|Shrestha, Babina - Texas Tech University|
|Anderson, Todd - Texas Tech University|
|Canas-carrell, Jaclyn - Texas Tech University|
Submitted to: Ecotoxicology and Environmental Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2015
Publication Date: N/A
Interpretive Summary: The use of nanomaterials, including multiwalled carbon nanotubes (MWNTs), is increasing in agriculture due to their unique physicochemical, mechanical, and electrical properties. However, the interaction of multiwalled carbon nanotubes (MWNTs) with soil, plants and contaminants such as polycyclic aromatic hydrocarbons (PAHs) is still not well understood. Greenhouse studies (49 days) were conducted where alfalfa plants where grown in two different soil types treated with a 100 mg/kg PAHs mixture (pyrene and phenanthrene) and four increasing rates of MWNTs (0, 25, 50, or 100 mg/kg MWNTs). At the end of the study, the soil microbial community composition and PAH residues were determined. The influence of MWNTs in PAH contaminated soil varied in the different soil types studied. Although no significant changes were observed in the PAH degradation in the soil with lower organic matter content (sandy loam), there was a significant difference in the microbial community composition between the control and other MWNT treatments. Some of the markers for G+ bacteria (i15:0), arbuscular mycorrhizal fungi (16:1'5c) and actinomycetes (10Me17:0, 10Me16:0) populations disappeared in the control soil due to toxic effects of highly bioavailable PAHs, but these populations were present in the soil under higher MWNT treatments. MWNTs appeared to minimize toxicity of highly bioavailable PAHs in the sandy loam soil evaluated to less tolerant microbial groups. In the soil with higher organic matter, the presence of MWNTs increased pyrene mineralization in the highest MWNTs treatment which might be related to increased bioavailability of PAHs in presence of MWNTs in this soil. This study indicates that MWNTs can influence microbial distribution and PAH mineralization, which will vary depending on soil type, specifically with varying organic matter content.
Technical 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 (49 d) were conducted with alfalfa plants in two different soil types. Four treatment conditions (0, 25, 50, or 100 mg/kg MWNTs + 100 mg/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 (50 mg/Kg and 100 mg/Kg MWNTs) showed a dramatic shift in the presence of MWNTs in sandy loam soil (1 % organic matter) in comparison to the control (0 mg/Kg MWNTs). Many microbial fatty acid methyl ester (FAMEs) markers (i15:0, 16:1'5c, 10 Me17:0, 10Me16:0) were missing in the control soil. However, there was a lower abundance of these FAMEs in the 25 mg/kg MWNT treatment (except 10Me 17:0) and a higher presence of these FAMEs in the 50 mg/kg and 100 mg/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 mineralization in sandy clay loam soil significantly increased by 21 % in the highest MWNT treatment group (100 mg/kg) and 11 % in 50 mg/kg MWNT treatment. Under the conditions tested in this study, MWNTs significantly impacted the soil microbial community distribution and PAH mineralization and effects were dependent on soil type, specifically organic matter content.