On how titanium dioxide nanoparticles attenuate the toxicity of mercuric chloride to Artemia salina: investigation of fatty acid composition, oxidative stress, and lipid peroxidation.

Titanium dioxide nanoparticles (TiO₂NPs) as an emerging pollutant in aquatic environments can interact with metals reducing or enhancing their toxicity in these environments. This study examined and compared the toxic effects of mercury ions (Hg²⁺ ions) on immobilization percentage, fatty acid profile, and oxidative stress of Artemia salina nauplii, individually (Hg) and simultaneously in the presence of 0.10 mg.L^-1 (Hg-0.1TiO₂NPs) and 1.00 mg.L^-1 TiO₂NPs (Hg-1TiO₂NPs). The interaction between Hg²⁺ ions and TiO₂NPs was evaluated using DLS and AAS-VGA. Simultaneous exposures exhibited an unexpected dual effect on A. salina nauplii. A synergistic effect was observed in Hg-0.1TiO₂NPs, while increasing the TiO₂NPs concentration in Hg-1TiO₂NPs prevented the synergy of the mixture compounds offering an antagonistic effect on nauplii. This dual effect was assigned to a greater number of available active sites and agglomeration of TiO₂NPs at higher concentrations. Oxidative stress and lipid peroxidation induced by Hg were diminished in Hg-1TiO₂NPs in line with the immobilization results. In Hg, total amounts of saturated fatty acids (∑SFA) increased while total monounsaturated (∑MUFA) and total polyunsaturated (∑PUFA) ones decreased compared with the control. However, they showed no significant change considering the control in Hg-1TiO₂NPs, again confirming the antagonistic effect on nauplii. The unsaturated to saturated fatty acids ratio decreased in both Hg and Hg-1TiO₂NPs compared with the control, however, this reduction in Hg-1TiO₂NPs was lower than in Hg. The present results emphasized getting a more comprehensive understanding of how TiO₂NPs impact the bioavailability and toxicity of co-contaminants through their combined effects and interactions.