Copper- and lead-based nanoparticles in freshwater sediments: Spatiotemporal trends and environmental impact

Metallic nanoparticles (MNPs) from anthropogenic activities pose emerging risks to aquatic ecosystems, yet their environmental distribution and occurrence remain poorly characterized due to the analytical complexity of quantifying NPs in sediment matrices. Here, we determine the size and quantify the mass and number concentrations of Cu- and Pb-containing NPs across 31 river and lake sediments in Croatia over a three-year period using single-particle inductively coupled plasma mass spectrometry (sp-ICP-MS). Based on measurements from diverse catchments, Cu NP number concentrations ranged from 1.49 × 10⁸ to 1.06 × 10¹⁰ particles/g with particle sizes of 26.8-46.0 nm, while Pb NPs ranged from 1.42 × 10⁸ to 7.63 × 10¹⁰ particles/g with smaller sizes of 19.1-26.4 nm. Mixed-effects models revealed spatial heterogeneity dominated temporal patterns, with catchment-scale factors explaining 72-91 % of concentration variance. This spatial structure reflected distinct anthropogenic sources, with Cu NPs from agricultural activities and Pb NPs from legacy mining sites and industrial emissions. In particular, agricultural sites showed elevated levels of bioavailable Cu, with extracted NPs representing up to ∼11 % of total Cu, thus identifying hotspots of ecological concern. While Pb NPs are predominantly associated with stable mineral forms such as PbS, the very high concentrations detected at certain sites (up to 25.4 μg g^-1 for Pb NPs) represent a persistent contamination reservoir with potential for remobilization under changing environmental conditions. This study reports the occurrence of Cu and Pb NPs in freshwater sediments and provides a basis for assessing the environmental risks of MNPs.