Ecotoxicological effects of TiO 2 and Fe 2 O 3 nanoparticles on physiological, biochemical, and behavioural responses in Daphnids: a systematic review

Production and release of engineered nanoparticles raise concerns about their potential effects on freshwater ecosystems. Daphnids are sentinel organisms because of their ecological role and sensitivity to contaminants. This systematic review synthesised evidence on the ecotoxicological effects of titanium dioxide (TiO2) and iron oxide (Fe2O3) nanoparticles on daphnids, focusing on physiological, biochemical, and behavioural responses. Searches of ScienceDirect, Google Scholar, and Scopus identified 2,780 records; 31 peer-reviewed studies met the inclusion criteria. Most used OECD (n = 22) or EPA (n = 9) toxicity protocols and investigated Daphnia magna (n = 22) or Ceriodaphnia dubia (n = 9). Acute tests predominated (61%), followed by combined acute-chronic (22%) and chronic (12%) studies. Endpoints included mortality, growth, reproduction, oxidative stress, bioaccumulation, and behavioural alterations. TiO2 nanoparticles showed size-, crystal-structure-, and light-dependent toxicity, impairing reproduction and growth at 0.01-2 mg/L. Only three studies assessed Fe2O3 nanoparticles, reporting concentration- and coating-dependent bioaccumulation, embryotoxicity, and altered life-history traits. Both nanoparticles were associated with mortality, reproductive impairment, growth inhibition, oxidative stress, bioaccumulation, and behavioural changes; effects depended on nanoparticle properties and environmental conditions. These findings underscore the need for mechanistic studies and improved environmental risk-assessment frameworks to predict long-term impacts of engineered nanoparticles on freshwater ecosystems.