Lead in the blood of children in northern Idaho's Silver Valley mining region, once the highest ever recorded, has been reduced dramatically in the last several years. But as government scientists learn more about how harmful even the smallest amounts of lead can be, they continue to lower the threshold of danger.
In October, the federal Centers for Disease Control reduced the limit at which children are considered "at risk" for lead poisoning from 25 micrograms per deciliter of blood to 10.
Consequently, when health officials enthusiastically announced recently that annual blood tests showed lead had diminished again and that 80% of the children in Smelterville, Silverton and other Silver Valley mining communities had acceptable levels, some parents were not as joyous.
"There shouldn't be any lead in the children," said Laurena Granger, whose two children showed 13 and 16 micrograms of lead, above the new at-risk level.
Using the new threshold, children were 6 1/2 times more "at risk" to suffer lead poisoning in Silver Valley in late 1974. That's when lead prices had nearly doubled to $480 a ton, prompting production at the Bunker Hill smelter to surge twentyfold--and spew showers of lead dust through damaged, filter-less smokestacks. The average blood-lead reading then was 65 micrograms, the highest ever.
So much dust, tailings and other wastes accumulated from decades of mining and processing that "in some areas the lead level in the soil is so high that it could be mined," a U.S. Environmental Protection Agency report said.
Today, the blood tests also serve as an annual reminder that 2,000 residential lots are part of a 21-square-mile area in Silver Valley that is one of the EPA's largest Superfund sites, its $150-million cleanup of mining wastes barely begun. Most of the mines have closed, leaving high unemployment.
Elsewhere, the battle against lead is waged in 13 Northeast and Midwest states where children's blood also is monitored under the 1988 Lead Contamination Control Act.
Nationally, the number of children at risk increased to about 4 million when the blood-level standard was lowered, one official estimated.
"We don't say a child at 10 micrograms is lead poisoned," said James Simpson, a public health adviser with the CDC in Atlanta who once worked with the problem in Silver Valley. Parents whose children have at least 15 micrograms are urged to participate in an intervention program that includes nutrition education, prenatal counseling and blood screening, he said.
Children are exposed to lead in soil, chipped paint, urban dust and food containers, among other sources. Excessive amounts are said to cause tooth and bone ailments, impair hearing and slow a child's intellectual development. Two children of a Silver Valley family that negotiated an $8.8-million settlement with smelter operators have persistent heart murmurs; one had to wear a leg brace while growing up because his bones were weak.
The nationwide campaign against lead in recent years has succeeded in removing or reducing the dangerous metal from paint, gasoline, waterfowl-hunting ammunition and other commodities. Bills pending in Congress would require labeling of products.
In Silver Valley, Simpson and health officials are pleased with the decline in lead levels in children. In 1988, 45% of those tested had levels over 10 micrograms; this year, it was down to 20%.
Jerry Cobb, an environmental health specialist with the public health agency in Silver Valley, attributes the decreasing lead levels to an aggressive education program and to the replacement of dozens of lawns where lead had settled.
But frustration lingers with what some parents, activist groups and other critics regard as few significant efforts to remove lead.
"They just line up kids every summer and take a vial of blood out of them," says Barbara Miller, of the grass-roots Idaho Citizens Network.
Now, activists are seeking to move the cleanup indoors, where lead is believed to have accumulated in carpets, furniture, attics and other areas.