Drought may be factor in leukemia
Cluster in kids in Sierra Vista
By Carla McClain
As Sierra Vista residents continue to wait for tests that may show why their children are developing leukemia, scientists are looking into a somewhat surprising suspect - drought.
Although the role of the severe drought that has parched Southern Arizona for years remains unproved, researchers say the dry weather may have intensified human exposure to airborne toxins, such as heavy metals, known to exist in the region.
So concerned are University of Arizona researchers about the possible health effects of this drought that they are pursuing federal funding to investigate if it could be behind the leukemia cluster, and even other diseases.
Leukemia in children is believed to be linked to environmental toxins, although only one - the solvent benzene - has ever been proved to cause it. Scientists also think genetics may play a role in making children susceptible to it.
Twelve leukemia cases have been officially diagnosed in Sierra Vista children since 1997, with several more in youngsters who have since moved elsewhere.
Most cases have occurred since 2000 - coinciding with the onset of the drought, which has ranged from "severe" to "extreme" in this area since 1999. The dry years actually started earlier in Sierra Vista, in 1997, according to National Weather Service rainfall figures.
In a town the size of Sierra Vista - about 40,000 people - statistically, only three cases should have appeared during this time period.
Finally recognizing Sierra Vista as the site of a "cancer cluster," state and federal health officials last year made plans to test victims' blood, urine and DNA to find out exactly what toxins, if any, may be affecting them.
But that testing has been delayed for months, leaving families with only continued worry and no answers about what is plaguing their children.
"They're never going to admit that anything in Sierra Vista has damaged our children, or could be causing this," said Veronica Herget, whose 9-year-old son, Cody, came down with leukemia in August 2002 after living in Sierra Vista for three years.
Herget is especially frustrated because Cody will not be included in the testing and is not even in the cluster case count because he was diagnosed a month after moving to Tucson.
"The real total in this cluster is 18 children, but they try not to include as many as possible," she said. "I would really like to know what pattern of exposures shows up in these children. But in Cody's case, I'll never know."
What small and preliminary studies have been done so far in Sierra Vista have pointed to the presence of a possible toxin there - the heavy metal tungsten. Tree-ring studies found elevated levels of it - up 72 percent - in trees from 1997 to 2002, compared with 20 years ago.
Even more compelling were air samples taken last year in the Sierra Vista area that showed airborne tungsten at levels 40 percent higher in two Sierra Vista "hot spots" than in the "control" communities of Benson, Willcox and Tucson.
Tungsten, a metal with a high melting point used to make tools, jet engines, brake linings and nose cones for bombs and rockets, has never been tested for its biological effects.
But now that very high levels of it have also been found at the site of an even worse childhood leukemia outbreak - in Fallon, Nev. - that is about to change. Tungsten has been nominated for study as a possible carcinogen by the National Toxicology Program.
With tungsten mines dotting two mountain ranges flanking Sierra Vista - the Huachucas and the Dragoons - researchers theorize the extreme lack of rainfall in recent years has put much higher levels of the metal in Sierra Vista's air than what was found in wetter times.
"This is the first time Southern Arizona has faced this kind of drought with this large a population, and we may be seeing the health effects of that," said Dr. Mark Witten, a UA pediatric researcher who has conducted the tree-ring and air studies with UA dendrochronologist Paul Sheppard.
"My current theory is that it may take tungsten and possibly other metals to initiate the leukemia process in children who are genetically predisposed to it," Witten said. "A big contributing factor to this process is the drought, when everything becomes airborne. With all the mining history and all the mine tailings in this area, with no appreciable rain since 1998, and a leukemia cluster that coincides exactly with the drought - well, there are too many coincidences not to take this seriously and study it."
With $220,000 in grants from the Gerber Foundation, Witten now is exposing laboratory mice to fine-particle tungsten to see if that triggers tumors or other health problems.
"We do know this is causing abnormal blood profiles in the mice. Tungsten is not benign," he said.
But other experts are urging caution on the drought-tungsten theory, which they say will be extremely hard to prove.
"Droughts do create more dust, of course, and could put higher levels of metals in the air," said J. Brent Hiskey, associate dean of the UA College of Engineering. "But you'd have to look at the sources of the tungsten to see if it is in a form to be airborne. Some forms are very refractory - they could not be metabolized."
Witten's co-researcher, Sheppard, noted that although the levels of airborne tungsten were higher than normal in Sierra Vista, they were not dramatically so - and nowhere near as elevated as in Fallon, where it also is found in the water.
"The drought is probably a theory to be considered, but we have not done extensive enough sampling to really know what's going on," he said, noting that he and Witten conducted another round of air sampling in Sierra Vista in December and are awaiting the results.
"What we really want to see is the testing in humans," Sheppard said. "We want to know what is actually in the people."
But at this point, that testing appears delayed about a year and will not begin until this March or April at the earliest, said Jill Smith, spokeswoman for the National Center for Environmental Health at the Centers for Disease Control and Prevention.
For families, the whole process has been "too painfully slow," said Terry Nordbrock, the mother of 6-year-old Linus, who also has leukemia.
Nordbrock founded Families Against Cancer and Toxins two years ago, when she thought health officials were dragging their feet on investigating the Sierra Vista cluster.
"I want answers, and in a hurry. I want to jump from finding the cause of this to preventing it," she said. "But we are a very long way from that."
Ï Contact reporter Carla McClain at 806-7754 or at cmcclain@azstarnet.com.
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