Elsevier

Chemosphere

Volume 83, Issue 8, May 2011, Pages 1124-1132
Chemosphere

Cellular uptake and mutagenic potential of metal oxide nanoparticles in bacterial cells

https://doi.org/10.1016/j.chemosphere.2011.01.025Get rights and content

Abstract

Extensive production and consumption of nanomaterials such as ZnO and TiO2 has increased their release and disposal into the environment. The accumulation of nanoparticles (NPs) in ecosystem is likely to pose threat to non-specific targets such as bacteria. The present study explored the effect of ZnO and TiO2 NPs in a model bacterium, Salmonella typhimurium. The uptake of ZnO and TiO2 bare NPs in nano range without agglomeration was observed in S. typhimurium. TEM analysis demonstrated the internalization and uniform distribution of NPs inside the cells. Flow cytometry data also demonstrates that both ZnO and TiO2 NPs were significantly internalized in the S. typhimurium cells in a concentration dependent manner. A significant increase in uptake was observed in the S. typhimurium treated even with 8 and 80 ng mL−1 of ZnO and TiO2 NPs with S9 after 60 min, possibly the formation of micelles or protein coat facilitated entry of NPs. These NPs exhibited weak mutagenic potential in S. typhimurium strains TA98, TA1537 and Escherichia coli (WP2uvrA) of Ames test underscoring the possible carcinogenic potential similar to certain mutagenic chemicals. Our study reiterates the need for re-evaluating environmental toxicity of ZnO and TiO2 NPs presumably considered safe in environment.

Research highlights

► Mutagenic potential of ZnO and TiO2 NPs was evaluated in S. typhimurium. ► Internalization of NPs was observed in the cells by TEM and flow cytometry. ► Mutagenicity observed at 0.008 μg/plate in TA98 and TA1537 strains of Salmonella. ► Our data suggest possible carcinogenic potential of ZnO and TiO2 NPs.

Introduction

Rapid advancement in the synthesis of nanoparticles (NPs) has enabled the production of new materials for industrial, medical and consumer applications. The use of NPs in electronics, tyres, fuel cells, and filters among other applications is leading to their inadvertent release in surface and subsurface environment through landfills and other waste disposal methods (Oberdorster et al., 2005). Personal-care products such as cosmetics and sunscreens are a significant component of over 1000 nanotech based consumer products in market (Bradford et al., 2009). NPs released from various products through washing or disposal may reach the environment leading to adverse effects in organisms thereby affecting the eco-system health (Lemos et al., 2009). The distinct lack of information on human health and environmental impact of engineered nanomaterials has drawn increasing attention over the last few years (RSRAE, 2004). Recently, the pulmonary damage in industrial workers in China has fueled the debate over the safety precautions to be taken in the work environment (Gilbert, 2009, Song et al., 2009).

Metal and metal oxide NPs (e.g. nanoiron magnetite, titanium oxide) have been proposed for groundwater remediation (McCormick and Adriaens, 2004, Liu et al., 2005, Mattigod et al., 2005), water treatment (Ferguson et al., 2005, Lee et al., 2005) and removal of toxic contaminants from air streams (Esterkin et al., 2005). Zinc oxide (ZnO) and titanium (IV) dioxide (TiO2) NPs are the most common metal oxide NPs being used in consumer products such as cosmetics, sunscreen, etc. due to their unique optical properties (Kiss et al., 2008). Their widespread use could expose biological systems through inhalation, dermal contact, ingestion or absorption through the digestive tract and ultimately affect the human population directly or indirectly (Gurr et al., 2005, Warheit and Frame, 2006, Warheit et al., 2007, Pan et al., 2009). While information about the safety/toxicity of these NPs is still scanty, toxicity and mutagenicity of these compounds cannot be predicted reliably on the physical and chemical behavior of the bulk materials and solutes that are used to make the NPs. Studies have shown that size, shape, chemistry, crystallinity, surface property and agglomeration state appears to be a critical parameter for toxicity (Pan et al., 2007, Jiang et al., 2008).

It is well known that algae and higher plants are primary producers while bacteria act as decomposers and play an important role in maintaining the ecosystem. However, very few studies have been done to assess the mutagenic potential of the ZnO NPs (Sawai et al., 1998, Yoshida et al., 2009) and TiO2 NPs (Wang et al., 2007, Kang et al., 2008, Karlsson et al., 2008) in bacteria. Our earlier study with human epidermal cells has shown that ZnO nanoparticles possess DNA damaging potential (Sharma et al., 2009). In the present study, we have attempted to elucidate the uptake and mutagenic potential of ZnO and TiO2 NPs in bacteria.

Section snippets

Particle preparation

Zinc oxide nanopowder (ZnO; CAS No. 1314-13-2, purity >99%), titanium (IV) dioxide nanopowder (TiO2; CAS No. 1317-70-0, purity 99.7%, anatase) were purchased from Sigma Chemical Co. Ltd. (St. Louis, MO, USA). Nanoparticle stock suspension (80 μg mL−1) was prepared by suspending 0.8 mg of ZnO or TiO2 nanoparticles in 10 mL of 0.22 μm filtered Milli-Q water. The stock suspension was sonicated (Sonics Vibra cell, Sonics & Material Inc., New Town, CT, USA) for 10 min at 30 W.

Characterization

Dynamic light scattering (DLS)

Particle characterization

The mean hydrodynamic diameter of the ZnO and TiO2 NPs in Milli-Q as measured by dynamic light scattering (DLS) was 165 nm and 124 nm whereas zeta potential was −26 mV and −17.6 mV respectively (Table 1). The average size of ZnO and TiO2 observed by transmission electron microscopy (TEM) were 30 nm and 50 nm respectively (Table 1). The NPs suspensions were stable, mono-dispersed and have a lower poly dispersity index.

Detection of nanoparticles uptake through TEM

S. typhimurium treated with ZnO and TiO2 NPs showed a significant cellular uptake of

Discussion

The present study demonstrates for the first time, the uptake of ZnO and TiO2 NPs in S. typhimurium (TA98 and TA1537) strains as well as their weak mutagenic potential leading to frameshift mutations. TiO2 NPs showed mutagenicity, both in presence and absence of metabolic activation. However, ZnO NPs exhibited mutagenic potential in the presence of metabolic activation (S9) only. This could be correlated to an increase in the uptake of TiO2 NPs compared to that of ZnO NPs as evident from the

Conflict of interest

The authors do not have any conflicts of interest.

Acknowledgement

The authors wish to thank the Dr. K.C. Gupta, Director, Indian Institute of Toxicology Research, Lucknow for his keen interest in the study. This study was financially supported by the Department of Science and Technology, New Delhi, India [SR/S5/NM-01/2007]. The authors also gratefully acknowledge the funding from CSIR, New Delhi under its network project [NWP34, NWP35], Supra-institutional Project [SIP-08], the Department of Science and Technology-UK India Education and Research Initiative

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