UC Irvine

Agricultural systems face challenges related to toxic heavy metal pollution, which increasingly leads to food insecurity and adverse impacts on human health. Traditional heavy metals remediation technologies are often not readily applicable on farms due to potential negative effects on agricultural crops. Based on a hypothesis that nanoparticles can be engineered to selectively interact with toxic heavy metals in polluted irrigation water sources and farm soils while not having any serious adverse effects on food crops, this dissertation focused on creating knowledge on the fundamentals of interactions between nanoscale zerovalent iron (NZVI) and metallic contaminants in water and farm soils. Modifications of NZVI were also synthesized to explore the possibilities of improving performance, which could decrease the amount of materials needed to achieve the same treatment goal. In Chapter 1, the use of engineered nanomaterials (ENMs) as tools for treatment and remediation was reviewed. The chapter also discusses the different pathways and mechanisms via which ENMs are used for different classes of target contaminants, including heavy metals. Chapter 2 examines the synergistic removal of copper (Cu2+) and phosphate (P) from industrial wastewater using pristine and sulfidated NZVI (SNZVI), which is aimed at repurposing this treated water for agricultural irrigation. This chapter established that the dissolved iron (Fe2+) from the reactions between the ENMs and Cu2+ serves as a reactant for P removal from water. This interconnecting role of Fe2+ drives the removal of both reactants based on Le Chatelier's principle. An artificial neural network (ANN) was used to model the co-removal processes and identify key treatment factors. The capacity of NZVI and SNZVI to immobilize arsenic (As) in an agricultural soil and prevent its bioavailability to lettuce (Lactuca sativa) was studied in Chapter 3. Different spectroscopic and spectrometric tools were employed to establish the mechanisms of interactions between the ENMs and arsenic in soil. That chapter also reveals that remobilization of previously immobilized As occurs in the presence of both NZVI and SNZVI. Chapter 4 details the role of silica-coating on the efficacy and safety of NZVI (to form NZVI@SiO2) for As immobilization in an agricultural soil. Silica-coating improved nanoparticle stability and provided additional sites for As immobilization. Details of As immobilization were revealed through sequential extraction processes and X-ray-based characterization of soils amended with the ENMs. Chapter 5 summarizes the whole dissertation and provides the scenarios where NZVI-based nanoparticles can be applied in the agricultural system. Overall, this dissertation contributes valuable mechanistic insights into using NZVI-based nanoparticles for water and agricultural soil treatment, addressing challenges posed by heavy metal/loid pollution. These insights are critical for tailoring NZVI modifications to meet specific remediation needs.