Colloidal stability of Fe3O4 magnetic nanoparticles differentially impacted by dissolved organic matter and cations in synthetic and naturally-occurred environmental waters

Authors: WANG, HAO - Chinese Research Academy Of Environmental Sciences; ZHAO, XIAOLI - Chinese Research Academy Of Environmental Sciences; HAN, XUEJIAO - Chinese Research Academy Of Environmental Sciences; ZHI, TANG - Chinese Research Academy Of Environmental Sciences; SONG, FANHAO - Chinese Research Academy Of Environmental Sciences; ZHANG, SHAOYANG - Chinese Research Academy Of Environmental Sciences; YUANRONG, ZHU - Chinese Research Academy Of Environmental Sciences; GUO, WENJING - Chinese Research Academy Of Environmental Sciences; He, Zhongqi; GUO, QINGWEI - Chinese Research Academy Of Environmental Sciences; WU, FENGCHANG - Chinese Research Academy Of Environmental Sciences; MENG, XIAONGUANG - Chinese Research Academy Of Environmental Sciences; GIESY, JOHN - Chinese Research Academy Of Environmental Sciences

Submitted to: Environmental Pollution
Publication Type: Research Notes
Publication Acceptance Date: 6/19/2018
Publication Date: 6/14/2018
Citation: Wang, H., Zhao, X., Han, X., Zhi, T., Song, F., Zhang, S., Yuanrong, Z., Guo, W., He, Z., Guo, Q., Wu, F., Meng, X., Giesy, J.P. 2018. Colloidal stability of Fe3O4 magnetic nanoparticles differentially impacted by dissolved organic matter and cations in synthetic and naturally-occurred environmental waters. Environmental Pollution. 241:912-921.
DOI: https://doi.org/10.1016/j.envpol.2018.06.029

Interpretive Summary: The effects of Fe-MNPs on aquatic organisms are dependent on their forms in surface waters. Thus, evaluating environmental risks posed by nanomaterials to aquatic systems requires understanding of effects of specific components of natural water on their stability and aggregation. Although some research has been done on effects of these factors on stability of nanoparticles under laboratory conditions, knowledge on the behaviors of nanoparticles in natural waters is limited. In this work, stability of Fe3O4 magnetic nanoparticles (Fe-MNPs) in eight natural waters and effects of fulvic and humic acids in combination with metal cations were investigated. Thus work found that aggregation of Fe-MNPs is significant due to the coexistence of multiple components of natural water, especially for waters containing more microbially-derived materials. However, waters with a relatively greater concentration of dissolved organic matter could also moderately stabilize the aggregation of Fe-MNPs, thus increasing the possibility of migration of Fe-MNPs in natural waters. Findings in this work are helpful for better understanding of the behaviors of nanomaterials in natural waters.

Technical Abstract: Suspension and aggregation of nanoparticles under various aqueous conditions are key factors in understanding their behaviors and toxicities in natural waters. However, the complexity and changeability of aqueous matrices make their behaviors less predictable. In this work, stability of Fe3O4 magnetic nanoparticles (Fe-MNPs) in eight natural waters and effects of fulvic and humic acids in combination with metal cations were investigated. Results indicated that stability of Fe-MNPs in natural waters is affected by type and concentration of DOM and metal cations, as well as pH of matrixes. Humic acid exhibited greater capacity for affecting stability of Fe-MNPs due to its larger nominal, molecule size and more carboxyl groups. Fourier transform infrared spectroscopy (FTIR) data indicated that bridging of Ca2+ and Mg2+ between adsorbed organic matter molecules was a key factor for directly promoting adsorption of DOM molecules on Fe-MNPs and causing aggregation of MNPs besides electrostatic screening effects. Due to competitive adsorption with the other components, hydrogen ions (pH) affected surface charges of MNPs and their dispersion in waters containing relatively less DOM and metal cations. In natural waters, the surface5electric property of Fe-MNPs was correlated with both DOM concentrations and cationic strengths (R2=0.848). With aging/degradation of organic molecules, resuspension of nanoparticles could occur. These processes might increase migration and biological availabilities of Fe-MNPs in natural waters, and long-term behaviors of the particles should be paid more attention.