Sampling for Mercury in Dental Waste

Determining Mercury Concentration in Waste Streams

Businesses that generate waste in Washington State are subject to the Washington State Dangerous Waste Regulations, Chapter 173-303, Washington Administrative Code (WAC), and must designate their waste streams to determine if their waste exceeds dangerous waste limits.

Dental offices across the state create a wide variety of waste during the course of a normal business day. Dental waste, which often includes mercury and silver, needs to be managed properly to avoid negative environmental impacts.

Because of the threat to human health and the environment posed by mercury and silver, dental offices are also subject to all of the dangerous waste requirements of the inspection requirements of Chapter 70.105 RCW Hazardous Waste Management.

A dental office that places or removes mercury amalgam fillings without an amalgam separator installed may exceed the dangerous waste designation limit for mercury (0.2 mg/L or ppm) for its waste water. To help prevent the discharge of mercury or other dangerous waste elements into the environment, the dental office have three options. They may:

The collected amalgam sludge and associated filters must be disposed of properly (most likely as a dangerous waste). If separator is maintained correctly, no additional information is needed. However, all records of waste shipments must be kept on-site and provided to the Department of Ecology (Ecology) or your local representative, if requested.

Contact Ecology for further information about this method.

Dental offices may test their waste stream and prove through analytical data that the waste stream does not designate as a dangerous waste. Although Ecology finds this option burdensome, expensive, and time-consuming, information on this process is included below.

Contact your local government representatives and your waste water treatment plant for additional requirements.

Discharging Dental Wastewater into the King County Sewer System. is a PDF publication that offers information on King County’s dental program requirements, as an example of the type of additional requirements that may be necessary.

Sampling Method

Collect all vacuum system waste water generated during the hours of operation in a standard work week for your office. It is important to obtain a representative sample of the waste stream that includes a typical amount of mercury work. Selecting a week which skews the data either toward higher or lower concentrations of mercury is inappropriate. If there is indication of such practices, Ecology reserves the right to collect its own samples for analysis or require additional analyses by the generator. Sampling is done using an Bergland Device, as described below.

Bergland or MCES Device

A Berglund device is a 5-gallon (20 liter) polypropylene carboy which has been adapted using PVC piping, to collect waste from dental chairs. It is plumbed into the vacuum line just prior to the vacuum pump and after the amalgam waste water treatment unit (if previously installed) indicated in this diagram:

The placement of the device assures the collection of all waste coming from the dental chairs while avoiding other waste streams generated in the office (sinks, sanitary sewers, etc.). It also avoids collecting any water that may be required for operation of the vacuum pump. If an office has more than one vacuum pump system, the waste from all pumps must be collected by adding a waste collector on each waste stream or some other process.

Once the device is installed, it allows the replacement of the plastic carboy when full. (Depending on the amount of waste generated, more than one carboy may be necessary to collect all the waste during the sample period.)  Each carboy is then shipped to a laboratory for analysis using standard EPA methods (SW-846).

Search for an accredited laboratory offers a list of accredited laboratories.

The laboratory is required to take a representative sample from each carboy for analysis. Protective procedures should be used while handling the samples to decrease exposures to possible metal and potential biological contaminants. The following analyses are requested for each carboy:

  1. Total metals via SW-846 8000/7000 Series

  2. The laboratory will report the concentrations of metals as mg/L (milligrams per liter), μg/L (micrograms per liter), or ppm (parts per million). If the laboratory reports the data in μg/L, the value must be divided by 1,000 (to convert from μg/L to mg/L) before the comparison can be made. Note: mg/L is equivalent to ppm so no conversion is necessary.

    If the amount of total Mercury in the waste stream exceeds 0.2 mg/L (or ppm) additional testing may be necessary. The laboratory can analyze for percentage of solids.


  3. Percentage of solids (the initial step in Method 1311 or equivalent)

Whether or not additional testing is needed depends on the percentage (%) of solids in your waste stream. Tf the percentage of solids is greater than 0.5% of the sample by weight, it is necessary to evaluate the test results to determine if an additional extraction and analysis are needed. If the mercury concentrations are greater than 4.0 mg/L (ppm) or the silver concentration is greater than 100.0 mg/L (ppm), it is necessary to designate the waste as required by the Dangerous Waste Regulations.

You must request a Sample prep via Method 1311) the TCLP (toxicity characteristic leaching procedure) extraction and a RCRA metals analysis via SW-846 8000/7000 Series Methods  if your waste stream has a percentage of solids concentration greater than 0.5%.

The two hazardous metals of most concern for dental offices are mercury and silver used in amalgams. Silver is also used in dental offices that develop their own X-rays. The final analytical results may be compared directly to the 0.2 mg/L (ppm) and 5.0 mg/L (ppm) dangerous waste limits for mercury and silver, respectively.

If you collected more than one carboy, the results from each carboy must be compared to these limits. If 50% or more of your carboys fail any of these limits, your waste water designates as a dangerous waste.

Based on what Ecology knows of a typical dental waste stream, it is unlikely that the second analysis will be needed. However, for those waste streams that have a high amount of solids, Washington’s Dangerous Waste Regulations require the second analysis for designation. The first analysis will still be useful to your local authorities. Also, it is still possible the waste stream is not a dangerous waste, even though it failed the first test.

Once the analyses have been completed, no further analyses are necessary, unless the waste stream changes in any way or unless local authorities request further information. Changes to the waste stream can include but are not limited to:

Designation information must be kept on file at the dental office and made available upon request to any Ecology, County or City representative who visits. Do not submit this information to Ecology until it is requested.

Decision Tree for designation of waste stream from dental offices


Construct and install a Berglund device for sampling dental waste water

Waste water sampling with a Berglund device

Specialized sampling equipment is required for establishing compliance by sampling and testing. Because of the heterogeneity of dental amalgam in wastewater, Ecology requires that all vacuum discharge wastewater must be collected to ensure representative sampling.

A modified 20 L sample collection bottle and manifold (“Berglund device,” or “MCES device”) has been adopted for use as the approved Ecology protocol for dental-waste-water sample collection. The Berglund device is based on a research program conducted by Metropolitan Council Environmental Services in St. Paul, MN. This Berglund device guidance was adapted from San Francisco Public Utilities Commission, Bureau of Environmental Regulation and Management.

Construction of a Berglund device to collect waste water for analysis

The Berglund device is made from a 20 L (5 gallon) vacuum-rated polypropylene (such as Nalgene®) carboy fitted with Schedule 80 bulkhead fittings, flexible 1” PVC, standard rigid 1” PVC, and unions, valves, tees, and elbows as shown in the steps below.

It takes about one day to construct a Berglund device. Procure and assemble the following materials:

Berglund device installation

Below is a Berglund device in the “sample collection” mode (bypass arm closed).

Berglund device in 'sample collection' mode

The manifold is supported by standard U-bolts and brackets, mounted on a 3/8” plywood stand. The stand, manifold, and modified carboy are placed in a 32 quart household storage tray to protect against spills.

Glued fittings are used (in preference to threaded fittings) wherever possible to minimize loss of particles. A segment of clear PVC may be used on the manifold bypass arm or outlet to show when an overflow condition exists.

Sample collection requires the use of several modified carboys. Individual sample collection carboys are switched out whenever they are full.

Switching carboys

Follow these steps.

Step 1

Switch valves to “bypass mode.” The bypass arm (on top) is opened and the sample collection arms closed to allow removal or replacement of the sample collection bottle. Vacuum service to the dental office continues uninterrupted. Break vacuum to the carboy by loosening the carboy lid.

Step 2

Detach the unions joining the sample collection arms.

Valves in 'bypass mode'Step 2

Step 3

Cap the open sample collection arms to prevent contamination. Tighten the carboy lid, if it has been loosened.

Step 4

Set the sealed carboy aside and put an empty carboy in its place. Reattach the unions as shown.

Step 3Step 4

Step 5

Reset the sample collection valves to the open position. Note that the bypass valve (on top) also remains open at this stage.

Step  6

Close the bypass valve to resume normal sample collection.  The carboys collected are transported to a State certified laboratory for special sample handling and analysis.

Step 5Step 6

Ecology personnel are available to assist you with any questions on this topic. Please contact your local regional office:mapstate

Related information

Dentists reminded to keep mercury out of their waste water is an Ecology press release from 2005.

Amalgam Separators is a section on the Web site of the American Dental Association.

Fact Sheet - Mercury Use in Dental Amalgam from the Interstate Mercury Education and Reduction Clearinghouse (IMERC).

Mercury-Dental Topic Hub™ from the Pollution Prevention Resource Exchange offers pollution prevention resources to dental offices.