Pollution Prevention for the Dental Industry
Mercury from Dental Offices
Most of the mercury pollution in the environment is a result of industrial activities such as coal burning. The EPA estimates that dental offices only contribute 1% of the mercury in the environment. Why regulate dental offices?
The City's Wastewater Treatment Plant's 2003 NPDES discharge permit regulates the amount of mercury that can enter the St. Vrain River (0.015 micrograms per liter is the 30 day average). This very low limit and based on river flow and the very stringent stream standards established by the State of Colorado for the St. Vrain River. To protect the stream quality, the Treatment Plant cannot exceed the discharge permit limitations.
The permit limit is used to determine the maximum amount of mercury that can be treated by the plant. For Longmont, the amount that can enter the plant and be treated to meet the limitations is 0.005 pounds per day. And remember, this is a total allowable amount from all domestic, commercial and industrial sources (not just our dental offices).
The EPA estimates that dental offices contribute over 70% of the mercury in sewage.
Mercury makes up 50% of the amalgam used in fillings.
Collectively, Americans have about 800 metric tons of amalgam in their mouths.
When the sewage coming into the plant exceeds the maximum value, the EPA requires that the Industrial Pretreatment Program establish a Mercury Reduction Program to control sources.
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Mercury Reduction Program
The City's Industrial Pretreatment Program has had a Mercury Reduction Program since 1998. The following changes were made in 2003:
- Sampling using "Clean-Hands-Dirty-Hands" method at the treatment plant allows us to meet the MDL requirements of the discharge permit while reducing potential contamination of samples. Review of the data collected since 2003 show a marked reduction in influent levels and an improvement in removal efficiencies. With the next local limits evaluation, it is expected that the MAHL will be increased from the current value.
- Industrial sources of mercury have been identified and removed. Currently, there are no known industrial dischargers.
- Annual monitoring of the City sewers since 1998 has shown that those servicing a greater number of dental offices have higher concentrations of mercury. Residential areas are below detection levels.
- P2 outreach has been used since 2004 to promote voluntary pollution reduction at our 40+ dental offices. Three dental offices have installed amalgam separators.
- With the initial P2 outreach in 2004, we saw an immediate 50% reduction in mercury in our plant biosolids which has continued to today.
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Mercury, Our Environment and the Wastewater Treatment Plant: download a PDF file (251KB)
Reducing Mercury Entering Our Sewer: download a PDF file (209KB)
Reducing the Amount of Silver Entering Our Sewer: download a PDF file (909 KB)
2004 P2 Award, Hazardous Waste Disposal: download a PDF file (167 KB)
2005 Mercury Reduction Program Update: download a PDF file (143 KB)
2006 P2 Award, Amalgam Recycling: download a PDF file (126 KB)
2007 Pharmaceutical Drop Off Day, Stormwater Quality & Mercury Reduction: download a PDF file ( 229 KB)
Can't download a PDF file? More information available for Acrobat Reader or call 303-651-8667 for hardcopies.
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This page was updated
January 4, 2012
City of Longmont Public Works & Natural Resources