Why Your Amalgam Separator May Not Comply

Your amalgam separator is basically a solids collection device designed to meet the ISO 11143 standard of 95% capture. That allows 5% of the amalgam (2.5% Mercury) to enter the aquatic environment.  The USEPA has established a limit of 12 ng/L to be allowed into the aquatic environment.  To put this into perspective Table 1 helps.

Table 1

  Represents ng/L Mercury  
5% Amalgam= 2.5% Mercury 2,500,000,000 ng/L 208,333,333 times US Limit
0.1% Amalgam=0.05% Mercury 50,000,000 ng/L 4,166,666 times the US Limit
The US Limit 12 ng/L  
Great Lakes Limit 1.3 ng/L  


Tests have shown that Amalgam will slowly dissolve in water and form dissolved mercury to concentrations exceeding 1,000,000 ng/L1.  This concentration is difficult to remove at the POTW.  The dissolved mercury issue was ignored because it was assumed that amalgam doesn’t dissolve.  Once Mercury becomes dissolved in water it is very difficult to remove and all POTWs don’t have the equipment to remove it.  This error in judgment by the EPA will become a real serious issue in the future.

To assist the POTW to meet their compliance levels, many municipalities have established maximum discharge limits for users of the system.  These limits are based upon a calculation that includes dilution by other non-mercury influents that will keep the POTW in compliance with Federal and State regulation.  If the POTW is not in compliance, they must find the source that is causing the issue.  Non-compliance can result in fines to the POTW in the thousands of dollars.

The Dental practice is now considered an Industrial User under 40 CFR Part 441.  This is due to the higher than average discharge into the POTW.

Table 2

Mercury Contributors Average Concentration
Residential 68 ng/L
Industrial 125 ng/L
Medical 368 ng/L
Dental 14,300 ng/L

Data accumulated since 20031


City A has an established mercury discharge limit from any industrial user of 10,000 ng/L based upon the treatment plant calculations.  Based upon this calculation, all sources discharging into the plant influent can’t exceed 10,000 ng/L.  This limit is high and seems reasonable, however, a recent evaluation of 11 dental offices in one city found only one office was under the 10,000 ng/L limit.  Only two offices didn’t have separators and they were just above the limit.  The 8 facilities had separators and exceeded the limit by factors as high as 100 times.  Clearly, the separators didn’t work.

The only way a Dental facility can meet a standard below 10,000 ng/L is with a separator that can treat the dissolved mercury.  Only one separator can meet that requirement because it uses activated carbon to remove dissolved mercury.  All the other separators on the market work for a 1-2 days before dissolved mercury builds up to levels greater than 100,000 ng/L.  There is only one separator that will meet compliance levels of 10,000 ng/L or less. In the Great Lakes Region there is a total containment system that solves the problem. For details contact Bill Purves at wpurves330@gmail.com or call him at 330-687-3360

1 Actual data available through Purves Environmental Inc.

Leave a Reply

Your email address will not be published. Required fields are marked *