Legacy Of Lead Measuring Lead Exposure More Art Than Science

Lead’s greatest riddle may be in its dose.

In 1974, lead in Arlene Yoss’ blood was 16 times higher than what is now considered safe - the highest ever recorded in a child.

Today, public health warnings suggest that levels significantly lower than hers can cause death.

Yet Yoss, a Silver Valley native, grew up, moved to Montana and is now raising her own family.

How did she survive? Doctors, lead experts and health specialists can’t say for sure.

Some suggest that heredity, physiology and diet played a role. Others speculate that zinc from the Bunker Hill mining complex may have offset lead’s worst effects.

But most agree the problem is in measuring the dose each child received.

It’s almost impossible to know exactly how much and for how long lead has been in the body. Both factors are important in assessing potential health problems.

Lead is inhaled from particles in air. Kids may eat it in dirt or on vegetables. It may get trapped in fingernails and end up in a child’s mouth.

Measuring that dose is more art than science.

Lead generally is measured in two ways - in the blood and in the bones.

Neither is perfect.

Lead in blood is mobile. It’s still traveling to the brain and other organs where it eventually does its damage.

“Drawing conclusions from blood lead levels is like trying to estimate somebody’s net worth by the flow of dough through their checking account,” says University of Washington chemist Dave Kalman.

“Just because they ran $10,000 through the account in a week doesn’t mean they must be wealthy.”

In other words, a single test showing high lead levels in blood doesn’t reveal how much is actually stored in the body.

The reverse is true of bone studies. Lead in bones can show how much has been ingested over a lifetime. But bone studies can’t show if lead came in one large toxic shot or in a stream of small amounts.

Amid this uncertainty, health officials must decide safety levels that protect the public.

Typically, they set thresholds at the lowest point where problems - however minor - have been found.

That’s why lead safety levels have dropped four times in 20 years. Scientists kept finding that smaller doses can cause health problems.

Yoss’ case still prompts critics to suggest that health guidelines are bogus.

Doctors say that criticism merely reveals a lack of understanding about public health.

“If someone is over the line (safety threshold) and not dead, that’s not clear evidence that the process is flawed,” Kalman said. “If they’re under the line and having problems, that is.”

, DataTimes ILLUSTRATION: Graphic: Health effects