Adsorption of cesium by leaf cuticular fractions of Photinia serrulata
LI Yun-gui1,2, XIA Kun1,2, LIAO Yang1, YANG Hui-min1, WU Cai-xia1, QIN Xin-ying1
1. Department of Environmental Engineeving, School of Environment and Resource, Southwest University of Science and Technology, Mianyang 621010, China;
2. Low-cost Wastewater Treatment Technology International Sci-Tech Cooperation Base of Sichuan Province, Mianyang, 621010, China
For accurately predicting foliar uptake of the radionuclide, leaf cuticular fractions of Photinia serrulata were isolated by chemical methods including Soxhlet extraction, saponification, and acid hydrolysis, yielding bulk foliar cuticle (PHC1), the dewaxed cuticular fraction (PHC2), the nonsaponifiable fraction (PHC3), and cutan (PHC4). Adsorption behavior of cesium (Cs) onto leaf cuticular fractions of Photinia serrulata (PHC1, PHC2, PHC3, PHC4) was investigated and the relative sorption contribution of the cuticular component was accessed. The leaf cuticle sheet of Photinia serrulata consisted of waxes (16.63%), cutin (63.41%), polysaccharide (24.0%) and cutan (7.10%). The apparent adsorption equilibrium was reached within 30min, and the maximum adsorption capacity were 1.73 (PHC1), 1.92 (PHC2), 4.67 (PHC3), 0.58 (PHC4) mg/g, respectively. The theoretical maximum adsorption capacity of cuticular fractions was binary positive linearly correlated with their polarity and aromaticity index, and the polarity played a more noteworthy role in nuclide accumulation. Sugars and cutin acted as the main adsorption medium of Cs on leaf cuticle layer while epicuticular waxes and cutan show minor contribution on nuclide accumulation. The relative adsorption contribution of cuticular fraction was followed as sugar (51.45%) > cutin (38.73%) >> waxes (7.51%) > cutan (2.31%). The adsorption capacity of Cs on leaf cuticle of Photinia serrulata distinctively declined with the presence of sodium ion which was negatively correlated with the concentration of sodium. When the concentration of sodium was 100times higher than that of Cs, adsorption amount of bulk cuticle reduced to 6% in comparison with the control (adsorption of Cs without sodium), indicating that the coexistence of ion can considerably reduce the adsorption of nuclide on leaf cuticle.
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