By Chris Bowman, The Sacramento Bee, Calif. Knight Ridder/Tribune Business News
Dec. 28--A south Sacramento County neighborhood hit by fears of a childhood leukemia cluster appears to be a hot spot for the metal tungsten, an environmental contaminant of emerging cancer concern, according to a tree-ring study commissioned by The Bee.
Two University of Arizona scientists who ran the study say in an unpublished paper that their findings mark 'an important discovery that justifies continued research on the Calvine-Florin childhood leukemia neighborhood as well as on clusters of childhood leukemia elsewhere.'
The study is a follow-up to tree-ring and water tests the newspaper commissioned a year ago after state health officials declined to do an environmental investigation of the neighborhood, which extends east of Highway 99 to Elk Grove Florin Road, between Calvine and Gerber roads.
The Bee focused on tungsten because the element has surfaced as the most notable find in a 2002 federal probe of a childhood leukemia cluster in Fallon, Nev., 60 miles southeast of Reno.
Though tungsten is not known to cause cancer, investigators with the U.S. Centers for Disease Control and Prevention found extraordinarily high levels of the metal in Fallon residents and in their drinking water. Those findings suggested to scientists that tungsten might be linked to the childhood cancer.
The newspaper's tests last December in Calvine-Florin found minute amounts of tungsten in the drinking water and surprisingly high levels of the metal in neighborhood trees.
State Department of Health Services officials said last week -- as they did after The Bee's first round of testing -- that the tungsten findings do not merit further inquiry. They also dispute the study's premise that leukemia rates are elevated in the neighborhood.
While ruling out tungsten testing, state officials said they are preparing to conduct limited tests of the neighborhood's drinking water for NDMA, a probable cancer-causing compound, at the urging of a resident activist group.
At least nine children who live or had resided within two miles of each other in the neighborhood have been diagnosed with acute lymphocytic leukemia since 1992.
State health officials last month confirmed the cancer numbers but said the incidence does not signify a cluster, which is an unusual grouping that is not likely due to chance.
Nonetheless, state health officials have granted residents' requests to re-evaluate the neighborhood's disease rates, looking at all types of cancer that have been diagnosed among children who drank from the same water system.
Little is known about the health effects of exposure to tungsten, a naturally occurring element used in hardening tools and military armor.
The National Toxicology Program of the National Institutes of Health, however, recently singled out tungsten and its soluble compounds for 'high priority' research to assess their cancer-causing potential. The decision was based mainly on the federal findings in Fallon.
Unlike Fallon, the Sacramento region's native soil and rock contains only slight traces of tungsten. That leads the scientists in the Sacramento study to suspect that the source is industrial.
The tree-ring specimen showing the biggest change -- 446 percent gain in 12 years -- came from a redwood between Union House Creek and a 1960s industrial center at Elsie Avenue and Cottonwood Lane. The Bee has not found any past or present commercial activities that for certain involved tungsten.
'The polluters may be long gone in the Calvine-Florin area, but their fingerprints are still there. They're embedded in the trees,' said Mark Witten, a University of Arizona professor of pediatric medicine who co-wrote the study with lead investigator Paul Sheppard.
The Bee focused on tree rings because the Arizona scientists had found tungsten levels rising in trees they examined in Fallon and Sierra Vista, Ariz., 70 miles southeast of Tucson, which like Fallon has a confirmed childhood leukemia cluster.
By measuring the changes in the chemicals taken up by trees and stored in the wood, scientists believe they can reconstruct a rough rendering of an area's past environmental exposures.
The Bee's first round of tests was confined to Calvine-Florin and found tungsten levels rising in all but one tree. But the study left open the question of whether the pattern is unique to the neighborhood.
The second round of tests was on trees elsewhere in the Sacramento region, in neighborhoods with no known concerns over leukemia incidence.
The trees sampled in these 'control' sites included a behemoth coast redwood shading the steps of the state Capitol, a sequoia in Folsom City Park, redwoods planted along a Mokelumne River vineyard east of Lodi, and trees surrounding the former Sacramento Army Depot just north of the Calvine-Florin area of cancer concern.
The scientists preferred redwoods because they showed the most dramatic increases in tungsten among the variety of species examined in the first tests.
Sheppard, a scientist at the University of Arizona's renowned Laboratory of Tree-Ring Research, took core samples of two growth rings representing two time periods in each of several trees.
The Bee hired Battelle Marine Sciences Laboratory of Sequim, Wash., to analyze the wood for tungsten. Battelle specializes in detection of environmental metals at ultra-low levels.
The 15 trees sampled in March in neighborhoods outside Calvine-Florin generally showed no change or slight decreases in the metal through time, according to the lab results.
By comparison, the 12 trees tested last December in Calvine-Florin generally showed high and rising levels of tungsten through time, measured in the dated tree rings.
'You now have the first solid chemical evidence that something is different in that area,' said Thomas Cahill, an international authority on measuring pollutants. 'Nobody can argue with these data.'
Cahill, a retired University of California, Davis, atmospheric physicist, helped The Bee design the study.
Sheppard and Witten recently submitted their findings for publication in a peer-reviewed scientific journal.
'High tungsten concentrations in the outermost rings of most Calvine-Florin trees are environmentally meaningful and should motivate research into the carcinogenicity of tungsten as well as its environmental sources near Calvine-Florin,' they wrote in a draft manuscript.
Earlier this month, at the American Geophysical Union annual conference in San Francisco, the scientists presented portions of the Calvine-Florin study.
Also this month, Witten, who had been paying for most of the research costs out of pocket, was awarded a $140,000 grant from the Gerber Foundation to continue investigating environmental links to leukemia in Calvine-Florin and in cities in Nevada, Arizona, Kansas and Vermont.
Scientists debate the use of tree rings as indicators of environmental exposure.
Wendy Silk, a UCD environmental scientist, said studies of metal contaminants generally show tree rings to be unreliable in relating time of exposure.
But Thomas Yanosky, a research botanist with the U.S. Geological Survey, said the Sacramento tree data are 'reasonably convincing that tungsten in the environment has recently increased' in Calvine-Florin.
'Whether this increase has caused an increased incidence of leukemia, I cannot say -- that's for the biomedical community to decide -- but the tree-ring results along with the (study's) citations certainly support that inference,' said Yanosky, who has worked with Sheppard on earlier projects.
Some Calvine-Florin residents have long suspected that portions of their neighborhood are victims of a leukemia cluster. But they have been at a loss to explain what they perceive to be unusually high rates of the cancer, particularly among children.
At residents' requests, state health officials have completed several statistical analyses of leukemia in the area. All have shown rates of the disease to be well within expected numbers.
'We feel very secure in that,' said Dr. Raymond Neutra, who heads the state's environmental health investigations.
In a significant response to residents' persistent concerns, however, Neutra last month offered to conduct limited drinking water tests for a chemical used in making rocket fuel. In the 1960s, a Union Carbide plant in the neighborhood produced liquid hydrogen to fuel rockets made at Aerojet's plant in Rancho Cordova.
The compound, n-nitrosodimethylamine, or NDMA, is federally classified as a probable cancer-causing agent.
Tests by The Bee last year turned up no trace of NDMA in water tapped from area wells. But the compound turned up in more recent tests commissioned by lawyers representing some residents, according to Dee Lewis, who has led the neighborhood's search for answers since 1996.
Neutra also agreed to expand the health agency's analysis of cancer incidence to all childhood cancers in the entire area served by the same water supplier, California-American Water.
'I'll be taking a look at the percent of leukemia (among children) served by the water company as opposed to others in the census tract,' Neutra said.
Richard Clapp, a professor at Boston University's School of Public Health, persuaded state officials to remap their cancer analysis, which had used conventional census tract boundaries.
'To me, this is the way it should have been looked at in the first place,' Clapp said. 'The suspicion was that a major route of exposure would be through the water.'
Clapp has signed on as a consultant for Concerned Residents Initiative, a community grass-roots group Lewis founded to press for a health investigation.
'This is quite incredible,' Lewis said of the state's new efforts.
Health investigators have great difficulty uncovering possible environmental causes of cancers in part because they seldom have a good fix on past exposures. Breast milk, blood, urine and body tissues can contain clues, but the sample collection and analysis are invasive and expensive.
Trees are widespread, stationary recorders of their environments, according to experts known as dendrochemists who measure and analyze chemicals in the dated growth rings. The wood stores a wide variety of non-nutrient metals and chemicals in soil and water, incidentally taken up through the roots. Dendrochemistry can show relative changes in elemental concentrations through time.
Though exposed in different ways, people and trees share the same soil, water and air, said Cahill, the UCD physicist.
'Every time you play in your yard, every time you vacuum your house, the soil that you have there is coming from the same area that the trees are living in,' he said.
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(c) 2003, The Sacramento Bee, Calif. Distributed by Knight Ridder/Tribune Business News.
