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Household Mercury Poses National Clean Water Compliance Concerns

NACWA reports that mercury levels in household wastewater are sufficiently high to pose Clean Water Act compliance problems for the nation's wastewater treatment plants. The findings of the NACWA study underscore the need for a comprehensive, priority-based, cost-effective national strategy to reduce mercury in the environment.

Mercury from domestic wastewater and municipal treatment plants accounts for less than 1 percent of mercury entering the environment. Still many wastewater treatment agencies are concerned that compliance will require the application of advanced treatment at their publicly owned treatment works (POTWs) that have been shown to cost $10 million - $100 million for every pound of mercury removed. In addition, such advanced treatment may not have much impact on resolving water quality issues as long as mercury continues to enter the environment from other sources such as air pollution or abandoned mines. EPA believes that by using new analytical and sampling techniques and pollution minimization, POTWs should have no difficulty in attaining these more stringent requirements. EPA's conclusions in large part are based on a 1994 mercury sampling project that showed four of nine wastewater treatment plants had non- detectable mercury levels. This approach, however, assumes that there is no background mercury concentration in domestic wastes. Until recently there has been very little information on mercury concentrations in domestic waste, mainly due to a lack of monitoring at a sufficiently low level.

To better understand the relative contributions of mercury in domestic wastes and potential source control options, NACWA initiated a study to collect information on concentrations of mercury in domestic wastewater, to identify the sources of mercury in domestic wastewater, and to evaluate the feasibility of controlling those mercury sources. Sources evaluated included common household products and food items, as well as research on mercury contributions from individuals with amalgam fillings.

The results of this study offer some important observations for sources of mercury in domestic wastewater and the feasibility of effective control options, and are available in a final report from NACWA. The major findings are listed below.

• Significant amounts of mercury at the average concentration of 138 parts per trillion were consistently found in strictly domestic wastewater in various parts of the country. This was wastewater that contained no industrial or commercial inputs, dental offices included. POTWs remove 97 percent of mercury that is discharged into sewage systems.
• Several common household and toiletry items were found to contain substantial concentrations of mercury when examined using sensitive analytical techniques. Although these products individually do not contribute significantly to a total concentration in wastewaters, their cumulative effect accounts for approximately 15 percent of the mercury concentration in domestic wastewater. The feasibility of controlling these sources would require a broad national effort.
• Although several sources contributing to the domestic mercury concentrations have been identified, human wastes (feces and urine) from individuals with dental amalgam fillings are believed to be the most significant source — greater than 80 percent. These results were corroborated by the results from chemical toilet and septic wastes that showed that a significant portion of the mercury in domestic wastewater is from uncontrollable sources such as dental amalgam fillings.
• While controlling human wastes is impractical, the long-term outlook is promising inasmuch as the trend in dental health is for fewer cavities and resulting in smaller and smaller populations of amalgam-loaded individuals over time.
• Based on this information, domestic waste contributes appreciable concentrations of mercury to POTW influent wastestreams and must be considered when addressing mercury control strategies and the likelihood of virtual elimination of mercury. Background mercury concentrations averaging more than 100 parts per trillion can be expected in POTW wastewater influents, even if complete elimination of industrial point source discharges is accomplished.

In EPA's cost analysis for the Great Lakes Water Quality Initiative, and in subsequent discussions with wastewater representatives, the Agency has supported the use of pollutant minimization programs as a way for achieving compliance. NACWA endorses and promotes pollution minimization efforts, but is concerned that these efforts may not be adequate to produce the desired level of permit compliance sought by regulatory authorities, highlighting the need for a national mercury compliance strategy for POTWs.

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