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Evaluating Phytoremediation of Lead-Contaminated Soils in Loʻi Agriculture

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Title:Evaluating Phytoremediation of Lead-Contaminated Soils in Loʻi Agriculture
Authors:Ueunten, Ryan
Contributors:Crow, Susan (advisor)
Lincoln, Noa (other)
Litton, Creighton (instructor)
Natural Resources and Environmental Management (department)
Masters of Environmental Management (department)
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heavy metals
Indian mustard
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Date Issued:May 2021
Abstract:Traditional irrigated pondfields, known as loʻi agriculture, are one of the most iconic forms of Hawaiian food cultivation. The practice of loʻi agriculture not only produces the ancestral food kalo (Colocasia esculenta), but also establishes key cultural connections to land. Soil lead (Pb) contamination, however, poses a serious hazard to the many people perpetuating this important practice. While phytoremediation (i.e., growing plants to remove contaminants from the soil) is often implemented to address soil contamination issues, no study has yet to test if phytoremediation is effective in loʻi systems. Thus, the goals of this study were to: (i) investigate whether certain plants are more effective at uptaking bioavailable Pb in loʻi soils, (ii) determine which parts of each plant (roots or shoots) accumulate the most Pb, (iii) and extrapolate the amount of rounds of phytoremediation needed to reduce soil Pb concentrations to a safe level. Three different phytoremediation plantings: (1) the native wetland plant ʻaeʻae (Bacopa monnieri), (2) the widely studied plant Indian mustard (Brassica juncea), and (3) a control containing naturally established weedy species (Honohono grass - Commelina diffusa, Mexican primrose - Ludwigia octovalvis, and nutsedge - Cyperus rotundus) were grown in situ at a Pb contaminated loʻi site until full maturation. Following one round of phytoremediation, the ʻaeʻae roots contained significantly higher Pb concentrations than any other plant biomass component (Tukey HSD test, P < 0.001). Furthermore, ʻaeʻae plantings had a higher total Pb uptake than Indian mustard plantings (Tukey HSD test, P < 0.001). There were no significant differences, however, between pre- and post-planting soil Pb concentrations. Based on the estimated mass of Pb at the loʻi site, ~1,000-120,000 rounds of phytoremediation would be required to reduce soil Pb concentrations to a safe level (0-75 mg/kg Pb), translating to 100-18,000 years of remediation time. In conclusion, implementing any of the tested plantings alone would not be practical to reduce Pb contamination at the loʻi site. Future efforts will need to consider other plants or alternative methods such as a combination of soil removal and phytoremediation to address Pb contamination issues in loʻi agriculture.
Description:Also includes a 24 page Presentation.
Pages/Duration:33 pages
Rights Holder:Ueunten, Ryan
Appears in Collections: 2021 Capstone Projects

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