Dental Amalgams and Mercury

    • What is a Dental Amalgam?
    • Why are Amalgams an Issue?
    • Collection, is it required?
    • What can Purves Environmental do for You?

What is Dental Amalgam?

Dental Amalgam is the silver material used to fill cavities in a tooth.  Dental amalgams have been used for over 100 years by dentists and is still the strongest filler being used.  The average amalgam is a blend of Tin (15%), Silver (35%) and Mercury (50%).  Mercury makes up half of the amalgam.  When removing and replacing amalgam fillings, it is the Mercury that becomes an environmental hazard issue for both the wastewater treatment plants and the environment.

Why are Amalgams an Issue?

Mercury is an environmental and biological hazard.  When the dentist places or removes the amalgam filling, the Mercury portion of the amalgam is collected through the vacuum used in the mouth.  The particles end up in the waste water stream and then migrate into the environment.  These particles slowly dissolve in water and contaminate the plants and fish of the biological systems.  Removing these particles before they are discharged to the sanitary sewer, helps reduce Mercury contamination in the environment.

Collection, is it required?

Currently, the collection of dental amalgam by the dentist offices is voluntary in much of the country.  Several cities and states have begun to require collection.  The collection is by a simple device called an Amalgam Separator.  The separator is required to remove 99% of the amalgam particles.  Dental offices have voluntarily installed such systems but many have not.

To enforce collection and control of the mercury amalgams, the USEPA has proposed amending a rule requiring separators be installed in all dental offices that discharge into a Waste Water Treatment Plant (POTW).  The Final Rule is expected to be implemented by late September / early October 2015.  However, the underlying story is that simply adding an amalgam separator does not completely solve the problem of mercury entering the environment.  Recent studies have demonstrated that more effort will be required.

Amalgam Separators

        • How They Work
        • Truth vs. Myth
        • Best Management Practices
        • The Present and the Next Generation Amalgam Separator
How They Work

Amalgam Separators work by gravity separation as the water, amalgam particles, other solids and fluids are removed from the mouth during various dental procedures by vacuum.  The vapor and liquid mixture is suctioned down to a separator unit where the vapor continues to go to the vacuum and the liquid mixture enters the separator chamber.  The liquid contains the amalgam/solids mixture which settles out from the liquid. As the liquid reaches the level of the discharge port, it enters the drain and goes to the waste water treatment plant or septic system depending upon where the office is located.

Truth vs. Myth

A well operating system should remove 99% of the solid amalgam from the dental office.  The separation process assumes that all of the Mercury in the amalgam is bound up and does not enter the environment.  Though 99% of the amalgam may be removed, the remaining 1% still presents an environmental hazard.  Studies have shown that as the co-mingled liquid/amalgam mixture collect in the bottom of the separator, the remaining 1% is highly solubilized in water and is discharged into the sewer.  Additionally, an amalgam does generate mercury vapor and is discharges to the atmosphere through the vacuum exhaust port (Research Paper “Dissolution of Amalgam”).

The USEPA has set a maximum allowable discharge limit of 12ng/L.  By comparison, the average quantity of total mercury entering the environment directly from amalgam separator, based upon data collected by Purves Environmental, is astonishingly over 1,000,000 ng/L and demonstrates that mercury is still entering the environment and the ecological systems, at a detrimental concentration.  Much of the mercury received at the POTW is diluted (17400 ng/L average) but still remains high relative to other waste influents.  As noted above, the majority of the dental influent is dissolved mercury, which is much more difficult for the POTWs to remove.

A comparison of the four main sources of mercury discharging to our sewers helps demonstrate the impact of dental amalgams on the POTWs, and eventually the environment.  Figure 1 provides a comparison of mercury concentrations entering the POTW, from a typical community.

Figure 1

Values in ng/L


Figure 1 definitively shows that dental offices generate more mercury than any other source into the POTW. This, in part, is due to the low levels of mercury expected from the Residential sources and that the source controls and the required pre-treatment for the Industrial and Medical sources. The data above represents samples collected, using the same sampling procedures, from city manholes where it is important to note that the discharges have already been diluted by wastewater from upstream homes and businesses. This suggests that of mercury waste discharging into the city sewers from the dental offices, (from the 1% that is not captured by the amalgam separators), is substantially higher than what is represented in Figure 1, above.

The amalgam is still the best material to date for long term stability and has been used safely for over 100 years.  Until a better non-mercury based material is developed, the amalgam is here to stay. Even if all dentists were to stop the use of amalgams for fillings today, the removal and replacement of them would still be a large source of mercury discharge to our environment for years to come.  The best that the dental office can do is reduce the discharge by proper maintenance and separator selection.

Best Management Practice

Best Management Practice (BMP) really means performing consistent routine maintenance.  The use of separator/vacuum line cleaners and proper control of pH is critical.  Such management not only reduces the concentration of mercury entering the environment but also improves the operation of the separator providing better vacuum/suction for the dentist at the patient’s chair.  Better maintenance results in fewer separator cartridge changes and ultimately, lower cost.

The use and type of line cleaner is critical.  Line cleaners must have a pH between 5 and 9.  A cleaner with a pH that is higher or lower than this range increases the concentration of mercury entering the sewers and the environment.  Chlorine bleach must not be used as they dissolve the amalgam and will increase the concentration of mercury entering the environment.

Line cleaners that contain antimicrobials in addition to pH controlled cleaners are typically the best type of to use.  Using the cleaners that also control non-amalgam materials (i.e., pastes, biologicals) will reduce clogging and vacuum loss, extending the life of the separator and the filter at the wet vacuum.  If the separator and line cleaning procedures are followed as required by the manufacturer, the filter at the wet vacuum unit will require less maintenance, leading to lower operating costs.

If the screen at the wet vacuum requires cleaning daily or weekly, it is an indication that the separator and/or vacuum lines are not clean or working properly and higher levels of mercury are entering the environment!!

Documentation such as the number of patients served, recording the level within the separator, or simply the date of the last service helps provide reminders when to perform cleaning procedures as well as having the separator serviced.  The manufacturer may have basic recommendations; however, many separators reach capacity much quicker than expected, based upon the variability of the number of patients and procedures.

Ultimately, using the proper cleaner may result in a lower discharge of amalgam because the cleaner should reduce the quantity non-amalgam material mixing with the amalgam.  Reducing this comingling affect will allow more amalgam to settle to the bottom of the separator and generate less suspended amalgam that would normally enter the environment.  If the system is properly maintained, the wet vacuum filter should require less maintenance and the vacuum at the chair will be more efficient.

The Present and the Next Generation Amalgam Separator

The Next Generation amalgam separator will be quite different from the current units. The change in the regulation will require separators that are clear or have some means to observe the contents.  This means that many of the current separators will not meet new regulatory requirements and will have to be replaced. The majority of the separators currently on the market are either single chamber units or have a separate chamber that are often too small to efficiently separate the amalgam from the water.  These designs require more maintenance and the wet vacuum filters clog more often which directly affects the vacuum available at the chair.

The new regulation will also require the annual change-out/replacement (minimum requirement) of the separator trap canister. Change-out/replacement may have to occur more often if the unit reaches maximum capacity prior to the anniversary date.   This means that whether the separators are a one chamber system or have a secondary trap, they will have to be replaced annually regardless of volume of amalgam that has accumulated.  This means many current designs will not meet regulatory requirements and changes will have to be made.

The Next Generation…

Based upon studies and observations by Purves Environmental, the separator should have at least two chambers that are either clear or have a site glass to observe amalgam level.  The chambers should also be large enough to provide good separation of the vapor from the water thus reducing solids from entering the vacuum trap.  The separated water will require treatment to reduce the mercury level discharging to the environment or the POTW.  The ultimate process will be a zero discharge to the POTW or environment.

What is out there now?

Purves Environmental has independently and extensively examined and sampled many separators that are currently in use in dental offices to generate the knowledge and understanding of their operational capabilities and their true discharge concentrations.  While all of the separators evaluated discharge mercury into the environment, the mercury concentration discharged depended significantly on both the design and the maintenance performed.  Blind samples were collected from amalgam separators of a variety of designs and configurations. Regardless of the design, two consistent observations were made regarding the reduction of mercury discharges and system maintenance.

Systems that were not properly maintained had discharge concentrations that averaged over 200 times above the average for dental offices presented in Figure 1 (>3,000,000 average vs. 17400).  The discharge water was gray to black and very cloudy.  The wet vacuum filters required cleaning at least weekly.  The doctors often complained of poor vacuum.

Systems that were properly maintained had lower discharge concentrations (<500,000 average vs. 17400 I Figure 1) but were still 28 times higher than average discharge levels.  The wet vacuum traps were cleaned monthly on average and there were no complaints regarding vacuum.  Maintenance was the key to the lower discharge concentrations but mercury levels were still high.  This data suggests that the basic design of the majority of the amalgam separators on the market needs to be improved in order to reduce mercury discharges to a treatment level which is manageable by the POTWs.

Purves Environmental – Positive Results

It must be stated that Purves Environmental is an independent firm, NOT a governmental entity, nor affiliated with the ADA or manufacturers of dental amalgam separators in any way.  All data and evaluation was generated and funded by Purves Environmental.  This is an independent study and Purves Environmental will make recommendations based upon the current study data.

Purves Environmental identified two amalgam separator/collection systems which consistently outperformed the other systems tested. The evaluation of the amalgam separator design with discharge to the POTW sewer systems, only the M.A.R.S. Biomed Liberty Boss system separator consistently had lower values than 500,000 ng/L (average of all units tested).  This unit discharged the lowest average concentration of mercury (25200 vs. 17400 ng/L) and used treatment media in one of three chambers.  Maintenance was not factored into this average.  Recent testing at a facility using this system in conjunction with a consistent maintenance program averaged 13500 vs 17400 ng/L mercury discharge.

Summary of the M.A.R.S. Biomed Liberty Boss

This unit is the only unit that has true treatment inline.
Large Separation Chambers
Easy to Install (All standard plumbing fittings)

Based upon the data generated, this unit consistently had the lowest discharge levels even after 6 months of operation.  The company has clearly outlined performance and setup requirements and a well-documented maintenance program.  Though the data did not clearly separate offices that followed maintenance requirements, the unit consistently had the best discharge for units that do not capture all of the liquid.  The separation chamber is sufficiently large enough to meet the minimum annual change out/replacement required by the regulation.

Difficult to see sludge level in separation chamber.
Sight glass or less opaque chamber material needed.

Purves Environmental also evaluated a zero discharge system manufactured by Anterior Quest, Inc.  This unit performed as the manufacturer stated.  One Hundred percent (100%) of the amalgam and liquids produced during filling removal/replacement at the dental chair is collected and contained on site at the dental office. The mercury is never discharge into the drain but is picked up based upon a schedule and treated at a central treatment facility.  After treatment the water discharged into the POTW is <200 vs 17400.  Additionally, Anterior Quest is completely responsible for the handling, maintenance, treatment and discharge of the waste water, removing that responsibility from the dental office.

Summary of the Anterior Quest Zero Discharge System

Absolutely the best solution for most offices.
The unit has a zero discharge.
Schedule is consistent, dentist has no involvement.
The central processing plant is regulated – not the dentist.

Though the dentist generates the waste, the collection procedure mixes multiple offices and reduces dentist’s liability as the company (anterior Quest) takes responsibility for the waste once it leaves the office.  There is no discharge to the POTW and the vapor returned to the wet vacuum has no particulate thus reducing maintenance at the pump.

The availability of this system from Anterior Quest is in a limited area at this time.
As more treatment facilities are constructed regionally, so will the availability of the service from this company.

What should a dental office do now and for the future?

Dentists must look carefully at the separators that are currently on the market and understand that only two systems are fully capable meeting future regulatory needs.  The dentist must also understand modifications will be made to improve current systems.  The only way to buy the best at this time and assure reduction of mercury into the environment is treatment or zero discharge along with proper maintenance.

What can Purves Environmental do for you?

Purves Environmental can survey your dental office and provide the recommendations needed to become compliant with the new regulations coming from the USEPA.  The USEPA regulations will require local waste water treatment plants (POTWs) to examine dental offices and attempt to control the mercury discharged from the offices.

This control of mercury discharge will require amalgam separators, maintenance programs and documentation.  Local POTWs may require testing of water discharged from the office and may (in the future) set discharge limits.  If testing and limits are set, the cost will be high.

To mitigate this risk, Purves Environmental has the testing equipment and knowledge to evaluate your risk and recommend actions that will reduce or eliminate your risk. We will make recommendations based upon best management practices and equipment available.  We also have significant waste water treatment plant experience that allows us to talk with the POTW and setup a plan for your office that will be acceptable to the POTW.