Nano-TiO impairs the health of crabs Charybdis japonica under warming conditions through waterborne and dietary exposures.

The widespread use of nano titanium dioxide (nano-TiO₂) poses ecological risks to marine ecosystems, especially when combined with ocean warming. However, most previous studies have only examined water-related exposures, leaving a gap in research on the impact of food transfer on organisms. In this work, the harmful impacts of nano-TiO on the Japanese swimming crab Charybdis japonica were studied through three scenarios: direct exposure (DE) of the crabs to warming and nano-TiO, indirect exposure (IE) via consumption of thick-shelled mussels Mytilus coruscus exposed to the same conditions, and combined exposure (CE), where crabs were directly subjected to warming and nano-TiO while feeding affected mussels. Moreover, a control group was established, consisting of Japanese swimming crab C. japonica and mussel M. coruscus that were raised under standard temperature (22 °C) and 0 mg L nano-TiO concentration conditions. Immune, oxidative, and gene expression parameters were measured in gills and hepatopancreas after 7 exposure days. Furthermore, titanium bioaccumulation, along with the morphometrical and histological analyses, were assessed in gills. Bioaccumulation results (1.69-6.83 μg/g) suggested that foodborne stressors induced higher titanium contents. Additionally, there were deformities in gills morphometry and histology. The multivariate analyses showed that warming and nano-TiO combination had a pronounced effect on the overall profile of biological responses in crabs; moreover, the exposure through food alone had the greatest impact on gills immune-oxidative parameters and hepatopancreas gene expressions. The harmful impacts of nano-TiO are significant and can manifest through waterborne and dietary exposure pathways, especially when combined with other stressors, warranting further research.