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    Aqueous aggregation and deposition kinetics of fresh and carboxyl-modified nanoplastics in the presence of divalent heavy metals

    Year: 2022

    Journal: Water Res., Volume 222, AUG 15

    Authors: Zhu, Shishu; Mo, Yijun; Luo, Wendan; Xiao, Zihan; Jin, Chao; Qiu, Rongliang

    Organizations: National Key Research and Development Program of China [2019YFC1805300]; National Natural Science Foundation of China [42007334, 42007115]

    Keywords: Nanoplastics; Aggregation; Deposition; QCM-D; Heavy metals; Urban water

    The presence of heavy metals alters the colloidal stability and deposition of nanoplastics (NPs) in urban waters. Such processes are important to assess the mobility and fate of NPs and their associated heavy metals. Up to date, few studies have reported the impact of heavy metals on the colloidal behaviors of NPs and the involved mechanisms. In the study, time-resolved dynamic light scattering (DLS) and quartz crystal microbalance with dissipation (QCM-D) methods were used to assess the aggregation and deposition kinetics of polystyrene nanospheres with divalent heavy metals. For comparison, carboxyl-modified polystyrene nanospheres were used. Results reveal that heavy metals destabilized NPs more significantly than calcium ions. Spectroscopy and transmission electron microscopy analysis propose that heavy metals destabilized NPs via inner-sphere coordi-nation with carboxyl groups and cation-pi interactions, further leading to the formation of different dimensional aggregates. QCM-D results suggest that the deposition rate, irreversibility, and film compactness of NPs on silica surfaces first increased but further decreased as heavy metal concentration increased. Such deposition behaviors depended on the bridging effects between NPs and silica and aggregation-induced diffusion limitation. In that case, the destabilization and retention ability of heavy metals for NPs were related to their electronegativity and hydration shell thickness. In urban waters, the presence of natural organic matter (NOM) decreased the desta-bilization and retention ability of heavy metals, whereas heavy metals with environmentally relevant concen-trations still enhanced the aggregation and deposition of NPs compared with other environmental cations. This study highlights the impact of heavy metal property on the colloidal behaviors of NPs, thus deepening our un-derstanding of the mobility and fate of NPs associated with heavy metals in urban waters.
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