Opportunistic gill infection is associated with TiO2 nanoparticle-induced mortality in zebrafish.

Chiao-Yi Huang,Ming-Der Lin,Wei-Sheng Yu,Shih-Che Hung,Geng-Chia Liu,Jen-Hsiang Chang,Hsin-Hou Chang,Chia-Liang Cheng,Yin-Jeh Tzeng,Wen-Ying Lin,Jen-Che Chang,Der-Shan Sun,Yogendra Kumar Mishra

doi:10.1371/journal.pone.0247859

Abstract

The large amounts of engineered titanium dioxide nanoparticles (TiO2NPs) that have been manufactured have inevitably been released into the ecosystem. Reports have suggested that TiO2 is a relatively inert material that has low toxicity to animals. However, as various types of NPs increasingly accumulate in the ocean, their effects on aquatic life-forms remain unclear. In this study, a zebrafish model was used to investigate TiO2NP-induced injury and mortality. We found that the treatment dosages of TiO2NP are positively associated with increased motility of zebrafish and the bacterial counts in the water. Notably, gill but not dorsal fin and caudal fin of the zebrafish displayed considerably increased bacterial load. Metagenomic analysis further revealed that gut microflora, such as phyla Proteobacteria, Bacteroidetes, and Actinobacteria, involving more than 95% of total bacteria counts in the NP-injured zebrafish gill samples. These results collectively suggest that opportunistic bacterial infections are associated with TiO2NP-induced mortality in zebrafish. Infections secondary to TiO2NP-induced injury could be a neglected factor determining the detrimental effects of TiO2NPs on wild fish.

Highlights

Titanium dioxide (TiO2) forms naturally as the well-known minerals rutile, anatase, and brookite phases
We hypothesized that the zebrafish in the groups treated with 5 mg/L TiO2NPs may have been subject to TiO2NP-induced injury prior to mortality, and the resulting release of blood or tissue fluids would subsequently cause optical-density changes in the water
To assess the physical condition of the fish, the motility (Fig 2A–2C, experiment setting; Fig 2D–2F) and body weight (Fig 2G) of the fish in the untreated groups were compared with those of the groups treated with 5 mg/L TiO2NPs prior to mortality

Summary

Introduction

Titanium dioxide (TiO2) forms naturally as the well-known minerals rutile, anatase, and brookite phases. Industrial production of TiO2 occurs at a large scale, and an estimated 165,050,000 metric tons of TiO2 were produced worldwide between 1916 and 2011 [1]. Products containing TiO2 nanoparticles (TiO2NPs), such as sunscreen, cosmetics, paints, and semiconductors, are widely manufactured in various industries [2, 3]. Upon ultraviolet (UV) irradiation, the photocatalytic properties of TiO2 in the form of anatase enable it to catalyze H2O to release reactive oxygen species [4,5,6], which can be used in disinfectants.

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Results

Conclusion