Impact of water chemistry on the behavior and fate of copper nanoparticles☆
Graphical abstract
Introduction
Metallic nanoparticles (NPs) are increasingly applied in industrial and consumer products. The release of NPs into the aquatic environment can occur via different routes like industrial and municipal wastewater discharges (Boxall et al., 2007), runoff (Osmond and McCall, 2010) and leaching from consumer products (Hendren et al., 2011). Fueled by the inevitable release of NPs into the aqueous environment, concern about the adverse effects of these materials on aquatic biota has been growing. Among other particles, copper NPs (CuNPs) have been demonstrated to be highly toxic to a wide range of aquatic organisms (Hua et al., 2014, von Moos and Slaveykova, 2014, Song et al., 2015). It is therefore essential to comprehensively understand the behavior and fate of CuNPs in the aquatic environment across a range of water chemistry, in order to better interpret and predict their hazards to organisms.
After being emitted into aquatic environments, NPs are subject to undergo a series of environmental processes. These processes include dissolution and aggregation and subsequent sedimentation, which consequently affect their ultimate fate, bioavailability and hazards to organisms. Currently, it is widely known that the behavior and fate of NPs are highly dependent on the water chemistry. In particular, environmental parameters like pH, electrolytes (especially divalent cations) and natural organic matter (NOM) can strongly influence the ultimate fate of NPs in the environment. For example, pH can affect the aggregation and dissolution of metallic NPs by influencing the surface potential of the NPs (von der Kammer et al., 2010, Peng et al., 2017). The divalent cations Ca2+ and Mg2+ are able to efficiently compress the electrical double-layer of NPs and consequently enhance aggregation of NPs (Zhang et al., 2009, Van Hoecke et al., 2011). NOM has been widely reported to enhance the stability of metallic NPs via electrostatic and/or steric repulsion (Gao et al., 2012, Romanello and Fidalgo de Cortalezzi, 2013), and to alter their dissolution profiles through chelation and/or complexation of the metallic NPs (Majedi et al., 2014, Wang et al., 2015). Destabilizing effects of NOM on metallic NPs have also been reported, especially in the presence of divalent cations. This is due to the formation of bridges between NOM and cations (Stankus et al., 2011). Nevertheless, few studies have systematically investigated the issue of the extent in which environmental parameters present at environmental relevant concentrations affect the behavior and fate of NPs (Majedi et al., 2014, Son et al., 2015). This is amongst others due to a lack of full-factorial experiments to quantitatively investigate the individual and interactive effects of each environmental parameter on the behavior and fate of NPs in environment.
In this study, a factorial test design was applied to systematically investigate the behavior and fate of CuNPs in various aqueous matrices. The aim of this study is to evaluate the contribution and significance of each environmental parameter (i.e., pH, divalent cation content, and NOM concentration) and their interactions to the variations of behavior and fate of CuNPs across a range of water chemistry. This study is meaningful for improving our understanding and predictive potential of behavior and fate of NPs in freshwater environments.
Section snippets
Preparation of CuNP suspensions
CuNPs (spherical surface area 30–50 m2/g; purity 99.9%) were purchased from IoLiTec, with a nominal size of 25 nm. Stock suspensions of CuNPs (250 mg/L) were freshly prepared in MilliQ water after 30 min of bath-sonication to disperse the particles, prior to each experiment.
For the study design, CuNP suspensions under a range of water chemistry conditions were prepared. The divalent cation composition of the exposure media was modified by adding CaCl2·2H2O and MgSO4·7H2O in a fixed molar ratio
Total Cu suspending in the water column upon modification of water chemistry
The total amount of Cu suspended in the water column represents the level of Cu to which pelagic organisms are likely exposed (Adeleye et al., 2014). It includes dissolved Cu shedding from CuNPs which freely suspended in the water column and suspended particulate Cu and may also include the dissolved Cu complexed by DOC. The dynamics of the total amount of Cu remaining in the water column within 48 h of incubation upon various environmental conditions are presented in Fig. 1. Due to
Conclusions
This study systematically investigated the main and interactive effects of pH and concentrations of divalent cations and DOC in the exposure medium on the behavior and fate of CuNPs. The results demonstrated that the total amount of Cu remaining in the water column after 48 h of incubation was mostly influenced by divalent cation content, DOC concentration and the interaction of divalent cations and DOC. DOC concentration was the predominant factor in explaining the variation of dissolution of
Acknowledgements
Yinlong Xiao is financially supported by the Chinese Scholarship Council (CSC). M.G. Vijver was funded by VIDI 864.13.010. We would like to thank Marja Wouters for the preparations of the DOC suspensions and for measuring DOC concentrations. The research described in this work was performed within the framework of the “NANOFASE” project supported by the European Union's Horizon 2020 research and innovation programme under grant agreement number 642007.
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