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. © 2013 Dalai et al.

Chandra Sekaran N

Centre for Nanobiotechnology

Vellore Campus

Amitava Mukherjee

Dalai S

Pakrashi S

Fulltext

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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PLoS ONE

Owing to the increase in the usage of titanium dioxide nanoparticles (TiO2 NPs), their release into the aquatic environment is inevitable. In the aquatic ecosystem, TiO2 NPs can bio-magnify at various trophic levels in the food chain through dietary exposure. In the current study, the trophic transfer potential of two crystalline phases of TiO2 anatase and rutile nanoparticles (individual as well as a binary mixture) has been evaluated in the lake water matrix using algae–daphnia system. Chlorella sp. and Ceriodaphnia dubia were used as test organisms to represent the algae–daphnia food chain of the freshwater ecosystem. Other than crystallinity, the effect of irradiation (visible and UV-A) was also investigated at the test concentrations, 75, 300, and 1200 μM. TiO2 NPs treated algal diet produced significant mortality only at the test concentrations, 300 and 1200 μM. The type of irradiation and crystallinity doesn't have any impact on the mortality of daphnids through the dietary exposure of TiO2 NPs. Comparing the mixture with individual NPs, binary mixture induced less mortality on C. dubia which signifies the antagonistic effect of NPs when they coexist. Statistical modeling confirmed the antagonistic effect of the binary mixture on C. dubia. As individual NPs, anatase and rutile forms showed a maximum Ti accumulation under UV-A and visible irradiation, respectively. BMF of TiO2 NPs has been in validation with the bioaccumulation noted in C. dubia. Individual NPs (75 μM) showed higher BMF value of ∼23 under both UV-A (anatase) and visible (rutile) irradiation. Individual NPs showing higher BMF confirmed their trophic transfer potential in the aquatic food chain, primarily through the diet. In contrast, the binary mixture obtained a higher BMF of 1.9 and 0.79 at 75 and 300 μM under visible and UV-A irradiation, respectively. The plausible reason behind this decrement was the antagonistic effect of the mixture which significantly reduced their Ti bioaccumulation on C. dubia. © 2018 Elsevier B.V.

Aquatic Toxicology

Trophic transfer potential of two different crystalline phases of TiO2 NPs from Chlorella sp. to Ceriodaphnia dubia

Metal nanoparticles production rate and its applications have raised concerns about their release and toxicity to the aquatic and terrestrial organisms. The primary size of Copper Oxide nanoparticles (CuO NP's) was found to be 114 ± 36 nm using Scanning Electron Microscopy (SEM) and a significant increase in the hydrodynamic diameter of CuO NP was seen within 1 h of interaction. The median lethal concentration (LC50) values obtained from the acute toxicity studies on different life stages of Artemia salina was found to be 61.4, 35, 12.2 and 175.2 mg/L for 1d, 2d, 7d old and adult, respectively. The toxicity associated changes in biochemical markers such as Catalase, Reduced glutathione and Glutathione-S-Transferase were evident. The accumulation of Cu nanoparticles into the gut of Artemia salina was the major reason for toxicity. This study demonstrate the toxicity of CuO NPs to Artemia salina, and the obtained results necessitate the detailed investigation on the possible eco-toxicological implication of these nanomaterials. © 2017 Elsevier B.V.

Environmental Toxicology and Pharmacology

Toxicity and accumulation of Copper oxide (CuO) nanoparticles in different life stages of Artemia salina

Increasing usage of engineered nanoparticles, especially Titanium dioxide (TiO2) in various commercial products has necessitated their toxicity evaluation and risk assessment, especially in the aquatic ecosystem. In the present study, a comprehensive toxicity assessment of anatase and rutile NPs (individual as well as a binary mixture) has been carried out in a freshwater matrix on Ceriodaphnia dubia under different irradiation conditions viz., visible and UV-A. Anatase and rutile NPs produced an LC50 of about 37.04 and 48 mg/L, respectively, under visible irradiation. However, lesser LC50 values of about 22.56 (anatase) and 23.76 (rutile) mg/L were noted under UV-A irradiation. A toxic unit (TU) approach was followed to determine the concentrations of binary mixtures of anatase and rutile. The binary mixture resulted in an antagonistic and additive effect under visible and UV-A irradiation, respectively. Among the two different modeling approaches used in the study, Marking-Dawson model was noted to be a more appropriate model than Abbott model for the toxicity evaluation of binary mixtures. The agglomeration of NPs played a significant role in the induction of antagonistic and additive effects by the mixture based on the irradiation applied. TEM and zeta potential analysis confirmed the surface interactions between anatase and rutile NPs in the mixture. Maximum uptake was noticed at 0.25 total TU of the binary mixture under visible irradiation and 1 TU of anatase NPs for UV-A irradiation. Individual NPs showed highest uptake under UV-A than visible irradiation. In contrast, binary mixture showed a difference in the uptake pattern based on the type of irradiation exposed. © 2016 Elsevier B.V.

Individual and binary toxicity of anatase and rutile nanoparticles towards Ceriodaphnia dubia

This study assesses the temporal changes in the physico-chemical behaviour of titanium dioxide nanoparticles (anatase and rutile phase) for a period of 120 h at environmentally relevant concentration of 1,000 µg/L, and the consequent impact on the microalgae population in a fresh water microcosm. The mean hydrodynamic size analysis in the medium revealed the differences in the aggregation behaviour of the two crystalline types of particles within first 12 h exposure before they had reached the micron size range. While the short term exposure (120 h) showed an immediate effect on the resident microalgae in the microcosm with respect to control, there were no significant differences in ecotoxicity effects of rutile and anatase phases of titania. The long term (90 days) exposure demonstrated a gradual recovery of the resident algal population. Summarizing the observations, the nanosized particles at low concentration may not retain the toxic potential for longer exposure time in a microcosm presumably owing to the complexity prevalent in the natural systems. © 2014, The National Academy of Sciences, India.

Proceedings of the National Academy of Sciences, India Section B: Biological Sciences

A Temporal Study on the Effects of TiO2 Nanoparticles in a Fresh Water Microcosm

The extensive environmental exposure of engineered metal oxide nanoparticles (NPs) may result in their bioaccumulation in aquatic organisms leading to their biotransfer in a food chain through various routes in a freshwater ecosystem. The present study focuses on the possible modes of TiO2 NP trophic transfer to Ceriodaphnia dubia, in presence and/absence of its diet, Scenedesmus obliquus (primary producer). The acute exposure studies (48h) were designed to have daphnids exposed to (i) the free NPs, (ii) both the free and the algae-borne NPs; and (iii) only the algae-borne NPs in separate tests to understand the possible routes of NP transfer. The dietary uptake of TiO2 NPs (algae-borne) was found to be the primary route for NP biotransfer with ~70% of total NP uptake. Interestingly, in a separate study it was noticed that the NPs coated with algal exudates were easily taken up by daphnids as compared to pristine NPs of same concentrations, leading to their higher bioaccumulation. A chronic toxicity study, where daphnids were exposed to both free and algae-borne NPs for 21 days was undertaken to comprehend the TiO2 NP effect on daphnia growth and reproduction upon chronic exposure and also the bioaccumulation potential. Both acute and chronic exposure studies suggested higher bioaccumulation of TiO2 in daphnids when the particles were less toxic to the diet (algae). © 2014 Elsevier B.V.

Different modes of TiO2 uptake by Ceriodaphnia dubia: Relevance to toxicity and bioaccumulation

The aim of the present study was to explore the difference in toxicity mechanism of TiO2 nanoparticles (NPs) at low concentrations (≤1 μg mL-1), in a freshwater bacterial isolate, Bacillus licheniformis, under light (UV-illuminated) and dark (non-illuminated) conditions. Standard plate count and MTT assays showed the dose dependent decrease in the bacterial cell viability. The difference in reduction of cell viability under light (20.7%) and dark conditions (21.3%) was statistically non-significant at 1 μg mL-1 concentration and 2 h interaction period. The fluorescence microscopy of the NP interacted cells (1.0 μg mL-1, 2 h) under light and dark conditions showed the mixture of live and dead cells. A significant dose dependent increase in intracellular ROS generation compared to control was noted. The ROS level after 2 h of interaction was significantly higher under light conditions (7.4 ± 0.13%) as compared to dark conditions (4.35 ± 0.12%). The LDH analyses confirmed a statistically significant increase in membrane permeability under dark conditions compared to the light conditions. The NPs were stable against aggregation in sterilized lake water matrix for a period of 24 h, under both light and dark conditions. However, in the presence of bacterial cells an elevated rate of sedimentation was noted under dark conditions. The electron microscopic (SEM, TEM) observations suggested the concentration buildup of NPs near the plasma membrane leading to internalization. The zeta-potential analysis proved that NP attachment was not charge based. The FTIR studies demonstrated the possible involvement of surface functional groups in the attachment. The concentration of dissolved Ti4+ ions was found to be negligible during the test period. The dominant cytotoxicity mechanism under light conditions was found to be ROS generation, whereas, NP attachment to the cell membrane leading to membrane damage significantly contributed in dark conditions. © 2012 The Royal Society of Chemistry.

Journal	PLoS ONE
Publisher	Public Library of Science (PLoS)
ISSN	19326203
Open Access	Yes