Background. Titanium dioxide (TiO2) is considered as an inert and safe material and has been used in many applications for decades. However, with the development of nanotechnologies TiO2 nanoparticles, with numerous novel and useful properties, are increasingly manufactured and used. Therefore increased human and environmental exposure can be expected, which has put TiO2 nanoparticles under toxicological scrutiny. Mechanistic toxicological studies show that TiO2 nanoparticles predominantly cause adverse effects via induction of oxidative stress resulting in cell damage, genotoxicity, inflammation, immune response etc. The extent and type of damage strongly depends on physical and chemical characteristics of TiO2 nanoparticles, which govern their bioavailability and reactivity. Based on the experimental evidence from animal inhalation studies TiO2 nanoparticles are classified as "possible carcinogenic to humans" by the International Agency for Research on Cancer and as occupational carcinogen by the National Institute for Occupational Safety and Health. The studies on dermal exposure to TiO2 nanoparticles, which is in humans substantial through the use of sunscreens, generally indicate negligible transdermal penetration; however data are needed on long-term exposure and potential adverse effects of photo-oxidation products. Although TiO2 is permitted as an additive (E171) in food and pharmaceutical products we do not have reliable data on its absorption, distribution, excretion and toxicity on oral exposure. TiO2 may also enter environment, and while it exerts low acute toxicity to aquatic organisms, upon long-term exposure it induces a range of sub-lethal effects. Conclusions. Until relevant toxicological and human exposure data that would enable reliable risk assessment are obtained, TiO2 nanoparticles should be used with great care.

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Titanium dioxide in our everyday life; is it safe?

Studies designed to investigate the environmental or biological interactions of nanoscale materials frequently rely on the use of ultrasound (sonication) to prepare test suspensions. However, the inconsistent application of ultrasonic treatment across laboratories, and the lack of process standardization can lead to significant variability in suspension characteristics. At present, there is widespread recognition that sonication must be applied judiciously and reported in a consistent manner that is quantifiable and reproducible; current reporting practices generally lack these attributes. The objectives of the present work were to: (i) Survey potential sonication effects that can alter the physicochemical or biological properties of dispersed nanomaterials (within the context of toxicity testing) and discuss methods to mitigate these effects, (ii) propose a method for standardizing the measurement of sonication power, and (iii) offer a set of reporting guidelines to facilitate the reproducibility of studies involving engineered nanoparticle suspensions obtained via sonication.

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Ultrasonic dispersion of nanoparticles for environmental, health and safety assessment--issues and recommendations.

Ecotoxicity of nanosized TiO2. Review of in vivo data

Microplastic pollution causes a major concern in the marine environment due to their worldwide distribution, persistence, and adverse effects of these pollutants in the marine ecosystem. Despite its global presence, there is still a lack of information on the effect of microplastics on marine organisms at the molecular level. Herein we demonstrated ingestion and egestion of nano- (0.05 μm) and micro-sized (0.5 and 6 μm) polystyrene microbeads in the marine copepod Paracyclopina nana, and examined molecular responses to exposure to microbeads with in vivo endpoints such as growth rate and fecundity. Also, we proposed an adverse outcome pathway for microplastic exposure that covers molecular and individual levels. This study provides the first insight into the mode of action in terms of microplastic-induced oxidative stress and related signaling pathways in P. nana.

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Adverse effects of microplastics and oxidative stress-induced MAPK/Nrf2 pathway-mediated defense mechanisms in the marine copepod Paracyclopina nana.

Background
To better understand the potential ecotoxicological impacts of silver nanoparticles released into freshwater environments, the Daphnia magna 48-hour immobilization test was used.

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Toxicity of various silver nanoparticles compared to silver ions in Daphnia magna

Oxidative stress responses of Daphnia magna exposed to TiO2 nanoparticles according to size fraction

Identification of toxicity variations in a stream affected by industrial effluents using Daphnia magna and Ulva pertusa.

A toxicity identification evaluation (TIE) based on Ulva pertusa spore release was conducted in 3 phases for the identification of the major toxicants in effluent from a wastewater treatment plant (WTP) and the receiving water in an adjacent stream. The toxicity of the final effluent (FE), as compared with raw wastewater, and primary and secondary effluent, showed a greater change over 12-monthly sampling events and appeared to have impacts on the toxicity of the downstream water with a significant correlation (r2 = 0.89, p < 0.01). In Phase I, toxicity characterization indicated that cations were likely to be the responsible toxicants for the FE. In Phase II, cations such as Cu, Ni, and Zn were found in the FE at higher concentrations than the EC50 concentrations determined for the standard corresponding metals. When the concentrations of each metal in the FE samples were plotted against the respective toxicity units, only zinc showed a statistically significant correlation with toxicity (r2 = 0.86, p < 0.01). In Phase III, using spiking and mass balance approaches, it was confirmed that Zn was the major toxicant in the effluent from the WTP. Following a change in the Fenton reagent used, to one with a lower Zn content, the toxicity of the FE greatly decreased in subsequent months. The TIE developed here enabled the toxicity of FEs of the WTP to be tracked and for Zn, originating from a reagent used for Fenton treatment, to be successfully identified as the key toxicant. The TIE method based on U. pertusa demonstrated utility as a low cost and simple tool to identify the risk factors for industrial effluents and provided information on regulatory control and management.

/pdf/application-of-the-ulva-pertusa-bioassay-for-a-toxicity-1xalki1755.pdf

Sanghoon Kim

Papers

Oxidative stress responses of Daphnia magna exposed to TiO2 nanoparticles according to size fraction

Identification of toxicity variations in a stream affected by industrial effluents using Daphnia magna and Ulva pertusa.

Application of the Ulva pertusa bioassay for a toxicity identification evaluation and reduction of effluent from a wastewater treatment plant