2022 Volume 32 Issue 3 Pages 64
Soil and water contamination with volatile organic compounds (VOCs) is one of global environmental problems not only in Japan but also in developing countries, many of which are located in semi-arid area. 1,4-Dioxane, one of the VOCs, is suspected as carcinogens and growing issue in difficult to remove from contaminated sites. Treatment of 1,4-dioxane by UV and ozone is at present an excellent technology; however, the treatment cost is still quite high. Phytoremediation of 1,4-dioxane is expected to be an inexpensive and effective method on widely sites in low concentration water containing of 1,4-dioxane. The objective of the study is to clarify contribution ratio of function concerning phytoremediation of three species of willow on 1,4-dioxane. This investigation studied phytoremediation of 1,4-dioxane removal efficiency and mechanism of willow, with three species of willow (Salix pet-susu (KKD), S. pseudolinearis (FXM), S. sachalinensis (SEN)).
Experimental Design and Method
In an experimental system using polypropylene 2 L bottles, three species of willow (KKD, FXM, SEN) were grown in Hoagland hydroponic solution contaminating 1,4-dioxane for 15 days, 3 cycles of 5 days per cycle. Two species of SEN and FXM were cultivated in summer 2021 and autumn 2020, KKD were in summer 2021 Six plants of each cultivar were grown separately in triplicate, with and without 13C labeling of 1,4-dioxane. Hydroponic solution was prepared to be 2 mg L+ of 1,4-dioxane, was exchanged every cycle, and the hydroponic solution was sampled before and after the exchange. Once per cycle, 1,4-dioxane volatilized by transpiration was adsorbed on activated carbon. The concentration of 1,4-dioxane in the hydroponic solution, the activated carbon eluate, and the plants was determined by headspace GC/MS, and the 13C content of the plants was determined by isotope ratio mass spectrometry.
Result and Discussion
The result in autumn season, the removal rate of 1,4-dioxane in 5 days was 12.2±8.0% for FXM and 14.0±1.5% for SEN. The functions that contributed to the removal by FXM were, in order, transpiration (52.5%), assimilation (20.4%), and accumulation (1.0%), and unknown (26.1%). Compared with the contribution of assimilation plus accumulation by poplar (6%) in the previous study, the contribution of FXM in this experiment was 3.4 times higher, suggesting the high assimilation capacity of 1,4-dioxane in willow. On the other hand, the contribution of FXM to assimilation may have been relatively higher due to the decrease from transpiration in autumn season. Further the results of KKD will be reported in the conference.
