Modulation of TiO₂ nanoparticles bio-transfer and digestive gland toxicity in the freshwater clam Caelatura nilotica by ascorbic acid

The widespread occurrence of titanium dioxide nanoparticles (TiO₂ NPs) in aquatic ecosystems is raising significant concerns about their potential toxic impacts on freshwater species. This study evaluated the bioaccumulation kinetics, digestive gland bioaccumulation transfer factor (BTF), and histopathological impairments in the freshwater clam Caelatura nilotica exposed to TiO₂ NPs, alongside the protective mechanisms of ascorbic acid (AA). Results revealed concentration- and time-dependent bioaccumulation of TiO₂ NPs within the clam digestive gland. Elevated exposure concentrations triggered severe sub-lethal physiological disruptions, leading to detrimental structural pathologies, including digestive tubule atrophy, luminal expansion, severe vacuolation, and inflammatory haemocyte infiltration. Ultrastructurally, TiO₂ NPs induced profound organelle damage—specifically mitochondrial swelling signalling bioenergetic dysfunction, and nuclear chromatin condensation indicative of apoptotic pathways. Co-exposure with 200 µg/L AA significantly mitigated these effects, reduced titanium accumulation, reduced BTF values, and attenuated toxic responses by scavenging reactive oxygen species, thereby preserving histological architecture and organelle integrity. These findings demonstrate that AA supplementation effectively counteracts TiO₂ NP-induced physiological and ultrastructural toxicity, offering an eco-friendly mitigation strategy to safeguard freshwater filter-feeders against nanomaterial ecotoxicity.