Temporal and Spatial Distributions of Ti-Containing Nanoparticles and On-Site Visitor Numbers in Three Recreation Waters in Eastern Taiwan.

The increase in Ti-containing nanoparticles (NPs) in the environment resulting from the anthropogenic water activities has raised health concerns in recent years. The aim of this study was to differentiate Ti-containing engineered NPs (ENPs) from natural Ti-containing NPs (NNPs) in water exposure through water activities. This was achieved by characterizing the temporal and spatial distributions of Ti-containing NPs in the three recreation waters in Eastern Taiwan, using the Ti/Y elemental ratio method and single-particle inductively coupled plasma mass spectrometry (sp-ICPMS). The mass concentration of the Ti-containing ENPs and the number concentration of NPs were generally higher during the peak season compared with the low season. These concentrations also fluctuated more widely than those of Ti-containing NNPs. The highest mass and number concentrations, 8.00 ng/mL and 850.5 × 10³ particles/mL, were found in the recreation waters of South Nan-Ao Creek and Lao Creek, respectively. The most frequent particle size ranged from 28 to 60 nm, with no significant variation across sampling seasons and creeks. Furthermore, the number of on-site visitors was significantly correlated with the mass concentration of Ti-containing NPs (p = 0.0069), the number concentration of Ti-containing NPs (p = 0.0023), and estimated TiO₂-ENPs (p = 0.0305). The elemental ratio method allowed for a clearer illustration of the impact of anthropogenic activities on the Ti-containing ENPs levels in the recreation waters. This method is valuable for future risk assessments regarding potential exposure to TiO₂-ENPs.