Junk science has united quite the political odd couple - Reps. Diane Watson, D-Calif., and Dan Burton, R-Ind. They recently co-sponsored a bill to end the use of mercury in dental fillings.

The bill would: ban dental amalgam containing mercury from children under 18 and pregnant and lactating women; require dentists to warn patients that mercury is "highly toxic" and poses "health risks"; and phase out mercury amalgam by 2007.

Rep. Watson, a Congressional Black Caucus member from Watts who claims to be "chemically sensitive," has targeted mercury-containing dental amalgam since CBS’ 60 Minutes spotlighted the scare in December 1990.

Rep. Burton, the anti-Clinton lightning rod, only recently converted to anti-mercury-ism. Burton blames thimerosal, a mercury-based preservative used in vaccines, for causing his grandson’s autism.

Also in on the mercury scare are - who else - unscrupulous personal injury lawyers. Class action lawsuits have been filed against the American Dental Association and the California and Maryland state dental associations seeking the return of monies paid for mercury-containing fillings - the great majority of fillings ever done.

Lawsuits alleging thimerosal causes autism also have been filed against vaccine manufacturers.

As to mercury in dental fillings, the lawsuits are among the best evidence that mercury in amalgam is harmless. Though the complaints allege that mercury-containing amalgam is harmful, they contain no specific allegations of harm to anyone.

This is hardly surprising.

Mercury has been a major ingredient of dental amalgam (35-42 percent) for more than 150 years. No other filling material has been proven to be safer, more durable and more cost-effective.

The National Institutes of Health reports only about 100 documented cases of allergy to mercury mentioned in the scientific literature since 1906 - despite billions of uses of mercury amalgam and tens of millions more of thimerosal-containing vaccines.

Mercury can have toxic effects on the nervous system - but only at sufficiently high exposures. As is the basic rule in toxicology, it is the dose that makes the poison. Paracelsus, the father of this principle, successfully used this principle - and mercury - to treat syphilis in the 16th century.

Fillings containing mercury typically emit about 1-3 millionths of a gram (micrograms) per day. An individual might be unavoidably exposed to another 5-6 micrograms of mercury through food, water and air. Such exposures are well below the World Health Organization’s "acceptable daily intake" for mercury, about 30 micrograms per day.

Keep in mind that the ADI is not a "safety" level; it’s a level set by regulatory agencies that is anywhere from tens to thousands of times below dose levels reported to cause biological effects in animal experiments. The ADI is set well below effect levels to provide a wide margin of safety for potential exposures.

Amalgam expert Dr. Rod Mackert says even the most sensitive individual would need about 450 fillings before exhibiting even slight symptoms of mercury toxicity.

Finally, even the hyper-cautious Food and Drug Administration concluded in March, 2002, that "No valid scientific evidence has ever shown that amalgams cause harm to patients with dental restorations, except in the rare case of allergy."

But why let a lack of factual support get in the way of a feel-good law and a chance at the lawsuit jackpot?

Rep. Burton’s anti-mercury rationale and the vaccine-related lawsuits are similarly deficient.

It’s true many children may have been exposed to relatively high levels of mercury through vaccines preserved with thimerosal. Even so, there’s no evidence these exposures harmed any child - a point reaffirmed by FDA researchers in a May 2001 article in the journal Pediatrics.

Moreover, no one knows what causes autism. A National Institutes of Health working group concluded in 1995 that autism likely was mostly genetic in origin. No evidence indicates that late-pregnancy or after-birth events - including extensively studied mass mercury poisonings - are associated with autism.

Burton’s desperate rush to blame an after-birth event for causing autism isn’t unusual.

Autistic behavior becomes apparent as children progress from saying a few words to generating more complex language, at ages of 16-36 months. Parents whose children "turn" autistic often erroneously associate the onset of autistic behavior with some contemporaneous event such as vaccination.

But public alarm about vaccine safety can be a public health problem. Outbreaks of measles, for example, occurred in the U.K. and Ireland where many worried parents shunned the measles-mumps-rubella (MMR) vaccine.

Instead of filling our minds with fear and the U.S. Code with needless laws (and our courtrooms with meritless lawsuits), Reps. Watson and Burton and the personal injury lawyers should fill themselves, as appropriate, with facts and scruples.

Steven Milloy is the publisher of JunkScience.com , an adjunct scholar at the Cato Institute and the author of Junk Science Judo: Self-defense Against Health Scares and Scams (Cato Institute, 2001).

Respond to the Writer