Comparison of chlorine and chloramine in the release of mercury from dental amalgam.
The purpose of this project was to compare the ability of chlorine (HOCl/OCl(-)) and monochloramine (NH(2)Cl) to mobilize mercury from dental amalgam. Two types of amalgam were used in this investigation: laboratory-prepared amalgam and samples obtained from dental-unit wastewater. For disinfectant exposure simulations, 0.5 g of either the laboratory-generated or clinically obtained amalgam waste was added to 250 mL amber bottles. The amalgam samples were agitated by end-over-end rotation at 30 rpm in the presence of 1 mg/L chlorine, 10 mg/L chlorine, 1 mg/L monochloramine, 10 mg/L monochloramine, or deionized water for intervals of 0 h, 2 h, 4 h, 8 h, and 24 h for the clinically obtained amalgam waste samples and 4 h and 24 h for the laboratory-prepared samples. Chlorine and monochloramine concentrations were measured with a spectrophotometer. Samples were filtered through a 0.45 microm membrane filter and analyzed for mercury with USEPA standard method 245.7. When the two sample types were combined, the mean mercury level in the 1 mg/L chlorine group was 0.020 mg/L (n=25, SD=0.008). The 10 mg/L chlorine group had a mean mercury concentration of 0.59 mg/L (n=25, SD=1.06). The 1 mg/L chloramine group had a mean mercury level of 0.023 mg/L (n=25, SD=0.010). The 10 mg/L chloramine group had a mean mercury level of 0.024 mg/L (n=25, SD=0.011). Independent samples t-tests showed that there was a significant difference between the natural log mercury measurements of 10 mg/L chlorine compared to those of 1 mg/L and 10 mg/L chloramine. Changing from chlorine to chloramine disinfection at water treatment plants would not be expected to produce substantial increases in dissolved mercury levels in dental-unit wastewater.
Stone
Mark E
ME
Naval Institute for Dental and Biomedical Research, Building 1-H, 310A B Street, Great Lakes, Illinois 60088-5259 USA. mark.stone@med.navy.mil
Scott
John W
JW
Schultz
Stephen T
ST
Berry
Denise L
DL
Wilcoxon
Monte
M
Piwoni
Marv
M
Panno
Brent
B
Bordson
Gary
G
D002700:Chloramines / Q000737:chemistry*; D002713:Chlorine / Q000737:chemistry*; D003723:Dental Amalgam / Q000737:chemistry*; D019551:Dental Disinfectants / Q000737:chemistry*; D018057:Dental Waste / Q000032:analysis*; D008628:Mercury / Q000032:analysis* / Q000302:isolation & purification; D013053:Spectrophotometry; D014865:Waste Disposal, Fluid; D014877:Water Pollution, Chemical / Q000032:analysis*
D002700:Chloramines; D019551:Dental Disinfectants; D018057:Dental Waste; D002713:Chlorine; D003723:Dental Amalgam; D008628:Mercury; C030816:chloramine