Mercury In Fillings Turns To Sulfide

The aged dental amalgam on the surface of your old fillings may have lost as much as 95% of its mercury, and what’s left has likely been converted into a form of mercuric sulfide, reports a group led by Graham N. George of the University of Saskatchewan (Chem. Res. Toxicol., DOI: 10.1021/tx900309c). Identifying the amount of metal present and in what form is critical for assessing toxicity related to using mercury in dental fillings. George and colleagues used X-ray absorption spectroscopy to determine the amount and identity of mercury species on the surface of both fresh amalgam and a filling estimated to be 20 years old. The fresh amalgam contained metallic mercury, but the older filling was composed primarily of the β crystal form of mercuric sulfide, HgS, also known as metacinnabar. The sulfur likely comes from organosulfur compounds in foods and beverages such as onion, garlic, and coffee, or it could arise from bacterial action in the mouth. Although β-mercuric sulfide is estimated to have low bioavailability compared with other mercury compounds, the researchers say, additional chemical work is needed to determine when, how, and in what form mercury is lost from fillings.