JADA Continuing Education
The effect of disinfectants and line cleaners on the release of mercury from amalgam
Hanu Batchu, MS,
Hwai-Nan Chou, MS,
Duane Rakowski, BS and
P.L. Fan, PhD
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ABSTRACT
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Background. Dental practices use disinfectants or line cleaners to flush dental unit wastewater lines to minimize odor generation, remove solid waste particles and remove biofilms in dental unit water lines (DUWLs).
Methods. The authors evaluated 47 disinfectants or line cleaners for their potential to release mercury from amalgam waste. They prepared each product concentration according to the manufacturer’s recommendations and gently agitated it along with one amalgam specimen for 24 hours. They filtered the combined decanted liquid and rinse and analyzed it for mercury using modified U.S. Environmental Protection Agency method 245.1.
Results. Six preparations released significantly more mercury from amalgam (about 17 to 340 times) than did the deionized water control (P < .001). The amount of mercury released by the other disinfectants/line cleaners was not statistically different from that released by the control. The pH values of all preparations ranged from 1.76 to 12.35.
Conclusion and Clinical Implications. This study and other published reports have demonstrated that preparations containing chlorine release more mercury from amalgam than did some other products and the deionized water control. As a result, the use of these products is not recommended for treating dental office wastewater lines or DUWLs.
Key Words: Disinfectants; line cleaners; dental unit water lines; amalgam wastewater
Dental practices use disinfectants or line cleaners to flush dental unit wastewater lines and wastewater plumbing to minimize odor generation and to remove solid waste particles. They also use these agents to remove biofilms in dental unit waterlines (DUWLs) and to maintain low microbial counts in dental unit water.
The release of mercury from amalgam occurs when some types of disinfectants and line cleaners come into contact with amalgam waste that has collected in chairside traps, dental unit waste line tubing, vacuum pump filters, amalgam separators (if installed) and waste-water plumbing. Because of growing environmental concerns, the U.S. Environmental Protection Agency (EPA) requires that publicly owned treatment works (POTWs)—that is, wastewater treatment facilities—meet increasingly stringent numeric limits for mercury in wastewater. In their compliance efforts, POTWs have identified dental office waste-water as a source of mercury in wastewater.1
Most mercury in dental office wastewater occurs in the form of dental amalgam2–4 that is captured by POTWs in grit chambers and as biosolids.4 However, dissolved mercury, which the EPA defines as mercury that can pass through a 0.45-micrometer filter, is too small to be captured by POTWs. As a result, dissolved mercury often appears in POTW effluent. Because disinfectants and line cleaners could react with amalgam waste to release dissolved mercury, choosing disinfectants and line cleaners that release little or no mercury from amalgam waste is a prudent approach.
Kielbassa and colleagues5 and Kummerer and colleagues6 reported that three of seven disinfectants caused more mercury release than water alone when either came in contact with amalgam waste in dental units. The investigators concluded that disinfectants containing oxidizing agents release mercury from amalgam. In an in vitro study, Rotstein and colleagues7 reported that hypochlorite solutions released mercury from amalgam. Roberts and colleagues8 reported that six of the eight disinfectants used in their laboratory study released more mercury from ground amalgam particles than did the water control. A disinfectant containing quaternary ammonium compounds released less mercury from amalgam than did water. Additionally, a combination of phenolic compounds released similar amounts of mercury from amalgam as did water. Disinfectants that contain chlorine, bromine, iodophor peroxide/peracetic acid and some phenolic compounds released more mercury from amalgam particulate than did the control (water). Stone and colleagues9 reported that iodine, found in some DUWL treatment formulations, released mercury from amalgam. The American Dental Association’s Best Management Practices for Amalgam Waste recommend against using chlorine-containing line cleaners.10
Our study involved the evaluation of 47 disinfectants or line cleaners for their potential to release mercury from amalgam waste. This report is intended to help dental professionals make product choices that minimize mercury release.
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MATERIALS AND METHODS
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We used deionized water as the control. The table
lists the products, manufacturers, intended use, active ingredients and recommended concentration for use. We prepared each product concentration according to the manufacturer’s recommendations. We measured the pH of each preparation using an Accumet Model 15 pH meter and Accumet pH electrode (Fisher Scientific International, Hampton, N.H.). We prepared cylindrical amalgam specimens measuring 4 x 7 millimeters using Tytin (lot no. 3-2239, Kerr, Orange, Calif.) according to American National Standards Institute/American Dental Association Specification No. 1-2003.11 We aged the amalgam cylinders for seven days in air at 25 ± 2 C. We measured the diameter and height of each specimen using a micrometer (Mitutoyo Model no. CD-6 in. CS, Mitutoyo USA, Aurora, Ill.) and calculated the surface area of each amalgam cylinder (113.10 ± 1.03 square millimeters). We placed each amalgam specimen in a polypropylene vial measuring 76 x 20 mm (Sarstedt, Newton, N.C.), containing 5.5 milliliters of disinfectant or line cleaner preparation. We prepared five samples of each disinfectant or line cleaner. We placed the vials on a rocking platform (Rocking Platform, Model 100, VWR Scientific, Philadelphia) and gently agitated them for 24 hours. We decanted the solution and separated the amalgam cylinder and rinsed the empty vials with 2.5 mL of 10 percent nitric acid/0.02 percent potassium dichromate. We combined the decanted liquid and rinse, filtered the mixture through 0.45-µm Teflon filters (National Scientific, Rockwood, Tenn.) and analyzed it for mercury using modified EPA method 245.1. We analyzed every disinfectant or line cleaner and calculated the amount of mercury released per unit surface area each time.
We performed statistical analysis using a one-way analysis of variance and multiple comparisons (Student-Newman-Keuls), and we determined the correlation coefficient (r2) for pH versus the mean amount of mercury released.
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RESULTS
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The table
summarizes the amounts of mercury released per unit surface area of amalgam after 24 hours and the pH values of the disinfectant or line cleaner preparations. Six preparations released significantly more mercury from amalgam (about 17 to 340 times) than did the deionized water control (P < .001). The amount of mercury released by the other line cleaners or disinfectants was not statistically different from that released by the control. The pH values of all preparations ranged from 1.76 to 12.35.
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DISCUSSION
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In this study, six disinfectant or line cleaner preparations released significantly more mercury from amalgam than did the control, which was deionized water. Three of these disinfectant or line cleaner preparations contained sodium hypochlorite as the active ingredient; the other three contained sodium dichloroisocyanate, ethylenediaminetetraacetic acid (EDTA), or hydrogen peroxide and peracetic acid as active ingredients. The results we obtained with sodium hypochlorite and sodium dichloroisocyanate preparations agree with those of previously reported studies.5,6,8 However, the results for the preparation that contained hydrogen peroxide and peracetic acid as active ingredients differed from those obtained by Roberts and colleagues.8 Those authors found no significant difference in mercury release with the hydrogen peroxide/peracetic acid preparations or distilled water. Interestingly, in our study, a preparation based on hydrogen peroxide without peracetic acid did not release significantly more mercury from amalgam than did deionized water. The results of our study also differ from those reported by Rotstein and colleagues’7 study of preparations containing EDTA.
Disinfectants or line cleaners that contained phenols, glutaraldehyde or quaternary ammonium compounds did not release more mercury from amalgam than did deionized water, a finding noted in other studies.6,8
In our study, we used standardized amalgam cylinders to provide a consistent surface area to react with the chemical preparations. Our approach differed from that of other studies that used ground amalgam particles.6,8 Even when the researchers in the other studies controlled particle size by sieving, the surface areas of each batch could have varied more substantially than would be the case with standardized amalgam cylinders, the surface area of which can be determined easily. Standardized cylinders, which other studies have featured,7,12 also provided a more controlled comparison of mercury release from the preparations.
The reaction kinetics between the preparations and the amalgam cylinders influences the amount of mercury released in a specified contact time. It is important to use the same contact time and the same surface for all preparations, because it provides a controlled basis for comparing the amount of mercury released from the amalgam cylinders. For all preparations in this study, we used a contact time of 24 hours and a surface area of 113.10 mm2. The results of our report can be compared more easily with those of Kummerer and colleagues,6 who used a contact time of 18 hours for their study. In contrast, Roberts and colleagues8 used contact times based on the manufacturers’ recommended times for disinfection, and those times ranged from two to 10 minutes. Also, they used milled amalgam with particle sizes between 710 and 900 µm. The milled amalgam that passed through the standard sieves of 710 and 900 µm varied in particle size because their irregular shape could vary substantially in surface area. In our study, we used amalgam cylinders of consistent surface area and a uniform contact time of 24 hours. The differences in contact times between the studies and the surface areas of amalgam samples may explain the observed differences in the relative amount of mercury released from amalgam.
Our results showed that pH is not a good predictor (correlation coefficient [r2] = 0.0236) of mercury release from amalgam; the six preparations that released more mercury from amalgam than deionized water were either highly acidic (pH 1.76–2.59) or highly alkaline (pH 10.72–2.35). However, some preparations had similar acidity levels (for example, pH 1.8) or alkalinity (for example, pH 11.4) that did not release significantly more mercury from amalgam than did deionized water. Soh and colleagues12 reported that a citric acid buffer at pH 2.5 released more mercury from amalgam than did a citric acid buffer at pH 7.0. Although the components of the buffers were mostly identical, the relative amounts of components used to achieve the different pH values differed between the two buffers. Thus, our study did not address the more complex differences in chemical composition of the disinfectants or line cleaners.
Our study suggested that the chemical compositions of some disinfectants or line cleaners primarily caused the release of mercury from amalgam. The intended use of each product determined its active ingredients (Table), according to manufacturers’ information. However, the list of active ingredients may not identify chemicals that are not active in disinfection or line cleaning, but these chemicals may contribute to the reaction kinetics and influence the type of reaction products. This may explain why our study results differ from those of Rotstein and colleagues’7 study on disinfectants containing EDTA or EDTA and sodium hypochlorite solutions. Thus, the information on active ingredients provided by a product’s manufacturer does not predict the potential of that product to release mercury from amalgam.
The aim of our study was to compare the effect of disinfectants and line cleaners on mercury release from amalgam in a highly controlled condition by using the same surface area for the amalgam samples. The heterogeneous nature of amalgam particles in clinical wastewater makes it difficult to quantify the release of mercury. Thus the use of clinical wastewater would introduce a hard-to-control factor into a comparison of the effect of disinfectants and line cleaners on mercury release from amalgam. Therefore, in our study, we used amalgam cylinders of consistent surface area and a uniform contact time of 24 hours.
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CONCLUSION
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This study and other published reports have demonstrated that preparations containing chlorine release more mercury from amalgam than some other products and the deionized water control. As a result, the use of these products is not recommended for treating dental office waste lines or DUWLs.10
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FOOTNOTES
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Mr. Batchu is the assistant director, Critical Issues, Research, Division of Science, American Dental Association, 211 E. Chicago Ave., Chicago, Ill. 60611, e-mail "batchuh{at}ada.org". Address reprint requests to Mr. Batchu.
Mr. Chou is a manager, Product and Standards Evaluation, Research and Laboratories, Division of Science, American Dental Association, Chicago.
Mr. Rakowski is a research assistant I, Research and Laboratories, Division of Science, American Dental Association, Chicago.
Dr. Fan is the senior director, International Science and Standards, Division of Science, American Dental Association, Chicago.
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REFERENCES
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- Association of Metropolitan Sewerage Agencies. Mercury source control and pollution prevention program evaluation: Final report. Washington: Association of Metropolitan Sewerage Agencies; 2002. Available at: "www.amsa-cleanwater.org/advocacy/mercgrant/". Accessed Aug. 24, 2006.
- Naleway CA, Ovsey V, Mihailova C, et al. Characterization of amalgam in dental wastewater (abstract 25). J Dent Res 1994;73 (special issue):105.
- Drummond JL, Cailas MD, Ovsey V, et al. Dental wastewater: quantification of constituent fractions. Acad Dent Mater Trans 1995;112:P-11.
- Vandeven JA, McGinnis SL. An assessment of mercury in the form of amalgam in dental wastewater in the United States. Water Air Soil Pollut 2005;164(1–4):349–66.
- Kielbassa AM, Attin T, Kummer K, Hellwig E. Mercury release from separated amalgam after the use of different disinfectants [in German]. Schweiz Monatsschr Zahnmed 1995;105(12):1534–8.[Medline]
- Kummerer K, Wallenhorst T, Kielbassa AM. Mercury emissions from dental chairs by disinfection. Chemoshere 1997;35(4):827–33.
- Rotstein I, Karawani M, Sahar-Helft S, Mor C, Steinberg D. Effect of sodium hypochlorite and EDTA on mercury released from amalgam. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;92(5):556–60.[Medline]
- Roberts HW, Marek M, Kuehne JC, Ragain JC. Disinfectants’ effect on mercury release from amalgam. JADA 2005;136(7):915–9.
- Stone ME, Kuehne JC, Cohen ME, Talbott JL, Scott JW. Effect of iodine on mercury concentrations in dental-unit wastewater. Dent Mater 2006;22(2):119–24.[Medline]
- American Dental Association. Best management practices for amalgam waste. Available at: "www.ada.org/prof/resources/topics/amalgam_bmp.asp". Accessed on Aug. 19, 2006.
- American National Standards Institute/American Dental Association. ANSI/ADA specification no.1-2003: Alloy for dental amalgam. Chicago: American Dental Association; 2003.
- Soh G, Chew CL, Lee AS, Yeoh TS. Significance of hydrogen ion concentration on the dissolution of mercury from dental amalgam. Quintessence Int 1991;22(3):225–8.[Medline]
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ABSTRACT
MATERIALS AND METHODS
