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May 23 – 25, 2005

Portland, Maine

For related information visit:



  • Mercury release is still a pressing issue
  • Increasing number of fish consumption advisories due to Hg
  • Dental offices are targets of regulatory scrutiny
  • Growing trend for POTWs to require use of BMPs and separators

Human Health Effects

  • Human Health concerns are the primary driver of low level Hg discharge limits
  • Even chronic low dose exposure is thought to be harmful, especially to the fetus and the developing infant
  • Human exposure primarily through fish consumption
  • Currently 45 states with fish consumption advisories due to Hg levels

Dental-Unit Wastewater

  • Avg. settling velocity ranges within 16.56 to 65.7 cm/hr (specific gravity of amalgam = 11.6)
  • Over 90% of amalgam particulate will settle in 2 hours
  • Substantial amounts of dissolved Hg may be present
    • 0.368 mg/L dissolved Hg
    • 3.905 mg/L total Hg

Forms of Hg Present in Dental-Unit Wastewater

  • Elemental mercury bound with other metals in amalgam, Hg(0) – 21,360 ppb
  • Free elemental mercury, Hg(0) – 24.6 ppb
  • Ionic mercury, Hg(+2) – 54 ppb
  • Monomethyl mercury, MeHg – 0.2778 ppb
  • Different forms of mercury have different toxicokinetics

Bioavailability of Dental Hg

  • A small percentage of the Hg in dental wastewater is in forms that can be incorporated into organisms
  • MeHg and ionic Hg have been measured in surprising concentrations
  • ~97% of Hg in wastewater is in the form of Hg(0) bound in amalgam particulate

Dental Hg Released to the Environment

  • Hg production per dentist is exceedingly variable
  • 484 mg/day (n=25, SD=420), from 1994
  • 971 mg/day (n=32, SD=716), from 2005
  • Units are in mg/Hg per chair per day
  • Samples collected after the chairside traps
  • Data is from U.S. Navy Dental Treatment Facilities

What is an amalgam separator?

  • Devices used to take amalgam (andhence Hg) out of dental wastewater
  • 8-to-80% of Hg WWTPs influent arises from dental sources, dependent upon location (AMSA study >35%, NEORSD – 41%)
  • Separators vary in complexity, cost and efficiency
  • Even “low tech” systems appear to be effective

Two Classes of Separators

  • Particulate Removal
    • Sedimentation (Specific Gravity amalgam=11.6)
    • Filtration
    • Centrifugation (Europe only)
  • Particulate and Dissolved Mercury Removal
    • Oxidation with chemicals to speciate Hg
    • Ion exchange resins capture Hg+2

Amalgam Separators

  • Separators need routine inspection and maintenance
  • More complex systems fail in more ways
  • Need for an integrative approach to managing mercury in dental office
  • Need for a simplified way to recycle mercury wastes

ISO 11143 Separator Standard

  • Laboratory made amalgam standard
    • 6 grams of amalgam3.15 mm to 500 microns
    • 1 gram of amalgam500 microns to 100 microns
    • 3 grams of amalgamless than 100 microns
  • Mixed in 1-liter of filtered tap water
  • Amalgam solution poured in separator
  • Effluent is filtered (12μm, 3μm, and 1.2μm), filters dried, and weighed
  • 95% removal efficiency, based on weight, needed to pass
    • Some areas call for 99% removal, e.g. RI, MN

ISO 11143 Separator Standard

  • Measures ability of separator to remove lab generated particulate sample
  • May not accurately model real wastewater
  • Regulators use Hg concentration limits, not particulate removal

Do Separators Really Work?

Toronto, Ontario Data

  • Toronto – 5th largest city in North America; over 1,100 dental practices
  • Required separator installation by January 1st, 2002
  • Since Installation of separators; 58% reduction in Hg levels in WWTP biosolids (sludge)
  • Hg in sludge reduced from 17 kg to 7 kg per month
  • Data obtained when compliance estimated to be 800 of 1100 clinics (~73%)

Do Separators Really Work?

  • MCES is the POTW for the Minneapolis/St. Paul, Minnesota metro area
  • Study done in Hastings and Cottage Grove
  • 24 of 25 dentists in these communities participated in study
  • Separators in place for 3 months
  • 44% and 29% reductions in Hg levels in WWTP biosolids

Do Separators Really Work?

  • Local POTW required Naval Base Great Lakes to install separators
  • Base has end-of-pipe Hg discharge limit of 0.5 g/liter, soon to be lowered to 0.1 g/liter
  • History of Hg exceedances from base
  • Dental clinics on base use 60,750 double spill amalgam capsules per year (~60 lbs of Hg)

Do Separators Really Work?

  • First pretreatment system was installed in largest Navy clinic in 1996
  • Since then all Navy dental clinics have systems installed
  • 52% decrease in Hg levels in local POTW sludge biosolids since separators installed
  • Yearly NOVs have decreased from 54 to 3

Do Separators Really Work?

  • Duluth Minnesota active since 1993
  • 50 dental practices with ~100 dentists
  • After separators installed Hg in biosolids decreased from 2.5 mg/kg to 0.19 mg/Kg
  • WWTP Hg influent has decreased from 0.18 lbs/day in 1993 to <0.02 lbs/day today
  • Hg in WWTP effluent decreased from 20.6 ng/liter to 1.9 ng/liter
  • Data from Denmark also supports efficacy of separators

Residual Hg in Wastewater Lines

  • Residual Hg in wastewater lines can be substantial
  • Plumbing lines act as a separator
  • TCLP studies on wastewater lines show pipes themselves can exceed RCRA limits for Hg
  • Hg can be mobilized from amalgam in waste lines e.g. by acids and oxidizing line cleaners

Residual Hg in Wastewater Lines

*One value exceeded the 0.2 mg/L threshold for Hg in TCLP leachate


Evaluation of Low Cost Chairside Filters as Amalgam Separators

Sample Size

Mean Hg Levels in mg

Standard Deviation

Filter Type

  • Units are in mg Hg per chair per daydischarged into plumbing system

100 m Cartridge

1 m Cartridge

1 m


0.5 m Cartridge

Removal Efficiency





ISO 11143 Efficiency





Calculated Removal Efficiencies

  • ISO 11143 testing completed by outside laboratory; empty test
  • Calculated removal efficiencies = (BHg – FHg / BHg) x 100; where BHg is the baseline Hg level, FHg is the amount of particulate Hg collected after the chairside filter)

Why are we still using amalgam?

  • Amalgam still widely used but decreasing
  • Good physical properties
  • Marginal seal from corrosion products
  • Easy to place -- not technique sensitive
  • Cost effective
  • Long track record – over 150 years
  • Large installed base of amalgam means amalgam removal for years to come

Amalgam Replacement Options

  • Gallium based alloys
    • 1 of 4 metals that are liquid near room temperature
    • Low vapor pressure
  • Direct condensed silver restorations
  • Cast metal alloys
  • Porcelain based restorations
  • Composite restorations (direct and indirect)

Composite Restorations

  • Organic Polymer Matrix
    • BIS-GMA or UDMA
  • Inorganic filler particles
    • Glass, Silica, or Quartz
  • Coupling agents
    • Organosilanes
  • Initiator-accelerators system (photo or self cure)
    • Camphoroquinone is photo activator
    • Organic amines accelerate reaction
    • Chemical activation by organic amine and organic peroxides

Composite Restorations

  • Composites more esthetic
  • Composites require more skill and time to place and finish
  • Wear issues are a concern – occlusion
  • Moisture control is crucial with composites – saliva prevents bonding to tooth
  • More costly than amalgam
  • Composites not indicated for restoration of large multi-surface carious lesions in posterior teeth


May 23 – 25, 2005

Portland, Maine

western lake superior sanitary district

Western Lake Superior Sanitary District

Mercury Reduction


Tim Tuominen

(218) 740-4815

early efforts
Early Efforts

Started in 1990, included:

  • Reduced internal sources from incinerator scrubbers
  • Engineering study of end-of-pipe treatment options: $16.7 million / year (’93 dollars) to meet GLI
  • Implemented Industrial limits
  • Started dental waste management efforts
    • Improved waste management practices
    • Waste amalgam recycling
further efforts
Further Efforts
  • MercAlert - a solid waste source reduction effort
  • Worked with Industrial Customers: Potlatch, Haarman & Reimer, and LSPI using P2 to improve raw materials.
continued efforts
Continued Efforts
  • HHW and Clean Shop collections
  • Zero Discharge Grant: Schools, Hospitals, and Dentists
recent efforts
Recent Efforts:
  • Region effort eliminating mercury equipment in schools -MN Great Award
  • Fever thermometer exchanges
  • St. Louis River Beneficiary Group for Environmental Improvement Grant:

WLSSD & NE MN Dental Society

Amalgam separator purchase

working with the dental community
Working with the Dental Community
  • 56 of 57 offices have improved treatment systems installed
  • Project has been cooperative
  • State-wide effort is being developed, based upon voluntary WLSSD program
  • Working to get systems installed at last practice
mercury in our environment
Mercury in our Environment
  • WLSSD Effluent: 2.6 ng/L (0.4 grams/day)
  • St. Louis River: 3.1 ng/L (19 grams/day)
  • Rain water: 12 ng/l
the future
The Future
  • Future limits are very aggressive
  • Most treatment plants will not meet the new limits
  • If present reduction trends continue we will meet the limits most of the time
  • Suspended solids capture will be critical
  • Source reduction efforts continue to be an important factor


May 23 – 25, 2005

Portland, Maine

reducing mercury in dental office wastewater king county s experience 1990 2005

Reducing Mercury in Dental Office Wastewater: King County’s Experience 1990 – 2005

Patricia Magnuson

Industrial Waste Program

King County Department of Natural Resources and Parks

king county wastewater treatment division
King County Wastewater Treatment Division

Sewer Service Area

  • 1.4 million people
  • Collect and treat municipal and industrial wastes
    • 200 mgd
  • 136 SIUs /286 other permitted
    • 3 mgd
  • 1300 dentists in about 900 offices
king county s concern with mercury in dental office wastewater in 1990
King County’s concern with mercury in dental office wastewater in 1990
  • 1989 NPDES violation of mercury at West Point Treatment Plant. Ecology required King County to investigate
    • No point sources found
    • Identified dental office wastewater as “significant and identifiable” source of mercury
  • 1991 -1994 Researched dental waste discharges and treatment options
findings at that time
Findings at that time
  • Dentists contributed approx 14% of mercury to WWTP
  • Dentists were not in compliance with discharge limits
  • Amalgam separators can remove mercury
  • Chairside ASU
  • Screen and settlement

Photo: Courtesy of: Thomas Barron, Civil Engineer, 925-283-8121 •

early policy choices
Early policy choices
  • 1994 King County drafted a rule for dentists that required the installation of amalgam separators
  • 1995 King County decided to postpone the rule and work with dental community to achieve voluntary compliance
king county s program 1995 2000
King County’s Program: 1995 - 2000
  • Intensive outreach program for dentists
    • Annual Poster
    • Monthly ads in local journal
    • Voucher Incentive Program
    • EnviroStars
    • Informational visits
    • Trade shows/mercury roundups
king county s concern with mercury in dental office wastewater in 2000
King County’s concern with mercury in dental office wastewater in 2000
  • Maintain “marketability” of biosolids
  • Equity - need to treat different industry sectors equitably

100% Recycled

biosolids quality
Biosolids Quality
  • Majority of mercury from amalgam goes to biosolids.
  • Biosolids “Exceptional Quality” limit 17 mg/kg
mercury limits
Mercury Limits
  • King County Local Limits for discharge to sewer
    • 0.1 mg/l for > 5000 gpd
    • 0.2 mg/l for < 5000 gpd
  • Limits apply to all businesses in King County sewer service area
    • Local limits achievable at dental office with pretreatment
goals for regulatory program
Goals for Regulatory Program
  • Minimize paperwork for dentists
  • Minimize expensive sampling
  • Minimize long term program costs for K.C.
  • Be equitable
  • Highest compliance possible
requirements by july 1 2003
Requirements by July 1, 2003:
  • Use best management practices (BMPs) for amalgam waste; and
  • Demonstrate compliance with K.C. Local Limits (0.2 mg/l) for mercury through ONE of three routes:
routes to compliance
Routes to Compliance
  • Install and maintain an approved amalgam separator unit; or
  • Apply for and receive a permit to discharge; or
  • Be an exempt specialty or practice
    • Orthodontist, oral surgeon, radiologist…
    • Place or remove amalgams less than 3 days peryear

Message to Dentists that Place or Remove Amalgam

  • Installation of “K.C. approved” amalgam separator unit = compliance
    • No permit required
    • No sampling required
    • Maintain equipment
    • Keep waste disposal records for at least 3 years
king county approved separator list
King County Approved Separator List
  • List’s main advantage is for determining compliance
  • List development
    • Required ISO certification – 95%
    • Checked paper work only


Photo Courtesy of DRNA

king county s program july 2001 july 2003
King County’s Program: July 2001 – July 2003
  • Develop and distribute informational documents
  • Web page
  • Articles in local and state dental society journals
  • Attend trade shows
  • Voucher incentive program
  • Personal visits by public health inspectors
king county s program after july 1 2003
King County’s Program After July 1, 2003
  • Random inspections of dental offices
  • Goal of inspecting 10% per year
  • Web page, brochures, follow up letters
  • Enforcements, including fines
outreach regulations compliance
Outreach + Regulations = Compliance

Amalgam Separators Installed

Data from Gail Savina and Olivia Chamberlain; KCLHWMP

more information
More Information

Patricia Magnuson

King County Industrial Waste Program206-263-3021