Mercury hygiene in the dental office: precapsulated alloy since 1984, an OSHA limit of 0.1 mg/m3, and no bleach in the vacuum lines

What it says#

Mercury hygiene in a dental office is two problems that share a metal. One is what the team breathes. The other is where the solid waste goes.

On the air, the enforceable federal number is 0.1 mg/m3 for inorganic mercury, and it comes with an unusual footnote. OSHA's Table Z-2 at 29 CFR 1910.1000 lists "Mercury (Z37.8-1971)" with an acceptable ceiling concentration of 1 mg/10m3, which is the same as 0.1 mg/m3, and with no 8-hour time-weighted average at all. A memorandum OSHA issued on September 3, 1996 says that entry is wrong: Table Z-2 incorrectly lists the inorganic mercury PEL as a ceiling value, the correction was originally issued in the old Field Operations Manual, and field personnel are told that when a mercury overexposure is cited, it is cited as an 8-hour TWA PEL. The NIOSH Pocket Guide reflects the correction, listing the OSHA PEL as TWA 0.1 mg/m3. The same Pocket Guide entry gives the NIOSH recommendation, which is stricter: Hg vapor TWA 0.05 mg/m3 with a skin notation, and an immediately dangerous to life or health value of 10 mg/m3 as Hg. OSHA's own mercury topic page tabulates the third opinion, ACGIH's 8-hour TWA of 0.025 mg/m3 with a skin notation, and California has made that number a rule: section 5155 of California's Title 8 lists mercury, metallic and inorganic compounds as Hg at a PEL of 0.025 mg/m3 with a ceiling of 0.1 and a skin notation.

Keep the categories straight, because the table has three mercury rows. Alkyl mercury compounds carry a much lower OSHA 8-hour TWA of 0.01 mg/m3 with a skin notation and a ceiling of 0.04. Aryl and inorganic compounds are the 0.1 mg/m3 line. Dental amalgam is elemental and inorganic, so the inorganic row is the one that applies.

On the material, the ADA's position is older and simpler than the exposure limits: do not have bulk mercury. Its Best Management Practices brochure states that the ADA recommends against the use of bulk elemental mercury, also referred to as liquid or raw mercury, for use in the dental office, and that since 1984 the ADA has recommended use of precapsulated amalgam alloy. If bulk mercury is still in the building, the brochure says to recycle it, to check whether a licensed recycler will accept it, not to pour it into the garbage, a red bag or down the drain, and to ask the state regulatory agency and the municipality whether a bulk mercury collection program exists.

Everything else is a sorting problem with one destination. ANSI/ADA Standard No. 109 defines amalgam waste to include amalgam scrap, chairside trap filters containing amalgam, vacuum pump filters containing amalgam, saliva ejectors if used in procedures involving amalgam, used amalgam capsules, extracted teeth with amalgam restorations, and waste items contaminated with amalgam. The ADA's practices are a do-and-do-not list: use precapsulated alloys and stock a variety of capsule sizes, and do not use bulk mercury; recycle used disposable capsules, and do not put them in biohazard containers; salvage, store and recycle non-contact scrap and contact amalgam, and do not put either in biohazard containers, red bags or regular garbage; use chairside traps, vacuum pump filters and separators and recycle their contents, and do not rinse devices containing amalgam over drains or sinks; recycle teeth with amalgam restorations and do not put them in biohazard containers, red bags, sharps containers or the trash; manage amalgam waste through recycling as much as possible and do not flush it down the drain or toilet; and use line cleaners that minimize dissolution of amalgam rather than bleach or chlorine-containing cleaners.

The containers themselves are specified. The brochure asks for wide-mouthed, airtight containers with well-sealed lids, marked by category: "Non-contact Amalgam Waste for Recycling" for scrap, "Amalgam Capsule Waste for Recycling" for empty and unemptiable capsules, and "Contact Amalgam Waste for Recycling" for disposable traps and the contents of reusable ones. A reusable trap goes back into the unit without being rinsed under running water, because rinsing introduces amalgam into the waste stream. Handling gets standard precautions: amalgam waste may be mixed with saliva or other potentially infectious material, so utility gloves, masks and protective eyewear go on first.

Spills and plumbing are the two situations the routine does not cover. The ADA Council on Scientific Affairs published Dental Mercury Hygiene Recommendations in JADA in November 2003, updating recommendations it had adopted in 1999; that report describes sources of mercury in the dental office, office engineering considerations, hygiene during the preparation and placement of amalgam restorations, and, new in that edition, the management of mercury spills. It is a journal article behind publisher access; this entry names it rather than paraphrasing it. For plumbing, the ADA has a separate free guideline from August 2005. Its finding is reassuring and its precautions are specific: there is very little data to indicate that appreciable levels of amalgam adhere to plumbing, no credible evidence that periodic cleaning is necessary, and precautions are needed only when plumbing work, renovation, demolition or third-party monitoring disturbs what has settled. When that happens, hire a licensed plumber, give the plumber a copy of the guideline and a written agreement to follow it, put a bucket and non-porous tarps under the work, avoid prolonged use of a torch because excessive heat may cause mercury in amalgam to vaporize, wear utility gloves and an impervious apron, check downstream traps and filters for blockage afterward, and put the collected waste and the disposable coverings into an amalgam recycling container.

Who it applies to#

Every office that has amalgam in the building, which includes offices that stopped placing it. The waste categories follow the material, so the drawer of unused capsules in the back of the sterilization area, the traps in an operatory that now does composite only, and the extracted molar in the specimen cup all sit inside the definition.

The person the rules protect most directly is the assistant, who empties the traps and changes the filters. The ADA's requirement of utility gloves, mask and protective eyewear is written for that job, not for the dentist. The plumbing guideline extends the same logic to a contractor, who will not know any of this unless the practice hands it over in writing.

Two things sit outside. The wastewater side, the separator itself, the One-Time Compliance Report and the three years of records, is a separate federal rule and has its own entry, slug epa-amalgam-separator-rule; this entry deliberately does not repeat it. And the patient-safety question, whether amalgam restorations are safe in the mouth, is a different subject with a different regulator; the FDA's 2020 recommendations for certain high-risk groups are at slug fda-dental-amalgam-high-risk-groups-2020.

What changed#

The direction of travel is that the mercury left the office. Precapsulated alloy replaced the dispenser and the squeeze bottle from 1984 onward, which removed the largest single source of vapor and the most likely spill. What is left is a set of handling habits and a plumbing question, and the ADA's own plumbing guideline concluded the plumbing question is smaller than regulators feared.

What did not change is the OSHA number, which still traces to a 1971 ANSI standard and still prints in Table Z-2 in a form OSHA has admitted since 1996 is wrong. That is worth knowing before an argument with an inspector or a consultant: the limit is 0.1 mg/m3, and OSHA's own instruction is to treat it as an 8-hour average.

Where the source is#

The ADA's Amalgam Separators and Waste Best Management Practices topic page is the link under the title and carries the do-and-do-not table, the ANSI/ADA Standard No. 109 definition of amalgam waste and the reference list. The 2007 Best Management Practices brochure and the 2005 plumbing guideline are free four-page PDFs from the same library. The 2003 JADA mercury hygiene recommendations are behind publisher access; the abstract, which is public, describes the scope of the report and is what is cited here. On the air limits, OSHA's Table Z-2, OSHA's mercury topic page and the 1996 standard interpretation are all free, as is the NIOSH Pocket Guide entry for mercury. California's rule is section 5155 of Title 8 of the California Code of Regulations. ANSI/ADA Standard No. 109 itself is sold by the ADA.