REDUCING AMALGAM WASTE & MERCURY LOADS TO SEWER
FROM VICTORIAN DENTAL SURGERIES
Rohan Ash
URS Australia, Melbourne, VIC
ABSTRACT
AiGroup, ADA Victorian Branch and Melbourne’s
water industry (represented by South East Water)
engaged URS to investigate mercury loads to
sewer from Victorian dental surgeries through
dentist surveys, interviews, waste audits, literature
reviews and development of an amalgam/mercury
cycle.
It was estimated that Victorian sewers received
about 210kg/yr of mercury from dental clinics about 80% of this to Melbourne’s sewers.
Significant mercury load reductions to sewer are
possible by installing amalgam separators in dental
surgeries. This should help to improve biosolids
quality produced at wastewater treatment plants,
and facilitate the recovery and reuse of mercury
and other useful metals used in amalgam alloys.
INTRODUCTION
In 2006 URS were engaged by the Australian
Industry Group (AiGroup) to carry out an
investigation of amalgam waste management
practices and mercury loads to sewers from
Victorian dental surgeries. AiGroup commissioned
this study in partnership with the Australian Dental
Association Victorian Branch (ADAVB) and the
Melbourne water industry, represented by South
East Water (SEW) as part of AiGroup’s
Sustainability Covenant with EPA Victoria.
This paper gives an overview of the study including
background on amalgam waste generation and
management and the potential impacts of mercury
on recycled water and biosolids. Dentist surveys,
interviews, surgery waste audits, literature reviews
and other data collection and assessment methods
were employed to estimate quantities of amalgam
mass and mercury loads generated by dentists.
This paper summarises the key findings, outcomes
and expected benefits of the study.
The first phase of surveys and associated data
collection activities were carried out by URS in
close collaboration with project partners: AiGroup,
ADAVB and SEW. Two online surveys were posted
on the ADAVB website in early 2007 comprising a
detailed quesionnaire, and then a shorter followup
quick survey. The surveys were road tested and
reality checked by focus groups and follow-up
interviews with a cross section of dental
practitioners. Note that this paper does not discuss
the survey results, but the key outcomes of the
surveys are reflected in the discussion on the
assessment of mercury loads.
URS audited the collection of amalgam waste from
six surgeries and the subsequent recovery of the
mercury by distillation at a specialist mercury waste
recycling facility in Melbourne (CMA EcoCycle).
The dentist surveys, interviews, audits, literature
reviews and other data collection activities
collectively provided the basis to estimate
quantities of amalgam and recoverable mercury
likely to be generated from Victorian dental
surgeries.
The assessment phase provided indicative
estimates of current mercury loads to sewer as well
as the potential reductions that might be achieved
through installation of amalgam separators. URS
also assessed the costs and benefits to the industry
of installing amalgam separators in dental clinics.
BACKGROUND & PROJECT DRIVERS
Victoria’s Dental Industry
The dental industry comprises both private and
public sectors. This study mainly focussed on the
private sector, but it was important to understand
the relative size and location of public dental
hospitals and clinics, which also generate amalgam
wastes and contribute mercury loads to sewer.
PROJECT METHODS
Private Sector Dental Surgeries
The study involved two key phases as follows:
There are around 1370 dental surgeries across
Victoria. These represent about 2800 practising
dentists and roughly 3560 dental chairs considered
to be generating amalgam wastes. In Metropolitan
Melbourne, there are approximately 1070 surgeries
(about 2782 chairs) believed to be generating
amalgam wastes.
1. Survey of private sector dentists (ADAVB
members) as the main data collection phase
2. Estimation of amalgam waste generation rates
and overall mercury loads to sewer.
Dental surgeries are spread all over Melbourne
area, but with clusters within the CBD and inner
suburbs as well as around major commercial
centres in outer suburbs.
About 300 private sector dental surgeries are
located within country Victoria, with most located in
larger regional towns such as Geelong, Ballarat
and Bendigo.
Public Sector Clinics (PSC)
There are 70 PSCs across Victoria, comprising
about 228 chairs. Over 30 of these are located in
Melbourne’s sewerage catchments.
Royal Dental Hospital Melbourne (RDHM)
The RDHM has 139 chairs. Based on its amalgam
purchasing records (inspected by URS), RDHM is
the largest amalgam user in Melbourne and
Victoria. On amalgam usage alone it is reasonable
to assume that RDHM is the largest individual
contributor of mercury load to sewer from the
Victorian dental industry.
A key driver for this study was that mercury levels
in biosolids (i.e. ongoing by-products generated)
remain at levels above or close to maximum
contaminant limits specified in EPA Victoria’s
biosolids land application and geotechnical fill
guidelines. Elevated mercury levels in biosolids
also restricts opportunities for energy recovery
because of the high cost of control for mercury
emissions in flue gases from combustion,
gasification or pyrolysis of biosolids.
Types of Dental Wastewater Systems
A conventional dental wastewater system would
consist of chairside traps for each chair followed by
a vacuum pump filter (usually only for a wet
system), then an air water separator prior to
discharge to the sewer outlet. For more recent or
advanced systems, an amalgam separator could
be installed either before or after the vacuum pump
or air/water separator. Figure 1 illustrates typical
wet
and dry dental wastewater system
configurations, and optional locations for an
amalgam separator.
What is Amalgam & Amalgam Waste?
Amalgam has been used by dentists for more than
150 years for dental restorations traditionally called
“silver fillings”. Dental amalgam used in Australia
typically contains up to 45-50% mercury, 35%
silver, 9% tin, 6% copper and 1% of other metals
including zinc. NHMRC (1999) reported that
amalgam use by Australian dentists was reducing
at around 10% per year, due to alternative
restorative materials such as plastics and
composites becoming increasingly used by dentists
and preferred by patients.
Amalgam waste is produced during dental drilling,
carving and polishing procedures when amalgam
fillings are placed, removed or repaired. Removal
and repair of old amalgam fillings is still the major
proportion of restorative work carried out by
general dental practitioners, and this generates the
largest amount of amalgam waste from dental
clinics.
The quantities of amalgam waste generated and
therefore mercury loads to sewers from dental
surgeries is expected to slowly reduce as amalgam
usage decreases. However, in the short to medium
term, mercury loads to sewer from the dental
industry could still remain significant given
continued
restorative
procedures
involving
amalgam for a sizeable proportion of the middle
and older aged population.
The form of mercury in dental amalgam is
regarded as inert and insoluble, having the ability
to form relatively stable alloys with other metals.
Mercury and as an alloy in amalgam has very high
specfic gravity. Therefore almost all amalgam
particles are expected to settle out at treatment
plants within sludge and biosolids by-products as
one of many of potential low level contaminants.
[adapted from Washington State Department of Ecology, www.ecy.wa.gov]
Figure 1: Dental Wastewater Systems (Wet & Dry)
Chairside Traps
A conventional chairside trap has 0.7 mm holes
(#25 mesh), with the literature quoting about 50%
removal efficiency of amalgam solids prior to
discharge to the dental wastewater system. This
capture efficiency can be increased through
smaller mesh size traps and more frequent
cleaning.
Vacuum Pump Systems
Pump filters (typical screen pore size of 0.425 mm
or #40 mesh) are almost always required for wet
systems, to protect vacuum pumps from damage
or blockage from solids that may enter the surgery
wastewater system. Dry vacuum systems may
also have a filter, but the air/water separator
installed before the pump prevents pump damage
or blockage. An additional 25% removal by pump
filters (ie. 50% of that which passes the chairside
filter) is typical mid-range quoted in the literature.
Amalgam Separators
A range modern amalgam separator designs are
commercially available employing sedimentation,
filtration, centrifugation and/or ion exchange
processes and capable of removing a wide range
of particle sizes including dissolved mercury.
Many amalgam separator suppliers with combined
or multiple stages claim amalgam removal
efficiencies of 99% and higher. The literature
reports removal rates as high as this, and some
even higher (Fan et al. 2002, Diroff 2004). To
obtain certification to International Standard (ISO
11143), amalgam separators are subjected to
rigorous independent testing to demonstrate 95%
removal efficiency.
A very low percentage of Victoria’s (and
Australia’s) dental surgeries had installed amalgam
separators at the time of this study.
Amalgam wastes not discharged to sewer
Amalgam wastes that are not normally discharged
to sewer include:

“non-contact” amalgam (or scrap) comprising:
- used capsules containing residual amalgam;
- unused (damaged or expired) capsules;
- amalgam carvings from fillings prior to
placement in human mouths;

fillings and whole teeth containing amalgam
fillings removed from patients mouths; and

particles/sludges from chairside traps, pump
filters and amalgam separators (if installed).
These amalgam wastes are disposed by dentists by
three possible routes:
1. dedicated amalgam waste containers for
collection by mercury recyclers (only 1 recycler
currently exists in Victoria),
2. biomedical waste or sharps containers for
transport to waste incinerators, and/or
3. general rubbish bins for disposal in municipal
landfills.
Mercury Discharges to Sewer from Dentists
Urban sewers receive wastes from a wide range of
industrial, commercial and human sources. The
dental industry is reported as a significant
contributor of mercury sewer loads, eg. 10% to
80% of total mercury received at US and Canadian
treatment plants (Sussman 2006). Dental mercury
sewer discharges are considered to contribute to
elevated concentrations of mercury and other
heavy metals in raw sewage inflows and biosolids
produced at sewage treatment plants, with potential
to limit the range of beneficial reuse opportunities
such as land application and energy recovery.
At the time of this study ADAVB and the Victorian
Water Industry
were proposing voluntary
installation of amalgam separators capable of
>95% amalgam removal in accordance with
International Standard ISO 11143:2008. The target
was installation of amalgam separators in 90% of
“eligible” dental surgeries within a 3 year period.
Eligible dentists are those expected to be using
amalgam and discharging to sewer including
General Practitioners and specialists such as
endodontists, prosthodontists and paediatrists.
Potential Impacts of Mercury
Mercury is produced mainly by volcanic emissions
but also by a range of other natural and manmade
processes such as mining, coal burning, chlorine
and vaccine manufacture, and dental surgeries.
Mercury and its compounds are persistent in the
environment and can readily bio-metabolise into
methyl-mercury, which is considered the most toxic
form. Methyl-mercury can bioaccumulate in the
food chain with potential impacts on higher level
animals such as fish, shellfish, sharks and birds.
Fish consumption is widely reported in the literature
as a main source of methyl-mercury intake in
humans (Kao, Dault, Pichay 2004, Jacobsson-Hunt
2007, Commission of the European Communities,
CEC 2005, USEPA July 2006). Methyl-mercury is a
known
neuro-toxicant
potential
affecting
development of brains and in acute doses is highly
toxic to humans and animals.
Environmental agencies and wastewater treatment
plant operators in Australia and overseas continue
to take a precautionary approach to mercury from
the dental industry and other industries, given the
potential for these significant loads to be an
ongoing contaminant source or “pool” entering the
soil, surface water and air environments via
effluent and biosolids treatment and disposal/reuse
pathways.
In many regions of Europe, United Kingdom, USA
and Canada the installation of amalgam separators
in dental surgeries has become law due to active
mercury reduction strategies in those countries.
Melbourne Water has recently undertaken
phytotoxicity and phytoextraction trials for selected
plant species grown in biosolids from Western
Treatment Plant. It was reported that some plant
species exhibited mercury stress or did not grow in
biosolids containing mercury levels ranging 3.5-8.4
mg/kg (Lomonte C et al, 2009).
Extensive coverage of mercury chemistry, potential
exposure pathways, toxicity (acute and chronic),
and impacts on humans, plants, soils and the
environment are found throughout the literature,
and is not discussed further in this paper.
LITERATURE REVIEW
There is very limited data in Australia on mercury
loads to sewers from the dental industry. However
there is extensive literature overseas including
from the USA, Canada, Europe and the UK. Most
Australian literature quotes overseas studies.
A wide-range of dental industry mercury loads from
and equally wide-ranging relative contributions
(10% to 80%) to overall sewerage system mercury
loads has been reported in overseas literature
(Sussman 2006). A summary of the key literature
reviewed in this study is listed in Table 1.
Table 1: Reported Dental Mercury Mass Loads
Daily
Annual
mg/dentist/day
g/dentist/yr
35 – 522
Scarmoutzos L, et al 2003
(11 refs. around the world)
100
101 (dry systems)
Reference
WLSSD 1996 (USA)
22
Barron T 2002 (USA)
138 (wet systems)
99-198
24.7 - 49.6
246
61.5
30-300
2.5 - 223
(0% - 100%
separators installed)
DEFRA 2001 (UK)
Environment Canada 2003
Johnson EIP Associates.
1999 (6 US refs., 1
Denmark)
Adegbembo A O Watson P
A 2004 (Canada)
Dental industry mercury loads reported in the
literature are usually based on amalgam waste
monitoring programs at dental surgeries or
theoretical mass balances of the mercury cycle in
surgeries. Reported loads are at best indicative
estimates or ranges, which are an indication of the
high variability between surgeries and at any one
point in time.
Dentist mercury loads depend on a wide range of
factors including:







quantity of amalgam used, and quantification
of non-contact amalgam;
numbers and types of dental procedures
carried out involving amalgam use or waste
generation;
proportion of amalgam carvings swallowed by
patients during amalgam placements;
proportion of amalgam carvings lost to dental
wastewater systems during placements;
efficiency of dental wastewater systems ie.
chairside traps, pump filters and separators;
proportion of surgeries having wet or dry
systems, pump filters and amalgam separators;
disposal/recycling routes for non-contact
amalgam and amalgam wastes captured by
filter systems.
Desktop mass balancing methods employed to
estimate dentist mercury loads require a large
number of assumption to be made regarding some
or all of the above factors.
AMALGAM WASTE COLLECTION AUDIT
In a parallel project with SEW and CMA Ecocycle,
amalgam waste was collected from amalgam
separators from 6 dental surgeries in Victoria
during May and June 2007. Four of these were in
Melbourne and two in rural Victoria. All of these
surgeries had ISO11143 compliant amalgam
separators installed within the previous 2-3 years.
URS accompanied Ecocycle collectors to these
dental surgeries to observe the collection of
amalgam wastes from the separators, and obtain
data on amalgam use rates and procedures
involving amalgam placements and removal. The
collected wastes were transported to Ecocycle’s
factory in Campbellfield Victoria, and weighed (wet
and after oven drying). The dried wastes were then
subject to distillation to volatise the mercury. The
residue (char) left over was sent to a
spectrographic laboratory for analyses of other
metals including silver, tin, copper and zinc.
Mercury loads found from the six surgeries ranged
60 - 90 g/chair/Yr, or 160 - 230 g/surgery/Yr. These
mercury loads were at the higher end of the range
reported in the literature (Table 1). It was
considered that these surgeries represented higher
amalgam usage compared with Victoria-wide
averages from the URS survey and RDHM
amalgam purchase records as reviewed by URS.
ASSESSMENT OF MERCURY LOADS
Amalgam/Mercury Cycle
An “amalgam/mercury cycle” was developed for a
an average sized GP dental surgery to illustrate
amalgam waste disposal pathways from surgery to
sewer – see Figures 3, 4 and 5 at end of this paper.
The amalgam/mercury cycle for the Victorian
dental industry was developed based on data from
URS and ADAVB surveys, follow up interviews,
dental surgery audits, RDHM amalgam purchase
records, and literature reviews. Amount of
amalgam waste generated per dental procedure
was estimated as a proportion of the amalgam
used or removed in each procedure, and in turn the
proportion of this waste trapped by the dental
wastewater system before sewer discharge.
The amount of amalgam waste trapped by the
surgery’s wastewater system depends on whether a
pump filter and amalgam separator is installed. All
dental surgeries were assumed to have a chairside
trap for each dental chair. The URS survey
indicated pump filters in around 60% of surgeries.
URS assumed as the “Base Case” Scenario an
existing “uptake” of amalgam separators in the
dental private sector of less than 2%.
The total amalgam waste loss to sewer for a typical
dental surgery was then estimated from average
weekly number of placement and removal
procedures carried out (from the URS survey). The
annual loads
days/year.
were
based
on
250
working
Key Assumptions
Due to the data gaps from the URS and ADAVB
surveys, and high variability of amalgam usage
and types of dental procedures across different
dental surgeries, numerous various assumptions
were made to ensure that the estimate of mercury
loads to sewer were reasonably representative of
current dental amalgam waste management
practices. Described below is an overview of key
assumptions used in the amalgam/mercury cycle.
Percentage Mercury in Amalgam
Amalgam was assumed to contain on average 45%
mercury, 35% silver, 9% tin, 6% copper and <1%
of other metals (eg. zinc, platinum). This is typical
for amalgam products supplied to Australian
dentists by Southern Dental Industries (SDI), which
supplies most of the amalgam to Victorian Dentists
Industry (pers. comm. SDI 2006, and Dental
Logistics 2007).
Amount of Non-Contact Amalgam
There is a proportion of amalgam that is not used
and is excess generated during preparation of the
amalgam. It is not place in the patient’s mouth and
is disposed of via offsite disposal/recycling routes.
Non-contact scrap amalgam was assumed as 20%
of the amalgam prepared and includes used
capsules. Most literature indicated higher noncontact amalgam proportions than the 10% as
suggested by the URS survey.
Amalgam Ingested by Patient and attached to tooth
Amalgam swallowed has been assumed at 10%,
occurring when amalgam is carved from the
patient’s teeth during placements or when
amalgam is drilled from teeth during removal
procedures. This is a conservative estimate based
on various overseas literature sources.
For
removals, it was assumed 10% of the amalgam
remained attached to the tooth, based on review of
overseas literature. The assumed amount of
amalgam swallowed or still attached to the tooth in
removals is closely related to the assumed size of
restorations removed.
Size of one Restoration (Filling)
Amalgam is supplied to dentists as sealed twocompartment capsules (one part mercury, the other
part alloy powder) ranging in size 800-2400mg
(total amalgam mix). The amalgam contained in
one filling ranges 500-1500mg as reported in
various US, EU and UK literature sources. It was
assumed that the average size of one filling
attached to the tooth is about 900mg.
Placements
It was assumed an average 1200mg of amalgam is
prepared, 200mg is non-contact amalgam scrap
(carved before placement and amalgam remaining
in the used capsules), 1000mg of amalgam is
placed in the patient’s mouth, 100mg is then
carved from the filling into the dental wastewater
system, leaving a 900mg filling attached to the
tooth.
Removals
It was assumed that when amalgam fillings are
removed (assumed 900mg in size attached to
tooth), that about 80% of is drilled out and enters
the dental wastewater system, 10% is ingested by
the patient and another 10% stays attached to the
tooth. It was assumed that numbers of amalgam
removal procedures are about three times greater
than the numbers of amalgam placement
procedures, based on the URS Survey and
interviews with GPs utilising amalgam. The amount
of amalgam waste generated by a removal
procedure is roughly ten times higher than the
placement procedure.
Whole Teeth Extractions
Mass of amalgam in whole teeth extractions was
assumed 900mg (same as placements), but
assumed to by-pass the dental wastewater system.
Dental Wastewater Solids Removal Efficiencies
The 50% removal efficiency for chairside traps is
widely quoted in the literature. The additional 25%
removal by pump filters (ie. 50% of that which
passes the chairside filter) is mid-range of that
quoted in the literature.
The amalgam/mercury cycle assumed any dental
surgery that has an amalgam separator in
combination with a chairside filter and with or
without a pump filter, will achieve 95% amalgam
solids removal
consistent with ISO11143
standards.
Amalgam/Mercury Load Estimates per Dentist
URS estimates of mercury mass loads for a typical
GP dental surgery (2 chairs) are shown in Table 2.
Table 2: Dental Mercury Mass Loads - URS Study
Daily
Annual
mg/dentist/day
g/dentist/yr
Basis
Basecase Scenario
(2% of surgeries with amalgam separators)
205
75
300 mg mercury/
dentist/working day
Best Practice Scenario
(90% of surgeries with amalgam separators)
33
12
50mg mercury/
dentist/working day
Daily mercury load estimates were averaged over
the year, based on 250 working days/year. URS
mercury load estimates per dentist were at the
upper end of the range reported in the literature
(Table 1). These estimates may reflect the low
uptake of amalgam separators (<2%) across
Victoria at the time, but also the conservative
nature of assumptions made by URS.
The literature reviewed for this report indicated that
mercury loads from dentists ranged 30 - 520
mg/dentist/day or 10 - 130 g/dentist/year. Loads
are highly variable from surgery to surgery and at
any particular time. Most of these reported dental
industry loads are indicative estimates only. Some
of the overseas reported mercury loads are
associated with areas having higher uptake of
amalgam separators compared to Victoria.
Amalgam/Mercury Loads to Sewer VictoriaWide
Figure 5 at the end of this paper provides a
conceptual Victoria-wide dental amalgam/mercury
cycle showing key data assumptions and estimates
for amalgam usage, waste generation and mercury
loads to sewers from both private and public sector
dental surgeries including RDHM.
Overall mercury loads to sewer from all dentists
were estimated by individual dentist loads
discussed earlier in this paper, and estimated
numbers of dental chairs in private and public
surgeries across Victoria. The overall mercury
loads to Victoria’s sewers from both the Private and
Public Sector Dentists (including RDHM) were
estimated to be of the order 210kg/yr.
Indicative estimates of overall Victoria-wide
amalgam/mercury waste loads to sewers relative to
amalgam usage and solid waste disposal routes
are summarised as follows:
to the Melbourne’s two main treatment plants:
Western Treatment Plant (WTP) and Eastern
Treatment Plant (ETP). Melbourne Water supplied
extensive data on annual mercury loads contained
in WTP and ETP inflows and in biosolids, providing
best indications of total load from all potential
sources
(domestic,
industrial,
commercial,
stormwater inflow, groundwater infiltration, etc).
The estimated dentist mercury loads to
Melbourne’s sewers were found to be close to or in
excess of combined mercury loads to WTP and
ETP as reported by Melbourne Water. The private
sector dental industry loads predicted in this study
could be more than 90% of the overall loads
received by Melbourne’s sewers - based on
mercury levels in treatment plant biosolids where
over 95% of the mercury is expected to have
settled out (Balogh and Liang 1995).
Discussion – Load Estimation Uncertainties
The literature reports wide-ranging mercury loads
from dental surgeries and equally wide-ranging
relative contributions (10% to 80%) to overall
sewerage system mercury loads (Sussman 2006).
The impact of dental industry loads depends on the
relative contributions from all other mercury load
sources in the sewerage catchment including
human, industrial, commercial, stormwater inflow
and groundwater infiltration.
It is also widely reported in the literature that
amalgam particles may be accumulating in dental
surgery wastewater pipes and within the sewerage
system. This could result in lower mercury loads
being measured in sewage treatment plant inflows
than the sum total loads from all sources in the
sewerage catchment discharging to sewer.
Total amalgam use
(Private Sector & Public Sector)
630 kg/yr
Total mercury mass in amalgam used
(Private Sector & Public Sector)
284 kg/yr
URS estimates of mercury loads to sewer were
also particularly sensitive to the following
assumptions:
Net mercury discharged to all Victorian
Sewers
210 kg/yr
(i)
Total mercury mass in amalgam waste
diverted from sewers (disposed to
biomedical waste, landfill or recycled)
600 kg/yr
(ii) mass of amalgam in each filling, estimated
from survey cross-checked against literature,
Amalgam waste not discharged to sewer, is
disposed of either to biomedical incinerators or
landfills or reused by mercury recyclers in roughly
equal proportions – based on the URS survey.
Amalgam/Mercury Loads to Melbourne’s Sewer
The load to Melbourne’s sewers was roughly 162
kg/yr, with about 93% of this from the private
sector dental surgeries, about 4.4% from the PSC’s
and 2.6% from RDHM.
To determine the relative contribution of mercury
loads in Melbourne’s sewerage catchment, the
dental mercury loads were divided by the total
estimated mercury loads in combined raw inflows
amount of amalgam used, estimated from the
URS survey and RDHM amalgam use records,
(iii) numbers of placements and removals carried
out, estimated from URS survey, and
(iv) Amalgam waste removal efficiencies for dental
wastewater systems as published in literature
and accounting for very low percentage of
amalgam separators in Victoria at the time.
Notwithstanding the above uncertainties and
assumptions, even if lower mercury loads of say
~25g mercury/dentist/year were adopted (ie. lower
end of that reported in the literature – see Table 1),
dental industry mercury loads could still be of the
order 30% of overall loads to Melbourne’s two
treatment plants. This is based on mercury
concentrations in biosolids.
Despite the limited accuracy of many of the dental
mercury loads reported in the literature and also in
this study, the dental industry is still regarded as
one of the more significant contributors of mercury
loads to Victoria’s sewers.
Mercury Reduction from Improved Practices
The mercury loads from dentists could reduce from
year 2007 levels of around 210kg/yr to about
33kg/yr (84% reduction) within the three years
proposed for the voluntary amalgam separator
installation program. For Melbourne’s sewers, it
was forecast that mercury loads could reduce from
about 162.5kg/yr to 25.3 kg/yr – see Figure 2 at
end of this paper.
If only the private dentists participated in the
voluntary amalgam separator installation program,
then mercury reductions would be about 77%.
The best practice scenario was for 90% of
Victoria’s dental surgeries (private and public
including RDHM) to voluntarily install amalgam
separators within 3 years and implement other best
practice measures to divert amalgam wastes from
sewers.
Amalgam Separator Installation Costs
The estimated overall cost of amalgam separator
purchase, installation and associated works across
90% of Victoria’s dental surgeries (both private and
public) was of the order $6.5 – 13 Million. For
Victoria’s private sector dentists, the cost was
roughly $5 - 10 million, including $3.7 - 7.4 Million
for Melbourne’s private dentists.
CONCLUSIONS
The URS study estimated 84% reduction in
mercury loads to sewer from private dental
surgeries could be achieved by installing ISO11143
compliant amalgam separators in 90% of dentists
across Victoria, at estimated cost range to the
industry of $5-10 Million.
There are a range of key benefits of mercury
reduction by Victoria’s dentist, such as:
(i)
Significant mercury load reductions to sewers
and sewage treatment plants;
(ii) Reduced mercury concentrations in biosolids
and recycled water;
(iii) Increased diversion of amalgam wastes from
current disposal routes to sewer, landfills
(reduced groundwater impacts) and biomedical
incinerators (lower mercury air emissions); and
(iv) Promotion of increased recycling and recovery
of mercury and other valuable metals (silver,
copper, tin, zinc) contained in the amalgam.
ACKNOWLEDGEMENTS
URS acknowledges the support and contributions
to this study by the following organisations:

Vicki Pryse, Sustainable Industry Consultant,
AiGroup

Garry Pearson, Chief Executive Officer,
Australian Dental Association, Victoria Branch.

Terry Anderson, South East Water, Victoria.

CMA Ecocycle, Campbellfield, Victoria.
REFERENCES
Adegbembo A O, Watson P A 2004. Estimated
quantity of Mercury in Amalgam Waste Water
Residue Released by Dentists into the Sewerage
System. Ontario Canada. J. Canadian Dental
Assoc. Dec 2004
ADA 2004. American Dental Association “Best
Management Practices For Amalgam Wastes”.
Balogh S & Liang L 1995. Mercury Pathways in
Municipal Wastewater Treatment Plants. J. Water,
Air & Soil Poll., Vol80, No.1-4, Feb 1995.
Barron T 2002. Mercury Headworks Analyses 2000.
Union Sanitary District 2002. CA. USA
CEC 2005. Communication from the Commission
to the Council and the European Parliament,
Community Strategy Concerning Mercury.
Commission of The European Communities,
Brussels 28.01.2005, COM(2005) 20 final.
DEFRA UK 2001. Environment Protection
Consultations, Department for Environment, Food
& Rural Affairs (DEFRA), United Kingdom (UK),
2001
Diroff N and Thomas A 2004. Options for Dental
Mercury Reduction Programs: Information for
State/Provincial and Local Governments. A report
of the Binational Toxics Strategy Mercury
Workgroup Co-chairs. Report for Great Lakes
National program Office, USEPA, Chicago August
2004.
Fan P L, Batchu H, Chou H-N, Gasparac W,
Sandrick J, Meyer D M 2002. Laboratory
Evaluation of Amalgam Separators. J. of the
American Dental Association (JADA) May 2002.
133:577-584.
Kao R T, Dault S, Pichay T 2004. Understanding
the Mercury Reduction issue: The Impact of
Mercury on the Environment and Human Health.
CDA Journal. Vol. 32, No.7, July 2004.
Environment Canada 2003. Dental Amalgam
Waste Mercury & Dentistry. Environment Canada.
Toronto Canada 2003 (Reference to Watson et al
2003/04).
Jacobsson-Hunt 2007
Amalgam and Mercury in
the Dental Setting and the Efficiency of Amalgam
Separators. Ulla Jacobsson-Hunt DDS, DMD.
Master of Science Thesis, Env. Sci. programme,
Linköpings University, Sweden 2007.
Johnson EIP Associates 1999, Technical Memo
Mercury Source Identification Update. Dental
Offices and Human Wastes. Palo Alto RWQCP.
Fillings. J. Water, Air, & Soil Poll. Vol.80, No.1-4.
Feb 1995.
Scarmoutzos L, et al 2003. Scarmoutzos L M, Boyd
O E, MVS Solutions, Solmetex (US amalgam
separator supplier). Mass., USA 2003
Lomonte C, et al 2009. Phytotoxicity of biosolids
and screening of selected plant species with
potential for mercury phytoextraction. University of
Melbourne, Melbourne Water, August 2009.
Sussman M 2006. A Comprehensive Approach to
Waste Management for the Dental Profession. J.
US Dentistry 2006, PP58-60.
NHMRC 1999. Dental Amalgam and Mercury in
Dentistry. Report of an NHMRC working party.
National Health & Medical Research Council,
Commonwealth of Australia. March 1999.
WLSSD 1996. Western Lake Superior Sanitary
District (WLSSD). Draft Wisconsin Mercury
Sourcebook, 1996
Skare I 1995. Mass Balance and Systemic Uptake
of Mercury Released from Dental Amalgam
USEPA July 2006. EPA’s Roadmap for Mercury.
Dental Industry Mercury Load (kg/Yr) Reduction to Melbourne's Sewers
Voluntary Amalgam Separator Installation Program
180
Voluntary Separator Program Starts
160
Load (kg/Yr)
Mercury
Mercury Load (kg/Yr)
140
Best Management Practice Scenario
120
RDHM Separator Installed in (say) 2009
100
PSC (90% uptake of separators within 3 Years)
80
Private Sector (90% uptake of separators within 3 Years)
60
40
20
0
2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
Year
Figure 2: Dental Industry Mercury Load Reductions (illustrative representation only)
Offsite Disposal/Recycling Methods
10001000 mg
67.5 mg
Swallowed by patient
(10% of scrapings)
Preparation of
amalgam (2 spill 600 mg alloy,
1200mg amalgam)
Placement of
amalgam restorations
(900mg retained in
tooth)
10 mg
Non-contact amalgam
(20% of amalgam used)
200 mg
Scrapings in mouth
100 mg
90 mg
Chairside traps and Pump Filters Rinsed down sink
(~10% depending on surgery practices)
Captured Amalgam
45 mg
22.5 mg
Chairside trap
(50% amalgam
removal)
Not trapped
45 mg
Vacuum Pump Filter
(50% removal of
amalgam passing
Chairside trap)
Not trapped
To Sewer
22.5 mg
Non-Contact amalgam Sucked up with vacuum (5%)
Sources
720 mg
Removal of Teeth
containing amalgam
(900mg removed per
tooth)
900 mg
Swallowed by patient (10%) +
still attached to tooth (10%)
900 mg
Whole Teeth Extracted
Removal of amalgam
(900mg removed per
tooth)
Chairside Traps present in 100%
of dentists (URS Survey)
Chairside trap
(50% amalgam
removal)
Not trapped
360 mg
Pump filters only present in 60%
of dentists (URS Survey)
Vacuum Pump Filter
(50% removal of
amalgam passing
Chairside trap)
180 mg
Not trapped
To Sewer
S
E
W
E
R
180 mg
360 mg
Captured Amalgam
540 mg
Chairside traps and Pump Filters Rinsed down sink
(~10% depending on surgery practices)
180 mg
Offsite Disposal/Recycling Methods
Figure 3: Dental Surgery Amalgam Cycle with conventional wastewater system (indicative values only)
Offsite Disposal/Recycling Methods
10001000 mg
85.5 mg
Swallowed by patient
(10% of scrapings)
Preparation of
amalgam (2 spill 600 mg alloy,
1200mg amalgam)
Placement of
amalgam restorations
(900mg retained in
tooth)
10 mg
Non-contact amalgam
(20% of amalgam used)
200 mg
Scrapings in mouth
100 mg
90 mg
Chairside traps and Pump Filters Rinsed down sink
(~10% depending on surgery practices)
Captured Amalgam
45 mg
18 mg
22.5 mg
Chairside trap
(50% amalgam
removal)
Not trapped
45 mg
Vacuum Pump Filter
(50% removal of
amalgam passing
Chairside trap)
Not trapped
22.5 mg
ISO 11143 Separator
(80% removal of
amalgam passing
pump filter)
To sewer
4.5 mg
Non-Contact amalgam Sucked up with vacuum (5%)
Sources
720 mg
Removal of Teeth
containing amalgam
(900mg removed per
tooth)
900 mg
Swallowed by patient (10%) +
still attached to tooth (10%)
900 mg
Whole Teeth Extracted
Removal of amalgam
(900mg removed per
tooth)
Chairside Traps present in 100%
of dentists (URS Survey)
Chairside trap
(50% amalgam
removal)
Pump filters only present in 60%
of dentists (URS Survey)
Not trapped
360 mg
Vacuum Pump Filter
(50% removal of
amalgam passing
Chairside trap)
180 mg
360 mg
URS Survey indicated Separators are in ~32% of
dentists, but Basecase assumes 2%
Not trapped
180 mg
ISO 11143 Separator
(80% removal of
amalgam passing
pump filter)
To sewer
36 mg
S
E
W
E
R
144 mg
Captured Amalgam
684 mg
Chairside traps and Pump Filters Rinsed down sink
(~10% depending on surgery practices)
180 mg
Offsite Disposal/Recycling Methods
Figure 4: Dental Surgery Amalgam Cycle with amalgam separator installed (indicative values only)
Note to figure:
Amalgam use Victoria wide in kg/yr
Mercury loads Victoria wide in kg/yr
all values are indicative only
Amalgam Cycle in Dental Surgeries
Amalgam
Purchased
TOTAL
748 kg/yr
337 kg/yr
Amalgam
Stored
On-Site
117 kg Amalgam
53 kg Mercury
Private
Sector
1370
3562
P.S.C.
690
310
Old/Expired/
Damaged
Caps
70
228
RDHM
44
20
1
139
No. Sites
No. Chairs
14
7
Amalgam kg/yr
Mercury kg/yr
Empty Caps &
Non-Contract
Amalgam
Sewerage System Route
Air
60kg/yr Mercury
5%
Amalgam
Used
TOTAL
631 kg/yr
284 kg/yr
Private
Sector
160
g/chair/yr
500
260
160
g/chair/yr
37
17
RDHM
Hospital
School
Total
11
3
14
7
Swallowed
Amalgam
Scrapings
Placements
(new fillings &
repairs)
Dental WW System
630 kg/yr Mercury
Human Waste
(domestic
sewage)
Teeth
Removed
170 kg/yr
Mercury
Removals
(old fillings)
Captured Amalgam
(chairside traps, pump filters, separators)
420 kg/yr Mercury
Deceased
Flue Gas
Treatment
(scrubbers,
ESP, etc)
Amalgam kg/yr
Mercury kg/yr
Amalgam
Fillings in
Patients &
Swallowed
Biomedical
Incinerator
200 kg/yr
Mercury
Rubbish/
Garbage
200 kg/yr
Mercury
Rinsed to sewer 10%
Air
Landfill
~95% of Mercury
Sewer
210 kg/yr
Mercury
Recycling
200 kg/yr
Mercury
Ash/Dust
Waste from
Flue Gas
Treatment
Biogas/
Energy
Recovery
Amalgam
Total Waste
600 kg/yr
Mercury
Sewer
~50 kg/yr
Mercury
Human Waste Route
P.S.C.
Metal
Recovery
Sewage
Treatment
Plant
~5% of Mercury
Sludge
Treatment
Storage at
STP
Recycled
Water
Land
Application
Effluent
Discharge
Surface
Waters
Ocean
Internment
Cremation
Dental
Industry/
Other
Waste Disposal Route
Figure 5: Victoria-wide Dental Industry Amalgam/Mercury Cycle (indicative values shown only)
This figure is copyright URS Australia Pty Ltd
Prescribed
Waste
Facility