacteria). These results suggest a possible shift in soil microbial community structure to more tolerant genera in the presence of extremely high MWNT concentrations. Though extremely high concentrations of MWNTs are less likely to occur in the actual environment, it is important to assess if these changes persist and how they can affect the long term soil metabolic functioning in a worst case scenario.