Line Cleanser/Disinfectant Effects on Soluble Mercury Content of Dental Wastewater.

M. E. STONE, E. D. PEDERSON, R. A. AUXER, and S. L. DAVIS
[The Naval Dental Research Institute, 310-A B Street, Building 1-H, Great Lakes, IL 60088-5259, USA].

Levels of mercury [Hg] released into the environment from dental treatment facilities continue to be closely monitored by local public waste treatment facilities due to stringent local, state, and federal EPA regulations. This preliminary study investigated Hg release from amalgam particles contained in air/water separators and holding tanks by the action of commercial and non-commercial line cleanser/disinfectants. Scrap amalgam was collected from dental unit amalgam traps. The scrap amalgam was pulverized and dry sieved at 710 and 20 mm to yield samples A (between 710 and 20 mm) in order to simulate what passes through the chairside amalgam trap, and B (< 20 mm) to simulate the colloidal portion of amalgam waste. Green and Clean [G/C], PureVac [P/V], Vacusol Plus [VAC], household bleach [HHB], 0.21% citric acid [C/A], and high purity water [HPW] (control) were mixed with dental amalgam. One-half gram of sample A and 0.05 gram of sample B were mixed with 500 ml of HPW and the manufacturers recommended concentration of each line cleanser. Samples of supernatant (50 ml) were taken prior to the daily mixing. Supernatant samples taken at days 1 (baseline), 4, and 8 were analyzed for total mercury by Perkin Elmer method 245.1A. The mg/L Hg for each baseline control was subtracted from the appropriate 4- and 8-day samples. After a four-day exposure, HPW, G/C, and C/A demonstrated no Hg increase in either treatment group when compared to baseline. After the same exposure, P/V released only 7.1 mg/L additional Hg with group A and no additional Hg with group B amalgam samples. HHB and VAC released 243.1 and 95.9 mg/L Hg with group A and 30.1 and 387.8 mg/L Hg with group B amalgams, respectively. Results with a separate <710 mm sieved amalgam sample yielded results similar to the totals of groups A and B samples which received identical treatment. Hg solubility increases continued into the 8-day samples. Our results indicate that some line cleansers can solubilize Hg from amalgam particles in dental wastewater. Supported by the Office of Naval Research, Naval Medical Research and Development Command, Project Number 0603706N M0095.006-0515. [Journal of Dental Research 78:207 #814, 1999] 

Graph showing the mobilization of mercury as a result of exposure to various line cleansers.
Note the effect of bleach on mercury concentrations at day 14.