Dispersion and Toxicity of Selected Manufactured Nanomaterials in Natural River Water Samples: Effects of Water Chemical Composition

Experimental conditions that mimic likely scenarios of manufactured nanomaterials (MNs) introduction to aquatic systems were used to assess the effect of nanoparticle dispersion/solubility and water chemical composition on MN-toxicity. Aqueous suspensions of fullerenes (C-60) nanosilver (nAg), and nanocopper (nCu) were prepared in both deionized water and filtered (0.45 mu m) natural river water samples collected from the Suwannee River basin, to emphasize differences in dissolved organic carbon (DOC) concentrations and solution ionic strengths (I). Two toxicity tests, the Ceriodaphnia dubia and MetPLATE bioassays were used. Results obtained from exposure studies show that water chemistry affects the suspension/solubility of MNs as well as the particle size distribution, resulting in a wide range of biological responses depending on the type of toxicity test used. Under experimental conditions used in this study, C60 exhibited no toxicity even when suspended concentrations exceeded 3 mg L-1. MetPLATE results showed that the toxicity of aqueous suspensions of nCu tends to increase with increasing DOC concentrations, while increasing I reduces nCu toxicity. The use of the aquatic invertebrate C. dubia on the other hand showed a tendency for decreased mortality with increasing DOC and I. MetPLATE results for nAg showed decreasing trends in toxicity with increasing DOC concentrations and I. However, C. dubia exhibited contrasting biological responses, in that increasing DOC concentrations reduced toxicity, while the latter increased with increasing I. Overall, our results show that laboratory experiments that use DI-water and drastic MN-suspension methods may not be realistic as MN-dispersion and suspension in natural waters vary significantly with water chemistry and the reactivity of MNs.