The Journal of the American Dental Association
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J Am Dent Assoc, Vol 137, No 7, 999-1005.
© 2006 American Dental Association
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RESEARCH

Evaluating amalgam separators using an international standard



Hanu Batchu, MS, Duane Rakowski, BS, P.L. Fan, PhD and Daniel M. Meyer, DDS


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSION
 REFERENCES
 
Background. Most amalgam particles generated during placement and removal of amalgam restorations are captured by chair-side traps and suction system traps and filters. Particles not captured can end up in the wastewater discharged from the dental office. Environmental initiatives to reduce the discharge of mercury-containing products such as dental amalgam waste into the environment have sparked interest in the use of amalgam separators.

Methods. The authors used International Organization for Standardization (ISO) Standard 11143 for Amalgam Separators in a laboratory test to evaluate the amalgam removal efficiency of 13 commercially available amalgam separators and two commercially available filtration devices not marketed as amalgam separators but that have the potential to be used as such.

Results. All 13 amalgam separators and the two filtration devices exceeded the ISO Standard 11143 requirement of 95 percent amalgam removal efficiency. The authors found statistical differences in the efficiency of the separators and filtration devices. No differences were found between the "empty" and "full" conditions for each separator.

Conclusion and Clinical Implications. This laboratory evaluation shows that amalgam separators and the filtration devices removed at least 97.05 percent of the amalgam in samples with particle-size distribution as specified in ISO Standard 11143.

Key Words: Amalgam separator; wasterwater; mercury

Most amalgam waste particles generated during placement and removal of amalgam restorations are discharged into a dental unit vacuum line. Chairside traps and vacuum pump filters remove 40 to 80 percent of the amalgam particles from this waste.1–3 In response to growing national and local interest in reducing the discharge of mercury and mercury-containing items into the environment and to respond to the requirement for low mercury concentration limits in wastewater treatment plant effluents, regulatory scrutiny has turned toward amalgam waste disposal practices. Specifically, the use of amalgam separators, whether mandated by regulation or installed voluntarily, has drawn increasing interest. Dental offices in some cities (for example, Milwaukee,4 San Francisco,5,6 Seattle7 and Wichita, Kan.8) are required to install amalgam separators, while other offices are encouraged by their state dental societies (for example, Minnesota,9 Washington10) to install amalgam separators voluntarily.

Amalgam separators are devices designed to remove amalgam particles from dental office wastewater11,12 using sedimentation, filtration, chemical removal by ion exchange or combinations of these technologies. McManus and Fan12 reviewed practical considerations on purchasing, installing and operating dental amalgam separators in a 2003 article.

In a 2002 laboratory evaluation,11 12 amalgam separators removed more than 95 percent of amalgam. The amalgam removal efficiency specified by the International Organization for Standardization (ISO) Standard 11143 for Amalgam Separators is 95 percent.13 Another study of amalgam separators installed in dental offices reported that the five types that were used in conjunction with vacuum pump filters removed more than 90 percent of amalgam particles in dental office wastewater.14 Recently, some cities began requiring or suggesting that dental offices install amalgam separators with 95 percent4–8 or even 99 percent9,15 amalgam removal efficiency. Since the 2002 evaluation, new models of amalgam separators have become available commercially, and some manufacturers of the products evaluated in 2002 have changed their recommended maximum flow rates for the products.

In our study, we used ISO Standard 11143 for Amalgam Separators13 to evaluate the amalgam removal efficiencies of 13 commercially available amalgam separators and two commercially available filtration devices not marketed as amalgam separators but that may be used for that purpose.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSION
 REFERENCES
 
We tested one sample from each of the 13 commercially available amalgam separators and two filtration devices. We did not evaluate 11 of the amalgam separators in our previous study.11 We re-evaluated the remaining two amalgam separators (ECO II, Pure Water Development, Miami; Hg5, SolmeteX, Northborough, Mass.), which we initially tested in 2002, because the manufacturers changed the recommended maximum flow rates. Table 1Go lists information about the amalgam separators and filtration devices, including the technologies used to remove amalgam and product information provided by the manufacturer.


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  		TABLE 1 Characteristics of evaluated amalgam separators and filtration devices.

 
Using a method described in a previous article,11 we determined the amalgam removal efficiency of each amalgam separator and filtration device using ISO Standard 11143 for Amalgam Separators.15 We flushed the amalgam separator or filtration device with tap water filtered with a polypropylene cartridge filter with 1 micrometer nominal pore size. After flushing 10.00 grams of amalgam particles with mass measured to ± 0.0001 g and a particle size distribution from 3.15 to 0.001 millimeters as specified by ISO Standard 11143, we made them into a slurry in 1 liter of filtered tap water with 1 g of sodium pyrophosphate. We stirred the resulting slurry and poured it into the amalgam separator or filtration device along with filtered tap water to achieve the maximum flow rate as specified by the manufacturer. We collected the effluent water from the amalgam separator or filtration device that contained amalgam particles not retained by the amalgam separator or filtration device in a vessel and filtered the water through a series of three preweighed filters (pore sizes 12 µm, 3 µm and 1.2 µm). We dried the filters and amalgam particles to constant mass in a desiccator at room temperature. We determined weight to the nearest 0.0001 g. We calculated the amalgam removal efficiency by using the following formula: percentage efficiency = 100 x [1 – (weight of amalgam filters)/(weight of sample)].

We tested each of the amalgam separators "empty" and "full" as specified by ISO Standard 11143. The "full" condition is defined as the amalgam separator filled to its stated capacity using 70 percent glass beads of 1-mm diameter and 30 percent amalgam scrap with a maximum particle size of 0.3 mm. We conducted three repeated tests for the "empty" amalgam separator and for the "full" amalgam separator. We calculated the mean value of amalgam removal efficiency for each condition. We used the lower of the two mean values as the amalgam removal efficiency value for the amalgam separator as specified in ISO Standard 11143.

We evaluated the filtration devices only in the "empty" condition because their configurations did not allow testing in the "full" condition without modifications, which would have changed the design of their amalgam removal technologies.

For statistical analysis, we analyzed the amalgam removal efficiencies of the amalgam separators and the filtration devices using an analysis of variance (ANOVA) and multiple comparison (Tukey) tests. We also used Student t tests to compare the amalgam removal efficiencies of the "empty" and "full" conditions for each amalgam separator. For each of the two previously evaluated amalgam separators, we used Student t test to compare amalgam removal efficiencies at the two different recommended maximum flow rates.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSION
 REFERENCES
 
The amalgam removal efficiencies of the amalgam separators and filtration devices we evaluated in this study were 97.05 percent or greater, which exceeded the ISO Standard 11143 requirement of 95 percent. Table 2Go shows the amalgam removal efficiencies, along with the flow rates used for the evaluation of each amalgam separator and filtration device. ANOVA and Tukey tests showed significant differences in the amalgam removal efficiencies of the amalgam separators and filtration devices (P < .001).


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  		TABLE 2 Amalgam removal efficiencies and flow rate.

 
Table 3Go shows the results of statistical analysis using ANOVA and Tukey tests, indicating significant differences. Vertical lines in the table indicate statistical groupings (P < .001) of amalgam separators with similar performances.


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  		TABLE 3 Amalgam removal efficiency as measured using International Organization for Standardization (ISO) Standard 11143.*

 
For each amalgam separator we evaluated in this study, there was no statistically significant difference between the amalgam removal efficiencies for the "empty" and "full" conditions (Student t test). In this study, the amalgam removal efficiency of the ECO II amalgam separator was 97.05 percent when evaluated at a flow rate of 2 liters per minute; in our previous study, its amalgam removal efficiency was 97.51 when evaluated at a flow rate of 3 L/minute. In this study, the amalgam removal efficiency of the Hg5 amalgam separator was 98.53 percent when evaluated at a flow rate of 0.5 L/minute; in our previous study, its amalgam removal efficiency was 99.28 when evaluated at a flow rate of 0.05 L/minute. For both of these amalgam separators, we found no statistically significant difference between the amalgam removal efficiencies evaluated at two different flow rates (Student t test).


   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSION
 REFERENCES
 
We used the test method specified in ISO Standard 11143 to conduct a laboratory evaluation of the amalgam removal efficiencies of 13 amalgam separators and two filtration devices. The particle size distribution requirement in ISO Standard 11143 was chosen on the basis of research in amalgam particles generated during dental office procedures.1,16 Our test results show that the 13 amalgam separators and the two filtration devices not marketed as amalgam separators that we evaluated in this study exceeded the ISO Standard 11143 amalgam removal efficiency requirement of 95 percent. In our 2002 laboratory evaluation, the 12 amalgam separators we tested exceeded the ISO Standard 11143 requirement for amalgam removal efficiency.

The use of chairside traps and vacuum pump filters would reduce the amount of amalgam particles reaching the amalgam separator and may prolong the operational life of the amalgam separator.

It may be reasonable to expect the removal of more than 95 percent of amalgam in dental office wastewater when amalgam separators are used in combination with chairside traps and vacuum pump filters. Because the amalgam sample specified by ISO Standard 11143 contains particles up to 3.15 mm in diameter, some amalgam particles would be removed by chairside traps, which have a pore size of about 0.7 mm in diameter, and vacuum pump filters, which have a pore size of about 0.4 mm in diameter, before reaching the separator. Thus, the use of chairside traps and vacuum pump filters would reduce the amount of amalgam particles reaching the amalgam separator and may prolong the operational life of the amalgam separator, as it would take a longer time to fill amalgam separator to capacity.

For each amalgam separator evaluated in the "empty" and "full" conditions, we did not find the differences in amalgam removal efficiencies between "empty" and "full" to be statistically significant. This is not unexpected because the technologies used in the design of amalgam separators are not influenced extensively by the extent of filling in the amalgam separators. Sedimentation technology is used, either alone or in combination with other amalgam removal technologies, in all of the amalgam separators we evaluated in this study. This technology is insensitive to the degree of filling in an amalgam separator. Because the specific gravity of amalgam is about 10 times that of water, sedimentation technology is effective in removing amalgam from water. One study analyzing the settling of amalgam particles in wastewater reported that more than 90 percent of amalgam particles in a water column settled from suspension in about two hours.17 In our current study, three amalgam separators that used only sedimentation technology had amalgam removal efficiencies of greater than 99 percent.

Regarding the two amalgam separators from our previous study11 that we re-evaluated because the manufacturers changed the recommended maximum flow rates, we found that the amalgam removal efficiencies were not statistically different at the two flow rates. Although flow rates might be expected to affect amalgam removal efficiency, a more important consideration would be the amount of time amalgam particles are allowed to settle before the supernatant wastewater is discharged from the amalgam separator. As a result, flow rates that do not significantly alter the time for amalgam to settle in the amalgam separator would produce relatively little change in the amalgam removal efficiency of an amalgam separator.

The results of our laboratory evaluation showed statistically significant differences among amalgam separators when we tested amalgam removal efficiency using ISO Standard 11143. A paucity of data exists on the efficiency of amalgam separators operated in clinical settings. For this reason, along with the reported wide disparity in amalgam removal efficiencies in the same amalgam separator system,10 we were unable to extrapolate these results.

We did not measure the total mercury concentration in the effluent. In our 2002 study,11 we measured total mercury in the test effluent to demonstrate that it is inappropriate and impractical to use the total mercury measurement to evaluate amalgam separators or as a regulatory requirement parameter. Measurements of total mercury in effluent of an ISO test do not simulate the episodic discharge of amalgam in dental office wastewater. The ISO test for amalgam removal efficiency is for the cumulative retention of amalgam particles by the amalgam separator, and it is an appropriate test for amalgam separators because it reflects the usage of amalgam separators in clinical conditions.

Because the ISO test uses amalgam particle samples, the test does not address the removal of dissolved mercury by amalgam separators. Some amalgam separators incorporate ion-exchange cartridges to remove some of the dissolved mercury in dental office wastewater. A laboratory study evaluated the effectiveness of these ion-exchange cartridges for removing dissolved mercury using cationic mercury solutions.18 It found that the effectiveness of the ion-exchange cartridges ranged from 70 to more than 99 percent.

The sources of dissolved mercury in dental office wastewater are not well-identified. Hypochlorite solutions used as line cleaners and other chlorine-containing line cleaners have been shown to cause increased dissolution of amalgam particles.19,20 Thus, one approach for decreasing the potential source of dissolved mercury from the interaction of line cleaners with amalgam waste is to avoid using chlorine-containing line cleaners.21


   CONCLUSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSION
REFERENCES
 
In this study, we evaluated the amalgam removal efficiency of 13 commercially available amalgam separators and two filtration devices using ISO Standard 11143 for Amalgam Separators. The amalgam removal efficiency of all devices surpassed the 95 percent requirement specified in ISO Standard 11143. This result favorably compares with the findings of our 2002 study,11 in which 12 amalgam separators exceeded the ISO Standard 11143 amalgam removal efficiency percentage requirement.


   FOOTNOTES
 

Mr. Batchu is the assistant director, Critical Issues, Division of Science, American Dental Association, Chicago.


Mr. Rakowski is a research assistant I, Division of Science, American Dental Association, Chicago.


Dr. Fan is the senior director, International Science and Standards, Division of Science, American Dental Association, 211 E. Chicago Ave., Chicago, Ill. 60611, e-mail "fanp{at}ada.org". Address reprint requests to Dr. Fan.


Dr. Meyer is the associate executive director, Division of Science, American Dental Association, Chicago.


The authors thank Bio-Sym Medical (Coquitlam, British Columbia, Canada), Pure Water Development (Miami), SolmeteX (Northborough, Mass.) and Sultan Healthcare (Englewood, N.J.) for use of their amalgam separators in this study.


   REFERENCES
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSION
 REFERENCES
 

  1. Naleway CA, Ovsey V, Mihailova C, et al. Characterization of amalgam in dental wastewater (abstract 25). J Dent Res 1994;73:105.

  2. Drummond JL, Cailas MD, Ovsey V, et al. Dental wastewater: quantification of constituent fractions (abstract P-22). Acad Dent Mater Trans 1995;8:112.

  3. Adegbembo AO, Watson PA, Lugowski SJ. The weight of wastes generated by removal of dental amalgam restorations and the concentration of mercury in dental wastewater. J Can Dent Assoc 2002;68:553–8.

  4. Milwaukee Metropolitan Sewerage District. Dentist offices and mercury. Available at: "www.mmsd.com/rules/dentist_offices_and_mercury.cfm". Accessed May 18, 2006.

  5. San Francisco Public Utilities Commission. Amalgam separator materials (option 1). Available at: "http://sfwater.org/detail.cfm/C_ID/1655/MC_ID/4/MSC_ID/85/MTO_ID/136". Accessed May 18, 2006.

  6. San Francisco Public Utilities Commission. Mandatory best management practices (BMPs). Available at: "http://sfwater.org/detail.cfm/MC_ID/14/MSC_ID/118/MTO_ID/228/C_ID/1852/ListID/2". Accessed May 18, 2006.

  7. Local Hazardous Waste Management Program in King County, Washington. Publications: Handling dental waste—2005 edition. Available at: "www.govlink.org/hazwaste/publications/index.cfm#129". Accessed May 18, 2006.

  8. City of Wichita Department of Water and Sewers. Silver and mercury monitoring: Silver and mercury CMP program. Available at: "www.wichita.gov/CityOffices/WaterAndSewer/SewageTreatment/SilverMercury.htm". Accessed May 11, 2006.

  9. Minnesota Dental Association. Amalgam Recovery Program. Available at: "www.mndental.org/professionals/amalgam_recovery/". Accessed May 11, 2006.

  10. Washington State Dental Association. Government affairs: Amalgam. Available at: "www.wsda.org/government/amalgam2.view". Accessed May 18, 2006.

  11. Fan PL, Batchu H, Chou HN, Gasparac W, Sandrik J, Meyer DM. Laboratory evaluation of amalgam separators. JADA 2002;133:577–84.

  12. McManus KR, Fan PL. Purchasing, installing and operating dental amalgam separators. JADA 2003;134:1054–65.

  13. International Organization for Standardization. Technical committee ISO TC 106, Dentistry, Subcommittee SC6, Dental Equipment: Dental equipment—amalgam separators, ISO 11143:1999(E). Geneva: International Organization for Standardization; 1999.

  14. Metropolitan Council, Environmental Services; Minnesota Dental Association. Evaluation of amalgam removal equipment and dental clinic loadings to the sanitary sewer. St. Paul, Minn.: Metropolitan Council, Environmental Services; Minnesota Dental Association; 2001.

  15. Rhode Island, Narragansett Bay Commission environmental best management practices for the management of waste dental amalgam. Available at: "www.narrabay.com/Documents/PDFs/DentalBMP.pdf". Accessed May 11, 2006.

  16. Letzel H, de Boer FA, van ‘t Hof MA. An estimation of the size distribution of amalgam particles in dental treatment waste. J Dent Res 1997;76:780–8.[Abstract/Free Full Text]

  17. Cailas M, Ovsey V, Mihailova C, et al. Physico-chemical properties of dental wastewater. In: Proceedings of the Water Environment Federation, 67th Annual Conference and Exhibition; Oct. 15–19, 1994; Chicago: 317–27.

  18. Batchu H, Chou H-N, Rakowski D, Fan P L. Amalgam separator cartridge evaluation: removing colloidial amalgam and cationic mercury (abstract 1864). Available at: "http://iadr.confex.com/iadr/2005Balt/techprogram/abstract_60749.htm". Accessed May 22, 2006.

  19. Stone ME, Pederson ED, Auxer RA, Davis SL. Line cleaners/disinfectant effects on soluble mercury content of dental wastewater (abstract 814). J Dent Res 1999;78:207.

  20. Batchu H, Chou HN, Rakowski D, Fan PL. Effect of line cleaners on dissolution of dental amalgam (abstract 611). Available at: "http://iadr.confex.com/iadr/2004Hawaii/techprogram/abstract_43805.htm". Accessed May 22, 2006.

  21. American Dental Association. Best management practices for amalgam waste. Available at: "www.ada.org/goto/amalgambmp". Accessed May 11, 2006.





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