Effect of multiwalled carbon nanotubes on uptake of pyrene by cucumber (Cucumis sativus L.): Mechanistic perspectives

Abstract

Three multiwalled carbon nanotubes (MWCNTs) with different outer diameters (<8 nm (M8), 20–30 nm (M30), >50 nm (M50)) were used to probe nanomaterial impacts on the bioaccumulation and translocation of pyrene in cucumber seedlings under hydroponic conditions during a 7 day exposure period. At nanotube exposures of 1, 10, 100, to 1000 mg/L, the root uptake of pyrene was significantly reduced by 54.32, 84.27, 95.45, and 99.21% for M8, respectively; by 40.15, 70.40, 94.11, and 99.23% for M30, respectively; and by 26.35, 55.71, 93.91, and 98.95% for M50, respectively. The extent of suppression decreased with increasing outer diameters. No overt phytotoxicity was observed upon MWCNTs and pyrene co-exposure. The observed effect of MWCNTs on pyrene bioaccumulation in cucumber seedlings likely resulted from analyte sorption to the nanotubes. The translocation factor of pyrene from plant root to shoot (a ratio of pyrene content in stem to that in root) was significantly increased from 0.009 ± 0.001 to 0.123 ± 0.036, 0.056 ± 0.055 and 0.051 ± 0.034 for M8, M30, and M50 as the exposure concentration of MWCNTs was increased from 0 to 1000 mg/L, respectively. This enhanced transport was due to analyte movement with internalized MWCNTs driven by transpiration within plant. The uptake of MWCNTs by the cucumber seedling roots was confirmed using the 13C-labeled M50. The findings from this study provide significant information on potential risks of MWCNTs upon application for pollution mitigation in agricultural soils.