Posted on August 2, 2017 by Susan Cooke
EPA’s new “Happy Tooth” standards should make you feel just a little bit better about that trip to the dentist. But before you learn the details, you first need to take this pop quiz and get the backgrounder.
Question #1: What earth element is linked to gold mining, volcanic eruptions, and dental amalgams?
Question #2: What is the environmental angle?
Answer: All three result in mercury releases that can eventually reach the aquatic environment where bacterial action produces toxic methylmercury.
According to the United Nations 2013 Global Mercury Assessment Report which is based on 2010 data, anthropogenic (human) activities are responsible for about 1960 metric tons, or 30%, of annual mercury emissions to the air. Artisanal and small-scale gold mining and coal burning represent the two largest sources of that 30% share, at 37% and 24% respectively. Another 10%, or about 653 metric tons, reportedly comes from natural geological sources. The remaining 60%, or about 3920 metric tons, comes from re-emission of previously released mercury that has built up in surface soils and oceans, with most of that originally coming from anthropogenic sources.
For the first time, the UN report includes an estimate of anthropogenic releases of mercury to water. That estimate is at least 1000 metric tons per year. The sources considered in making that estimate were: mercury releases to land and water from artisanal and small-scale gold mining (800 metric tons); mercury releases to lakes and rivers from deforestation (260 metric tons); and mercury releases from contaminated sites such as old mines, landfills, and waste disposal locations (8-33 metric tons).
Once again, artisanal and small-scale gold mining operations, which are often illegal and hard to measure precisely, constituted the “leader of the pack”. Indeed, gold rush activities from 1850 to 1884 appear as orange peaks on a graph included in the UN report, the graph showing mercury levels found in two Wyoming ice core samples. The graph also shows that major volcanic eruptions, denoted as natural events in green, have been an important contributor, as evidenced by spikes attributable to the Mt. St. Helens, Krakatoa, and Tambora eruptions:
The third member of my mercury triumvirate is dental amalgam waste. Mercury is mixed with some other metals to make dental amalgam because it is soft enough to create the mixture and the amalgam hardens quickly after it is pressed into a tooth. Until recent years, waste dental amalgam was often discharged in a dental office’s wastewater. However, some state and local governments have started to regulate those discharges. EPA has now joined that effort
EPA’s standards cover dental office mercury discharges to Publicly Owned Treatment Works or POTWs and are set forth at 40 C.F.R. §§ 441.10-441.50. Those standards, which are applicable regardless of state and local government requirements, were published in the June 14, 2017 Federal Register and became effective on July 14, 2017. The regulatory preamble notes that dental offices have been the main source of mercury reaching POTWs which remove about 90% of such mercury prior to surface water discharge. The preamble also estimates that the new standards will reduce the POTW discharge of dental mercury from 1003 to 11 pounds per year, a very significant reduction.
Under the final rule, existing dental offices discharging wastewater containing dental amalgam to a POTW must use a device to capture and remove at least 95% of the amalgam mass by July 14, 2020, and must implement two best management practices by the same date. Dental offices that commence such a discharge after July 14, 2017 (so-called “new sources”) must utilize an amalgam separator and institute those two best management practices when the discharge begins.
One of the two best management practices prohibits the discharge to a POTW of waste or scrap dental amalgam, such as flushing it from traps or filters. The other best management practice prohibits the use of so-called line cleaners, such as bleach or chlorine containing cleaners, which could dissolve solid mercury when cleaning chair-side traps and vacuum lines whose discharge goes to the POTW.
Certain types of activities are exempted from the rule’s coverage. They include dental practices that are not engaged in replacing or making new fillings containing mercury, dental offices that collect all dental amalgam and do not discharge it to a POTW, mobile dental units, and dental practices that discharge dental amalgam only in limited circumstances such as an emergency situation.
I call these new provisions the “Happy Tooth” standards for two reasons besides their obvious connection to the treatment of tooth decay. First, they will reduce POTW discharges of mercury by two orders of magnitude. Second, the standards will not be delayed by appeals since EPA worked cooperatively with the American Dental Association (ADA) to develop them. Indeed, the ADA president has stated that the rule represents a “fair and reasonable approach to the management of dental amalgam waste”, and that such a federal standard “is preferable to a patchwork of rules and regulations across various states and localities”.
It is important to note that the new regulations do not cover direct discharges to waterways under an NPDES permit or its state equivalent. In addition, they do not cover the management of mercury in POTW sludge, such sludge being subject to EPA standards set forth at 40 C.F.R. §§ 503.1-503.48 that include mercury limits.