Rebecca Capua is an assistant conservator in the Paper Conservation Department at the Metropolitan Museum of Art since 2009. She received an MA in art history and an Advanced Certificate in art conservation from the Conservation Center, Institute of Fine Arts, New York University in 2007. Her primary area of research is on the materials of American artists of the late 19th and early 20th century. Address: The Sherman Fairchild Center for the Conservation of Works on Paper, Metropolitan Museum of Art, 1000 Fifth Avenue, New York, NY 10028. Email: rebecca.capua@metmuseum.org.

Nano-sized TiO₂ generally shows low or no acute toxicity in both invertebrates and vertebrates. However, exposure of Daphnia magna to 20 ppm TiO₂ for 8 consecutive days was found to cause 40 % mortality. Zhu et al. showed minimal toxicity to D. magna after 48 h exposure, while upon chronic exposure for 21 days, D. magna suffered severe growth retardation and mortality. A significant amount of nano-sized TiO₂ was found also accumulated in the body of the animals. Similar findings with coated nano-sized TiO₂ (T-Lite™ SF, T-Lite™ SF-S and T-Lite™ MAX; BASF SE) were reported by Wiench et al. Biochemical measurements showed that exposure to TiO₂ NPs induces significant concentration-dependent antioxidant enzyme activities in D. magna. Lee et al. showed that 7 and 20 nm-sized TiO₂ induced no genotoxic effect in D. magna and in the larva of the aquatic midge Chironomus riparius.