Toxicity of Titanium Dioxide Nanoparticles on Aquatic and Human Health In Vitro and In Vivo Assessment Using Zebrafish (Danio rerio)

Abstract

One of the most common nanomaterials produced in the world today is titanium dioxide nanoparticles (TiO2 -NPs), which are produced in large quantities of over five million tons each year and are becoming a cause of concern because of their rising release into water bodies that threaten the health of the ecosystem as well as the human population that relies on the water resources. Irrespective of their commercial ubiquity, the sub-lethal toxicological effects of environmentally-relevant TiO2-NP concentrations on hematological integrity, blood biochemical homeostasis and cellular oxidative defensive mechanisms are yet to be fully characterized in parallel in aquatic model organisms and human cell lines. As part of this research, a two-way in vitro and in vivo toxicological assessment of TiO2-NPs (Aeroxide P25, anatase, 21 nm, 99.5% purity) was conducted with adult zebrafish (Danio rerio) as the in vivo model and using HepG2 (human hepatocytes), HEK-293 Adult zebrafish were exposed to 0, 10, 50 and 100 mg/L TiO2-NPs in water over a 96-hour (acute) and 28 days (subchronic) period. After 28 days of subchronic exposure, hematological analysis showed that the 96-hour LC 50 was 84.7 mg/L, and that a normocytic normochromic anemia was induced in the test animals, with a dose-dependent reduction of both the red blood cell counts (28.4 percent) and hemoglobin levels (29.2 percent) The indices of erythrocyte (MCV, MCH, MCHC) were stable and confirmed normocytic, but not nutritional anemia. Blood biochemistry showed that there was a significant hepatocellular injury (ALT 4.2-fold, AST 3.7-fold, ALP 2.2-fold above control at 100 mg/L), renal dysfunction (creatinine 2.4-fold, urea 2.5-fold increase) and metabolic disruption (hyperglycaemia, hypop The oxidative stress analysis revealed the dramatic depletion of glutathione (47.2% of control in gill at 100 mg/L), clear lipid peroxidation (MDA 3.8-fold increase in gill) and dose-dependent inactivation of all antioxidant enzymes analyzed (SOD, CAT, GPx). TiO₂-NPs killed HepG2, HEK-293 and zebrafish gill cell viabilities with IC 50 values of 89.2, 97.8, and 71.4mg/L respectively and caused concentration-dependent accumulation of intracellular ROS. The concentration where the effect was no longer observed (NOEC) of the most sensitive hematological and oxidative stress endpoints, was 10 mg/L, and the lowest concentration where the effect was observed (LOEC) was 25mg/L. Those results define a unified, multi-target toxicological profile of TiO₂ -NPs that goes beyond individual-organ testing and gives translatable hematological and biochemical biomarkers to evaluate environmental health risks in aquatic environments and occupational health risks in human beings.