Toxicity assessment of nano-TiO2 in Apis mellifera L., 1758: histological and immunohistochemical assays

The aim of this study was to evaluate the toxicity of titanium dioxide nanoparticles (TiO2NPs) by short-term toxicity tests in Apis mellifera, considered an excellent bioindicator organism mainly due to its sensitivity. Bees have been exposed to several concentrations of TiO2NPs (1 × 10−3, 1 × 10−4, 1 × 10−5, 1 × 10−6 mg/10 ml) for 10 days. Morphostructural and histological assays were done on gut and honey sac. The research of exposure biomarkers like metallothioneins 1 (MT1) and Heat Shock Protein 70 (HSP70) was performed to verify if a detoxification mechanism has been activated in the exposed animals. No histological alteration on the epithelium of the gut and honey sac were observed in exposed samples. A significant positivity for anti-MT1 antibody was observed only in the honey sac cells. A weak positivity for HSP70 was observed in both structures analyzed. In several studies have shown the non-toxicity of TiO2NPs on other model organisms, in our study, titanium dioxide nanoparticles was proven to be highly toxic at the highest concentration tested (100% of lethality to 1 × 10−3 mg/10 ml) and moderately toxic at lower concentrations. Honey bees proved to be excellent models for study of NPs toxicity and for monitoring environment.