Abstract: Nanoparticles (NP) in natural waters with particle sizes <0.22 μm significantly influence the chemical properties and
bioavailability of dissolved elements. However, the small size and low concentration of NPs make their quantification challenging. This study employed inductively coupled plasma mass spectrometry (ICP-MS) and high-resolution transmission electron microscopy (HR-TEM) to analyze the species, spatiotemporal distribution, and trace element characteristics of NPs in Chaohu Lake. Results show that ICP-MS direct measurements of elements (truly dissolved fraction) in 0.22 μm membrane-filtered water samples exhibited high precision, validating this method for NP analysis in natural waters. NP-associated elements (dissolved fraction minus truly dissolved fraction) were dominated by Fe and Al, with their average concentrations remaining stable between spring and summer. High NP-Fe concentrations were consistently observed in the southeastern area near the lake outlet across both seasons, while NP-Al hotspots shifted from the southern lake region in spring to the northern region in summer. Correlation analysis revealed that Cr, Mn, Zn, Ge, and Cd showed positive correlations with NP-Fe in both seasons, whereas Pb, rare earth elements (REEs), and Ni exhibited summer-specific correlations with NP-Fe. For NP-Al, only Ti, Sc, and middle REEs displayed summer correlations. HR-TEM characterization identified amorphous Fe (hydr)oxides, aluminosilicates, and Ca carbonates as the predominant NP phases, with the first category playing a critical role in regulating dissolved element cycling in Chaohu Lake. The study concluded that riverine inputs constitute the primary NP source, with increased summer discharge enhancing NP influx. The increase in lake water pH during summer facilitates the precipitation of NP-iron (hydr)oxides and the dispersion of NPaluminosilicates. 

Key words: Chaohu Lake, nanoparticle, inductively coupled plasma-mass spectrometry, transmission electron microscopy, iron
(hydr)oxide, trace elements