The influence of multiwalled carbon nanotubes on polycyclic aromatic hydrocarbon (PAH) bioavailability and toxicity to soil microbial communities in alfalfa rhizosphere

Abstract

Carbon nanotubes (CNTs) may affect bioavailability and toxicity of organic contaminants due to their adsorption properties. Recent studies have observed the influence of multiwalled carbon nanotubes (MWNTs) on the fate of polycyclic aromatic hydrocarbons (PAHs) and other organic contaminants. Greenhouse studies (49d) were conducted with alfalfa plants in two different soil types. Four treatment conditions (0, 25, 50, or 100mg/kg MWNTs+100mg/kg PAHs mixture-pyrene and phenanthrene) were tested in order to determine their effects on soil microbial community composition and PAH residues. Microbial community structure in the two highest treatments (50mg/kg and 100mg/kg MWNTs) showed a dramatic shift in the presence of MWNTs in sandy loam soil (1% organic matter) in comparison to the control (0mg/kg MWNTs). Many microbial fatty acid methyl ester (FAMEs) markers (i15:0, 16:1ω5c, 10Me17:0, 10Me16:0) were missing in the control soil. However, there was a lower abundance of these FAMEs in the 25mg/kg MWNT treatment (except 10Me17:0) and a higher presence of these FAMEs in the 50mg/kg and 100mg/kg MWNT treatments compared to control. In contrast, microbial community composition was not influenced by the MWNT treatments in sandy clay loam soil (5.9% organic matter). However, pyrene degradation in sandy clay loam soil significantly increased by 21% in the highest MWNT treatment group (100mg/kg) and 9.34% in 50mg/kg MWNT treatment. Under the conditions tested in this study, MWNTs significantly impacted the soil microbial community distribution and PAH degradation and effects were dependent on soil types, specifically organic matter content.