Abstract
The ever increasing industrial and consumer applications of titanium dioxide nanoparticles (TiO2 NPs) raise concern over the possible risk associated with their environmental exposure. Still, the knowledge regarding nanoparticle behavior in a freshwater ecosystem is lacking. The current study focuses on the toxicity of TiO2 NPs towards Ceriodaphnia dubia (a dominant daphnid isolated from the freshwater) under two different conditions; (1) light and dark photoperiod (16:8 h) and (2) continuous dark conditions, for a period of 48 h. An increase in toxicity was observed with an increase in the concentration, until a certain threshold level (under both photoperiod and dark conditions), and beyond which, reduction was noted. The decrease in toxicity would have resulted from the aggregation and settling of NPs, making them less bioavailable. The oxidative stress was one of the major contributors towards cytotoxicity under both photoperiod and dark conditions. The slow depuration of TiO2 NPs under the photoperiod conditions confirmed a higher NP bioaccumulation and thus a higher bioconcentration factor (BCF) compared to dark conditions. The transmission electron micrographs confirmed the bioaccumulation of NPs and damage of tissues in the gut lining.
Highlights
The multitude of usage of titanium dioxide nanoparticles (TiO2 NPs) in various consumer and industrial products has increased the frequency of its potential environmental release [1,2]
The studies of TiO2 NPs effect on aquatic organisms have mostly been done on water fleas (Daphnia magna, Daphnia pulex, Ceriodaphnia dubia etc.), and the 48 h mortality (EC50) was noted to be more than 100 mg L–1 [4,5,6]
The current study focuses on the cytotoxicity potential of TiO2 NPs towards a dominant freshwater crustacean, Ceriodaphnia dubia, in a lake water system
Summary
The multitude of usage of titanium dioxide nanoparticles (TiO2 NPs) in various consumer and industrial products has increased the frequency of its potential environmental release [1,2]. The direct evidence of environmental release of TiO2 NPs from the domestic products has been documented [3]. Most of the previous studies on risk assessment and environmental impacts of TiO2 NPs have focused on their biological impacts and cytotoxicity. The previous ecotoxicity studies on aquatic organisms have emphasized the photocatalytic behavior of TiO2 NPs in the presence of simulated sunlight [7] or UV irradiation conditions [8,9]. A recent study reported the absence of toxicity for anatase and rutile TiO2 NPs to Daphnia similis under both visible light and dark conditions even at 100 mg L–1 [6]. There are evidences showing free radical generation by TiO2 NPs under visible light and dark conditions [10,11], cytotoxicity under these circumstances needs to be evaluated
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