The increasing use of nanosilver in consumer products and the likelihood of environmental exposure warrant investigation into the toxicity of nanosilver to aquatic organisms. A series of studies were conducted comparing the potency of nanosilver to ionic silver (Ag(+)) at acute and sublethal levels using two test organisms (Daphnia magna and Pimephales promelas). The 48-h D. magna median lethal concentration (LC50) of multiple sizes (10, 20, 30, and 50 nm) of commercially prepared nanosilver (nanoComposix) ranged from 4.31 to 30.36 µg total Ag L(-1) with increasing toxicity associated with decreasing particle size. A strong relationship between estimated specific particle surface area and acute toxicity was observed. Nanosilver suspensions (10 nm) treated with cation exchange resin to reduce the concentration of Ag(+) associated with it were approximately equally toxic to D. magna compared to untreated nanosilver (48-h LC50s were 2.15 and 2.79 µg total Ag L(-1), respectively). The 96-h LC50 and 7-d sublethal 20% effective concentrations (EC20s) for P. promelas were 89.4 and 46.1 µg total Ag L(-1), respectively, for 10 nm nanosilver and 4.70 and 1.37 µg total Ag L(-1), respectively, for Ag(+); the resulting ratios of 96-h LC50 to 7-d EC20 were not significantly different for nanosilver and ionic silver. Overall, these studies did not provide strong evidence that nanosilver either acts by a different mechanism of toxicity than ionic silver, or is likely to cause acute or lethal toxicity beyond that which would be predicted by mass concentration of total silver. This in turn suggests that regulatory approaches based on the toxicity of ionic silver to aquatic life would not be underprotective for environmental releases of nanosilver.

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23As a component of sunscreen formulations, TiO 2 engineered nanomaterials (ENM) are coated to 24 prevent reactive oxygen species from causing damage to skin. We investigated the stability of an 25 Al(OH) 3 coating by exposing 25 nm Al(OH) 3 ·TiO 2 ENM to simulated swimming pool water 26 (SPW) for 45 minutes, 1, 3, 10, or 14 days. Electron microscopy and spectroscopy indicated that 27 exposure to SPW caused a redistribution of the Al(OH) 3 coating allowing photocatalytic 28 formation of hydroxyl radicals. Aged ENM showed significantly greater phototoxicity under 29 UVA irradiation than un-aged ENM in a human-derived retinal pigment epithelium cell line 30 (ARPE-19). Photocatalytic activity and phototoxicity of aged Al(OH) 3 ·TiO 2 was significantly 31 less than that of the positive control-uncoated P25 TiO 2 . In summary, the aging of 32 Al(OH) 3 ·TiO 2 ENM in SPW redistributed the coating and reduced its protective properties, 33 thereby increasing reactivity and potential phototoxicity.34 35 those of toxic effects, including acute phototoxicity in aquatic species. 41 They concluded that the 403 probability distributions for TiO 2 environmental exposures and sensitive effects were relatively 404 close, with only about one order of magnitude separation. Assessments of potential 405 environmental risks of nanomaterials to date, have not considered the combination of 406 environmental transformations (demonstrated here), long-term bioaccumulation, and 407 phototoxicity from co-exposure to UV wavelengths (or visible wavelengths in the case of doped 408 TiO 2 varieties).409 410 Acknowledgment 411

Abstract-Solar irradiance (W/m 2 ) and downwelling diffuse attenuation coefficients (K d ; 1/m) were determined in several locations in Prince William Sound (AK, USA) between April 2003 and December 2005 to assess temporal and spatial variation in solar radiation and the risks of photo-enhanced toxicity from spilled oil. Weekly irradiance measurements of surface visible light, ultraviolet B (UVB), and ultraviolet A (UVA) radiation in Valdez (AK, USA) followed expected trends of maximum solar irradiance at each summer solstice and minimum values at each winter solstice. Variation from weekly maximum expected surface irradiances was attributed to large variations in environmental conditions over the 142-week monitoring period. Season and proximity to glacial meltwater were significant determinants of K d , with 1% attenuation depths ranging from 0.4 to 15 m (UVB and UVA) and from 0.5 to 28 m (visible light). The probability of photo-enhanced toxicity risks estimated from UVA dosimetry decreased with increasing water depth, with higher risks during spring and summer and lower risks during fall and winter. These results demonstrate substantial temporal and spatial variation in solar radiation in Prince William Sound and the potential for significant season-and locationspecific photo-enhanced toxicity risks from spilled oil.