New mercury source targeted

Group reports 60 percent of neurotoxin in Bay Area wastewater is from dentists

By Beth Winegarner

Staff Writer

As mercury levels rise in Bay Area water systems, officials are targeting one of the neurotoxin’s primary sources: dentists.

As much as 60 percent of the mercury in the region’s wastewater comes from dental offices, according to studies from the Bay Area Pollution Prevention Group. However, wastewater treatment plants aren’t designed to remove heavy metals such as mercury from the water. By 2010, mercury discharges at the South Bayside System Authority treatment plant could exceed allowable levels, according to a recent article in the authority’s newsletter.

In San Francisco, Palo Alto and the East Bay, laws requiring dentists to stop flushing amalgams have reduced mercury levels significantly, according to Karin North, member of the Bay Area Pollution Prevention group.

“We saw a 94 percent reduction in the average mercury concentration coming out of [dental offices] and a 64 percent reduction once it reached the sewer lateral, where you have multiple businesses feeding into it,” North said.

Now, roughly 1,500 Bay Area dental offices no longer dump mercury-laden materials, according to Teresa Pischay, policy analyst with the California Dental Association. In unregulated parts of the Bay Area, including San Mateo County, wastewater officials and the CDA are urging dentists to divert those materials voluntarily.

The elemental mercury contained in dental fillings is safe, but once it enters local waters — particularly the shallow waters in parts of the San Francisco Bay — it becomes methylated mercury, which can contribute to symptoms of mercury poisoning, including birth defects and brain damage, according to North.

While many dentists want to reduce the amount of mercury they’re flushing into local sewer systems, setting up the technology for proper disposal can be costly, according to Pichay. A unit that collects amalgam waste at the dentist’s chair can cost $800 to $900, plus $400 a year in maintenance costs.

“We are members of the community at large,” Pischay said. “[Diverting mercury] naturally falls into our responsibility as citizens.”

bwinegarner@examiner.com

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