Bisphenol-a Disturbs Bio-Mineralization in Mussels: Potential Implications for Molar-Incisor Hypomineralization

Objectives: Molar-incisor hypomineralization (MIH) is a global health problem and the etiology is currently unclarified. Recently, mussels were used as target organisms because of their bio-mineralization of carbonate shells during growth and ethical concerns regarding the use of vertebrate animals. The study aims to investigate the feasibility of zebra mussel (Dreissena polymorpha) as a new model species to screen potential factors of MIH.
Methods: 252 zebra mussels were randomly divided into 36 groups (n=7) for three experiments (12 groups/experiment). Zebra mussels of six groups per experiment were incubated with 100mg/l calcein (mineralization marker) solution for 96h, another six groups with tap water only (negative controls). Then zebra mussels with and without calcein pre-incubation were exposed to cadmium sulfate hydrate (3CdSO₄●8H₂O, as positive control; 0, 0.01, 0.1, 1, 10 and 100mg/l), possible etiological factors of MIHincluding bisphenol-A (BPA; 0, 0.02, 0.2, 2, 20 and 200mg/l) and erythromycin (0, 0.1, 1, 10, 100 and 1000mg/l) as mineralization “disruptors” for 96h, respectively. After two weeks, mussels were sacrificed, the shells were collected and embedded with methylmethacrylate.
Results: Mortality was 100% in 20 and 200mg/l BPA groups. No difference with or without calcein incubation was observed. The median lethal concentration (96h-LC50) of BPA was 6.3mg/l with a 1.3-34.4mg/l confidence interval (CI) in zebra mussels. Moreover, the fluorescence intensity of calcein decreased (p<0.05) in both 2 mg/l BPA groups and 1 mg/l 3CdSO₄●8H₂O, whereas no increased mortality and decreased fluorescence intensity were found after erythromycin exposures. Mortality was 100% in 10 and 100 mg/l 3CdSO₄●8H₂O groups (positive control), thereby the 96h-LC50 of cadmium was 3.1mg/l (95% CI, 0.7-10.5mg/l).
Conclusions: These results suggest that BPA may act as a potential causing factor for disturbed bio-mineralization. The bio-mineralization in zebra mussels seems to be an effective model for investigating potential causative factors of MIH.