Nanoscale lead dioxide (nPbO₂(s)) is a corrosion byproduct, formed from the chlorination of lead-containing plumbing materials. This metal oxide nanoparticle (NP) plays a key role in determining lead pollution in drinking water and receiving water bodies. Natural water matrices with different salts or organic matters may affect aqueous redox conditions, thus altering the stability of nPbO₂(s) or contributing to lead (Pb²⁺) releasing. Lead is a toxic metal that causes multiple adverse effects including neurotoxicity, nephrotoxicity, deleterious effects on the hematologic and cardiovascular systems. However, the interactions of nPbO₂(s) with water matrices associated toxicity are less known. This study evaluates the aqueous chemistry and toxicological responses of nPbO₂(s) associated to different water matrices using medaka fish (Oryzias latipes) as a model organism. The medaka larvae were treated with solutions containing either nPbO₂(s) or Pb(II)_(aq) in soft water with 5mg/L humic acid (SW+HA) or very hard water (VHW) for 10 days. At the endpoint, in vivo toxic effects, consisting of locomotor activity and neurotoxicity related gene expressions were measured. The result showed that dissolved salts enhanced aggregation and sedimentation of nPbO₂(s) in VHW water. On the contrary, the presence of HA in water enhanced the particle stability and slightly accelerated lead dissolution. We observed that nPbO₂(s) in VHW solutions showed higher interference in locomotor activities of medaka larvae, as compared to those in SW+HA solutions. Furthermore, genes involved central nervous system development (e.g. α1-tubulin and myelin basic protein) or acetylcholinesterase were downregulated with nPbO₂ (10 and 20 mg/L) in VHW, as compared to the control. Our investigation indicated a higher toxicological risk (e.g., neurotoxic effect) of metal oxide NP (e.g., nPbO₂) when they are present in hard water matrices of higher ion strength.

Keyword: nPbO₂; nanoparticle; hard water; locomotor activity; toxicity