Analyst Insight

Drobne et al. used the terrestrial arthropod Porcellio scaber as a test organism for determining the cytotoxic effect of TiO₂ NPs (anatase). The animals were exposed to TiO₂ NPs of two different sizes (25 nm and 75 nm) in the concentration range 10–1000 μg TiO₂/g dry food for 3 to 14 days. No adverse effects, such as mortality, body weight changes or reduced feeding, were observed. In fact, quite the opposite, an enhanced feeding rate, food absorption efficiency and increase in catalase activity were observed. The intensity of these responses appeared to be time- but not dose-dependent. It should also be noted that the concentrations tested in this study were much higher than the predicted concentration (4.8 μg/g soil) at high emission scenario of nano-sized TiO₂. Using the same test organism another group showed that exposure to TiO₂ NPs induced destabilization of cell membrane in the epithelium of digestive glands isolated from exposed animals. They also showed that this effect can be observed after just 30 minutes of exposure.

Although barium sulfate is almost completely inert, zinc sulfide degrades upon exposure to UV light, leading to darkening of the pigment. The severity of this UV reaction is dependent on a combination of two factors; how much zinc sulfide makes up the pigments formulation, and its total accumulated UV exposure. Depending on these factors Lithopone B301, Lithopone B311 powder itself may vary in shade over time, ranging from pure white all the way to grey or even black. To suppress this effect, a dopant might be used, like small amount of cobalt salts, which would be added to the formulation. This process creates cobalt-doped zinc sulfide. The cobalt salts help to stabilize zinc sulfide so it will not have as severe a reaction to UV exposure.

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