San Francisco Chronicle
Jane Kay, Chronicle Environment Writer
Wednesday, June 30, 2004
The largest controllable source of mercury to Bay Area sewage treatment plants comes from thousands of dentists flushing the toxic metal down the drain when they fill their patients' cavities -- but San Francisco officials expect these mercury levels to fall over the coming months.
The San Francisco Public Utilities Commission will begin the state's first regulatory program Thursday to catch the bits of mercury released during the preparation, placement and removal of silver fillings. Other Bay Area counties will begin similar plans later.
In San Francisco, the PUC is requiring about 600 dentist offices to get wastewater treatment permits -- just like other businesses that discharge toxic chemicals -- and prevent mercury from heading for sewage plants and, eventually, San Francisco Bay and the ocean.
"The dentists were the last controllable source that we hadn't addressed through a permit," said Lewis Harrison, the PUC's director of water-pollution prevention. "The beautiful thing is that the mercury will be going to recyclers."
Under the federal Clean Water Act of 1972, sewage treatment plants have authority to set limits on discharges from businesses. In San Francisco, where the PUC oversees sewage treatment, some of the businesses that already get wastewater treatment permits include chromium platers, auto body shops, food processors and semiconductor manufacturers.
To enforce the new dentist office permits, San Francisco is ready with seven inspectors and possible $10,000 fines for violations. Dental offices must install special devices costing around $1,000. The dentists must follow certain waste-cutting practices developed with dental societies, which, after early resistance, now support the regulation.
"Most of our dentists have selected to install the dental amalgam separators, which we feel demonstrates a positive approach to working with the PUC and other regulatory agencies. Like any other public health professionals, we're also stewards of the environment,'' said Deborah Elam, executive director of the San Francisco Dental Society.
The separators are simple devices that allow the heavier amalgam particles used in fillings -- about half mercury and the rest silver, tin, copper and other metals -- to settle to the bottom. Periodically, the dentists will send the metal waste to licensed disposal companies that will recycle it.
Mercury, along with PCBs and dioxins, is one of the most potent pollutants contaminating fish and other aquatic life in the bay. The state advises the public to limit sport fish because of health hazards, particularly to women of child-bearing age and to children.
In an attempt to reduce mercury, the state regulators in May issued a plan to cut mercury discharges into the bay by 40 percent over the next 20 years to produce fish that are safe to eat. Municipalities, in turn, are looking at every controllable source of mercury they can find -- including dental offices.
While the San Francisco Bay Regional Water Quality Control Board says that the 39 sewage treatment plants ringing the bay discharge only 1 percent of the new mercury that flows into the bay, the several thousand dental offices in the area are responsible for one-third to one-half of that amount.
The greatest sources of mercury to the bay come from mining activities dating back to the Gold Rush era and storm runoff from cities and farms.
Even small amounts of mercury can impair neurological development in the fetus and growing children. In adults, it can cause tremors, memory loss and other health problems. Scientists are still studying possible health risks from the dental amalgams. The elemental mercury in the silver fillings is poorly absorbed by the body -- but when it reaches the bay, the organic matter transforms into the potent neurotoxin methylmercury, which can contaminate some fish.
It's not just mercury in effluent that the sewage plants have to worry about reducing, either. About 90 percent of the toxic metal ends up in sludge. San Francisco's two plants and the East Bay Municipal Utilities District plants send their sludge to agricultural lands; Palo Alto and Central Contra Costa plants incinerate their sludge, sending into the air mercury that falls to the ground as a pollutant.
San Francisco, which decided to go for a mandatory program after seeing Seattle's success when it switched from a voluntary one, has about 1,600 dentists working in 600 dental offices. Every dental office has applied and received a permit that spells out the dentists' obligations. About 65 percent of the 540 that install or remove dental amalgams have met the deadline to install separators by Thursday.
The East Bay MUD will require the 300 dental offices in its service area to have separators by January.
The combined plant that serves Palo Alto, Los Altos, Mountain View and Stanford will require its 200 dental offices to install the devices by April.
Progress at the other treatment plants is mixed. While the city of Richmond required its eight dental offices to install separators four years ago, Central Contra Costa Sanitary District is only beginning to work with dentists.
E-mail Jane Kay at jkay@sfchronicle.com.
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