In the debate around water fluoridation, partisans use science the way gladiators wield broadswords.

Fluoridation supporters can mobilize a mountain of studies dating from the 1940s calling water fluoridation the safest, surest and least-expensive way to fight tooth decay.

Fluoride foes challenge those studies. Most are outdated, they say. And they leave too many questions unanswered about fluoride’s long-term health hazards, opponents claim.

So where’s an undecided, confused voter to go for objective information on fluoridation’s risks and benefits?

Fluoridation supporters and opponents do agree on a few facts.

Fluoride is the 13th most abundant mineral in the earth’s crust. It leaches into groundwater. Plants suck it up from the soil. Animals store it in their bones. So the mineral is already a small part of every human diet.

Dentists noticed as early as 1908 that some of their patients sported stained but virtually cavity-free teeth. By the early 1930s, researchers realized fluoride in the water caused the stains and the strong teeth.

The calcium-friendly fluoride ion helps rebuild the tooth after decay-causing acids in the saliva eat away at it. When fluoride’s swallowed, the teeth absorb 20 percent. The body sucks up the rest, where it eventually settles in the skeleton, including the teeth.

Redding’s water supply contains hardly any natural fluoride. As a public health measure, the city could raise fluoride to 1 part per million (ppm).

That’s as far as the agreement goes.

The federal Centers for Disease Control and Prevention (CDC) is the nation’s top public health agency and one of its strongest fluoridation boosters. The agency sets the 1 ppm level as optimal for the warm north state.

That’s enough fluoride to fight tooth decay but not enough to stain the teeth, the agency claims.

Not so, fluoride foes say. They call water fluoridation a one-size-fits-all solution to tooth decay that ignores individual chemical sensitivities. Some people drink far more water than others, they note.

And we may get all the fluoride we need through toothpaste and foods processed with fluoridated water. Opponents point out that some Redding youngsters suffer tooth stains from too much fluoride even without water fluoridation.

Hydrofluorosilicic acid — the chemical that Redding would use to mimic natural water fluoridation — also accumulates in the bone, where it would deposit heavy metals like lead and arsenic over time, Measure A supporters warn.

Fluoridation supporters dismiss those arguments as scare tactics.

Thomas Reeves, CDC’s national fluoride engineer, has said an adult could drink 60 liters of fluoridated water a day for 20 years before overdosing.

Fluoride works the same whether it’s in sodium fluoride or hydrofluorosilicic acid, said Dean Germano, Shasta Community Health Center executive director.

Federal toxicologists have yet to test hydrofluorosilicic acid for safety. They agreed to do so in April after National Institute of Environmental Health Sciences researchers nominated it for studies.

Even so, CDC in a 2001 report recommended water fluoridation’s “continuation and expansion.”

Water fluoridation alone is not as effective today as it was in the 1940s, the CDC’s recommendation report acknowledges.

In those days, fluoridation cut tooth decay in children by up to 60 percent, CDC claims. Today, people drinking fluoridated water may experience 18 percent to 40 percent fewer cavities.

Water fluoridation is a victim of its own success, the CDC literature suggests. There are far more fluoride sources now than 60 years ago. People may get up to 75 percent of their fluoride from soft drinks and fruit juices processed with fluoridated water.

But that’s still not enough to effectively fight tooth decay, especially in poorer areas like Redding. Lower-income youngsters, adults and seniors suffer more tooth decay because of poorer diet and less medical care, the CDC notes.

Fluoride foes and proponents have drawn starkly different conclusions from the same information — especially on fluoridation’s cancer risks.

A National Toxicology Program (NTP) study that fed sodium-fluoridated water to rats and mice shows “equivocal” evidence of bone cancer in male rats.

A 1991 federal Department of Health and Human Services literature review of the NTP and other studies noted that “equivocal” means “uncertain.”

There’s no way to link bone cancer to water fluoridation, the review concludes. It points to the NTP study and others conducted on humans in New Jersey, Washington state and Iowa.

Fluoridation’s benefits outweigh its risks, the 1991 Health and Human Services department review concludes. However, it calls for more refined studies on fluoridation risks, including its potential to damage genes.

William Hirzy, a U.S. Environmental Protection Agency toxicologist, is one of the nation’s most authoritative fluoridation foes. Hirzy has sounded the alarm on fluoridation’s cancer link, pointing to the NTP, New Jersey, Washington state and Iowa studies.

Male rats and human males drinking fluoridated water experienced more bone cancer tumors than those that did not, Hirzy wrote in a 1999 article reviewing the toxicology literature on fluoridation.

Hirzy has called for a water fluoridation moratorium until studies prove it’s safe.

Under Measure A, any fluoride chemical the city would add to the water supply must earn federal Food and Drug Administration approval for its tooth decay-fighting claims.

A yes vote on Measure A is a vote against the city of Redding’s planned water fluoridation program.

The FDA’s current position on fluoridation probably won’t convince Measure A supporters to accept the Redding program.

Robert Sherman, who works in the FDA’s division of OTC (over-the-counter) Drug Products in its Center for Drug Evaluation and Research, said the agency does not take a position on water fluoridation.

However, the FDA has approved fluoride in dental rinses that people swallow, as they would fluoridated water, Sherman said. The agency has also approved fluoride in toothpaste, bottled water and gels.

Sherman points to a 1992 New Jersey study as evidence that fluoridation does not cause cancer. Hirzy and other fluoride foes use the same study as proof that the chemical is carcinogenic.

The FDA hasn’t ruled on whether hydrofluorosilicic acid is safe in public water supplies.

Measure A supporters note that hydrofluorosilicic acid is not the sodium fluoride the FDA has approved in toothpaste. It’s extracted from smoke stack pollution scrubbers in central Florida’s phosphate fertilizer industry.

A study the city of Redding commissioned this year recommends hydrofluorosilicic acid for its water fluoridation program.

The CDC’s water fluoridation manual for engineers and technicians confirms that hydrofluorosilicic acid is a fertilizer industry byproduct. The acid is far and away the most commonly used compound in public water systems.

The CDC manual instructs technicians how to handle the highly corrosive chemical, which can severely burn the skin. But it’s silent on the acid’s long-term health risks.

Hydrofluorosilicic acid contains lead and other metals. An LCI Ltd. product data sheet sets the maximum heavy metal concentration in the acid at 0.02 percent of the total. Fluoride itself is 18 percent of the acid mixture, the LCI data sheet shows. The Jacksonville Beach, Fla.-based LCI wholesales hydrofluorosilicic acid and other fluoride chemicals.

City taps already spout lead, arsenic and other metals, such as aluminum, nitrate, nickel and copper, the city’s 2001 water quality report shows. Household plumbing corrosion, fertilizer runoff, natural erosion and sewage all contribute to the metal count, the report claims.

Mike Robertson, the city’s water utility manager, said fluoridation would not significantly boost lead or arsenic in the water supply.

The chemical, though corrosive itself, won’t spur corrosion in lead pipes, he said.

Water officials recently found that hydrofluorosilicic acid added to well water at the proposed fluoridation level of 1 ppm boosted arsenic from 10.4 to 10.6 parts per billion.

The city would refuse any fluoridation chemical that fails American Water Works Association, state and federal standards for metal contaminants, Robertson said.