Stability of Titanium Dioxide Nanoparticle Agglomerates in Transitional Waters and Their Effects Towards Plankton from Lagoon of Venice (Italy)

The present study explores the effect of salinity and dissolved organic carbon(DOC) gradients on the stability and reactivity of titanium dioxide nanoparticle (TiO2-NP)agglomerates in ambient water from the Lagoon of Venice and their possible effect onnaupliisampled at the same locations. In all ambient water samples, TiO2-NPs formedrapidly micrometre-sized agglomerates. The increase in the salinity and concomitantdecrease in DOC content induced the formation of larger agglomerates, with z-averagehydrodynamic diameter increasing with TiO2-NP concentration and exposure duration.Under the studied conditions,f-potential exhibited negative values. In line with agglom-eration results, enhancement of the salinity and lower DOC resulted in less negativef-potential with close to 0 values in the dispersions of 100 mg L-1TiO2-NPs in sea water.Two-hour exposure to micrometre-sized agglomerates of TiO2-NPs resulted in an increasein the fluorescence of propidium iodide (PI) stainednaupliiin comparison with unexposedcontrols, but had no effect at 24-h exposure. The increase innauplii-associated PI fluo-rescence was more noticeable in dispersions containing 100 mg L-1than those containing10 mg L-1TiO2-NPs, suggesting membrane permeability alteration in a concentration-dependent manner. However, the PI staining results have to be interpreted with cautionbecause of the possible dye binding to thenaupliisurface without penetration of cellularmembrane. The effect of TiO2-NPs onnaupliiwas more pronounced at higher salinity anddecreased with increasing DOC concentrations at 2 h, while no trends were found at 24-hexposure, as well as exposure to 100 mg L-1TiO2-NPs.