Interactions between polybrominated diphenyl ethers (PBDEs) and TiO2 nanoparticle in artificial and natural waters

doi:10.1016/j.watres.2018.09.019

Water Research

Volume 146, 1 December 2018, Pages 98-108

https://doi.org/10.1016/j.watres.2018.09.019 Get rights and content

Highlights

•
PBDEs influenced the surface charge of TiO₂ NP even in the presence of NOM.
•
Agglomeration of TiO₂ NP was suppressed by PBDEs in artificial and natural waters.
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The aromatic ether groups of PBDEs facilitated their interactions with TiO₂ NP.
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BDE 47 exhibited a stronger influence than BDE 209 on the fate of TiO₂ NP.

Abstract

Polybrominated diphenyl ethers (PBDEs) are widely used as flame retardants in a variety of products, including textiles. PBDEs are thus exposed to the natural environment, including wastewater, waterbodies and sediments (at different phases of products' lifecycles), where they will interact with other pollutants. Studies on the interactions between organic pollutants and engineered nanoparticles (NPs) in natural waters are rare. In this study, we investigated the effects of two common PBDEs—BDE 47 and BDE 209—on the physicochemical properties and colloidal stability of TiO₂ NP in simple aqueous media and two natural waters (river water and wastewater). Upon the addition of BDE 47 and BDE 209, the zeta (ζ) potential of TiO₂ NP increased in magnitude in artificial waters and in natural waters (river water and wastewater), but the magnitude of influence on the NP's surface charge was specific to each natural water considered. Despite the presence of high content of natural organic matter in river water (DOC = 15.8 mg/L) and wastewater (DOC = 26.1 mg/L), low levels of the PBDEs (e.g. 0.5 mg/L) strongly impacted the surface charge and hydrodynamic diameter of TiO₂ NP. Both PBDE congeners suppressed the agglomeration of TiO₂ NP in the presence of monovalent and divalent cations, and in both natural waters. BDE 47 exhibited a stronger influence than BDE 209 on the surface charge, hydrodynamic diameter, and agglomeration of TiO₂ NP in both artificial and natural waters. As such, the interactions between TiO₂ NP and the PBDEs can increase the exposure of aquatic organisms to both pollutants. Infrared spectroscopy showed the importance of the aromatic ether groups in the adsorption of PBDEs to TiO₂ NP.

Introduction

Nanoscale titanium dioxide (TiO₂) is one of the most heavily produced and used engineered nanoparticles (NPs) (Keller et al., 2013). It is often included as a pigment or as the active ingredient in consumer products such as foods and snacks, personal care products, pharmaceuticals, paints, and coatings; and has industrial applications as a catalyst, among others (Chen et al., 2015; Gondikas et al., 2014; Hoffmann et al., 1995). More than 80,000 tons of TiO₂ NP was produced globally in 2010, and a considerable fraction of the TiO₂ NP produced annually ends up in natural aquatic systems (Kaegi et al., 2008; Keller and Lazareva, 2014). Keller and Lazareva (2014) estimated that the concentration of TiO₂ NP in wastewater treatment plants is 5–20 μg/L; and is expected to increase over time with continued increase in the use of the NP (Song et al., 2017). Negative impacts of TiO₂ NP to micro- and macro-organisms and their biochemical processes have been demonstrated over the years (e.g. Bettini et al., 2017; Priester et al., 2014), which underlines the need to thoroughly assess the risk of this widely used NP. Understanding of the fate of TiO₂ NP in aquatic systems is necessary for a reliable environmental risk assessment of the particles in natural waters.

Several studies have investigated the behavior of pristine TiO₂ NP in aqueous systems and the geochemical factors controlling its behavior, such as electrolyte concentration and valence (Adeleye and Keller, 2016; Domingos et al., 2009; Lin et al., 2017; French et al., 2009; Guzman et al., 2006), media pH (Adeleye and Keller, 2016; Domingos et al., 2009), and natural organic macromolecules (such as fluvic acid and humic acid (Domingos et al., 2009), and extracellular polymeric substances (EPS) (Adeleye and Keller, 2016; Lin et al., 2016, 2017)). Keller and coworkers showed that TiO₂ NP will be completely unstable in natural waters with high ionic strength (e.g. seawater) but may be stable in waters with low salt content and high amount of natural organic matter (NOM) (Keller et al., 2010). In natural waters, the surface of TiO₂ NP will be coated by NOM, including EPS, which can improve the colloidal stability of the NP (Adeleye and Keller, 2016; Domingos et al., 2009; Lin et al., 2016).

Aside from naturally occurring organic compounds (such as NOM), natural waters also contain synthetic organic compounds resulting from direct or indirect anthropogenic pollution. Several studies have shown that NPs can adsorb organic pollutants from water (Vittadini et al., 2000). However, to date few studies have addressed the implications of interactions between organic pollutants and NPs on the environmental fate of NPs. In this study, we chose polybrominated diphenyl ethers (PBDEs) as representative organic pollutants and investigated their influence on the fate of a commercially-sourced TiO₂ NP.

PBDEs have been widely used as flame retardants in paints, plastics, textiles, electronic appliances, and other consumer products (Zhu and Hites, 2004). PBDEs are thus released to the natural environment at different phases of the lifecycle of these products (Branchi et al., 2003; Hale et al., 2003). Although the use of PBDEs has been restricted in several developed countries, these persistent pollutants are still found in products manufactured before the phase-out completion in these countries, and in products made in other parts of the world where the use of PBDEs is unrestricted. PBDEs have been detected in surface waters (including wastewaters, which may have concentrations up to 1000 ng/L) (Peng et al., 2009; U. S. EPA, 2010; Zhang et al., 2009), the atmosphere (Moon et al., 2007), sediments (U. S. EPA, 2010), and humans (Covaci et al., 2008).

We hypothesized that PBDEs will adsorb and concentrate onto the surface of TiO₂ NP in surface waters due to the hydrophobicity of PBDEs and the high surface area of the NP. The objective of this study was to investigate the effect of PBDEs on the physicochemical properties and colloidal stability of TiO₂ NP in both artificial and natural waters. Two widely used congeners of PBDEs, BDE 47 and BDE 209, were selected for this study.

Section snippets

Materials

The TiO₂ NP used in this study has a particle size of 20–50 nm (Fig. 1a), and was purchased from Shanghai Macklin Biochemical Co. (Shanghai, China). The NP is a mixture of anatase (64.2%) and rutile (35.8%), as confirmed via X-ray diffraction analysis (Fig. 1b). Fourier transform infrared (FTIR) spectroscopy (Bruker TENSOR 27, Bruker Optics Inc., Germany) showed a broad intense absorption band in the range of 400–900 cm⁻¹, which is associated with the vibrations of the Ti-O and Ti-O-Ti bonds (

Effects of PBDEs on the surface charge of TiO₂ NP

The ζ potential of TiO₂ (10 mg/L NP dispersion) at pH 7 was −13.3 mV. The isoelectric point of TiO₂ NP that contains anatase and rutile is ∼ pH 5–6 (Jallouli et al., 2014; Zhou et al., 2013), thus, TiO₂ NP are slightly negatively charged at pH 7. Upon the addition of BDE 47 and BDE 209, the ζ potential of TiO₂ NP increased in magnitude (became more negative) as shown in Fig. 2a. More importantly, the ζ potential of TiO₂ NP further increased in magnitude with higher concentrations of the PBDEs.

Conclusions

PBDEs are hydrophobic and are thus found dissolved in natural waters at low concentrations. However, TiO₂ NP has a very high surface area, and can adsorb hydrophobic compounds from the aqueous phase. The adsorption of PBDEs may lead to an accumulation of the organic compounds on the surface of TiO₂ NP when released into natural waters (e.g. from sunscreen). The concentration of PBDEs in natural waters in much lower than some of the concentrations considered in this study. We hypothesized that

Acknowledgments

This research was supported by the National Basic Research Program of China (Grant 2015CB459000), the National Natural Science Foundation of China (Project No. 21677078), 111 program, Ministry of Education, China (Grants T2017002).

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¹: Current address: Department of Civil and Environmental Engineering, University of California Irvine, Irvine, CA 92697, United States.

View full text

Interactions between polybrominated diphenyl ethers (PBDEs) and TiO2 nanoparticle in artificial and natural waters

Highlights

Abstract

Introduction

Section snippets

Materials

Effects of PBDEs on the surface charge of TiO2 NP

Conclusions

Acknowledgments

Neurotoxicology (Little Rock)

J. Colloid Interface Sci.

Chemosphere

J. Hazard Mater.

Environ. Int.

Environ. Pollut.

Nanoimpact

Environ. Pollut.

Water Res.

Chemosphere

Environ. Int.

J. Hazard Mater.

J. Mol. Catal. Chem.

Adv. Colloid Interface Sci.

Environ. Pollut.

Environ. Pollut.

Long-term colloidal stability and metal leaching of single wall carbon nanotubes: effect of temperature and extracellular polymeric substances

Water Res.

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Environ. Sci. Technol.

Interactions between algal extracellular polymeric substances and commercial TiO2 NPs in aqueous media

Environ. Sci. Technol.

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Interactions between polybrominated diphenyl ethers (PBDEs) and TiO₂ nanoparticle in artificial and natural waters

Effects of PBDEs on the surface charge of TiO₂ NP

Interactions between algal extracellular polymeric substances and commercial TiO₂ NPs in aqueous media

Food-grade TiO₂ impairs intestinal and systemic immune homeostasis, initiates preneoplastic lesions and promotes aberrant crypt development in the rat colon

Colloidal properties of aqueous fullerenes: isoelectric points and agglomeration kinetics of C₆₀ and C₆₀ derivatives

Agglomeration and deposition kinetics of fullerene (C₆₀) NPs